Positive electrode active material and preparation method thereof, positive electrode and lithium ion battery

Abstract

The invention relates to a positive electrode active material and a preparation method thereof, a positive electrode and a lithium ion battery. The positive electrode active material comprises lithium manganate particles and a sodium phytate layer coating the surfaces of the lithium manganate particles. According to the technical scheme, in the positive electrode active material, the sodium phytate layer serves as a coating layer, and six phosphate groups in molecules of the sodium phytate layer and manganese ions dissolved out of lithium manganate particles can form a stable complex, so that the dissolved-out manganese ions are efficiently captured and prevented from being further migrated into an electrolyte to damage the performance of a battery; meanwhile, the sodium phytate layer forms a layer of compact physical barrier on the surfaces of the lithium manganate particles, so that direct contact between the lithium manganate particles and an electrolyte can be effectively blocked, and dissolution of manganese ions is inhibited from the source. Through a synergistic effect of a chelation effect and a physical barrier effect of the sodium phytate layer, the dissolution amount of manganese ions can be remarkably reduced, and the crystal structure of lithium manganate particles is prevented from being distorted, so that the structural stability of the positive electrode active material is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. The positive electrode active material is one of the key factors determining the performance, safety, and cost of lithium-ion batteries.

[0003] Spinel-type lithium manganese oxide (LiMn2O4, or LMO for short) is an important cathode material for lithium-ion batteries. Manganese is abundant in the Earth's crust and its price is much lower than metals such as cobalt and nickel. Compared with mainstream cathode materials such as lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (NCM), and lithium iron phosphate (LiFePO4), lithium manganese oxide has significant advantages such as low raw material cost, environmental friendliness, strong overcharge resistance, good safety, and excellent power performance. These characteristics make lithium manganese oxide a promising candidate for large-scale energy storage and lightweight electric vehicles.

[0004] However, during the charging and discharging process, manganese ions in lithium manganese oxide are easily dissolved, leading to structural distortion. Especially under high temperature conditions, the performance degradation is more obvious, which limits its cycle life and storage performance. Summary of the Invention

[0005] Therefore, it is necessary to provide a positive electrode active material and its preparation method, as well as a positive electrode and lithium-ion battery, to address the issues of how to effectively suppress manganese ion dissolution, significantly improve cycle performance and high-temperature storage stability.

[0006] The first aspect of this application provides a positive electrode active material, which includes lithium manganese oxide particles and a sodium phytate layer coated on the surface of the lithium manganese oxide particles.

[0007] In one embodiment, the mass ratio of sodium phytate layer to lithium manganese oxide particles is (0.2~1):100.

[0008] In one embodiment, the lithium manganese oxide particles are pure lithium manganese oxide particles.

[0009] In one embodiment, the lithium manganese oxide particles are metal-doped lithium manganese oxide particles, and the doping metal in the metal-doped lithium manganese oxide includes one or more of Mg, Al, Ca, Ti, Cu, Zn, Y, Zr, Ru, Sn and Sb.

[0010] In one embodiment, the thickness of the sodium phytate layer is 1 nm to 15 nm.

[0011] The method for preparing the positive electrode active material according to any one of the above claims of this application includes the following steps: Lithium manganese oxide granules are available; Lithium manganese oxide particles were dispersed in a solvent to obtain the first dispersion; Sodium phytate was added to the first dispersion and mixed thoroughly to obtain a slurry; The slurry was spray-dried to obtain precursor powder; and The precursor powder was heat-treated to obtain the positive electrode active material.

[0012] In one embodiment, lithium manganese oxide particles are prepared using the following steps: Lithium carbonate and manganese tetroxide were mixed evenly at a molar ratio of (0.5~0.65):0.667, heated to 600℃~800℃ in air atmosphere, held at that temperature for 10h~20h, then cooled to room temperature, and crushed and sieved to obtain lithium manganese oxide particles.

[0013] In one embodiment, the temperature of the spray drying equipment is 250°C to 300°C; the temperature of the heat treatment is 60°C to 100°C, and the time is 6 hours to 15 hours.

[0014] A third aspect of this application provides a positive electrode comprising any of the above-described positive electrode active materials.

[0015] A fourth aspect of this application provides a lithium-ion battery comprising the above-described positive electrode.

[0016] This application has at least the following technical effects: In the positive electrode active material of this application, the sodium phytate layer serves as a coating layer. The six phosphate groups in its molecules can form stable complexes with manganese ions dissolved from lithium manganese oxide particles, thereby efficiently capturing the dissolved manganese ions and preventing them from further migrating into the electrolyte and damaging battery performance. Simultaneously, the sodium phytate layer forms a dense physical barrier on the surface of the lithium manganese oxide particles, effectively preventing direct contact between the lithium manganese oxide particles and the electrolyte, thus inhibiting the dissolution of manganese ions at the source. Through the synergistic effect of the chelating and physical barrier effects of the sodium phytate layer, the amount of manganese ions dissolved can be significantly reduced, preventing distortion of the crystal structure of lithium manganese oxide particles and improving the structural stability of the positive electrode active material.

[0017] The preparation method of this application is simple and convenient to operate. It can be achieved using conventional equipment such as mixing, spray drying, and heat treatment, without the need for complex special equipment, and the production cost is low.

[0018] The lithium-ion battery of the present invention, due to the use of the positive electrode active material of the present invention, not only has excellent cycle performance and high temperature stability, but also has high energy density and good safety, which can meet the needs of different fields such as portable electronic devices, electric vehicles, and energy storage systems, and has broad application prospects. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for preparing a positive electrode active material according to an embodiment of the present invention. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In lithium manganese oxide materials, trivalent manganese ions are prone to disproportionation reactions under the induction of substances such as HF in the electrolyte, generating divalent manganese ions, which dissolve and cause crystal structure distortion and collapse, resulting in deterioration of battery capacity performance. Moreover, at higher temperatures, such as >50°C, the side reactions between lithium manganese oxide and the electrolyte are intensified, causing the battery's high-temperature storage performance to deteriorate.

[0023] The first aspect of this application provides a positive electrode active material, which includes lithium manganese oxide particles and a sodium phytate layer coated on the surface of the lithium manganese oxide particles.

[0024] Sodium phytate has significant advantages, including wide availability, low price, and environmental friendliness. Its molecular structure contains six phosphate groups, each with strong chelating ability. These groups can form stable complexes with manganese ions dissolved from lithium manganese oxide particles, efficiently capturing them and preventing further migration into the electrolyte that could damage battery performance. Simultaneously, the sodium phytate layer forms a dense physical barrier on the surface of the lithium manganese oxide particles, effectively preventing direct contact between the particles and the electrolyte, thus inhibiting manganese ion dissolution at its source. Through the synergistic effect of the chelating and physical barrier effects of the sodium phytate layer, the amount of manganese ion dissolution can be significantly reduced, preventing distortion of the crystal structure of lithium manganese oxide particles and thereby improving the stability of the positive electrode active material.

[0025] In some embodiments, the mass ratio of sodium phytate layer to lithium manganese oxide particles is (0.2~1):100. Experimental verification has shown that this ratio ensures the coating layer has a suitable thickness, guaranteeing both the suppression of manganese ion dissolution and preventing a significant increase in battery internal resistance due to excessive coating thickness, thus achieving a good balance between material cycle performance and electrochemical performance. If the mass ratio of sodium phytate layer to lithium manganese oxide particles is less than 0.2:100, the coating layer is too thin, failing to form a complete and dense physical barrier, resulting in limited blocking effect on manganese ions and difficulty in effectively suppressing manganese ion dissolution. If the mass ratio of sodium phytate layer to lithium manganese oxide particles is greater than 1:100, the coating layer is too thick, significantly increasing the resistance to electron and lithium ion transport, leading to increased battery internal resistance and intensified polarization, which in turn reduces the battery's cycle performance and rate performance.

[0026] Furthermore, the mass ratio of sodium phytate layer to lithium manganese oxide particles may be, but is not limited to, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100 or 1.0:100.

[0027] In some embodiments, the lithium manganese oxide particles are pure lithium manganese oxide particles. It is understood that "pure lithium manganese oxide particles" here refers to undoped or uncoated lithium manganese oxide particles. Pure lithium manganese oxide particles have advantages such as low cost and simple preparation process.

[0028] In some embodiments, the lithium manganese oxide particles are metal-doped lithium manganese oxide particles, where the doping metal includes one or more of Mg, Al, Ca, Ti, Cu, Zn, Y, Zr, Ru, Sn, and Sb. By introducing specific doping metals, metal-doped lithium manganese oxide particles can further optimize the crystal structure of lithium manganese oxide and improve its structural stability, thereby synergistically enhancing the performance of the cathode active material. For example, doping with metals such as Mg and Al can enhance the stability of the lithium manganese oxide crystal structure and suppress distortion of the crystal structure during charging and discharging; doping with metals such as Ti and Zr can improve the electronic conductivity and lithium-ion diffusion rate of lithium manganese oxide; and doping with metals such as Cu and Zn can further suppress the dissolution of manganese ions. By selecting different doping metals or combinations of doping metals, the performance of lithium manganese oxide particles can be specifically optimized according to actual application requirements, thereby enabling the cathode active material to possess superior overall performance.

[0029] In some embodiments, the thickness of the sodium phytate layer is 1 nm to 15 nm. The thickness of the sodium phytate layer can be, but is not limited to, 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, 11 nm, 13 nm, and 15 nm. The thickness of the sodium phytate layer directly affects its inhibitory effect on manganese ion dissolution and the electrochemical performance of the battery. When the thickness of the sodium phytate layer is 1 nm to 15 nm, it can effectively inhibit manganese ion dissolution while ensuring smooth transport of electrons and lithium ions. If the thickness of the sodium phytate layer is less than 1 nm, a complete physical barrier cannot be formed, and the blocking effect on manganese ions is limited, making it difficult to achieve the ideal modification effect. If the thickness of the sodium phytate layer is greater than 15 nm, it will significantly increase the transport resistance of electrons and lithium ions inside the electrode, leading to a significant increase in the internal resistance of the battery, severe polarization during charging and discharging, and a significant deterioration in the battery's cycle performance and rate performance.

[0030] Please see Figure 1 A second aspect of the present invention provides a method for preparing a positive electrode active material, comprising the following steps: S10 provides lithium manganese oxide particles.

[0031] Lithium manganese oxide particles can be obtained by purchasing or by preparation.

[0032] In one embodiment, lithium manganese oxide particles are prepared using the following steps: Lithium carbonate and manganese tetroxide were mixed evenly at a molar ratio of (0.5~0.65):0.667, heated to 600℃~800℃ in air atmosphere, held at that temperature for 10h~20h, then cooled to room temperature, and crushed and sieved to obtain lithium manganese oxide particles.

[0033] In the preparation of lithium manganese oxide particles, lithium carbonate (preferably ≥99.9% purity) and manganese tetroxide (preferably ≥99% purity) are used as raw materials. Precise control of their molar ratio is crucial for the crystal structure and electrochemical performance of lithium manganese oxide. A molar ratio within the range of (0.5~0.65):0.667 ensures sufficient reaction, forming spinel-type lithium manganese oxide with high purity and good crystallinity. Sintering in an air atmosphere ensures the stability of the manganese valence state, forming a lithium manganese oxide crystal structure with good electrochemical performance. Heating to 600℃~800℃ and holding for 10h~20h ensures sufficient reaction of the raw materials, forming lithium manganese oxide particles with high crystallinity and stable structure. After sintering, cooling to room temperature, followed by crushing and sieving, yields lithium manganese oxide particles with uniform particle size, laying a good foundation for subsequent coating processes.

[0034] For the preparation of metal-doped lithium manganese oxide particles, appropriate metal compounds (such as metal oxides, metal carbonates, etc.) can be added to the above raw materials, and the mixture, sintered, crushed, and sieved are carried out according to the same process steps as described above to obtain metal-doped lithium manganese oxide particles. The amount of metal compound added can be precisely controlled according to the target doping amount to ensure that the doped metal can be uniformly distributed in the lithium manganese oxide crystal structure and achieve the best modification effect.

[0035] S20. Disperse the lithium manganese oxide particles obtained in step S10 in a solvent to obtain the first dispersion.

[0036] In one implementation, the solvent is water or a mixture of water and an organic solvent. The choice of solvent primarily considers the dispersion effect of lithium manganese oxide particles and the solubility of sodium phytate. Water, as a solvent, has advantages such as wide availability, low cost, and environmental friendliness. It can uniformly disperse lithium manganese oxide particles while ensuring sufficient dissolution of sodium phytate to form a stable slurry. When using a mixture of water and an organic solvent, solvents such as ethanol and propylene glycol, which are miscible with water and have no adverse effects on lithium manganese oxide and sodium phytate, can be selected. The mixed solvent can further improve the dispersibility of lithium manganese oxide particles and the solubility of sodium phytate, thereby improving the uniformity of coating.

[0037] In some embodiments, the mass ratio of lithium manganese oxide particles to solvent is 1:(1~10). This ratio ensures that the lithium manganese oxide particles are fully dispersed in the solvent, forming a stable first dispersion and preventing particle agglomeration from affecting the coating effect. If the amount of solvent is too small (mass ratio less than 1:1), the lithium manganese oxide particles cannot be fully dispersed and are prone to agglomeration, making it difficult for sodium phytate to be uniformly coated on their surface. If the amount of solvent is too large (mass ratio greater than 1:10), it will increase the energy consumption and time of subsequent spray drying and heat treatment, increasing production costs. It may also affect the concentration and stability of the slurry, which is not conducive to uniform coating.

[0038] Further, in step S20, after dispersing the lithium manganese oxide particles in the solvent, the mixture is stirred for 20-30 minutes to ensure that the lithium manganese oxide particles are uniformly dispersed in the solvent, resulting in a stable first dispersion. The stirring speed can be controlled between 300-500 r / min. Mechanical stirring or ultrasonic stirring can be used during the stirring process. Ultrasonic stirring can further improve the dispersion effect and prevent particle agglomeration. S30. Add sodium phytate to the first dispersion obtained in step S20, mix well, and obtain a slurry.

[0039] In step S30, after adding sodium phytate to the first dispersion, continue stirring for 30-60 minutes to ensure that the sodium phytate is fully dissolved and in full contact with the surface of the lithium manganese oxide particles, forming a uniform slurry. The amount of sodium phytate added is precisely calculated based on the mass ratio of the target sodium phytate layer, ensuring that the mass ratio of the sodium phytate layer to the lithium manganese oxide particles is within the range of 0.2%-1.0%. During stirring, the stirring speed should be kept uniform to avoid localized excessively high or low slurry concentrations, which would affect the uniformity of the coating.

[0040] S40. Spray dry the slurry obtained in step S30 to obtain precursor powder.

[0041] Spray drying technology has advantages such as fast drying speed, uniform product particle size, and dense coating layer. It can quickly dry slurry into powder and at the same time make sodium phytate uniformly coated on the surface of lithium manganese oxide particles.

[0042] In some embodiments, the spray drying equipment temperature is 250°C to 300°C. This temperature range ensures rapid solvent evaporation without causing decomposition or deterioration of the sodium phytate, thus ensuring the structural stability and performance integrity of the sodium phytate layer. Furthermore, the spray drying equipment temperature can be, but is not limited to, 250°C, 260°C, 270°C, 280°C, 290°C, or 300°C.

[0043] S50. The precursor powder obtained in step S40 is subjected to heat treatment to obtain the positive electrode active material.

[0044] The precursor powder after spray drying still contains a small amount of residual solvent and moisture. These residual components can be completely removed by heat treatment, while further strengthening the bonding force between the sodium phytate layer and the lithium manganese oxide particles, ensuring the stability of the coating layer.

[0045] In some embodiments, the heat treatment temperature is 60°C to 100°C, and the time is 6 hours to 15 hours. This range of process parameters can thoroughly remove residual solvents and moisture while avoiding damage to the structure of the sodium phytate layer and lithium manganese oxide particles caused by high temperatures.

[0046] The preparation method of the positive electrode active material of the present invention is simple and convenient, and can be achieved using conventional equipment such as mixing, spray drying, and heat treatment, without the need for complex special equipment, resulting in low production costs. The prepared positive electrode active material, through the synergistic effect of the chelating and physical barrier effects of the sodium phytate layer, can significantly reduce the dissolution of manganese ions, prevent distortion of the crystal structure of lithium manganese oxide particles, and thus improve the cycle life and high-temperature storage performance of the positive electrode active material.

[0047] A third aspect of this application provides a positive electrode comprising any of the above-described positive electrode active materials.

[0048] The positive electrode of the present invention comprises the above-mentioned high-performance positive electrode active material, which has good conductivity, structural stability and electrochemical performance.

[0049] In some embodiments, the specific steps of the positive electrode preparation method are as follows: the positive electrode active material, conductive agent, and binder are mixed evenly in a certain mass ratio, a solvent is added, and the mixture is stirred to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained.

[0050] Aluminum foil can be selected as the positive electrode current collector, as it has good conductivity and mechanical strength, meeting the requirements for positive electrode applications. The coating method can employ conventional techniques in the field, such as blade coating or slot coating, with the coating thickness adjusted according to the actual battery design requirements.

[0051] In some embodiments, the specific steps of the positive electrode preparation method are as follows: the positive electrode active material, conductive agent and binder are mixed evenly in a certain mass ratio, fiberized, and then rolled in multiple stages to obtain the positive electrode sheet.

[0052] In some embodiments, the positive electrode includes a positive electrode layer, wherein the mass of the positive electrode active material accounts for 50% to 95% of the mass of the positive electrode layer.

[0053] In some embodiments, the positive electrode layer further includes a positive electrode binder, which improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode layer and the positive electrode current collector.

[0054] In some embodiments, the positive electrode binder may be selected from polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), and combinations thereof.

[0055] In some implementations, the mass of the positive electrode binder accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0056] In some embodiments, the positive electrode layer further includes a positive electrode conductive agent, which imparts conductivity to the electrode.

[0057] In some embodiments, the positive electrode conductive agent may include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include particles such as carbon black, graphite, SuperP, acetylene black (such as KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene)polysulfonated styrene, etc.

[0058] In some embodiments, the conductive agent accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0059] In some embodiments, the positive electrode layer also includes a fast ion conductor to improve the ionic conductivity of the positive electrode layer. This application does not limit the type of fast ion conductor; it can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc.

[0060] In some embodiments, the oxide solid electrolyte may include one or more garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. For example, garnet ceramics include Li 6.5 La 24 Zr 1.75 Te 0.25 O 12 、Li7La 24 Zr2O 12 Li 6.2 Ga 0.24 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La 24 Zr2O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 And their combinations. LISICON-type oxides include Li14 Zn(GeO4)4, Li 24+x (P 1-x Si x O4 (where 0 < x < 1), Li 24+x Ge x V 1-x O4 (where 0 < x < 1) and their combinations. NASICON-type oxides can be derived from LiMM′(PO4). 24 Defined where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. NASICON-type oxides include Li. 1+x Al x Ge 2-x (PO4) 24 (LAGP) (where 0 ≤ x ≤ 2), Li 1+x Al x Ti 2-x (PO4) 24 (LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr 2-x (PO4) 24 (LYZP) (where 0≤x≤2), Li 1.24 Al 0.24 Ti 1.7 (PO4) 24 LiTi2(PO4) 24 LiGeTi(PO4) 24 LiGe2(PO4) 24 LiHf2(PO4) 24 And their combinations. Perovskite ceramics include Li 24.24 La 0.524 TiO 24 LiSr 1.65 Zr 1.24 Ta 1.7 O9、Li 2x-y Sr 1-x Ta y Zr 1-y O 24 (where x = 0.75y and 0.60 < y < 0.75), Li 24 / 8 Sr 7 / 16 Nb 24 / 4 Zr 1 / 4 O 24 Li 24x La( 2 / 24-x TiO 24 (where 0 < x < 0.25) and their combinations.

[0061] In some embodiments, the sulfide solid electrolyte includes Li2S-P2S5 and Li2S-P2S5-MS. x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 24.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.24 Li 9.6 P 24 S 12 Li7P 24 S 11 Li9P 24 S9O 24 Li 10.245 Si 1.245 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li (Ge 0.5 Sn 0.5 P2S 12 Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br, or I), Li7P2S8I, Li 10.245 Ge 1.245 P 1.65 S 12 Li 24.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li 10 SiP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.24 At least one of (1-x)P2S5-xLi2S (where 0.5≤x≤0.7).

[0062] In some embodiments, the halide solid electrolyte includes Li a M b X c N dM includes one or more of the basic metal elements, such as Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. M also includes doped metal elements, used in conjunction with the aforementioned basic metal elements, such as one or more of Nb, Ta, Al, La, Mg, Ca, Ba, and Ag. X includes one or more of F, Cl, Br, and I. N includes one or more of O and S, and satisfies a + mb = c + nd, where m and n are the weighted valences of M and N, respectively, and 1 ≤ a ≤ 4.

[0063] For example, the halide solid electrolyte particles can be Li₂ZrCl₆, Li₂ZrCl₅F, or Li₂ZrCl₆. 5.5 O 0.25 At least one of Li3InCl6, Li3YCl6, Li2HfCl6, LiInBr4, Li3InBr6, Li3LaI6, Li3LuCl6, and Li3ErCl6.

[0064] In some embodiments, the lithium salt includes LiNbO3 and Li4Ti5O. 12 At least one of Li2TiO3, LiAlO2, LiTaO3, LiMoO3, Li2RuO3 or Li2WO4.

[0065] In some implementations, the mass of the fast ion conductor accounts for 0.1% to 40% of the mass of the positive electrode layer.

[0066] In some embodiments, the thickness of the positive electrode layer is 50 μm to 300 μm. For example, the thickness of the positive electrode layer can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] A fourth aspect of this application provides a lithium-ion battery comprising the above-described positive electrode.

[0068] The lithium-ion battery also includes a negative electrode, an electrolyte, and a separator.

[0069] The lithium-ion battery of the present invention, due to the use of the positive electrode active material of the present invention, not only has excellent cycle performance and high temperature stability, but also has high energy density and good safety, which can meet the needs of different fields such as portable electronic devices, electric vehicles, and energy storage systems, and has broad application prospects.

[0070] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and additives. The organic solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC). The electrolyte salt may include a lithium salt, which may include, but is not limited to, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiOTF), lithium hexafluorophosphate (LiPF6), lithium hexafluoroborate (LiBF6), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium hexafluoroarsenate, etc. Lithium tri(pentafluoroethyl)-trifluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium cyclodifluoromethane-1,1-bis(sulfonyl)imide, lithium cyclodifluoromethane-1,1-bis(sulfonyl)imide, lithium bis(perfluoroethanesulfonyl)imide, lithium bis(fluoromalonic acid)borate, lithium tetracyanoborate, lithium dicyanotriazole, lithium dicyano-trifluoromethyl-imidazolium, lithium dicyano-pentafluoroethyl)-imidazolium, etc., may be one or more of the following: vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinate (SN), adiponitrile (AND).

[0071] When a liquid electrolyte is used, a separator should also be provided in the battery system. The separator separates the negative electrode from the positive electrode and provides a path for lithium ions to move. There are no particular limitations on the separator in this application; any separator can be used, as long as it is a separator commonly used in secondary batteries. Preferably, the separator is selected to have excellent electrolyte wettability and low resistance to ion movement in the electrolyte. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made of polyolefin polymers, including but not limited to ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. In addition, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0072] In some embodiments, the negative electrode includes a negative electrode layer; the negative electrode layer includes at least a negative electrode active material and a negative electrode binder.

[0073] The negative electrode active material in this application embodiment is not particularly limited, as long as it is a substance that can electrochemically adsorb and release s-region metal ions such as lithium ions, sodium ions, potassium ions, and magnesium ions, such as carbonaceous materials, metal compound materials, or their oxides, carbides, nitrides, silicides, sulfides, phosphides, etc. These substances can be used alone, or two or more can be used in combination.

[0074] In some embodiments, the negative electrode active material includes a carbon material, specifically one or more of the following: graphite, needle coke, amorphous carbon, carbon-containing mesophase, carbon fiber, and carbon materials with low graphitization. Graphite may include natural graphite, artificial graphite, etc. Alternatively, materials obtained by coating these materials with carbon materials, such as amorphous carbon or graphitides, may also be used. Amorphous carbon includes, but is not limited to, particles obtained by sintering a monolithic mesophase, and particles obtained by sintering a carbon precursor after a non-melting treatment. Examples of carbonaceous particles with low graphitization include particles obtained by sintering organic matter at temperatures typically below 2500°C.

[0075] In some embodiments, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0076] In some embodiments, the negative electrode active material in the negative electrode material coating has a mass percentage of 80wt% to 99wt%, for example, 80wt%, 85wt%, 90wt%, 95wt%, 97wt%, 99wt%, etc., preferably 95wt% to 97wt%.

[0077] When the negative electrode active material is a non-metallic material such as carbon, the negative electrode binder can be an aqueous binder, such as one or more of sodium carboxymethyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, etc. The negative electrode active material layer can be obtained by coating the negative electrode current collector with a negative electrode slurry and then drying it. The negative electrode slurry includes at least the negative electrode active material and the negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, it is preferable to use a thickener for slurry formation. Thickeners are generally used to adjust the viscosity of the slurry.

[0078] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0079] Example 1 1) Preparation of LMO particles: Lithium carbonate (99.9% purity) and manganese tetroxide (99% purity) particles were weighed at a molar ratio of 0.6:0.667 and poured into a high-speed mixer for mixing. The mixture was stirred at low speed (5Hz) for 5 minutes and then at high speed (45Hz) for 20 minutes until homogeneous. The mixture was then poured into a crucible and placed in a muffle furnace. The temperature was raised to 700℃ at a heating rate of 3℃ / min and held for 15 hours with air circulation throughout. After heating, the mixture was slowly cooled to room temperature. The mixture was then crushed using a roller crusher and finally sieved to obtain untreated LMO particles.

[0080] 2) Preparation of sodium phytate-coated LMO: 1 kg of LMO particles obtained above were added to 5 kg of pure water and stirred for 20 min to obtain the first dispersion. Next, add 5g of sodium phytate to the first dispersion, and then stir for 30 minutes to obtain a slurry; While stirring, the slurry is added to the spray drying equipment at a temperature of 270℃. After all the slurry has been spray dried, the precursor powder is obtained. The obtained precursor powder was placed in a forced-air drying oven and dried at 80℃ for 12 hours to obtain LMO particles coated with sodium phytate. The thickness of the sodium phytate layer was 5 nm.

[0081] Example 2 1) Preparation of LMO particles: Same as in Example 1.

[0082] 2) Preparation of sodium phytate-coated LMO: 1 kg of LMO particles were added to 5 kg of pure water and stirred for 20 min to obtain the first dispersion. Next, 2g of sodium phytate was added to the first dispersion, and then stirred for 30 minutes to obtain a slurry; While stirring, the slurry is added to the spray drying equipment at a temperature of 270℃. After all the slurry has been spray dried, the precursor powder is obtained. The obtained precursor powder was placed in a forced-air drying oven and dried at 80℃ for 12 hours to obtain LMO particles coated with sodium phytate. The thickness of the sodium phytate layer was 1 nm.

[0083] Example 3 1) Preparation of LMO particles: Same as in Example 1.

[0084] 2) Preparation of sodium phytate-coated LMO: 1 kg of LMO particles were added to 5 kg of pure water and stirred for 20 min to obtain the first dispersion. Next, 10g of sodium phytate was added to the first dispersion, and then stirred for 30 minutes to obtain a slurry; While stirring, the slurry is added to the spray drying equipment at a temperature of 270℃. After all the slurry has been spray dried, the precursor powder is obtained. The obtained precursor powder was placed in a forced-air drying oven and dried at 80℃ for 12 hours to obtain LMO particles coated with sodium phytate. The thickness of the sodium phytate layer was 10 nm.

[0085] Example 4 1) Preparation of LMO particles: Same as in Example 1.

[0086] 2) Preparation of sodium phytate-coated LMO: 1 kg of LMO powder was added to 5 kg of pure water and stirred for 20 min to obtain the first dispersion. Next, 20g of sodium phytate was added to the first dispersion, and then stirred for 30 minutes to obtain a slurry; While stirring, the slurry is added to the spray drying equipment at a temperature of 270℃. After all the slurry has been spray dried, the precursor powder is obtained. The obtained precursor powder was placed in a forced-air drying oven and dried at 80℃ for 12 hours to obtain LMO particles coated with sodium phytate. The thickness of the sodium phytate layer was 15 nm.

[0087] Comparative Example 1 This comparative example is a comparative example of Example 1, providing an LMO particle and its preparation method. The only difference between this and the preparation method of Example 1 is that sodium phytate was not used for coating, i.e., only step 1 is included.

[0088] Performance testing: The cycle number and high-temperature storage stability of the sodium phytate-coated LMO particles in Examples 1-4 and the LMO particles in Comparative Example 1 were tested. The test methods are as follows, and the test results are shown in Table 1.

[0089] Cycle count: 1. Place the battery sample in an ambient temperature of 25±2℃, charge at 1C until the charging termination voltage is 4.2V and the cutoff current is 0.05C, and let it stand for 1 hour; 2. At an ambient temperature of 25±2℃, discharge at a constant current of 1C to the lower limit voltage of 3.0V, and let stand for 1 hour; 3. Repeat steps 1-2 until the battery capacity is reduced to 80% of the initial capacity, and record the number of cycles.

[0090] High-temperature storage stability: A fully charged battery (100% SOC) was stored at 60°C for 90 days, and then discharged at 25°C for 1C. The remaining capacity was recorded and the capacity residual rate was calculated.

[0091] Table 1 As can be seen from Table 1: (1) The cycling performance and high-temperature storage performance of the sodium phytate-coated LMO positive electrode active materials in Examples 1 to 4 of the present invention are better than those of the uncoated LMO in Comparative Example 1. Among them, Example 1 has the best cycling performance, with 480 cycles when the cutoff capacity drops to 80% SOC, which is much higher than the 310 cycles of Comparative Example 1. This fully demonstrates that sodium phytate coating can effectively improve the cycling performance of lithium manganese oxide. (2) The mass ratio of sodium phytate to LMO in Example 2 is 2:1000, and the coating thickness is only 1 nm. The blocking effect on manganese ions is limited. Therefore, although the number of cycles (421 cycles) is higher than that of Comparative Example 1, it is lower than that of Example 1. This indicates that when the coating thickness is reduced, the effect of inhibiting the dissolution of manganese ions is not ideal, and the barrier to the electrolyte is reduced. There is still a possibility of side reactions between the positive electrode active material and the electrolyte. (3) The mass ratio of sodium phytate to LMO in Example 3 was 1:100, the coating thickness was 10 nm, and the number of cycles was 397, which was higher than that in Comparative Example 1. This is because the increased coating thickness improved the blocking effect on manganese ions, but also increased the internal resistance of the battery and intensified polarization, resulting in a limited improvement in cycle performance. However, the increased coating thickness was beneficial to improving the isolation effect between the positive electrode active material and the electrolyte. (4) In Example 4, the mass ratio of sodium phytate to LMO was 2:100, the coating thickness reached 15nm, and the number of cycles was only 355, which was slightly higher than that of Comparative Example 1. This is because the coating was too thick, which significantly increased the resistance to electron and lithium ion transmission, greatly increased the internal resistance of the battery, and caused severe polarization during charging and discharging, resulting in deterioration of cycle performance. As the coating continued to thicken, the kinetic performance of the positive electrode deteriorated, and the high-temperature storage performance was affected.

[0092] The above are merely possible speculations about the mechanism of the technical solution of this application and do not constitute a limitation on the scope of protection of this application.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes lithium manganese oxide particles and a sodium phytate layer coating the surface of the lithium manganese oxide particles.

2. The positive electrode active material according to claim 1, characterized in that, The mass ratio of the sodium phytate layer to the lithium manganate particles is (0.2~1):

100.

3. The positive electrode active material according to claim 1, characterized in that, The lithium manganese oxide particles are pure lithium manganese oxide particles.

4. The positive electrode active material according to claim 1, characterized in that, The lithium manganese oxide particles are metal-doped lithium manganese oxide particles, and the doping metal in the metal-doped lithium manganese oxide includes one or more of Mg, Al, Ca, Ti, Cu, Zn, Y, Zr, Ru, Sn and Sb.

5. The positive electrode active material according to claim 1, characterized in that, The thickness of the sodium phytate layer is 1 nm to 15 nm.

6. The method for preparing the positive electrode active material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Lithium manganese oxide granules are available; The lithium manganese oxide particles are dispersed in a solvent to obtain a first dispersion; Sodium phytate was added to the first dispersion and mixed thoroughly to obtain a slurry; The slurry is spray-dried to obtain precursor powder; and The precursor powder is subjected to heat treatment to obtain the positive electrode active material.

7. The preparation method according to claim 6, characterized in that, The lithium manganese oxide particles were prepared using the following steps: Lithium carbonate and manganese tetroxide were mixed evenly at a molar ratio of (0.5~0.65):0.667, heated to 600℃~800℃ in air atmosphere, held at that temperature for 10h~20h, then cooled to room temperature, and crushed and sieved to obtain lithium manganese oxide particles.

8. The preparation method according to claim 6, characterized in that, The temperature of the spray drying equipment is 250℃~300℃; the temperature of the heat treatment is 60℃~100℃, and the time is 6 hours~15 hours.

9. A positive electrode, characterized in that, The positive electrode active material comprises any one of claims 1 to 5.

10. A lithium-ion battery, characterized in that, It includes the positive electrode as described in claim 9.

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