Positive electrode material and preparation method and application thereof

Abstract

The invention discloses a positive electrode material as well as a preparation method and application thereof, and relates to the technical field of batteries. The positive electrode material is coated with a composite plastic crystal composed of an ionic plastic crystal and a lithium salt in a molar ratio of 1: 3-1: 5; in the preparation of the positive pole piece, the problems of interface impedance and stability of sulfide electrolyte are solved through the dielectric property and fluidity of composite plastic crystal by using a non-polar mixed solvent, a composite plastic crystal infiltration process and low-temperature annealing treatment for cooperative treatment during the preparation of the positive pole piece; a specific type of non-polar mixed solvent is selected, so that dissolution and decomposition of sulfide electrolyte can be reduced to the maximum extent; a three-dimensional lithium conduction network formed by infiltration of the composite plastic crystal coating layer and the melt ensures that the sulfide electrolyte constructs a continuous transmission path in a wet process; and the low-temperature annealing treatment promotes interface fusion of plastic crystals and sulfide electrolyte to form a stable high-conductivity ion phase, so that the comprehensive performance of the battery is promoted to be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Due to its inherent safety and high energy density characteristics, the all-solid-state battery has become a key research object in the fields of electric vehicles, aerospace, etc. In the all-solid-state battery, sulfide solid electrolytes (such as Li6PS5Cl, Li3PS4) are widely studied due to their high ionic conductivity (10 -3 -10 -2 S / cm). However, in the wet positive electrode preparation process of the sulfide all-solid-state battery, there are many outstanding problems in the positive electrode material related technology, which are as follows: High interface impedance: In the wet-prepared positive electrode, there are a large number of "solid-solid" contact interfaces between the positive electrode active material, the solid-state electrolyte and the conductive agent. Due to the pores generated after the slurry is dried in the wet process, the contact tightness of these interfaces is further reduced, which greatly increases the transmission resistance of lithium ions at the interface. Taking the sulfide all-solid-state battery as an example, the space charge layer between the electrode and the solid-state electrolyte, the interface side reaction and other problems are aggravated due to poor interface contact, and the Li + depleted layer formed at the interface between the active material and the electrolyte is more serious, which seriously hinders the charge transport.

[0003] Ion transport network is discontinuous: when the positive electrode is prepared by the wet process, the positive electrode active material powder, the sulfide solid electrolyte powder and the conductive agent are in a solid-solid contact state during the dry mixing stage, and the porosity between the powders is large. During the subsequent slurry preparation, coating and drying process, more pores and cracks are easily formed in the electrode due to uneven solvent evaporation, etc., which leads to the difficulty in constructing a continuous and dense ion transport network, and the transmission path of lithium ions in the electrode is seriously blocked.

[0004] Poor adaptability of coating process to wet process: in the existing positive electrode active material coating technology, the wet coating process using transition metal oxides and carbon-containing materials to crystallize and precipitate has poor adaptability when combined with the wet preparation process of the all-solid-state battery positive electrode. The coating layer is easy to fall off, and has poor compatibility with other components. Moreover, the dispersion of the traditional coating material in the wet slurry is poor, which further affects the performance of the electrode.

[0005] Significant influence of solvent: the selection of the solvent in the wet process is crucial. The polar solvent will cause the stability of the sulfide solid electrolyte to decrease. At the same time, if the solvent remains in the electrode, it will reduce the ionic conductivity of the electrode, and completely removing the solvent may cause the structure of the electrode to shrink and generate more pores, which affects the contact between the components.

[0006] Therefore, reducing the interface impedance, improving the stability of the sulfide electrolyte, stabilizing the ion transmission network, improving the interface compatibility, and further improving the comprehensive performance of the battery become technical problems to be solved in the field.

[0007] In view of this, the present application is proposed. SUMMARY

[0008] The present application aims to provide a positive electrode material and a preparation method and application thereof to solve the above technical problems.

[0009] The present application is implemented as follows: In a first aspect, embodiments of the present application provide a positive electrode material, the surface of the positive electrode material being coated with a lithium ion-conducting plastic crystal layer. The lithium ion-conducting plastic crystal layer has a thickness of 5-15 nm and is composed of a composite plastic crystal of an ion plastic crystal and a lithium salt in a molar ratio of 1:3-1:5.

[0010] In a second aspect, embodiments of the present application provide a preparation method of the positive electrode material as described above, comprising the following steps: The positive electrode material is added to a solvent and ultrasonically dispersed at a power of 300-500 W under inert gas protection for 15-20 min to form a dispersion liquid with a concentration of 0.1-0.3 g / mL; The composite plastic crystal is added to the dispersion liquid, and after reaction at 50-65℃ and 600-800 rpm for 30-40 min, the positive electrode material with a thickness of 5-15 nm is prepared; The mass ratio of the composite plastic crystal to the positive electrode material is 1:5-1:8.

[0011] In a third aspect, embodiments of the present application provide a positive electrode tab, comprising the positive electrode material as described above or prepared by the preparation method as described above.

[0012] In a fourth aspect, embodiments of the present application provide a preparation method of the positive electrode tab as described above, comprising the following steps: The positive electrode material, the conductive agent, the sulfide electrolyte, and the binder are mixed in a mass ratio of (75-85):(3-8):(5-12):(2-5) and then added to a solvent to prepare a slurry with a solid content of 40%-50%; The slurry is coated on an aluminum foil, gradient dried, and then roll-pressed, and the roll-pressed tab is soaked in a composite plastic crystal melt for 20-40 min and then annealed to prepare the positive electrode tab.

[0013] In a fifth aspect, embodiments of the present application provide a solid-state battery, comprising the positive electrode material as described above or prepared by the method as described above or the positive electrode tab as described above or prepared by the method as described above.

[0014] The present application has the following beneficial effects: The positive electrode material, the preparation method and the application provided by the embodiments of the present application have the characteristics of reducing interface impedance, improving stability of sulfide electrolyte, stabilizing ion transmission network, and improving interface compatibility, and the analysis is as follows: (1) The interface impedance is greatly reduced: through the lithium ion conducting plastic crystal coating process, the composite plastic crystal infiltration process and the low-temperature annealing treatment, the interface impedance of the wet positive electrode using the sulfide electrolyte is reduced to 70 Ω-90 Ω, which is reduced by 30%-40% compared with the traditional wet positive electrode.

[0015] (2) The stability of the sulfide electrolyte is improved: the synergistic effect of the non-polar solvent and the composite plastic crystal makes the decomposition rate of the sulfide electrolyte in the wet process controlled below 5%, and the electrode ion conductivity is maintained at 1×10 -3 S / cm or above.

[0016] (3) The ion transmission network is continuous and stable: the sulfide electrolyte is uniformly dispersed with the assistance of the lithium ion conducting plastic crystal, and the network integrity is still maintained after drying and rolling, the lithium ion migration rate is increased by 40%-50%, and the 1C rate discharge capacity retention rate is increased to more than 92%.

[0017] (4) The interface compatibility is significantly improved: the composite plastic crystal coating layer has no adverse reaction with the sulfide electrolyte, the interface reaction product is reduced by more than 90%, and the impedance increase during the cycle process is controlled within 10%.

[0018] (5) The comprehensive performance of the battery is optimized: the first coulomb efficiency of the solid-state battery reaches 82%-85%, the 0.1C cycle life is extended to 130-150 cycles, and the energy density is increased by 8%-12% compared with the traditional process. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0020] In a first aspect, embodiments of the present application provide a positive electrode material, and a surface of the positive electrode material is coated with a lithium ion conducting plastic crystal layer. The lithium ion-conducting plastic crystal layer has a thickness of 5-15 nm and is composed of a composite plastic crystal of ion plastic crystal and lithium salt in a molar ratio of 1:3-1:5.

[0021] It should be noted that the positive electrode material provided by the present application is a positive electrode active material, which is beneficial to reduce the interface impedance between the sulfide electrolyte and the positive electrode active material and the conductive agent, and alleviate the adverse effects of the space charge layer effect. Specifically, the lithium ion-conducting plastic crystal layer forms a buffer layer between the positive electrode material and the sulfide electrolyte, and the high dielectric constant (ε=10-25) can effectively shield the space charge layer effect, effectively shield the charge accumulation at the interface between the sulfide electrolyte and the active material, so that the organic cations (such as 1-butyl-3-methyl imidazole cation, BMIM + ) in the composite plastic crystal can be adsorbed on the surface of the active material, neutralize the interface negative charge, reduce the thickness of the space charge layer (from the traditional 20-30 nm to 5-10 nm), and reduce the interface charge accumulation by more than 60%. At the same time, the fluidity of the composite plastic crystal fills the interface micropores, changes the "solid-solid" contact into "solid-liquid" contact, reduces the interface energy barrier of lithium ion migration, and reduces the interface impedance from the traditional 120-150 Ω to 70-90 Ω, and the interface resistance is reduced by more than 40%.

[0022] In optional embodiments, the ion plastic crystal is composed of an organic cation and a fluorosulfonylimide anion or a fluorocarboxylic acid anion; wherein the organic cation is at least one of imidazole, quaternary ammonium salt, and pyrrolidine; and / or the lithium salt is at least one of LiTFSI, LiFSI, and LiPF6.

[0023] The fluorosulfonylimide anion can be at least one of bis(trifluoromethanesulfonyl)imide (TFSI - ), bis(fluorosulfonyl)imide (FSI - ), bis(pentafluoroethanesulfonyl)imide (BETI - ), and tris(trifluoromethanesulfonyl)methane (CF3SO2)3C - ); the fluorocarboxylic acid anion can be at least one of trifluoroacetate (CF3COO - ), pentafluoropropionate (CF3CF2COO - ), heptafluorobutyrate (CF3CF2CF2COO - ), and nonafluoropentanoate (CF3CF2CF2CF2COO - ); the imidazole can be at least one of 1-butyl-3-methyl imidazole cation (BMIM + ), 1-ethyl-3-methyl imidazole cation (EMIM +), 1-propyl-3-methylimidazolium cation (PMIM) + ), 1-hexyl-3-methylimidazolium cation (HMIM) + ) and 1-octyl-3-methylimidazolium cation (OMIM) + At least one of the following; the quaternary ammonium salt may be selected from tetramethylammonium cation (N(CH3)4) + ), tetraethylammonium cation (N(C2H5)4 + ), tetrabutylammonium cation (N(C4H9)4 + ), triethylmethylammonium cation (N(C2H5)3CH3) + ) and diethyldimethylammonium cation (N(C2H5)2(CH3)2 + At least one of the following; pyrrolidines may be selected from 1-methyl-1-propylpyrrolidine cationic (MPPY) + ), 1-methyl-1-butylpyrrolidone cation (MBPY) + ), 1-Ethyl-1-methylpyrrolidine cation (EMPY) + ) and 1-methyl-1-hexylpyrrolidine cation (MHPY) + At least one of the following.

[0024] In optional embodiments, the cathode material is selected from layered oxides, lithium-rich manganese-based materials, olivine-type materials, and spinel-type materials; wherein, the layered oxides include the NCM series or NCA series, the olivine-type materials include LFP, and the spinel-type materials include LMO. Among them, the NCM series can be selected from NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2), NCM622 (LiNi) 0.6 Co 0.2 Mn 0.2 O2), NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2), NCM90505 (LiNi) 0.9 Co 0.05 Mn 0.05 O2) and NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 At least one of O2), the NCA series can be selected from LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi0.9 Co 0.05 Al 0.05 O2 and LiNi 0.92 Co 0.06 Al 0.02 O2.

[0025] Preferably, the particle size of the positive electrode material is 2-5 μm. Preferably, the positive electrode material is prepared after hydroxylation and silanization modification treatment.

[0026] It should be noted that the modified positive electrode material is beneficial to enhance its bonding force with the composite plastic crystal.

[0027] In a second aspect, embodiments of the present application provide a preparation method of the positive electrode material as described above, comprising the following steps: adding the positive electrode material into a solvent, and ultrasonically dispersing at a power of 300-500 W under inert gas protection for 15-20 min to form a dispersion liquid with a concentration of 0.1-0.3 g / mL; adding the composite plastic crystal into the dispersion liquid, and reacting at 50-65℃ and 600-800 rpm for 30-40 min to prepare the positive electrode material with a thickness of 5-15 nm; The mass ratio of the composite plastic crystal to the positive electrode material is 1:5-1:8.

[0028] In an optional embodiment, the preparation method further comprises: removing the solvent at a pressure of -0.08 to -0.09 MPa and a temperature of 40-50℃, and then drying at a temperature of 70-90℃ for 10-12 h to prepare the positive electrode material; The solvent is a non-polar or weakly polar organic solvent, with a water content of ≤10 ppm and a dissolution rate of <0.1% for sulfide electrolyte; The water content of the positive electrode tab after drying treatment is <10 ppm.

[0029] It should be noted that the non-polar or weakly polar organic solvent avoids solvation decomposition of the sulfide electrolyte, and the composite plastic crystal coating layer forms a physical barrier to prevent water from contacting the sulfide electrolyte, so that the decomposition rate of the electrolyte is controlled within 5%.

[0030] Specifically, the synergistic effect of the non-polar solvent and the composite plastic crystal is conducive to improving the stability of the sulfide electrolyte in the wet process and avoiding adverse reactions with the solvent and the composite plastic crystal coating layer. The non-polar / weakly polar solvent (such as an aromatic-alkane mixed solvent) has weak solvation ability (solvation energy ≤ 10 kJ / mol) and will not destroy the crystal structure of the sulfide electrolyte; at the same time, the composite plastic crystal coating layer forms a physical barrier, and the molecular chain thereof can be tightly adsorbed to the surface of the sulfide electrolyte to prevent solvent molecules from contacting the sulfide electrolyte particles and reduce solvation decomposition.

[0031] Preferably, the solvent is selected from at least one of benzene, toluene, xylene, pentane, hexane, cyclohexane, dichloromethane and trichloromethane. Among them, benzene, toluene and xylene belong to aromatic hydrocarbons, pentane, hexane and cyclohexane belong to alkanes, and dichloromethane and trichloromethane belong to halogenated hydrocarbons.

[0032] In an embodiment of the present application, the solvent is removed by rotary evaporation. In other embodiments of the present application, other methods can be selected to remove the solvent according to actual needs.

[0033] In a third aspect, an embodiment of the present application provides a positive electrode tab, which comprises the positive electrode material as described above or the positive electrode material prepared by the preparation method as described above.

[0034] In a fourth aspect, an embodiment of the present application provides a preparation method of the positive electrode tab as described above, which comprises the following steps: The positive electrode material, the conductive agent, the sulfide electrolyte and the binder are mixed in a mass ratio of (75-85):(3-8):(5-12):(2-5), and then added into the solvent to prepare a slurry with a solid content of 40%-50%; The slurry is coated on an aluminum foil, and then subjected to gradient drying and rolling treatment. The rolled tab is immersed in a composite plastic crystal melt for 20-40 min, and then subjected to annealing treatment to prepare the positive electrode tab.

[0035] The positive electrode tab provided by the present application constructs a continuous ion transmission network with the sulfide electrolyte as the core to prevent network fracture caused by uneven dispersion, drying and rolling processes.

[0036] The composite plastic crystal can act as a dispersing aid in the slurry. During the drying process, the adhesion of the composite plastic crystal prevents electrolyte particles from agglomerating, and the molecular chain thereof can be adsorbed to the surface of the sulfide electrolyte particles to reduce the agglomeration force between the particles, so that the dispersion particle size of the sulfide electrolyte particles is controlled to be below 1 μm (the agglomeration particle size is reduced from the traditional 5-10 μm to below 1 μm), and the sulfide electrolyte particles are uniformly distributed between the positive electrode active materials to ensure uniform distribution of the sulfide electrolyte particles before drying. The plastic deformation of the plastic crystal during rolling cushions the impact on the brittle sulfide electrolyte to ensure the integrity of the transmission network.

[0037] The composite plastic crystal used has high matching degree with the solubility parameter of the sulfide electrolyte (the difference in solubility parameter Δδ is less than or equal to 2 (J / cm 3 ) 1 / 2 ), the interface impedance stability of the two is significantly improved, indicating that there is no obvious chemical reaction activity; the compatibility of the reinforced coating layer and the sulfide electrolyte is enhanced, the interface side reaction is eliminated, and the ion transmission is ensured to be smooth. At the same time, the fluorosulfonylimide anion (such as TFSI⁻) in the composite plastic crystal can form a weak coordination with Li + + on the surface of the sulfide electrolyte, which not only enhances the interface bonding force, but also does not hinder the migration of lithium ions, avoiding the problem that the traditional oxide coating layer (such as Al2O3) reacts with the sulfide electrolyte to generate high impedance LiAlO2 (the interface reaction product is reduced by more than 90%).

[0038] Through the lithium ion-conducting plastic crystal coating process, the composite plastic crystal infiltration process and the low-temperature annealing treatment, the interface impedance of the wet cathode using the sulfide electrolyte is reduced to 70 Ω-90 Ω, which is reduced by 30%-40% compared with the traditional wet cathode.

[0039] The way in which the slurry is coated on the surface of the aluminum foil is not particularly limited in the present application, and in the embodiments of the present application, a slot coater, a doctor blade coater or the like is used; in other embodiments of the present application, other coating methods can be selected according to actual needs.

[0040] In optional embodiments, the conductive agent is selected from at least one of Super P, VGCF, CNT and graphene; and / or, the binder is selected from at least one of PVDF, PTFE and SBR; and / or, the sulfide electrolyte is selected from at least one of Li6PS5X and derivatives thereof, Li 10 MP2S 12 and derivatives thereof and Li3PS4 and derivatives thereof; wherein X is at least one of Cl, Br and I, and M is at least one of Ge, Sn and Si; Preferably, the particle size of the sulfide electrolyte is 0.5 μm-4 μm; The sulfide is a solid-state electrolyte, the purity of which is greater than or equal to 99.5%, and the water content is less than or equal to 5 ppm.

[0041] The sulfide electrolyte is uniformly dispersed with the aid of the composite plastic crystal, and the network integrity is still maintained after drying and rolling, the lithium ion migration rate is increased by 40%-50%, the 1C rate discharge capacity retention rate is increased to more than 92%, and the ion transmission network is continuous and stable.

[0042] And / or, the viscosity of the composite plastic crystal melt is 50 mPa·s-100 mPa·s, the melting point of the composite plastic crystal is controlled between 40℃ and 70℃, and the ionic conductivity at room temperature is ≥1×10⁻⁶. -4 S / cm.

[0043] During the immersion treatment in the composite plastic crystal melt, a negative pressure environment is used. The melt is gently stirred every 5-10 minutes during the negative pressure process to promote melt penetration. After immersion, the electrode is removed from the composite plastic crystal melt, and excess melt is gently wiped from the electrode surface with a lint-free cloth to ensure that only the plastic crystal remains in the pores, avoiding surface residue that could affect subsequent battery assembly. The immersion treatment is conducted in a glove box filled with inert gas (such as argon or nitrogen), ensuring that the ambient water and oxygen content is <0.1 ppm to prevent moisture absorption by the composite plastic crystal and sulfide electrolyte.

[0044] The composite plastic crystal melt comprises ion-derived plastic crystals and lithium salts in a molar ratio of 1:3 to 1:5. Viscosity control of the composite plastic crystal melt ensures melt flowability while avoiding excessive dilution.

[0045] In an optional embodiment, gradient drying is carried out in an inert atmosphere, including drying at 50°C-80°C for 10 min-60 min, followed by drying at 80°C-110°C for 1 h-4 h. During the drying process, the adhesiveness of the plastic crystal (adhesion strength ≥ 0.5 MPa) can fix the relative position of the electrolyte particles and the active material, avoiding particle detachment caused by solvent evaporation.

[0046] And / or, the rolling pressure is 3 MPa-7 MPa, controlling the electrode density to be 3.0 g / cm³. 3 -3.5 g / cm 3 During the roll forming process, the plastic deformation of the composite plastic crystal (elongation at break ≥200%) can buffer the pressure impact and reduce the breakage rate of brittle sulfide electrolyte particles (from the traditional 25%-30% to 5%-8%).

[0047] And / or, the immersion treatment temperature is 50℃-70℃, and the pressure is -0.08MPa to -0.095MPa; the composite plastic crystal impregnation process further fills the pores and forms a continuous transport channel of "positive electrode active material-composite plastic crystal-sulfide electrolyte" to ensure network integrity.

[0048] And / or, the annealing temperature is 100℃-150℃, and the time is 1 h-3 h.

[0049] Annealing promotes the fusion of the composite crystallizer and the sulfide electrolyte interface, generating a composite conductive phase, such as the composite conductive phase Li3PS4-LiTFSI. This composite conductive phase has a lithium-ion conductivity of 2.5 × 10⁻⁶. -3S / cm) is higher than that of a single sulfide electrolyte (1.8 x 10 -3 S / cm), further reducing the ion transport resistance.

[0050] A low-temperature annealing temperature of 100-150°C can activate the thermal motion of plastic crystal molecules, causing them to transform from a "semi-solid state" to a "high flowability" state, more fully filling the micro-gaps between sulfide electrolyte particles and positive active materials (especially nanoscale gaps generated after rolling), increasing the interface contact area by 25-30%, reducing impedance sites caused by interface voids, promoting the interface fusion of plastic crystals and sulfide electrolyte, and forming a stable ion conduction phase.

[0051] Further isolation of moisture (water oxygen content <0.1 ppm) reduces the decomposition rate of the sulfide electrolyte from the traditional 15-20% to less than 5%.

[0052] In a fifth aspect, embodiments of the present application provide a full solid-state battery comprising the positive electrode material as described above or prepared by the method as described above, or the positive electrode sheet as described above or prepared by the method as described above.

[0053] It should be noted that the room temperature ion conductivity of the full solid-state battery is ≥1 x 10 -3 S / cm, and the 1C cycle life is ≥130 cycles.

[0054] The features and performance of the present application are further described in detail below in conjunction with the examples.

[0055] Example 1 This example provides a positive electrode sheet, which comprises the following preparation steps: (1) Preparation of a positive electrode material 10 g of NCM811 (positive electrode material) was added to 50 mL of a toluene-cyclohexane mixed solvent (volume ratio 1:1), ultrasonically dispersed for 18 min, 1.7 g of BMIM-TFSI / LiTFSI composite plastic crystal (molar ratio of BMIM to TFSI / LiTFSI 4:1) was added, and stirred at 55°C for 35 min. After evaporation and drying, a positive electrode material with a coating layer thickness of 10 nm was obtained, denoted as coated NCM811.

[0056] (2) Preparation of a slurry The proportions were weighed, 8.2 g of the positive electrode material prepared in step (1) (coated NCM811) + 0.6 g of Super P (conductive agent) + 0.9 g of Li6PS5Cl (sulfide electrolyte) + 0.3 g of PVDF (binder) were added to 20 mL of a toluene-cyclohexane mixed solvent (volume ratio 1:1), and a slurry with a solid content of 45% was prepared.

[0057] The particle size of the sulfide electrolyte is 3 μm.

[0058] (3) Preparation of the positive electrode sheet The slurry prepared in step (2) is coated on the surface of the aluminum foil with a coating thickness of 70 μm, and after gradient drying (65°C / 40 min→95°C / 2.5 h), the slurry is rolled under a pressure of 5 MPa to a density of 3.3 g / cm 3 The positive electrode sheet is prepared after soaking treatment in a composite plastic crystal melt at a temperature of 60°C (molar ratio of BMIM to TFSI / LiTFSI is 4:1, viscosity is 80 mPa·s, and negative pressure is -0.09 MPa for 30 min) and annealing treatment at 120°C for 2 h.

[0059] Example 2 The present example provides a positive electrode sheet, which comprises the following preparation steps: (1) Preparation of the positive electrode material 12 g of lithium-rich manganese-based (positive electrode material) is added into 60 mL of a toluene-hexane mixed solvent (volume ratio 2:1) and ultrasonically dispersed for 20 min, 2 g of EMI-TFSI / LiFSI composite plastic crystal (molar ratio of EMI to TFSI / LiFSI is 1:4) is added, and the positive electrode material is stirred at 58°C for 38 min to obtain a positive electrode material with a coating layer thickness of 11 nm, which is denoted as coated lithium-rich manganese-based.

[0060] (2) Preparation of the slurry The positive electrode material (coated lithium-rich manganese-based) prepared in step (1) is weighed according to the proportion, 8.0 g, 0.7 g of CNT (conductive agent), 1.0 g of Li 10 MP2S 12 ( sulfide electrolyte), and 0.3 g of PVDF (binder) are added into 22 mL of a toluene-hexane mixed solvent (volume ratio 1:1) to prepare a slurry with a solid content of 46%.

[0061] The particle size of the sulfide electrolyte is 4 μm.

[0062] (3) Preparation of the positive electrode sheet The slurry prepared in step (2) is coated on the surface of the aluminum foil with a coating thickness of 80 μm, and after gradient drying (70°C / 35 min→100°C / 2 h), the slurry is rolled under a pressure of 5 MPa to a density of 3.2 g / cm 3 The positive electrode sheet is prepared after soaking treatment in a composite plastic crystal melt at a temperature of 65°C (molar ratio of EMI to TFSI / LiFSI is 1:4, viscosity is 100 mPa·s, and negative pressure is -0.085 MPa for 35 min) and annealing treatment at 130°C for 1.5 h.

[0063] Example 3 This example provides a positive electrode tab, which includes the following preparation steps: (1) Preparation of positive electrode material 8 g of LFP (positive electrode material) was added to 40 mL of a cyclohexane-dichloromethane mixed solvent (volume ratio 3:1), ultrasonic dispersion for 16 min, 1.3 g of Pyr 14 -TFSI / LiPF6complex plastic crystal (Pyr 14 with a TFSI / LiPF6molar ratio of 1:3), stirring at 52°C for 32 min, and after evaporation and drying, a positive electrode material with a coating layer thickness of 8 nm was obtained, denoted as coated LFP.

[0064] (2) Preparation of slurry According to the proportion, 7.5 g of the positive electrode material (coated LFP) prepared in step (1) + 0.5 g of VGCF (conductive agent) + 1.2 g of Li3PS4derivative (sulfide electrolyte) + 0.3 g of PTFE (binder) were weighed, and 15 mL of a cyclohexane-dichloromethane mixed solvent (volume ratio 1:1) was added to prepare a slurry with a solid content of 42%.

[0065] (3) Preparation of tab: coating thickness 60 μm, gradient drying (60°C / 30 min→90°C / 3 h) and then rolling to 3.1 g / cm 3 , 55°C melt immersion (-0.08 MPa negative pressure for 25 min), and then 110°C annealing for 2.5 h.

[0066] Comparative Example 1 This comparative example provides a positive electrode tab, which includes the following preparation steps: (1) Preparation of slurry According to the proportion, 8.2 g of NCM811 (positive electrode material) + 0.6 g of Super P (conductive agent) + 0.9 g of Li6PS5Cl (sulfide electrolyte) + 0.3 g of PVDF (binder) were weighed, and 20 mL of a toluene-cyclohexane mixed solvent (volume ratio 1:1) was added to prepare a slurry with a solid content of 45%.

[0067] Among them, the positive electrode material NCM811 was not coated, and the particle size of the sulfide electrolyte was 3 μm.

[0068] (2) Preparation of positive electrode tab The slurry prepared in step (1) was coated on the surface of an aluminum foil, with a coating thickness of 70 μm, gradient drying (65°C / 40 min→95°C / 2.5 h), and then rolling under a pressure of 5 MPa to a density of 3.3 g / cm 3 , to prepare a positive electrode tab.

[0069] No soaking treatment and annealing treatment in the composite plastic crystal melt.

[0070] Comparative Example 2 This comparative example provides a positive electrode tab, the preparation steps of which are the same as those of Example 1, the only difference being that: (3) Preparation of the positive electrode tab The slurry prepared in step (2) is coated on the surface of an aluminum foil with a coating thickness of 70 μm, and after gradient drying (65℃ / 40min→95℃ / 2.5 h), it is rolled under a pressure of 5 MPa to a density of 3.3 g / cm 3 , to prepare the positive electrode tab.

[0071] No soaking treatment and annealing treatment in the composite plastic crystal melt.

[0072] Comparative Example 3 This comparative example provides a positive electrode tab, the preparation steps of which are the same as those of Example 1, the only difference being that: (3) Preparation of the positive electrode tab The slurry prepared in step (2) is coated on the surface of an aluminum foil with a coating thickness of 70 μm, and after gradient drying (65℃ / 40min→95℃ / 2.5 h), it is rolled under a pressure of 5 MPa to a density of 3.3 g / cm 3 , and then soaked in a composite plastic crystal melt at a temperature of 60℃ (molar ratio of BMIM to TFSI / LiTFSI is 4:1, viscosity is 80 mPa·s, and negative pressure is -0.09 MPa for 30 min) to prepare the positive electrode tab.

[0073] No annealing treatment.

[0074] Comparative Example 4 This comparative example provides a positive electrode tab, the preparation steps of which are the same as those of Example 1, the only difference being that: (3) Preparation of the positive electrode tab The slurry prepared in step (2) is coated on the surface of an aluminum foil with a coating thickness of 70 μm, and after gradient drying (65℃ / 40min→95℃ / 2.5 h), it is rolled under a pressure of 5 MPa to a density of 3.3 g / cm 3 , and then annealed at 120℃ for 2h to prepare the positive electrode tab.

[0075] No soaking treatment in the composite plastic crystal melt.

[0076] Comparative Example 5 This comparative example provides a positive electrode tab, the preparation steps of which are the same as those of Example 2, the only difference being that: (1) Preparation of the positive electrode material 12 g lithium-rich manganese-based coated with Al2O3, instead of plastic crystal coating. Specifically as follows: 12 g lithium-rich manganese-based (cathode material) was added to 60 mL of toluene-hexane mixed solvent (volume ratio 2:1), ultrasonic dispersion for 20 min, 2 g of Al2O3 was added, and the cathode material was stirred at 58°C for 38 min. The cathode material with a coating layer thickness of 11 nm was recorded as coated lithium-rich manganese-based.

[0077] Comparative Example 6 This comparative example provides a positive electrode sheet, and the preparation steps are the same as Example 3, the only difference is: (1) Preparation of cathode material 8 g LFP (cathode material) was added to 40 mL of cyclohexane solvent and ultrasonically dispersed.

[0078] (2) Preparation of slurry After weighing the raw materials according to the proportion, 15 mL of cyclohexane solvent was added to prepare a slurry with a solid content of 42%.

[0079] Test Example 1 This test example is used to study the constant current charge and discharge test, as follows: Mold selection: CR2032 type solid-state battery mold made of stainless steel material, including upper cover, lower cover, gasket, spring, to ensure that the internal pressure is stable at 5 MPa-8 MPa after assembly.

[0080] Sample preparation: In a glove box with strict humidity and oxygen control (H2O / O2 concentration <0.1 ppm), the lower cover, spring, gasket, metal lithium sheet (counter electrode, diameter 10 mm), solid-state electrolyte layer (diameter 10 mm, thickness 0.3-0.5 mm), the positive electrode sheet (diameter 10 mm), gasket, and the upper cover were sequentially loaded. After tightening the mold with a torque wrench at a torque of 8 N·m-10 N·m.

[0081] Test equipment: battery test system (such as LAND CT2001A).

[0082] Test conditions: The test temperature is room temperature (25±2°C), and the voltage range is determined according to the cathode material (such as 2.0 V-3.7 V for ternary materials). During the test, the mold maintains a constant pressure.

[0083] Test procedure: first, charge to the cut-off voltage at 0.1C rate, then discharge to the cut-off voltage at the same rate, record the first cycle charge-discharge specific capacity; then, cycle test, charge-discharge at 1C rate, calculate the capacity retention rate after 100 cycles (capacity retention rate = n cycle discharge specific capacity / first cycle discharge specific capacity x 100%), the above results are recorded in Table 1.

[0084] AC impedance test: after 100 cycles, the battery is connected to a four-point probe test system in a strictly controlled humidity and oxygen glove box (H2O / O2 concentration <0.1 ppm): apply a starting current of 1 mA and stabilize for 30 seconds, then start recording, increase the current in steps of 10 mA to 100 mA, hold each current point for 60 seconds and collect 10 Hz voltage data, finally calculate the resistivity (t is the thickness of the electrode) by Van der Pauw formula, ρ = [πt / ln2] x (V / I), repeat the measurement three times and take the average, the above results are recorded in Table 1, the whole test is completed in a constant temperature environment of 25.0±0.5℃.

[0085] Table 1: Charge-discharge capacity, first efficiency, impedance and cycle capacity retention rate of all-solid-state battery

[0086] From the data in Table 1, it can be seen that: plastic crystal coating is the core, lithium ion conducting plastic crystal (imidazole, quaternary ammonium salt, pyrrolidine) can form a "buffer-conducting" dual functional layer between the active material and the sulfide electrolyte, effectively reducing the interface impedance (≤85Ω), improving the 1C rate performance (1C / 0.1C≥0.918), and the performance is significantly better than that without coating or oxide coating; mixed solvent and process synergy is the key: non-polar / weakly polar mixed solvents (such as toluene-cyclohexane, n-hexane-dichloromethane) can ensure the stability of the sulfide electrolyte (decomposition rate ≤5%), build a continuous ion transport network, extend the 0.1C cycle life to 130-150 cycles, and increase the energy density by 8%-12%; wide material compatibility: this technical solution can adapt to various positive active materials such as layered oxides, lithium-rich manganese-based, olivine-type, spinel-type, etc., by adjusting the type of plastic crystal and process parameters, the interface impedance can be reduced by more than 30%, the 1C rate capacity retention rate is ≥92%, and it has the potential for large-scale application.

[0087] To sum up, the embodiment of the present application adopts the matching design of sulfide electrolyte and lithium ion-conducting plastic crystal, solves the interface impedance and stability problems of sulfide electrolyte through the dielectric properties and fluidity of the composite plastic crystal, selects a specific type of non-polar mixed solvent to minimize the dissolution and decomposition of the sulfide electrolyte, forms a three-dimensional lithium ion-conducting network through the composite plastic crystal coating layer and melt infiltration, ensures the construction of continuous transmission path of the sulfide electrolyte in the wet process, and promotes the interface fusion of the plastic crystal and the sulfide electrolyte through low-temperature annealing treatment, forms a stable high ion-conducting phase, and significantly improves the comprehensive performance of the battery.

[0088] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A positive electrode material, characterized by, The surface of the positive electrode material is coated with a lithium ion conductive plastic crystal layer; The thickness of the lithium ion conductive plastic crystal layer is 5-15 nm, and the lithium ion conductive plastic crystal layer is composed of a composite plastic crystal with a molar ratio of 1:3-1:

5.

2. The positive electrode material of claim 1, wherein, The ion plastic crystal is composed of an organic cation and a fluorosulfonylimide anion or a fluorocarboxylic acid anion; The organic cation is at least one of imidazole, quaternary ammonium salt and pyrrolidine; The lithium salt is at least one of LiTFSI, LiFSI and LiPF6.

3. The positive electrode material of claim 1, wherein, The positive electrode material is selected from layered oxides, lithium-rich manganese-based materials, olivine-type materials and spinel-type materials; the layered oxides include NCM series or NCA series, the olivine-type materials include LFP, and the spinel-type materials include LMO; Preferably, the particle size of the positive electrode material is 2-5 μm; Preferably, the positive electrode material is prepared after hydroxylation and silanization modification treatment.

4. A method for producing the positive electrode material according to any one of claims 1 to 3, characterized by, The method comprises the following steps: The positive electrode material is added to a solvent and ultrasonically dispersed at a power of 300-500 W under inert gas protection for 15-20 min to form a dispersion liquid with a concentration of 0.1-0.3 g / mL; The composite plastic crystal is added to the dispersion liquid, and after reaction at 50-65℃ and 600-800 rpm for 30-40 min, a positive electrode material with a thickness of 5-15 nm is prepared; The mass ratio of the composite plastic crystal to the positive electrode material is 1:5-1:

8.

5. The preparation method according to claim 4, characterized in that, The preparation method further comprises: The solvent is removed at a pressure of -0.08 to -0.09 MPa and a temperature of 40-50℃, and then dried at a temperature of 70-90℃ for 10-12 h to prepare the positive electrode material; The solvent is a non-polar or weakly polar organic solvent with a water content of ≤10 ppm and a solubility in sulfide electrolyte of <0.1%; Preferably, the solvent is at least one of benzene, toluene, xylene, pentane, hexane, cyclohexane, dichloromethane and trichloromethane.

6. A positive electrode sheet characterized by comprising: The positive electrode material is prepared by the method of any one of claims 1-3 or the method of any one of claims 4-5.

7. A method of making the positive electrode sheet of claim 6, wherein The method comprises the following steps: The positive electrode material, conductive agent, sulfide electrolyte and binder are mixed in a mass ratio of (75-85):(3-8):(5-12):(2-5) and then added to a solvent to prepare a slurry with a solid content of 40-50%; The slurry is coated on an aluminum foil, gradient dried and roll-pressed, and then the roll-pressed electrode sheet is immersed in a composite plastic crystal melt for 20-40 min and annealed to prepare a positive electrode sheet.

8. The preparation method according to claim 7, characterized in that, The conductive agent is at least one of Super P, VGCF, CNT and graphene; The binder is at least one of PVDF, PTFE and SBR; and / or the sulfide electrolyte is selected from the group consisting of Li6PS5X and derivatives thereof, Li 10 MP2S 12 and at least one of Li3PS4 and derivatives thereof; wherein X is at least one of Cl, Br and I, and M is at least one of Ge, Sn and Si; Preferably, the particle size of the sulfide electrolyte is 0.5-4 μm; And / or, the viscosity of the composite plastic crystal melt is 50 mPa·s-100 mPa·s.

9. The preparation method according to claim 7, characterized in that, The gradient drying is carried out in an inert atmosphere, including drying treatment at a temperature of 50-80℃ for 10-60 min; drying treatment at a temperature of 80-110℃ for 1-4 h; And / or, the pressure of the roll-pressing process is 3 MPa-7 MPa, and the density of the pole piece is controlled to be 3.0 g / cm 3 -3.5 g / cm 3 ; And / or, the temperature of the soaking treatment is 50-70℃, and the pressure is-0.08 MPa to-0.095 MPa. And / or, the temperature of the annealing treatment is 100-150℃, and the time is 1-3 h.

10. An all-solid battery, characterized by, The positive electrode material as claimed in any one of claims 1-3 or prepared by the preparation method as claimed in any one of claims 4-5 or the positive electrode tab as claimed in claim 6 or prepared by the preparation method as claimed in any one of claims 7-9.

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