A ternary precursor material, a ternary positive electrode material, a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery materials, and particularly relates to a ternary precursor material, a ternary positive electrode material and a preparation method and application thereof. The ternary precursor material comprises a substrate and a coating layer on the surface of the substrate, the substrate is an active metal hydroxide, and the coating layer is an active metal oxalate. The preparation method of the ternary precursor material comprises adding an oxalic acid solution into a dispersion liquid of the active metal hydroxide, and performing an in-situ coating reaction to obtain the ternary precursor material. According to the application, a layer of active metal oxalate is coated on the surface of the active metal hydroxide in-situ, and after being mixed with a lithium source, the oxalate on the surface of the precursor can be decomposed to generate pores in the sintering process, the pores can increase the porosity between primary particles, inhibit the agglomeration of the primary particles, and facilitate the effective dispersion of the primary particles in the crushing process, and further improve the electrochemical performance of the single-crystal ternary positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a ternary precursor material, a ternary positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, lithium ion batteries have become the most promising energy equipment in the world's science and technology and industrial fields due to their high energy density, long cycle life and good safety performance. Among the many positive electrode materials for preparing lithium ion batteries, ternary positive electrode materials have attracted widespread attention due to their high reversible capacity, good safety and relatively low cost.

[0003] Generally, single-crystal ternary positive electrode materials are primary particles without grain boundaries, which have high crystallinity and strong mechanical strength. Compared with traditional polycrystalline ternary positive electrode materials, single-crystal ternary positive electrode materials have more excellent surface chemical stability and high-temperature storage performance, which is beneficial to improve the mechanical stability of the positive electrode material during the charge and discharge cycle process and effectively suppress the capacity decay of the lithium ion battery. Dispersion is one of the important technical indicators of single-crystal ternary positive electrode materials, and highly dispersed single-crystal particles can significantly improve the tap density and compaction density of the ternary positive electrode material and reduce the micro-cracks caused by anisotropy during the cycle process.

[0004] The precursor required for preparing single-crystal ternary materials is usually small-particle-size spherical particles, and the dispersion of the precursor particles has a direct impact on the dispersion of the single-crystal ternary material. Meanwhile, excellent dispersion of the single-crystal ternary material has an important influence on the electrochemical performance of the lithium ion battery prepared therefrom. The single-crystal ternary precursor particles prepared by the commonly used co-precipitation reaction mostly have the problems of small particle size, large specific surface area, easy agglomeration and difficult rapid dispersion, which further affects the dispersion of the positive electrode material and makes the electrochemical performance of the lithium ion battery prepared therefrom worse.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] In view of the problems of easy agglomeration and poor dispersion of the single-crystal ternary positive electrode material prepared by the prior art, the present application aims to provide a ternary precursor material, a ternary positive electrode material and a preparation method and application thereof, which are intended to improve the dispersion and compaction density of the ternary positive electrode material and further improve the electrochemical performance of the lithium ion battery.

[0007] To achieve the object of the present application, the following technical solutions are adopted:

[0008] In a first aspect, the present application provides a ternary precursor material, the ternary precursor material comprising a substrate and a coating layer on the surface of the substrate, the substrate being an active metal hydroxide, and the coating layer being an active metal oxalate; the active metal comprising nickel, cobalt, manganese and N; the N being selected from one or more doping elements of magnesium, copper, aluminum, titanium, tantalum or niobium.

[0009] In an optional embodiment, the ternary precursor material particle has a median particle size of 5-7 μm.

[0010] In an optional embodiment, the ternary precursor material particle has a carbon element content of 0.2-0.5%.

[0011] In a second aspect, the present application provides a preparation method of a ternary precursor material, the preparation method comprising the following steps:

[0012] adding an oxalic acid solution to a dispersion of the active metal hydroxide, and stirring to obtain the ternary precursor material.

[0013] In an optional embodiment, the preparation method of the active metal hydroxide comprises: dissolving nickel salt, cobalt salt, manganese salt and N salt in water to obtain a metal salt solution, and then adding the metal salt solution, a complexing agent and a precipitant into a reaction kettle with pure water as a base solution to perform a co-precipitation reaction.

[0014] In an optional embodiment, the nickel salt, the cobalt salt and the manganese salt comprise at least one of a sulfate, a chloride and a nitrate.

[0015] In an optional embodiment, the N salt comprises at least one of soluble salts of magnesium, copper, aluminum, titanium, tantalum and niobium.

[0016] In an optional embodiment, the molar concentration of nickel ions, cobalt ions, manganese ions and N ions in the metal salt solution is 1.5-2.5 mol / L.

[0017] In an optional embodiment, in the metal salt solution, the molar ratio of the nickel salt, the cobalt salt, the manganese salt and the N salt is (35-90):(6-35):(3-35):(1-5) based on 100 mol of the total molar number of the metal salt.

[0018] In an optional embodiment, the complexing agent is ammonia water with a molar concentration of 4-6 mol / L.

[0019] In an optional embodiment, the precipitant is a sodium hydroxide solution or a potassium hydroxide solution with a molar concentration of 9-11 mol / L.

[0020] In an optional embodiment, the co-precipitation reaction has a pH value of 9-12, a reaction temperature of 40-70 DEG C, a reaction time of 48-72 h, and a stirring rate of 300-600 r / min.

[0021] In an optional embodiment, the oxalic acid solution has a mass concentration of 100-500 g / L, and the mass of oxalic acid in the oxalic acid solution is 10%-80% of the mass of the active metal hydroxide.

[0022] In an optional embodiment, the stirring reaction has a temperature of room temperature and a reaction time of 4-8 h.

[0023] In a third aspect, the application provides a ternary positive electrode material, which is prepared by mixing the ternary precursor material of the first aspect with a lithium source and sintering.

[0024] In an optional embodiment, the lithium source comprises at least one of lithium hydroxide, lithium acetate and lithium oxalate.

[0025] In an optional embodiment, the ratio of the total moles of the active metal elements to the moles of lithium elements is 1: (1-1.05).

[0026] In an optional embodiment, the sintering comprises two-stage sintering, the first-stage sintering is performed at a temperature increasing rate of 3-5 DEG C / min to 650 DEG C-750 DEG C, and the sintering is performed in an oxygen atmosphere for 3-5 h, the second-stage sintering is performed at a temperature increasing rate of 7-9 DEG C / min to 900 DEG C-1000 DEG C, and the sintering is performed in an oxygen atmosphere for 9-11 h, and after cooling to room temperature, the sintered product is crushed, ground and sieved through a 400-mesh sieve.

[0027] In a fourth aspect, the application further provides a use of the ternary positive electrode material in preparing a lithium ion battery.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] (1) The ternary precursor material prepared by the application has a substrate and a coating layer, the substrate is an active metal hydroxide, and the coating layer is an active metal oxalate, and during subsequent sintering with a lithium source, the active metal oxalate can be decomposed to produce gas to form a pore structure, the pore structure can increase the porosity between primary particles, thereby improving the dispersity of the single-crystal ternary positive electrode material. In addition, the active metal hydroxide is used to coat the substrate, thereby ensuring a high tap density and a high compaction density of the single-crystal ternary positive electrode material. In summary, the application combines the respective advantages of the active metal oxalate and the active metal hydroxide, and thus obtains a single-crystal ternary positive electrode material which is highly dispersed and has a high compaction density.

[0030] (2) The application adds oxalic acid solution into the dispersion liquid of active metal hydroxide, uses the acid-base neutralization reaction of oxalic acid and active metal hydroxide to deposit a layer of active metal oxalate on the surface of active metal hydroxide in situ, the preparation method is simple in process, mild in reaction condition, low in production cost and easy for industrialized production.

[0031] Other aspects can become apparent from a review of the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings are included to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification, and are used together with the embodiments of the present application to explain the technical solutions of the present application, and do not constitute a limitation on the technical solutions of the present application.

[0033] Figure 1 SEM images of the active metal hydroxide (a) and the active metal ternary precursor material (b-c) prepared in Example 4 in the present application;

[0034] Figure 2 SEM images of the active metal ternary precursor material prepared in Comparative Example 1 (a), Comparative Example 2 (b) and Comparative Example 3 (c) in the present application, and the particle section SEM image of the active metal ternary precursor material prepared in Comparative Example 4 (d);

[0035] Figure 3 SEM images of the active metal ternary single-crystal cathode material prepared in Example 4 (a), Comparative Example 1 (b) and Comparative Example 2 (c) in the present application;

[0036] Figure 4 XRD images of the active metal ternary precursor material prepared in Example 4 and Comparative Examples 1-4 in the present application. DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be further described below through specific embodiments. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure, and should not be regarded as a specific limitation on the present application.

[0038] It should be noted that, in the embodiments, the specific conditions not mentioned are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, and are all conventional products that can be obtained by market purchase.

[0039] The present application provides a ternary precursor material, which comprises a substrate and a coating layer on the surface of the substrate, the substrate is active metal hydroxide, and the coating layer is active metal oxalate; the active metal comprises nickel, cobalt, manganese and N; the N is selected from one or more doping elements of magnesium, copper, aluminum, titanium, tantalum or niobium.

[0040] In some embodiments, the ternary precursor material satisfies one or more of the following characteristics I-II:

[0041] Characteristic I: the ternary precursor material particles have a median particle size of 5-7 μm;

[0042] Characteristic II: the ternary precursor material particles have a carbon element content of 0.2%-0.5%

[0043] The carbon element content of the ternary precursor material particles can indirectly reflect the content of oxalate on the surface of the active metal hydroxide. The more active metal oxalate coating, the more carbon element content of the precursor particles. Further, the more pores produced during the subsequent sintering process of the ternary precursor material, the better the dispersibility of the obtained single-crystal cathode material particles.

[0044] The present application provides a preparation method of a ternary precursor material, which comprises the following steps:

[0045] S1, first dissolve nickel salt, cobalt salt, manganese salt and N salt in water to obtain a metal salt solution, then add the metal salt solution, a complexing agent and a precipitating agent to a reaction kettle with pure water as the base solution to perform a co-precipitation reaction, and obtain active metal hydroxide;

[0046] S2, add oxalic acid solution to the dispersion liquid of the active metal hydroxide, and perform a stirring reaction to obtain the ternary precursor material.

[0047] The present application slowly adds the oxalic acid solution to the dispersion liquid of the active metal hydroxide. The protons provided by the oxalic acid in the solution can react with the hydroxyl groups on the surface of the active metal hydroxide, and dissolve part of the metal ions. At the same time, the oxalate ions react with these metal ions to obtain active metal oxalate precipitates, which are deposited and coated on the surface of the active metal hydroxide in situ. The reaction formula is as follows:

[0048]

[0049] wherein a+b+c+d=1, 0

[0050] Specifically, the present application will be described one by one for each of the above steps.

[0051] S1, add the prepared active metal salt solution, complexing agent and precipitating agent solution to the reaction kettle with pure water as the base solution through a metering pump, control the reaction temperature, reaction time, stirring rate and pH value of the reaction liquid, perform a co-precipitation reaction, and then filter, wash and dry the obtained product to obtain the active metal hydroxide.

[0052] In some embodiments, the sum of the molar concentrations of nickel ions, cobalt ions, manganese ions and N ions in the metal salt solution is 1.5-2.5 mol / L, for example, it can be 1.5 mol / L, 2.0 mol / L or 2.5 mol / L, but is not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0053] In some embodiments, in the metal salt solution, the molar ratio of the nickel salt, the cobalt salt, the manganese salt and the N salt is (35-90):(6-35):(3-35):(1-5) based on 100 mol of the total moles of metal salts, for example, it can be 35:35:28:2, 40:20:35:5 or 90:6:3:1, but is not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0054] In some embodiments, the complexing agent is ammonia water with a molar concentration of 4-6 mol / L, for example, it can be 4 mol / L, 5 mol / L or 6 mol / L, and the precipitating agent is sodium hydroxide solution or potassium hydroxide solution with a molar concentration of 9-11 mol / L, for example, it can be 9 mol / L, 10 mol / L or 11 mol / L, but is not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0055] In some embodiments, the pH value of the co-precipitation reaction is 9-12, for example, it can be 9, 10, 11 or 12, the reaction temperature is 40-70°C, for example, it can be 40°C, 50°C, 60°C or 70°C, the reaction time is 48-72 h, for example, it can be 48 h, 60 h or 72 h, and the stirring rate is 300-600 r / min, for example, it can be 300 r / min, 400 r / min, 500 r / min or 600 r / min, but is not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0056] S2, oxalic acid solution is slowly added to the dispersion of active metal hydroxide by peristaltic pump, and stirring reaction is carried out at room temperature to obtain active metal ternary precursor material.

[0057] In some embodiments, the mass concentration of the oxalic acid solution is 100-500 g / L, for example, it can be 100 g / L, 300 g / L or 500 g / L, and the mass of oxalic acid in the oxalic acid solution is 10%-80% of the mass of the active metal hydroxide, for example, it can be 10%, 20%, 30%, 50% or 80%, but is not limited to the listed values, and other values not listed in the above numerical range are also applicable.

[0058] In some embodiments, the stirring reaction time is 4-8 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0059] The amount of oxalic acid in the present application will affect the tap density of the precursor. If the amount of oxalic acid is too much, the coating amount of oxalate on the surface of the active metal ternary precursor is more, and the carbon content of the precursor particles is also more, which will reduce the tap density of the precursor, and further reduce the tap density of the single crystal positive electrode material. If the amount of oxalic acid is too little, the coating amount of oxalate on the surface of the active metal ternary precursor is less, and the subsequent sintering process with lithium source produces less pores, and the dispersibility of the single crystal positive electrode material is poor.

[0060] The present application provides a kind of ternary positive electrode material, the ternary positive electrode material is made of ternary precursor material and lithium source is mixed, is made in two-stage sintering in muffle furnace in oxygen atmosphere.

[0061] In some embodiments, the ratio of the total number of moles of active metal elements to the number of moles of lithium elements is 1: (1-1.05), for example, it can be 1:1, 1:1.02, 1:1.03, 1:1.04 or 1:1.05, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0062] In some embodiments, the heating rate of the first stage sintering is 3-5 ℃ / min, for example, it can be 3 ℃ / min, 4 ℃ / min or 5 ℃ / min, the sintering temperature is 650-750 ℃, for example, it can be 650 ℃, 700 ℃ or 750 ℃, the holding time is 3-5 h, for example, it can be 3 h, 4 h or 5 h, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0063] In some embodiments, the heating rate of the second stage sintering is 7-9 ℃ / min, for example, it can be 7 ℃ / min, 8 ℃ / min or 9 ℃ / min, the sintering temperature is 900-1000 ℃, for example, it can be 900 ℃, 950 ℃ or 1000 ℃, the holding time is 9-11 h, for example, it can be 9 h, 10 h or 11 h, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0064] The present application adopts two-stage sintering process in the process of preparing active metal ternary positive electrode material: one low-temperature pre-sintering and one high-temperature sintering, the low-temperature pre-sintering temperature is about 700 DEG C, the pre-sintering heating rate is slow, the holding time is short, the low-temperature pre-sintering is helpful to strengthen the binding force between the grains, and at the same time, the appropriate pore size and gap are reserved; after a certain time of low-temperature pre-sintering, the second stage of high-temperature sintering is directly carried out, the temperature is generally about 950 DEG C, the heating rate is relatively large, the holding time is relatively long, the high-temperature sintering further improves the crystallinity and density of the material, and the defects and impurities are repaired and removed, so that the high-quality single-crystal positive electrode material is obtained. The temperature of two-stage sintering will affect the grain size, if the sintering temperature is too low, the grain size is small, if the sintering temperature is too high, the grain size is too large.

[0065] Example 1

[0066] The present embodiment provides a preparation method of ternary precursor material and positive electrode material, the method comprises the following steps:

[0067] S1, according to the molar ratio of Ni, Co, Mn and Cu elements of 90:6:3:1, dissolve nickel sulfate, cobalt sulfate, manganese sulfate and copper sulfate in pure water to obtain a mixed metal salt solution with a total metal ion molar concentration of 2mol / L, and prepare 10mol / L sodium hydroxide solution and 5mol / L ammonia water; then the mixed metal salt solution is pumped into the stirring reaction kettle with pure water as the bottom liquid at a flow rate of 5L / h, the sodium hydroxide solution is pumped into the stirring reaction kettle at a flow rate of 1L / h, and the ammonia water is pumped into the stirring reaction kettle at a flow rate of 1L / h, the reaction temperature is controlled at 65 DEG C, the reaction time is 60h, the stirring speed is 500r / min, and the pH value of the reaction solution is 11.0, the co-precipitation reaction is carried out, the product is collected after filtration, and the active metal hydroxide is obtained after washing and drying.

[0068] S2, prepare 500g / L oxalic acid solution 12L, take 20kg active metal hydroxide and disperse in pure water, add oxalic acid solution to the reaction kettle by peristaltic pump at a speed of 5L / h, maintain the stirring speed at 400r / min, and stir at room temperature for 8h, then centrifuge, wash, dry, sieve and remove the magnetism to obtain the active metal ternary precursor material. (The mass of oxalic acid is 30% of the mass of active metal hydroxide)

[0069] S3, the active metal ternary precursor material is mixed with lithium hydroxide in a ratio of 1:1.03 of the total moles of active metal elements to the moles of lithium element, and then two-stage sintering is performed in a muffle furnace under an oxygen atmosphere, the first-stage sintering has a heating rate of 4 ℃ / min, a sintering temperature of 700 ℃, and a holding time of 4 h, after the first-stage sintering is completed, the second-stage sintering is directly performed, the second-stage sintering has a heating rate of 8 ℃ / min, a sintering temperature of 950 ℃, and a holding time of 10 h. After being cooled to room temperature, the sintered product is ground and broken and passed through a 400-mesh sieve, thereby obtaining the active metal ternary single-crystal cathode material.

[0070] Example 2

[0071] The present embodiment provides a preparation method of a ternary precursor material and a cathode material, the method comprising the following steps:

[0072] S1, nickel sulfate, cobalt sulfate, manganese sulfate, and copper sulfate are dissolved in pure water to obtain a mixed metal salt solution with a total metal ion molar concentration of 1.5 mol / L, a 9 mol / L sodium hydroxide solution and a 4 mol / L ammonia water are prepared, then the mixed metal salt solution is fed into a stirring reaction kettle with pure water as the base liquid at a flow rate of 5 L / h, the sodium hydroxide solution is fed into the stirring reaction kettle at a flow rate of 1 L / h, and the ammonia water is fed into the stirring reaction kettle at a flow rate of 1 L / h, the reaction temperature is controlled at 40 ℃, the reaction time is 48 h, the stirring rate is 300 r / min, and the pH value of the reaction solution is 9.0, a co-precipitation reaction is performed, the product is collected after filtration, and the active metal hydroxide is obtained after washing and drying.

[0073] S2, 33.4 L of a 300 g / L oxalic acid solution is prepared, 20 kg of the active metal hydroxide is dispersed in pure water, the oxalic acid solution is added to the reaction kettle at a speed of 5 L / h through a peristaltic pump, the stirring rate is maintained at 400 r / min, and the stirring reaction is performed at room temperature for 6 h, then the product is centrifuged, washed, dried, sieved, and demagnetized to obtain the active metal ternary precursor material. (The mass of the oxalic acid is 50% of the mass of the active metal hydroxide)

[0074] S3, the active metal ternary precursor material is mixed with lithium hydroxide in a ratio of 1:1 of the total moles of active metal elements to the moles of lithium element, and then two-stage sintering is performed in a muffle furnace under an oxygen atmosphere, the first-stage sintering has a heating rate of 3 ℃ / min, a sintering temperature of 650 ℃, and a holding time of 3 h, after the first-stage sintering is completed, the second-stage sintering is directly performed, the second-stage sintering has a heating rate of 7 ℃ / min, a sintering temperature of 900 ℃, and a holding time of 9 h. After being cooled to room temperature, the sintered product is ground and broken and passed through a 400-mesh sieve, thereby obtaining the active metal ternary single-crystal cathode material.

[0075] Example 3

[0076] The present embodiment provides a preparation method of a ternary precursor material and a positive electrode material, which comprises the following steps:

[0077] S1, dissolve nickel sulfate, cobalt sulfate, manganese sulfate and copper sulfate in pure water to obtain a mixed metal salt solution with a total metal ion molar concentration of 2.5 mol / L, according to the molar ratio of Ni, Co, Mn and Cu elements of 40:20:35:5, and prepare 11 mol / L sodium hydroxide solution and 6 mol / L ammonia water; then simultaneously feed the mixed metal salt solution at a flow rate of 5 L / h, the sodium hydroxide solution at a flow rate of 1 L / h and the ammonia water at a flow rate of 1 L / h into a stirred reaction kettle with pure water as the base liquid through a metering pump, control the reaction temperature to be 70℃, the reaction time to be 72h, the stirring rate to be 600r / min and the pH value of the reaction solution to be 12.0, carry out co-precipitation reaction, collect the product after filtration, and obtain active metal hydroxide after washing and drying.

[0078] S2, prepare 20L of 100g / L oxalic acid solution, take 20kg of active metal hydroxide precursor and disperse it in pure water, add the oxalic acid solution into the reaction kettle through a peristaltic pump at a speed of 5L / h, maintain the stirring rate at 400r / min, and stir at room temperature for 4h, then centrifuge, wash, dry, sieve and demagnetize the product to obtain the active metal ternary precursor material. (The mass of oxalic acid is 10% of the mass of active metal hydroxide)

[0079] S3, mix the active metal ternary precursor material and lithium hydroxide uniformly according to the ratio of the total molar number of active metal elements to the molar number of lithium elements of 1:1.05, then carry out two-stage sintering in a muffle furnace under oxygen atmosphere, the first-stage sintering has a heating rate of 5℃ / min, a sintering temperature of 750℃ and a holding time of 5h, the second-stage sintering is directly carried out after the first-stage sintering is completed, the second-stage sintering has a heating rate of 9℃ / min, a sintering temperature of 1000℃ and a holding time of 11h. After cooling to room temperature, grind and crush the sintered product and sieve it through a 400 mesh sieve to obtain the active metal ternary single-crystal positive electrode material.

[0080] Example 4

[0081] Compared with Example 1, the amount of oxalic acid solution in step S2 is changed to 20L, the mass of oxalic acid is 50% of the mass of active metal hydroxide, and the remaining steps are unchanged.

[0082] Example 5

[0083] Compared with Example 1, the amount of oxalic acid solution in step S2 is changed to 32 L, and the mass of oxalic acid is 80% of the mass of active metal hydroxide, and the remaining steps are unchanged.

[0084] Example 6

[0085] Compared with Example 1, the amount of oxalic acid solution in step S2 is changed to 4 L, and the mass of oxalic acid is 10% of the mass of active metal hydroxide, and the remaining steps are unchanged.

[0086] Example 7

[0087] Compared with Example 2, the mass concentration of the oxalic acid solution in step S2 is changed to 200 g / L, and the amount is 50 L, and the remaining steps are unchanged.

[0088] Example 8

[0089] Compared with Example 2, the mass concentration of the oxalic acid solution in step S2 is changed to 400 g / L, and the amount is 25 L, and the remaining steps are unchanged.

[0090] Example 9

[0091] Compared with Example 1, the one-stage sintering temperature in step S3 is changed to 650°C, and the two-stage sintering temperature is 900°C, and the remaining steps are unchanged.

[0092] Example 10

[0093] Compared with Example 1, the one-stage sintering temperature in step S3 is changed to 750°C, and the two-stage sintering temperature is 1000°C, and the remaining steps are unchanged.

[0094] Comparative Example 1

[0095] A ternary precursor material and a ternary positive electrode material with active metal hydroxide surface uncoated active metal oxalate are prepared in this comparative example, and the preparation method comprises the following steps:

[0096] Compared with Example 4, step S2 is not performed, and the remaining steps are unchanged.

[0097] Comparative Example 2

[0098] The ternary precursor material prepared in this comparative example adopts a non-in-situ coating method, and the active metal hydroxide is used as a seed crystal and mixed with a mixed solution of active metal-containing metal liquid and oxalic acid, and the preparation method comprises the following steps:

[0099] S1, the same as step S1 of Example 4.

[0100] S2, 20 L of 500 g / L oxalic acid solution was prepared, 20 kg of active metal hydroxide was dispersed in pure water, and the active metal-containing metal solution was added at a flow rate of 5 L / h and the oxalic acid solution was added at a flow rate of 5 L / h simultaneously through a peristaltic pump into the reaction kettle, the stirring rate was maintained at 400 r / min, and the reaction was stirred at room temperature for 8 h, then the product was centrifuged, washed, dried, sieved, and demagnetized to obtain the active metal ternary precursor material. (The mass of oxalic acid is 50% of the mass of active metal hydroxide)

[0101] S3, the same as step S3 of example 4.

[0102] Comparative example 3

[0103] In this comparative example, oxalic acid and sodium hydroxide were used as co-precipitants to prepare active metal oxalate / active metal hydroxide composite precursor material and positive electrode material, and the preparation method comprises the following steps:

[0104] S1, nickel sulfate, cobalt sulfate, manganese sulfate and copper sulfate were dissolved in pure water to obtain a mixed metal salt solution with a total metal ion molar concentration of 2 mol / L, and 10 mol / L of sodium hydroxide solution, 5 mol / L of oxalic acid solution and 5 mol / L of ammonia water were prepared; then the mixed metal salt solution was fed into a stirring reaction kettle with pure water as the bottom liquid through a metering pump at a flow rate of 5 L / h, the sodium hydroxide solution was fed at a flow rate of 1 L / h, and the ammonia water was fed at a flow rate of 1 L / h, the reaction temperature was controlled at 65°C, the reaction time was 60 h, the stirring rate was 500 r / min, and the pH value of the reaction solution was 11.0, the co-precipitation reaction was carried out, and the product was collected after filtration, washed and dried to obtain the active metal oxalate / active metal hydroxide composite precursor material.

[0105] S2, the active metal oxalate / active metal hydroxide composite precursor material was mixed with lithium hydroxide at a ratio of 1:1.05 of the total active metal element molar number to the lithium element molar number, and the remaining steps were the same as step S3 of example 4.

[0106] Comparative example 4

[0107] In this comparative example, a ternary precursor material and a ternary positive electrode material were prepared using active metal oxalate / active metal hydroxide composite as the matrix and active metal hydroxide as the coating layer, and the preparation method comprises the following steps:

[0108] S1, dissolve nickel sulfate, cobalt sulfate, manganese sulfate and copper sulfate in pure water according to the molar ratio of Ni, Co, Mn, Cu elements of 90:6:3:1 to obtain a mixed metal salt solution with a total molar concentration of metal ions of 2 mol / L, and prepare 10 mol / L sodium hydroxide solution, 5 mol / L oxalic acid solution and 5 mol / L ammonia water; then, the mixed metal salt solution is fed into a stirred reaction kettle with pure water as the base liquid at a flow rate of 5 L / h, the sodium hydroxide solution is fed at a flow rate of 1 L / h, and the ammonia water is fed at a flow rate of 1 L / h through a metering pump, the reaction temperature is controlled at 65°C, the reaction time is 60 h, the stirring rate is 500 r / min, and the pH value of the reaction solution is 11.0, and the co-precipitation reaction is carried out, when the particle size reaches 2.0 um, stop feeding the oxalic acid solution, continue the reaction with sodium hydroxide as the only precipitant, and filter, wash and dry the obtained product to obtain an active metal ternary precursor material with active metal oxalate / active metal hydroxide composite as the matrix and active metal hydroxide as the coating layer.

[0109] S2, same as step S3 of example 4.

[0110] The active metal ternary positive electrode material prepared in examples 1-10 and comparative examples 1-4 is assembled into a button cell, and its electrochemical performance is evaluated, which includes the following steps:

[0111] (1) Preparation of button cell

[0112] The active metal ternary single crystal positive electrode material is uniformly mixed according to the mass ratio of positive electrode: conductive agent: binder = 80:10:10, and the slurry is uniformly coated on the level sheet with a coating surface density of 20 mg / cm 2 The electrode sheet is placed in an oven and dried at 80°C for 8 h, then rolled and taken out, and the electrode sheet, separator and negative electrode are assembled in a glove box and injected with electrolyte to form a button cell.

[0113] (2) Particle size test

[0114] The particle size of the active metal ternary precursor material is tested using a GSL-101BI type laser particle size analyzer.

[0115] (3) Carbon content test

[0116] The active metal ternary precursor powder is placed in a sulfur carbon tester to test its carbon content.

[0117] (4) Compaction density test

[0118] The active metal single crystal ternary positive electrode material powder is placed in an FTYS-50KN type compaction density instrument to test its compaction density at 200 MPa.

[0119] (5) Electrochemical performance testing

[0120] The charge-discharge cycle characteristics of the above-mentioned button batteries were tested at 25℃ using a Blue Electric test cabinet. The charge-discharge test was carried out at a charge-discharge rate of 0.1C within a voltage range of 2.8V-4.3V. The results are shown in Table 1.

[0121] Table 1

[0122]

[0123] From the attached diagram, we can conclude that:

[0124] Figure 1 a, Figure 2 a is an SEM image of the active metal hydroxide before coating. Figure 1 b is a SEM image of the active metal ternary cathode precursor obtained after coating with active metal oxalate. Figure 1 As shown in b, the morphology of the active metal hydroxide changes significantly after being coated with active metal oxalate, with the active metal oxalate distributed in particulate form on the surface of the active metal hydroxide.

[0125] Comparative Example 2 ( Figure 2 b) and Example 4 ( Figure 1 From the SEM images of (bc), it can be seen that in Comparative Example 2, the active metal ternary precursor prepared by the non-in-situ coating method has many small particles around it. This is because the precipitated active metal oxalate forms nuclei individually and is not coated on the surface of the active metal hydroxide. In Example 4, the active metal ternary precursor prepared by the in-situ coating method has no obvious small particles around it, and the active metal oxalate is uniformly coated on the surface of the active metal hydroxide, avoiding the individual nucleation of oxalate. From Comparative Example 3 ( Figure 2 c) and Example 4 ( Figure 1 From the SEM image of Comparative Example 3 (c), it can be seen that the particle surface of the active metal oxalate / active metal hydroxide composite precursor is blurred, and the primary particles are not clear. This is because the generated active metal oxalate is easily redissolved under alkaline conditions. From Comparative Example 4 (...) Figure 2 The SEM image of the particle profile in d) shows that the core-shell structure of the active metal ternary precursor has hollow interiors. This is because the oxalate / hydroxide crystal nuclei of the active metal will dissolve in an alkaline environment, resulting in hollow interiors.

[0126] According to Comparative Example 1 ( Figure 3 b) Comparative Example 2 Figure 3 c) and Example 4 ( Figure 3 a) The SEM image of the prepared active metal single crystal ternary cathode material shows that the single crystal ternary cathode particles prepared by sintering and crushing the active metal ternary precursor in Example 4 have basically no agglomeration phenomenon, and therefore have better dispersibility.

[0127] According to Figure 4 The XRD pattern of the active metal ternary precursor material according to The XRD curves of Comparative Example 2 and Example 4 show that the nickel oxalate phase exists in both active metal ternary precursors. Compared with the XRD curve of Example 4, the proportion of the oxalate phase in the active metal oxalate / active metal hydroxide composite precursor prepared in Comparative Example 3 is obviously lower, because the generated oxalate is easy to dissolve again in an alkaline environment; and the oxalate phase in the core-shell structure active metal ternary precursor prepared in Comparative Example 4 is hardly visible, because the oxalate in the active metal oxalate / active metal hydroxide crystal nucleus is easy to dissolve in an alkaline environment.

[0128] As can be seen from Table 1:

[0129] As can be seen from Examples 1-10, when the oxalate coating amount is 10-50%, the single-crystal positive electrode material prepared by the method has a high compaction density, and the discharge capacity and cycle performance are obviously improved compared with the sample without coating; but when the coating amount is too high (for example, 80%), the compaction density of the single-crystal positive electrode material is obviously reduced.

[0130] As can be seen from the comparison between Example 1 and Examples 4-6, the coating amount of the active metal oxalate on the surface of the active metal hydroxide will affect the performance of the active metal ternary precursor and the positive electrode material prepared by the method, if the coating amount is too low (for example, 10% coating amount), the discharge capacity is low and the cycle performance is poor; if the coating amount is too high (for example, 80% coating amount), the compaction density is obviously reduced, the discharge capacity is low, and the cycle performance is poor.

[0131] As can be seen from the comparison between Example 2 and Examples 7-8, the mass concentration of the oxalic acid solution will not affect the compaction density, discharge capacity and cycle performance of the active metal ternary precursor and the positive electrode material prepared by the method.

[0132] As can be seen from the comparison between Example 1 and Examples 9-10, the temperature of the two-stage sintering will affect the performance of the active metal ternary precursor and the positive electrode material prepared by the method, if the sintering temperature is too high, the grain size is large, the compaction density is increased, but the discharge capacity is low and the cycle performance is increased; if the sintering temperature is too low, the grain size is small, the compaction density is reduced, the discharge capacity is high, but the cycle performance is poor.

[0133] It is concluded from Examples 1, 4, 6 and Comparative Example 1 that the active metal ternary precursor material and the positive electrode material thereof are obtained after the active metal hydroxide is coated in situ with the active metal oxalate, the discharge capacity and the cycle performance of the lithium ion battery prepared therefrom are obviously improved, and as the coating amount of the active metal oxalate increases, the discharge capacity is higher and the cycle performance is better, because the coated active metal oxalate decomposes to produce gas to form a pore structure in the sintering process, which can obviously improve the dispersibility of the ternary single-crystal positive electrode material particles, and make the particle size distribution of the single-crystal particles more uniform.

[0134] It is concluded from Examples 4 and Comparative Example 2 that under the same coating amount of the active metal oxalate, the discharge capacity and the cycle performance of the lithium ion battery can be obviously improved by coating the active metal hydroxide with the oxalate in situ, because the uniformity of the active metal oxalate obtained by in-situ coating is better, and the phenomenon of separate nucleation of the oxalate is prone to occur by non-in-situ coating, and the active metal oxalate that is separately nucleated will quickly decompose to form fine powder in the sintering process, resulting in a large difference in the particle size of the ternary single-crystal positive electrode material particles, which is not conducive to the capacity and the cycle performance.

[0135] It is concluded from Examples 4 and Comparative Example 3 that the discharge capacity and the cycle performance of the lithium ion battery of Comparative Example 3 are lower than those of Example 4 due to the small amount of oxalate in the active metal oxalate / active metal hydroxide composite precursor, because the oxalate is unstable in an alkaline environment and is prone to decomposition, resulting in a low content of oxalate in the active metal oxalate / active metal hydroxide composite precursor, less gas production in the sintering process, and thus less pore structure, which is not conducive to the dispersion of the ternary single-crystal positive electrode material particles, the widening of the particle size distribution of the single-crystal particles, and the improvement of the discharge capacity and the cycle performance of the lithium ion battery.

[0136] It is concluded from Examples 4 and Comparative Example 4 that the discharge capacity and the cycle performance of the lithium ion battery of Comparative Example 4 are lower than those of Example 4 because the active metal ternary precursor material of Comparative Example 4 is a core-shell structure active metal ternary precursor material with the active metal oxalate / active metal hydroxide as the core and the active metal hydroxide as the shell, and the content of the oxalate in the core layer active metal oxalate / active metal hydroxide is extremely small, because the oxalate in the active metal oxalate / active metal hydroxide crystal nucleus is unstable in an alkaline environment and is prone to dissolution, resulting in a hollow structure in the particles, and due to the extremely small amount of oxalate, less pore structure is produced in the sintering process, and the hollow structure in the particles further deteriorates the discharge capacity and the cycle performance of the ternary single-crystal positive electrode material.

[0137] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A method of preparing a ternary precursor material, characterized by, The method comprises the following steps: adding an oxalic acid solution into a dispersion of active metal hydroxide, and stirring to obtain a ternary precursor material; the ternary precursor material comprises a substrate and a coating layer on the surface of the substrate, wherein the substrate is active metal hydroxide, and the coating layer is active metal oxalate; the active metal comprises nickel, cobalt, manganese and N; the N is selected from one or more doping elements of magnesium, copper, aluminum, titanium, tantalum or niobium.

2. The method of claim 1, wherein the method further comprises: The ternary precursor material satisfies one or more of the following characteristics I and II: Characteristic I: the median particle size of the ternary precursor material particles is 5 μm to 7 μm; Characteristic II: the carbon content of the ternary precursor material particles is 0.2% to 0.5%.

3. The method of producing a ternary precursor material according to claim 1 or 2, characterized in that, The preparation method of the active metal hydroxide comprises the following steps: dissolving nickel salt, cobalt salt, manganese salt and N salt in water to obtain a metal salt solution, and then adding the metal salt solution, a complexing agent and a precipitant into a reaction kettle with pure water as the base solution to perform a co-precipitation reaction.

4. The method of producing a ternary precursor material according to claim 3, wherein The nickel salt, the cobalt salt and the manganese salt comprise at least one of sulfate, chloride and nitrate; Or / and, the N salt comprises at least one of soluble salts of magnesium, copper, aluminum, titanium, tantalum and niobium; Or / and, the sum of the molar concentrations of nickel ions, cobalt ions, manganese ions and N ions in the metal salt solution is 1.5 to 2.5 mol / L; Or / and, in the metal salt solution, the molar ratio of the nickel salt, the cobalt salt, the manganese salt and the N salt is (35 to 90):(6 to 35):(3 to 35):(1 to 5) based on 100 mol of the total molar number of metal salts; Or / and, the complexing agent is ammonia water with a molar concentration of 4 to 6 mol / L; Or / and, the precipitant is a sodium hydroxide solution or a potassium hydroxide solution with a molar concentration of 9 to 11 mol / L; Or / and, the co-precipitation reaction has a pH value of 9 to 12, a reaction temperature of 40 to 70 ℃, a reaction time of 48 to 72 h and a stirring rate of 300 to 600 r / min.

5. The method of producing a ternary precursor material according to claim 1 or 2, wherein The mass concentration of the oxalic acid solution is 100 to 500 g / L; Or / and, the mass of oxalic acid in the oxalic acid solution is 10% to 80% of the mass of the active metal hydroxide; Or / and, the stirring reaction is performed at room temperature for 4 to 8 h.

6. A ternary positive electrode material, characterized by, The ternary positive electrode material is prepared by mixing the ternary precursor material prepared by the preparation method of the ternary precursor material in claim 1 or 2 with a lithium source, and then sintering.

7. The ternary cathode material of claim 6, wherein, The lithium source comprises at least one of lithium hydroxide, lithium acetate and lithium oxalate; Or / and, the ratio of the total molar number of active metal elements to the molar number of lithium elements is 1:(1 to 1.05). 8.The ternary cathode material of claim 6, wherein, The sintering comprises two-stage sintering, the first-stage sintering is performed at a temperature increasing rate of 3 to 5 ℃ / min to 650 ℃ to 750 ℃, and then the temperature is kept constant in an oxygen atmosphere for 3 to 5 h, the second-stage sintering is performed at a temperature increasing rate of 7 to 9 ℃ / min to 900 ℃ to 1000 ℃, and then the temperature is kept constant in an oxygen atmosphere for 9 to 11 h.

9. Application of the ternary positive electrode material in any one of claims 6 to 8 in the preparation of a lithium ion battery.

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