CN100511782C - Alkaline secondary battery positive electrode material and alkaline secondary battery - Google Patents

Abstract

A positive electrode material for an alkaline secondary battery, the material contains nickel hydroxide powder, cobalt additives and a binder, wherein the positive electrode material also contains metal powder, and the metal is selected from the group consisting of vanadium, titanium, molybdenum, manganese, niobium, One or more of hafnium, zirconium, yttrium, and tantalum. The alkaline secondary battery provided by the invention containing the positive electrode material not only has better self-discharge performance at the beginning and after several cycles, but also has higher discharge capacity.

Description

A kind of positive electrode material of alkaline secondary battery and alkaline secondary battery

technical field

The invention relates to an alkaline secondary battery cathode material and the alkaline secondary battery.

Background technique

Alkaline secondary batteries, such as nickel-cadmium secondary batteries, nickel-zinc secondary batteries or nickel-hydrogen secondary batteries, generally include an electrode group and an alkaline electrolyte sealed in a battery case. The electrode group includes a positive electrode, a negative electrode and a separator. The positive electrode includes a conductive substrate and a positive electrode material coated and/or filled on the conductive substrate, and the positive electrode material contains nickel hydroxide powder and a binder as main components. The negative electrode includes a negative electrode conductive substrate and a negative electrode material coated and/or filled on the negative electrode conductive substrate. The negative electrode material contains a main component and a binder, and the main component is selected from the oxide and/or hydroxide of cadmium , zinc oxides and/or hydroxides, or hydrogen storage alloys. The separator is arranged between the positive electrode and the negative electrode, has electrical insulation performance and liquid retention performance, and accommodates the electrode group and the alkaline electrolyte together in the battery case. The battery case typically also doubles as the negative terminal.

Due to its stable performance and good adaptability under various conditions, the alkaline secondary battery has been widely used, and its application field is constantly expanding.

With the continuous expansion of secondary battery application fields, existing secondary batteries cannot meet the requirements of some fields. For example, secondary batteries used as power supplies for electric tools that require high Charging efficiency. In order to improve these performances of secondary batteries, predecessors have done a lot of useful work.

For example, after the battery is assembled, when it is charged, due to the oxidation of the charge, the active material nickel hydroxide of the positive electrode is activated, that is, the non-conductive nickel hydroxide is transformed into a trivalent conductive β- Nickel oxyhydroxide (β-NiOOH). However, since there is a large difference in current collection efficiency between the surface part and the central part of nickel hydroxide as an active material, when the depth of charging is 100% or higher, the surface part of nickel hydroxide is inevitably in overcharge state. Therefore, the surface portion is excessively oxidized, forming γ-nickel oxyhydroxide (γ-NiOOH) in a trivalent or higher valence state. Compared with β-NiOOH, γ-NiOOH is more inert and has a lower density, which is responsible for the decrease in charging efficiency and swelling of the positive electrode. The expansion of the positive electrode redistributes the additives in the positive electrode (such as cobalt additives) and the active material of the positive electrode falls off, resulting in increased self-discharge after several charge-discharge cycles and reduced battery life. Introducing Zn, Cd, and CdO into the positive electrode can improve the structural stability of the battery during charge and discharge, thereby increasing the cycle life of the battery.

On the other hand, when charging the nickel hydroxide electrode, there is also a side reaction that generates oxygen from the alkaline electrolyte. At the beginning of charging, the overpotential of the nickel hydroxide charging reaction is greater than the potential required for the reaction of generating oxygen from the alkaline electrolyte (oxygen precipitation potential). Therefore, the charging reaction of nickel hydroxide proceeds first, and at the end of charging, due to the nickel electrode Due to the uneven self-polarization and charging state, the oxygen precipitation potential gradually balances with the overpotential of the nickel hydroxide charging reaction, even greater than the overpotential of the nickel hydroxide charging reaction, so that the oxygen precipitation inevitably occurs. Oxygen evolution increases the pressure inside the battery, reducing the cycle life and charging efficiency of the battery.

Introducing cobalt additives in nickel hydroxide powder, together with nickel hydroxide as an active material, can improve the conductivity between positive electrode active materials and between positive electrode active materials and current collectors (current collectors are conductive substrates), the cobalt additives Selected from Co, Co(OH) ₂ , Co ₂ O ₃ , Co ₃ O ₄ , CoO or mixtures thereof.

However, due to the limitations of the preparation conditions, the cobalt additives introduced into the nickel oxide powder are easy to cluster, and it is difficult to completely and evenly disperse in the nickel hydroxide, so that the dispersion of these cobalt additives in the positive electrode is very uneven, which makes the charging and oxidation process difficult. The oxidation overpotentials in the battery are different, so that the oxidation reaction of some cobalt is not complete, and it is difficult to completely oxidize divalent cobalt to trivalent cobalt by charging. Furthermore, the trivalent cobalt formed by charging itself is also reduced to divalent cobalt due to self-discharge, and these divalent cobalts gradually dissolve and precipitate into the battery electrolyte, and finally precipitate in the form of Co ₃ O ₄ , resulting in battery damage. Micro-short circuit increases the self-discharge of the battery.

CN1159793C discloses a nickel-metal hydride secondary battery, which includes an electrode group, including a positive electrode on which is loaded an active material powder containing nickel hydroxide as a main component, a negative electrode on which a hydrogen storage alloy powder is loaded, and The separator is arranged between the positive electrode and the negative electrode, and the electrode group is sealed in the battery casing together with the alkaline electrolyte, wherein W element and Na element exist simultaneously in the electrolyte solution. The W element and Na element exist in the form of tungstate ions and sodium ions respectively. In this patent, the W compound and the sodium compound electrolyte can maintain the stability of the formed trivalent cobalt compound to a certain extent, and improve the utilization rate and charging performance of the active material in the secondary battery. However, due to these additives at the same time It also delays the dissolution of the cobalt additive in the electrolyte before charging, so that the cobalt added to the positive electrode during the initial charging process cannot be effectively utilized, and the residual divalent cobalt that cannot be oxidized by charging increases. These divalent cobalt will still be dissolved and precipitated in the subsequent storage process, causing the self-discharge of the battery, resulting in poor self-discharge performance of the battery.

Contents of the invention

The purpose of the invention is to overcome the disadvantage of poor self-discharge performance of the existing alkaline secondary battery positive electrode material, and provide a kind of alkaline secondary battery positive electrode material with better self-discharge performance.

Another object of the present invention is to provide an alkaline secondary battery having better self-discharge performance.

The positive electrode material of alkaline secondary battery provided by the present invention contains nickel hydroxide powder, cobalt additive and binding agent, wherein, this positive electrode material also contains metal powder, and described metal is selected from vanadium, titanium, molybdenum, manganese, niobium, hafnium , zirconium, yttrium, tantalum in one or more.

The alkaline secondary battery provided by the present invention includes an electrode group and an alkaline electrolyte, the electrode group and the alkaline electrolyte are sealed together in a battery case, the electrode group includes a positive pole, a negative pole and a separator, and the positive pole includes a conductive matrix And the positive electrode material coated and/or filled on the conductive substrate, the positive electrode material contains nickel hydroxide powder, cobalt additive and binder, wherein, the positive electrode material also contains metal powder, the metal is selected from vanadium, titanium , molybdenum, manganese, niobium, hafnium, zirconium, yttrium, tantalum in one or more.

The vanadium, titanium, molybdenum, manganese, niobium, hafnium, zirconium, yttrium, and tantalum metal powder contained in the positive electrode material of the alkaline secondary battery provided by the present invention exist in a metal state before charging, and are insoluble in alkaline electrolyte, so , does not affect the full dissolution and redispersion of cobalt additives before charging, and is beneficial to the oxidation of divalent cobalt during charging. After charging, metal powders of vanadium, titanium, molybdenum, manganese, niobium, hafnium, zirconium, yttrium, and tantalum are oxidized into oxides soluble in alkaline electrolyte, and these oxides dissolve into the electrolyte to form a film on the solid surface , play a role in delaying the dissolution of the trivalent cobalt compound, which prevents or reduces the precipitation of cobalt in the storage process of the existing alkaline secondary battery, thereby improving the self-discharge performance of the battery.

Due to the use of the positive electrode material provided by the invention, the alkaline secondary battery provided by the invention containing the positive electrode material not only has better self-discharge performance at the beginning and after several cycles, but also has a higher discharge capacity.

Detailed ways

According to the positive electrode material of the alkaline secondary battery provided by the present invention, a very small content of the metal powder can obviously delay the dissolution of the cobalt compound after charging. Although the dissolution of the cobalt compound after charging can be delayed more obviously when the content of the metal powder increases, when the content of the metal powder is greater than 5% by weight of nickel hydroxide, the active material nickel hydroxide in the positive electrode becomes relatively less, and the discharge capacity It will also cause the difference between the charge and discharge states of the positive and negative electrodes to increase, which will affect the life of the battery. Therefore, taking the weight of nickel hydroxide as the basis, the content of the metal powder is preferably greater than zero to 5% by weight, more preferably 0.1-3% by weight.

The type and content of the cobalt additive are well known to those skilled in the art, such as the cobalt additive can be selected from one or more of Co, Co(OH) ₂ , Co ₂ O ₃ , Co ₃ O ₄ , CoO . Based on the weight of nickel hydroxide and based on the cobalt element, the content of the cobalt additive is preferably greater than zero to 10% by weight, more preferably 2-7% by weight.

The type and content of the binder are known to those skilled in the art, as the binder can be selected from one or more of carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene Generally speaking, depending on the type of binder used, the content of the binder is preferably 0.01-5% by weight, more preferably 0.02-3% by weight, based on the weight of nickel hydroxide.

According to the positive electrode material provided by the present invention, the material may further contain a solvent. The type and amount of the solvent are known to those skilled in the art. For example, the solvent may be selected from any solvent capable of forming the mixture into a paste, preferably water. The amount of solvent used is such that the paste is viscous and can be applied to solid materials. Based on the weight of nickel hydroxide, the content of the solvent is preferably 15-40% by weight, more preferably 20-35% by weight.

The positive electrode material may also contain other additives, such as one or more of metals and compounds of zinc, cadmium, and magnesium. Based on the weight of nickel hydroxide, the content of the other additives is 0-8 wt%, preferably 0.5-5 wt%.

The alkaline secondary battery provided by the present invention includes an electrode group and an alkaline electrolyte, the electrode group and the alkaline electrolyte are sealed together in a battery case, the electrode group includes a positive pole, a negative pole and a separator, and the positive pole includes a conductive matrix And the positive electrode material coated and/or filled on the conductive substrate, the positive electrode material contains nickel hydroxide powder, cobalt additive and binder, wherein, the positive electrode material also contains metal powder, the metal is selected from vanadium, titanium , molybdenum, manganese, niobium, hafnium, zirconium, yttrium, tantalum in one or more.

According to the battery provided by the present invention, the separator is disposed between the positive electrode and the negative electrode, has electrical insulation performance and liquid retention performance, and accommodates the electrode group together with the alkaline electrolyte in the battery case. The separator may be selected from various separators used in alkaline secondary batteries, such as non-woven fabrics of polyamide fibers or sheet-like elements containing polyolefin fibers and introducing acid groups on the surface. The location, nature and type of said separators are well known to those skilled in the art.

The positive electrode of the battery includes a conductive base and a positive electrode material coated and/or filled on the conductive base. Except that the positive electrode material provided by the present invention is used for the positive electrode material, other things such as the type of the conductive matrix, the preparation method of the positive electrode, etc. can all use the existing technology. For example,

The positive electrode of the battery can be formed by coating and/or filling the paste on the conductive base, drying, and pressing or not pressing. Wherein, the methods and conditions of drying and compression molding are well known to those skilled in the art. The conductive matrix is a conductive matrix used in alkaline secondary batteries, such as a nickel foam matrix, a matrix with a felt sheet structure, a metal perforated plate or a porous drawn metal mesh.

The battery negative pole is a negative pole used in various alkaline secondary batteries. The negative electrode includes a conductive base and a negative electrode material coated and/or filled on the negative conductive base. The conductive substrate of the negative electrode can use the same conductive substrate as that of the positive electrode.

The negative electrode material contains a main component and a binder, and the main component is selected from oxides and/or hydroxides of cadmium, oxides and/or hydroxides of zinc, or hydrogen storage alloys. The hydrogen storage alloy can be selected from any hydrogen storage alloy that can be used as the main component of the negative electrode of the alkaline secondary battery, and the hydrogen storage alloy can absorb the hydrogen produced by the alkaline electrolyte in the electrochemical reaction, and when discharging Absorbed hydrogen can be decomposed reversibly. The hydrogen storage alloy is described in detail in CN1159793C.

The negative electrode material may contain a solvent, and the solvent may be selected from any solvent capable of making the mixture form a paste, preferably water. The amount of solvent used is such that the paste is viscous and can be applied to solid materials. Based on the weight of the main component, the content of the solvent is preferably 15-40% by weight, more preferably 20-35% by weight.

The negative electrode material may also contain a conductive agent, the type of which is known to those skilled in the art, such as graphite and/or carbon black, nickel powder. Based on the weight of the main component, the content of the conductive agent is 0-8 wt%, more preferably 2-5 wt%.

The binder described in the negative electrode can be used with the binder used in the positive electrode. Based on the weight of the main component, the content of the binder is preferably 0.01-5% by weight, more preferably 0.02-3% by weight.

The preparation method of the negative electrode is well known to those skilled in the art, for example, the main components of the negative electrode material, the binder and the solvent, and the optional conductive material are mixed into a paste, coated and/or filled in the The conductive base is dried and molded or not, and becomes the negative electrode of the battery.

The electrolyte is an electrolyte used in alkaline secondary batteries, such as one or more of potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, and lithium hydroxide aqueous solution. The concentration of the electrolyte is generally 4-9 equivalents/liter.

A separator is arranged between the prepared positive electrode and negative electrode to form an electrode group, the electrode group is accommodated in a battery casing, an electrolyte is injected, and then the battery casing is sealed to obtain an alkaline secondary battery. The injection amount of the electrolyte is generally 0.9-1.2g/Ah.

The following examples will further illustrate the present invention.

Example 1

This example illustrates the positive electrode material provided by the present invention, the alkaline secondary battery containing the positive electrode material and their preparation methods.

(1) Preparation of positive electrode

The spherical nickel hydroxide of 100 parts by weight, the cobaltous oxide of 5 parts by weight, the metal molybdenum powder of 0.5 parts by weight, the aqueous dispersion of carboxymethyl cellulose of 5 parts by weight (containing the carboxymethyl cellulose of 1 weight %) , 2 parts of weight of polytetrafluoroethylene (PTFE) dispersion liquid (solid content is the standard commodity of 60 weight percent), 20 parts of weight of water mixing and stirring, be mixed into pasty slurry, this slurry is filled into surface density of 430 g/m ² , in nickel foam with one side welded with a nickel strip drain terminal, then dried, rolled, and cut to produce a positive plate with a size of 85 mm × 40 mm × 0.65 mm, in which the hydrogen oxide The content of nickel active material is about 8.4 grams.

(2) Preparation of negative electrode

Take by weighing 100 parts by weight of MmNi _3.55 Co _0.75 AL _0.3 Mn _0.4 type alloy powder (wherein Mm is misch metal), 1 part by weight of conductive carbon black, 2.5 parts by weight of PTFE dispersion (solid content is 60% by weight), 5 parts by weight Parts of weight of carboxymethyl cellulose aqueous dispersion (containing 1% by weight of carboxymethyl cellulose) and 20 parts of weight of water are mixed, stirred into a paste, coated on a punched nickel-plated steel strip, dried, Rolling and cutting into a negative electrode plate with a size of 115 mm×40.7 mm×0.34 mm, wherein the content of the alloy powder is about 10 grams.

(3) Battery assembly

The positive electrode plate obtained in (1), the separator grafted with polypropylene separator, and the negative electrode plate obtained in (2) are sequentially stacked and wound into a scroll-shaped electrode group, and the obtained electrode group is placed in a cylindrical battery case with one end open In, add electrolyte solution 2.3 grams (electrolyte solution is the mixed aqueous solution of KOH and LiOH, contains the LiOH of 30% by weight KOH and 15 g/liter in the mixed aqueous solution), is made into AA type metal hydride-nickel battery B1 of 2100mAh after sealing.

Comparative example 1

This comparative example illustrates the positive electrode material without metal molybdenum powder, the alkaline secondary battery containing the positive electrode material and its preparation method.

An alkaline secondary battery was prepared according to the method of Example 1, except that no metal molybdenum powder was added when preparing the positive electrode material, and a reference battery BB1 was made.

Example 2-9

This example illustrates the positive electrode material provided by the present invention, the alkaline secondary battery containing the positive electrode material and its preparation method.

The battery positive electrode material and the battery were prepared according to the method of Example 1, except that when preparing the positive electrode, metal powder was added as shown in Table 1, and the amount of cobaltous oxide added was 2.5 parts by weight to make batteries B2-B9.

Example 10

This example illustrates the positive electrode material provided by the present invention, the alkaline secondary battery containing the positive electrode material and its preparation method.

Prepare the positive electrode material and the battery according to the method of Example 1 respectively, the difference is that when preparing the positive electrode, the addition of metal manganese powder in Example 10 is 2 parts by weight, and cobalt metal powder and dicobalt oxide are used instead of cobaltous oxide In terms of cobalt element, the amount of cobalt metal powder and dicobalt trioxide is 4 parts by weight and 3 parts by weight respectively, and the battery B10 is made.

The performance of the battery provided by the present invention will be described below.

(1) The batteries B1-B10 made in Examples 1-10 and the battery BB1 made in Comparative Example 1 were respectively charged at 210mA (0.1C) for 15 hours, left for 30 minutes, and discharged at 630mA (0.3C) to 1.0V.

(2) After three cycles according to the steps in (1), charge at 0.1C (210mA) for 15 hours, discharge at 0.2C (420mA) to 1.0V, and record the discharge capacity Q1 of the battery. Then charge them at 0.1C (210mA) for 15 hours, place them at 40°C for 7 days, then discharge them at 0.2C (420mA) to 1.0V, and record the battery capacity as q1. Calculate the initial battery self-discharge rate by the following formula.

Initial battery self-discharge rate L1=(1-q1/Q1)×100%.

(3) After three cycles according to the steps in (1), charge at 1C (2100mA) for 70 minutes, -ΔV=10mV, discharge at 1C to 1.0V, and cycle 100 times like this. Charge at 0.1C (210mA) for 15 hours, discharge at 0.2C (420mA) to 1.0V, and record the discharge capacity Q2 of the battery. After charging at 0.1C (210mA) for 15 hours, place it in an environment of 40°C for 7 days, then discharge at 0.2C (420mA) to 1.0V, and record the battery capacity as q2. Calculate the self-discharge rate after 100 cycles according to the following formula.

The self-discharge rate L2=(1-q2/Q2)×100% after 100 cycles.

The results are listed in Table 1.

Table 1

Battery Metal powder and its content (based on 100 parts by weight of nickel hydroxide) Q1(mAh) q1(mAh) Q2 (mAh) q2(mAh) L1(%) L2(%) B1 0.5 parts by weight molybdenum 2198 1819 2046 1602 17.2 21.7 BB1 0 2164 1723 2010 1493 20.4 25.7 B2 0.5 parts by weight niobium 2174 1792 2015 1590 17.5 twenty one B3 1 part by weight molybdenum 2176 1785 2013 1535 18.0 23.7 B4 1 part by weight vanadium 2170 1781 2016 1546 17.9 23.3 B5 1.5 parts by weight titanium 2184 1802 2021 1592 17.5 21.2 B6 2 parts niobium by weight 2182 1786 2018 1580 18.2 21.7 B7 2.2 parts by weight zirconium 2180 1787 2016 1592 18.0 21.0 B8 2.5 parts by weight manganese 2175 1780 2013 1548 18.2 23.1 B9 2.8 parts by weight yttrium 2163 1760 2028 1571 18.6 22.5 B10 2 parts by weight manganese 2183 1790 2043 1581 18 22.6

As can be seen from Table 1, the self-discharge performance of batteries B1-B10 provided by the present invention is better than that of reference battery BB1 at the initial stage and after 100 cycles. In addition, the capacity of batteries B1-B10 provided by the present invention is also significantly higher than that of Reference battery BB1. This shows that due to the use of the positive electrode material provided by the invention, the alkaline secondary battery provided by the invention containing the positive electrode material not only has better self-discharge performance at the beginning and after several cycles, but also has a higher discharge capacity.

Claims (10)

1. An alkaline secondary battery positive electrode material, which contains nickel hydroxide powder, cobalt additives and binders, is characterized in that the positive electrode material also contains metal powder, and the metal is selected from vanadium, molybdenum, hafnium, One or more of zirconium and tantalum. 2. The material according to claim 1, wherein the content of the metal powder is greater than zero to 5% by weight based on the weight of nickel hydroxide. 3. The material according to claim 2, wherein the content of the metal powder is 0.1-3% by weight based on the weight of nickel hydroxide. 4. The material according to claim 1, wherein, based on the weight of nickel hydroxide, the content of the cobalt additive is greater than zero to 10% by weight based on the cobalt element. 5. The material according to claim 1 or 4, wherein the cobalt additive is selected from one or more of Co, Co(OH) ₂ , Co ₂ O ₃ , Co ₃ O ₄ and CoO. 6. The material according to claim 1, wherein the binder is selected from one or more of carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polytetrafluoroethylene; Based on the weight of the binder, the content of the binder is 0.01-5% by weight. 7. The material according to claim 1, characterized in that the material further contains a solvent, and the content of the solvent is 15-40% by weight based on the weight of nickel hydroxide. 8. An alkaline secondary battery, the battery includes an electrode group and an alkaline electrolyte, the electrode group and the alkaline electrolyte are sealed together in a battery case, the electrode group includes a positive pole, a negative pole and a separator, the positive pole Comprising a conductive substrate and a positive electrode material coated and/or filled on the conductive substrate, the positive electrode material contains nickel hydroxide powder, cobalt additives and binders, and is characterized in that the positive electrode material also contains metal powder, and the metal One or more selected from vanadium, molybdenum, hafnium, zirconium, and tantalum. 9. The battery according to claim 8, wherein the content of the metal powder is greater than zero to 5% by weight based on the weight of nickel hydroxide. 10. The battery according to claim 9, wherein the content of the metal powder is 0.1-3% by weight based on the weight of nickel hydroxide.