Manganese-based composite lithium supplement and preparation method thereof and positive plate

Abstract

The application provides a manganese-based composite lithium supplementing agent, a preparation method thereof and a positive plate, and belongs to the technical field of lithium batteries. The positive plate prepared from the manganese-based composite lithium supplementing agent provided by the application utilizes a three-dimensional structure framework formed by Li6MnO4 to form a high-energy barrier for lithium ion migration of Li2O in a crystal gap, so that only Li6MnO4 releases lithium ions to supplement lithium at a low voltage (less than or equal to 4.2 V); and at a high voltage (greater than 4.2 V), the energy barrier is broken, and Li2O and Li6MnO4 jointly release lithium ions to supplement lithium, so that gradient lithium supplementing at high and low voltages is realized; and the lattice gap of Li6MnO4 is small, so that only lithium ions can migrate out after Li2O is decomposed at a high voltage (greater than 4.2 V), and oxygen anions after the decomposition of Li2O are bound in the lattice framework due to a very high migration potential barrier, so that secondary reactions with high-voltage electrolyte are avoided.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a manganese-based composite lithium supplement agent, its preparation method, and a positive electrode sheet. Background Technology

[0002] During the first charge of a lithium-ion battery, the formation of a solid electrolyte interphase (SEI) film on the negative electrode surface irreversibly consumes the active lithium in the battery system, affecting the battery's energy density and cycle life. Replenishing the active lithium through lithium replenishment technology is an effective way to solve this problem. Among these technologies, positive electrode lithium replenishment agents are more easily applied on a large scale due to their strong compatibility with existing battery manufacturing processes, high safety, and controllable cost.

[0003] With the continuous development of power batteries, energy storage devices, and consumer electronics, the market has placed higher demands on the energy density, cycle stability, and wide operating condition adaptability of lithium-ion batteries, especially battery systems that are compatible with both high and low voltage charging. Currently, existing cathode lithium supplements are all designed based on a single voltage system; that is, high-voltage cathode lithium supplements and low-voltage cathode lithium supplements can only be adapted to their respective charging voltage windows. For example, for high-voltage cathode systems with a charging cutoff voltage > 4.2V, existing high-voltage lithium replenishing agents, such as zirconium-based lithium oxides, can fully delithigate and replenish lithium under high-voltage charging. However, in low-voltage charging scenarios (charging cutoff voltage ≤ 4.2V), it is difficult to trigger an effective delithiation reaction, resulting in a significant decrease in lithium replenishment efficiency. In some cases, the potential mismatch can even damage the stability of the structure and trigger side reactions. On the other hand, for low-voltage lithium replenishing agents (such as lithium oxalate), the delithiation potential is concentrated between 2.5 and 3.8V, which can meet the first-efficiency improvement requirements in low-voltage scenarios. However, in high-voltage charging modes, such low-voltage lithium replenishing agents not only cannot achieve lithium replenishment, but their decomposition products may also react with the high-voltage electrolyte in a secondary reaction, releasing gas or damaging the stability of the electrode interface, leading to a decrease in battery cycle life. Summary of the Invention

[0004] The purpose of this invention is to provide a manganese-based composite lithium supplement agent, its preparation method, and a positive electrode sheet. The positive electrode sheet prepared by the manganese-based composite lithium supplement agent provided by this invention can achieve gradient lithium supplementation under high and low voltages.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A manganese-based composite lithium supplement includes Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 lattice; the mass ratio of Li2O to Li6MnO4 is 1:(6~100).

[0006] This invention also provides a method for preparing the manganese-based composite lithium supplement described in the above technical solution, comprising: After mixing manganese and lithium sources, a first sintering and a second sintering are performed sequentially to obtain a manganese-based composite lithium supplement. After the first sintering is completed, the obtained product is directly cooled from the temperature of the first sintering to the temperature of the second sintering for a second sintering. The cooling rate is 10~80℃ / min.

[0007] Preferably, the molar ratio of manganese in the manganese source to lithium in the lithium source is 1:(6~9).

[0008] Preferably, the lithium source includes one or more of Li2O, LiOH·H2O, Li2CO3, LiNO3, Li2SO4 and CH3COOLi.

[0009] Preferably, the manganese source includes one or more of Mn3O4, MnCO3, MnO2 and MnO.

[0010] Preferably, the temperature of the first sintering is 800~1200℃, and the time of the first sintering is 10~20h.

[0011] Preferably, the second sintering temperature is 300~700℃, and the second sintering time is 15~30h.

[0012] Preferably, the atmosphere for the first sintering, cooling, and second sintering can be one or more of Ar, N2, CO, H2, Ar+5%H2, and Ar+10%H2.

[0013] Preferably, the mixing of the manganese source and the lithium source is carried out under ball milling; the ball milling speed is 250~1500 rpm, and the ball milling time is 3~10 h.

[0014] The present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, wherein the positive electrode material comprises a lithium active material, a manganese-based composite lithium supplement, a conductive agent and a binder, wherein the manganese-based composite lithium supplement is the manganese-based composite lithium supplement described in the above technical solution or the manganese-based composite lithium supplement prepared by the preparation method described in the above technical solution.

[0015] This invention provides a manganese-based composite lithium replenisher, comprising Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 lattice; the mass ratio of Li2O to Li6MnO4 is 1:(6~100). The positive electrode sheet made from the manganese-based composite lithium replenisher provided by this invention utilizes the three-dimensional structural framework formed by Li6MnO4 to create a high-energy barrier for lithium ion migration from Li2O in the interstitial spaces, thereby achieving lithium replenishment only by Li6MnO4 at lower voltages (≤4.2V); while at higher voltages (>4.2V), the energy barrier is broken, and both Li2O and Li6MnO4 release lithium ions for replenishment, thus achieving gradient lithium replenishment at high and low voltages; furthermore, the small interstitial spaces of Li6MnO4 ensure that only lithium ions migrate out after Li2O decomposes at higher voltages (>4.2V), while the oxygen anions after Li2O decomposition are bound in the lattice framework due to the extremely high migration barrier, thus avoiding secondary reactions with the high-voltage electrolyte. The results of the examples show that the positive electrode sheets prepared with the manganese-based composite lithium supplement provided by the present invention can achieve a first-cycle charging capacity of 400.5 mAh / g and 674 mAh / g when tested at 4.2V and 4.4V, respectively. Attached Figure Description

[0016] Figure 1 The image shows the XRD pattern of the manganese-based composite lithium supplement of Example 1 of this invention. Figure 2 This is a SEM image of the manganese-based composite lithium supplement of Example 1 of the present invention; Figure 3 This is a graph showing the first charge curve of the lithium-ion battery made from the positive electrode sheet of Test Example 3 of the present invention. Detailed Implementation

[0017] The present invention provides a manganese-based composite lithium supplement, comprising Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 lattice; the mass ratio of Li2O to Li6MnO4 is 1:(6~100).

[0018] The manganese-based composite lithium replenisher provided by this invention comprises Li6MnO4. In this invention, the phase structure of the Li6MnO4 is an antifluorite structure. This invention utilizes the antifluorite structure of Li6MnO4 to form a three-dimensional structural framework, creating a high-energy barrier for lithium ion migration from Li2O in the intergranular spaces. This allows only Li6MnO4 to release lithium ions for replenishment at lower voltages (≤4.2V); and utilizes the small intergranular spaces of Li6MnO4 to ensure that only lithium ions migrate out after Li2O decomposition at higher voltages (>4.2V), while the oxygen anions after Li2O decomposition are bound within the lattice framework due to the extremely high migration barrier, thus avoiding secondary reactions with the high-voltage electrolyte; simultaneously, it utilizes the Mn content in Li6MnO4... 3+The electrostatic repulsion effect can reduce the permeation rate of gas molecules by 1 to 2 orders of magnitude. In addition, the dense three-dimensional structure of Li6MnO4 requires water and carbon dioxide in the air to penetrate Li6MnO4 before they can come into contact with Li2O, thereby delaying the contact between Li2O and air and improving the stability of manganese-based composite lithium supplement. Furthermore, the small interstitial gaps of Li6MnO4 can reduce the contact area between Li2O and air, further improving the stability of manganese-based composite lithium supplement.

[0019] The manganese-based composite lithium replenisher provided by this invention further includes Li₂O dispersed in the interstitial spaces of the Li₆MnO₄ crystal lattice. In this invention, the phase structure of the Li₂O is an antifluorite structure. By limiting the dispersion of Li₂O in the interstitial spaces of the Li₆MnO₄ crystal lattice, this invention allows Li₂O to overcome the energy barrier of the Li₆MnO₄ crystal lattice under higher voltages (>4.2V) and release lithium ions together with Li₆MnO₄ for lithium replenishment.

[0020] In this invention, the mass ratio of Li₂O to Li₆MnO₄ can be 1:(6~100). In embodiments of this invention, the mass ratio of Li₂O to Li₆MnO₄ can specifically be 1:10, 1:20, 1:40, 1:60, 1:80, or 1:100. This invention ensures that Li₂O can be dispersed in the interstitial spaces of the Li₆MnO₄ lattice by limiting the mass ratio of Li₂O to Li₆MnO₄, and ensures that the three-dimensional structural framework of Li₆MnO₄ forms a high-energy barrier for lithium ion migration of Li₂O in the interstitial spaces. This allows for lithium ion release by only Li₆MnO₄ at lower voltages (≤4.2V) to provide lithium replenishment; while at higher voltages (>4.2V), the energy barrier is broken, and both Li₂O and Li₆MnO₄ release lithium ions to provide lithium replenishment, thus achieving gradient lithium replenishment at high and low voltages.

[0021] In one embodiment of the present invention, the particle size of the manganese-based composite lithium supplement can be 0.5~10 μm. In the embodiments of the present invention, the particle size of the manganese-based composite lithium supplement can specifically be 1 μm, 3 μm, 5 μm, 7 μm, 9 μm or 10 μm. The present invention, by limiting the particle size of the manganese-based composite lithium supplement to have a larger specific surface area, provides more reactive sites, promotes the interfacial charge transfer between lithium ions and electrolyte, and further accelerates the lithium supplementation reaction kinetics.

[0022] The positive electrode sheet prepared by the manganese-based composite lithium replenishing agent provided by this invention utilizes the three-dimensional structural framework formed by Li6MnO4 to create a high-energy barrier for the migration of lithium ions from Li2O in the intergranular gaps. This allows only Li6MnO4 to release lithium ions to provide lithium replenishment at lower voltages (≤4.2V). At higher voltages (>4.2V), the energy barrier is broken, and both Li2O and Li6MnO4 release lithium ions to provide lithium replenishment, thus achieving gradient lithium replenishment at high and low voltages. Furthermore, the small intergranular gaps of Li6MnO4 ensure that only lithium ions migrate out after Li2O decomposes at higher voltages (>4.2V), while the oxygen anions after Li2O decomposes are bound in the lattice framework due to the extremely high migration barrier, thereby avoiding secondary reactions with the high-voltage electrolyte.

[0023] This invention also provides a method for preparing the manganese-based composite lithium supplement described in the above technical solution, comprising: After mixing manganese and lithium sources, a first sintering and a second sintering are performed sequentially to obtain a manganese-based composite lithium supplement. After the first sintering is completed, the obtained product is directly cooled from the temperature of the first sintering to the temperature of the second sintering for a second sintering. The cooling rate is 10~80℃ / min.

[0024] In one embodiment of the present invention, the manganese source may include one or more of Mn3O4, MnCO3, MnO2, and MnO. In another embodiment, the particle size of the manganese source may be 2-10 μm or 4-8 μm. The present invention can control the phase composition of Li6MnO4 by limiting the type and particle size of the manganese source, which is beneficial for the synthesis of Li6MnO4 with an anti-fluorite phase structure.

[0025] In one embodiment of the present invention, the lithium source may include one or more of Li₂O, LiOH·H₂O, Li₂CO₃, LiNO₃, Li₂SO₄, and CH₃COOLi. By limiting the type of lithium source, the present invention facilitates the preparation of high-purity manganese-based composite lithium supplements with manganese sources. The present invention does not impose any special limitation on the particle size of the lithium source; lithium sources with particle sizes commonly used in the art can be employed.

[0026] In one embodiment of the present invention, the molar ratio of manganese in the manganese source to lithium in the lithium source can be 1:(6~9). In embodiments of the present invention, the molar ratio of manganese in the manganese source to lithium in the lithium source can specifically be 1:6.5, 1:7, 1:7.5, 1:8, or 1:9. The present invention ensures that some lithium ions precipitate in the form of Li2O and disperse in the interstitial spaces of Li6MnO4 by limiting the molar ratio of manganese in the manganese source to lithium in the lithium source.

[0027] In one embodiment of the present invention, the manganese source and the lithium source are mixed under ball milling. In another embodiment, the ball milling speed can be 250~1500 rpm. Specifically, in embodiments of the present invention, the ball milling speed can be 250 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, or 1500 rpm. In one embodiment, the ball milling time can be 3~10 hours. Specifically, in embodiments of the present invention, the ball milling time can be 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, or 15 hours.

[0028] In one embodiment of the present invention, the ball milled material can be sieved, and the mesh size of the sieve can be 300-500 mesh. In embodiments of the present invention, the mesh size of the sieve can specifically be 300 mesh, 400 mesh, or 500 mesh.

[0029] In one embodiment of the present invention, the temperature of the first sintering can be 800~1200℃, or 900~1000℃. In another embodiment, the time of the first sintering can be 10~20h, 12~18h, or 14~16h. The present invention ensures that Li₂O is dispersed in the interstitial spaces of the Li₆MnO₄ lattice by limiting the temperature and time of the first sintering. In another embodiment, the atmosphere of the first sintering can be one or more of Ar, N₂, CO, H₂, Ar+5%H₂, and Ar+10%H₂. The present invention ensures that the manganese source and lithium source react fully to generate Li₆MnO₄ by limiting the temperature and time of the first sintering, and promotes the uniform dispersion of Li₂O in the interstitial spaces of the Li₆MnO₄ lattice, forming a stable two-phase composite structure.

[0030] In one embodiment of the present invention, after the first sintering is completed, the obtained product can be directly cooled from the temperature of the first sintering to the temperature of the second sintering for a second sintering; the cooling rate is 10~80℃ / min. The present invention obtains Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 crystal structure by limiting the formation of a three-phase structure of Li6MnO4, Li2O, and MnO in the first sintering, and then limiting the cooling rate to reduce the manganese oxide content; subsequently, it holds the product at a certain temperature to further fill the lattice defects of Li6MnO4, making its crystal form more complete; at the same time, it promotes the uniform dispersion of Li2O in the matrix and avoids local enrichment.

[0031] In one embodiment of the present invention, the cooling rate can be 10~80℃ / min. In specific embodiments of the present invention, the cooling rate can be 10℃ / min, 20℃ / min, 25℃ / min, 30℃ / min, 40℃ / min, 50℃ / min, 55℃ / min, 60℃ / min, 70℃ / min, or 80℃ / min. The present invention eliminates manganese oxide by limiting the cooling rate, thereby obtaining Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 lattice. In one embodiment of the present invention, the second sintering temperature can be 300~700℃. In specific embodiments of the present invention, the second sintering temperature can be 300℃, 450℃, 500℃, or 600℃. In one embodiment of the present invention, the second sintering time can be 15~30h. In specific embodiments of the present invention, the second sintering time can be 15h, 20h, 25h, or 30h. This invention fills the lattice defects of Li6MnO4 by limiting the temperature and time of the second sintering, making its crystal form more complete; at the same time, it promotes the uniform dispersion of Li2O in the matrix and avoids local enrichment.

[0032] In one embodiment of the present invention, the atmosphere of the first sintering is the same as that of the second sintering, and will not be described again here. The present invention does not impose any particular limitation on the cooling method; any cooling method well known in the art can be used.

[0033] In one embodiment of the present invention, after the second sintering is completed, the product after the second sintering is sequentially subjected to furnace cooling and ball milling. The ball milling described in the present invention uses the same rotation speed and time as the ball milling described in the above-mentioned technical solution, and will not be repeated here.

[0034] This invention ensures the full reaction of manganese and lithium sources by sintering a mixture of the two sources to generate Li6MnO4 and promotes the uniform dispersion of Li2O in the interstitial spaces of the Li6MnO4 lattice, forming a stable two-phase composite structure. The invention also limits the cooling to a second sintering temperature after sintering to remove manganese oxide impurities. A second sintering process further fills the lattice defects in Li6MnO4, making its crystal structure more complete. Simultaneously, it promotes the uniform dispersion of Li2O in the matrix, avoiding localized enrichment.

[0035] The present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector. The positive electrode material comprises a lithium active material, a manganese-based composite lithium supplement, a conductive agent, and a binder. The manganese-based composite lithium supplement is the manganese-based composite lithium supplement described in the above technical solution or the manganese-based composite lithium supplement prepared by the above preparation method.

[0036] In one embodiment of the present invention, the current collector may include aluminum foil, carbon-coated aluminum foil, or titanium foil. In one embodiment of the present invention, the lithium active material may include one or more of lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium manganese oxide. In one embodiment of the present invention, the conductive agent may include one or more of graphene, acetylene black, carbon nanotubes, and carbon black. In one embodiment of the present invention, the adhesive may include one or more of polyvinylidene fluoride, polyethyl methacrylate, polyethylene glycol, nitrile rubber, polytetrafluoroethylene, polymethyl methacrylate, polyethyl methacrylate, and poly(3-methoxymethyl acrylate). In one embodiment of the present invention, the organic solvent may include one or more of N-methylpyrrolidone, dimethylformamide, diethylformamide, and tetrahydrofuran.

[0037] In one embodiment of the present invention, the mass ratio of the lithium active material to the manganese-based composite lithium supplement can be 100:(1~10). In embodiments of the present invention, the mass ratio of the lithium active material to the manganese-based composite lithium supplement can specifically be 100:1.26, 100:3.89, or 100:6.66.

[0038] In one embodiment of the present invention, the mass of the manganese-based composite lithium supplement can be 1-5% or 2-3% of the mass of the cathode material.

[0039] In one embodiment of the present invention, the method for preparing the positive electrode sheet may include: mixing a manganese-based composite lithium supplement, a lithium active material, a conductive agent, a binder, and an organic solvent, and then sequentially coating, drying, rolling, and die-cutting the mixture on the surface of a current collector to obtain the positive electrode sheet. In one embodiment of the present invention, the drying temperature may be 80~120℃, and the drying time may be 4~5 hours. In one embodiment of the present invention, the rolling process uses a double roller, the thickness of the roller gap may be 10 μm, and the pressure applied during the rolling process may be 50 t.

[0040] As one embodiment of the present invention, the mass ratio of the manganese-based composite lithium supplement, the lithium active material, the conductive agent and the binder can be (1.0~5.0):(70~79):(5.0~15):(5.0~15).

[0041] This invention does not impose any particular limitation on the mixing of the manganese-based composite lithium supplement, lithium active material, conductive agent, binder, and organic solvent. A mixing method well-known in the art can be used to mix the manganese-based composite lithium supplement, lithium active material, conductive agent, binder, and organic solvent. In one embodiment of this invention, the manganese-based composite lithium supplement, lithium active material, conductive agent, binder, and organic solvent are mixed to obtain a slurry; the solid content of the slurry can be 55-75%. In embodiments of this invention, the solid content of the slurry can specifically be 50%, 55%, 60%, 70%, or 75%.

[0042] In one embodiment of the present invention, the drying temperature can be 80~120℃, and the drying time can be 4~5h.

[0043] The present invention does not impose any special limitations on the coating and die-cutting methods; any coating and die-cutting methods well known in the art can be used.

[0044] The positive electrode sheet prepared by this invention can achieve gradient lithium replenishment under high and low voltage conditions.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Example 1 A manganese-based composite lithium supplement is composed of Li6MnO4 with an antifluorite structure and Li2O with an antifluorite structure dispersed in the interstitial spaces of the Li6MnO4 lattice; the mass ratio of Li2O to Li6MnO4 is 1:6.

[0047] The preparation method of the above-mentioned manganese-based composite lithium supplement is as follows: MnO with an average particle size of 5 μm and Li₂O with an average particle size of 10 μm were ball-milled at 400 rpm for 10 h, then passed through a 400-mesh sieve. The mixture was then placed in a muffle furnace and sintered for 15 h at a heating rate of 2 °C / min from room temperature to 850 °C by argon atmosphere. The mixture was then sintered for 20 h by furnace cooling at a cooling rate of 35 °C / min to 500 °C. Finally, the mixture was ball-milled at 800 rpm for 10 h to obtain a manganese-based composite lithium supplement with an average particle size of 2 μm, denoted as Li₆MnO₄ / Li₂O₁. The molar ratio of manganese in MnO to lithium in Li2O is 1:6.6.

[0048] Example 2 The difference between this embodiment and Example 1 is that the molar ratio of manganese in MnO to lithium in Li2O is 1:7.2, and the manganese-based composite lithium supplement with an average particle size of 1.5 μm is prepared and denoted as Li6MnO4 / Li2O-2.

[0049] Example 3 The difference between this embodiment and Example 1 is that the molar ratio of manganese in MnO to lithium in Li2O is 1:7.8, and the manganese-based composite lithium supplement with an average particle size of 1.5 μm is prepared and denoted as Li6MnO4 / Li2O-3.

[0050] Application Example 1 A positive electrode sheet: comprising an aluminum foil current collector and a positive electrode material coated on the surface of the aluminum foil current collector. The positive electrode material is composed of a manganese-based composite lithium supplement agent prepared in Example 1, LiFePO4, acetylene black conductive agent, and polyvinylidene fluoride (PVDF) binder; the mass ratio of the manganese-based composite lithium supplement agent, LiFePO4, acetylene black, and PVDF is 3:77:10:10; the mass ratio of LiFePO4 to the manganese-based composite lithium supplement agent is 100:3.89; and the mass of the manganese-based composite lithium supplement agent is 3% of the mass of the positive electrode material.

[0051] Method for preparing positive electrode: The manganese-based composite lithium supplementer, LiFePO4, acetylene black conductive agent, and polyvinylidene fluoride (PVDF) binder prepared in Example 1 were mixed in N-methylpyrrolidone (NMP) solvent to obtain a positive electrode slurry. The positive electrode slurry was coated on one side of an aluminum foil current collector, dried in a vacuum oven at 120°C for 6 hours, and then rolled and die-cut using a two-roller pressing method at a roll gap thickness of 10 μm and a pressure of 50t to obtain a positive electrode sheet. The solid content of the positive electrode slurry was 60%.

[0052] Application Example 2 The difference between this application example and application example 1 is that the manganese-based composite lithium supplement prepared in example 2 is used.

[0053] Application Example 3 The difference between this application example and application example 1 is that the manganese-based composite lithium supplement prepared in example 3 is used.

[0054] Application Example 4 The difference between this application example and application example 1 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 1:79:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:1.26; and the mass of the manganese-based composite lithium supplement is 1% of the mass of the cathode material.

[0055] Application Example 5 The difference between this application example and application example 1 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 5:75:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:6.66; and the mass of the manganese-based composite lithium supplement is 5% of the mass of the cathode material.

[0056] Application Example 6 The difference between this application example and application example 2 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 1:79:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:1.26; and the mass of the manganese-based composite lithium supplement is 1% of the mass of the cathode material.

[0057] Application Example 7 The difference between this application example and application example 2 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 5:75:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:6.66; and the mass of the manganese-based composite lithium supplement is 5% of the mass of the cathode material.

[0058] Application Example 8 The difference between this application example and application example 3 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 1:79:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:1.26; and the mass of the manganese-based composite lithium supplement is 1% of the mass of the cathode material.

[0059] Application Example 9 The difference between this application example and application example 3 is that the mass ratio of manganese-based composite lithium supplement, LiFePO4, acetylene black and PVDF is 5:75:10:10; the mass ratio of LiFePO4 to manganese-based composite lithium supplement is 100:6.66; and the mass of the manganese-based composite lithium supplement is 5% of the mass of the cathode material.

[0060] Comparative Application Example 1 The difference between this comparative application example and application example 1 is that the use of manganese-based composite lithium supplement is omitted, and the mass ratio of LiFePO4, acetylene black and PVDF is 80:10:10.

[0061] Test Example 1 The difference between this comparative application example and application example 1 is that the mass ratio of manganese-based composite lithium supplement, acetylene black and PVDF is 80:10:10.

[0062] Test Example 2 The difference between this comparative application example and application example 2 is that the mass ratio of manganese-based composite lithium supplement, acetylene black and PVDF is 80:10:10.

[0063] Test Example 3 The difference between this comparative application example and application example 3 is that the mass ratio of manganese-based composite lithium supplement, acetylene black and PVDF is 80:10:10.

[0064] The positive electrode sheets prepared in Application Examples 1-9, Comparative Application Example 1, and Test Examples 1-3 were assembled and pressed with the negative electrode sheet, electrolyte, and 16mm polypropylene separator to obtain a 2032 coin cell. The electrolyte was composed of 1 mol / L lithium hexafluorophosphate and a mixed solvent, wherein the mixed solvent was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0065] The 2032 coin cells prepared with positive electrode sheets corresponding to Case 1 to 9, Comparative Application Example 1, and Test Examples 1 to 3 were subjected to initial charge-discharge tests at voltages of 4.2V and 4.4V, and currents of 0.1C / 0.1C, respectively. They were also subjected to 500 charge-discharge cycles at voltages of 4.2V and 4.4V, and currents of 1C / 1C, respectively, corresponding to Case 1 to 3 and Comparative Application Example 1. The results are shown in Table 1.

[0066] Table 1. Test Results of Lithium-ion Batteries

[0067] Table 1 shows that, based on the first charge-discharge specific capacity and cycle performance data of the 2032 coin cells prepared by the cathode sheets of Application Examples 1-9 and Comparative Application Example 1, it can be seen that the lithium-ion batteries assembled with cathode sheets prepared by Application Examples 1-9 at 1%, 3%, and 5% of the cathode material mass have higher first discharge specific capacity and specific capacity retention than the lithium-ion battery assembled with cathode sheets prepared by Comparative Application Example 1 without adding manganese-based composite lithium supplementer. This is because the addition of manganese-based composite lithium supplementer can play a good role in lithium supplementation, compensating for the irreversible lithium loss during the first charge-discharge process of the lithium-ion battery, and at the same time, it plays a role in stabilizing the SEI interface and improving the long-term cycle stability of the lithium-ion battery. The 2032 coin cells prepared by the positive electrode sheets of Application Examples 1-3 and Comparative Application Example 1 were compared by conducting first charge-discharge tests at 4.2V and 4.4V respectively. It can be seen that the 2032 coin cells prepared by the positive electrode sheets of Application Examples 1-3 of the present invention have a higher first charge capacity at 4.4V, which replenishes more lithium, thereby achieving gradient lithium replenishment at different voltages.

[0068] According to the initial charge-discharge specific capacity data of Test Examples 1-3, the initial charge specific capacities at 4.2V are 453.2, 437.2, and 400.5 mAh / g, respectively; and at 4.4V, the initial charge specific capacities are 588, 623, and 674 mAh / g, respectively. This is because Li6MnO4 in the manganese-based composite lithium replenisher can release lithium at a lower voltage (4.2V); and Li2O is activated at a higher voltage (4.4V) to continue releasing lithium, thus significantly increasing the initial charge capacity. This indicates that the manganese-based composite lithium replenisher prepared in this invention can provide sufficient irreversible lithium at different voltages to meet the irreversible lithium loss of lithium-ion batteries during the first charge-discharge process.

[0069] The phase composition of the manganese-based composite lithium supplement prepared in Example 1 was analyzed using X-ray diffraction, and the results are as follows: Figure 1 As shown in the figure, the phase composition of the obtained material is a two-phase composite structure of Li6MnO4 and Li2O.

[0070] The morphology of the manganese-based composite lithium supplement prepared in Example 1 was analyzed using scanning electron microscopy, and the results are as follows: Figure 2 As shown in the figure, the particle size of the manganese-based composite lithium supplement is basically below 10 μm, and the morphology is mainly similar to single crystals.

[0071] The lithium-ion battery prepared from the positive electrode of Test Example 3 was tested for its first charge and discharge at different voltages using a button cell electrochemical testing device. The results are as follows: Figure 3 As shown in the figure, the lithium-ion battery prepared by the positive electrode in Test Example 3 has an increased specific capacity during the first charge as the voltage increases. At a voltage of 4.8 V, the specific capacity during the first charge is 935 mAh / g.

[0072] In summary, the positive electrode sheet prepared by the manganese-based composite lithium replenishing agent provided by the present invention can achieve gradient lithium replenishment under high and low voltages and has good air stability.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A manganese-based composite lithium supplement, comprising Li6MnO4 and Li2O dispersed in the interstitial spaces of the Li6MnO4 lattice; wherein the mass ratio of Li2O to Li6MnO4 is 1:(6~100).

2. The preparation method of the manganese-based composite lithium supplement according to claim 1, comprising: Manganese source and lithium source are mixed and then subjected to first sintering and second sintering in sequence to obtain manganese-based composite lithium supplement; After the first sintering is completed, the resulting product is directly cooled from the temperature of the first sintering to the temperature of the second sintering for a second sintering; the cooling rate is 10~80℃ / min.

3. The preparation method according to claim 2, characterized in that, The molar ratio of manganese in the manganese source to lithium in the lithium source is 1:(6~9).

4. The preparation method according to claim 2 or 3, characterized in that, The lithium source includes one or more of Li2O, LiOH·H2O, Li2CO3, LiNO3, Li2SO4, and CH3COOLi.

5. The preparation method according to claim 2 or 3, characterized in that, The manganese source includes one or more of Mn3O4, MnCO3, MnO2, and MnO.

6. The preparation method according to claim 2, characterized in that, The first sintering temperature is 800~1200℃, and the first sintering time is 10~20h.

7. The preparation method according to claim 2, characterized in that, The second sintering temperature is 300~700℃, and the second sintering time is 15~30h.

8. The preparation method according to claim 2, characterized in that, The atmosphere for the first sintering, cooling, and second sintering can be one or more of Ar, N2, CO, H2, Ar+5%H2, and Ar+10%H2.

9. The preparation method according to claim 2, characterized in that, The manganese source and lithium source are mixed in a ball mill; the ball milling speed is 250~1500 rpm, and the ball milling time is 3~10 h.

10. A positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, characterized in that, The positive electrode material includes a lithium active material, a manganese-based composite lithium supplement, a conductive agent, and a binder. The manganese-based composite lithium supplement is the manganese-based composite lithium supplement according to claim 1 or the manganese-based composite lithium supplement prepared by any one of claims 2 to 8.

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