CZ20004409A3 - Mixed metal hydroxide with brucite structure as active material for rechargeable batteries and process for preparing thereof - Google Patents

Abstract

The brucite-structured metal hydroxide comprises nickel hydroxide as the main component and at least one trivalent metal from the group of Co, Fe, Al, Ga, In, Sc, Y and La in an amount of 12 to 30 atomic%, based on the sum of the metal components including nickel. The process consists in precipitating the mixed hydroxide with the pyroaurite structure from the corresponding salt solutions, suspending the precipitated product in at least 0.5 molar alkaline solution, separating from the solution and drying.

Description

Technical field

The present invention relates to active material for rechargeable batteries, especially nickel hydroxide substituted with trivalent metal ions with a brucite structure, to a process for its production and also to its use as a material for electrodes for secondary batteries.

BACKGROUND OF THE INVENTION

Nickel hydroxide is used as a cathode material for alkaline secondary batteries such as nickel-cadmium batteries or nickel-metal hydride batteries. The decisive electrochemical quantity for technical use is the mass-related capacity. This is dependent on the nickel content of the nickel hydroxide and the use of nickel. The correlation of the capacity Q relative to the mass in Ah / g as a function of the nickel content in% by weight of the cathode material and the use of nickel in the EES (one electron transition) is as follows:

% Ni x% EES x F q ₌ - [mAh / g]

58.69 x 3600 x 10 where marks

F Faraday constant

58.69 molecular weight of nickel g / mol

3600 conversion factor from seconds to hours

factor for conversion of% in ratio of numbers and mA to A.

This also results in a theoretical weight-related capacity at 100% EES of 289 mAh / g. However, technically useful nickel hydroxides contain between 4 and 6% of the modifying metals as well as 1 to 2% of water based on the total metal content, so that at 100% nickel utilization these hydroxides have a capacity based on only 252 to 266 mAh / g. The 100% nickel utilization of this nickel hydroxide is associated with a 1-electron transition (and a 1-proton transition) to the nickel atom β-Ni (OH) 2 to β-^ί ^^^ ΟΟΗ while charging the battery.

When the battery is overcharged, further deprotonation occurs and oxidation of some of the nickel to Nito results in the formation of garaa-NiOOH. In this process, water molecules and alkaline ions are deposited in the interlayer to compensate for charging. Thus, gammaNiOOH formation is associated with increasing the distance of nickel layers in the grid. Discharge of gamma-NiOOH takes place with the release of alkaline ions into the electrolyte, forming α-Ni (OH) 2. The alpha-gamma transition is theoretically associated with 1.67 electron transition, that is 167% EES. However, the 1,67-electron transition is technically not possible, since α-Ni (OH) ₂ is unstable in alkaline electrolyte and aging to β-Ni (OH) ₂ , which again results in β-NiOOH - gamma-NiOOH increasing volume.

By introducing trivalent metals into nickel hydroxide, the α-structure (pyroaurite) has been stabilized. However, in this pyroaurite structure, anions and water molecules are anchored between the nickel layers to ensure charging neutrality, so that the grid is expanded. Although these trivalent metal modified nickel hydroxides are used with pyroauf fll to flfl I to flfl.

I · 1 flfl 4 flfl fl flflfl

»· The graphite structure has succeeded in realizing a stable 1.5-electron transition, but the charging capacity is reduced both by electrochemically inactive trivalent ions and by anchored anions and water molecules.

It has now been discovered that by suspending trivalent ion pyroaurite hydroxide in an alkaline solution, separating from the alkaline solution and drying with the still alkaline solution, the pyroaurite structure is converted to a brucite structure to give a 1.67-electron transition. In this case, anions and water are removed from the interlayer of the grid, so that the distance between the layers is reduced while increasing the charging density.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a mixed metal hydroxide having a brucite structure, a nickel hydroxide as the main constituent and at least one trivalent metal of the group Co, Fe, Al, Ga, In, Sc, Y, and La in an amount of 12 to 30 atomic%. metal components including nickel.

Preferably, the trivalent metal is present in an amount of 12 to 25 atomic percent based on the sum of all metal components.

Preferred trivalent metals are Co, Fe and Al, particularly preferred is Al.

Particularly preferred mixed metal hydroxides according to the invention having a brucite structure contain, in addition to the aforementioned first group of trivalent metals, at least one of the elements Co, Fe, Mn,

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Cr, Ti, Zr and Cu, the element of the second group being different from the trivalent metal of the first group and replacing the trivalent metal of the first group in an amount of up to 40 atomic%.

Preferred mixed metal hydroxides according to the invention comprise Al and Co, the atomic ratio of Al to Co being up to 4, particularly preferably 2.5 to 3.5.

The mixed metal hydroxides of the invention are further determined by a layer spacing of from 4.3 to 4.8 Å by the determined X-ray diffraction. The reflex is expanded to smaller 16-angles by one arm, which corresponds to a grid spacing of 5.2 to 5.7 Å.

The present invention also provides a process for preparing the mixed hydroxides of the present invention by co-precipitating the mixed hydroxides with a pyroaurite structure from the corresponding metal salt solutions, suspending the precipitated product in an alkaline solution, separating from the alkaline solution and drying in the presence of an adherent alkaline solution.

Preferably, at least 0.5 molar alkali hydroxide solution is used.

Preferably, at least 0.9 molar alkali hydroxide solution, particularly preferably at least 1 molar alkali hydroxide solution is used for alkaline drying. A preferred alkaline hydroxide is sodium hydroxide.

The preparation of mixed hydroxides with a pyroaurite structure is carried out by preparing an aqueous solution by dissolving the corresponding metal salts of the water-soluble metal components in the desired ratio and precipitating from this solution by treatment

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The pH was adjusted to 10-13 by addition of an alkaline hydroxide solution. The process can be carried out batchwise or continuously by simultaneously bringing the metal salt solution and the alkaline hydroxide solution into one reaction vessel and continuously withdrawing the precipitated suspension. Suitable metal salts are halides (preferably fluorides or chlorides), carbonates, sulphates, nitrates, acetates, oxalates, borates and / or phosphates, provided these salts have sufficient solubility.

In order to achieve oxidation of the divalent metal ion modifications optionally present in the precipitated suspension to a trivalent stage, it may further be expedient to add an oxidizing agent, such as, for example, oxygen, hydrogen peroxide, hypochlorite or peroxodisulphate to the precipitated suspension.

Suitable alkaline solutions for the precipitation are ammonium hydroxide, lithium hydroxide, potassium hydroxide or sodium hydroxide. Sodium hydroxide is preferred.

Further, it may be expedient to replace the anions of the pyro-auritic structure embedded in the mixed metal hydroxides with carbonate ions, following precipitation. This can be accomplished by treating the precipitated product with an alkali carbonate or alkaline bicarbonate solution.

After separation from the mother liquors and washing to remove residual mother liquor, the precipitation product is preferably resuspended in an alkaline hydroxide solution without drying.

After separation from the alkaline hydroxide solution, it is carefully dried at a temperature below 80 ° C, in particular below 60 ° C, further preferably under reduced pressure. The lower the drying pressure is selected, the higher the minimum concentration should be • 9 99 · ·

• 99 99 • 9 9 9 9 9 9 9 9

9

Alkaline hydroxide solution. For example, at a drying pressure of 1 kPa, a concentration of at least 1.3 moles of alkali hydroxide solution is preferred.

Mixed metal hydroxides with brucite structure which can be prepared according to the invention are at the same time an excellent starting material for the production of lithium mixed metal oxides. Lithium mixed metal oxides are produced by mixing the mixed metal hydroxides with suitable lithium compounds such as lithium hydroxide or lithium nitrate, and then firing at temperatures above 600 ° C.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 represents an ideal illustration of the electron transitions obtainable with different nickel hydroxides. The top four structures represent the well-known Bodediagram.

Figure 2 shows the X-ray diffraction spectrum of alkali-dried mixed hydroxides from different concentrations of sodium hydroxide solution according to the following example.

Figure 3 shows the discharge capacity of mixed brucite hydroxide depending on the number of cycles according to the following example.

DETAILED DESCRIPTION OF THE INVENTION

Example 1 φ · φφφφ φφφφ • φ φ φ

ΦΦ

(a) Production

Simultaneous precipitation of the substituted nickel hydroxides is carried out by dropping a mixed solution of metal salts into a constant pH value template. The composition of the metal salt solution, the caustic solution, and the feed are described herein for example by precipitation of 0.125 moles of nickel hydroxide with metal ion composition.

the composition of the metal ions is appropriately adjusted to the composition of the metal salt solution. At this batch size, about 10 g of dried hydroxide is obtained.

Salt solution

Total metal ion concentration 0,5 M 26,28 g NiSO ₄ x 6 H ₂ 0 (= 0,10 mol Ni ²⁺ )

12.48 g A1 ₂ (SO ₄ ) ₃ x 18 H ₂ 0 (= 1.88 x 10 " ² mol Al ³⁺ ) 1.76 g CoSO ₄ x 7 H ₂ 0 (= 6.25 x 10 ^-3 Co ²⁺ ) demineralized water to 250 ml

2. Equalizing liquor

Concentration of hydroxide ions 1,0 M 10 g NaOH pellet (99,5%) demineralized water up to 250 ml

3. Handle

Concentration of carbonate ions 0,5 M 26,50 g Na ₂ CO ₃ demineralized water to 500 ml before the start of precipitation 8 M NaOH is added dropwise until pH 12,5

The batch is thermostatized to 34 ° C prior to precipitation. During precipitation, the pH is measured and changed »♦ 4499 • 4 9 ··

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494 44 44 the addition liquor is kept constant. The stirring speed during the precipitation is 300 rpm.

The salt solution is metered into the batch at a rate of 5 ml / minute and the pH is kept constant by the addition of a buffer solution.

After the precipitation was complete, the precipitate was aged for 18 hours at room temperature without stirring.

The precipitate is then centrifuged for 10 minutes at 6000 rpm, the centrifuged liquor is removed and the product is stirred in 1 liter of wash liquor (NaOH) to adjust the precipitation pH at room temperature for about 3 minutes and then centrifuged again. This procedure is repeated until eluted anions are no longer detectable.

After the last centrifugation, the washed gel is suspended in 200 ml of a sodium hydroxide solution of a certain concentration according to Table 1, stirred for 1 hour, centrifuged and dried with stuck lye at 50 ° C under water pump vacuum. This process is referred to herein as alkaline drying.

In the products, the degree of reaction increases with the concentration of hydroxide used as the suspension liquor (Figure 2). Thus, after drying from 0.03 molar and 0.1 molar caustic, the pyroaurite type is obtained, from 0.4 molar caustic a spectrum with low proportions of brucite is obtained. Upon drying from 0.7 molar lye, the conversion to brucite type is almost complete. The metal ion ratio does not change by this treatment. Thus, no aluminum is precipitated from the substance by alkaline drying.

The obtained brucite type differs from the classical brucite type 9 · · 9 9 9 9 9 19 9 1

1 1 9 111

9 1 1 1 9 1 1 8

11 1111 1111 Φ ΦΦΦ ΦΦΦ ΦΦ ·· differentiates in that reflex 001 is somewhat shifted to lower d-values of 4.56 Å instead of 4.63 Å. In addition, there is no reflex leg 001 in the 5.20 Å region, which indicates a partial expansion of the layer spacing over the normal brucite type. With pure nickel hydroxide, this deviation from the known brucite structures does not occur after alkaline drying, peak 001 is at 4.63 Å and there is no arm at higher d-values.

The content of nickel hydroxide in Νί ΑΙθ γ ^ ^ Οοθ 25 increases ^with increasing proportion brucitové structure (Table 1), as well as pycnometric density.

Table 1

Values of analysis for hydroxide Νί ^ ΑΙθ 75C0Q 25 ^with pyroaurite structure (top) and brucite structure (bottom)

Drying liquor for Ni4 ^Al 0.75 ^ 0.25 Content nickel Ratio nickel / carbon Ratio nickel / hydrogen Pycnometric density 0.13M-pH12.5 45,03% 1: 0.138 1: 3.85 2.65 g / cm 2 0,07 M 46,66% 1: 0.076 1: 3.71 3.05 g / cm 2 1,0 M 49,14% 1: 0.071 1: 3.58 3.21 g / cm @ 2

In the pyro-aurite-type nickel hydroxides, the hydroxide layers have a positive charge due to the partial substitution with trivalent cations (Al @ ^{+ →} Co @ ⁺ or Fe @ ⁺ ). Due to the necessary charge equalization by carbonate or other anions, the separation of the hydroxide layers between them is increased to 7.8 Å. In addition, there are water molecules in the interlayer. In order to convert to a brucite structure, the positive * «· ·

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9 4 50 99

4 9 4

4 4 9 · The charge of the hydroxide layers.

As a mechanism to de-charge the main layer to accept partial deprotonation of hydroxide ions, the process can proceed according to the following scheme:

1. A single main group hydroxide group is deprotonated onto the metal ion (III)

2. The positive charge of the main layer is removed by removing H ⁺ ions

3. A negative interlayer of water and carbonate ions is no longer necessary for the electrical neutrality of the structure and can be eliminated

4. The layer spacing is reduced from 7.8 Å to 4.6 Å.

The fully reacted product (dried from 1.0 M NaOH) has a pycnometer density of 3.21 g / cm. Pure nickel hydroxide, which is produced under the same precipitation conditions, has a pycnometer density of 3.57 g / cm. If it is replaced in this pure nickel hydroxide in the sense of the formula N 1 Al 2 O 75 CO 2 25

17.65% of nickel ions by lighter aluminum ions, a density of 3.23 g / cm @ 2 was obtained in good agreement with the measured value of 3.21 g / cm @ 2.

b) Investigation of behavior during cycles

Galvanostatic charges and discharges are performed to investigate electrochemical properties. The electrolyte is 10 Μ KOH, 100 mg of active material is mixed with 50 mg of graphite and 3 mg of PTFE powder, wiped on a dry paste and incorporated.

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Jí • 0 0 9 9 φ 9 9 9 9 jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jí jíφ jí jí jí jí jí jí jí jí jí φ jí jí jí jí jí jí jí jí jí jí jí jí jí φ jí. The molding is carried out for 14 hours at a current of 5 mA, further charging for 12 hours at the same current strength. The discharge is carried out with a current of 2.5 mA up to a final discharge voltage of 0.9 V for Cd / Cd (0H) ₂ or 0 v for Hg / HgO. When carrying out cycles of brucite Νί ^ ΑΙθ 75C0Q 25 ⁱⁿ 00 M KOH, when brucite is produced by drying from 0.7 M NaOH, the maximum utilization of nickel is above 147%. This corresponds to a maximum capacity based on a mass of 313 mAh / g (Figure 2). The nickel content of this material is 46.7%.

The maximum utilization of nickel in bί ₄ Α1θ ₇₅ 0ο _{0 25 of the} brucite type is 147%, with a similar value for 144% roaurite type 75ί ^ ΑΙθ ₇₅ 0οθ ₂ $ PY “. However, since the nickel content of the brucite type is 6.1% higher than the pyroaurite type of 44.0% at 46.7%, its 310mAh / g weight capacity is also higher than the pyroaurite type of 290 mAh / g.

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Claims (11)

PATENT CLAIMS Mixed metal hydroxide with a brucite structure, comprising nickel hydroxide as the main component and at least one trivalent metal of the group Co, Fe, Al, Ga, In, Sc, Y and La in an amount of 12 to 30 atomic%, based on the sum of the metals components including nickel. Mixed metal hydroxide according to claim 1, further comprising at least one of Co, Fe, Mn, Cr, Ti, Zr or Cu which differs from the trivalent metal in an amount of up to 15% atomic, based on the sum of all metal components . Mixed metal hydroxide according to claim 1 or 2, containing 12 to 25% atomic aluminum. Mixed metal hydroxide according to any one of claims 1 to 3, containing 4 to 9% atomic Co. Mixed metal hydroxide according to any one of claims 1 to 4, with a spacing of nickel layers of 4.3 to 4.8 Å, as determined by X-ray diffraction. A rechargeable battery comprising the mixed metal hydroxide of any one of claims 1 to 5 as an electrochemically active material. Process for producing mixed hydroxides according to any one of claims 1 to 6, precipitating a mixed hydroxide with a pyroaurite structure from the corresponding metal salt solutions, suspending the precipitated product in at least 0.5 molar alkaline solution, separating from the alkaline solution and drying in adhering condition. alkaline solution. The process according to claim 7, wherein at least 0.9 molar sodium hydroxide solution is used. The process according to claim 7 or 8, wherein the precipitation is carried out in the presence of an oxidizing agent. The process according to any one of claims 7 to 9, wherein the precipitated nickel hydroxide is suspended in the carbonate solution before being suspended in the alkaline solution, separated therefrom and washed. A secondary battery comprising a mixed metal hydroxide according to any one of claims 1 to 6.