Positive electrode materials, positive electrode sheets, and batteries

Abstract

This application relates to the field of battery technology, specifically to cathode materials, cathode sheets, and batteries. The cathode material includes a substrate and a coating layer; the coating layer includes compounds containing Li, Nb, and W elements. The Li, Nb, and W compounds on the surface of the substrate can optimize the surface of the cathode material, reduce impedance, and thereby improve the cycle stability and thermal stability of the lithium-ion battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to cathode materials, cathode sheets, and batteries. Background Technology

[0002] Over the past two decades, with the increasing demand for energy density and higher operating voltage in lithium-ion batteries, the problems and challenges that have arisen also urgently need to be addressed.

[0003] Under high voltage, the large-scale extraction of lithium leads to a gradual imbalance of charge within the material. Multiple phase transitions occur after lithium extraction, and lithium atoms are extracted from the surface first. Therefore, during prolonged charging, the amount of lithium in the surface structure is less than that in the bulk structure. Clearly, the surface structure requires much higher structural stability than the bulk structure, necessitating specific phase transition suppression strategies for surface-containing lithium cathode materials. Common strategies involve coating the cathode material surface, and many coatings exist. However, their affinity for the cathode material is limited, making them prone to detachment under long-term cycling, leading to random failures. Summary of the Invention

[0004] In view of this, the present invention provides a positive electrode material, a positive electrode sheet, and a battery. The positive electrode material exhibits good bulk and surface structure stability under high voltage, thereby improving the cycle stability and thermal stability of lithium-ion batteries under high voltage.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a cathode material comprising a matrix and a coating layer;

[0007] The coating layer includes compounds containing Li (lithium), Nb (niobium), and W (tungsten).

[0008] Preferably, compounds containing Li, Nb, and W elements include Li d Nb e W f O6,

[0009] Among them, 0.95 < d < 1.05, 0.95 < e < 1.05, and 0.95 < f < 1.05;

[0010] Preferably, the compound containing Li, Nb, and W elements is a lithium niobium tungsten oxide compound, LiNbWO6.

[0011] More preferably, the compound containing Li, Nb, and W elements is a lithium niobium tungsten oxide compound LiNbWO6 with a P-421m structure.

[0012] Preferably, the mass content of compounds containing Li, Nb, and W elements in the cathode material is 0.02% to 1%. For example, it can be any value or a range between any two values ​​from 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, to 1%. Cathode materials within the above content range exhibit higher discharge specific capacity and better rate performance, which is beneficial for improving cycle stability and the thermal stability of the material. Excessive content of compounds containing Li, Nb, and W elements will reduce discharge specific capacity and worsen rate performance; conversely, insufficient content of compounds containing Li, Nb, and W elements will have little effect on improving the surface stability of the matrix material under high voltage and the stability of the interface with the electrolyte, which is detrimental to improving cycle stability and the thermal stability of the material.

[0013] Preferably, the coating layer thickness is 10–50 nm.

[0014] Preferably, the coating layer also includes spinel-structured compounds.

[0015] Preferably, the general chemical formula of the spinel-structured compound is AB. 2-m C m O4,

[0016] Where 0 ≤ m < 0.01, A and B are each independently selected from one of Al, Mg, Ti, Co, and Ni, and A and B are different, and C is selected from at least one of Al, Mg, Ti, W, Nb, Mo, Te, and Ce.

[0017] Preferably, the spinel structure compound in the cathode material has a mass content of 0.02% to 1%; for example, any value or range between any two values ​​from 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, to 1%. Cathode materials with spinel structure compound content within the above range exhibit higher discharge specific capacity and better rate performance, which is beneficial for improving cycle stability and thermal stability. Excessive spinel structure compound content reduces discharge specific capacity and deteriorates rate performance; insufficient content has little effect on improving the surface stability of the matrix material under high voltage and the stability of the interface with the electrolyte, which is detrimental to improving cycle stability and thermal stability.

[0018] In a specific embodiment provided by this invention, the spinel-structured compound is NiCo. 1.995 W0.005 O4 or NiCo 1.995 Ti 0.005 O4.

[0019] In embodiments of the present invention, the coating layer is one layer or two layers.

[0020] Preferably, the coating layer is a two-layer coating layer, including a coating layer of spinel structure compound as the first coating layer, which is disposed on the surface of the substrate; and a coating layer of compound containing Li, Nb and W elements as the second coating layer, which is disposed on the surface of the substrate covering the first coating layer.

[0021] Spinel-structured compounds are coated onto the surface of the matrix material, either completely or partially. Coating the cathode material with spinel-structured compounds can alleviate the instability of the surface and interface structure during high-voltage cycling, reduce microcrack formation, and improve the cycle performance and safety of the cathode material.

[0022] Compounds containing Li, Nb, and W are coated onto the surface of spinel-structured compounds, with coatings being either complete or partial. By employing surface-coated lithium-niobium-tungsten-oxygen fast-ion conductor compounds, the radius W of the high-valence ions in the fast-ion conductor compounds is increased. 6+ and Nb 5+ It can penetrate to the surface of the cathode material, increasing the interlayer spacing and improving the lithium-ion diffusion performance on the cathode material surface, thereby improving the kinetic performance. Furthermore, lithium-niobium-tungsten-oxygen fast-ion conductor compounds can provide an additional lithium source, exhibiting a certain lithium replenishment effect, thus increasing the specific capacity of the cathode material.

[0023] Among them, spinel structure compounds on the substrate surface can not only stabilize the structure of cathode materials under high voltage, but also form a gradient doping structure from the surface to the bulk phase during the synthesis process, thereby improving the bulk phase structure stability of the cathode material. Compounds containing Li, Nb, and W elements on the surface of spinel structure compounds can further optimize the surface of the cathode material, reduce impedance, and thus improve the cycle stability and thermal stability of lithium-ion batteries.

[0024] Preferably, the thickness of the first coating layer is 5–30 nm; for example, any value or any pair of values ​​from 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, and 30 nm. Cathode materials within this thickness range exhibit higher discharge capacity and better rate performance, which is beneficial for improving cycle stability and the thermal stability of the material. Excessive thickness reduces discharge capacity and deteriorates rate performance; insufficient thickness has little effect on improving the surface stability of the substrate material under high voltage and the stability of the interface with the electrolyte, which is detrimental to improving cycle stability and the thermal stability of the material.

[0025] Preferably, the thickness of the second coating layer is 5–30 nm; for example, any value or any pair of values ​​from 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, and 30 nm. Cathode materials within this thickness range exhibit higher discharge capacity and better rate performance, which is beneficial for improving cycle stability and the thermal stability of the material. Excessive thickness reduces discharge capacity and deteriorates rate performance; insufficient thickness has little effect on improving the surface stability of the substrate material under high voltage and the stability of the interface with the electrolyte, which is detrimental to improving cycle stability and the thermal stability of the material.

[0026] Preferably, the sum of the thicknesses of the first and second coating layers is 10–50 nm. For example, it can be any value or a range between any two values ​​from 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, to 50 nm. Cathode materials within this thickness range exhibit higher discharge capacity and better rate performance, which is beneficial for improving cycle stability and the thermal stability of the material. Excessive thickness reduces discharge capacity and deteriorates rate performance; insufficient thickness has little effect on improving the surface stability of the substrate material under high voltage and the stability of the interface with the electrolyte, which is detrimental to improving cycle stability and the thermal stability of the material.

[0027] In an embodiment of the present invention, the matrix is ​​doped with elements A and B, each of which is independently selected from one of Al, Mg, Ti, Co, and Ni, and A and B are different; elements A and B are in a gradient doping state in the matrix, and the content of gradient doping gradually decreases from the surface to the bulk phase.

[0028] According to an embodiment of the present invention, AB 2-mC m O4 and Li d Nb e W f O6 is introduced during the second or third sintering process. During the sintering process, AB 2-m C m The A and B elements in O4 also diffuse uniformly into the surface of the matrix material, exhibiting gradient doping characteristics. The diffusion of A element can effectively suppress the H1-3 phase transition under high voltage (i.e., the high delithiation state of the material). 2-m C m O4 not only enhances the stability of the surface structure but also mitigates the electrolyte oxidative decomposition and surface byproduct accumulation caused by the strong oxidizing properties of the matrix material under high voltage and highly deLi-depleted conditions. It inhibits the dissolution of transition metal elements and surface structure damage on the matrix material surface, further improving the interfacial stability between the electrolyte and the matrix material under high voltage. Simultaneously, the fast-ion conductor coating also facilitates lithium-ion diffusion, thereby improving kinetic performance. Furthermore, the lithium-niobium-tungsten oxide compound Li... d Nb e W f O6 can also provide an additional lithium source during charging and discharging, thus ensuring capacity during the charging and discharging process. Therefore, AB 2-m C m O4 and Li d Nb e W f The O6 coating improves the structural and thermal stability of the matrix material, thereby enhancing its electrochemical performance under high voltage.

[0029] In embodiments of the present invention, the matrix includes one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium-rich manganese-based materials.

[0030] As a preferred option, the general chemical formula of the matrix is ​​Li. x1 Co 1-x-y Al x M y O2 and / or Li x2 Ni 1-a-b-z Co a R b N z O2,

[0031] Wherein, 0.95 < x1 < 1.05, 0.03 ≤ x ≤ 0.05 or x = 0, 0.0005 ≤ y ≤ 0.01, M includes at least one of Mg, Mn, Ni, Ti, La, Y, Zr, W, Nb, Te, and Ce; R includes Mn and / or Al;

[0032] 0.95 < x2 < 1.05, 0 ≤ a ≤ 1 / 3, 0 ≤ b ≤ 1 / 3, 0 ≤ z ≤ 0.01, and N is selected from at least one of Mn, Al, Mg, Ti, Zr, W, Nb, B, La, Y, Mo, and Si;

[0033] Preferably, 0 ≤ a + b ≤ 0.5.

[0034] Preferably, the particle size D50 of the cathode material is 3–20 μm; for example, any value or a range between any two values ​​from 3 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, to 20 μm. With a D50 within this range, the cathode material can balance compaction and rate performance.

[0035] In one specific embodiment of the present invention, the general chemical formula of the matrix is ​​Li. x1 Co 1-x-y Al x M y When O2 is present, the particle size D50 of the positive electrode material is 10–20 μm; for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm.

[0036] The range of values ​​within 20 μm, either any single value or any pairwise values. Within this range, the cathode material's D50 balances both compaction and rate performance.

[0037] In another specific embodiment of the present invention, the chemical formula of the matrix is ​​Li. x2 Ni 1-a-b-z Co a Mn b N z In O2, the particle size D50 of the positive electrode material is 3–15 μm. For example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm.

[0038] The value can be any value within 13μm, 14μm, or 15μm, or any range between any two values. If the D50 of the cathode material falls within this range, the cathode material can balance compaction and rate performance.

[0039] Preferably, the compaction density of the cathode material is 3.5–5 g / cm³. 3 For example, 3.5g / cm³ 3 3.6g / cm 3 3.8g / cm 3 4g / cm 3 4.2g / cm 3 4.4 g / cm 3 ,

[0040] 4.6g / cm 3 4.8g / cm 3 5g / cm 3 The compaction density is any value or any range between any two values ​​in the range. Within this compaction density range, the cathode material has a higher compaction density, resulting in higher battery capacity and better cycle performance. Excessive compaction density causes the material particles to be too tightly packed, increasing electronic conductivity but reducing ion mobility channels, leading to increased polarization during discharge, faster voltage drop, and reduced capacity. Conversely, insufficient compaction density results in larger particle distances, leading to greater electrolyte absorption and facilitating ion movement, but also smaller contact area between particles, reducing electronic conductivity and increasing discharge polarization.

[0041] In one specific embodiment of the present invention, the general chemical formula of the matrix is ​​Li. x1 Co 1-x-y Al x M y In O2, the compaction density of the cathode material is 3.5–4.5 g / cm³. 3 For example, 3.5g / cm³ 3 3.6g / cm 3 3.8g / cm 3 4g / cm 3 4.2g / cm 3 4.4 g / cm 3 4.5g / cm 3 The compaction density is any value or any range between any two values ​​in the range. Within this compaction density range, the cathode material has a higher compaction density, resulting in higher battery capacity and better cycle performance. Excessive compaction density causes the material particles to be too tightly packed, increasing electronic conductivity but reducing ion mobility channels, leading to increased polarization during discharge, faster voltage drop, and reduced capacity. Conversely, insufficient compaction density results in larger particle distances, leading to greater electrolyte absorption and facilitating ion movement, but also smaller contact area between particles, reducing electronic conductivity and increasing discharge polarization.

[0042] In another specific embodiment of the present invention, the chemical formula of the matrix is ​​Li. x2 Ni 1-a-b-z Co a Mn b N z In O2, the compaction density of the cathode material is 4–5 g / cm³. 3 For example, 4g / cm³ 3 4.2g / cm 3 4.4 g / cm 3 4.6g / cm 3 4.8g / cm 35g / cm 3 The compaction density is any value or any range between any two values ​​in the range. Within this compaction density range, the cathode material has a higher compaction density, resulting in higher battery capacity and better cycle performance. Excessive compaction density causes the material particles to be too tightly packed, increasing electronic conductivity but reducing ion mobility channels, leading to increased polarization during discharge, faster voltage drop, and reduced capacity. Conversely, insufficient compaction density results in larger particle distances, leading to greater electrolyte absorption and facilitating ion movement, but also smaller contact area between particles, reducing electronic conductivity and increasing discharge polarization.

[0043] The present invention also provides a method for preparing the above-mentioned cathode material, comprising the following steps:

[0044] a) Preparation of the matrix;

[0045] b) The matrix prepared in step a) is mixed with the spinel structure compound and subjected to a first sintering to obtain a cathode material coated with the first coating layer;

[0046] c) The cathode material coated with the first coating layer prepared in step b) is mixed with the fast ion conductor compound, and then subjected to a second sintering to obtain the final cathode material.

[0047] In an embodiment of the present invention, the general chemical formula of the matrix is ​​Li. x1 Co 1-x-y Al x M y O2 or Li x2 Ni 1-a-b- z Co a Mn b N z O2,

[0048] In one embodiment of the present invention, the matrix Li x1 Co 1-x-y Al x M y The method for preparing O2 includes the following steps:

[0049] (a11) Soluble aluminum salt, soluble cobalt salt, solvent, and complexing precipitant are mixed and co-precipitated to obtain Al-doped Co3O4 precursor.

[0050] (a12) The precursor prepared in step (a11), the oxide containing element M, and the lithium source are mixed and sintered in air at 800–1100°C for 8–16 h to obtain the matrix material Li. x1 Co 1-x-y Al x M y O2.

[0051] Preferably, the soluble aluminum salt and soluble cobalt salt can be sulfates, carbonates, acetates, chlorides, nitrates, etc.

[0052] Preferably, the solvent is water and / or an organic solvent.

[0053] In the embodiments provided by the present invention, the solvent includes any one or a combination of at least two of the following: water, methanol, ethanol, acetone, propanol, isopropanol, ethylene glycol, n-butanol, cyclohexane, ethylenediamine, N-methylpyrrolidone, benzene, toluene, xylene, dimethyl ether, or diethyl ether.

[0054] Preferably, the complexing precipitant includes, but is not limited to, one or more of hydroxides, carbonates, oxalates, and ammonia.

[0055] In the embodiments provided by the present invention, the complexing precipitant is ammonia and sodium carbonate.

[0056] Preferably, the oxide containing element M can be any form of oxide or a mixture thereof.

[0057] In the embodiments provided by the present invention, the lithium source includes at least one of lithium carbonate, lithium nitrate, and lithium hydroxide.

[0058] In the specific embodiments provided by the present invention, the lithium source is lithium carbonate.

[0059] According to an embodiment of the present invention, in step (a11), the molar ratio of cobalt in the soluble cobalt salt to aluminum in the soluble aluminum salt, n(Co):n(Al), is 100:(3-5).

[0060] According to an embodiment of the present invention, in step (a11), the solvent is water, and the mass ratio of soluble cobalt salt to water is (500-700):1500.

[0061] According to an embodiment of the present invention, in step (a11), the complexing precipitant includes ammonia water, the concentration of ammonia water is 10% to 15%, and the volume ratio of ammonia water to water is 2:1.

[0062] According to an embodiment of the present invention, in step (a11), the coprecipitation reaction is carried out under an inert atmosphere and with stirring.

[0063] In a specific embodiment of the present invention, the inert atmosphere is nitrogen.

[0064] According to an embodiment of the present invention, step (a11) is carried out under the conditions of nitrogen gas and stirring, with the nitrogen gas flow rate being 20-40 mL / min and the stirring speed being 650-850 rpm.

[0065] According to an embodiment of the present invention, in step (a11), the pH of the coprecipitation reaction is 6-8, the reaction temperature is 50-65°C, and the reaction time is 36-50 h.

[0066] According to an embodiment of the present invention, in step (a12), the ratio of n(Li):n(Co+Al):n(M) in the lithium source, Al-doped Co3O4, and oxide containing M element is 1.0~1.08:1:(0.0005~0.01).

[0067] As a preferred option, the conditions for the first sintering are: the sintering environment is an air atmosphere or an oxygen atmosphere, the sintering temperature is 800-1000℃, and the sintering time is 5-10h.

[0068] Preferably, the conditions for the first or second sintering are: the sintering environment is an air atmosphere or an oxygen atmosphere, the sintering temperature is 700-1000℃, and the sintering time is 4-10h.

[0069] In another embodiment of the present invention, the matrix material Li x2 Ni 1-a-b-z Co a Mn b N z The method for preparing O2 includes the following steps:

[0070] (a21) A soluble nickel salt, a soluble cobalt salt, a soluble manganese salt, a solvent, and a complexing precipitant are mixed and subjected to a co-precipitation reaction to obtain Ni. 1-a-b Co a Mn b (OH)2 precursor;

[0071] (a22) The above-mentioned precursor, lithium source, and N-containing oxide are mixed and sintered at 700–1000°C for 8–16 h in an air or oxygen atmosphere to obtain the matrix material Li. x2 Ni 1-a-b-z Co a Mn b N z O2.

[0072] Preferably, the soluble nickel salt, soluble cobalt salt, and soluble manganese salt can be sulfates, carbonates, acetates, chlorides, nitrates, etc.

[0073] Preferably, the solvent is water and / or an organic solvent.

[0074] In the embodiments provided by the present invention, the solvent includes any one or a combination of at least two of the following: water, methanol, ethanol, acetone, propanol, isopropanol, ethylene glycol, n-butanol, cyclohexane, ethylenediamine, N-methylpyrrolidone, benzene, toluene, xylene, dimethyl ether, or diethyl ether.

[0075] Preferably, the complexing precipitant includes, but is not limited to, one or more of hydroxides, carbonates, oxalates, and ammonia.

[0076] In the embodiments provided by the present invention, the complexing precipitant is ammonia and sodium hydroxide.

[0077] Preferably, the oxide containing nitrogen can be any form of oxide or a mixture thereof.

[0078] In the embodiments provided by the present invention, the lithium source includes at least one of lithium carbonate, lithium nitrate, and lithium hydroxide.

[0079] In the specific embodiments provided by the present invention, the lithium source is lithium hydroxide.

[0080] According to an embodiment of the present invention, in step (a21), the molar ratio n(Ni):n(Co):n(Mn) of nickel in soluble nickel salt, cobalt in soluble cobalt salt, and manganese in soluble manganese salt is (0.5~1):(0~1 / 3):(0~1 / 3).

[0081] According to an embodiment of the present invention, in step (a21), the pH of the coprecipitation reaction is 10-12, the reaction temperature is 50-60°C, and the reaction time is 24-48h.

[0082] According to an embodiment of the present invention, in step (a21), the complexing precipitant includes ammonia water, the concentration of ammonia water is 10% to 18%, and the volume ratio of ammonia water to water is 2:1.

[0083] According to an embodiment of the present invention, in step (a21), the coprecipitation reaction is carried out under an inert atmosphere and with stirring.

[0084] In a specific embodiment of the present invention, the inert atmosphere is nitrogen.

[0085] According to an embodiment of the present invention, in step (a22), the lithium source and Ni 1-a-b Co a Mn b In the precursor of (OH)2 and oxides containing N, n(Li):n(Ni+Co+Mn):n(N) = (1.0~1.05):(0.9~1):(0~0.1).

[0086] According to an embodiment of the present invention, the nano-spinel structure compound AB 2-m C m O4 coating agent and nano-lithium niobium tungsten oxide coating agent Li d Nb e W fO6 can be obtained by purchase or experimental preparation, and the preparation method is a common preparation method in this field.

[0087] The present invention also provides a positive electrode sheet comprising the above-mentioned positive electrode material.

[0088] Preferably, the compaction density of the positive electrode sheet is 3.2–4.5 g / cm³. 3 .

[0089] In one specific embodiment of the present invention, the general chemical formula of the matrix is ​​Li. x1 Co 1-x-y Al x M y In O2, the compaction density of the positive electrode is 4.0–4.5 g / cm³. 3 .

[0090] In another specific embodiment of the present invention, the chemical formula of the matrix is ​​Li. x2 Ni 1-a-b-z Co a Mn b N z In O2, the compaction density of the positive electrode is 3.2–4.0 g / cm³. 3 .

[0091] Within the aforementioned compaction density range, it is evident that the positive electrode has a high compaction density, thereby increasing the energy density of the battery.

[0092] According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on at least one side surface of the positive current collector, wherein the positive active material layer includes the aforementioned positive electrode material.

[0093] According to embodiments of the present invention, the positive electrode active material layer further includes a conductive agent. In some embodiments, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, carbon fiber, graphene, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0094] According to embodiments of the present invention, the positive electrode active material layer further includes a binder. In some embodiments, the binder is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, epoxy resin, butadiene rubber binders, and acrylonitrile binders.

[0095] According to an embodiment of the present invention, the mass percentage of each component in the positive electrode active material layer is as follows:

[0096] 91–97.5 wt% positive electrode material, 0.5–4 wt% conductive agent, and 2–5 wt% binder.

[0097] The present invention also provides a battery comprising the above-described positive electrode material or positive electrode sheet.

[0098] Preferably, the battery is a lithium-ion battery.

[0099] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0100] This invention utilizes lithium niobium tungsten oxide compound Li d Nb e W f O6, as a coating layer, can optimize the surface of the cathode material, reduce impedance, and thus improve the cycle stability and thermal stability of lithium-ion batteries.

[0101] This invention utilizes spinel-structured compounds AB, which exhibit high structural and thermal stability under high voltage. 2-m C m O4 is used as the first coating layer of the matrix material, and then lithium niobium tungsten oxide compound Li is applied. d Nb e W f O6 serves as the second coating layer. The spinel structure compound on the substrate surface not only stabilizes the structure of the cathode material under high voltage, but also forms a gradient doping structure from the surface to the bulk phase during the synthesis process, thereby improving the bulk structural stability of the cathode material. The fast ion conductor compound on the surface of the spinel structure compound can further optimize the surface of the cathode material, reduce impedance, and thus improve the cycle stability and thermal stability of the lithium-ion battery. Attached Figure Description

[0102] Figure 1 A schematic diagram of the cathode material in Example 1;

[0103] Figure 2 Morphology diagram of the cathode material in Example 1;

[0104] Figure 3 Cross-sectional morphology of the cathode material in Example 1.

[0105] Figure label:

[0106] 1. Matrix; 2. First coating layer; 3. Second coating layer. Detailed Implementation

[0107] This invention discloses a positive electrode material, a positive electrode sheet, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0108] Terminology Explanation:

[0109] Spinel-type structure: In this crystal structure, oxygen ions are arranged in a cubic close-packed configuration. Divalent cations fill one-eighth of the tetrahedral voids, and trivalent cations fill one-half of the octahedral voids. Magnesium aluminum spinel (MgAl₂O₄) is a typical example: the spinel unit cell can be divided into eight small cubic units, each composed of four A-type and four B-type units. Each A-type and B-type unit has four oxygen ions. 2- Ions, O in the unit cell 2- The number is 8 * 4 = 32. Mg 2+ Located at the center and half of the vertices of type A small units and half of the vertices of type B small units, Mg in the unit cell 2+ The number is 4*(1+4 / 8)+4*4 / 8. Mg 2+ It exhibits tetracoordination, meaning it occupies O 2- Tetrahedral voids in close-packed structures. Each type B unit contains 4 Al atoms. 3+ Al in the unit cell 3+ The number of them is 4*4=16. Al 3+ It exhibits hexacoordination, meaning it occupies O 2- Octahedral voids in close packing.

[0110] Fast ionic conductors, also known as superionic conductors or solid electrolytes, are distinguished from ordinary ionic conductors by their fundamental characteristic: within a certain temperature range, they possess ionic conductivity (0.01 Ω·cm) comparable to liquid electrolytes and a low ionic activation energy (≤0.40 eV). Most fast ionic conductors are inorganic compounds, but many organic materials are also fast ionic conductors of silver, copper, and hydrogen ions.

[0111] LiNbWO6 exhibits both tetragonal and hexagonal phases. The space group for the tetragonal LiNbWO6 is P-421m, while the space group for the hexagonal LiNbWO6 is R3c. Crystal structure characterization results indicate that the tetragonal LiNbWO6 possesses relatively wide transport channels (OO spacing within the channels is...). It can be used for the insertion and extraction of alkali ions; while the shortest distance between O and O in the transport channels of hexagonal LiNbWO6 is Furthermore, due to the surface energy of tetragonal LiNbWO6 (0.419 J / m²), 2 The surface energy is very low, and it tends to form a thin (~300 nm) disc-like structure; while hexagonal LiNbWO6 has a very high surface energy (6.074 J / m²). 2 This makes it easy to form cubic micron-like structures with a thickness of about 5 micrometers.

[0112] The reagents, instruments, and materials used in this invention can all be obtained through commercial channels.

[0113] The present invention will be further illustrated below with reference to the embodiments:

[0114] Example 1

[0115] I. Preparation of cathode materials

[0116] 1) An Al-doped Co3O4 precursor was synthesized using a co-precipitation method. Aluminum sulfate and cobalt sulfate were prepared in a molar ratio of n(Al):n(Co) = 3.5:96.5, dissolved in deionized water, and subjected to a co-precipitation reaction in a reactor to obtain the Al-doped Co3O4 precursor. The reaction temperature was 50℃, the reaction time was 36 h, and ammonia and sodium carbonate were introduced to adjust the pH of the reaction to 7.5. The Al-doped Co3O4 precursor, lithium carbonate, MgO, and La2O3 were mixed in a molar ratio of n(Li):n(Co+Al):n(Mg):n(La) = 1.05:1:0.004:0.0005 and sintered in air at 1050℃ for 12 h to obtain the matrix material LiCo. 0.9605 Al 0.035 Mg 0.004 La 0.0005 O2;

[0117] 2) The matrix material LiCo from step 1) 0.9605 Al 0.035 Mg 0.004 La 0.0005 O2 and spinel-structured compound NiCo 1.995 W 0.005 O4 was mixed uniformly at a weight ratio of 1:0.5% and sintered at 900°C in air for 8 hours to obtain the spinel-structured compound NiCo. 1.995 W 0.005 O4-coated cathode material;

[0118] 3) NiCo in step 2) 1.995 W 0.005O4-coated cathode material and LiNbWO6 were mixed uniformly at a weight ratio of 1:0.5% and sintered in air at 800°C for 6 hours to obtain the final spinel structure compound NiCo. 1.995 W 0.005 A cathode material co-coated with O4 and the fast ion conductor compound LiNWO6.

[0119] Figure 2 and Figure 3 The overall morphology and cross-sectional morphology of the cathode material in this embodiment are shown respectively.

[0120] II. Button Battery Assembly:

[0121] The above-mentioned positive electrode material, conductive agent, and binder PVDF were weighed and uniformly mixed at a mass ratio of 95:2.5:2.5, and dispersed in N-methylpyrrolidone (NMP) solvent to form a slurry. The slurry was uniformly coated on aluminum foil and dried at 80°C for 12 hours to obtain a positive electrode sheet. The dried positive electrode sheet was rolled and cut into round pieces and placed in a glove box for later use. Using the prepared round pieces as the positive electrode, lithium metal as the negative electrode, Celgard 2400 (microporous polypropylene membrane) as the separator, and 1 mol / L LiPF6+ (EC:EMC:DMC=1:1:1) as the electrolyte, a 2032 coin cell was assembled.

[0122] III. Lithium-ion battery assembly:

[0123] (1) Preparation of positive electrode

[0124] The prepared cathode material, binder, conductive carbon black (SP), and carbon nanotubes (CNTs) were mixed in a weight ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum to form a homogeneous and fluid cathode slurry. NMP was added during the process to adjust the solid content of the cathode slurry. The cathode slurry was then uniformly coated onto 12μm aluminum foil, with the coating density controlled at 15.0 mg / cm². 2 The coated aluminum foil was baked in ovens with five different temperature gradients. The baked electrode was then rolled twice. After rolling, the electrode was slit and super-welded to obtain the desired positive electrode.

[0125] (2) Preparation of negative electrode

[0126] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber (SBR), and conductive agent acetylene black (SP) were mixed in a weight ratio of 96.5:1.0:1.0:1.5, and deionized water was added as a solvent. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto copper foil. The coated copper foil was baked in an oven with three different temperature gradients. The baked electrode was then rolled twice. After rolling, the electrode was slit and super-welded to obtain the desired negative electrode.

[0127] (3) Electrolyte preparation and separator preparation

[0128] The electrolyte uses a commercially available electrolyte, with ethylene carbonate, propylene carbonate, and diethyl carbonate in a mass ratio of 1:1:1 as the solvent, and 1 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt. Film-forming additives and high-voltage additives are also added to the composition. A 7+3μm hybrid coating membrane (polypropylene substrate + PVDF & ceramic hybrid coating) is selected as the separator.

[0129] (4) Preparation of lithium-ion batteries

[0130] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence. The positive electrode is connected to aluminum tabs via aluminum foil sheets, and the negative electrode is connected to nickel tabs via copper foil sheets, thus preparing a multi-tab type battery cell. Two layers of separator sheets wrap the negative electrode sheet, and the positive electrode sheet is placed on the separator sheets, ensuring that the separator sheets are between the positive and negative electrodes to isolate and subsequently transport lithium ions. Then, the cells are wound to obtain bare cells without electrolyte filling. The bare cells are heat-sealed in a shell made of aluminum-plastic film, and electrolyte is injected into the bare cells with a moisture content of <200ppm after baking. After vacuum sealing, hot and cold pressing, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0131] Example 2

[0132] The preparation method is the same as in Example 1, except that the spinel structure compound in step 2) of the cathode material preparation is NiCo. 1.995 Ti 0.005 O4.

[0133] Example 3

[0134] The preparation method is the same as in Example 1, except that the mass percentage of the fast ion conductor compound in step 3) of the cathode material preparation is 0.75%.

[0135] Example 4

[0136] The preparation method is the same as in Example 1, except that step 1) of the cathode material preparation is as follows:

[0137] Al-doped Co3O4 precursor was synthesized by co-precipitation. Aluminum sulfate and cobalt sulfate were prepared in a molar ratio of n(Al):n(Co) = 3.5:96.5, dissolved in deionized water, and co-precipitated in a reactor to obtain the Al-doped Co3O4 precursor. The reaction temperature was 50℃, and the reaction time was 36 h. Ammonia and sodium carbonate were introduced to adjust the pH to 7.5. The Al-doped Co3O4 precursor, lithium carbonate, MgO, and ZrO2 were mixed in a molar ratio of n(Li):n(Co+Al):n(Mg):n(Zr) = 1.05:1:0.004:0.0005 and sintered in air at 1050℃ for 12 h to obtain the matrix material LiCo. 0.9605 Al 0.035 Mg 0.004 Zr 0.0005 O2, the rest are prepared according to the preparation steps in Example 1.

[0138] Example 5

[0139] The preparation method is the same as in Example 1, except that the content of the spinel structure compound in step 2) of the cathode material preparation is 0.02%.

[0140] Example 6

[0141] The preparation method is the same as in Example 1, except that the content of the spinel structure compound in step 2) of the cathode material preparation is 1%.

[0142] Example 7

[0143] The preparation method is the same as in Example 1, except that step 1) of the cathode material preparation is as follows:

[0144] Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared in a molar ratio of n(Ni):n(Co):n(Mn) = 8:1:1, dissolved in deionized water, and subjected to a co-precipitation reaction in a reactor to obtain Ni. 0.8 Co 0.1 Mn 0.1 (OH)₂; ammonia and sodium hydroxide were introduced to adjust the pH of the reaction to 11, the reaction temperature was 55℃, and the reaction time was 48h under a nitrogen atmosphere; Ni 0.8 Co 0.1 Mn 0.1 (OH)2, lithium hydroxide, ZrO2, and WO3 were mixed in a molar ratio of n(Li):n(Ni+Co+Mn):n(Zr):n(W) = 1.05:1:0.002:0.001 and sintered at 800℃ for 12 hours in an oxygen atmosphere to obtain the matrix material LiNi. 0.8 Co 0.097 Mn 0.1 Zr0.002 W 0.001 O2, the rest are prepared according to the preparation steps in Example 1.

[0145] Example 8

[0146] The preparation method is the same as in Example 1, except that step 1) of the cathode material preparation is as follows:

[0147] Nickel sulfate and manganese sulfate were prepared in a molar ratio of n(Ni):n(Mn) = 7.5:2.5, dissolved in deionized water, and then co-precipitated in a reactor to obtain Ni. 0.75 Mn 0.25 (OH)₂; ammonia and sodium hydroxide were introduced to adjust the pH of the reaction to 11, the reaction temperature was 55℃, and the reaction time was 48h under a nitrogen atmosphere; Ni 0.75 Mn 0.25 Li(OH)₂, lithium hydroxide, Al₂O₃, and ZrO₃ were mixed in a molar ratio of n(Li):n(Ni+Mn):n(Al):n(Zr) = 1.05:1:0.006:0.002 and sintered at 850°C for 12 hours in an oxygen atmosphere to obtain the matrix material LiNi. 0.75 Mn 0.242 Al 0.006 Zr 0.002 O2, the rest are prepared according to the preparation steps in Example 1.

[0148] Example 9

[0149] The preparation method is the same as in Example 1, except that step 2) of coating with spinel structure compound is not performed during the preparation of the cathode material.

[0150] Comparative Example 1

[0151] The preparation method is the same as in Example 1, except that the coating of spinel structure compound in step 2) and the coating of fast ion conductor compound in step 3) are omitted during the preparation of the cathode material.

[0152] Comparative Example 2

[0153] The preparation method is the same as in Example 1, except that the fast ion conductor compound coating in step 3) is not included in the preparation of the cathode material.

[0154] Comparative Example 3

[0155] The preparation method of Example 8 is the same, except that the coating of spinel structure compound in step 2) and the coating of fast ion conductor compound in step 3) are not performed during the preparation of the cathode material.

[0156] Comparative Example 4

[0157] The preparation method of Example 8 is the same, except that the spinel structure compound is not coated in step 2) during the preparation of the cathode material.

[0158] Comparative Example 5

[0159] The preparation method of Example 8 is the same, except that the fast ion conductor compound coating in step 3) is not included in the preparation of the cathode material.

[0160] Table 1. Feature parameters of the embodiments and comparative examples

[0161]

[0162]

[0163] Test case

[0164] a) Discharge capacity and rate testing

[0165] The button batteries prepared above were tested at a temperature of 25°C and a voltage range of 3.0 to 4.6V, with a charging rate of 0.1C and a discharging rate of 0.1C, 0.2C, 0.5C, 1C, and 2C respectively.

[0166] b) Cyclic capacity test

[0167] The battery cells were placed in an environment of 25℃±2℃ (45℃±2℃);

[0168] 1) Discharge at 0.7C to the lower limit voltage (3.0V), and let stand for 10 minutes;

[0169] 2) Charge at 2C to the upper limit voltage (4.5V), then stop at 0.05C and let stand for 10 minutes;

[0170] 3) Discharge at 2C to the lower limit voltage (3.0V), and let stand for 10 minutes;

[0171] 4) Charge at 2C to the upper limit voltage (4.5V), cut off at 0.05C, and let stand for 10 minutes; repeat steps 3-4 for 1000 cycles.

[0172] Capacity retention formula: The capacity tested in the first cycle is recorded as A1, and the capacity tested after 800 cycles is recorded as A2; Capacity retention = A2 / A1 × 100%.

[0173] The specific test results are shown in Table 2.

[0174] Table 2 Battery performance of the examples and comparative examples

[0175]

[0176] As can be seen from the specific test results of the examples and comparative examples in Table 2, the battery using the embodiment of the present invention exhibits excellent electrochemical performance in terms of specific capacity, rate performance and cycle performance at a high voltage of 3.0 to 4.6V, while the battery of the comparative example is inferior to the battery of the example in terms of specific capacity, rate performance and cycle performance.

[0177] Compared with Comparative Example 1, Example 9 was coated with the fast ion conductor compound LiNWO6, which improved the rate performance and capacity. This is mainly because the fast ion conductor compound LiNWO6 improves the diffusion performance of lithium ions, enhances the kinetic performance of the battery, and can provide an additional Li source, thus having a certain Li replenishment effect.

[0178] The main difference between Example 1 and Comparative Examples 1 and 2 is that Comparative Example 1 did not have any coating, so its overall electrochemical performance was poor; Comparative Example 2 was coated with a spinel-structured compound, which improved the bulk and structural stability of the cathode material; and the effect of coating the two individually was not as good as that of coating them together, indicating that coating the spinel-structured compound and the fast-ion conductor compound together achieved a synergistic effect and enhanced the battery performance.

[0179] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a substrate and a coating layer; the coating layer includes Li d Nb e W f O6, wherein 0.95 < d < 1.05, 0.95 < e < 1.05, 0.95 < f < 1.05; the coating layer further includes a spinel-structured compound with the general chemical formula AB. 2-m C m O4, wherein 0≤m<0.01, A and B are each independently selected from one of Al, Mg, Ti, Co, Ni, and A is different from B, and C is selected from at least one of Al, Mg, Ti, W, Nb, Mo, Te, Ce; The coating layer consists of two layers, with the first coating layer being a spinel-structured compound coating layer, including Li... d Nb e W f The coating layer of O6 is a second coating layer, with the first coating layer disposed on the surface of the substrate and the second coating layer disposed on the surface of the first coating layer.

2. The cathode material according to claim 1, characterized in that, Li d Nb e W f The mass content of O6 in the cathode material is 0.02%~1%.

3. The cathode material according to claim 1, characterized in that, The coating layer includes LiNbWO6; And / or, the coating layer thickness is 10~50nm.

4. The cathode material according to claim 1, characterized in that, The spinel-structured compound has a mass content of 0.02% to 1% in the cathode material.

5. The positive electrode material according to claim 3, characterized in that, The thickness of the first coating layer is 5~30nm; And / or, the thickness of the second coating layer is 5~30nm.

6. The cathode material according to claim 1, characterized in that, The matrix is ​​doped with elements A and B, each of which is independently selected from one of Al, Mg, Ti, Co, and Ni, and A and B are different. Elements A and B are in a gradient doping state in the matrix.

7. The cathode material according to claim 6, characterized in that, The gradient doping involves a gradual decrease in content from the surface to the bulk phase.

8. The cathode material according to any one of claims 1-7, characterized in that, The matrix includes one or more of the following: transition metal lithium oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium-rich manganese-based materials.

9. The cathode material according to claim 8, characterized in that, The general chemical formula of the matrix is ​​Li. x1 Co 1-x- y Al x M y O2 and / or Li x2 Ni 1-a-b-z Co a R b N z O2, Wherein, 0.95 < x1 < 1.05, 0.03 ≤ x ≤ 0.05 or x = 0, 0.0005 ≤ y ≤ 0.01, M includes at least one of Mg, Mn, Ni, Ti, La, Y, Zr, W, Nb, Te, and Ce; R includes Mn and / or Al; 0.95 < x2 < 1.05, 0 ≤ a ≤ 1 / 3, 0 ≤ b ≤ 1 / 3, 0 ≤ z ≤ 0.01, and N is selected from at least one of Mn, Al, Mg, Ti, Zr, W, Nb, B, La, Y, Mo, and Si.

10. The cathode material according to claim 9, characterized in that, 0≤a+b≤0.

5.

11. The cathode material according to claim 1, characterized in that, The particle size D50 of the positive electrode material is 3~20μm; and / or, the compaction density of the positive electrode material is 3.5~5g / cm³. 3 .

12. The cathode material according to claim 9, characterized in that, The general chemical formula of the matrix is ​​Li. x1 Co 1-x- y Al x M y When O2 is present, the particle size D50 of the positive electrode material is 10~20μm; the compaction density of the positive electrode material is 3.5~4.5g / cm³. 3 ; And / or, the general chemical formula of the matrix is ​​Li x2 Ni 1-a-b-z Co a Mn b N z In O2, the particle size D50 of the positive electrode material is 3~15μm; the compaction density of the positive electrode material is 4~5g / cm³. 3 .

13. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1-12.

14. The positive electrode sheet according to claim 13, characterized in that, The compaction density of the positive electrode sheet is 3.2~4.5 g / cm³. 3 .

15. The positive electrode sheet according to claim 14, characterized in that, The general chemical formula of the matrix is ​​Li x1 Co 1-x-y Al x M y When O2 is present, the compaction density of the positive electrode is 4.0~4.5 g / cm³. 3 ; And / or, the general chemical formula of the matrix is ​​Li x2 Ni 1-a-b-z Co a Mn b N z When O2 is present, the compaction density of the positive electrode is 3.2~4.0 g / cm³. 3 .

16. A battery, characterized in that, The battery includes the positive electrode as described in any one of claims 13-15.

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