Composite material, positive pole piece, battery and manufacturing method

Abstract

The invention provides a composite material, a positive pole piece, a battery and a manufacturing method. Specifically, the composite material comprises lithium nickel manganese spinel, a first coating layer and a second coating layer located on the side, away from the lithium nickel manganese spinel, of the first coating layer; wherein the first coating layer comprises LiF (lithium fluoride); the second coating layer comprises Li < 7-x > La < 3 > Zr < 2-x > M < x > O < 12 >, M is at least one of Ta and Nb, and x is larger than or equal to 0 and smaller than 0.7. According to the composite material, the first coating layer and the second coating layer are matched, so that the high-temperature cycle life of the lithium nickel manganese spinel in a high-temperature environment is prolonged, and the high-pressure potential of the lithium nickel manganese spinel is realized.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to a composite material, a positive electrode, a battery, and a method for manufacturing the same. Background Technology

[0002] Lithium nickel manganese spinel (LNMO) is prized for its high voltage (~4.7 V vs. Li). + With its high cost (cobalt-free) and good rate performance, LNMO is considered one of the ideal cathode materials for next-generation high-energy-density batteries. The spinel structure of LNMO provides 3D lithium-ion diffusion channels, supporting rapid charge-discharge (above 5C), making it suitable for scenarios requiring high power output, such as fast charging for electric vehicles and drone batteries. Compared to "high-nickel, low-cobalt" layered oxide cathode materials, LNMO is cobalt-free, resulting in lower raw material costs and making it more suitable for large-scale energy storage and power battery applications. Furthermore, the spinel structure is more stable than layered oxides, with a lower risk of thermal runaway, making it suitable for long-term energy storage requirements. Currently, the large-scale commercialization of lithium nickel manganese spinel still faces challenges such as interface stability, manganese dissolution, and electrolyte matching. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide a composite material, a positive electrode, a battery, and a method for manufacturing the same.

[0004] To achieve the above objectives, a first aspect of this disclosure provides a composite material comprising lithium nickel manganese spinel, a first coating layer, and a second coating layer located on the side of the first coating layer away from the lithium nickel manganese spinel; wherein... The first coating layer comprises LiF; the second coating layer comprises Li 7-x La3Zr 2-x M x O 12 , where M is at least one of Ta and Nb, and 0 ≤ x < 0.7.

[0005] In some embodiments, the first coating layer further includes at least one of Li2ZrO3, LiNbO3, Li3PO4, and Li3BO3; and / or The second coating layer also includes Li 1+y Al y Ti 2-y (PO4)3, Li 1+z Al z Ge 2-z (PO4)3 and Li 3n La 2 / 3-n At least one of TiO3; wherein 0 < y < 2, 0 < z < 2, 0 < n < 0.16.

[0006] In some embodiments, the mass fraction of LiF in the first coating layer is ≥80%; and / or Li in the second coating layer 7-x La3Zr 2-x M x O 12 The quality fraction is ≥80%.

[0007] In some embodiments, the thickness of the first coating layer is 2-6 nm; and / or The thickness of the second coating layer is 2~6nm.

[0008] In some embodiments, the Li 7-x La3Zr 2-x M x O 12 Including Li7La3Zr2O 12 .

[0009] Based on the same inventive concept, a second aspect of this disclosure also provides a method for manufacturing any of the aforementioned composite materials, comprising: The nickel-manganese hydroxide precursor and lithium carbonate are mixed and then subjected to a first sintering, followed by a first crushing to obtain the first powder. The first powder and the material of the first coating layer are mixed evenly and then subjected to a second sintering, followed by a second crushing to obtain the second powder. The second powder and the material of the second coating layer are mixed and then subjected to a third sintering, followed by a third crushing to obtain the composite material.

[0010] In some embodiments, the first sintering condition is sintering at 850~950°C for 9~11 hours; and / or The second sintering condition is sintering at 400~500℃ for 5~7 hours; and / or The third sintering condition is sintering at 300~400℃ for 5~7 hours.

[0011] In some embodiments, the mass ratio of the material of the first coating layer to the first powder is 1000~2000 ppm; and / or The mass ratio of the material of the second coating layer to the second powder is 1000~2000ppm.

[0012] Based on the same inventive concept, a third aspect of this disclosure also provides a positive electrode sheet, comprising the composite material described in any of the preceding claims or the composite material obtained by the manufacturing method described in any of the preceding claims.

[0013] Based on the same inventive concept, the fourth aspect of this disclosure also provides a battery, including any of the aforementioned positive electrode plates.

[0014] As can be seen from the above description, this disclosure provides a composite material, a positive electrode sheet, a battery, and a manufacturing method. The composite material includes lithium nickel manganese spinel, a first coating layer, and a second coating layer located on the side of the first coating layer away from the lithium nickel manganese spinel. The first coating layer includes LiF; the second coating layer includes Li 7-x La3Zr 2- x M x O 12 Where M is at least one of Ta and Nb, and 0 ≤ x < 0.7. Such a composite material, employing a combination of a first coating layer and a second coating layer, helps to improve the high-temperature cycle life of lithium nickel manganese spinel in high-temperature environments and realize the high-pressure potential of lithium nickel manganese spinel. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0016] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0017] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~130 and 70~120 are listed for a specific parameter, it is expected that ranges of 60~120 and 70~130 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this disclosure, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0018] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0019] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0020] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0021] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0022] Terminology Explanation Solid-state electrolytes (SSEs) are a class of electrolytes that can conduct lithium ions (Li-ions) in a solid state. + ) or other charge carriers (such as Na) + Mg² + Materials are the core components of all-solid-state batteries (ASSBs).

[0023] As described in the background section, lithium nickel manganese spinel still faces challenges in its large-scale commercialization, including interface stability, manganese dissolution, and electrolyte compatibility. Specifically, lithium nickel manganese spinel readily reacts with the electrolyte at voltages >4.5V, leading to manganese dissolution and capacity decay. Furthermore, as a manganese-based cathode material, lithium nickel manganese spinel inevitably undergoes manganese dissolution and structural phase transitions during battery charge-discharge cycles, damaging the electrode structure. This structural damage results in a significant decrease in lifespan, which is particularly pronounced at high temperatures.

[0024] In view of this, the present disclosure provides a composite material, a positive electrode sheet, a battery, and a method for manufacturing the same. The composite material includes lithium nickel manganese spinel, a first coating layer, and a second coating layer located on the side of the first coating layer away from the lithium nickel manganese spinel. The first coating layer includes LiF, and the second coating layer includes Li 7-x La3Zr 2- x M x O 12 Where M is at least one of Ta and Nb, and 0 ≤ x < 0.7. Such a composite material, employing a combination of a first coating layer and a second coating layer, helps to improve the high-temperature cycle life of lithium nickel manganese spinel in high-temperature environments and realize the high-pressure potential of lithium nickel manganese spinel.

[0025] To make the technical solutions of this disclosure clearer and easier to understand, the composite materials, positive electrode sheets, batteries and manufacturing methods provided in this disclosure will be described in detail below with reference to specific embodiments.

[0026] Composite materials LNMO at high voltage (~4.7 V vs. Li) + Lithium lanthanum zirconium oxide (Li7La3Zr2O) readily undergoes oxidative decomposition with liquid electrolytes. 12 LLZO (Lithium Nitrogen Al₂O₃) is a typical oxide solid-state electrolyte material with high ionic conductivity, high shear modulus, and high voltage resistance. It exhibits good compatibility with LNMO cathode materials and can suppress lithium dendrite penetration, thus contributing to improved battery safety. Simultaneously, LLZO possesses a wide electrochemical stability window (>5V vs. Li₂O₃). + The voltage of LLZO (Li) is much higher than that of LNMO (~4.7V), which is a significant advantage for high-voltage LNMO materials. This means that LLZO can directly withstand the high-voltage oxidation environment of LNMO without decomposing itself, which helps to fundamentally solve the problem of LNMO oxidizing and decomposing under high voltage with liquid electrolyte and thus failing.

[0027] The inventors of this disclosure have noted that both LLZO and LNMO are rigid ceramic materials. When used as a surface insulating coating layer for nickel manganese spinel, the contact between them is a point-to-point physical contact with a small effective contact area and extremely limited ion transport channels, which leads to increased interfacial impedance and easy delamination during cycling.

[0028] Therefore, the inventors of this disclosure introduce a buffer layer containing LiF between LNMO and LLZO to realize the high-pressure potential of LNMO.

[0029] In a first aspect, embodiments of this disclosure provide a composite material. Specifically, the composite material comprises a lithium nickel manganese spinel, a first coating layer, and a second coating layer located on the side of the first coating layer away from the lithium nickel manganese spinel; wherein the first coating layer comprises LiF; and the second coating layer comprises Li 7-x La3Zr 2-x M x O 12 , where M is at least one of Ta and Nb, and 0 ≤ x < 0.7. Here, x can be 0, 0.1, 0.3, 0.5, etc., and this disclosure does not limit it.

[0030] It should be noted that the second coating layer can directly withstand the high-voltage oxidation environment of lithium nickel manganese spinel without decomposing, which helps to solve the oxidation failure problem of lithium nickel manganese spinel under high voltage. By bridging the lithium nickel manganese spinel and the second coating layer with a first coating layer including LiF, not only can the interface between the lithium nickel manganese spinel and the second coating layer be stabilized, but direct contact between LNMO and the electrolyte is also isolated, reducing the instability of the cathode electrolyte interphase (CEI) layer and the dissolution of transition metals, effectively suppressing interfacial side reactions. Simultaneously, the high ionic conductivity (10⁻⁶ Ω·cm) of the second coating layer... -4 ~10 -3 S / cm) can compensate for the Li-induced loss from the first coating layer. + To address the problem of transport obstruction, optimize ion migration at the cathode / electrolyte interface, reduce interface impedance, and improve high-voltage cycling stability.

[0031] Furthermore, due to the high chemical inertness of LiF, it achieves a high voltage plateau at lithium nickel manganese spinel (4.7 V vs. Li). + Li is not easily oxidized, which can effectively prevent the decomposition and gas production of the electrolyte. At the same time, the first coating layer can also alleviate the problem of Mn in lithium nickel manganese spinel through physical barrier. 3+ The dissolution of the substance (especially under high temperature conditions) ultimately helps to slow down capacity decay.

[0032] In some embodiments, the first coating layer further includes at least one of Li2ZrO3, LiNbO3, Li3PO4, and Li3BO3.

[0033] In some embodiments, the second coating layer further includes Li 1+y Al y Ti 2-y (PO4)3 (LATP), Li 1+z Al z Ge 2-z (PO4)3 (LAGP) and Li 3n La 2 / 3-n At least one of TiO3 (LLTO); wherein 0 < y < 2, 0 < z < 2, 0 < n < 0.16. For example, y can be 0.1, 0.5, 1, 1.5, etc., and this disclosure does not limit it. For example, z can be 0.1, 0.2, 0.5, 1, 1.2, 1.6, etc., and this disclosure does not limit it. For example, n can be 0.05, 0.02, 0.1, 0.12, 0.15, etc., and this disclosure does not limit it.

[0034] In some embodiments, the mass fraction of LiF in the first coating layer is ≥80%. Exemplarily, the mass fraction of LiF in the first coating layer is 80%, 85%, or 90%, etc. Such a mass fraction ensures that LiF dominates in the first coating layer, bridging the nickel-manganese spinel and the second coating layer.

[0035] In some embodiments, the Li in the second coating layer 7-x La3Zr 2-x M x O 12 The mass fraction is ≥80%. For example, the Li in the second coating layer... 7-x La3Zr 2-x M x O 12 The mass fraction is 80%, 86%, or 91%, etc. Such a mass fraction ensures that the second coating layer has the functions of high pressure resistance and high ionic conductivity.

[0036] In some embodiments, the Li 7-x La3Zr 2-x M x O 12 Including Li7La3Zr2O 12 .

[0037] LiF has low ionic conductivity; an excessively thick first coating layer will affect the conductivity of LiF. + Transmission leads to increased polarization and decreased rate performance. In some embodiments, the thickness of the first coating layer is 2-6 nm, such as 2 nm, 3 nm, 4 nm, 5 nm, or 6 nm. Such a thickness can effectively bridge the nickel-manganese spinel and the second coating layer without significantly affecting the rate performance.

[0038] In some embodiments, the thickness of the second coating layer is 2-6 nm, such as 2 nm, 2.5 nm, 3.5 nm, 4 nm, 5 nm, or 6 nm. This thickness range allows for better synergy with nickel-manganese spinel.

[0039] Methods for manufacturing composite materials Secondly, embodiments of this disclosure also provide a method for manufacturing any of the aforementioned composite materials. Specifically, the manufacturing method includes: First, the nickel manganese hydroxide precursor and lithium carbonate are mixed and then subjected to a first sintering, followed by a first crushing to obtain a first powder; Optionally, the ratio of nickel to manganese in the nickel-manganese hydroxide precursor can be 1:3.

[0040] Optionally, the first sintering conditions are sintering at 850~950°C for 9~11 hours. For example, sintering at 900°C for 10 hours.

[0041] Next, the first powder and the material of the first coating layer are mixed and then subjected to a second sintering, followed by a second crushing to obtain the second powder.

[0042] Optionally, the mass ratio of the material of the first coating layer to the first powder is 1000~2000ppm, for example, 1000ppm, 1500ppm, 2000ppm, etc.

[0043] Optionally, the second sintering conditions are sintering at 400~500°C for 5~7 hours. For example, sintering at 450°C for 6 hours.

[0044] Finally, the second powder and the material of the second coating layer are mixed and then subjected to a third sintering, followed by a third crushing to obtain the composite material.

[0045] Optionally, the mass ratio of the material of the second coating layer to the second powder is 1000~2000ppm, for example, 1000ppm, 1200ppm, 1500ppm, 1800ppm, 2000ppm, etc.

[0046] Optionally, the third sintering condition is sintering at 300~400°C for 5~7 hours. For example, sintering at 350°C for 6 hours.

[0047] Positive electrode sheet Thirdly, embodiments of this disclosure also provide a positive electrode sheet comprising any of the aforementioned composite materials, as detailed in the fourth aspect below.

[0048] Battery Fourthly, embodiments of this disclosure also provide a battery comprising the composite material provided above.

[0049] In some embodiments, the battery may include a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0050] Positive electrode sheet The positive electrode includes a positive current collector and a positive electrode film layer disposed on the surface of the positive current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0051] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0052] In some embodiments, the positive electrode active material includes any of the composite materials described above.

[0053] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0054] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0056] Negative electrode sheet The negative electrode can be a lithium metal foil with a thickness of 0.1~1.0mm.

[0057] electrolyte The electrolyte may include a base solvent and a lithium salt.

[0058] In some embodiments, the base solvent may include ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl acetate (EA), propylene carbonate (PC), etc.

[0059] In some embodiments, the lithium salt may include at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethylsulfonate.

[0060] Separating membrane In some embodiments, the secondary battery further includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0061] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0062] Example The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0063] The button cell of Embodiment 1 of this disclosure is prepared by the following specific method: (1) Preparation of lithium nickel manganese cathode: Step 1: The nickel-manganese hydroxide precursor and lithium carbonate are mixed evenly in a high-speed mixer and then sintered at high temperature in a box furnace at 900℃ for 10 hours. After exiting the furnace, the mixture is mechanically ground and sieved to obtain the first powder. Here, the crushing parameters are: feed rate - classifier speed - induced draft: 4-60-35. The powder obtained after crushing is sieved through a 300-mesh screen to obtain the first powder.

[0064] Step 2: Next, the first powder and LiF (1500ppm) are mixed evenly using a high-speed mixer and then sintered again in a box furnace at a low temperature of 450℃ for 6 hours. The resulting powder is then crushed and sieved to obtain the second powder. Here, a mechanical mill is used for crushing, with the following crushing parameters: feed rate - classifier speed - induced draft: 4-50-35. The crushed powder is then sieved through a 400-mesh screen to obtain the second powder.

[0065] The thickness of the LiF layer (corresponding to the first coating layer) is 5 nm.

[0066] Step 3: Finally, the second powder and LLZO (1500ppm) are mixed evenly using a high-speed mixer and then sintered for the third time at 350℃ for 6 hours. The resulting powder is then crushed and sieved to obtain the third powder. Here, a mechanical mill is used for crushing, with the following parameters: feed rate - classifier speed - induced draft: 4-40-35. The crushed powder is then sieved through a 400-mesh screen to obtain the third powder.

[0067] The thickness of the LLZO layer (corresponding to the second coating layer) is 5nm.

[0068] Step 4: Mix the positive electrode active material (third powder), polyvinylidene fluoride (PVDF) as a binder, and Super P as a conductive agent in a mass ratio of 90:5:5. First, add the conductive agent and PVDF to an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a conductive adhesive. Then, add the positive electrode active material to the conductive adhesive, mix thoroughly using a homogenizer, and coat it onto an aluminum current collector. After drying, form the positive electrode sheet, which is then cut into electrode sheets with a diameter of 16 mm. The mass loading of the positive electrode active material is 8.6~8.7 mg. cm -2 .

[0069] (2) Preparation of the negative electrode: A lithium foil with a diameter of 19 mm and a thickness of 0.6 mm was used as the negative electrode.

[0070] (3) Preparation of electrolyte: In an argon-atmosphere glove box with a water content of <10ppm, battery-grade ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed uniformly at a volume ratio of 1:1:1 to form a base solvent. Lithium hexafluorophosphate with a concentration of 1mol / L is then added to the base solvent to form an electrolyte.

[0071] (4) Preparation of the separating membrane: Polypropylene film is used as the separator.

[0072] (5) Preparation of button batteries: The positive electrode, separator, and negative electrode of the CR2430 button cell are assembled, electrolyte is injected, and then the cell is sealed. Electrolysis is carried out to finally produce the button cell.

[0073] Example 2 The only difference between this embodiment and embodiment 1 is that in step 2, Li3PO4 is added at the same time as LiF, and the mass ratio of LiF to Li3PO4 is 9:1. The other conditions are the same as in embodiment 1.

[0074] Example 3 The only difference between this embodiment and embodiment 1 is that in step 2, Li3PO4 is added at the same time as LiF, and the mass ratio of LiF to Li3PO4 is 8:2. The other conditions are the same as in embodiment 1.

[0075] Example 4 The only difference between this embodiment and Embodiment 1 is that in step 3, Li is added simultaneously with LLZO. 1+z Al z Ge 2-z (PO4)3, and LLZO and Li 1+z Al z Ge 2-z The mass ratio of (PO4)3 was 9:1, and the other conditions were the same as in Example 1.

[0076] Example 5 The only difference between this embodiment and Embodiment 1 is that in step 3, Li is added simultaneously with LLZO. 1+z Al z Ge 2-z (PO4)3, and LLZO and Li 1+z Al z Ge 2-z The mass ratio of (PO4)3 was 8:2, and the other conditions were the same as in Example 1.

[0077] Example 6 The only difference between this embodiment and Embodiment 1 is that the mass ratio of LiF added in step 2 is changed to 800 ppm, resulting in a LiF layer thickness of 3 nm. The mass ratio of LLZO added in step 3 is changed to 700 ppm, resulting in an LLZO layer thickness of 3 nm. All other conditions are the same as in Embodiment 1.

[0078] Example 7 The only difference between this embodiment and Embodiment 1 is that the mass ratio of LiF added in step 2 is changed to 500 ppm, resulting in a LiF layer thickness of 2 nm. The mass ratio of LLZO added in step 3 is changed to 400 ppm, resulting in an LLZO layer thickness of 2 nm. All other conditions are the same as in Embodiment 1.

[0079] Example 8 The only difference between this embodiment and Embodiment 1 is that the mass ratio of LiF added in step 2 is changed to 1800 ppm, resulting in a LiF layer thickness of 6 nm. The mass ratio of LLZO added in step 3 is changed to 1700 ppm, resulting in an LLZO layer thickness of 6 nm. All other conditions are the same as in Embodiment 1.

[0080] Comparative Example 1 The only difference between this comparative example and Example 1 is that LiF is not added in step 2 and LLZO is not added in step 3; the other conditions are the same as in Example 1.

[0081] Comparative Example 2 The only difference between this comparative example and Example 1 is that LLZO is not added in step 3, while the other conditions are the same as in Example 1.

[0082] Comparative Example 3 The only difference between this comparative example and Example 1 is that LiF is not added in step 2, while the other conditions are the same as in Example 1.

[0083] Comparative Example 4 The only difference between this comparative example and Example 1 is that LLZO is added in step 2 and LiF is added in step 3, while the other conditions are the same as in Example 1.

[0084] Test methods The electrochemical performance of the button batteries prepared in the above embodiments and comparative examples was tested using a battery testing instrument (CT). 2001A, Wuhan Lande). The charging and discharging voltage range is 3.5~4.95V.

[0085] (1) First-cycle discharge capacity At 25°C, the newly prepared button cell was charged at a constant current and constant voltage rate of 0.1C to the cutoff voltage of 4.95V, and then discharged at a rate of 0.1C to the voltage of 3.5V, thus obtaining the discharge capacity at 0.1C.

[0086] (2) Coulomb efficiency in the first lap At 25℃, the newly prepared button cell was charged at a constant current and constant voltage rate of 0.1C to the cutoff voltage of 4.95V, and then discharged at a rate of 0.1C to the voltage of 3.5V. The charging capacity and discharging capacity at 0.1C were obtained, and the first-cycle coulombic efficiency was calculated according to "discharging capacity / charging capacity × 100%".

[0087] (3) Capacity retention rate after 100 cycles of 3C charge and discharge at room temperature At 25°C, the newly prepared button battery was first activated at 0.1C for two cycles, and then subjected to 100 cycles of 3C charge-discharge, where 1C = 140 mAh / g.

[0088] Capacity retention rate after 100 cycles (25℃) = discharge capacity after 100 cycles / discharge capacity after the first cycle (after activation) × 100%.

[0089] (4) Gas production of the electrode in 21 days The electrode sheet coated with positive active material is used, along with electrolyte, encapsulated, and the bulge size is measured to determine the ratio.

[0090] (5) Capacity retention rate after 100 cycles of high-temperature 2C charge and discharge The newly prepared button cell was activated at 0.1 C for two cycles at 45°C, and then subjected to 100 cycles of 2C charge-discharge. The discharge capacity of the first cycle (the first cycle out of 100 cycles after activation) and the discharge capacity of the 100th cycle were obtained. Wherein 1 C = 140 mAh / g.

[0091] The capacity retention rate after 100 cycles at 45℃ is calculated based on the discharge capacity of the first cycle and the discharge capacity of the 100th cycle. The specific calculation formula is as follows: Capacity retention rate after 100 cycles (45℃) = discharge capacity after 100 cycles / discharge capacity after the first cycle (after activation) × 100%.

[0092] (6) Mn dissolution test The battery was disassembled after high-temperature cycling test to obtain the cycled negative electrode sheet. The cycled negative electrode sheet was placed in a centrifuge tube, and a dilute nitric acid solution was added to dissolve the manganese deposited on the surface of the negative electrode sheet into the dilute nitric acid solution. After centrifugation, the supernatant was subjected to ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) to obtain the Mn dissolution.

[0093] Table 1. Performance test results of positive electrode active materials and batteries in different groups of examples and comparative examples.

[0094] Comparative Examples 1 and 4 show that forming a first coating layer mainly composed of LiF and a second coating layer mainly composed of LLZO on the surface of lithium nickel manganese spinel can significantly improve the first-cycle coulombic efficiency, cycle stability under both room temperature and high temperature conditions, and reduce electrode gas generation and manganese dissolution. Here, the first and second coating layers, to a certain extent, prevent direct contact between the lithium nickel manganese spinel and the electrolyte, while also enabling the second coating layer to withstand the high-voltage oxidation environment of the lithium nickel manganese spinel without decomposition, thus helping to solve the oxidation failure problem of lithium nickel manganese spinel under high voltage. Furthermore, the first coating layer can stabilize the interface between the second coating layer and the lithium nickel manganese spinel, reducing the dissolution of excess metals (e.g., Mn), suppressing interfacial side reactions, and helping to reduce capacity decay. Also, due to the high chemical inertness of LiF, at the high-voltage plateau of lithium nickel manganese spinel (4.7V vs. Li), the capacity decay is reduced. + / Li) is not easily oxidized, which can effectively prevent the decomposition and gas generation of the electrolyte. The high ionic conductivity (10) of the second coating layer -4 ~10 -3 S / cm) can compensate for the Li-induced loss from the first coating layer.+ To address the problem of transport obstruction, optimize ion migration at the cathode / electrolyte interface and improve capacity retention under cycling conditions.

[0095] Table 2 Performance test results of positive electrode active materials and batteries in different groups of examples

[0096] Comparing Examples 1 to 3, it can be seen that in addition to LiF, other lithium salts can also be included in the first coating layer formed on the surface of lithium nickel manganese spinel with LiF material as the main component. When the proportion of other lithium salts does not exceed 20%, the battery still has a high first-cycle coulombic efficiency, good cycle stability under room temperature and high temperature conditions, and relatively ideal electrode gas generation and manganese dissolution.

[0097] Comparing Examples 1, 4, and 5, it can be seen that, in addition to LLZO, other components, such as Li, can also be included in the second coating layer formed on the surface of lithium nickel manganese spinel, which is mainly composed of LLZO material. 1+z Al z Ge 2-z (PO4)3, with other components accounting for no more than 20%, still has high first-cycle coulombic efficiency, good cycle stability under both room temperature and high temperature conditions, and relatively ideal electrode gas generation and manganese dissolution.

[0098] Table 3 Performance test results of positive electrode active materials and batteries in different groups of examples

[0099] Comparing Examples 6 to 8, it can be seen that when the thickness of the first coating layer, which is mainly composed of LiF material, is in the range of 2nm to 6nm, and the thickness of the second coating layer, which is mainly composed of LLZO material, is in the range of 2nm to 6nm, the battery has a higher first-cycle coulombic efficiency, better cycle stability under both room temperature and high temperature conditions, and more ideal electrode gas generation and manganese dissolution.

[0100] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0101] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A composite material, characterized in that, The composite material comprises lithium nickel manganese spinel, a first coating layer, and a second coating layer located on the side of the first coating layer away from the lithium nickel manganese spinel; wherein... The first coating layer comprises LiF; the second coating layer comprises Li 7-x La3Zr 2-x M x O 12 , where M is at least one of Ta and Nb, and 0 ≤ x < 0.

7.

2. The composite material according to claim 1, characterized in that, The first coating layer further includes at least one of Li2ZrO3, LiNbO3, Li3PO4, and Li3BO3; and / or The second coating layer also includes Li 1+y Al y Ti 2-y (PO4)3, Li 1+z Al z Ge 2-z (PO4)3 and Li 3n La 2 / 3-n At least one of TiO3; wherein 0 < y < 2, 0 < z < 2, 0 < n < 0.

16.

3. The composite material according to claim 1, characterized in that, The mass fraction of LiF in the first coating layer is ≥80%; and / or Li in the second coating layer 7-x La3Zr 2-x M x O 12 The quality fraction is ≥80%.

4. The composite material according to claim 1, characterized in that, The thickness of the first coating layer is 2~6 nm; and / or The thickness of the second coating layer is 2~6nm.

5. The composite material according to claim 1, characterized in that, The Li 7-x La3Zr 2-x M x O 12 Including Li7La3Zr2O 12 .

6. The method for producing the composite material according to any one of claims 1 to 5, characterized in that, include: The nickel-manganese hydroxide precursor and lithium carbonate are mixed and then subjected to a first sintering, followed by a first crushing to obtain the first powder. The first powder and the material of the first coating layer are mixed evenly and then subjected to a second sintering, followed by a second crushing to obtain the second powder. The second powder and the material of the second coating layer are mixed and then subjected to a third sintering, followed by a third crushing to obtain the composite material.

7. The manufacturing method according to claim 6, characterized in that, The first sintering condition is sintering at 850~950℃ for 9~11 hours; and / or The second sintering condition is sintering at 400~500℃ for 5~7 hours; and / or The third sintering condition is sintering at 300~400℃ for 5~7 hours.

8. The manufacturing method according to claim 6, characterized in that, The mass ratio of the material of the first coating layer to the first powder is 1000~2000 ppm; and / or The mass ratio of the material of the second coating layer to the second powder is 1000~2000 ppm.

9. A positive electrode sheet, characterized in that, The composite material includes the composite material according to any one of claims 1 to 5 or the composite material obtained by the manufacturing method according to any one of claims 6 to 8.

10. A battery, characterized in that, Including the positive electrode sheet according to claim 9.

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