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(19) 



J) 



(12) 



(43) Date of publication: 

07.02.1996 Bulletin 1996/06 

(21 ) Application number: 951 1 2239.9 

(22) Date of filing: 03.08.1995 



Europaisches Patentamt 
European Patent Office 
Off ice europ6en des brevets (11) EP 0 696 076 A1 

EUROPEAN PATENT APPLICATION 

(51) tnt.CI.6: H01M4/52 



(84) Designated Contracting States: 


• Shinyama, Katsuhiko 


DE FR GB 


Sakal, Osaka 591 (JP) 




• Chikano, YoshHo 


(30) Priority: 04.08.1994 JP 183446/94 


Hirataka, Osaka 573 (JP) 




• Nishlo, Koji 


(71) Applicant: SANYO ELECTRIC CO. LTD 


Hirataka, Osaka 573 (JP) 


Moriguchi-City, Osaka 570 (JP) 


• Saito, Toshihiko 


(72) Inventors: 


Mlhara-gun, Hyogo, 656-01 (JP) 


• Yano, Matsumi 


(74) Representative: VOSSIUS & PARTNER 


HIrakata, Osaka 573 (JP) 


D-81675MQnchen (DE) 


• Nogami, MItsuzo 


Takatsuki, Osaka 569 (JP) 





(54) Active material powder for non-sintered nickel electrode, non-sintered nickel electrode for 
alkaline battery and process for producing the same 

(57) An non-sintered nickel electrode of alkaline bat- 
teries uses an active material powder which conprises 
composite particles comprising nickel hydroxide parti- 
cles or solid solution particles consisting essentially of 
nickel hydroxide the surface of which is covered with a 
mixed crystal of cobalt hydroxide and the hydroxide of at 
least one metal (M) selected from the group consisting 
of aluminum, magnesium, indium and zinc. With this 
electrode, the cobalt hydroxide, which covers as a com- 
ponent of the mixed crystal the surface of the nickel 
hydroxide particles, minimally diffuses into them. Alka- 
line batteries using this electrode as positive electrode 
can therefore maintain, for a long period of time of 
charge-discharge cycles, the function of the cobalt 
hydroxide of Increasing the conductivity of the electrode, 
thereby suppressing decrease in the discharge capacity 
in the course of charge-discharge cycles. 



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EP0 696 076 A1 



Description 

This application claims the priority of Japanese Patent Application No. 6-183446 filed on August 4, 1994 which is 
incorporated herein by reference. 

5 The present Invention relates to an active material powder for non-sintered nickel electrodes of alkaline batteries 
such as nickel-hydrogen battery and nickel-cadmium battery and a process for producing the same, and to a non-sintered 
nickel electrode for alkaline batteries and a process for producing the same. 

The known nickel electrodefor alkaline batteries has been prepared by impregnating a substrate {sintered substrate) 
obtained by sintering nickel powder onto a perforated steel plate or the like, with an active material. This type of nickel 

10 electrode is known as "sintered nickel electrode". With this sintered nickel electrode, in which particles of the nickel 
powder bonds together only weakly, so that increasing the porosity of the substrate causes the nickel powder to drop 
off from the substrate. The maximum porosity of the substrate practically attained has therefore been 80%. The sintered 
nickel electrode has the problem of the active material having a low packing density, since the substrate such as perfo- 
rated steel plate should be provided and it cannot have a sufficiently high density. 

15 Besides, it becomes necessary, in order to pack the sintered substrate with an active material, to employ a solution 
immersion process which requires repeating a complex step several times. This is because the sintered body formed 
by sintering has too fine holes having a diameter of not more than 1 0jim. 

To solve the above problems, there is available what is known as "paste-type nickel electrode", which is obtained 
by impregnating or coating a sintered alkali-resistant metal fiber or a carbon fiber nonwoven fabric or the like plated with 

20 an alkali -resistant metal, with a slurry or paste containing nickel hydroxide (active material), a binder and a solvent. 
However, the paste-type nickel electrode, which contains the binder and permits a conductive network to form only to a 
small extent, has the problem of markedly low rate of utilization of the active material. 

Japanese Patent Application Laid-open Nos. 234867/1987 and 237667/1987 propose, in order to increase the uti- 
lization rate of the paste-type nickel electrode, increasing the conductivity of the surface of the active material particles 

25 by covering the surface of the nickel hydroxide particles with cobalt hydroxide. The cobalt hydroxide then dissolves in 
the alkaline electrolyte used and forms monovalent HCo02-ion, which is further converted into highly conductive CoOOH 
(cobalt oxyhydroxide) at high voltage and deposits on the surface of the nickel hydroxide particles. Likewise, Japanese 
Patent Application Laid-open No. 62457/1991 proposes a process of covering the surface of nickel hydroxide particles 
with a solid solution film of nickel hydroxide and cobalt hydroxide. 

30 However, with the paste-type nictel electrodes obtained by the above processes, in which the cobalt hydroxide 
covering the surface of nickel hydroxide particles diffuses into the particles in the course of repeated charge-discharge 
cycles, cannot maintain over a long period of charge-discharge cycles the inherent function of cobalt hydroxide of increas- 
ing the conductivity of the surface of the electrodes. As a result, it has been very difficult to obtain a paste-type nickel 
electrode with the discharge capacity decreasing only to a small extent in the course of charge-discharge cycles. 

35 Accordingly, an object of the present Invention is to provide an active material powder for non-sintered nickel elec- 
trodes of alkaline batteries with v^ich the diffusion of cobalt hydroxide covering the surface of nickel hydroxide particles 
Into the particles is suppressed, so that the function of the cobalt hydroxide of increasing the conductivity of electrode 
can be maintained over a long period of charge-discharge cycles. 

Another object of the present invention is to provide a process for producing the above active material powder. 

40 Still another object of the present invention is to provide a non-sintered nickel electrode for alkaline batteries which 
has the same effect as above. 

Yet another object of the present invention is to provide a process for producing the above electrode. 
The present invention provides an active material powder for non-sintered nickel electrodes for alkaline batteries, 
which comprises composite particles comprising nickel hydroxide particles or solid solution particles consisting essen- 

45 tially of nickel hydroxide and a mixed crystal covering the surface thereof, said mixed crystal comprising cobalt hydroxide 
and a hydroxide of at least one metal (M) selected from the group consisting of aluminum, magnesium, indium and zinc. 

The present invention further provides a process for producing the above active material powder for non-sintered 
nickel electrodes of alkaline batteries, which comprises immersing nickel hydroxide particles or solid solution particles 
consisting essentially of nickel hydroxide In a solution of a cobalt salt and a salt of at least one metal (M) selected from 

50 the group consisting of aluminum, magnesium, indium and zinc, adding an alkali to the solution to co-precipitate cot>alt 
hydroxide and a hydroxide of the metal, thereby covering the surface of the nickel hydroxide particles or solid solution 
particles consisting essentially of nickel hydroxide with the resulting mixed crystal of cobalt hydroxide and the hydroxide 
of the metal (M). 

The present invention still further provides a non-sintered nickel electrode for alkaline batteries, which uses an active 
55 material powder which comprises composite particles comprising nickel hydroxide particles or solid solution particles 
consisting essentially of nickel hydroxide and a mixed crystal covering the surface thereof, said mixed crystal corrprising 
cobalt hydroxide and a hydroxide of at least one metal (M) selected from the group consisting of aluminum, magnesium, 
indium and zinc. 



2 



EP 0 696 076 A1 



The present invention yet further provides a process for producing the above non-sintered nickel electrodefor alkaline 
batteries, which comprises: 

the step 1 of immersing nickel hydroxide particles or solid solution particles consisting essentially of nickel hydroxide In 
a solution of a cobalt salt and a salt of at least one metal (M) selected from the group consisting of aluminum, magnesium, 

s indium and zinc, adding an alkali to the solution to co-precipitate cobalt hydroxide and a hydroxide of the metal (M) , 
thereby covering the surface of the nickel hydroxide particles or solid solution particles consisting essentially of nickel 
hydroxide with tiie resulting mixed crystal of cobalt hydroxide and the hydroxide of the metal (M), to prepare an active 
material powder comprising composite particles, and the step 2 of coating or filling a substrate with the obtained active 
material powder, and drying tiie powder. 

10 With the electrode of the present invention, cobalt hydroxide, which covers as a component of a mixed crystal with 
the hydroxide of at least one metal (M) selected from the group consisting of aluminum, magnesium, indium and zinc, 
the surface of the active material particles (nickel hydroxide particles or solid solution particles of nickel hydroxide), 
minimally diffuses Into the active material particles. Alkaline batteries using the electrode of the present invention as 
positive electrode can therefore maintain, for a long period of time of charge-discharge cycles, tiie function of tiie cobalt 

15 hydroxide of increasing the conductivity of the electrode, tiiereby suppressing deaease in the discharge capacity in tiie 
course of charge<lischarge cydes. 

BRIEF DESCRIPTION OF THE DRAWINGS 

20 A more complete appreciation of tiie invention arxJ many of the attendant advantages thereof will be readily obtained 
as tiie same become better understood by reference to tiie following detailed description when considered in connection 
with the accompanying drawings, wherein: 

FIGURE 1 is a graph showing the charge-discharge characteristic of the nickel-cadmium batteries prepared in Exam- 
25 pies, 

FIGURE 2 is another graph showing tiie charge-discharge characteristic of the nickel-cadmium batteries prepared 
in Examples, and 

FIGURE 3 is a graph showing tiie relationship between tiie content of mixed crystal in composite particles and tiie 
discharge capacity at tiie 300-th cyde. 

30 

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 

Among the composite partides usable in tiie present invention, tiiose of nickel hydroxide or its solid solution covered 
with a mixed crystal of cobalt hydroxide, and magnesium oxide and/or zinc oxide: in particular those covered with a 

35 mixed crystal of cobalt hydroxide and magnesium hydroxide. 

In the at>ove case, it is desirable that the mixed crystal in the invention contain 0.5 to 50% by weight In terms of 
metal of magnesium hydroxide and/or zinc hydroxide, based on the total weight of cobalt, and magnesium and/or zinc 
contained in the mixed crystal. 

If the content is less tiian 0.5% by weight, it will become difficult to suppress the diffusion of cobalt hydroxide into 

40 the active material particles (particles of nickel hydroxide or its solid sdution] effectively and further to obtain an electrode 
capable of providing a battery with which the discharge capacity decreases only slightiy as the charge-discharge cycles 
proceed. On tiie other hand, if the content exceeds 50% by weight, tiie conductivity will decrease and hence it becomes 
difficult to obtain an electrode capable of providing a battery tiie discharge capadty of which decreases only slightiy as 
the charge-discharge cydes proceed. 

45 It is desirable that the composite particles used in the invention contain 3 to 25% by weight of the mixed crystal 
(solid solution] containing cobalt hydroxide and a hydroxide of at least one metal (M) selected from the group consisting 
of magnesium, zinc, aluminum and indium. Witii a content of tiie mixed crystal of less than 3% by weight, which means 
thai the amount of cobalt hydroxide is insufficient, it is difficult to increase the conductivity of the resulting electrode 
suffidentiy and to obtain an electiode capable of providing a battery witii large discharge capadty. On the otiier hand, 

50 witii tile content of mixed crystal exceeding 25% by weight, the amount of nickel hydroxide as active material becomes 
small and hence it becomes also difficult to obtain an electrode capable of providing a battery with large discharge 
capadty. In summary, the most preferable is composite particles containing 3 to 25%, by weight of the mixed crystal 
which contains 0.5 to 50% by weight in terms of metal of cobalt hydroxide, and magnesium hydroxide and/or zinc hydrox- 
ide, based on the total weight of cobalt, and magnesium and/or present in the mixed crystal. 

55 Salts of tiie above metal (M) preferably used in tiie processes of the present invention are sulfates and nitrates and 
those of cobalt are cobalt sulfate and cobalt niti-ate. Witii use of these metal salts, impurities that impair the electrode 
characteristics mix into the active material particles (partides of nickel hydroxide or solid solution particles containing 
nickel hydroxide as a main component) only to a small extent, so that the adive material particles are not particularly 



3 



EPoege 076ai 



affected adversely. The sulfates and nitrates may be used in combination with each other and so are cobalt sulfate and 
cobalt nitrate. Furthermore, either or both of the sulfates and nitrates may be used in combination of 2 or more. 

With the processes of the present irrvention and where the mixed aystal consists of cobalt hydroxide and at least 
one metal (M) selected from magnesium and zinc, it is desirable to adjust the composition of the solution such that the 

5 resulting mixed crystal present on the composite particles will contain the hydroxide of metal (fW) in an amount in terms 
of metal (M) of 0.5 to 50% by weight based on the total weight of cobalt and the metal (M) contained In the mixed crystal. 
In general, the ratio of metals between the salt of at least one metal (M) selected from the group consisting of aluminum, 
magnesium, indium and zinc and the cobalt salt contained in the solution becomes equal to the ratio between the metal 
(M) and cobalt present in the mixed crystal. It is also desirable to adjust the amount (coating amount) of the mixed crystal 

10 precipitated on the surface of active material particles such that the resulting composite particles contain 3 to 25% by 
weight of the mixed crystal. The amount (coating amount) of the mixed crystal can be adjusted by adjusting the concen- 
trations of a salt of the metal (M) and a cobalt salt in the solution. To summarize, the most preferred embodiments of 
the processes of the present invention use a solution containing a cobalt salt and a salt of at least one metal selected 
from magnesium and zinc and carry out both of the above two adjustments. 

IS Examples of the alkali used in the process of the invention are sodium hydroxide, potassium hydroxide and lithium 
hydroxide. 

Examples of the substrate used in the process of the invention include foamed porous metallic bodies, metal fibers, 
carbon fiber, metallic meshes and perforated metal plates. 

Examples of solid solution particles usable for the articles and processes of the present invention are those com- 
20 prising nickel hydroxide particles in which at least one element selected from calcium, zinc, cobalt or cadmium has been 
dissolved as solid. 

EXAMPLES 

25 Other features of the invention vAW become apparent in the course of the descriptions of exemplary emt>odiments 
which are given for illustration of the invention and are not intended to be limiting thereof. 

Example 1 

30 [Preparation of active material powders] 

In 1,000 ml of an aqueous solution of 14.3 g of cobalt sulfate and 10.7 g of magnesium sulfate, 100 g of nickel 
hydroxide powder was put and a 1 M aqueous sodium hydroxide solution was, with stirring, added dropwise to the mixture 
to a pH of 12, and the mixture was then allowed to stand for 1 hour. The pH was measured with a glass electrode pH 

35 meter equipped wKh an automatic temperature compensator. The obtained mixtjre was filtered, arxJ the residue was 
washed with water and vacuum-dried to yield an active material powder which conrprises composite particles comprising 
nickel hydroxide particles the surface of which Is covered with a mixed crystal of magnesium hydroxide artd cobalt hydrox- 
ide. The ratio between the cobalt hydroxide and magnesium hydroxide was adjusted by adjusting the ratio between the 
cobalt salt (cobalt sulfate) and the magnesium salt (magnesium sulfate) to be dissolved in water. The content of the 

40 mixed crystal in the composite particles was adjusted by adjusting the amounts of the cobalt salt and magnesium salt 
used The content of magnesium hydroxide in the mixed crystal was 1% by weight [Mg/ (Mg + Co) x 100 ] in terms of 
metal based or the total weight of cobalt and magnesium contained in the mixed crystal . The content of the mixed crystal 
in the composite particles was 5% by weight. Botii of these values were obtained based on measurements by atomic 
absorption analysis. 

45 In the same manner as above, there were prepared active material powders which comprised composite particles 
comprising nickel hydroxide particles the surface of which was covered with a mixed crystal of cobalt hydroxide-zinc 
hydroxide, cobalt hydroxide-indium hydroxide, cobalt hydroxide-aluminum hydroxide, cobalt hydroxide-magnesium 
hydroxide-zinc hydroxide, cobalt hydroxide-magnesium hydroxide-aluminum hydroxide or cobalt hydroxide-zinc hydrox- 
ide-indium hydroxide. Sulfates were used for all of the cobalt, zinc, indium, aluminum and magnesium materials. In each 

50 of the above, the content of the fiydroxide of the metal (M) in the mixed crystal was 1% by weight in terms of metal based 
on the total weight of cobalt and the metal (M) contained in the mixed crystal. All of the composite particles had the 
same mixed crystal content of 5% by weight. 

[Preparation of non-sintered nickel electrodes] 

55 

Pastes were prepared by kneading 80 parts by weight of the above active material powders and 20 parts by weight 
of a 1% by weight aqueous methylcellulose solution. Porous bodies formed of a nickel-plated foamed metal (porosity: 
95, average particle diameter 20Q)im) were each filled with each of the pastes thus prepared and then dried and shaped 
into non-sintered nickel electrodes. 



4 



EP 0 696 076 A1 



[Preparation of batteries] 

AA-size nickel-cadmium batteries Al through A7 (discharge capacity: 1.100 mAh) were prepared by assembling 

the above non-sintered nickel electrodes as positive electrode and a known paste-type cadmium electrode as negative 
5 electrode, together with a nylon nonwoven separator, an alkaline electrolyte, a metal battery container, a metal lid and 

other battery parts. An aqueous solution (density: 1 .285) of potassium hydroxide, sodium hydroxide and lithium hydroxide 

in a ratio by weight of 8:1 :1 was used as the alkaline electrolyte. 

The batteries A1 through A7 use active material powders which conprise composite particles comprising nickel 

hydroxide particles the surfaces of which are covered with mixed crystals of cobalt hydroxide-magnesium hydroxide, 
10 cobalt hydroxide-zinc hydroxide, cobalt hydroxide-indium hydroxide, cobalt hydroxide-aluminum hydroxide, cobalt 

hydroxide-magnesium hydroxide-zinc hydroxide, cobalt hydroxide-magnesium hydroxide-aluminum hydroxide and 

cobalt hydroxide-zinc hydroxide-Indium hydroxide, respectively 

Comparative Example 1 

15 

To 1 ,000 ml of an aqueous solution of 14.3 g of cobalt sulfate, 100 g of the same nickel hydroxide powder as used 
in Example 1 was added with stirring and a 1 M aqueous sodium hydroxide solution was, with stirring, added dropwise 
to the mixture to a pH of 12. and the mixture was then allowed to stand for 1 hour. The obtained mixture was filtered, 
and the residue was washed with water and vacuum-dried to yield an active material powder which comprises composite 
20 particles comprising nickel hydroxide particles the surface of which is covered with cobalt hydroxide. The content of 
cobalt hydroxide in the composite particles was 5% by weight. A comparison battery X was prepared in the same manner 
as in Example 1 except for using the obtained active material powder. The comparison battery X was thus prepared 
nearly in accordance with the process disclosed in Japanese Patent Application Laid-open No. 234867/1987. 

25 Qgrnparativg Exgmplg 2 

To 1 ,000 ml of an aqueous solution of 14.3 g of cobalt sulfate and 4.52 g of nickel sulfate, 100 g of the same nickel 
hydroxide powder as used in Example 1 was added with stirring and a 1 M aqueous sodium hydroxide solution was, with 
stirring, added dropwise to the mixture to a pH of 1 2, and the mixture was then allowed to stand for 1 hour. The obtained 

30 mixture was filtered, and the residue was washed with water and vacuum-dried to yield an active material powder which 
comprises composite particles comprising nickel hydroxide particles the surface of which Is covered with a mixed crystal 
of cobalt hydroxide and nickel hydroxide. The content of nickel hydroxide in the mixed crystal was 20% by weight in 
terms of metal based on the total weight of cobalt and nickel contained in the mixed crystal. The content of the mixed 
crystal in the composite particles was 5% by weight. A comparison battery Y was prepared in the same manner as in 

35 Example 1 except for using the obtained active material powder. The comparison battery Y was thus prepared nearly 
in accordance with the process disclosed In Japanese Patent Application Laid-open No. 62457/1991 . 

Charoe-discharae cvcle characteristi cs of the batteries 

40 The batteries Al through A7 and the comparison batteries X and Y were subjected to a charge-discharge cycle test 
in which one cycle consists of charging at a charge cun'ent of 0.1 C to 1 60% and then discharging at a discharge current 
of 1 C to a terminal voltage of 1 .0 V, to study their charge-discharge cyde characteristics. 

FIGURE 1 1s a graph showing the charge-discharge characteristics of the batteries tested, with the ordinate repre- 
senting the discharge capacity (an index assuming that the discharge capacity at the 1st cycle is 100) and the abscissa 

45 the number of charge-discharge cycles. As seen from FIGURE 1 , while the discharge capacity of the comparison bat- 
teries X and Y decreased as the charge-discharge cycles proceeded, that of the batteries Al through A7 using the 
electrodes of the invention did not appreciably decrease. This is because with the batteries Al through A7, each using 
composite particles comprising nickel hydroxide particles covered with a mixed crystal of cobalt hydroxide and the hydrox- 
ide of at least one metal (M) selected from the group consisting of aluminum, magnesium, indium and zinc, it ts difficult 

so for the cobalt hydroxide to diffuse into the nickel hydroxide particles. 

It was also found, in separate experiments, that covering the surface of a solid solution particles confprising nickel 
hydroxide particles Into which at least one element selected from calcium, zinc, cobalt or cadmium has been dissolved, 
with the above mixed crystals provides batteries having charge-discharge cycle characteristics of the same excellent 
level as that of the batteries Al through A7. 

55 

Exampig 2 

There were prepared non-sintered nickel electrodes for alkaline batteries using as active material composite parti- 
cles comprising nickel hydroxide particles the surface of which was covered with mixed crystals of cobalt hydroxide and 



5 



EP0 696 076 A1 



magnesium hydroxide each having a different content of magnesium hydroxide in terms of metal as follows: 0.1% by 
weight, 0.25% by weight, 0.5% by weight, 1% by weight, S% by weight, 10% by weight, 25% by weight, 35% by weight, 
50% by weight, 55% by weight or 60% by weight. Then, nickel -cadmium batteries B1 through B11 were prepared by 
using these electrodes in this order. With all of the electrodes, the content of the mixed crystal in the composite particles 
5 was adjusted to be 1 0% by weight. 

The batteries B1 through 81 1 thus prepared were subjected to the same charge discharge cycle test as conducted 
in Example 1, to study their charge-discharge cycle characteristics. The results are shown in FIGURE 2 with the same 
coordinate system as in FIGURE 1 and in Table 1 . Table 1 shows the discharge capacity at the 300-th cycle of each 
battery in terms of an index with that of the battery 84 being 100. 

10 

Table 1 



Battery 


83 


B4 


85 


86 


87 


88 


B9 


810 


811 


Content of Mg (% by weight) 


0.5 


1 


5 


10 


25 


35 


50 


55 


60 


Discharge capacity 


100 


100 


100 


100 


99 


99 


99 


90 


85 



As seen front FIGURE 2, the batteries 83 through 811, having a content of magnesium hydroxide in the mixed 
20 crystal of at least 0.5% by weight in terms of metal, have better charge-discharge cycle characteristics than those of the 
batteries 81 and B2 with the content being less than 0.5% by weight. From this fact, it is understood that the content is 
desirably at least 0.5% by weight. 

On the other hand, as seen from Table 1 , the batteries BIO and B1 1 , having a content of magnesium hydroxide in 
the mixed crystal exceeding 50% by weight in terms of metal, have a smaller discharge capacity than that of any one 
25 of the batteries B3 through B9 having the content of less than 50% by weight. From this fact, it is understood that the 
content is desirably not more than 50%. In summary, the content of magnesium hydroxide in the mixed crystal is desirably 
in a range of 0.5 to 50% by weight in terms of metal. 

The content in the mixed crystal is desirably in a range of 0.5 to 50% also for zinc. 

30 Ex^mpl^ 3 

There were prepared non sintered nickel electrodes for alkaline batteries, using as active material conrposite par- 
ticles comprising nickel hydroxide particles the surface of which was covered with mixed crystals of cobalt hydroxide 
and magnesium hydroxide, with the content of the mixed crystals differing as follows: 0% by weight, 2% by weight, 3% 
35 by weight, 5% by weight, 10% by weight, 1 5% by weight. 20% by weight, 25% by weight. 26% by weight, 28% by weight 
and 30% by weight. Then, nickel-cadmium batteries CI through C1 1 were prepared by using these electrodes in this 
order. With all of the electrodes, the content of magnesium hydroxide in the mixed crystal was adjusted to be 10% by 
weight. 

The batteries CI through C1 1 thus prepared were subjected to the same charge-discharge cycle test as conducted 
40 in Example 1, to study their discharge capacity at the 300-th cyde. The results are shown in FIGURE 3 in which the 
ordinate represents the discharge capacity (in terms of an index with the discharge capacity of the battery C4 at the 10- 
th cycle being 100) of each battery at the 300-th cycle and the abscissa the content (% by weight) of mixed crystal in 
the composite particles. 

As seen from FIGURE 3, the batteries C3 through C8, having a mixed crystal content in a range of 3 to 25% by 
45 weight, have a larger discharge capacity at the 300-th cycle than those of the batteries C1 and C2 and C9 through C1 1 
with the content deviating from this range. From this fact, it is understood that the mixed crystal content in composite 
particles is desirably in a range of 3 to 25% by weight. 

Thedesirable mixed crystal corrtent is also in a range of 3 to 25% for aluminum, indium and zinc, besides magnesium. 

50 Example 4 

There were prepared, in the same manner as in Example 1. non-sintered nickel electrodes for alkaline batteries, 
using as active material composite particles comprising nickel hydroxide particles the surface of which was covered with 
mixed crystals of cobalt hydroxide-magnesium hydroxide, cobalt hydroodde-zinc hydroxide, cobalt hydroxide-indium 
55 hydroxide or cobalt hydroxide-aluminum hydroxide, with the content of magnesium, zinc, indium or aluminum in the 
copreclpitates differing as shown in Table 2. Then, nickel-cadmium batteries were prepared by using these electrodes 
in the same manner as In Example 1. In every case, the content of co-precipitate (not of mixed crystal) in magnesium 
hydroxide in the mixed crystal was adjusted to be 10% by weight. 

The batteries thus prepared were tested, in order to study the influence of the co-precipitate used, as follows. 



6 



EP0 696 076 A1 



Each of the batteries was subjected to 10 charge-discharge cycles where one cycle consisted of charging at a 
charge current of 0.1 C to 160% and discharging at a discharge current of 1C to a terminal voltage of 1 .0 V. and then 
charged at a charge current of 0.1 C to 160%. Each battery thus charged was, while being connected to a resistor of 
5U allowed to stand at a temperature of 70<'C for 7 days. The batteries were then charged at a charge current of 0.1 C 
5 to 1 60% and discharged at a discharge current of 1 C to a terminal voltage of 1 .0 V and, thereafter, tested for discharge 
capacity, D1 . The ratio (%} between D1 and the discharge capacity D2 at the 10-th cycle for each battery was obtained. 
The results are shown in Table 2. A larger value of this ratio indicates that the discharge capacity decreases, after the 
battery is connected to a load, to a smaller extent. 



Content of metal (M) in co-preciprtate (%) \M/{Co + M) x 100] 


0 


0.5 


1 


5 


10 


25 


35 


50 


55 


Tvoe of metal 




















Magnesium 




94 


96 


97 


98 


96 


95 


94 


90 


Zinc 




86 


92 


93 


92 


93 


92 


87 


86 


Indium 




77 


76 


(Mixed crystal not formed.) 


Aluminum 




80 


82 


(Mixed crystal not formed.) 


{Co(OH)2 alone) 


72 



















It is understood from Table 2, that non-sintered nickel electrodes using as active material composite particles com- 
25 prising nickel hydroxide particles the surface of which is covered with cobalt hydroxide magnesium hydroxide co-precip- 
itate or cobalt hydroxide-zinc hydroxide co-precipitate provide batteries the discharge capacity of which deaeases, after 
they are connected to load, only slightly. This is considered to be due to the fact that the co-precipitates of cobalt hydroxide 
and magnesium hydroxide and those of cobalt hydroxide and zinc hydroxide are present while having the structure of 
mixed crystal in wide composition ranges. In particular, the cobalt hydroxide-magnesium hydroxide co-predpitates 
30 yielded batteries with the smallest decrease in the discharge capacity after deep discharge at high temperature under 
a loaded condition. As regards indium and aluminum, where the content of indium hydroxide or aluminum hydroxide is 
large, no mixed crystals were obtained due to separation of irKlium hydroxide or aluminum hydroxide. 

Although the above Exanples used as active material powder nickel hydroxide particles, use of solid solution par- 
ticles consisting essentially of nickel hydroxide can produce the same excellent effect. 
35 Although the above description has been made in the Examples while taking nickel cadmium batteries as examples, 
the present invention is widely applicable to alkaline batteries in general, including nickel-hydrogen battery. 

Obviously, numerous modifications and variations of the present invention are possible in light of the above teach- 
ings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced 
otherwise than as specifically described herein. 

40 

Claims 

1. An active material powder for non-sintered nickel electrodes of alkaline batteries, which comprises composite par- 
ticles comprising nickel hydroxide particles or solid solution particles consisting essentially of nickel hydroxide and 

45 a mixed crystal covering the surface thereof, said mixed crystal comprising cobalt hydroxide and a hydroxide of at 
least one metal (M) selected from the group consisting of aluminum, magnesium, indium and zinc. 

2. The active material powder for non-sintered nickel electrodes of alkaline batteries according to Claim 1 , wherein 
said solid solution particles are nickel hydroxide particles in which at least one element selected from the group 

50 consisting of zinc, cobalt, calcium and cadmium has been dissolved. 

3. The active material powder for non-sintered nickel electrodes of alkaline batteries according to claim 1 or 2, wherein 
said composite particles contain 3 to 25% by weight of said mixed crystal. 

55 4. The active material powder for non-sintered nickel electrodes of alkaline batteries according to any of claim 1 to 3, 
wherein said mixed crystal comprises magnesium hydroxide and cobalt hydroxide, zinc hydroxide and cobalt hydrox- 
ide, or n^gneslum hydroxide, zinc hydroxide and cobalt hydroxide. 



7 



EP0 696 076 A1 



5. The active material powder for non-sintered nickel electrodes of alkaline batteries according to claim 4, wherein 
said mixed crystal contains 0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide 
based on the total weight of cobalt, and magnesium and/or zinc. 

5 6. The active material powder tor non-sintered nickel electrodes of alkaline batteries according to Claim 4, wherein 
said mixed crystal contains 0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide 
based on the total weight of cobalt, and magnesium and/or zinc and said composite particles contain 3 to 25% by 
weight of said mixed crystal. 

10 7. The active material powder for non -sintered nickel electrodes of alkaline batteries according to any of claims 1 to 
3, wherein said mixed crystal comprising nnagnesium hydroxide and cobalt hydroxide. 

8. A non-sintered nickel electrode for alkaline batteries, which uses an active material powder which comprises com- 
posite particles comprising nickel hydroxide particles or solid solution particles consisting essentially of nickel hydrox- 

15 ide and a mixed crystal covering the surface thereof, said mixed crystal comprising cobalt and a hydroxide of at 
least one metal (M) selected from the group consisting of aluminum, magnesium, indium and zinc. 

9. The non-sintered nickel electrode for alkaline batteries according to Claim 8, wherein said solid solution particles 
are nickel hydroxide particles in which at least one element selected from the group consisting of zinc, cobalt, calcium 

20 and cadmium has been dissolved. 

10. The non-sintered nickel electrode for alkaline batteries according to claim 8 or 9, wherein said composite particles 
contain 3 to 25% by weight of said mixed crystal. 

25 1 1 . The non-sintered nickel electrode for alkaline batteries according to any of claims 8 to 1 0, wherein said mixed crystal 
comprises nnagnesium hydroxide and cobalt hydroxide, zinc hydroxide and cobalt hydroxide, or magnesium 
hydroxde, zinc hydroxide and cobalt hydroxide. 

12. The non-sintered nickel electrode for alkaline batteries according to Claim 1 1 , wherein said mixed crystal contains 
30 0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide based on the total weight of 

cobalt, and magnesium and/or zinc. 

13. The non-sintered nickel electrode for alkaline batteries according to Claim 1 1 , wherein said mixed crystal contains 
0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide based on the total weight of 

35 cobalt, and magnesium and/or zinc and said composite particles contain 3 to 25% by weight of said mixed crystal. 

14. The non-sintered nickel electrode for alkaline batteries according to any of claims 8 to 1 0, wherein said mixed crystal 
comprises magnesium hydroxide and cobalt hydroxide. 

40 1 5. A process for producing active material powders for non-sintered nickel electrodes of alkaline batteries, which com- 
prises immersing nickel hydroxide particles or solid solution particles consisting essentially of nickel hydroxide in a 
solution of a cobalt salt and a salt of at least one metal (M) selected from the group consisting of aluminum, mag- 
nesium, indium and zinc, adding an alkali to the solution to co-predpitate cobalt hydroxide and a hydroxide of the 
metal (M), thereby covering the surface of the nickel hydroxide particles or solid solution particles consisting essen- 

45 tially of nickel hydroxide with the resulting mixed crystal of cobalt hydroxide and the hydroxide of the metal (M). 

1 6. The process for producing active material powders for non-sintered nickel electrodes of alkaline batteries according 
to Claim 15, wherein said salt of at least one metal (M) is sulfate and/or nitrate and said cobalt salt is cobalt sultete 
and/or cobalt nitrate. 

50 

1 7. The process for producing active material powders for non-sintered nickel electrodes of alkaline tjatteries according 
to claim 15 or 16, wherein the concentrations of the salt of said metal (M) and said cobalt salt are adjusted such 
that said composite particles contain 3 to 25% by weight of said mixed crystal. 

55 18. The process for producing active material powders for non-sintered nickel electrodes of alkaline batteries according 
to any of claims 15 to 17, wherein said solution is a solution of a magnesium salt and a cobalt salt, a zinc salt and 
a cobalt salt, or a magnesium salt, a zinc salt and a cobalt salt and the composition of the solution is adjusted such 
that said mixed crystal contains 0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide 
based on the total weight of cobalt, and magnesium and/or zinc. 



8 



EP 0 696 076 A1 



19. The process for producing active material powders for non-sintered nickel electrodes of alkaline batteries according 
to any of claims 15 to 1 8, wherein said solution is a solution of a magnesium salt and a cobalt salt, a zinc salt arxJ 
a cottalt salt, or a magnesium salt, a zinc salt and a cobalt salt; the composition of the solution is adjusted such that 
said mixed crystal contains 0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide 
based on the total weight of cobalt, and magnesium and/or zinc; and the concentrations of said magnesium salt 
and/or zinc salt and said cobalt salt are adjusted such that said composite particles contain 3 to 25% by weight of 
said mixed crystal. 

20. A process for producing non-sintered nickel electrodes for alkaline batteries, which comprises: 

the step 1 of immersing nickel hydroxide particles or solid solution particles consisting essentially of nickel hydroxide 
in a solution of a cobalt salt and a salt of at least one metal (M) selected from the group consisting of aluminum, 
magnesium, indium and zinc, adding an alkali to the solution to co-predpitate cobalt hydroxide and the hydroxide 
of the metal (M), thereby covering the surface of the nickel hydroxide particles or solid solution particles consisting 
essentially of nickel hydroxide with the resulting mixed crystal of cobalt hydroxide and the hydroxide of the metal 
(M], to prepare an active material powder comprising composite particles, and 

the step 2 of coating or filling a substrate with the obtained active material powder, and drying the powder. 

21 . The process for producing non-sintered nickel electrodes for alkaline batteries according to Claim 20, wherein said 
salt of at least one metal (M) is sulfate and/or nitrate and said cobalt salt is cobalt sulfate and/or cobalt nitrate. 

22. The process for producing non-sintered nickel electrodes for alkaline batteries according to claim 20 or 21 , wherein 
the concentrations of the salt of said metal (M) and said cobalt salt are adjusted such that said composite particles 
contain 3 to 25% by weight of said mixed crystal. 

23. The process for producing non-sintered nickel electrodes for alkaline batteries according to any of claims 20 to 22, 
wherein said solution is a solution of a magnesium salt and a cobalt salt, a zinc salt and a cobalt salt, or a magnesium 
salt, a zinc salt and a cobalt salt and the composition of the solution is adjusted such that said mixed crystal contains 
0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide based on the total weight of 
cobalt, and magnesium and/or zinc. 

24. The process for producing non-sintered nickel electrodes for alkaline batteries according to any of claims 20 to 22, 
wherein said solution is a solution of a magnesium salt and a cobalt salt, a zinc salt and a cobalt salt, or a magnesium 
salt, a zinc salt and a cobalt salt; the composition of the solution is adjusted such that said mixed crystal contains 
0.5 to 50% by weight in terms of metal of magnesium hydroxide and/or zinc hydroxide based on the total weight of 
cobalt, and magnesium and/or zinc; and the concentrations of said magnesium salt and/or zinc salt and said cobalt 
salt are adjusted such that said conrtposite particles contain 3 to 25% by weight of said mixed crystal. 



EP 0 696 076 A1 




EP 0 696 076 A1 




EP0 696 076 A1 




EP 0 696 076 A1 



European Patent 
OflSce 



EUROPEAN SEARCH REPORT 



AppUcatlon Number 

EP 95 11 2239 



DOCUMENTS CONSIDERED TO BE RELEVANT 



Category 



Citatioa of documeitt with indication, where appropriate, 
of rdevant pasBages 



Relevant 
to dain 



CLASSmCATION OF THE 
APPUCAHON antCL6) 



X 

X 

P,X 



EP-A-0 557 522 (YUASA CORP) 1 September 
1993 

* page 5, line 28 - line 36; claim 8 * 

EP-A-0 575 093 (INCO LTD) 22 December 1993 

* claims 1-10 * 

EP-A-0 544 Oil (YUASA CORP ;YUASA BATTERY 
CO LTD (JP)) 2 June 1993 

* claims 1-7 * 

EP-A-O 650 207 (FURUKAWA BATTERY CO LTD) 
26 April 1995 

* claims 1-11 * 

US-E-RE34752 (M. OSHITANI ET AL.) 4 
October 1994 

* column 6, line 65 - column 7, line 65; 
claims 1-7 * 

DE-A-27 31 064 (VOLKSWAGENWERK AG) 11 
January 1979 

* claims 1-11 * 



The present search report has been drawn up for lU daiois 



1.15 

1,15 
1,15 

1,15 
1,15 

1-24 



H01M4/52 



TECHNICAL FIELDS 
SEARCHED aBt.a.6) 



HOIM 



THE HAGUE 



16 November 1995 



Battistig, M 



CATEGORY OF OTED DOCUMENTS 

X : particultriy rdevant if taken alone 

Y : pardculariy rtkvant If combined wHb ■notbcr 

document of the laae categoty 
A ; technological backcnund 
O : Dan>«Tittai dltdonire 
P : fntenD«4i»te document 



T : theory or principle nndcriyittg the inventioD 
E : earlier patmt docutnent, but published on, or 

■ftv the filing date 
D : doouKcnt dted Id the applicaHoo 
L : docunat cited for other reaions 



A : Bcnber of the sanM patent faml^, cnrrei^dbig 
doctnacot 



13