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STA 154-FC 

%5)P(tf L # 09/868995 

/ . , . JC18 Rec'd PCT/PTO 2 0 JUN 20D 



<=\vl / 




.p^ ^ Nickel mixed jfrydroxide, process for the preparation thereof and the use thereof 



as cathode material in alkaline batteries 



y 3 / 5 The present invention relates to a nickel mixed hydroxide with Ni as the main 
element and with an expanded layer structure, a process for the preparation thereof 
by cb-precipitation of the hydroxides in an alkaline medium and to the use thereof as 
cathode material in alkaline batteries. 

10 p-Nickel(II) hydroxide is used in alkaline accumulators as positive electrode 

& material. Changes in certain electrochemical properties may be obtained by 

*S incorporating foreign ions, 

? jf The incorporation of trivalent ions in the nickel hydroxide matrix in molar 

*B 15 proportions of >20 mol % leads to a new structure. The materials thus altered have 

Si the structure of hydrotalcite and, in comparison with p-Ni(OH) 2 , are characterised by 



an expanded layer structure in the intermediate layers of which water and various 
anions are present. The layer expansion alone has a fundamental influence on the 
electrochemistry, in this case on the potential position and electrochemical 
20 usefulness of the nickel ions. The trivalent cation used in each case exerts an 
additional effect on the electrochemical behaviour of the materials. 



Single-substituent variants containing the substituents Fe, Mn, Co and Al are known 
from the literature. Most have improved utilisation of the nickel ions but their 
25 stability is not very pronounced. Others, on the other hand, have good cycle stability 
but the nickel utilisation is lower. 

Substitution with a combination of two different cations is also found in the 
literature. EP 0 793 285 Al describes nickel hydroxide materials which contain, for 
30 example, the elements Co or Mn in combination with elements such as, e.g., Fe, Al, 
La and others. Co and Mn are used in divalent form in the preparation of materials, 



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no oxidising agents being used in the further course of preparation. Where 
preparation takes place by electrochemical (cathodic) deposition, precipitation even 
takes place in a reducing environment due to accompanying hydrogen evolution. Co 
is therefore present in the divalent form in the finished active material, together with 
t rivalen t cations such as Fe, Al, La amongst others The materials are analysed and 
assessed in terms of their potential position during the discharge process and charge 
acceptance at relatively high temperatures, but there are no details whatsoever about 
the cycle stability and actual electrochemical utilisation in the form of absolute 
values. Only relative capacities are given. 

EP 0 712 174 A2 describes nickel hydroxides in which, in contrast to EP 0 793 285 
Al, trivalent instead of divalent Mn ions are used as substituents in combination 
with other trivalent elements such as Al, Fe and Co. Mn is present in the product in 
the trivalent form together with Al, Fe or Co, and it is also possible for Mn to be 
present in several oxidation states simultaneously ("mixed valent") in the solid. 
These Mn-containing materials exhibit pronounced cycle stability but the nickel 
utilisation is only slightly above that of the conventional nickel hydroxides. No 
practical indications that the use of mixed valent systems other than Mn may lead to 
an improvement in the capacity and nickel utilisation can be derived from this prior 
art. 

The object of the present invention is to provide a nickel mixed hydroxide which, 
whilst having good cycle stability, exhibits a marked improvement in the 
electrochemical utilisation of the nickel ions and the mass-related capacity. 
Moreover, a simple process for the preparation of such a nickel mixed hydroxide 
should be given. 

This object is achieved by a nickel mixed hydroxide according to claim 1. 
Advantageous embodiments of the nickel mixed hydroxide according to the 
invention are given in subclaims 2 to 6. 



STA 154-FC 




The invention provides, therefore, a nickel mixed hydroxide with Ni as the main 
element and with a layer structure comprising 

a) at least one element M a from the group comprising Fe, Cr, Co, Ti, Zr and Cu, 
which is present in two different oxidation states which differ by one electron 
in terms of the number of outer electrons; 

b) at least one element M b present in the trivalent oxidation state from the group 
comprising B, Al, Ga, In and RE (rare earth metals, preferably Sc, Y or La); 

c) optionally at least one element M c present in the divalent oxidation state 
from the group comprising Mg, Ca, Sr, Ba and Zn; 

d) apart from the hydroxide, at least one additional anion from the group 
comprising halides (preferably fluoride or chloride), carbonate, sulfate, 
acetate, oxalate, borate and phosphate in a quantity at least sufficient to 
preserve the electroneutrality of the mixed hydroxide; and 

e) water of hydration in a quantity that stabilises the relevant structure of the 
mixed hydroxide. 

Surprisingly, it became apparent according to the invention that particularly cycle- 
stable nickel mixed hydroxides with markedly increased nickel utilisation are 
obtained in particular when, apart from nickel, at least two other cations are present 
in the nickel hydroxide matrix, one of which (M a ) is selected from the group 
comprising Fe, Cr, Co, Ti, Zr and Cu, this being present in two different oxidation 
states which differ by one electron in terms of the number of outer electrons, that is, 
in a defined mixed valent form, and the other (M b ) from the group comprising B, Al, 
Ga, In and RE (rare earth metals) is present in the fixed trivalent oxidation state. 



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Such a material exhibits very good cycle stability in half-cell tests, a maximum 
electronic utilisation of 1.5 electrons per nickel ion being obtained. 

In full-cell tests this material exhibits a utilisation of a constant 1.5 electrons per 
nickel ion during a measurement over 100 cycles, which corresponds to a specific 
capacity of more than 260 mAh/g. 

The nickel hydroxide materials according to the invention exceed those in which the 
two additional cations (Ni substituents), as described in EP 0 793 285 Al, are 
present in a uniform oxidation state in each case, as shown by an electrochemical 
comparison in the example part below. They also exceed those nickel hydroxide 
materials in which, according to EP 0 712 174 A2, one additional cation is, for 
example, trivalent Al or Co and the other additional cation is Mil, which may be 
present simultaneously in different oxidation states. 

The nickel hydroxide materials according to the invention may be prepared in 
densities favourable for use in secondary batteries, which densities correspond to 
those of p-nickel hydroxides having a regular morphology. 

Without being bound by any particular theory, it may be assumed that several effects 
can be held responsible for these improvements: 

1. It is assumed that lattice defects arise if the various Ni substituents M b (III), 
M a (III) and M a (II) are present in the material. If, for example, the element M a 
is present in the oxidation states (III)/(II), the proportion of trivalent cations 
and hence the charge of the main layer can be regulated by means of the 
M a (III)/M a (II) ratio. The anion and water content of the structure depend on 
the latter. In hydrotalcite compounds, the anions in the interlayer are bound 
solely by electrostatic forces. If however, as in the material according to the 
invention, a substituent is also present in the divalent form in a defined 
proportion, it is conceivable that the anions in these domains (if the a- 
structure is present) may be bound in the same way as in basic salts, i.e. 
linked directly to the main layer. As a result, anisotropic lattice defects are 
induced (i.a. layer shifts) which may have positive effects on the activity of 



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the material. Even when an electrochemical load is applied, lattice defects in 
the starting structure and hence the activity of the material remain intact over 
a relatively long period. 

2. It is also possible that, if the material is used as an electrode material in the 
5 electrode, Co(II) ions, e.g., which are present in the edge regions, may 

develop a kind of cobalt coating on the particle surface by way of a solution- 
recrystallisation process which, apart from the above-mentioned 
considerations, may explain the improvement in the electrochemical 
properties by an increase in the electronic conductivity. 

p 10 The proportion of Ni in the nickel mixed hydroxide according to the invention is 

preferably 60 to 92 mol %, more preferably 65 to 85 mol % and particularly 
It! preferably 75 to 80 mol %. In other words, the total proportion of the elements M a , 

d M b and Mc is preferably 40 to 8 mol %, more preferably 35 to 15 mol % and 

particularly preferably 25 to 20 mol %, in each case based on the total amount of Ni, 
15 M a , M b and M c . 

The proportion of the mixed valent metal M a present is preferably 10 to 40 mol %, 
more preferably 20 to 30 mol %, based on the total amount of the elements M a , M b 
and M c . 

The proportion of the optionally used doping element M c is preferably 1 to 30 mol 
20 %, based on the total amount of the elements M a , M b and M c but a maximum of 5 
mol % based on the total amount of the elements Ni, M a , M b and M c . 

The proportion of the trivalent elements M b is particularly preferably more than 60 
mol %, based on the total amount of the elements M a , M b and Mc, 

The degree of oxidation a of the mixed valent element M a present, defined 
25 according to the following formula (I), is preferably from 0.01 to 0.99, more 
preferably 0.1 to 0.9, most preferably 0.25 to 0.75, 

M a +(x+1) 

a - (I), 

M/ (x+1, + M+ x 



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wherein M a +(xM) means the molar quantity of the element M a in the higher oxidation 

state, M a +(x) the molar quantity of the element M a in the lower oxidation state, and x 
a number between 1 and 3. 

The nickel mixed hydroxides according to the invention are provided suitably in 
5 powder form, the average particle size of the powder being preferably 0.5 to 1000 
jam, particularly preferably 2 to 1 00 p,m and particularly preferably more than 3 jam, 
more preferably 3-15 pm. 

The invention also provides a process for the preparation of the nickel mixed 
hydroxides described above, comprising the reaction of the reaction components 

10 required to obtain the relevant mixed hydroxides in the form of water-soluble salts 
of Ni and of the elements M a , M b and optionally M c in a basic, aqueous medium for 
the co-precipitation of hydroxide reaction products with the formation of a 
homogeneous suspension of said reaction products, wherein either water-soluble 
salts of the element M a are used in different oxidation states or a water-soluble salt 

15 of the element M a is used in the lower oxidation state and a partial oxidation is 
carried out until the desired ratio is obtained between the different oxidation states of 
the element M a , or a water-soluble salt of the element M a is used in the higher 
oxidation state and a partial reduction is carried out until the desired ratio is obtained 
between the different oxidation states of the element M a , separation from the mother 

20 liquor, washing and drying of the reaction products. 

The mixed hydroxides according to the invention may be prepared both in spherical 
and regular (non-spherical) morphology, the reaction in the first case being carried 
out advantageously in the presence of ammonia or ammonium salts. 

The reaction must be carried out under basic conditions, preferably at a pH from 8 to 
25 13. 

If a partial oxidation of the element M a is carried out, oxidising agents known for 
such applications may be used, oxygen, H2O2, hypochlorite or peroxodisulfates 
being used in preference. The partial oxidation may be carried out advantageously 



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by a controlled introduction of oxygen into the suspension forming. Generally 
speaking, a less than stoichiometric use of oxidising agents is suitable for partial 
oxidation. The desired ratio between the different oxidation states of the element M a 
may be controlled by varying the oxygen supply (for example, by mixing in pure 
oxygen to influence the oxygen partial pressure), the reaction temperature and/or the 
pH value. 

In the case of Co, for example, a partial oxidation is achieved in an advantageous 
manner by the controlled use of atmospheric oxygen. 

In the case of Fe, for example, water-soluble salts of both oxidation states may be 
used simultaneously. 

If a partial reduction of the element M a is carried out, reducing agents known for 
such applications may be used. 

If the process is carried out batchwise (batch process), it is expedient, after co- 
precipitation has ended, to carry out an ageing over several hours, for example, 15 to 
20 hours, before further work up. 

If the process is carried out continuously, the residence time is adjusted 
advantageously such that the desired mixed valent state of element M a is obtained. 
Average residence times of several hours, for example, 5 hours, have proved to be 
advantageous. 

According to a further preferred process, the mixed nickel hydroxides according to 
the invention are prepared by anodi c oxid ation of at least one of the metal elements, 
particularly preferably at least the nickel component. To this end, the aqueous 
precipitation suspension is pumped round continuously between an electrolytic cell 
with nickel anode and a thermostat arranged outside the cell. In the circuit outside 
the electrolytic cell, the other metal components in the form of their water-soluble 
salts are added to the precipitation suspension, as well as alkali hydroxide, 
preferably sodium hydroxide, to adjust the pH. Moreover, the oxidising agent, 
preferably atmospheric oxygen, is introduced into the pumping circuit in order to 



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adjust the degree of oxidation of the M a element. Precipitation suspension is 
discharged continuously or periodically by means of an overflow, precipitation 
product is filtered, washed, dried and optionally ground. 

The anions incorporated in the precipitation product to ensure electroneutrality may 
3 then be exchanged for the preferred C0 3 anions by treating the precipitation product 
in an alkali carbonate or alkali hydrogen carbonate solution, preferably Na 2 C0 3 
solution. 

A device for the electrolytic preparation of nickel mixed hydroxide is shown 
schematically in Fig. 6. 

10 Figure 6 shows an electrolytic cell 1 which contains two cathodes 2 and an anode 3. 
The electrolytic brine is pumped in the base of the cell 1 via the pump 4, the heat 
exchanger 5 and the pH sensor 6. Depending on the pH measurement 6, alkali 
hydroxide or hydrochloric acid is metered into the pumping circuit as indicated by 
arrow 7. Nickel hydroxide suspension is discharged from the pumping circuit by 

15 means of pump 9 and fed to the solids separating device 10. As shown by arrow 12, 
the solids are discharged. The brine from which solids have been removed may be 
recycled by means of pump 11 to the pumping circuit via electrolyte work up 16, 
optionally with the addition of water 15. Moreover, as indicated by arrow 17, a 
means is provided for introducing the oxidising agent. Moreover, doping salt 

20 solutions are fed into the pumping circuit by means of inlet 8. According to a 
preferred embodiment, the separating device 10 is designed in the form of a screen- 
type centrifuge which is operated in such a way that fine-particle nickel hydroxide 
particles are recycled with the filtrate to the pumping circuit via pump 1 1 . Hydrogen 
gas generated during electrolysis is drawn off above the filling volume of the cell, as 

25 indicated by arrow 13. 



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In the drawings, 

Fig. 1 shows the cycle behaviour of the sample A obtained in the examples and of 
comparison samples E, F, N and V in the half-cell test; 

Fig. 2 shows the charge curve of sample A in the 10th cycle; 

Fig. 3 shows the discharge curve of sample A in the 10th cycle; and 

Fig. 4 shows the x-ray diffraction spectrum of sample A. 

The nickel mixed hydroxide according to the invention is used preferably as a 
constituent of cathode materials in alkaline batteries, as in Ni/Cd or Ni/MH batteries, 
together with activators and auxiliaries known to the expert in the art. 

The invention is explained in more detail on the basis of the examples below. 




STA 154-FC 



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A) Preparation of various nickel mixed hydroxides 
Example 1 

Sample A: (3:1 Ni:dop., 3:1 Al:Co) Ni 0 .75Alo. 18 8Coo.o63(OH) 2 *m C0 3 *n H 2 0 

0. 1 mol of Ni(N0 3 ) 2 *6H 2 0 are dissolved in 200 ml of H 2 0 with 0.025 mol of 
A1CN0 3 ) 3 *9H 2 0 and 0.0083 mol of Co(N03) 2 *6H 2 0 and, with vigorous stirring 
(speed 400 rpm) to promote an increased introduction of atmospheric oxygen, 
metered into a charge of 0.02 mol of Na 2 C0 3 + NaOH in 500 ml of water (pH = 
12.5; 75°C) over a period of 2 h. During precipitation and the post-reaction time 
(about 3 h), the pH and temperature are kept constant. After an ageing period (with 
stirring) of about 1 8 h, the suspension is filtered over a pressure filter and washed to 
a neutral pH with water. The product mixture is then diluted to 750 ml and spray- 
dried. 

Example 2 

Sample B: (3:1 Ni:dop., 3:1 Al:Co) Ni 0 .75Alo.i8 8 Coo.o63(OH)2 *m C0 3 *nH 2 0 

10 mol of NiS0 4 *7H 2 0, 1.25 mol of A1 2 (S0 4 ) 3 *16 H 2 0 and 0.83 mol of 
CoS0 4 *7H 2 0 are dissolved in 9 1 H 2 0. The solution is adjusted with H 2 S0 4 to pH = 

1, heated to 75°C and, with vigorous stirring (400 rpm) to promote an increased 
introduction of atmospheric oxygen, metered into a charge of 15.58 mol of Na 2 S0 3 
+ NaOH in 25 1 of water (pH = 12.5; 65 - 70°C) (t = 70 min). During precipitation 
and the post-reaction time (about 2 h) the pH and temperature are kept constant. 
After an ageing period (with stirring) of about 16 h, the suspension is filtered over a 
membrane filter press and pressed, then dried at 50°C in a circulating air drying 
cabinet. The ground intermediate product is washed on a suction filter in portions 
with water, sodium hydroxide solution at pH = 12.5 and then again with water and 
dried at 50°C in a vacuum drying cabinet until a constant weight is obtained. 



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Example 3 

Sample C 

Composition as for sample B, but continuous process. 

Batch size: 180 mol (incl. 6 x preliminary run) 

Reactor volume: 28 I 

Average residence time: 5 h 

Volumetric flow: 5.2 1/h 

Substance flow: 2 mol/h based on Ni 2+ 

pH: 12.5 

Temperature: 75°C 

Equalising alkali: NaOH, 7 mol/1 

Carbonate stream: 1.321 mol/h 

The collected reaction suspension is filtered over a membrane filter press after an 
ageing period of about 18 h (with stirring), pressed and then dried at 50°C in a 
circulating air drying cabinet. The (ground) intermediate product is re-suspended in 
water and filtered again over a membrane filter press and washed. The washed 
product is dried at 50°C in a circulating air drying cabinet until a constant weight is 
obtained. 



The analytical results of the samples A to C prepared according to the above 
examples are summarised in table 1 below. 



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Table 1 Analysis of samples A-C 



Example 


Ni 

(wt.%) 


Al 

(wt.%) 


Co(II) 
(wt.%) 


Co(III) 
(wt.%) 


co 3 

(wt.%) 


S0 4 
(ppm) 


N0 3 
(ppm) 


Loss on 
drying 
105°C/2h 
(wt.%) 


Sample A 


38.80 


3.4 


4.8 


1.5 


10.5 




<2000 


5.2 


Sample B 


39.55 


4.62 


3.31 


1.4 


9.1 


6350 


<4 


4.94 


Sample C 


40.09 


4.7 


3.55 


1.6 


8.4 


6800 




2.20 



Example 4 

Sample D: (3.32:1 Ni/Mg:dop., 3:1 Al:Co) Nio. 6 9Mgo.o74AIo.,74Co 0 .o 5 8(OH) 2 *mC0 3 
*nH 2 0 

0.1 mol of Ni(N0 3 )2*6H 2 0 are dissolved in 100 ml of H 2 0 with 0.0107 mol of 
Mg(N0 3 ) 2 *6H 2 0 and 0.025 mol of A1(N0 3 ) 3 *9H 2 0 + 0.0083 mol of 
Co(N0 3 ) 2 *6H 2 0 and, with vigorous stirring (speed 400 rpm) to promote an 
increased introduction of atmospheric oxygen, metered into a charge (75°C) of 0.02 
mol of K 2 C0 3 + KOH in 150 ml of water (pH = 12.5) (t = 10 min). During 
precipitation and the post-reaction time (about 3 h), the pH and temperature are kept 
constant. After an ageing period (with stirring) of about 15 h, the suspension is 
filtered over a pressure filter and washed to a neutral pH with water. The product is 
then dried under vacuum at 50°C until a constant weight is obtained. 

Comparison example 1 

Comparison sample E: (3:1 Ni:dop., 3:1 AI:Co) Ni 0 .75A!o.i88Co 0 .o63(OH) 2 *mC0 3 
*nH 2 0 

0.1 mol of Ni(S0 4 )*7H 2 0, 0.0125 mol of A1 2 (S0 4 ) 3 *6H 2 0 and 0.0083 mol of 
20 Co(S0 4 )*7H 2 0 are dissolved in 100 ml of H 2 0 (introduction of N 2 ) and, with 
vigorous stirring (400 rpm), metered into a charge (75°C under an N 2 atmosphere) of 
0.245 mol of Na 2 C0 3 and NaOH in 200 ml of water (pH = 12.5). During 




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precipitation and the post-reaction time (about 2.5 h) the pH and temperature are 
kept constant. After an ageing period (with stirring) of about 18 h, the suspension is 
filtered over a pressure filter and washed to a neutral pH with water, then dried at 
50°C until a constant weight is obtained. 

Cobalt is present in the divalent form as well as Al(III), corresponding to a material 
according to the prior art according to EP 793 285, 

Comparison example 2 

Comparison sample F: (3:1 Ni:dop., 3:1 Al:Co) Nio.75A1o.,88Coo.o6 3 (OH) 2 0.1 88 N0 3 
*nH 2 0 

0.1 mol of Ni(N0 3 ) 2 *6H 2 0, 0.025 mol of A1(N0 3 ) 3 *9H 2 0 and 0.0083 mol of 
Co(N0 3 ) 2 *6H 2 0 are dissolved in 200 ml of H 2 0 with 0.15 mol of hexamethylene 
tetramine and adjusted to pH 4. The solution is heated slowly to boiling point, with 
vigorous stirring (400 rpm) and further hexamethylene tetramine is added in 0.075 
mol portions (dissolved in 30 ml of water) until a sample of the supernatant solution 
exhibits no further precipitation with hexamethylene tetramine. After an ageing 
period of about 96 h, the suspension is filtered over a pressure Filter, washed with 
water to a neutral pH and dried. Yield: 10.4 g (69.5%). 

The preparation took place with the use of hexamethylene tetramine under reducing 
conditions. Reducing conditions are also present in the cathodic deposition process 
which is used in the case of materials according to the prior art according to EP 793 
285. 

Example 5 

Sample G: (3:1 Ni:dop., 3:1 AI:Co) Ni 0 .75AIo.i88Coo.o63(OH)2*mS04*nH 2 0 

0.1 mol of Ni(S0 4 )*7H 2 0 are dissolved in 100 ml of H 2 0 with 0.0125 mol of 
A1 2 (S0 4 ) 3 *6H 2 0 and 0.0083 mol of Co(SO) 4 *7H 2 0 and, with vigorous stirring (400 
rpm) to promote a high introduction of atmospheric oxygen, metered into a charge 
(75°C) of NaOH in 150 ml of water (pH = 12.5) (t = 10 min). During precipitation 



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and the post-reaction time (about 15 h) the pH and temperature are kept constant. 
After an ageing period (with stirring) of about 17 h, the suspension is filtered over a 
pressure filter and washed to a neutral pH with water. The product is then dried 
under vacuum at 50°C until a constant weight is obtained. 

The preparation took place without carbonate and thus leads to the incorporation of 
sulfate instead of carbonate ions in the intermediate layer. A subsequent partial 
carbonation by admission of air (CO2) was permitted. 

Example 6 

Sample H: (2:1 Ni:dop., 3:1 Al:Co) Nio.66Alo.248Coo.o825(OH)2*mC03*nH 2 0 

s 

0.1 mol of Ni(N0 3 ) 2 *6H 2 0 are dissolved in 100 ml of H 2 0 with 0.0375 mol of 
A1(N0 3 ) 3 *9H 2 0 and 0.0125 mol of Co(N0 3 ) 2 *6H 2 0 and, with vigorous stirring 
(400 rpm), introduced dropwise into a charge (75°C) of 0.02 mol of Na 2 C0 3 + KOH 
in 150 ml of water (pH = 12.5) (t = 3 h). During precipitation and the post-reaction 
time (about 4 h), the pH and temperature are kept constant. After an ageing period 
(with stirring) of about 1 5 h, the suspension is filtered over a pressure filter and 
washed to a neutral pH with water, during which process the suspension should 
never be filtered completely to dryness. The product mixture is then dried at 
50°C/200 mbar until a constant weight is obtained. 

Example 7 

Sample I: (11:1 Ni:dop., 2:1 Al:Co; (superlattice 33:2:1)) 

0.165 mol of Ni(N0 3 ) 2 *6H 2 0 are dissolved in 400 ml of H 2 0 with 0.01 mol of 
A1(N0 3 ) 3 *9H 2 0 and 0.005 mol of Co(N0 3 ) 2 *6H 2 0. With vigorous stirring (400 
rpm) and the introduction of atmospheric oxygen over a frit, the solution is metered 
into a charge of 0.04 mol of Na 2 N0 3 +NaOH in 1000 ml of H 2 0 (pH = 12.5; 75°C) 
(t = 3 h). During precipitation and the post-reaction time (with stirring) of about 18 
h, the suspension is filtered over a pressure filter and washed to a neutral pH with 
water; the product mixture is then diluted to 1500 ml and then spray-dried. 



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Example 8 

Sample J: (3:1 Ni:dop., 2:1 Al:Co; (superlattice 9:2:1)) 

0.09 mol of Ni(N0 3 ) 2 *6H 2 0, 0.02 mol of A1(N0 3 ) 3 *9H 2 0 and 0.01 mol of 
Co(N0 3 ) 2 *6H 2 0 are dissolved in 200 ml of H 2 0 and, with the introduction of an 
oxygen/air mixture, introduced into a charge of 0.02 mol of Na 2 C0 3 and NaOH in 
500 ml of water (pH = 12.5; 75°C) over a period of 2 h. During precipitation and the 
post-reaction time (about 3 h), the pH and temperature are kept constant. After 1 8 h 
ageing (with stirring), the suspension is filtered over a pressure filter, washed to a 
neutral pH and dried in a vacuum drying cabinet at 50°C 

Example 9 

Sample K (3:1 Ni:dop.,2:l AI:Fe) 

0.09 mol of Ni(N0 3 ) 2 *6H 2 0 and 0.02 mol of AI(N0 3 ) 3 *9H 2 0 are dissolved with 
0.0033 mol of Fe(N0 3 ) 2 *6H 2 0 and 0.0066 mol of Fe(N0 3 ) 3 *6H 2 0 and metered, 
with stirring, into a charge (35°C) of 0.02 mol of Na 2 C0 3 + NaOH in 500 ml of 
water (pH = 12.5) (t = 2h). During precipitation and the post-reaction time (about 3 
h), the pH and temperature are kept constant. After an ageing period of 18 h (with 
stirring), the suspension is filtered over a pressure filter, washed to a neutral pH and 
dried in a vacuum drying cabinet at 50°C. All the steps are carried out under a 
nitrogen atmosphere. 



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Example 10 

Sample L: (2.9:1 Ni: dop., 3:1 Al:Co) 

800 ml/h of an electrolyte solution having the composition 63.5 g/1 of NaCl, 7.6 g/1 
of CoCl 2 and 23.4 g/1 of AICI3 were pumped continuously at 8 into a test electrolytic 
cell 1 with a capacity of 3 1 (according to Fig.6, but without brine recycling), which 
is fitted with two Ni cathodes 2 and an Ni anode 3. Electrolysis was carried out at a 
current density of about 65 mA/cm 2 (I = 30 A), at a temperature of 20°C (thermostat 
5) with anodic Ni dissolution of about 32.8 g/h. The pH was kept at 12.0 (pH 
measurement 6) during electrolysis by the automatic addition 7 of 2.5 molar sodium 
hydroxide solution. The electrolyte solution was pumped by means of pump 4. 
Oxygen was injected into the pumping circuit at 11. Electrolysis took place 
throughout the period in a stable manner at a voltage of about 3 V. The overflow was 
drawn off by means of pump 9 and filtered by suction at 10. The solid 12 obtained 
was dried in a circulating air drying cabinet at a temperature of 60°C. The dried 
material was ground (<500 \x) using a laboratory mill and carbonated in a 1 molar 
Na 2 CC>3 solution in a ratio to the dry material of 5:1 for about 2 hours at 70°C, with 
stirring, in a glass beaker. The suspension containing the product was then filtered 
by suction and the resulting solid on the filter was washed with about 8 1 of a hot 
(about 65 °C) 1 g/1 sodium hydroxide solution. The product was then dried in a 
circulating air drying cabinet at a temperature of 60°C. Yield: 80.3 g of nickel 
hydroxide material per hour. 

The chemical analysis of the product gives the following composition: 
Ni 40.4 wt.% 



Al 



4.87 wt.% 



Co, total 



3.52 wt.% (1.7 wt.% Co J+ ) 



CO3 



6.47 wt.% 



CI 



<50 



ppm 



STA 154-FC 



- 17- 

S0 4 <50 ppm 

Na 325 ppm. 

The average particle size (Mastersizer D50) was 16 ^im, the BET surface 3.3 m 2 /g, 
the density (He pyknometer) 2.51 g/cm 3 and the tap density 1.6 g/cm 3 . 



Example 11 

Sample M: (4.5:1 Ni:dop., 3:1 AI:Co) 

Electrolysis was carried out in the same way as in example 10. The electrolyte 
solution fed in had a composition of 57.4 g/1 of NaCl, 4.56 g/1 of CoCl 2 and 14.01 
g/1 of AICI3. The pH was kept at 12.5. The voltage was 3.2V; the anodic Ni 
dissolution was 29.5 g/h. 

The overflow from the electrolytic cell was collected over 6 hours, left to stand for 
about 20 hours to age and then filtered by suction. The resulting solid was washed 
on the suction filter with about 3.8 1 of a 1 g/1 sodium hydroxide solution, then with 
about 1.9 1 of a 1 molar Na 2 C03 solution and then again with about 3.8 1 of a 1 g/1 
sodium hydroxide solution. The temperature of the wash solutions was about 20°C. 
The product was then dried in a circulating air drying cabinet at a temperature of 
about 60°C. The dried material was ground using a laboratory mill (<500 p,) and 
then analysed. Yield: 453 g of nickel hydroxide material. 

The chemical analysis gave the following composition: 

Ni 43.4 wt.% 

Al~ 3.33 wt.% 

Co, total 2.42 wt.% (1.12 wt.% Co 3+ ) 

CO3 9.09 wt.% 

CI 510 ppm 

SO4 <50 ppm 



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Na 0.83 ppm. 

The average particle size (Mastersizer D50) was 38 urn, the BET surface <1 m 2 /g, 
the physical density (He pyknometer) 2.45 g/cm 3 and the tap density 1.6 g/cm 3 and 
the loss on drying (105°C, 2h) was 4.75 wt.%. 

Example 12 

Sample N: (4:1 Ni:dop., 3:1 Al:Co) 

An electrolytic cell with a capacity of 400 1 was used. Electrolysis was carried out in 
a similar way to example 10. 55 1/h of an electrolyte solution having the composition 
52.7 g/1 of NaCI, 5.5 g/1 of CoCl 2 and 17.0 g/1 A1C1 3 were added. The electrolysis 
current was 2000 A with an anode current density of 69 mA/cm 2 . The Ni dissolution 
was 2187 g/h, the pH 12.0. After a preliminary run time of about 20 h, the 
outflowing suspension was collected for 28 hours. This 28-hour collection sample 
(1648 1) was then filtered by suction and the resulting solid dried in a circulating air 
drying cabinet at a temperature of 70 to 80°C. The dried material was ground (<1000 
Urn) using a conical grinder and carbonated with a 1 molar Na 2 C0 3 solution in a 
ratio to the dry material of 5:1 for about 2 hours at 70°C, with stirring, in a 450 1 
reactor. The suspension was then filtered by suction and the resulting solid was 
washed on the suction filter with about 2.5 m 3 of a hot (about 65°C) 1 g/1 sodium 
hydroxide solution. The product was then dried in a circulating air drying cabinet at 
a temperature of 70 to 80°C. 

The chemical analysis gave the following composition of the product: 

Ni 44.40 wt.% 

Al 3.75 wt.% 

Co, total 2.82 wt.% (2.0 wt.% Co 3+ ) 

C0 3 8.33 wt.% 

CI 360 ppm 

S0 4 <50 ppm 



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Na 270 ppm. 

The average particle size (Mastersizer D50) was 51.8 urn, the BET surface 6.35 
m 2 /g, the physical density (He pyknometer) 2.7 g/cm 3 and the tap density 1.8 g/cm 3 . 
Fig 7 shows an SEM photo of the powder. 

B) Electrochemical characterisation 

In order to obtain an electrochemical characterisation of the samples, 
charging/discharge cycles were carried out with a five-hour charging and discharge 
current in 30% KOH against Hg/HgO with a charging factor of 1.5. The electrode 
material of nickel mixed hydroxide (active material), 33% graphite as conductive 
additive and hydroxypropylmethylcellulose as binder was pasted into nickel foam as 
substrate. 

Figure 1 shows the cycle behaviour of samples A and N and of comparison samples 
E and F according to the prior art (EP 0 793 285) and of comparison sample V, a 
Co(III), Mn(III) and Al(III)-containing nickel hydroxide powder according to EP 0 
712 174 in the half-cell test. 

Comparison samples E and F according to EP 0 793 285 contain divalent cobalt in 
addition to trivalent other additional cations since divalent cobalt e.g. in combination 
with trivalent aluminium is used as starting compounds and also no oxidising agent 
is used. No details about cycle behaviour and capacity values can be derived from 
EP 0 793 285 so comparison samples were prepared: samples E and F were prepared 
maintaining the divalency for cobalt, once under an N 2 atmosphere (E) and once 
under reducing conditions (F), and compared as prior art with sample A according to 
the invention. 

As Figure 1 shows, both the capacity values and the cycle behaviour of samples A 
and N in which Co(III) as well as Co(II) ions are present are markedly superior to 
the materials according to the prior art in which the cobalt ions are present only in 
the divalent form. The positive influence of the mixed valency for cobalt becomes 
particularly pronounced by a comparison with sample E which was prepared not 



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under reducing conditions but only with the exclusion of oxygen. Slight partial 
oxidation of the surface during work up is conceivable here, which could explain the 
improvement compared with the material prepared under reducing conditions 
(sample F). Samples A and N also exhibit marked improvements in terms of 
capacity and cycle stability compared with comparison sample V. 

The potential curve of sample A is shown in Figures 2 and 3, Figure 2 showing the 
charging curve and Figure 3 showing the discharge curve in the 10th cycle, in each 
case against Hg/HgO. 

The X-ray diffraction spectrum of sample A is shown in Figure 4. The material of 
sample A shows the reflections of the hydrotalcite type with a distance of about 7.8 
A between the layers. In contrast to P-Ni(OH) 2 (brucite type), an expanded layer 
structure is present. Figure 5 shows the X-ray diffraction spectrum of sample L.