A modified positive electrode additive, a preparation method and use thereof

Abstract

The application belongs to the technical field of lithium ion battery materials, and provides a modified positive electrode additive, a preparation method and application thereof. The preparation method is as follows: lithium oxalate is synthesized in a solution system containing conductive agents and catalysts by adopting a precipitation method and a hydrothermal method, and is assisted by a binder and a dispersant, and is affected by the dispersion of the conductive agents, so that the modified lithium oxalate which is more closely combined with the catalysts and the conductive agents and has reduced particle size is obtained, so as to improve the problems of large particle size, high decomposition voltage and low capacity of the existing lithium oxalate as a positive electrode additive.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and relates to a modified positive electrode additive as well as a preparation method and application thereof. BACKGROUND

[0002] Under the background of current global energy transformation and sustainable development, lithium ion batteries, as the mainstay of new generation energy storage technology, are facing unprecedented market demand and technical challenges. With the vigorous development of electric vehicles, smart homes, renewable energy storage systems and other fields, more stringent requirements are put forward for the energy density, cycle life and safety of lithium ion batteries.

[0003] During the initial charging and discharging process of lithium ion batteries, lithium loss inevitably occurs in the positive electrode material, that is, part of lithium ions are lost in the negative electrode to form a solid electrolyte interface film (SEI film), which restricts the theoretical capacity of the battery.

[0004] To solve this problem, the prior art adopts a scheme of adding lithium-rich substances in the negative electrode or the positive electrode to make up for the loss of lithium. Among them, adding lithium-rich substances in the negative electrode significantly increases the instability of the battery, and there is a great safety risk. Compared with this, adding lithium-rich substances in the positive electrode material as an additive is simple in process, can improve the utilization rate of lithium ions and optimize the battery performance on the premise of ensuring the safety of the battery.

[0005] Under this trend, a series of lithium-rich additives such as Li2NiO2, Li5FeO4 and Li6CoO4 are widely used in positive electrode materials, however, these traditional additives have exposed several problems in practical application, including: ① residual substances are produced during charging, which not only occupies the internal space of the battery, but also catalyzes the decomposition of the electrolyte, thereby causing the battery to produce gas, affecting the cycle life and safety of the battery; ② poor air stability makes the material prone to deterioration during storage and processing, increasing the complexity and cost of the manufacturing process; ③ low deintercalation efficiency of lithium, low utilization rate, cannot fully play the positive lithium supplement performance.

[0006] In view of the above problems, lithium oxalate (LiC2O4) as a new type of positive electrode additive exhibits unique advantages. Its most prominent feature is that the decomposition in the charged state only generates carbon dioxide without any residual material, theoretically realizing the complete utilization of lithium. In addition, lithium oxalate exhibits excellent air stability, greatly enhancing the applicability and long-term storage reliability of the material. However, lithium oxalate is not perfect, and its relatively high decomposition voltage (about 4.7V) poses a barrier to its actual use. In a low-voltage environment, the lithium supplement effect cannot be achieved effectively, while in a high-voltage environment, the internal side reactions of the battery are accelerated, leading to decomposition of the electrolyte, degradation of the positive electrode material structure, and greatly increasing the difficulty of battery thermal management, posing a potential threat to the safety, cycle stability, and service life of the battery. Therefore, lithium oxalate needs to be modified and optimized.

[0007] Among the currently reported technologies, the process routes for improving lithium oxalate are mainly dry and wet methods. Although the dry method route has a lower cost, the lithium oxalate synthesized by the dry method usually has a larger particle size and a higher voltage, which cannot meet the high requirements of lithium batteries today. The existing wet method route mostly uses metal quantum dots synthesized in an organic phase as catalysts to reduce the decomposition voltage. Although lithium oxalate with better performance can be synthesized, the use of a large amount of organic matter brings safety problems and high costs, making it difficult to be industrialized, and the particle size of the synthesized lithium oxalate still has room for further adjustment and improvement. SUMMARY

[0008] In view of the problems in the prior art, the purpose of the present application is to provide a modified positive electrode additive and a preparation method and use thereof. The preparation method uses a precipitation method and a hydrothermal method in a solution system containing a conductive agent and a catalyst, assisted by a binder and a dispersant, so that the conductive agent has excellent dispersibility and plays a physical isolation role for the synthesized lithium oxalate. This can not only make the combination of the catalyst and the conductive agent with the lithium oxalate more closely, but also facilitate the obtaining of modified lithium oxalate with reduced particle size, thereby improving the problems of large particle size, high decomposition voltage, and low capacity of existing lithium oxalate as a positive electrode additive. To achieve this purpose, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a preparation method of a modified positive electrode additive, which comprises:

[0010] A composite base solution is prepared, which comprises a base base solution, a catalyst, a conductive agent, a binder, and a dispersant. The base base solution comprises lithium oxalate and first oxalic acid. A reactant is added to the composite base solution, which comprises a lithium source and second oxalic acid. A precipitation reaction and a hydrothermal composite reaction are sequentially carried out to obtain a modified positive electrode additive.

[0011] The present application provides a suitable pH environment by using a basic solution to provide a basis for controlling the particle size of lithium oxalate. If the pH of the basic solution is too high, it will easily lead to the particle size of the obtained lithium oxalate being too large. The addition of the catalyst in the basic solution can weaken the Li-O bond in lithium oxalate, making it easier for lithium ions to be released, thereby reducing the working voltage of lithium oxalate. The conductive agent can improve the overall conductivity of the material. The catalyst and the conductive agent are the main modified components for modification. In addition, the conductive agent itself can play a dispersing role, thereby promoting the formation of small particle size lithium oxalate. The binder can make the synthesized lithium oxalate more closely combined with the conductive agent and the catalyst, and the dispersant can make the conductive agent and the catalyst better dispersed in the solution, thereby improving the dispersibility of the conductive agent and reducing agglomeration, so that the conductive agent can play a physical isolation role in the formation process of lithium oxalate, thereby facilitating the synthesis of small particle size lithium oxalate, and also facilitating the uniform distribution of the modified components when they are wrapped inside and outside the lithium oxalate. Therefore, the present application uses a precipitation method and a hydrothermal method to synthesize lithium oxalate in a composite solution containing a conductive agent and a catalyst, and uses a binder and a dispersant for assistance, thereby obtaining modified lithium oxalate with a smaller particle size and a more closely combined catalyst and conductive agent. The small particle size and the uniform distribution of the modified components can make the modified lithium oxalate as a positive electrode additive have a lower working voltage, better capacity, and better electrical performance.

[0012] The following is a preferred technical solution of the present application, but is not a limitation of the technical solutions provided by the present application. The following technical solution can better achieve and realize the technical purposes and beneficial effects of the present application.

[0013] As a preferred technical solution of the present application, the mass percentage concentration of lithium oxalate in the basic solution is 0.5% to 8%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, or 8%, etc.

[0014] Preferably, the mass percentage concentration of the first oxalic acid in the basic solution is 0.5% to 10%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%, etc.

[0015] Preferably, the solvent of the basic solution comprises water.

[0016] The preparation method of the present application can be synthesized in an aqueous system, which is conducive to large-scale production.

[0017] As a preferred technical solution of the present application, the catalyst comprises at least one of nickel hydroxide, nickel oxide, nickel acetate, cobaltous hydroxide, cobalt oxyhydroxide, tricobalt tetraoxide, manganese hydroxide or manganese oxide, for example, typical but non-limiting combinations include a combination of nickel hydroxide and nickel oxide, a combination of nickel acetate and manganese oxide, a combination of cobaltous hydroxide and nickel oxide, or a combination of manganese hydroxide and cobalt oxyhydroxide, etc.

[0018] Preferably, the particle size of the primary particles of the catalyst is 100-300 nm, for example, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm or 300 nm, etc.

[0019] Preferably, the amount is controlled according to 0.5%-15% of the mass of the metal elements in the catalyst with respect to the mass of the lithium oxalate theoretically generated by the reaction, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc.

[0020] As a preferred technical solution of the present application, the conductive agent comprises at least one of carbon black, graphite powder, ketjen black, carbon nanotubes, graphene or polyaniline, for example, limited but non-limiting examples include a combination of carbon black and graphite powder, a combination of carbon black and ketjen black, a combination of carbon black and carbon nanotubes, a combination of graphene and polyaniline, a combination of graphene and carbon nanotubes, a combination of carbon black and polyaniline, or a combination of polyaniline and graphite powder, etc.

[0021] Preferably, the specific surface area of the conductive agent is 1000-1400 cm 2 / g, for example, 1000 cm 2 / g, 1050 cm 2 / g, 1100 cm 2 / g, 1150 cm 2 / g, 1200 cm 2 / g, 1250 cm 2 / g, 1300 cm 2 / g, 1350 cm 2 / g or 1400 cm 2 / g, etc.

[0022] Preferably, the amount is controlled according to 1%-30% of the mass of the conductive agent with respect to the mass of the lithium oxalate theoretically generated by the reaction, for example, 1%, 2%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28% or 30%, etc.

[0023] As a preferred technical solution of the present application, the binder comprises at least one of polyvinyl alcohol, polyvinyl ether, polyacrylic acid or carboxymethyl cellulose, for example, typical but non-limiting combination examples include a combination of polyvinyl alcohol and polyvinyl ether, a combination of polyvinyl alcohol and polyacrylic acid, a combination of polyvinyl alcohol and carboxymethyl cellulose, or a combination of carboxymethyl cellulose and polyvinyl ether, etc.

[0024] Preferably, the amount is controlled according to 0.5% to 5% of the mass of the base solution, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc.

[0025] As a preferred technical solution of the present application, the dispersant comprises at least one of sodium polyacrylate, sodium dimethyl sulfonate or polyacrylamide. For example, typical but non-limiting combination examples include a combination of sodium polyacrylate and sodium dimethyl sulfonate, a combination of sodium polyacrylate and polyacrylamide, or a combination of polyacrylamide and sodium dimethyl sulfonate, etc.

[0026] Preferably, the amount is controlled according to 0.1% to 2% of the mass of the base solution, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, etc.

[0027] As a preferred technical solution of the present application, the viscosity of the composite base solution is controlled to be ≥800 Pa·S, for example, 800 Pa·S, 900 Pa·S, 1000 Pa·S, 1100 Pa·S, 1200 Pa·S, 1300 Pa·S, 1400 Pa·S, 1500 Pa·S, 1600 Pa·S, 1700 Pa·S or 1800 Pa·S, etc., and further preferably 1000 to 1300 Pa·S.

[0028] The viscosity of the composite base solution in the present application is adjusted by the amount of conductive agent, binder and dispersant, and the amount of solvent. The viscosity affects the catalyst and the bonding force between the conductive agent and lithium oxalate, so it needs to be reasonably controlled. If the viscosity is too low, the catalyst, the conductive agent and lithium oxalate will have weak binding force, which will affect the performance of the electric performance. If the viscosity is too high, it is not conducive to the subsequent dehydration and drying process. However, compared with the prior art, the viscosity of the liquid phase system (composite base solution) of the present application is relatively high, and it is not suitable to obtain the modified positive electrode material by spray drying.

[0029] Preferably, the rate of adding the reactants is controlled to be 30-300 g / min, such as 30 g / min, 50 g / min, 80 g / min, 100 g / min, 130 g / min, 150 g / min, 180 g / min, 200 g / min, 220 g / min, 240 g / min, 260 g / min, 280 g / min, or 300 g / min, etc.

[0030] In the preparation method, the rate of adding the reactants has an effect on the particle size of the modified lithium oxalate. If the rate is too fast, the lithium oxalate precipitates rapidly and in large amounts, and the problem of not timely dispersion and formation of large particles of lithium oxalate in local areas is prone to occur. If the rate is too slow, the production capacity is low, and the production cost is high.

[0031] Preferably, the amount of the lithium source and the second oxalic acid is controlled according to the molar ratio of lithium element to oxalate of (2-2.2):1, such as 2:1, 2.02:1, 2.04:1, 2.06:1, 2.08:1, 2.1:1, 2.12:1, 2.14:1, 2.16:1, 2.18:1, or 2.2:1, etc.

[0032] Preferably, the lithium source comprises at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium peroxide, or lithium nitrate.

[0033] Preferably, the pH of the precipitation reaction is 6-8, such as 6, 6.3, 6.5, 6.8, 7.3, 7.5, 7.7, or 8, etc.

[0034] In the present application, the pH of the precipitation reaction is controlled by controlling the amount and the rate of adding the reactants (lithium source and second oxalic acid) to maintain the whole precipitation reaction process at a pH of 6-8.

[0035] Preferably, the hydrothermal compounding reaction is carried out under pressure and stirring.

[0036] Preferably, the pressure maintaining pressure is 10-200 kPa, such as 10 kPa, 30 kPa, 50 kPa, 80 kPa, 100 kPa, 120 kPa, 140 kPa, 160 kPa, 180 kPa, or 200 kPa, etc.

[0037] In the preparation method, maintaining a certain pressure is beneficial to the compounding of the generated lithium oxalate with the catalyst and the conductive agent, improves the compounding tightness, and has an effect on the particle size of the obtained lithium oxalate. The pressure maintaining pressure is a relative pressure based on atmospheric pressure, i.e., 10-200 kPa higher than the atmospheric pressure.

[0038] Preferably, the stirring speed is 200-400 rpm, such as 200 rpm, 220 rpm, 240 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm or 400 rpm, etc.

[0039] Preferably, the temperature of the hydrothermal complex reaction is 50-100℃, such as 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃, etc., and the time is 1-10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc.

[0040] As a preferred technical solution of the present application, after the hydrothermal complex reaction is completed, the natural cooling is performed to <40℃, and then the solid-liquid separation, crushing and drying are sequentially performed to obtain the modified positive electrode additive.

[0041] Preferably, the method of solid-liquid separation includes pressure filtration.

[0042] Preferably, the moisture content of the filter cake obtained by pressure filtration is ≤50wt%, such as 50wt%, 45wt%, 40wt%, 35wt%, 30wt%, 25wt%, 20wt%, 15wt%, 10wt%, 5wt% or 1wt%, etc.

[0043] Preferably, the filtrate obtained after the solid-liquid separation is reused as a basic base liquid.

[0044] Preferably, the crushing adopts a crushing and drying all-in-one machine, and the rotation speed of the crushing is 1000-3000 rpm, such as 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm, 2600 rpm, 2800 rpm or 3000 rpm, etc.

[0045] Preferably, the temperature of the drying is 100-140℃, such as 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃ or 140℃, etc.

[0046] Preferably, after the drying, the moisture content of the obtained modified positive electrode additive is ≤0.5wt%, such as 0.5wt%, 0.4wt%, 0.3wt%, 0.2wt%, 0.1wt% or 0wt% (water-free), etc.

[0047] In the preparation method of the present application, the particle size of the lithium oxalate secondary particles is further controlled through crushing and drying. Preferably, the specific process of the drying is a flash drying process, which has larger production capacity, lower energy consumption and easier control of the secondary particles compared with the spray drying.

[0048] Preferably, the Dv50 particle size of the secondary particles of the modified cathode additive is ≤10 μm, such as 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, and the like, further preferably 2-5 μm, and the Dv90 particle size is ≤30 μm, such as 30 μm, 28 μm, 26 μm, 24 μm, 22 μm, 20 μm, 18 μm, 16 μm, 14 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm or 3 μm, and the like, further preferably ≤15 μm.

[0049] In a second aspect, the present application provides a modified cathode additive prepared according to the method of the first aspect.

[0050] In a third aspect, the present application provides a lithium ion battery containing the modified cathode additive of the second aspect.

[0051] It should be noted that, due to the limitation of the length of the article and to avoid redundancy, the present application does not list all the specific values in the above numerical range, and it should be understood that the values not listed in the above numerical range are also applicable.

[0052] Compared with the prior art, the present application has at least the following beneficial effects:

[0053] The preparation method of the present application uses the precipitation method and the hydrothermal method to synthesize lithium oxalate under the dispersion effect of the conductive agent, with the aid of the binder and the dispersant, and then obtains modified lithium oxalate with smaller particle size and more closely combined with the catalyst and the conductive agent. When the obtained modified lithium oxalate is used as a cathode additive, it has the advantages of small particle size, low decomposition voltage and high capacity. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 SEM test diagram of the modified cathode additive obtained in Example 1;

[0055] Figure 2 XRD test diagram of the modified cathode additive obtained in Example 1. DETAILED DESCRIPTION

[0056] The technical solutions of the present application will be further described below through specific embodiments.

[0057] Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0058] Embodiment 1

[0059] The present embodiment provides a preparation method of a modified positive electrode additive, the preparation method comprising:

[0060] (1) Take oxalic acid powder as a first oxalic acid, lithium oxalate and pure water are added into a reaction kettle, and fully stirred until completely dissolved to obtain a basic bottom solution; the mass of the pure water in the basic bottom solution is controlled to be 20 kg, the mass percentage concentration of lithium oxalate is 5%, and the mass percentage concentration of the first oxalic acid is 8%;

[0061] (2) A catalyst, a conductive agent, a dispersing agent and a binder are added into the basic bottom solution, and fully stirred until uniformly dispersed and the system viscosity reaches 1200 Pa·S to obtain a composite bottom solution; wherein the catalyst is nickel hydroxide with a particle size of 100-300 nm, the conductive agent is carbon black with a BET specific surface area of 1200 cm 2 / g, the dispersing agent is sodium polyacrylate, and the binder is polyvinyl alcohol; the amount of the catalyst is controlled according to that the mass of nickel element in the catalyst accounts for 3% of the mass of the target generated lithium oxalate, the amount of the conductive agent is controlled according to that the mass of the conductive agent accounts for 20% of the mass of the target generated lithium oxalate, the amount of the dispersing agent is controlled according to that the mass of the dispersing agent accounts for 0.2% of the mass of the basic bottom solution, and the amount of the binder is controlled according to that the mass of the binder accounts for 0.5% of the mass of the basic bottom solution;

[0062] (3) A reactant is added into the composite bottom solution at an adding rate of 100 g / min, the reactant is lithium hydroxide and oxalic acid powder as a second oxalic acid with a molar ratio of 2:1, a precipitation reaction is carried out, the pH is controlled to be in the range of 6-8 during the reaction, after the addition of the reactant is completed, the reaction kettle is heated and pressure is maintained, and fully stirred, the stirring speed is set to 300 rpm, the solution temperature is heated to 80℃, the pressure in the kettle is 150 kPa, after the hydrothermal composite reaction is carried out for 3 h, cooling is carried out, the precipitate is formed, when the natural cooling temperature is lower than 40℃, pressure filtration dehydration is carried out for solid-liquid separation, the filter cake with a water content of ≤50wt% and the filtrate are obtained, the filter cake is crushed at a speed of 2000 rpm, and then dried at 120℃ to obtain the modified positive electrode additive.

[0063] Embodiment 2

[0064] The present embodiment provides a preparation method of a modified positive electrode additive, in step (1), the mass percentage concentration of lithium oxalate in the basic bottom solution is adjusted from 5% to 0.2%, and other conditions are the same as those in Embodiment 1.

[0065] Example 3

[0066] The present example provides a preparation method of a modified positive electrode additive, wherein in step (1), the mass percentage concentration of lithium oxalate in the base solution is adjusted from 5% to 8%, and other conditions are the same as those in Example 1.

[0067] Example 4

[0068] The present example provides a preparation method of a modified positive electrode additive, wherein in step (1), the mass percentage concentration of the first oxalate in the base solution is adjusted from 8% to 0.2%, and other conditions are the same as those in Example 1.

[0069] Example 5

[0070] The present example provides a preparation method of a modified positive electrode additive, wherein in step (1), the mass percentage concentration of the first oxalate in the base solution is adjusted from 8% to 10%, and other conditions are the same as those in Example 1.

[0071] Example 6

[0072] The present example provides a preparation method of a modified positive electrode additive, wherein in step (1), the mass percentage concentration of the first oxalate in the base solution is adjusted from 8% to 11%, and other conditions are the same as those in Example 1.

[0073] Example 7

[0074] The present example provides a preparation method of a modified positive electrode additive, wherein in step (2), the mass of the dispersant is adjusted from 0.2% to 0.05% of the mass of the base solution, and other conditions are the same as those in Example 1.

[0075] Example 8

[0076] The present example provides a preparation method of a modified positive electrode additive, wherein in step (2), the mass of the dispersant is adjusted from 0.2% to 2% of the mass of the base solution, and other conditions are the same as those in Example 1.

[0077] Example 9

[0078] The present example provides a preparation method of a modified positive electrode additive, wherein in step (2), the mass of the binder is adjusted from 0.5% to 0.2% of the mass of the base solution, and other conditions are the same as those in Example 1.

[0079] Example 10

[0080] The present example provides a preparation method of a modified positive electrode additive, wherein the mass of the binder is adjusted from 0.5% to 2.5% of the mass of the base stock solution in step (2), and other conditions are the same as those in Example 1.

[0081] Example 11

[0082] The present example provides a preparation method of a modified positive electrode additive, wherein the mass of the binder is adjusted from 0.5% to 5% of the mass of the base stock solution in step (2), and other conditions are the same as those in Example 1.

[0083] Example 12

[0084] The present example provides a preparation method of a modified positive electrode additive, wherein the mass of the binder is adjusted from 0.5% to 5.3% of the mass of the base stock solution in step (2), and other conditions are the same as those in Example 1.

[0085] Example 13

[0086] The present example provides a preparation method of a modified positive electrode additive, wherein the amount of pure water is adjusted in step (1), and the amounts of the catalyst, the conductive agent, the dispersing agent, and the binder are kept unchanged in step (2), so that the viscosity of the composite stock solution is adjusted from 1200 Pa·S to 700 Pa·S, and other conditions are the same as those in Example 1.

[0087] Example 14

[0088] The present example provides a preparation method of a modified positive electrode additive, wherein the amount of pure water is adjusted in step (1), and the amounts of the catalyst, the conductive agent, the dispersing agent, and the binder are kept unchanged in step (2), so that the viscosity of the composite stock solution is adjusted from 1200 Pa·S to 800 Pa·S, and other conditions are the same as those in Example 1.

[0089] Example 15

[0090] The present example provides a preparation method of a modified positive electrode additive, wherein the amount of pure water is adjusted in step (1), and the amounts of the catalyst, the conductive agent, the dispersing agent, and the binder are kept unchanged in step (2), so that the viscosity of the composite stock solution is adjusted from 1200 Pa·S to 1300 Pa·S, and other conditions are the same as those in Example 1.

[0091] Example 16

[0092] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method adjusts the amount of pure water in step (1), keeps the amounts of the catalyst, the conductive agent, the dispersant and the binder unchanged in step (2), and adjusts the viscosity of the composite base solution from 1200 Pa·S to 1600 Pa·S, and other conditions are completely same with those in the embodiment 1.

[0093] Embodiment 17

[0094] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method adjusts the adding rate of the reactant from 100 g / min to 20 g / min in step (3), and other conditions are completely same with those in the embodiment 1.

[0095] Embodiment 18

[0096] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method adjusts the adding rate of the reactant from 100 g / min to 30 g / min in step (3), and other conditions are completely same with those in the embodiment 1.

[0097] Embodiment 19

[0098] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method adjusts the adding rate of the reactant from 100 g / min to 300 g / min in step (3), and other conditions are completely same with those in the embodiment 1.

[0099] Embodiment 20

[0100] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method adjusts the adding rate of the reactant from 100 g / min to 330 g / min in step (3), and other conditions are completely same with those in the embodiment 1.

[0101] Embodiment 21

[0102] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method uses the filtrate obtained in step (3) of the embodiment 1 as the base base solution in step (1), and other conditions are completely same with those in the embodiment 1.

[0103] Embodiment 22

[0104] The embodiment provides a preparation method of a modified positive electrode additive, wherein the preparation method replaces the dispersant sodium polyacrylate with sodium dimethyl sulfonate and replaces the binder polyvinyl alcohol with polyacrylic acid in step (2), and other conditions are completely same with those in the embodiment 1.

[0105] Embodiment 23

[0106] The present example provides a preparation method of a modified positive electrode additive, wherein the dispersant sodium polyacrylate is replaced by polyacrylamide and the binder polyvinyl alcohol is replaced by carboxymethyl cellulose in step (2), and other conditions are the same as in Example 1.

[0107] Comparative Example 1

[0108] The present comparative example provides a preparation method of a modified positive electrode additive, wherein no binder is used in step (2), and other conditions are the same as in Example 1.

[0109] Comparative Example 2

[0110] The present comparative example provides a preparation method of a modified positive electrode additive, wherein no dispersant is used in step (2), and other conditions are the same as in Example 1.

[0111] Comparative Example 3

[0112] The present comparative example provides a preparation method of a modified positive electrode additive, wherein no base solution is used in step (2), and pure water is used instead of the base solution in step (2), and other conditions are the same as in Example 1.

[0113] Control Group 1

[0114] The present control group uses commercially purchased lithium oxalate (Ganfeng Lithium Industry), which has a Dv50 of 65 μm, as a modified positive electrode additive.

[0115] Control Group 2

[0116] The present control group uses lithium oxalate prepared by evaporation crystallization according to the prior art, which has a Dv50 of 40 μm as a modified positive electrode additive.

[0117] Characterization and testing:

[0118] I. Morphology and phase testing: Figure 1 The SEM test graph of the modified positive electrode additive obtained in Example 1 shows that the lithium oxalate particles and the conductive agent and catalyst are well dispersed, the particles are small, and there is no obvious large particle agglomeration; Figure 2 The XRD test graph of the modified positive electrode additive obtained in Example 1 shows that the synthesized substance is a relatively pure lithium oxalate phase, and has good crystallinity.

[0119] II. Particle size testing: The modified positive electrode additives obtained in the examples, comparative examples and control groups were subjected to particle size testing to obtain Dv50 and Dv90 particle sizes, and the results are recorded in Table 1.

[0120] III. The mass content of catalytic metal elements in the catalyst was tested at different positions in the modified positive electrode additive obtained in the examples, comparative examples and control group, and the mass content range was obtained, and the results are shown in Table 1.

[0121] IV. The modified positive electrode additives obtained in the examples, comparative examples and control group were respectively made into button cells, and the electrical performance comparison characterization was carried out, wherein the button cell manufacturing specifically comprises:

[0122] ①Material preparation, 4g of modified positive electrode additive and conductive agent were weighed and mixed with binder, wherein the mass ratio of modified positive electrode additive, conductive agent and binder was 8:1:1, the binder used was PVDF, and the conductive agent was conductive carbon;

[0123] ②Coating, using a scraper to coat on an aluminum foil;

[0124] ③Drying, the coated pole piece was dried in a vacuum drying oven, the drying temperature was 120°C, and the drying time was 2h;

[0125] ④Pressing, the dried pole piece was pressed using a roller machine, the rolling pressure was 5T, and a punching machine was used to cut the pole piece with a diameter of 1.2cm;

[0126] ⑤Assembly, the positive pole piece, negative pole piece, separator, electrolyte and other battery parts were assembled into a button cell. The specific capacity was tested under the conditions of charging voltage 4.35V and charging rate 0.1C, and the test results are shown in Table 1:

[0127] Table 1

[0128]

[0129]

[0130] From Table 1, it can be seen that:

[0131] The particle size of the synthesized lithium oxalate has a relatively obvious influence on the capacity and decomposition voltage, and the catalyst, dispersant and binder all have a certain influence on the performance.

[0132] From the comparison of Example 1 and Examples 2-6, it can be seen that when the amount of lithium oxalate is reduced or the amount of first oxalic acid is increased, the pH value of the basic bottom liquid and the composite bottom liquid decreases, and the product with smaller particle size, relatively higher capacity and lower decomposition voltage can be synthesized.

[0133] From the comparison of Example 1 and Examples 7-8, it can be seen that when the amount of dispersant is insufficient, the particle size of the synthesized lithium oxalate is larger, resulting in a decrease in capacity and a relatively higher decomposition voltage; however, an excessive amount of dispersant cannot further improve the particle size, capacity and decomposition voltage, and the amount of dispersant should be appropriately matched according to the amount of reactants.

[0134] As can be seen from the comparison of Example 1 with Examples 9-12, the decrease of the binder content leads to the increase of the particle size of the synthesized lithium oxalate, the decrease of the capacity and the relatively high decomposition voltage; but when the content of the binder is excessive, the decrease of the particle size has no obvious improvement, and even the capacity and the decomposition voltage are deteriorated to some extent, therefore, the content of the binder should be matched according to the amount of the reactants.

[0135] As can be seen from the comparison of Example 1 with Examples 13-16, within the suitable range, the lower the viscosity, the larger the particle size of the synthesized lithium oxalate, the lower the capacity and the higher the voltage; when the viscosity is too high, the improvement of the viscosity on the particle size is relatively not obvious.

[0136] As can be seen from the comparison of Example 1 with Examples 17-20, the adding rate of the reactants has an important influence on the control of the particle size, and the particle size can be controlled by controlling the suitable adding rate.

[0137] As can be seen from the comparison of Example 1 with Example 21, the filtrate obtained by the preparation method of the present application can be recycled as the basic base liquid, and compared with the control groups 1 and 2 and the comparative examples 1-3, the modified lithium oxalate with improved particle size, capacity and compaction can still be obtained.

[0138] As can be seen from the comparison of Example 1 with Examples 22 and 23, the present application is not limited to the combination of the dispersant and the binder in Example 1, and the selection of the materials can be reasonably adjusted within the range specified in the present application.

[0139] As can be seen from the comparison of Example 1 with the comparative examples 1-3, when no binder is added during the synthesis, the capacity of the synthesized lithium oxalate is low and the voltage is high, mainly because the combination of the synthesized lithium oxalate with the catalyst and the conductive agent is poor without the action of the binder; when no dispersant is added during the synthesis, the particle size of the synthesized lithium oxalate is large, especially the Dv99 increases obviously, leading to the decrease of the capacity and the increase of the decomposition voltage; and when no base substrate liquid is used during the synthesis, the synthesized lithium oxalate particles are prone to have large particle size and low capacity.

[0140] The above examples are used to illustrate the detailed process equipment and process flow of the present application, but the present application is not limited to the above detailed process equipment and process flow, that is, the present application does not mean that it must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

[0141] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0142] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0143] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for preparing a modified cathode additive, characterized by, The preparation method comprises: The preparation method comprises:

2. The production method according to claim 1, characterized by, The preparation method comprises:

3. The preparation method according to claim 1, characterized in that, The mass percentage concentration of the lithium oxalate in the base solution is 0.5%-8%.

4. The preparation method according to claim 1, characterized in that, The mass percentage concentration of the first oxalic acid in the base solution is 0.5%-10%.

5. The preparation method according to claim 1, characterized in that, The catalyst comprises at least one of nickel hydroxide, nickel oxide, nickel acetate, cobaltous hydroxide, cobalt hydroxide, tricobalt tetroxide, manganese hydroxide or manganese oxide.

6. The method of claim 1, wherein, The particle size of the primary particles of the catalyst is 100-300 nm.

7. The preparation method according to claim 1, characterized in that, The amount of the catalyst is controlled according to 0.5%-15% of the mass of the metal elements in the catalyst relative to the mass of the lithium oxalate theoretically generated in the reaction.

8. The method of claim 1, wherein, The specific surface area of the electrically conductive agent is 1000 to 1400 cm 2 / g.

9. The method of claim 1, wherein, The conductive agent comprises at least one of carbon black, graphite powder, ketjen black, carbon nanotube, graphene or polyaniline.

10. The method of claim 1, wherein, The amount of the conductive agent is controlled according to 1%-30% of the mass of the conductive agent relative to the mass of the lithium oxalate theoretically generated in the reaction.

11. The method of claim 1, wherein, The binder comprises at least one of polyvinyl alcohol, polyvinyl ether, polyacrylic acid or carboxymethyl cellulose.

12. The method of claim 1, wherein, The amount of the binder is controlled according to 0.5%-5% of the mass of the binder relative to the mass of the base solution.

13. The method of claim 1, wherein, The dispersant comprises at least one of sodium polyacrylate or polyacrylamide.

14. The method of claim 1, wherein, The amount of the dispersant is controlled according to 0.1%-2% of the mass of the dispersant relative to the mass of the base solution.

15. The method of claim 1, wherein, The viscosity of the composite solution is controlled to be greater than or equal to 800 Pa·S.

16. The method of claim 1, wherein, The addition rate of the reactant is controlled to be 30-300 g / min.

17. The method of claim 1, wherein, The amount of the lithium source and the second oxalic acid is controlled according to a molar ratio of lithium elements to oxalate radicals of (2-2.2):

1.

18. The method of claim 1, wherein, The pH of the precipitation reaction is 6-8.

19. The method of claim 18, wherein, The hydrothermal compounding reaction is performed under pressure and stirring.

20. The method of claim 18, wherein, The pressure is 10-200 kPa.

21. The method of claim 1, wherein, The stirring speed is 200-400 rpm.

22. The method of claim 1, wherein, The temperature of the hydrothermal compounding reaction is 50-100 ℃, and the time is 1-10 h.

23. The method of claim 22, wherein, After the hydrothermal compounding reaction, the modified positive electrode additive is obtained by sequentially performing solid-liquid separation, crushing and drying after natural cooling to less than 40 ℃.

24. The method of claim 23, wherein, The method for the solid-liquid separation comprises pressure filtration.

25. The preparation method according to claim 22, characterized in that, The moisture content of the filter cake obtained by the pressure filtration is less than or equal to 50 wt%.

26. The method of claim 22, wherein, The crushing speed is 1000-3000 rpm.

27. The preparation method according to claim 22, characterized in that, The drying temperature is 100-140 ℃.

28. The method of claim 1, wherein, After the drying, the moisture content of the modified positive electrode additive is less than or equal to 0.5 wt%.

29. The method of claim 28, wherein, The Dv50 particle size of the secondary particles of the modified positive electrode additive is less than or equal to 10 μm, and the Dv90 particle size is less than or equal to 30 μm.

30. A modified cathode additive, characterized in that, The Dv50 particle size of the secondary particles of the modified positive electrode additive is 2-5 μm, and the Dv90 particle size is less than or equal to 15 μm.

31. A lithium-ion battery, characterized in that, The preparation method according to any one of claims 1-29 is used. The lithium ion battery contains the modified positive electrode additive according to claim 30.

Images