A composite positive electrode lithium supplementing material, a preparation method thereof, a positive electrode sheet, and a secondary battery

Abstract

The application provides a composite positive electrode lithium supplementing material, which has a general chemical formula of Li x M y N (1‑y) O z @Li a C b O c The composite positive electrode lithium supplementing material comprises a core and a shell coated on the surface of the core; the core is a doped inorganic ternary compound, which has a general chemical formula of Li x M y N (1‑y) O z The shell is an organic lithium supplementing agent, which has a general chemical formula of Li a C b O c The composite positive electrode lithium supplementing material has good stability and high capacity; the coating of the shell can effectively prevent the material from contacting with humid air; the core material is doped, which is beneficial to improve the conductivity of the positive electrode sheet; meanwhile, the composite positive electrode lithium supplementing material does not have gelation under a conventional environment, the prepared composite positive electrode lithium supplementing material can effectively supplement the active lithium consumed by the negative electrode SEI film, and improve the energy density and high-temperature cycle performance of the full battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a composite positive electrode lithium supplementing material, a preparation method thereof, a positive electrode sheet and a secondary battery. BACKGROUND

[0002] In the traditional consumer 3C electronic field, the most convenient way to pursue high volume energy density is to improve the overall voltage system of lithium cobalt oxide, thereby obtaining high active lithium content, which puts higher requirements on the performance of lithium cobalt oxide positive electrode material such as energy density, so that the lithium cobalt oxide positive electrode material is also developing towards high voltage. However, high voltage under the lithium cobalt oxide system means that high delithiation state is equivalent to cobalt oxide being more unstable, thereby causing capacity loss and energy density decline. In order to improve the energy density of lithium ion batteries, many lithium compensation methods have been reported. According to different compensation methods and positions, they can be roughly divided into the following three categories: (1) electrochemical method of pre-intercalating lithium; (2) lithium compensation from the negative electrode; (3) lithium compensation from the positive electrode.

[0003] At present, the way of positive electrode lithium supplement is to use positive electrode lithium supplement additives in the positive electrode material system to improve the energy density and cycle life of the battery system. The mechanism of the positive electrode lithium supplement additive is to release a large amount of lithium ions during the first charge process, which reaches the negative electrode through the electrolyte, compensates for the loss of Li ions caused by the formation of SEI film during battery formation, and the excess lithium ions are also stored in the negative electrode material and slowly released with the cycle to improve the cycle performance of the battery. There are several representative positive electrode lithium active substances on the market: binary compounds Li2O, Li2O2, Li3N, ternary compounds Li2NiO2, Li5FeO4, Li6CoO4, and numerous organic compounds Li2C2O4, Li2C3O5, Li2C4O4. Even though there are so many types of positive electrode lithium materials, but they are limited by their own characteristics and cannot be completely used in high-voltage lithium cobalt oxide systems, such as poor processing performance, high cost, etc.

[0004] At present, the main material manufacturers use Li2NiO2 and Li5FeO4 as the main material. Due to the strong water absorption and carbon dioxide absorption characteristics of these two main materials, the process environment is extremely strict, and the absorption of more moisture and carbon dioxide in the process workshop will cause more residual lithium in the electrode sheet. These residual lithium often causes severe side reactions in the internal system of the full battery.

[0005] Therefore, it is necessary to provide a technical solution to solve the above problems. SUMMARY

[0006] One of the purposes of the present application is to provide a composite positive electrode lithium supplement material to improve the instability of the positive electrode lithium supplement active material caused by water absorption and carbon dioxide absorption in the process workshop, and to improve the energy density and cycle performance of the full battery.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A composite positive electrode lithium supplement material, the chemical general formula of which is Li x M y N (1-y) O z @Li a C b O c , the composite positive electrode lithium supplement material comprises a core and a shell coated on the surface of the core;

[0009] The core is a doped inorganic ternary compound, the chemical general formula of which is Li x M y N (1-y) O z , wherein M and N are respectively selected from at least one of Ti, W, Ni, Cu, Zn and Mg, 2≤x≤6, 0.1≤y≤0.5, 2≤z≤6;

[0010] The shell is an organic lithium supplement agent, the chemical general formula of which is Li a C b O c , wherein 2≤a≤4, 2≤b≤4, 2≤c≤4. Preferably, the organic lithium supplement agent comprises at least one of Li2C2O4, Li2C3O5 and Li2C4O4.

[0011] Preferably, the mass ratio of the shell to the total mass of the composite positive electrode lithium supplement material is 0.05% to 10%, and the mass ratio of the core to the shell is 1:0.1 to 0.3.

[0012] Preferably, the thickness D of the shell, the material median particle size R1 of the shell, the material median particle size R2 of the core and the material pH value E of the core satisfy the relationship: D-5≤10E*R1 / R2≤D+5.

[0013] Preferably, the thickness D of the shell is 45 to 55 nm, the material median particle size R1 of the shell is 1 to 5 μm, the material median particle size R2 of the core is 9 to 13 μm, and the material pH value E of the core is 10 to 12.

[0014] The second purpose of the present application is to provide a preparation method of a composite positive electrode lithium supplement material, the preparation environment of which is in an environment with a humidity of less than 2%, comprising the following steps:

[0015] S1, mix the lithium source and the metal source; sieve the mixed material, and then pre-sinter in an air environment; after natural cooling, crush and sieve, and then secondary sinter; after natural cooling, crush and sieve, and then airflow crushing, to obtain a core material;

[0016] S2, heat and stir the lithium source and the organic acid in an ethanol solvent, and then dry to obtain a shell material;

[0017] S3, ball mill mix the core material and the shell material, and then vacuum dry, to obtain a composite positive electrode lithium supplement material.

[0018] Preferably, in step S1, the molar ratio of the lithium source to the metal source is 2-6.8.

[0019] Preferably, in steps S1 and S2, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium oxide, and lithium nitrate, and the organic acid in step S2 is one of oxalic acid, ethanedioic acid, and squaric acid.

[0020] Preferably, in step S1, the pre-sintering temperature is 300-400 DEG C, the heating rate is 5 DEG C / min, and the holding time is 5-7 h; the secondary sintering is calcination in an inert gas, the heating rate is 2 DEG C / min, the sintering temperature is 700-800 DEG C, and the holding time is 13-16 h.

[0021] The third object of the present application is to provide a positive electrode sheet comprising the composite positive electrode lithium supplement material described above.

[0022] The fourth object of the present application is to provide a secondary battery comprising the positive electrode sheet described above.

[0023] Compared with the prior art, the composite positive electrode lithium supplement material provided by the present application has the following advantages: the composite positive electrode lithium supplement material comprises a core material and a shell material coated on the surface of the core material; the coating of the shell material improves the air stability of the composite positive electrode lithium supplement material, effectively prevents the material from contacting with humid air, solves the problem that the current positive electrode lithium supplement material easily fails in a workshop environment, the metal element doped in the core material reduces the initial efficiency of lithium-rich lithium nickelate, provides more active lithium sources, the residual product of lithium-rich lithium nickelate is a metal oxide, which is beneficial to improving the conductivity of the positive electrode sheet; at the same time, the composite positive electrode lithium supplement material does not have the gelation condition in the slurry viscosity experiment in a conventional environment, and the composite positive electrode lithium supplement material has high capacity, which can effectively supplement the active lithium consumed by the negative electrode SEI film, and improve the energy density and high-temperature cycle performance of the full battery. DETAILED DESCRIPTION

[0024] In order to make the technical solutions and advantages of the present application clearer, the following will further describe the present application and its beneficial effects in detail with specific embodiments, but the embodiments of the present application are not limited thereto.

[0025] The terms "first", "second", "third", etc. are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0026] In a first aspect of the present application, a composite positive electrode lithium supplementing material is provided, comprising a core and a shell coated on the surface of the core, and the chemical formula is Li x M y N (1-y) O z @Li a C b O c , the core is a doped inorganic ternary compound, and the chemical formula is Li x M y N (1-y) O z , wherein M and N are selected from at least one of Cu, Ti, Zn, Mg and W, 2≤x≤6, 0.1≤y≤0.5, 2≤z≤6; the shell is an organic lithium supplementing agent, and the chemical formula is Li a C b O c , wherein 2≤a≤4, 2≤b≤4, 2≤c≤4. Among them, the doped inorganic ternary compound Li x M y N (1-y) O z provides a large amount of irreversible active lithium, and the doping element does not affect the active lithium content of the core, and the metal oxide left after delithiation can reduce the decomposition potential of the organic lithium supplementing agent Li x C y O z of the shell, which can be completely decomposed at this potential, provides a small amount of active lithium, which is beneficial to improve the conductivity of the positive electrode sheet; therefore, the positive electrode lithium supplementing material needs to be charged in multiple steps to completely release the active lithium.

[0027] In the shell organic positive electrode lithium supplementing agent Li a C b O cThe coating prolongs the invalidation time of the positive electrode lithium supplement agent, and can solve the problem of side reactions of the positive electrode sheet in the process workshop under the conventional process environment. The composite lithium supplement material has high capacity and strong low gel probability, and even after being mixed with the conventional positive electrode main material and rolled into a positive electrode sheet, it has high hydrophobic and carbon dioxide repellent properties. At the same time, when assembled into a full battery with the conventional negative electrode main material, it can significantly improve the energy density and cycle performance.

[0028] In some embodiments, the organic lithium supplement agent includes at least one of Li2C2O4, Li2C3O5, and Li2C4O4. The organic lithium supplement agent can be in close contact with the metal oxide generated when the inner core material is completely separated. When charging continues, the decomposition potential of the organic lithium supplement agent decreases, and the decomposition can be completed within the normal lithium ion secondary battery operating voltage range.

[0029] In some embodiments, the ratio of the shell mass to the total mass of the composite positive electrode lithium supplement material is 0.05% to 10%, and can be 0.05%, 0.1%, 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%, 10%, and can include but not limited to the above-mentioned values; the mass ratio of the inner core material to the shell material is 1:0.1 to 0.3, and can be 1:0.1, 1:0.2, 1:0.3, and can include but not limited to the above-mentioned values, and is preferably 1:0.1.

[0030] In some embodiments, the thickness D of the shell, the median particle size R1 of the shell material, the median particle size R2 of the inner core material, and the pH value E of the inner core material satisfy the relationship: D-5≤10E*R1 / R2≤D+5.

[0031] In some embodiments, the thickness D of the shell is 45 to 55 nm, the median particle size R1 of the shell material is 1 to 5 μm, the median particle size R2 of the inner core material is 9 to 13 μm, and the pH value E of the inner core material is 10 to 12.

[0032] The thickness D of the shell material layer can be 45 nm, 50 nm, 55 nm, and can include but is not limited to the above-mentioned values, and is preferably 50 nm; the specific value of the median particle size R1 of the shell material can be 1 mu m, 2 mu m, 3 mu m, 4 mu m, 5 mu m, and can include but is not limited to the above-mentioned values; the specific value of the median particle size R2 of the core material can be 9 mu m, 10 mu m, 11 mu m, 12 mu m, 13 mu m, and can include but is not limited to the above-mentioned values; the pH value E of the core material can be 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12, and can include but is not limited to the above-mentioned values.

[0033] In a second aspect of the present application, a preparation method of the above-mentioned composite positive electrode lithium supplement material is provided, and the preparation environment is in an environment with a humidity of less than 2%, and the method comprises the following steps:

[0034] S1, physically mixing a lithium source and a metal source, and the whiteness cannot be observed by naked eyes; screening the mixed material, and pre-sintering in an air environment; crushing and screening after natural cooling; secondary sintering; crushing and screening after natural cooling; and airflow crushing to obtain a core material;

[0035] S2, heating and stirring a lithium source and an organic acid in an ethanol solvent, and obtaining a shell material after drying;

[0036] S3, loading the core material and the shell material in a ball milling tank, and ball milling; vacuum drying the obtained material to obtain a composite positive electrode lithium supplement material.

[0037] In step S1, the molar ratio of the lithium source to the metal source is 2-6.8, and the lithium ratio is a key parameter when preparing the core material. When the M source is a nickel source, the lithium-nickel molar ratio is 2.03; when the M source is an iron source, the lithium-iron molar ratio is 5.3; and when the M source is a cobalt source, the lithium-cobalt molar ratio is 6.5. In this way, a relatively pure main material can be obtained, the specific capacity is improved, and the residual lithium and the polarization degree of the material are also increased.

[0038] In some embodiments, the lithium source in steps S1 and S2 is at least one of lithium carbonate, lithium hydroxide, lithium oxide, and lithium nitrate, and the organic acid in step S2 is one of oxalic acid, ethanedioic acid, and squaric acid.

[0039] In some embodiments, in step S1, the pre-sintering temperature is 300-400℃, the temperature rising speed is 5℃ / min, and the holding time is 5-7h; wherein the pre-sintering temperature can be specifically 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃; can include but not limited to the above listed values, preferably 350℃; the holding time can be specifically 5h, 6h, 7h, can include but not limited to the above listed values, preferably 5h; the secondary sintering is calcination under inert gas, the temperature rising speed is 3℃ / min, the sintering temperature is 700-800℃, and the holding time is 13-16h; wherein the sintering temperature can be specifically 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, can include but not limited to the above listed values, preferably 730℃; the holding time can be specifically 13h, 14h, 15h, 16h, can include but not limited to the above listed values, preferably 14h.

[0040] The third aspect of the present application further provides a positive electrode sheet comprising the composite positive electrode lithium supplementing material described above, specifically comprising a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, wherein the positive electrode active material is the positive electrode material described in the present application.

[0041] The positive electrode current collector can be any material suitable for use as a positive electrode current collector in a lithium ion battery, for example, the positive electrode current collector can be, but is not limited to, a metal foil, and more specifically can be, but is not limited to, an aluminum foil.

[0042] The fourth aspect of the present application aims to provide a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described above.

[0043] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector, and the negative electrode active material layer can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based material, tin-based material, lithium titanate, or other metals capable of forming alloys with lithium, etc. Among them, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be any material suitable for use as a negative electrode current collector in a lithium ion battery, for example, the negative electrode current collector can be, but is not limited to, a metal foil, and more specifically can be, but is not limited to, a copper foil.

[0044] The separator can be any of a variety of materials suitable for use as a separator in a lithium ion battery in the art, for example, can be a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers, among others.

[0045] The secondary battery further includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt, and an additive. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in a high-temperature electrolyte, at least one of LiBF4, LiBOB, and LiPF6 used in a low-temperature electrolyte, at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in an overcharge-preventing electrolyte, or at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate including PC and EC, a chain carbonate including DFC, DMC, or EMC, or a carboxylic acid ester including MF, MA, EA, and MP. The additive includes at least one of a film-forming additive, a conductive additive, a flame-retardant additive, an overcharge-preventing additive, an additive for controlling the contents of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

[0046] In order to make the technical solutions and advantages of the present application clearer, the following will further describe the present application and its beneficial effects in detail with reference to the specific embodiments, but the embodiments of the present application are not limited thereto.

[0047] Embodiment 1

[0048] The composite positive electrode lithium supplement material provided in the embodiment includes a core material and a shell material coated on the surface of the core material, wherein the chemical formula of the core material is Li2Ni 0.5 Cu 0.5 O2, the chemical formula of the shell material is Li2C4O4, and the chemical formula of the composite positive electrode lithium supplement material is Li2Ni 0.5 Cu 0.5 O2@Li2C4O4.

[0049] The thickness D of the shell material layer is 50.99 nm, the median particle size R1 of the shell material is 5 μm, the median particle size R2 of the core material is 11 μm, and the pH value E of the core material is 11.2, and the following relationship is satisfied: D-5≤10E*R1 / R2≤D+5.

[0050] The preparation method of the composite positive electrode lithium supplement material is as follows:

[0051] Step 1, physically mix lithium oxide, nickel oxide and copper oxide, and visually check the whiteness, wherein the molar ratio of Li:Ni is 2.03, and the molar ratio of Ni:Cu is 5:5, sieve the mixed materials through a 100-mesh sieve, then load into a crucible, and pre-sinter in an air environment using a muffle furnace, with a calcination program set at 350°C for 5 hours, and a temperature rising speed of 5°C / min; after natural cooling, crush and sieve through a 100-mesh sieve, re-load into a crucible, and load into a ventilable muffle furnace; set the calcination program at 730°C for 14 hours, and a temperature rising speed of 2°C / min. After natural cooling, crush and sieve through a 200-mesh sieve, to obtain a core material with a D50 of 11 μm, and a chemical formula of Li2Ni 0.5 Cu 0.5 O2, and then seal and store;

[0052] Step 2, directly dissolve the squaric acid crystal and lithium nitrate in an ethanol solution, continuously heat and stir in the squaric acid crystal solution, slowly add the lithium nitrate solution after stirring for 5 minutes at 80°C, continuously stir for 30 minutes after the lithium nitrate solution is added, and then spray dry to obtain a shell material Li2C4O4.

[0053] Step 3, load the core material and the shell material into a ball mill jar according to a mass ratio of 1:0.1, adjust the rotation speed to 400 RPM, and ball mill for 20 minutes; vacuum dry the obtained material at 120°C for 12 hours to obtain a composite positive electrode lithium supplement material Li2Ni 0.5 Cu 0.5 O2@Li2C4O4.

[0054] Preparation of the positive electrode sheet:

[0055] Mix the composite positive electrode lithium supplement material in Example 1 above and the conventional lithium cobaltate according to a ratio of lithium cobaltate: composite positive electrode lithium supplement material: conductive carbon: binder = 96.42:1.7:0.63:1.05, and NMP to form a positive electrode slurry, coat after vacuum stirring and defoaming to form a positive electrode sheet.

[0056] Preparation of the secondary battery:

[0057] Assemble the above positive electrode sheet and the conventional 10% silicon-carbon negative electrode sheet (i.e. the silicon content in the negative electrode material is 10% of the mass of the silicon-carbon), a high-voltage lithium supplement system electrolyte, and a separator into a secondary lithium ion soft-pack battery. Except for the above positive electrode sheet, the remaining components can be purchased on the market.

[0058] Example 2

[0059] The difference between this example and Example 1 is that the raw materials prepared in Step 1 are lithium oxide, nickel oxide and titanium oxide; and the chemical formula of the core material obtained is Li2Ni 0.5 Ti 0.5O2, the composite anode lithium supplement material obtained in step 3 is Li2Ni 0.5 Ti 0.5 O2@Li2C4O4;

[0060] The rest is the same as example 1, which will not be repeated here.

[0061] Example 3

[0062] The difference between this example and example 1 is that the raw materials prepared in step 1 are lithium oxide, nickel oxide, and zinc oxide; and the chemical formula of the obtained core material is Li2Ni 0.5 Zn 0.5 O2, the composite anode lithium supplement material obtained in step 3 is Li2Ni 0.5 Zn 0.5 O2@Li2C4O4;

[0063] The rest is the same as example 1, which will not be repeated here.

[0064] Example 4

[0065] The difference between this example and example 1 is that the raw materials prepared in step 1 are lithium oxide, nickel oxide, and magnesium oxide; and the chemical formula of the obtained core material is Li2Ni 0.5 Mg 0.5 O2, the composite anode lithium supplement material obtained in step 3 is Li2Ni 0.5 Mg 0.5 O2@Li2C4O4;

[0066] The rest is the same as example 1, which will not be repeated here.

[0067] Example 5

[0068] The difference between this example and example 1 is that the raw materials prepared in step 1 are lithium oxide, nickel oxide, and tungsten oxide; and the chemical formula of the obtained core material is Li2Ni 0.5 W 0.5 O2, the composite anode lithium supplement material obtained in step 3 is Li2Ni 0.5 W 0.5 O2@Li2C4O4;

[0069] The rest is the same as example 1, which will not be repeated here.

[0070] Comparative Example 1

[0071] Lithium oxide and nickel oxide are physically mixed, and the rest of the synthesis method is the same as step 1 of example 1, and the chemical formula of the obtained anode lithium supplement material is Li2NiO2.

[0072] Comparative Example 2

[0073] The comparative example is different from example 1 in that it only contains step 1, and does not contain step 2 and step 3, i.e. the positive electrode lithium supplement material Li2Ni 0.5 Cu 0.5 O2;

[0074] The rest is the same as example 1, which will not be repeated here.

[0075] Comparative example 3

[0076] The comparative example is different from example 2 in that it only contains step 1, and does not contain step 2 and step 3, i.e. the positive electrode lithium supplement material Li2Ni 0.5 Ti 0.5 O2.

[0077] The rest is the same as example 2, which will not be repeated here.

[0078] Comparative example 4

[0079] The comparative example is different from example 3 in that it only contains step 1, and does not contain step 2 and step 3, i.e. the positive electrode lithium supplement material Li2Ni 0.5 Zn 0.5 O2.

[0080] The rest is the same as example 3, which will not be repeated here.

[0081] Comparative example 5

[0082] The comparative example is different from example 4 in that it only contains step 1, and does not contain step 2 and step 3, i.e. the positive electrode lithium supplement material Li2Ni 0.5 Mg 0.5 O2.

[0083] The rest is the same as example 4, which will not be repeated here.

[0084] Comparative example 6

[0085] The comparative example is different from example 5 in that it only contains step 1, and does not contain step 2 and step 3, i.e. the positive electrode lithium supplement material Li2Ni 0.5 W 0.5 O2.

[0086] The rest is the same as example 5, which will not be repeated here.

[0087] Comparative example 7

[0088] The positive electrode material in the comparative example is a conventional lithium cobaltate material on the market, and the positive electrode slurry is prepared by mixing lithium cobaltate: conductive carbon: binder = 98.12: 0.63: 1.05 with NMP, and then coating to prepare the positive electrode sheet after vacuum stirring and defoaming.

[0089] Comparative example 8

[0090] In the present comparative example, the D50 of the core material obtained in Step 1 was 13 pm by using inert gas to adjust the gas flow and the internal pressure of the gas cavity through an air flow mill.

[0091] The rest was the same as in Example 1, which will not be repeated here.

[0092] Comparative Example 9

[0093] In the present comparative example, the mass ratio of the core material to the shell material in Step 3 was 1:0.5.

[0094] The rest was the same as in Example 1, which will not be repeated here.

[0095] Comparative Example 10

[0096] In the present comparative example, the mass ratio of the core material to the shell material in Step 3 was 1:0.05.

[0097] The rest was the same as in Example 1, which will not be repeated here.

[0098] The positive electrode materials and secondary batteries obtained in Examples 1-5 and Comparative Examples 1-10 were subjected to the following tests:

[0099] 1. Material physical property test: The positive electrode lithium supplement material was mixed with PVDF conductive carbon and NMP to observe its viscosity and gel condition; the formulation was mixed according to the positive electrode lithium supplement active material: conductive carbon: PVDF = 8:1:1, an equal amount of NMP was added to each group, a viscosity detector was used to detect the viscosity, and the gel condition was observed with the naked eye.

[0100] No gel means that the slurry can be normally stirred and processed;

[0101] Gel refers to the fact that the prepared slurry cannot be normally stirred after defoaming, i.e., it cannot be coated;

[0102] Light gel refers to the fact that the prepared slurry is slightly gelled after defoaming.

[0103] 2. Lithium ion secondary battery test: The thickness and capacity of the battery after the capacity test were tested through the capacity test, and the volume energy density was calculated,

[0104] The volume energy density calculation formula is: the capacity after the capacity test / the volume of the battery;

[0105] The 400-cycle high-temperature cycle capacity retention rate calculation formula is: the 400-cycle high-temperature cycle capacity / the first-cycle normal-temperature cycle capacity, and the 400-cycle high-temperature cycle expansion rate calculation formula is: the 400-cycle battery PPG thickness / the first-cycle normal-temperature half-electricity PPG thickness. At the same time, the 400-cycle cycle retention rate after adding different composite positive electrode lithium supplement materials was compared.

[0106] The test results of the above examples and comparative examples are arranged in Table 1.

[0107] Table 1

[0108]

[0109] From the above table, compared with the uncoated comparative examples, the composite positive electrode lithium supplement active material provided by the application does not have the problem of physical / chemical gelation in the conventional humidity workshop, and the slurry viscosity of the examples is lower than that of comparative examples 1-6, which shows that the coating layer can effectively isolate the moisture in the workshop, solve the characteristics of the current positive electrode lithium supplement active material that is easy to absorb water and carbon dioxide, and improve the practicability.

[0110] In addition, the composite positive electrode lithium supplement active material provided by the application improves the energy density of the lithium ion secondary battery. Compared with comparative example 7 without lithium supplement, comparative examples 1-6 without shell, comparative example 8 not satisfying the relationship D-5≤10E*R1 / R2≤D+5, and comparative examples 9-10 not satisfying the mass ratio of the core to the shell being 1:0.1-0.3, the retention rate of the examples is significantly improved after 400 cycles at high temperature, and the expansion rate after 400 cycles at high temperature is significantly reduced. This is very obvious for improvement under the high-silicon system, and is conducive to improving the cycle retention rate and providing a clear direction for improving the cycle expansion rate under the high-silicon system.

[0111] In summary, the application provides a composite positive electrode lithium supplement material, which comprises a core and a shell coated on the surface of the core; the core is a doped inorganic ternary compound, and its chemical general formula is Li x M y N (1-y) O z The shell is an organic lithium supplement agent, and its chemical general formula is Li a C b O c The coating of the shell can improve the air stability of the composite positive electrode lithium supplement material, effectively prevent the contact of the material with humid air, solve the problem that the current positive electrode lithium supplement material is easy to fail in the workshop environment, the metal element is doped in the core, which can reduce the initial efficiency of lithium-rich lithium nickelate, provide more active lithium source, and the residual product of lithium-rich lithium nickelate is metal oxide, which is conducive to improving the conductivity of the positive electrode sheet; the composite positive electrode lithium supplement material synthesized by the application does not have gelation condition during the slurry viscosity experiment in the conventional environment, and the composite positive electrode lithium supplement material has high capacity, which can effectively supplement the active lithium consumed by the negative electrode SEI film, and improve the energy density and high-temperature cycle performance of the full battery.

[0112] Those skilled in the art can make various modifications and variations to the above embodiments based on the disclosure and teachings of this specification. Therefore, the present application should not be limited to the above specific embodiments, and any obvious modifications, replacements or variations made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation on the present application.

Claims

1. A composite cathode lithium supplementation material, characterized in that, Its general chemical formula is Li x M y N (1-y) O z @Li a C b O c The composite cathode lithium replenishment material includes a core and a shell covering the surface of the core material; The core is a doped inorganic ternary compound with the general chemical formula Li. x M y N (1-y) O z Where M is Ni, N is selected from at least one of Ti, W, Zn, and Mg, 2≤x≤6, 0.1≤y≤0.5, and 2≤z≤6; The outer shell is an organic lithium supplement, specifically lithium squartz oxide. The mass ratio of the core to the outer shell is 1:0.1~0.3; The thickness of the outer shell is D nm, the median particle size of the outer shell material is R1 μm, the median particle size of the core material is R2 μm, and the pH value E of the core material satisfy the following relationship: D-5≤10E*R1 / R2≤D+5.

2. The composite cathode lithium replenishment material according to claim 1, characterized in that, The thickness D of the outer shell is 45~55nm, the median particle size R1 of the outer shell material is 1~5μm, the median particle size R2 of the core material is 9~13μm, and the pH value E of the core material is 10~12.

3. A method for preparing a composite cathode lithium supplementation material according to any one of claims 1-2, characterized in that, The preparation environment is in an environment with humidity less than 2%, and includes the following steps: S1. Mix the lithium source and the metal source; after sieving the mixed material, pre-sinter it in an air environment, and after natural cooling, crush and sieve it for secondary sintering. After natural cooling, crush and sieve it for air jet pulverization to obtain the core material. S2. The lithium source and organic acid are heated and stirred in ethanol solvent, and dried to obtain the shell material; S3. The core material and the shell material are ball-milled and mixed, and the resulting material is vacuum-dried to obtain the composite positive electrode lithium replenishment material.

4. The method for preparing a composite cathode lithium supplementation material according to claim 3, characterized in that, In step S1, the molar ratio of lithium source to metal source is 2 to 6.8; And / or, the lithium source in steps S1 and S2 is at least one of lithium carbonate, lithium hydroxide, lithium oxide, and lithium nitrate; And / or, the organic acid in step S2 is squaric acid.

5. The method for preparing a composite cathode lithium supplementation material according to claim 3, characterized in that, In step S1, the pre-sintering temperature is 300~400℃, the heating rate is 5℃ / min, and the holding time is 5~7h; the secondary sintering is calcination under inert gas, the heating rate is 2℃ / min, the sintering temperature is 700~800℃, and the holding time is 13~16h.

6. A positive electrode plate, characterized in that, The composite cathode lithium replenishment material described in any one of claims 1 to 2 above.

7. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 6.

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