Composite manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a composite manganese-based positive electrode material, a preparation method thereof and a lithium ion battery, and the composite manganese-based positive electrode material comprises a manganese-containing positive electrode material and a coating layer coated on the surface of the manganese-containing positive electrode material, and the coating layer comprises a dioxole-containing organic matter and a 2-oxazolidone-containing organic matter. The manganese-containing positive electrode material is modified by the dioxole-containing organic matter and the 2-oxazolidone-containing organic matter, and the surface of the manganese-containing positive electrode material is physically formed into a film under the action of physical adsorption, which makes the ethylene oxide free radicals in the dioxole-containing organic matter and the 2-oxazolidone in the 2-oxazolidone-containing organic matter rapidly crosslink with each other in the charging and discharging process, so that a uniform, thin and stable CEI film with small polarization degree is formed on the surface of the positive electrode material, the dissolution of manganese is effectively inhibited, the interface resistance is reduced, and the cycle and rate performance of the positive electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to a composite manganese-based cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the development of new energy vehicles, lithium-ion power batteries have attracted much attention as the most popular power batteries for electric vehicles. Among them, the research and development of cathode materials with high capacity, long life, low cost and safety and environmental protection is particularly urgent. Currently, commercially available lithium battery cathode materials mainly include layered lithium cobalt oxide, ternary materials, spinel-structured lithium manganese oxide, and olivine-structured lithium iron phosphate.

[0003] With the development of new energy vehicles, expectations for lower battery cell costs are constantly increasing. Therefore, from a material cost reduction perspective, the reduction or even elimination of cobalt is an inevitable trend. The decrease in cobalt will lead to an increase in the availability of cheaper manganese. Positive electrode materials with relatively high manganese content include lithium manganese oxide, spinel lithium nickel manganese oxide, layered lithium nickel manganese oxide, and lithium manganese iron phosphate, which are attracting increasing attention and their application is accelerating. However, during battery charging and discharging, +3 valent manganese ions exhibit the Jan Taylor effect, causing lattice distortion and leading to manganese dissolution and deposition on the negative electrode surface, damaging the solid electrolyte interphase (SEI) film. Specifically, manganese dissolution on the positive electrode surface creates a manganese-deficient phase, hindering lithium-ion diffusion during subsequent charging and discharging, resulting in increased battery polarization and capacity loss. On the negative electrode surface, Mn... 2+ Manganese diffuses to the negative electrode, where it is reduced to elemental form from the surface to the inner layer, then oxidized to divalent form, in a repeated cycle. Simultaneously, the increase in low-lithium-intercalated graphite in the negative electrode and the increased disorder on the graphite surface also promote SEI film regeneration. In summary, manganese leaching leads to the destruction of the SEI film on the negative electrode surface. The continuous regeneration and repair of the SEI film consumes a large amount of active lithium, causing rapid degradation of cell life and severe gas generation.

[0004] To address the above issues, various modification methods exist, such as bulk doping and surface doping during the cathode material preparation process, and the introduction of other transition metals (V / Mg / Fe / Zn, etc.) to improve the ionic conductivity and reduce the polarization of the material, especially since the size of Mg ions is between that of Mn. 2+ / Mn 3+In the process of transitioning between divalent and trivalent manganese, the structural collapse caused by manganese transformation can be mitigated, stabilizing the material structure and inhibiting manganese dissolution. For example, CN115810733A discloses a carbon-based coating modification treatment for lithium manganese iron phosphate (LMFP), which can significantly improve the electronic conductivity of the material, reduce polarization, and slow down the dissolution of manganese ions. Another example is the electrolyte solution with a special formulation. CN111864270B discloses a non-aqueous electrolyte, including formulations such as LiDFOB+PS, which can better form a film on the positive electrode surface, reducing battery impedance and reducing gas generation during cell cycling. CN114709412A also discloses a high-temperature resistant positive electrode material and electrolyte combination, a lithium battery, and a preparation method. The functional additives in the electrolyte include LiPF6+VC, which reduces interfacial resistance through VC coating film formation.

[0005] However, the above methods all have some limitations. For example, the doping components of the cathode material are mostly inorganic and carbon materials, and organic materials are rarely used for coating modification. Electrolyte modification methods are mostly to form a film on the cathode surface through complex electrolyte additives in the pre-charge formation process after battery injection, thereby reducing the corrosion between HF and the cathode material surface and preventing the collapse and deterioration of the material structure. However, the film formation mechanism of the material surface inside the battery is still inconclusive, and the reaction sequence and degree of reaction completion of the additives are highly uncertain. Although VC coating of the cathode film can improve the cathode interface resistance to a certain extent and is an innovative method different from the conventional one, the VC is prone to oxidation and decomposition when the ambient temperature exceeds 80°C during the addition process, resulting in low VC utilization and slightly high interface resistance.

[0006] Therefore, developing manganese-based cathode materials with low interfacial resistance while suppressing manganese dissolution is an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a composite manganese-based cathode material, its preparation method, and a lithium-ion battery. The present invention modifies the surface of the manganese-containing cathode material using organic compounds containing dioxacyclopentene and 2-oxazolidinone. Under the action of physical adsorption, a physical film forms on the surface of the manganese-containing cathode material. This allows for rapid cross-linking between the ethylene oxide radicals in the dioxacyclopentene-containing organic compound and the 2-oxazolidinone in the 2-oxazolidinone-containing organic compound during charge and discharge. This results in the formation of a highly uniform, thin, and stable CEI film on the cathode material surface, characterized by low polarization, effectively inhibiting manganese dissolution, reducing interfacial resistance, and thus improving the cycle and rate performance of the cathode material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a composite manganese-based cathode material, the composite manganese-based cathode material comprising a manganese-containing cathode material and a coating layer covering the surface of the manganese-containing cathode material, the coating layer comprising an organic compound containing dioxane and an organic compound containing 2-oxazolidinone.

[0010] This invention modifies the surface of manganese-containing cathode materials using organic compounds containing dioxane and 2-oxazolidinone. Under the action of physical adsorption, a physical film is formed on the surface of the manganese-containing cathode material. This allows the ethylene oxide free radicals in the dioxane-containing organic compounds to rapidly cross-link with the 2-oxazolidinone in the 2-oxazolidinone-containing organic compounds during charge and discharge. As a result, a highly uniform, thin, and stable cathode-electrolyte interface (CEI) film with low polarization is formed on the surface of the cathode material. This effectively inhibits the dissolution of manganese, reduces the interfacial resistance, and thus improves the cycle and rate performance of the cathode material.

[0011] Preferably, the manganese-containing cathode material includes any one of lithium manganese oxide cathode material, lithium nickel manganese oxide cathode material, lithium nickel manganese oxide cathode material, or lithium manganese iron phosphate cathode material.

[0012] Preferably, the mass ratio of the dioxacyclopentene-containing organic compound to the 2-oxazolidinone-containing organic compound is (1-10):(1-100), wherein the range of the dioxacyclopentene-containing organic compound "1-10" can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, and the range of the 2-oxazolidinone-containing organic compound "1-100" can be, for example, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100, preferably 1:1.

[0013] In this invention, if the mass ratio of the organic compound containing dioxane to the organic compound containing 2-oxazolidinone is too small, the composite coating effect will be poor; if the mass ratio of the organic compound containing dioxane to the organic compound containing 2-oxazolidinone is too large, the excess components will react with the manganese-containing cathode material, reducing the cathode's specific capacity.

[0014] Preferably, the organic compound containing 2-oxazolidinone also contains a silicon group.

[0015] In this invention, the silicon group structure in the organic compound containing 2-oxazolidinone and silicon group can act as an acid remover, react with HF to generate SiF4 product, suppress HF attack on the positive electrode surface, maintain the stability of the positive electrode structure, and suppress the dissolution of transition metals.

[0016] Preferably, the 2-oxazolidinone-containing organic compound includes any one or a combination of at least two of 3-trimethylsilyl-2-oxazolidinone, (R)-4-methyl-2-oxazolidinone, (S)-4-phenyloxazolidinone, 3(2-1-propenyl)-2-oxazolidinone, 5-(3,5-dimethylphenoxy)methyl-2-oxazolidinone, 3-isopropyl-2-oxazolidinone, 5-(5-bromo-2-pyridyl)-3-methyl-2-oxazolidinone, or (S)-4-ethyl-2-oxazolidinone, preferably 3-trimethylsilyl-2-oxazolidinone.

[0017] Preferably, the thickness of the coating layer is 1-100nm, for example, it can be 1nm, 5nm, 10nm, 30nm, 50nm, 70nm, 90nm or 100nm, etc., preferably 1-10nm, and more preferably 5nm.

[0018] In this invention, if the thickness of the coating layer is too small, more precise process conditions, equipment accuracy and operation methods are required, and the subsequent process cost is too high; if the thickness of the coating layer is too large, the internal resistance is high and polarization voltage is easily generated, which affects the rate performance of the cell.

[0019] Secondly, the present invention provides a method for preparing a composite manganese-based cathode material, the method comprising the following steps:

[0020] The composite coating agent and manganese-containing cathode material are mixed and then heat-treated to obtain the composite manganese-based cathode material.

[0021] The composite coating agent includes organic compounds containing dioxane and organic compounds containing 2-oxazolidinone.

[0022] This invention modifies the surface of manganese-containing cathode materials using a composite coating agent, enabling more uniform film formation in advance. Specifically, a uniform physical film is formed on the cathode surface before chemical film formation, although no new chemical bonds are present; the process is primarily physical adsorption. While the reaction potential affects the reaction priority of additives and the degree of reaction completion is influenced by additive concentration and location, at the same trigger potential, the film formed on the surface of the cathode active material is more uniform, has a higher molecular concentration, and a shorter reaction path.

[0023] During the charge-discharge process, the composite manganese-based cathode material prepared by this invention allows for rapid free radical polymerization of dioxacyclopentene-containing organic compounds and 2-oxazolidinone-containing organic compounds. Specifically, the ethylene oxide free radicals in the dioxacyclopentene-containing organic compounds crosslink with the 2-oxazolidinone-containing organic compounds, thereby forming a highly uniform, thin, and stable CEI film on the surface of the cathode material. This not only inhibits the dissolution of manganese and other transition metals and reduces interfacial resistance, but also effectively improves the cycle and rate performance of the cathode material and enhances its stability.

[0024] Preferably, based on the mass of the manganese-containing cathode material, the mass content of the composite coating agent is 0.01-5 wt.%, for example, it can be 0.01 wt.%, 0.05 wt.%, 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, or 5 wt.%.

[0025] In this invention, if the mass content of the composite coating agent is too low, the CEI film construction will be unstable, the electrolyte solvent will be oxidized, the battery will produce gas, and the cycle and high-temperature capabilities will decrease; if the mass content of the composite coating agent is too high, after the CEI is constructed, the positive electrode surface side reaction is likely to occur, affecting the specific capacity and cycle performance of the positive electrode material.

[0026] Preferably, the mixing method includes the following steps:

[0027] (a) A manganese-containing cathode material and an organic solvent are mixed to obtain a first dispersion;

[0028] (b) The composite coating agent and the first dispersion are mixed to obtain a second dispersion;

[0029] (c) The second dispersion is dispersed to obtain a third dispersion.

[0030] Preferably, the organic solvent in step (a) includes any one or a combination of at least two of N-methylpyrrolidone, ethanol, or acetone.

[0031] Preferably, the mixing process in step (a) is accompanied by stirring for 1-3 hours, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, preferably 1 hour.

[0032] Preferably, the mixing process in step (b) is accompanied by stirring.

[0033] Preferably, the mixing method in step (b) includes ultrasonic dispersion.

[0034] Preferably, the mixing time in step (b) is 15-45 min, for example, it can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min or 45 min, etc., preferably 30 min.

[0035] Preferably, the dispersion rate in step (c) is 800-1200 rpm, for example, it can be 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm, and preferably 1000 rpm.

[0036] Preferably, the dispersion time in step (c) is 15-45 min, for example, it can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min or 45 min, etc., preferably 30 min.

[0037] Preferably, the heat treatment temperature is 180-250℃, for example, it can be 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃. The present invention does not limit the method of heat treatment; for example, it can be spray drying.

[0038] In this invention, if the heat treatment temperature is too low, the solvent will not evaporate completely, affecting the particle size of the product and the specific capacity. If the heat treatment temperature is too high, the equipment requirements will be higher, and the coating agent may dry quickly, easily shrinking into clumps, which is not conducive to the uniform distribution of the coating agent, resulting in local uncoated areas and excessively thick coatings, thus reducing the overall coating effect.

[0039] Preferably, the heat treatment time is 0.5-3 hours, for example, it can be 0.5 hours, 1 hour, 2 hours or 3 hours.

[0040] As a preferred technical solution, the preparation method includes the following steps:

[0041] (I) Mix the manganese-containing cathode material and organic solvent under stirring for 1-3 hours to obtain the first dispersion;

[0042] (II) The composite coating agent and the first dispersion are mixed and stirred under ultrasonic dispersion for 15-45 min to obtain the second dispersion;

[0043] The composite coating agent, based on the mass of the manganese-containing cathode material, has a mass content of 0.01-5 wt.%, and the composite coating agent includes organic compounds containing dioxane and organic compounds containing 2-oxazolidinone in a mass ratio of (1-10):(1-100).

[0044] (III) The second dispersion is dispersed and stirred at a speed of 800-1200 rpm for 15-45 min to obtain the third dispersion;

[0045] (IV) The third dispersion is subjected to heat treatment at 180-260℃ for 0.5-3h to obtain the composite manganese-based cathode material.

[0046] Thirdly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises a composite manganese-based positive electrode material as described in the first aspect.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) This invention modifies the surface of manganese-containing cathode materials using a composite coating agent, enabling more uniform film formation in advance. That is, a uniform physical film is formed on the cathode surface before chemical film formation, but no new chemical bonds exist yet; it is more of a physical adsorption process. Although the reaction potential also affects the reaction priority of the additives and the degree of reaction completion is affected by the additive concentration and distribution location, at the same trigger potential, the film formed on the surface of the cathode active material is more uniform, has a higher molecular concentration, and a shorter reaction path.

[0050] (2) During the charging and discharging process, the organic compounds containing dioxane and 2-oxazolidinone in the composite manganese-based cathode material provided by the present invention can undergo rapid free radical polymerization. The ethylene oxygen free radicals in the organic compounds containing dioxane crosslink with the 2-oxazolidinone in the organic compounds containing 2-oxazolidinone, thereby forming a highly uniform, thin and stable CEI film on the surface of the cathode material. This not only inhibits the dissolution of manganese and other transition metals and reduces the interfacial resistance, but also effectively improves the cycle and rate performance of the cathode material and enhances the stability of the cathode material. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the mechanism of the free radical polymerization reaction that occurs during the charging and discharging process of the composite manganese-based cathode material provided in Example 1 of the present invention. Detailed Implementation

[0052] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0053] Example 1

[0054] This embodiment provides a manganese-based composite cathode material, which includes a manganese-containing cathode material and a coating layer covering the surface of the manganese-containing cathode material. The coating layer includes an organic compound containing dioxane and an organic compound containing 2-oxazolidinone.

[0055] The coating layer has a thickness of 50 nm, the manganese-containing cathode material is lithium manganese iron phosphate cathode material, the dioxane-containing organic compound is vinylene carbonate, the 2-oxazolidinone-containing organic compound is 3-trimethylsilyl-2-oxazolidinone, and the mass ratio of vinylene carbonate to 3-trimethylsilyl-2-oxazolidinone is 1:1.

[0056] This embodiment provides a method for preparing a composite manganese-based cathode material, the method comprising the following steps:

[0057] (1) The lithium manganese iron phosphate cathode material and organic solvent were mixed under stirring for 2 hours to obtain the first dispersion;

[0058] The organic solvent is N-methylpyrrolidone;

[0059] (2) The composite coating agent and the first dispersion are mixed and stirred for 30 min under ultrasonic dispersion to obtain the second dispersion;

[0060] Among them, based on the mass of lithium manganese iron phosphate cathode material, the mass content of composite coating agent is 2 wt.%, and the composite coating agent includes vinylene carbonate and 3-trimethylsilyl-2-oxazolidinone;

[0061] (3) The second dispersion was dispersed and stirred at 1000 rpm for 30 min to obtain the third dispersion;

[0062] (4) The third dispersion was spray-dried at 220°C for 2 hours with an air velocity of 80% and a pump speed of 30% to obtain the composite manganese-based cathode material.

[0063] Example 2

[0064] This embodiment provides a composite manganese-based cathode material, which includes a manganese-containing cathode material and a coating layer covering the surface of the manganese-containing cathode material. The coating layer includes an organic compound containing dioxane and an organic compound containing 2-oxazolidinone.

[0065] The coating layer has a thickness of 10 nm, the manganese-containing cathode material is lithium manganese iron phosphate cathode material, the dioxane-containing organic compound is vinylene carbonate, the 2-oxazolidinone-containing organic compound is 3-isopropyl-2-oxazolidinone, and the mass ratio of vinylene carbonate to 3-isopropyl-2-oxazolidinone is 1:1.1.

[0066] This embodiment provides a method for preparing a composite manganese-based cathode material, the method comprising the following steps:

[0067] (1) The lithium manganese iron phosphate cathode material and organic solvent were mixed under stirring for 1 hour to obtain the first dispersion;

[0068] The organic solvent is N-methylpyrrolidone;

[0069] (2) The composite coating agent and the first dispersion were mixed and stirred for 45 min under ultrasonic dispersion to obtain the second dispersion;

[0070] Among them, based on the mass of lithium manganese iron phosphate cathode material, the mass content of composite coating agent is 1 wt.%, and the composite coating agent includes vinylene carbonate and 3-isopropyl-2-oxazolidinone;

[0071] (3) The second dispersion was dispersed and stirred at 800 rpm for 45 min to obtain the third dispersion;

[0072] (4) The third dispersion was spray-dried at 180°C for 1 hour with an air velocity of 80% and a pump speed of 30% to obtain the composite manganese-based cathode material.

[0073] Example 3

[0074] This embodiment provides a composite manganese-based cathode material, which includes a manganese-containing cathode material and a coating layer covering the surface of the manganese-containing cathode material. The coating layer includes an organic compound containing dioxane and an organic compound containing 2-oxazolidinone.

[0075] The coating layer has a thickness of 100 nm, the manganese-containing cathode material is lithium manganese iron phosphate cathode material, the dioxane-containing organic compound is vinylene carbonate, the 2-oxazolidinone-containing organic compound is (R)-4-methyl-2-oxazolidinone, and the mass ratio of vinylene carbonate to (R)-4-methyl-2-oxazolidinone is 1:0.9.

[0076] This embodiment provides a method for preparing a composite manganese-based cathode material, the method comprising the following steps:

[0077] (1) The lithium manganese iron phosphate cathode material and organic solvent were mixed under stirring for 3 hours to obtain the first dispersion;

[0078] The organic solvent is N-methylpyrrolidone;

[0079] (2) The composite coating agent and the first dispersion are mixed and stirred for 15 minutes under ultrasonic dispersion to obtain the second dispersion;

[0080] Among them, based on the mass of lithium manganese iron phosphate cathode material, the mass content of composite coating agent is 5 wt.%, and the composite coating agent includes vinylene carbonate and (R)-4-methyl-2-oxazolidinone;

[0081] (3) The second dispersion was dispersed and stirred at 1200 rpm for 15 min to obtain the third dispersion;

[0082] (4) The third dispersion was spray-dried at 250°C for 2 hours with an air velocity of 80% and a pump speed of 30% to obtain the composite manganese-based cathode material.

[0083] Example 4

[0084] The difference between this embodiment and Example 1 is that the mass ratio of vinylene carbonate and 3-trimethylsilyl-2-oxazolidinone in step (2) is 12:1.

[0085] The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 5

[0087] The difference between this embodiment and embodiment 1 is that the mass ratio of vinylene carbonate and 3-trimethylsilyl-2-oxazolidinone in step (2) is 1:105.

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Example 6

[0090] The difference between this embodiment and Embodiment 1 is that the mass content of the composite coating agent in step (2) is 0.005 wt.%.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Example 7

[0093] The difference between this embodiment and embodiment 1 is that the mass content of the composite coating agent in step (2) is 7 wt.%.

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 8

[0096] The difference between this embodiment and embodiment 1 is that step (2) is replaced with the following steps:

[0097] First, vinylene carbonate and the first dispersant are ultrasonically dispersed and mixed for 15 minutes. Then, 3-trimethylsilyl-2-oxazolidinone is added and ultrasonically dispersed and mixed for 15 minutes to obtain the second dispersion.

[0098] The remaining preparation methods and parameters are consistent with those in Example 1.

[0099] Example 9

[0100] The difference between this embodiment and embodiment 1 is that the spray drying temperature in step (4) is 150°C.

[0101] The remaining preparation methods and parameters are consistent with those in Example 1.

[0102] Example 10

[0103] The difference between this embodiment and embodiment 1 is that the spray drying temperature in step (4) is 258°C.

[0104] The remaining preparation methods and parameters are consistent with those in Example 1.

[0105] Example 11

[0106] The difference between this embodiment and Embodiment 1 is that the thickness of the coating layer is 50 nm.

[0107] The remaining preparation methods and parameters are consistent with those in Example 1.

[0108] Example 12

[0109] The difference between this embodiment and Embodiment 1 is that the thickness of the coating layer is 500 nm.

[0110] The remaining preparation methods and parameters are consistent with those in Example 1.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that the composite coating agent in step (2) is replaced with vinylene carbonate.

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is that the composite coating agent in step (2) is replaced with 3-trimethylsilyl-2-oxazolidinone.

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is that step (2) is not performed, i.e., no composite coating agent is added.

[0119] The remaining preparation methods and parameters are consistent with those in Example 1.

[0120] Performance testing

[0121] The manganese-based composite cathode materials provided in Examples 1-12 and Comparative Examples 1-3 were homogenized with conductive agent SP (i.e., conductive carbon black) and binder PVDF (i.e., polyvinylidene fluoride) at a mass ratio of 92:4:4. After coating, the mixture was dried to obtain electrode sheets coated with the corresponding active materials, with a compaction density of 2.2 g / cm³. 3 The negative electrode uses a 600um thick lithium sheet, with the corresponding electrolyte added, and is assembled into a 2032 coin cell, packaged and tested.

[0122] Cyclic performance test conditions: Within the 2.0V-4.35V range, at 0.1CC / 0.1CD, first maintain a constant current of CC+CV, i.e., first charge at a constant current of 0.1C to 4.35V, then maintain a constant voltage of 4.35V until the current is less than 0.05C. Discharge is also performed first at a constant current, then at a constant voltage of 2.0V until the current is less than 0.05C. After two charge / discharge cycles according to the above requirements, switch to 1.0CC / 1.0CD, and continue cycling for 50 cycles before removing the clasp.

[0123] Rate performance test conditions: Within the 2.0V-4.35V range, at 0.1CC / 0.1CD, first maintain a constant current of CC+CV, i.e., first charge at a constant current of 0.1C to 4.35V, then maintain a constant voltage of 4.35V until the current is less than 0.05C. Discharge is also performed first at a constant current, then at a constant voltage of 2.0V until the current is less than 0.05C. Following these requirements, after two charge / discharge cycles, switch to 1.0CC / 1.0CD; after two charge / discharge cycles, switch to 2.0CC / 2.0CD; after two charge / discharge cycles, switch to 3.0CC / 3.0CD. Maintain 3C cycles for 50 cycles and record the 3C capacity retention rate.

[0124] Test results are as follows Figure 1 As shown in Table 1.

[0125] Figure 1The diagram illustrates the mechanism of free radical polymerization of the composite manganese-based cathode material in Example 1. As shown, vinylene carbonate loses electrons on the cathode surface, breaking the carbon-oxygen single bond (CO) of the carbon-oxygen double bond (C=O), resulting in an open-ring chain of free radical products. These further dissociate to produce ethylene oxide free radical intermediates and carbon dioxide gas. The resulting products react with different solvents to produce different products, significantly impacting the CEI film. When exposed to vinylene carbonate, it polymerizes into a vinyl ethylene carbonate polymer on the cathode surface, forming an organic layer. This organic layer then gradually differentiates into a lower inorganic layer and an upper porous organic layer CEI film during continuous electron loss. When exposed to oxazolidinone, the vinyl free radicals attack the oxazolidinone, causing the CO single bond to break and the ring to open, forming a polymer with a stronger amide group. This polymer forms a film on the cathode surface, creating the lower inorganic CEI film earlier, which promotes early and complete CEI stability, inhibits contact between the electrolyte and the cathode surface, and reduces gas production and side reactions.

[0126] Table 1

[0127] Example 1 98.0％ 95.1％ Example 2 98.2％ 92.3％ Example 3 94.2％ 96.3％ Example 4 92.6％ 91.2％ Example 5 93.3％ 92.4％ Example 6 93.9％ 95.5％ Example 7 94.4％ 91.7％ Example 8 91.7％ 89.3％ Example 9 95.8％ 96.1％ Example 10 96.6％ 94.2％ Example 11 98.8％ 96.2％ Example 12 97.3％ 93.7％ Comparative Example 1 90.3％ 89.7％ Comparative Example 2 91.9％ 94.6％ Comparative Example 3 88.2％ 85.1％

[0128] EIS test:

[0129] The EIS test conditions include: starting the test on an electrochemical workstation on the 4th cycle after coin cell formation with a small current, while maintaining 50% SOC; and immediately performing impedance measurements after cycling at a potential amplitude of 5mV in the frequency range of 100kHz to 10mHz.

[0130] The EIS test results after 50 cycles of tethering are shown in Table 2.

[0131] Table 2

[0132]

[0133] ICP element test:

[0134] The method for ICP elemental testing includes the following steps: (1) Disassemble the battery, remove the lithium metal negative electrode, and rinse it repeatedly with dimethyl carbonate solvent three times to remove the lithium salt and solvent on the surface; (2) Place the lithium sheet with metal deposits into 25 mL of dilute nitric acid solution with a mass concentration of 4% for digestion to obtain the corresponding solution; (3) Perform ICP injection testing on the digested solution to obtain the corresponding elemental results.

[0135] ICP tests were performed on the negative electrode before battery cycling and when the battery was cycled to 70% capacity decay. The test results are shown in Table 3.

[0136] Table 3

[0137]

[0138] analyze:

[0139] As shown in Tables 1, 2, and 3, this invention modifies the surface of manganese-containing cathode materials using a composite coating agent. Under the action of physical adsorption, a physical film is formed on the surface of the manganese-containing cathode material. This allows the ethylene oxide free radicals in dioxacyclopentene-containing organic compounds and the 2-oxazolidinone in 2-oxazolidinone-containing organic compounds to rapidly undergo cross-linking reactions during charging and discharging. This results in the formation of a highly uniform, thin, and stable CEI film on the surface of the cathode material, which effectively inhibits the dissolution of manganese, reduces interfacial resistance, and thus improves the cycle and rate performance of the cathode material.

[0140] A comparison of the data results from Examples 1 and 4-5 shows that if the mass ratio of vinylene carbonate to 3-trimethylsilyl-2-oxazolidinone is too small, the composite coating effect will be poor, reducing the specific capacity of the cathode; if the mass ratio of vinylene carbonate to 3-trimethylsilyl-2-oxazolidinone is too large, the excess vinylene carbonate will react with the manganese-containing cathode material, reducing the specific capacity of the cathode.

[0141] A comparison of the data results from Examples 1 and 6-7 shows that if the mass content of the composite coating agent is too low, the CEI film will be unstable, resulting in the oxidation of the electrolyte solvent, gas generation in the battery, and a decrease in cycle and high-temperature performance. If the mass content of the composite coating agent is too high, side reactions on the cathode surface will easily occur, thereby affecting the specific capacity and cycle performance of the cathode material.

[0142] A comparison of the data results from Example 1 and Example 8 shows that if vinylene carbonate and 3-trimethylsilyl-2-oxazolidinone are added sequentially, vinylene carbonate and 3-trimethylsilyl-2-oxazolidinone cannot be evenly dispersed first, and the subsequent reaction may result in localized uneven concentrations, increasing the individual coating reaction between the two and the positive electrode surface and reducing the efficiency of the coating reaction.

[0143] A comparison of the data results from Examples 1 and 9-10 shows that if the heat treatment temperature is too low, the solvent will not evaporate completely, affecting the particle size of the product and the specific capacity. If the heat treatment temperature is too high, the equipment requirements will be higher, and the coating agent may dry quickly, easily shrinking into clumps, which is not conducive to the uniform distribution of the coating agent, resulting in some areas not being coated or the coating being too thick, thus reducing the overall coating effect.

[0144] A comparison of the data results from Example 1 and Examples 11-12 shows that a smaller coating thickness requires more precise process conditions, equipment accuracy, and operating methods, resulting in excessively high subsequent process costs; while a larger coating thickness results in higher internal resistance and is prone to generating polarization voltage, affecting the rate performance of the battery cell.

[0145] A comparison of the data results from Example 1 and Comparative Example 1 shows that if only vinylene carbonate is used as a coating agent, there are more side reactions and the inhibition of ion dissolution is limited.

[0146] A comparison of the data results from Example 1 and Comparative Example 2 shows that if only 3-trimethylsilyl-2-oxazolidinone is used as the coating agent, there will be more side reactions on the positive electrode surface, the inorganic layer will be too thick, the wettability will be poor, and the rate and cycle performance will decrease.

[0147] A comparison of the data results from Example 1 and Comparative Example 3 shows that if the manganese-containing cathode material is not coated, the ion dissolution phenomenon is particularly serious, the gas generation is serious, and the capacity, cycle and rate performance are all poor.

[0148] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite manganese-based positive electrode material, characterized in that, The composite manganese-based cathode material includes a manganese-containing cathode material and a coating layer covering the surface of the manganese-containing cathode material. The coating layer includes organic compounds containing dioxane and organic compounds containing 2-oxazolidinone.

2. The composite manganese-based cathode material of claim 1, wherein, The manganese-containing cathode material includes any one of lithium manganese oxide cathode material, lithium nickel manganese oxide cathode material, or lithium manganese iron phosphate cathode material.

3. The composite manganese-based cathode material of claim 1, wherein, The mass ratio of the organic compound containing dioxacyclopentene to the organic compound containing 2-oxazolidinone is (1-10):(1-100).

4. The composite manganese-based cathode material of claim 1, wherein, The dioxacyclopentene-containing organic compounds include any one or a combination of at least two of vinylene carbonate, 4,5-dimethyl-1,3-dioxacyclopenten-2-one, 4-chloromethyl-5-methyl-1,3-dioxacyclopenten-2-one, or 4-bromomethyl-5-methyl-1,3-dioxacyclopenten-2-one.

5. The composite manganese-based cathode material of claim 1, wherein, The organic compound containing 2-oxazolidinone also contains silicon groups.

6. The composite manganese-based cathode material of claim 1, wherein, The organic compounds containing 2-oxazolidinone include any one or a combination of at least two of the following: 3-trimethylsilyl-2-oxazolidinone, (R)-4-methyl-2-oxazolidinone, (S)-4-phenyloxazolidinone, 3(2-1-propenyl)-2-oxazolidinone, 5-(3,5-dimethylphenoxy)methyl-2-oxazolidinone, 3-isopropyl-2-oxazolidinone, 5-(5-bromo-2-pyridyl)-3-methyl-2-oxazolidinone, or (S)-4-ethyl-2-oxazolidinone.

7. The composite manganese-based cathode material according to claim 6, characterized in that, The organic compound containing 2-oxazolidinone is 3-trimethylsilyl-2-oxazolidinone.

8. The composite manganese-based cathode material of claim 1, wherein, The thickness of the coating layer is 1-100 nm.

9. The composite manganese-based positive electrode material according to claim 8, characterized in that, The thickness of the coating layer is 1-10 nm.

10. A method of producing the composite manganese-based positive electrode material according to any one of claims 1 to 9, characterized by, The preparation method includes the following steps: The composite coating agent and manganese-containing cathode material are mixed and then heat-treated to obtain the composite manganese-based cathode material. The composite coating agent includes organic compounds containing dioxane and organic compounds containing 2-oxazolidinone.

11. The method of claim 10, wherein, Based on the mass of the manganese-containing cathode material, the mass content of the composite coating agent is 0.01-5 wt.%.

12. The method of claim 10, wherein, The mixing method includes the following steps: (a) The manganese-containing cathode material and an organic solvent are mixed to obtain a first dispersion; (b) The composite coating agent and the first dispersion are mixed to obtain a second dispersion; (c) The second dispersion is dispersed to obtain a third dispersion.

13. The preparation method according to claim 12, characterized in that, The organic solvent in step (a) includes any one or a combination of at least two of N-methylpyrrolidone, ethanol, or acetone.

14. The preparation method according to claim 12, characterized in that, The mixing process in step (a) is accompanied by stirring, and the stirring time is 1-3 hours.

15. The preparation method according to claim 12, characterized in that, The mixing process described in step (b) is accompanied by stirring.

16. The preparation method according to claim 12, characterized in that, The mixing method described in step (b) includes ultrasonic dispersion.

17. The preparation method according to claim 12, characterized in that, The mixing time in step (b) is 15-45 minutes.

18. The preparation method according to claim 12, characterized in that, The dispersion rate in step (c) is 800-1200 rpm.

19. The preparation method according to claim 12, characterized in that, The dispersion time in step (c) is 15-45 minutes.

20. The preparation method according to claim 10, characterized in that, The heat treatment temperature is 180-250℃.

21. The preparation method according to claim 10, characterized in that, The heat treatment time is 0.5-3 hours.

22. The preparation method according to claim 12, characterized in that, The preparation method includes the following steps: (I) The manganese-containing cathode material and organic solvent are mixed under stirring for 1-3 hours to obtain the first dispersion; (II) The composite coating agent and the first dispersion are mixed and stirred under ultrasonic dispersion for 15-45 min to obtain the second dispersion; The composite coating agent, based on the mass of the manganese-containing cathode material, has a mass content of 0.01-5 wt.%, and the composite coating agent includes organic compounds containing dioxane and organic compounds containing 2-oxazolidinone in a mass ratio of (1-10):(1-100). (III) The second dispersion is dispersed and stirred at a speed of 800-1200 rpm for 15-45 min to obtain the third dispersion; (IV) The third dispersion is heat-treated at 180-250℃ for 0.5-3h to obtain the composite manganese-based cathode material.

23. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes a composite manganese-based positive electrode material as described in any one of claims 1-9.

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