Positive electrode additive and preparation method thereof

Abstract

The invention relates to a positive electrode additive and a preparation method thereof. The positive electrode additive comprises a metal salt MxCyOz and a catalyst which are uniformly mixed, and the catalyst with a relatively small particle size is uniformly dispersed and introduced into the metal salt MxCyOz, so that the catalyst can be in full contact with the metal salt, the catalytic effect of the catalyst is fully exerted, and the decomposition voltage of the metal salt MxCyOz is effectively reduced. The positive electrode additive is prepared by adopting coprecipitation and sintering, so that the metal salt MxCyOz and the catalyst can be uniformly mixed at a relatively small particle size level, the catalytic effect of the catalyst is improved, and the decomposition voltage of the metal salt MxCyOz is reduced. The method is simple in process step and suitable for large-scale industrial popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly to a cathode additive and a preparation method thereof. Background Art

[0002] During the first-week charging of lithium-ion batteries and sodium-ion batteries, an SEI film is formed on the surface of the negative electrode, resulting in irreversible capacity loss of the cathode material, thereby affecting the capacity and cycle life of the battery. Therefore, the capacity and cycle performance of the battery can be improved by adding lithium or sodium to the cathode or the negative electrode. Compared with adding lithium or sodium to the negative electrode, adding lithium or sodium to the cathode is simpler and easier, without the need to increase the production process, and only needs to add a lithium supplement agent or a sodium supplement agent during the cathode homogenization.

[0003] Additives such as lithium oxalate, lithium carbonate, sodium oxalate, and sodium carbonate have a high theoretical charge specific capacity, and will decompose after charging, and the products are gases without solid residues, and can be used as lithium supplement agents for lithium batteries and sodium supplement agents for sodium batteries in specific application environments. However, additives such as lithium oxalate, lithium carbonate, sodium oxalate, and sodium carbonate have a high decomposition voltage in the battery and cannot decompose. Therefore, it is necessary to reduce the decomposition voltage of these additives in the battery. Summary of the Invention

[0004] In view of the problems in the background art, the present invention provides a cathode additive, which comprises a metal salt M x C y O z and a catalyst. By uniformly dispersing the catalyst into the metal salt M x C y O z , the decomposition voltage of the metal salt M x C y O z can be effectively reduced.

[0005] In a first aspect, the present invention provides a cathode additive, comprising: a metal salt M x C y O z and a catalyst, wherein the metal salt is a micron-sized particle and the catalyst is a nano-sized particle;

[0006] wherein M is lithium or sodium, x is an integer from 1 to 3, y is an integer from 1 to 6, and z is an integer from 3 to 6;

[0007] The catalyst is a transition metal oxide.

[0008] The present invention selects the metal salt M x C y O zAs a sodium supplement or lithium supplement, by uniformly dispersing a catalyst with a smaller particle size into the metal salt M x C y O z it is possible to enable the catalyst to come into full contact with the metal salt, giving full play to the catalytic effect of the catalyst, thereby effectively reducing the decomposition voltage of the metal salt M x C y O z . Using this cathode additive in the cathode can effectively supplement lithium or sodium to a sufficient extent.

[0009] In some specific embodiments, the catalyst particles are embedded on the surface and inside of the metal salt particles.

[0010] In the conventional technology, the metal salt M x C y O z particles and the catalyst particles are physically mixed. The two types of particles are independent and loose from each other, and the mixed state is like fine sand. The sizes of both types of particles are relatively large. This will cause a large number of metal salt molecules inside the metal salt particles to be difficult to contact with the catalyst molecules, and the catalyst molecules inside the particles cannot contact the metal salt molecules, resulting in a deterioration of the catalytic effect, waste of raw materials, and an increase in cost.

[0011] Compared with the above physical mixing, the catalyst and the metal salt in the present invention are mixed at a smaller particle size level, and the catalyst particles are embedded on the surface and inside of the metal salt particles. The catalyst particles are in close contact with the metal salt, and there is no gap or only a very small gap between them. This enables the catalyst and the metal salt to come into full contact, which is conducive to giving full play to the catalytic effect of the catalyst.

[0012] In some embodiments, in the cathode additive, the mass ratio of the catalyst can be 0.5%-16%.

[0013] By optimizing the dosage of the catalyst, it is conducive to giving full play to the catalytic effect of the catalyst. As the dosage of the catalyst increases, the decomposition voltage of the metal salt M x C y O z shows a trend of first decreasing and then increasing.

[0014] In some specific embodiments, the mass ratio of the catalyst can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or 16%.

[0015] In some embodiments, x can be 1, 2 or 3. y can be 1, 2, 3, 4, 5 or 6. z can be 3, 4, 5 or 6.

[0016] In some specific embodiments, x can be 2, y can be 1 or 2, and z can be 3 or 4.

[0017] Preferably, the positive electrode additive can be lithium oxalate, lithium carbonate, sodium oxalate or sodium carbonate. These additives have a relatively high theoretical charge specific capacity and will decompose after charging. The product is CO2 without solid residue, which is one of the ideal materials as lithium or sodium supplement agents.

[0018] In some embodiments, the transition metal oxide includes one or more of Ni oxide, Co oxide, Mn oxide, and Fe oxide, such as including one or more of Co3O4, NiO, Mn2O3 or Fe2O3. These catalysts are easy to synthesize and compatible with the coprecipitation process.

[0019] Preferably, the transition metal oxide is Co oxide, such as Co3O4.

[0020] In some embodiments, the particle size range of the metal salt is 0.5 - 10 μm. The maximum particle size of the metal salt is below 10 μm. The particle size range of the catalyst is 5 - 200 nm. The particle sizes of both the metal salt particles and the catalyst particles are relatively small, which is conducive to the full contact between the catalyst and the metal salt, giving full play to the catalytic effect of the catalyst, thereby effectively reducing the decomposition voltage of the metal salt M x C y O z .

[0021] In some specific embodiments, the particle size of the metal salt particles can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0022] In some specific embodiments, the particle size of the catalyst particles can be 5 - 20 nm, 20 - 50 nm, 50 - 100 nm or 100 - 200 nm.

[0023] In some embodiments, the specific surface area of the positive electrode additive is 5 - 50 m 2 / g, and can be, for example, 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 22.4 m 2 / g, 25 m 2 / g, 30 m 2 / g, 35 m 2 / g, 40 m 2 / g, 45 m 2 / g or 50 m 2 / g. Controlling the specific surface area within this range is beneficial to improving the catalytic activity of the catalyst.

[0024] In a second aspect, the present invention provides a method for preparing the positive electrode additive, comprising the following steps:

[0025] Dissolve a soluble transition metal salt and a soluble M salt in a first solvent to obtain a first solution, where M is lithium or sodium;

[0026] Dissolve oxalic acid in a second solvent to obtain a second solution;

[0027] Mix the first solution with the second solution, so that the transition metal ions and M ions in the first solution are co-precipitated in the form of oxalates respectively, and the precipitate is separated;

[0028] Sinter the precipitate to obtain the positive electrode additive.

[0029] The positive electrode additive prepared by the method of the present invention includes: metal salt M x C y O z and a catalyst, the metal salt is in the form of micron-sized particles, and the catalyst is in the form of nano-sized particles; wherein, M is lithium or sodium, x is an integer from 1 to 3, y is an integer from 1 to 6, and z is an integer from 3 to 6; the catalyst is a transition metal oxide.

[0030] The present invention first dissolves the transition metal salt and the M salt in a suitable first solvent. The dissolution step is a prerequisite for obtaining a positive electrode additive mixed at a smaller particle size level; then the co-precipitation method is adopted, using oxalic acid as a precipitating agent, to precipitate the transition metal ions and M ions in the form of oxalates respectively, forming a uniformly mixed precipitate (the precipitate contains the oxalate of the transition metal and the oxalate of M), achieving uniform mixing at a smaller particle size level; then through sintering, the precursor of the catalyst (i.e., the oxalate of the transition metal) is converted into an oxide catalyst, realizing the uniform distribution of the catalyst and the metal salt M x C y O z so as to fully exert the catalytic effect of the catalyst. The method of the present invention has simple process steps and is suitable for large-scale industrial promotion.

[0031] In order to prepare the metal salt M x C y O z with a relatively high theoretical charge specific capacity, the present invention selects oxalic acid as a precipitating agent. Utilizing the property that the oxalate of M (sodium oxalate or potassium oxalate) is insoluble in organic solvents such as ethanol, the oxalate of the transition metal is co-precipitated and precipitated out during the co-precipitation process to form a precipitate.

[0032] The amount of oxalic acid used is related to the amounts of the soluble transition metal salt and the soluble M salt. The amount of substance of oxalic acid can be calculated according to the following formula:

[0033] N 草酸 = N 可溶性M盐 *0.5 + N 可溶性过渡金属盐

[0034] Wherein, N 草酸 is the amount of substance of oxalic acid, N 可溶性M盐 is the amount of substance of the soluble M salt, and N 可溶性过渡金属盐 is the amount of substance of the soluble transition metal salt.

[0035] In some embodiments, the soluble transition metal salt may be an acetate of Ni, Co, Mn or Fe; a nitrate of Ni, Co, Mn or Fe; a sulfate of Ni, Co, Mn or Fe; or a chloride of Ni, Co, Mn or Fe. These transition metal salts are all soluble in water, ethanol, etc., and have good solubility, which is beneficial to the co-precipitation.

[0036] In some embodiments, the soluble M salt may be an acetate of lithium or sodium; a nitrate of lithium or sodium; a sulfate of lithium or sodium; or a chloride of lithium or sodium. These salts have good solubility in water, ethanol, etc., which is beneficial to the co-precipitation.

[0037] Regarding the types of the first solvent and the second solvent, those skilled in the art can select according to the principle of the co-precipitation method, which is an operation generally known to those skilled in the art and is not particularly limited.

[0038] For example, in some embodiments, the first solvent includes one or more of water, ethanol, methanol, ether, n-propanol, glycerol, dimethyl sulfoxide, n-butanol, ethyl acetate, formic acid. These solvents can well dissolve the soluble transition metal salt and the soluble M salt, increase the concentrations of the transition metal ions and M ions in the solvent, and promote the effective progress of the co-precipitation.

[0039] For example, in some embodiments, the second solvent may be a poor solvent for the oxalate; preferably, the second solvent includes one or more of ethanol and methanol. Introducing the poor solvent into the reaction system is beneficial to the precipitation of the oxalate co-precipitate.

[0040] In some embodiments, the sintering temperature is preset according to the composition of the cathode additive. The sintering temperature is 200 - 340 °C (such as 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C or 340 °C), and the obtained cathode additive includes one of lithium oxalate and sodium oxalate and a transition metal oxide. Preferably, when the sintering temperature is 200 - 340 °C, the sintering time is 5 - 150 min, such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min or 150 min, etc. The sintering temperature is 350 - 500 °C (such as 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C or 500 °C), and the obtained cathode additive includes one of lithium carbonate and sodium carbonate and a transition metal oxide. Preferably, when the sintering temperature is 350 - 500 °C, the sintering time is 30 - 180 min, such as 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min, etc.

[0041] When the temperature of the sintering is too low, the oxalate of the transition metal cannot be completely decomposed, and the catalytic effect is poor. As the reaction temperature increases, the oxalate of the transition metal is completely decomposed, and the catalytic effect reaches the optimum. When the temperature continues to rise, the oxalate of M begins to decompose to form the carbonate of M, and the charge specific capacity decreases compared with that of the oxalate of M. When the sintering temperature is too high, the decomposition of the oxalate of the transition metal is accompanied by the decomposition of lithium oxalate, resulting in an increase in the charge voltage of the oxalate of M.

[0042] The main purpose of sintering is to decompose the transition metal oxalate in the precipitate into a transition metal oxide, and the transition metal oxide has a catalytic function and can reduce the metal salt M x C y O zThe decomposition voltage is achieved to fully compensate for lithium or sodium. At the sintering temperature that satisfies the decomposition of the transition metal oxalate, a lower sintering temperature (below 350 °C) will not cause the decomposition of the oxalate of M (i.e., sodium oxalate or potassium oxalate) in the precipitate. Therefore, the cathode additive obtained at a lower sintering temperature includes one of lithium oxalate and sodium oxalate and a transition metal oxide; while a higher sintering temperature (above 350 °C) will not only cause the decomposition of the transition metal oxalate in the precipitate, but also cause the decomposition of the oxalate of M in the precipitate into the carbonate of M (i.e., sodium carbonate or potassium carbonate). Therefore, the cathode additive obtained at a higher sintering temperature includes one of lithium carbonate and sodium carbonate and a transition metal oxide. During the sintering process, in the presence of a transition metal oxide catalyst, the thermal decomposition temperature of the oxalate of M will be lower than that without the catalyst.

[0043] Advantages of the present invention compared with the prior art:

[0044] 1. The present invention provides a cathode additive, which includes a uniformly mixed metal salt M x C y O z and a catalyst. By uniformly dispersing a catalyst with a smaller particle size into the metal salt M x C y O z , it can enable the catalyst to be in full contact with the metal salt, fully exert the catalytic effect of the catalyst, and thus effectively reduce the decomposition voltage of the metal salt M x C y O z .

[0045] 2. The present invention also provides a preparation method of the cathode additive. By using co-precipitation and sintering to prepare the cathode additive, it can make the metal salt M x C y O z and the catalyst be uniformly mixed at a smaller particle size level, improve the catalytic effect of the catalyst, and reduce the decomposition voltage of the metal salt M x C y O z . The method of the present invention has simple process steps and is suitable for large-scale industrial promotion. Description of the Drawings

[0046] Figure 1 is a flowchart for preparing a cathode additive in an embodiment of the present invention.

[0047] Figure 2 is a schematic structural diagram of a Co3O4@Li2C2O4 composite material prepared in an embodiment of the present invention.

[0048] Figure 3Schematic diagram of the Co3O4@Li2C2O4 composite material prepared by the ball milling method for Comparative Example 2.

[0049] Figure 4 Charge curve of the coin cell prepared with the Co3O4@Li2CO3 composite material prepared in Example 20 as the cathode material.

[0050] Figure 5 Scanning electron microscope photograph of the Co3O4@Li2C2O4 composite material prepared in Example 1.

[0051] Figure 6 Scanning electron microscope photograph of the Co3O4@Li2CO3 composite material prepared in Example 20.

[0052] Figure 7 Scanning electron microscope photograph of the Co3O4@Na2C2O4 composite material prepared in Example 34. Detailed implementation manners

[0053] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0054] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The experimental reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments and equipment used in the following embodiments can all be obtained through market purchase or can be obtained by existing methods; the dosages of the experimental reagents are all the dosages of the reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0055] Preparation of Co3O4@Li2C2O4 composite material

[0056] Example 1

[0057] 1) Design the mass ratio of Co3O4 in the cathode additive to be 6%. According to the ratio, 66.0 g of anhydrous lithium acetate (CH3COOLi) and 10.1 g of cobalt acetate ((CH3COO)2Co·4H2O) are dissolved in 500 mL of an ethanol aqueous solution (ethanol: water volume ratio = 50:50) to form a first solution;

[0058] 2) Dissolve 58.5 g of oxalic acid in 250 mL of absolute ethanol to form a second solution;

[0059] 3) After the first solution is mixed with the second solution, a precipitate is formed. The precipitate is collected by suction filtration, washed three times with ethanol, and then dried in an oven at 60 °C for 5 h;

[0060] 4) The dried precipitate in step 3 is sintered in air at 270 °C for 60 min to obtain the Co3O4@Li2C2O4 composite material, which is the cathode additive. The scanning electron microscope photograph is as Figure 5 shown. The measured specific surface area is 22.4 m 2 / g.

[0061] Examples 2 - 6

[0062] The cathode additive is prepared according to the method described in Example 1, except that the sintering time in step 4 is different from that in Example 1, as shown in Table 1 below.

[0063] Table 1

[0064] Number Sintering time / min Example 1 60 Example 2 5 Example 3 30 Example 4 90 Example 5 150 Example 6 180

[0065] Examples 7 - 10

[0066] The cathode additive is prepared according to the method described in Example 1, except that the sintering temperature in step 4 is different from that in Example 1, as shown in Table 2 below.

[0067] Table 2

[0068] Number Sintering temperature / °C Example 1 270 Example 7 200 Example 8 290 Example 9 340 Example 10 180

[0069] Examples 11 - 16

[0070] The cathode additive is prepared according to the method described in Example 1, except that the mass ratio of Co3O4 in step 1 is different from that in Example 1, as shown in Table 3 below.

[0071] Table 3

[0072] Number <![CDATA[Mass ratio of Co3O4]]> Example 1 6％ Example 11 0.5％ Example 12 4％ Example 13 8％ Example 14 12％ Example 15 16％ Example 16 18％

[0073] Examples 17 - 19

[0074] The cathode additive is prepared according to the method described in Example 1, except that a transition metal oxide different from that in Example 1 is used, as shown in Table 4 below.

[0075] Table 4

[0076] Number Transition metal oxide Example 1 <![CDATA[Co3O4]]> Example 17 NiO Example 18 <![CDATA[Mn2O3]]> Example 19 <![CDATA[Fe2O3]]>

[0077] Comparative Example 1

[0078] The cathode additive is prepared according to the method described in Example 1, except that cobalt acetate is not added in step 1.

[0079] Comparative Example 2

[0080] The cathode additive was prepared by the ball milling method, and the specific steps were as follows:

[0081] 1) 94 g of lithium oxalate and 6 g of cobalt oxide (Co3O4) were subjected to wet ball milling and compounding, controlling the ball-to-material ratio to be 10:1, the rotation speed to be 300 rpm, and the ball milling time to be 5 h;

[0082] 2) After drying and sieving the material, Co3O4 composite lithium oxalate material was obtained.

[0083] Comparative Example 3

[0084] The cathode additive was prepared according to the method described in Comparative Example 2, except that cobalt oxide was not added, and lithium oxalate was directly subjected to wet ball milling.

[0085] Performance test of cathode additive

[0086] 1. The Co3O4@Li2C2O4 composite material prepared in Examples 1-19 and Comparative Examples 1-3 was used as the cathode material for button cell assembly. A metal lithium sheet was used as the anode, a 2032 button cell case, a separator was Celgard 2400, and the electrolyte was 1 M LiPF6 dissolved in EC:EMC:DEC = 1:1:1; among them, the mass ratio of Co3O4@Li2C2O4 composite material: conductive carbon black (SP): PVDF = 7:2:1. The lithium ion button cell was subjected to charge and discharge tests. The theoretical specific capacity of lithium oxalate was calculated according to 500 mAh / g. After the battery assembly was completed, it was left standing for 2 h and charged at a constant current of 0.05 C to 4.5 V. The obtained specific capacity was the first-cycle charging specific capacity of lithium oxalate. The results are shown in Table 5 below. The median voltage was defined as the voltage when the battery charging capacity was 50%, and the median voltage was used here to represent the decomposition voltage of the sample.

[0087] Table 5

[0088]

[0089]

[0090] As can be seen from Table 5, when the cathode additive prepared by the method of the present invention was directly used as the cathode material, the first-cycle charging specific capacity of the battery was significantly higher than that of the batteries prepared in Comparative Examples 1-3, which reflected that the cathode additive of the present invention had a low decomposition voltage and could play a role in fully compensating for lithium when added to the cathode.

[0091] Preparation of Co3O4@Li2CO3 composite material

[0092] Example 20

[0093] 1) The mass ratio of Co3O4 in the designed cathode additive is 8.5%. According to the ratio, 50.0 g of anhydrous lithium acetate (CHCOOLi) and 8.2 g of cobalt acetate ((CH3COO)2Co·4H2O) are dissolved in 500 mL of an ethanol aqueous solution (ethanol:water volume ratio = 50:50) to form a first solution;

[0094] 2) Dissolve 44.5 g of oxalic acid in 200 mL of anhydrous ethanol to form a second solution;

[0095] 3) After the first solution and the second solution are mixed to form a precipitate, collect the precipitate by suction filtration, wash it three times with ethanol, and then dry the precipitate in an oven at 60 °C for 5 h;

[0096] 4) Sinter the dried precipitate in step 3 in air at 450 °C for 60 min to obtain a Co3O4@Li2CO3 composite material, which is the cathode additive. Its scanning electron microscope photograph is as shown in Figure 6 shown. The measured specific surface area is 35.7 m 2 / g.

[0097] Examples 21 - 24

[0098] Prepare the cathode additive according to the method described in Example 20, except that the sintering time in step 4 is different from that in Example 20, as shown in Table 6 below.

[0099] Table 6

[0100] Number Sintering time / min Example 20 60 Example 21 30 Example 22 90 Example 23 180 Example 24 200

[0101] Examples 25 - 28

[0102] Prepare the cathode additive according to the method described in Example 20, except that the sintering temperature in step 4 is different from that in Example 20, as shown in Table 7 below.

[0103] Table 7

[0104] Number Sintering temperature / °C Example 20 450 Example 25 350 Example 26 400 Example 27 500 Example 28 550

[0105] Examples 29 - 33

[0106] Prepare the cathode additive according to the method described in Example 20, except that the mass ratio of Co3O4 in step 1 is different from that in Example 20, as shown in Table 8 below.

[0107] Table 8

[0108] Number <![CDATA[Mass percentage of Co3O4]]> Example 20 8.5％ Example 29 0.5％ Example 30 4.5％ Example 31 12.5％ Example 32 15％ Example 33 18％

[0109] Comparative Example 4

[0110] The positive electrode additive was prepared according to the method described in Example 20, except that cobalt acetate was not added in Step 1.

[0111] Comparative Example 5

[0112] The positive electrode additive was prepared by ball milling method, and the specific steps are as follows:

[0113] 1) 91.5 g of lithium carbonate and 8.5 g of cobalt oxide (Co3O4) were subjected to wet ball milling and compounding, controlling the ball-to-material ratio to be 10:1, the rotation speed to be 300 rpm, and the ball milling time to be 5 h;

[0114] 2) After drying and sieving the material, the Co3O4 composite lithium carbonate material was obtained.

[0115] Performance test of cathode additive

[0116] 1. The Co3O4@Li2CO3 composite materials prepared in Examples 20 - 33 and Comparative Examples 4 - 5 were used as the positive electrode materials for button cell assembly. A metal lithium sheet was used as the negative electrode, a 2032 button cell case, a Celgard 2400 diaphragm, and an electrolyte of 1 M LiPF6 dissolved in EC:EMC:DEC = 1:1:1; wherein the mass ratio of Co3O4@Li2CO3 composite material: conductive carbon black (SP): PVDF = 7:2:1. Charge-discharge tests were carried out on the lithium-ion button cells. The theoretical specific capacity of lithium oxalate was calculated as 500 mAh / g. After the battery assembly was completed, it was left standing for 2 h and then charged at a constant current of 0.1C to 4.8V. Charge-discharge tests were carried out on the lithium-ion button cells (the test conditions were: 2.0 - 4.8V, and the test step was 0.1C constant current charging, 1C = 500 mAh / g). The first-cycle charge specific capacity results of the battery are shown in Table 9 below. The median voltage is defined as the voltage when the battery charge capacity reaches 50%, and here the median voltage represents the decomposition voltage of the sample.

[0117] Table 9

[0118]

[0119]

[0120] As can be seen from Table 9, when the positive electrode additive prepared by the method of the present invention is directly used as the positive electrode material, the first-cycle charge specific capacity of the battery is significantly higher than that of the batteries prepared in Comparative Examples 4 - 5, which reflects that the positive electrode additive of the present invention has a low decomposition voltage and can play a role in fully supplementing lithium when added to the positive electrode.

[0121] Preparation of Co3O4@Na2C2O4 composite material

[0122] Example 34

[0123] 1) The mass ratio of Co3O4 in the designed cathode additive is 3%. According to the ratio, 66.15 g of anhydrous sodium acetate (CH3COONa) and 8.85 g of cobalt acetate ((CH3COO)2Co·4H2O) are dissolved in 500 mL of an ethanol aqueous solution (ethanol: water volume ratio = 50:50) to form a first solution;

[0124] 2) Dissolve 47.40 g of oxalic acid in 200 mL of absolute ethanol to form a second solution;

[0125] 3) After the first solution and the second solution are mixed to form a precipitate, the precipitate is collected by suction filtration, washed three times with ethanol, and then dried in an oven at 60 °C for 5 h;

[0126] 4) Sinter the dried precipitate in step 3 in air at 250 °C for 60 min to obtain the Co3O4@Na2C2O4 composite material, i.e., the cathode additive, and its scanning electron microscope photograph is as shown in Figure 7 shown. The measured specific surface area is 17.4 m 2 / g.

[0127] Examples 35 - 39

[0128] Prepare the cathode additive according to the method described in Example 34, except that the sintering time in step 4 is different from that in Example 34, as shown in Table 10 below.

[0129] Table 10

[0130]

[0131]

[0132] Examples 40 - 43

[0133] Prepare the cathode additive according to the method described in Example 34, except that the sintering temperature in step 4 is different from that in Example 34, as shown in Table 11 below.

[0134] Table 11

[0135] Number Sintering temperature / °C Example 34 250 Example 40 200 Example 41 290 Example 42 340 Example 43 180

[0136] Examples 44 - 48

[0137] Prepare the cathode additive according to the method described in Example 34, except that the mass ratio of Co3O4 in step 1 is different from that in Example 34, as shown in Table 12 below.

[0138] Table 12

[0139]

[0140]

[0141] Comparative Example 6

[0142] The positive electrode additive was prepared according to the method described in Example 34, except that cobalt acetate was not added in Step 1.

[0143] Comparative Example 7

[0144] The positive electrode additive was prepared by ball milling method, and the specific steps were as follows:

[0145] 1) Wet ball milling and compounding of 94 g of sodium oxalate and 6 g of cobalt oxide (Co3O4), controlling the ball-to-material ratio to be 10:1, the rotation speed to be 300 rpm, and the ball milling time to be 5 h;

[0146] 2) The material was dried and sieved to obtain Co3O4 composite sodium oxalate material.

[0147] Performance test of cathode additive

[0148] 1. The Co3O4@Na2C2O4 composite materials prepared in Examples 34 - 48 and Comparative Examples 6 - 7 were used as the positive electrode materials for button cell assembly. The metal sodium sheet was used as the negative electrode, the 2032 button cell case, the separator was glass fiber separator, and the electrolyte was 1 M NaClO4 in PC:FEC = 97:3 (mass ratio); among them, the mass ratio of Co3O4@Na2C2O4 composite material: conductive carbon black SP:PVDF = 7:2:1. The sodium ion button cell was subjected to charge and discharge tests (test conditions: 2.0 - 4.3 V, test step: constant current charging at 0.1 C, 1 C = 400 mAh / g). The first-cycle charge specific capacity results of the battery are shown in Table 13 below. The median voltage is defined as the voltage when the battery charge capacity is 50%, and here the median voltage represents the decomposition voltage of the sample.

[0149] Table 13

[0150]

[0151]

[0152] As can be seen from Table 13, when the positive electrode additive prepared by the method of the present invention is directly used as the positive electrode material, the first-cycle charge specific capacity of the battery is significantly higher than that of the batteries prepared in Comparative Examples 6 - 7, which reflects that the positive electrode additive of the present invention has a low decomposition voltage and can play a role in fully supplementing lithium when added to the positive electrode.

[0153] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims described above.

Claims

1. A positive electrode additive, characterized in that, Comprising: Metal salt M x C y O z and a catalyst, wherein the metal salt is in the form of micron-sized particles and the catalyst is in the form of nano-sized particles; Wherein, M is lithium or sodium, x is an integer from 1 to 3, y is an integer from 1 to 6, and z is an integer from 3 to 6; The catalyst is a transition metal oxide.

2. The cathode additive according to claim 1, characterized in that, The catalyst particles are embedded on the surface and inside of the metal salt particles.

3. The positive electrode additive according to claim 1 or 2, characterized in that, In the positive electrode additive, the mass ratio of the catalyst is 0.5%-16%.

4. The cathode additive according to claim 1 or 2, characterized in that, x is 2, y is 1 or 2, and z is 3 or 4; Preferably, the positive electrode additive is lithium oxalate, lithium carbonate, sodium oxalate or sodium carbonate.

5. The positive electrode additive according to claim 1 or 2, characterized in that The transition metal oxide includes one or more of Ni oxide, Co oxide, Mn oxide, and Fe oxide.

6. The positive electrode additive according to claim 1 or 2, characterized in that, The particle size range of the metal salt is 0.5-10 μm; the maximum particle size of the metal salt is below 10 μm; The particle size range of the catalyst is 5-200 nm.

7. The positive electrode additive according to claim 1 or 2, characterized in that, The specific surface area of the positive electrode additive is 5-50 m 2 / g.

8. A method for preparing a cathode additive, characterized in that, Including the following steps: Dissolve the soluble transition metal salt and the soluble M salt in the first solvent to obtain a first solution, where M is lithium or sodium; Dissolve oxalic acid in the second solvent to obtain a second solution; Mix the first solution and the second solution so that the transition metal ions and M ions in the first solution are co-precipitated in the form of oxalates respectively, and separate to obtain a precipitate; Sinter the precipitate to obtain the positive electrode additive.

9. The preparation method according to claim 8, characterized in that, The soluble transition metal salt is acetate of Ni, Co, Mn or Fe; nitrate of Ni, Co, Mn or Fe; sulfate of Ni, Co, Mn or Fe; or chloride of Ni, Co, Mn or Fe; The soluble M salt is acetate of lithium or sodium; nitrate of lithium or sodium; sulfate of lithium or sodium; or chloride of lithium or sodium; The first solvent includes one or more of water, ethanol, methanol, ether, n-propanol, glycerol, dimethyl sulfoxide, n-butanol, ethyl acetate, and formic acid; The second solvent is a poor solvent for the oxalate; preferably, the second solvent includes one or more of ethanol and methanol.

10. The preparation method according to claim 8 or 9, characterized in that, The sintering temperature is preset according to the composition of the positive electrode additive; The sintering temperature is 200-340 °C, and the obtained positive electrode additive includes one of lithium oxalate and sodium oxalate and a transition metal oxide; preferably, when the sintering temperature is 200-340 °C, the sintering time is 5-150 min; The sintering temperature is 350-500 °C, and the obtained positive electrode additive includes one of lithium carbonate and sodium carbonate and a transition metal oxide; preferably, when the sintering temperature is 350-500 °C, the sintering time is 30-180 min.

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