Iron-based lithium supplement agent based on defect regulation and control, preparation method of iron-based lithium supplement agent, positive pole piece and all-solid-state lithium ion battery

Abstract

The invention provides an iron-based lithium supplement agent based on defect regulation and control and a preparation method thereof, a positive pole piece and an all-solid-state lithium ion battery, the iron-based lithium supplement agent carries out defect regulation and control on lithium ferrite (Li5FeO4) through high-adaptability transition metal element doping and low-temperature sintering, and Li < + > diffusivity and conductivity are improved by combining collaborative optimization of gradient composite interface layer modification; the interface side reaction is inhibited. Wherein the gradient composite layer comprises an inner LiF passivation layer and an outer LiBO2 composite layer, and the compact composite layer forms a conductive network to coat the surface of the doped Li5FeO4, so that the lithium supplement agent can exert higher capacity under lower charging voltage, and the lithium supplement efficiency is improved. The iron-based lithium supplement agent disclosed by the invention has high interfacial compatibility, high structural stability and high ion diffusion coefficient, can adapt to relatively large volume change, and meets the requirements of the lithium supplement agent of the all-solid-state lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and in particular to an iron-based lithium supplement agent based on defect regulation, a preparation method thereof, a positive electrode sheet, and an all-solid-state lithium-ion battery. Background Art

[0002] Lithium batteries (LIBs) have become a core energy storage unit for electric vehicles and energy storage systems due to their high energy density, long cycle life, rapid charge and discharge capabilities, and low self-discharge. However, due to inherent limitations of liquid electrolytes, such as heat resistance and the electrochemical window, LIBs' thermal stability, fast charging capability, and cycle life are in urgent need of improvement. All-solid-state lithium-ion batteries (ASSLBs) can significantly improve battery safety and energy density by replacing liquid electrolytes with solid electrolytes. However, during the initial charge and discharge process, a dense solid electrolyte interface (SEI) film still forms on the anode surface, causing irreversible loss of active lithium (approximately 5%-20%) and a decrease in the initial coulombic efficiency (ICE). Furthermore, as cycling progresses, the anode side experiences severe volume expansion and contraction, leading to particle pulverization and repeated SEI film rupture and regeneration. This continuous consumption of active lithium leads to capacity decay and performance degradation, resulting in energy density below the theoretical value.

[0003] Active lithium loss can be effectively compensated through negative electrode pre-lithiation technology, the addition of positive electrode lithium replenishers, material microstructure optimization, and solid-state electrolyte modification. Among them, lithium replenishers such as Li5FeO4, Li6CoO4, Li2NiO2, and Li3N can be added directly during the positive electrode slurry preparation process, which has the advantages of simple process and high safety. Positive electrode lithium replenishers preferentially delithiate during the battery charging phase, effectively filling the loss of active lithium by releasing additional lithium sources, ensuring sufficient lithium inventory, and can increase the battery's initial capacity by 3%-5%. Compared with the high-cost and highly toxic nickel-based lithium replenishers, iron-based lithium replenishers have good compatibility with battery systems, a relatively simple synthesis process, low production cost, high theoretical capacity, and are non-toxic. Adding 1-2% can increase the energy density by 4-6%. However, iron-based lithium supplements have intrinsic defects, Li-Fe antisite defects and Li-Frenkel defects. This lattice dislocation and high vacancy concentration cause iron-based lithium supplements to exhibit poor lithium ion conductivity and electronic conductivity, severely limiting the delithiation kinetics of the lithium supplements and significantly reducing the actual lithium supplement efficiency.

[0004] Therefore, it is necessary to regulate the bulk and surface of the current positive electrode iron-based lithium supplement agent to provide an efficient lithium supplement additive suitable for high-voltage solid-state batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide an iron-based lithium supplement agent based on defect control, its preparation method, positive electrode sheet and all-solid-state lithium-ion battery. In view of the requirements of structural stability, interface compatibility and lithium loss compensation efficiency of lithium supplement agents in solid-state batteries, the defects of Li5FeO4 are controlled by doping with highly compatible transition metal elements and sintering at low temperature, and the synergistic optimization of gradient composite interface layer modification is combined to improve Li + The team designed an efficient iron-based lithium supplement for solid-state batteries by optimizing its diffusion capacity and conductivity, inhibiting interfacial side reactions, and adapting to volume changes. The iron-based lithium supplement has good chemical stability, high interfacial compatibility, high structural stability, and a high ion diffusion coefficient. It can also adapt to large volume changes, is compatible with existing battery manufacturing processes, and is suitable for industrial-scale production.

[0006] To achieve the above object, the present invention provides an iron-based lithium supplement agent based on defect regulation, comprising a doped Li5FeO4 and a composite layer partially or completely coated on the surface of the doped Li5FeO4; the composite layer comprises an inner LiF passivation layer and an outer LiBO2 layer; the molecular formula of the iron-based lithium supplement agent is Li x Fe y M z O4@LiF@LiBO2, wherein 4.95≤x≤5.05, 0.9≤y≤1, 0<z≤0.1, and M is one or more of Mg, Sc, Ti, V, Cr, Mn, Ni, Co, Cu, Zn, Zr, Nb, Mo, Ta, W, Al, Si, Sn, and Sb; the composite layer has a thickness of 2-10 nm, wherein the LiF passivation layer has a thickness of 1-5 nm, and the LiBO2 layer has a thickness of 1-5 nm; and the particle size of the iron-based lithium supplementer satisfies D10≥0.1 μm and D90≤30 μm.

[0007] The doped Li5FeO4 utilizes elements of varying valence, ionic radius, and low oxidation potential to partially replace iron ions in the crystal structure. This reduces Li-Fe antisite defects in the Li5FeO4 lattice, inhibits iron ions from occupying lithium ion lattice sites, reduces lithium site disorder, and improves the lithium ion diffusion coefficient. Reasonable control of the elemental molar ratio facilitates the sintering of the lithium source, iron source, and dopant into doped lithium ferrite with higher purity and enhanced electrochemical performance. A slight excess of lithium source is permitted during preparation.

[0008] The inner layer of LiF is created through a simple solution impregnation method, while the outer layer of LiBO2 is produced through a controlled atomic vapor deposition (ALD) process. This dense composite layer forms a conductive network that coats the surface of the doped Li5FeO4. This not only anchors oxygen vacancies and passivates the surface of the iron-based lithium supplement, providing protection, but also serves as a lithium ion migration channel, increasing the interparticle lithium ion transfer rate and ensuring the supplement achieves high capacity at low charging voltages, improving lithium supplement efficiency.

[0009] The present invention provides a method for preparing an iron-based lithium supplement based on defect regulation, comprising the following steps: (1) Weighing a lithium source, a doped iron source or a lithium source, an iron source, and a dopant in proportion, and mixing and grinding the lithium source and the doped iron source or the lithium source, the iron source, and the dopant at high speed; (2) sintering the mixed raw material obtained in step (1) in an inert atmosphere at a low temperature in stages, and then crushing and screening the mixed raw material to obtain doped Li5FeO4; (3) dispersing the doped Li5FeO4 particles in an organic solvent and performing ultrasonic cleaning to remove impurities on the particle surface, then immersing them in a fluorine source solution for fluorination treatment and drying; (4) The thoroughly dried doped Li5FeO4 precursor is cyclically deposited under the atomic vapor deposition (ALD) process to achieve LiBO2 coating, and then screened and demagnetized to obtain the defect-controlled iron-based lithium supplement material Li x Fe y M z O4@LiF@LiBO2.

[0010] The present invention reduces the Li-Fe antisite defects in the Li5FeO4 lattice by element doping and repairs the Frenkel defects in the lattice by low-temperature sintering; the surface is partially or completely covered with a gradient composite layer, which not only improves the interface compatibility and the interface lithium ion conduction capability, but also can fix active oxygen and prevent gas production inside the composite positive electrode from affecting the solid-solid contact interface.

[0011] Preferably, in step (1), the lithium source includes one or more of Li2O, Li2O2, Li2CO3, Li2C2O4, Li3CPO4, and LiOH; the iron source includes one or more of iron powder, Fe2O3, Fe3O4, FeC2O4, Fe(OH)3, and FeO(OH); the doped iron source includes one or more of Fe2O3, Fe3O4, Fe(OH)3, and FeO(OH) doped with M elements, and the M elements include Mg, Sc, Ti, V, Cr, Mn, Ni, One or more of Co, Cu, Zn, Zr, Nb, Mo, Ta, W, Al, Si, Sn, and Sb, and the dopant includes one or more of MgO, Sc2O3, TiO2, V2O5, VO2, Cr2O3, CrO3, MnO2, Mn3O4, NiO, LiNiO2, Co3O4, LiCoO2, CuO, Cu2O, ZnO, ZrO2, Nb2O5, MoO3, Ta2O5, WO3, Al2O3, SiO2, SnO2, Sb2O3, and Sb2O5.

[0012] Preferably, in step (1), the high-speed mixed grinding adopts one or more of high mixing, sand milling, dry ball milling or wet ball milling. The high mixing speed is 100-3000 rpm, the ball-to-material ratio during ball milling is 50-30:1, the ball milling time is 3-24 h, the speed is 100-1000 rpm; and the particle size of the ground raw material is 0.1-30 μm. In a preferred embodiment, the high mixing speed is 1000-1500 rpm, the ball-to-material ratio during ball milling is 50-40:1, the ball milling time is 10-15 h, the speed is 800-1000 rpm, and the particle size of the ground raw material is 0.5-30 μm.

[0013] Sand milling or wet ball milling can grind the raw materials to the level of hundreds of nanometers by introducing a suitable medium, thereby achieving nanoscale contact between the raw materials, ensuring sufficient lithium ion diffusion channels during the synthesis of lithium ferrite, and helping to improve the purity of the product. Preferably, in step (1), the medium used in the high-speed mixed grinding is a gas or an organic medium, the gas is nitrogen and / or argon, and the organic medium includes one or more of decane, ethanol, ether, anisole, acetone, isobutyl isobutyrate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and xylene.

[0014] Low temperature segmented sintering can reduce the lithium volatilization rate during the synthesis of lithium ferrite, control the grain size and inhibit lattice dislocation, repair the Frenkel defect of lithium ferrite, and reduce the Li + Vacancy concentration, thereby increasing the lithium ion diffusion coefficient inside the lithium ferrite material. Preferably, in step (2), the low-temperature staged sintering includes: heating from room temperature to 300-500°C under an inert atmosphere at a heating rate of 1-10°C / min and holding for 3-6 hours; continuing heating to 550-650°C in the second stage at a heating rate of 1-5°C / min and holding for 2-18 hours; and finally, annealing in the third stage at a cooling rate of 1-5°C / min to room temperature. The inert atmosphere is nitrogen and / or argon.

[0015] Preferably, in step (2), the pulverization is performed by a pulverizer or air flow pulverization: the pulverization is performed by a pulverizer for 5 to 10 minutes per time and 3 to 5 times; the air flow pulverization gas source is nitrogen and / or argon. The particle size of the lithium ferrite precursor after pulverization and screening is D10 ≥ 0.1 μm and D90 ≤ 30 μm. In a preferred embodiment, the particle size of the doped Li5FeO4 after pulverization and sieving is D10 ≥ 0.2 μm and D90 ≤ 15 μm.

[0016] Preferably, in step (3), the organic solvent comprises one or more of ethanol, acetonitrile, N-methylpyrrolidone, and isopropanol. The fluorine-containing source solution used in the fluorination treatment comprises NH4F ethanol solution (wherein NH4F is the solute and ethanol is the solvent, and the following writings have the same meaning), LiPF6 acetonitrile solution, HF solution, and NaF acidic solution, with a molar concentration of 0.5-1 mol / L; the fluorination treatment temperature is 50-100°C, and the treatment time is 5-10 h.

[0017] Preferably, in step (3), the drying method includes but is not limited to conventional drying, vacuum drying, freeze drying, and forced air drying, the drying temperature is 60-80°C, and the drying time is 12-24 hours.

[0018] Preferably, in step (4), the boron source used in the ALD process includes one or more of trimethoxyborane, triethylborane, boron trichloride, and triisopropyl borate, and the lithium source used is lithium tert-butoxide or lithium hydroxide. The ALD process deposition temperature is 80-150°C, the number of cycles is 10-50, and the layer thickness is precisely controlled to 0.1 nm / time, achieving a gradient distribution of the B element.

[0019] Preferably, in step (4), the Li x Fe y M z The particle size of O4@LiF@LiBO2 (4.95≤x≤5.05, 0.9≤y≤1, 0<z≤0.1) is D10≥0.1 μm, D90≤30 μm.

[0020] A positive electrode sheet, wherein any of the above-mentioned Li x Fe y M z O4@LiF@LiBO2, positive electrode active material, solid electrolyte and conductive carbon are mixed evenly, a binder solution is added to prepare slurry, wet coating is performed and then dried to obtain the positive electrode sheet, wherein Li x Fe y M z The mass ratio of O4@LiF@LiBO2: positive electrode active material: solid electrolyte: conductive carbon is (1-6): (60-85): (10-40): (2-5), and the added amount of the binder is 1%-5%.

[0021] Preferably, the positive electrode active material includes one or more of lithium iron phosphate, lithium cobalt oxide, NCM ternary positive electrode material, lithium-rich manganese-based positive electrode material and sulfur-based positive electrode material; the solid electrolyte includes one or more of polymer electrolyte, oxide electrolyte, sulfide electrolyte and halide electrolyte; the conductive agent includes one or more of Super P, Ketjen black, acetylene black, graphene, carbon nanotube and carbon nanofiber; the binder includes one or more of PVDF, SEBS, SBR, SES, SEPS, EVA, CMC, PAA, PMMA, EP and PIB; the solvent used for wet coating includes one or more of alkanes, alcohols, ethers, ketones, esters and benzenes, including but not limited to decane (C 10 H 22 ), ethanol (C2H6O), ether (C4H 10 O), anisole (C7H8O), acetone (C3H6O), isobutyl isobutyrate (C8H 16 O2), ethyl methyl carbonate (C3H6O3), dimethyl carbonate (C3H6O3), diethyl carbonate (C5H 10 O3), xylene (C8H 10 ).

[0022] An all-solid-state lithium-ion battery is constructed by assembling the above-mentioned positive electrode sheet, electrolyte and negative electrode together and finally encapsulating them in a battery shell.

[0023] Preferably, the electrolyte includes electrolyte powder and electrolyte membrane, and the negative electrode includes one or more of carbon-based active materials, silicon-based active materials, tin-based active materials, phosphorus-containing active materials, sulfur-containing active materials, lithium titanate, lithium and lithium alloys.

[0024] Preferably, the battery assembly steps are to sequentially add the positive electrode sheet, electrolyte, and negative electrode into the mold, apply a manufacturing pressure of 0.5 to 5 tons, and after demolding, use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0025] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: (1) The present invention synergistically optimizes the iron-based lithium supplement through defect regulation and gradient interface layer modification, repairing intrinsic defects while stabilizing the material structure, avoiding gas production inside the composite positive electrode, and improving solid-solid interface contact.

[0026] (2) Defect-regulated Li prepared by the present invention x Fe y M z O4@LiF@LiBO2 has good chemical stability, high interfacial compatibility, high structural stability and high ion diffusion coefficient, and can adapt to large volume changes.

[0027] (3) Defect-regulated Li prepared by the present invention x Fe y M z O4@LiF@LiBO2 positive electrode iron-based lithium replenisher meets the requirements of all-solid-state lithium battery lithium replenisher, improves the positive electrode lithium replenishment efficiency during the cycle process, improves the battery's first cycle performance and long-cycle stability. The assembled all-solid-state lithium battery has the advantages of high safety, high energy density and high cycle stability.

[0028] (4) Li disclosed in the present invention x Fe y M z The preparation method of O4@LiF@LiBO2 is simple, the process is controllable and repeatable, and the corresponding positive electrode and all-solid-state lithium battery process flow is compatible with existing battery preparation processes and is suitable for industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is the SEM morphology of the lithium supplement prepared in Example 1; Figure 2 This is the SEM morphology of the positive electrode with the addition of lithium supplement; Figure 3 for the reason Figure 2 Schematic diagram of all-solid-state battery assembled with positive electrode shown. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention.

[0030] Example 1 A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and Nb2O5 were weighed according to the molar ratio of lithium, iron, and niobium (Nb) of 5.05:0.91:0.09. The lithium source, iron source, and dopant were mixed and ground at high speed by wet ball milling with a ball-to-material ratio of 50:1, a ball milling speed of 800 rpm, and a ball milling time of 12 h. The ball milling medium was diethyl carbonate. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 450 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the second stage was continued to heat to 600 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the third stage was annealing, with a cooling rate of 2 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.9 Nb 0.1 O4; (3) Li5Fe 0.91 Nb 0.09 The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. They were then immersed in a 1 mol / L NH4F‌ ethanol solution for fluorination at 80°C for 5 h. The particles were then vacuum dried at 80°C for 12 h. (4) After thorough drying, Li5Fe 0.9 Nb 0.1 The O4 precursor was cyclically deposited under the atomic vapor deposition ALD process, with trimethoxyborane as the boron source, lithium tert-butoxide as the lithium source, the deposition temperature at 120°C, 10 cycles, and a LiBO2 thickness of 1 nm. Li5Fe2O3 with a particle size of D50 ≥ 1.5 μm was obtained by sieving and demagnetization. 0.91 Nb 0.09 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.91 Nb 0.09 O4@LiF@LiBO2, ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed evenly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare slurry, wet-coated and then dried to obtain the positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 t to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0031] Example 2: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and Ta2O5 were weighed according to the molar ratio of lithium, iron, and tantalum (Ta) of 5.05:0.92:0.08. The lithium source, iron source, and dopant were mixed and ground by wet ball milling at a high speed with a ball-to-material ratio of 40:1, a ball milling speed of 850 rpm, and a ball milling time of 10 h. The ball milling medium was anisole. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 400 ° C, with a heating rate of 3 ° C / min, and kept warm for 3 hours; the second stage continued to heat to 550 ° C, with a heating rate of 3 ° C / min, and kept warm for 10 hours; the third stage was annealing, with a cooling rate of 3 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.92 Ta 0.08 O4; (3) Li5Fe0.92 Ta 0.08 The O₄ particles were dispersed in acetonitrile and ultrasonically cleaned to remove surface impurities. The particles were then immersed in a 0.5 mol / L ‌LiPF₆‌ acetonitrile solution for fluorination at 70°C for 6 h. The particles were then vacuum dried at 60°C for 20 h. (4) After thorough drying, Li5Fe 0.92 Ta 0.08 The O4 precursor was cyclically deposited under the atomic vapor deposition (ALD) process. The boron source was triethylborane, the lithium source was lithium tert-butoxide, the deposition temperature was 100°C, the number of cycles was 20, the LiBO2 thickness was 2nm, and the Li5Fe2O3 with a particle size of D50≥1.5 μm was obtained by sieving and demagnetization. 0.92 Ta 0.08 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.92 Ta 0.08 O4@LiF@LiBO2, lithium iron phosphate, halide electrolyte LYC and conductive carbon Super P were mixed evenly in a mass ratio of 2:85:11:2, and SEBS dissolved in xylene was added to prepare a slurry. The positive electrode was obtained by wet coating and drying. (6) Add the prepared positive electrode sheet, electrolyte powder and nano-silicon negative electrode into the mold in sequence, apply a manufacturing pressure of 2.5 tons to assemble into a battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0032] Example 3: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O and Ni-Fe2O3 were weighed according to the molar ratio of lithium, iron and nickel (Ni) of 5.05:0.95:0.05. The lithium source and the doped iron source were mixed and ground at high speed by a high-mix sand mill at a speed of 900 rpm for 10 h. The sand milling medium was ethyl methyl carbonate at a speed of 550 rpm for 10 h. (2) The mixed raw material obtained in step (1) was sintered in sections at low temperature under argon atmosphere, starting from room temperature to 350℃, with a heating rate of 3℃ / min, and kept warm for 4 hours; the second section continued to heat to 650℃, with a heating rate of 3℃ / min, and kept warm for 15 hours; the third section was annealing, with a cooling rate of 3℃ / min, down to room temperature. Then, it was crushed and sieved by argon gas flow to obtain Li5Fe 0.95 Ni 0.05 O4; (3) Li5Fe 0.95 Ni0.05 O4 particles were dispersed in N-methylpyrrolidone and ultrasonically cleaned to remove surface impurities. They were then immersed in 0.85 mol / L NaF N-methylpyrrolidone, which had been acidified with nitric acid, for fluorination at 100°C for 8 h. The particles were then vacuum dried at 70°C for 24 h. (4) After thorough drying, Li5Fe 0.95 Ni 0.05 The O4 precursor was cyclically deposited under the atomic vapor deposition (ALD) process. The boron source was triisopropyl borate, the lithium source was lithium hydroxide, the deposition temperature was 150°C, the number of cycles was 20, the LiBO2 thickness was 2 nm, and the Li5Fe2O3 with a particle size of D50 ≥ 1.5 μm was obtained by sieving and demagnetization. 0.95 Ni 0.05 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.95 Ni 0.05 O4@LiF@LiBO2, sulfur-based cathode, sulfide electrolyte LPSC and conductive carbon nanotubes were mixed uniformly in a mass ratio of 6:70:22:2, SBR dissolved in decane was added to prepare slurry, wet-coated and then dried to obtain a positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte powder and micron silicon negative electrode into the mold in sequence, apply a manufacturing pressure of 4 tons to assemble into a battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0033] Example 4: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and Sc2O3 were weighed according to the molar ratio of lithium, iron, and scandium (Sc) of 5.05:0.94:0.06. The lithium source, iron source, and dopant were mixed and ground by dry ball milling at a high speed with a ball-to-material ratio of 35:1, a ball milling speed of 950 rpm, and a ball milling time of 12 h. (2) The mixed raw material obtained in step (1) was sintered in sections at low temperature under argon atmosphere, starting from room temperature to 300℃, with a heating rate of 4℃ / min, and kept warm for 6 hours; the second section continued to heat to 600℃, with a heating rate of 4℃ / min, and kept warm for 18 hours; the third section was annealing, with a cooling rate of 4℃ / min, down to room temperature. Then it was crushed by a pulverizer for 10 minutes and sieved to obtain Li5Fe 0.94 Sc 0.06 O4; (3) Li5Fe 0.94 Sc 0.06The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. The particles were then immersed in a 0.5 mol / L HF ethanol solution for fluorination at 50°C for 10 h. The particles were then vacuum dried at 80°C for 18 h. (4) After thorough drying, Li5Fe 0.94 Sc 0.06 The O4 precursor was cyclically deposited under the atomic vapor deposition (ALD) process. The boron source was boron trichloride, the lithium source was lithium hydroxide, the deposition temperature was 80°C, the number of cycles was 20, the LiBO2 thickness was 2nm, and the Li5Fe2O3 with a particle size of D50≥1.5 μm was obtained by sieving and demagnetization. 0.94 Sc 0.06 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.94 Sc 0.06 O4@LiF@LiBO2, lithium-rich manganese cathode, halide electrolyte LZC and conductive carbon nanofibers are mixed uniformly in a mass ratio of 2:74:22:2, and PIB dissolved in xylene is added to prepare slurry. After wet coating, the positive electrode sheet is dried. (6) Add the prepared positive electrode sheet, electrolyte powder and tin-based negative electrode into the mold in sequence, apply a manufacturing pressure of 5 tons to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0034] Comparative Example 1: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and MgO were weighed according to the molar ratio of lithium, iron, and magnesium (Mg) of 5.05:0.91:0.09. The lithium source, iron source, and dopant were mixed and ground at high speed by wet ball milling. The ball-to-material ratio was 50:1, the ball milling speed was 800 rpm, the ball milling time was 12 h, and the ball milling medium was diethyl carbonate. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 450 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the second stage was continued to heat to 600 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the third stage was annealing, with a cooling rate of 2 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.91 Mg 0.09 O4; (3) Li5Fe 0.91 Mg 0.09The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. They were then immersed in a 1 mol / L NH4F‌ ethanol solution for fluorination at 80°C for 5 h. The particles were then vacuum dried at 80°C for 12 h. (4) After thorough drying, Li5Fe 0.91 Mg 0.09 The O4 precursor was cyclically deposited under the atomic vapor deposition ALD process, with trimethoxyborane as the boron source, lithium tert-butoxide as the lithium source, the deposition temperature at 120°C, 20 cycles, and a LiBO2 thickness of 2 nm. The Li5Fe2O3 particles with a particle size of D50 ≥ 1.5 μm were obtained by sieving and demagnetization. 0.91 Mg 0.09 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.91 Mg 0.09 O4@LiF@LiBO2, ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed evenly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare slurry, wet-coated and then dried to obtain the positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 t to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0035] Comparative Example 2: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and TiO2 were weighed according to the molar ratio of lithium, iron, and titanium (Ti) of 5.05:0.91:0.09. The lithium source, iron source, and dopant were mixed and ground at high speed by wet ball milling with a ball-to-material ratio of 50:1, a ball milling speed of 800 rpm, and a ball milling time of 12 h. The ball milling medium was diethyl carbonate. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 450 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the second stage was continued to heat to 600 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the third stage was annealing, with a cooling rate of 2 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.91 Ti 0.09 O4; (3) Li5Fe 0.91 Ti 0.09The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. They were then immersed in a 1 mol / L NH4F‌ ethanol solution for fluorination at 80°C for 5 h. The particles were then vacuum dried at 80°C for 12 h. (4) After thorough drying, Li5Fe 0.91 Ti 0.09 The O4 precursor was cyclically deposited under the atomic vapor deposition ALD process, with trimethoxyborane as the boron source, lithium tert-butoxide as the lithium source, the deposition temperature at 120°C, 30 cycles, and a LiBO2 thickness of 3 nm. Li5Fe2O3 with a particle size of D50 ≥ 1.5 μm was obtained by sieving and demagnetization. 0.91 Ti 0.09 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.91 Ti 0.09 O4@LiF@LiBO2, ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed evenly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare slurry, wet-coated and then dried to obtain the positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 t to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0036] Comparative Example 3: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and V2O5 were weighed according to the molar ratio of lithium, iron, and vanadium (V) of 5.05:0.91:0.09. The lithium source, iron source, and dopant were mixed and ground by wet ball milling at a high speed with a ball-to-material ratio of 50:1, a ball milling speed of 800 rpm, and a ball milling time of 12 h. The ball milling medium was diethyl carbonate. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 450 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the second stage was continued to heat to 600 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the third stage was annealing, with a cooling rate of 2 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.91 V 0.09 O4; (3) Li5Fe 0.91 V 0.09The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. They were then immersed in a 1 mol / L NH4F‌ ethanol solution for fluorination at 80°C for 5 h. The particles were then vacuum dried at 80°C for 12 h. (4) After thorough drying, Li5Fe 0.91 V 0.09 The O4 precursor was cyclically deposited under the atomic vapor deposition ALD process, with trimethoxyborane as the boron source, lithium tert-butoxide as the lithium source, the deposition temperature at 120°C, 40 cycles, and a LiBO2 thickness of 4 nm. Li5Fe2O3 with a particle size of D50 ≥ 1.5 μm was obtained by sieving and demagnetization. 0.91 V 0.09 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.91 V 0.09 O4@LiF@LiBO2, ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed evenly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare slurry, wet-coated and then dried to obtain the positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 t to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0037] Comparative Example 4: A defect-controlled iron-based lithium supplement additive, a preparation method thereof, a positive electrode sheet, and a solid-state lithium battery, the method mainly comprising the following steps: (1) Li2O, Fe2O3, and Mn3O4 were weighed according to the molar ratio of lithium, iron, and manganese (Mn) of 5.05:0.91:0.09. The lithium source, iron source, and dopant were mixed and ground at high speed by wet ball milling with a ball-to-material ratio of 50:1, a ball milling speed of 800 rpm, and a ball milling time of 12 h. The ball milling medium was diethyl carbonate. (2) The mixed raw material obtained in step (1) was sintered in a nitrogen atmosphere at low temperature, starting from room temperature to 450 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the second stage was continued to heat to 600 ° C, with a heating rate of 2 ° C / min, and kept at this temperature for 5 h; the third stage was annealing, with a cooling rate of 2 ° C / min, and cooled to room temperature. Then, it was crushed and sieved by nitrogen gas flow to obtain Li5Fe 0.91 Mn 0.09 O4; (3) Li5Fe 0.91 Mn 0.09The O4 particles were dispersed in ethanol and ultrasonically cleaned to remove surface impurities. They were then immersed in a 1 mol / L NH4F‌ ethanol solution for fluorination at 80°C for 5 h. The particles were then vacuum dried at 80°C for 12 h. (4) After thorough drying, Li5Fe 0.91 Mn 0.09 The O4 precursor was cyclically deposited under the atomic vapor deposition ALD process, with trimethoxyborane as the boron source, lithium tert-butoxide as the lithium source, the deposition temperature at 120°C, 50 cycles, and a LiBO2 thickness of 5 nm. Li5Fe2O3 with a particle size of D50 ≥ 1.5 μm was obtained by sieving and demagnetization. 0.91 Mn 0.09 O4@LiF@LiBO2 iron-based lithium supplement; (5) Li5Fe 0.91 Mn 0.09 O4@LiF@LiBO2, ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed evenly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare slurry, wet-coated and then dried to obtain the positive electrode sheet; (6) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 t to assemble the battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0038] Comparative Example 5: A positive electrode sheet and a solid-state lithium battery without adding a positive electrode lithium supplement agent, the method mainly includes the following steps: (1) The ternary positive electrode NCM, halide electrolyte LIC and conductive carbon VGCF are mixed uniformly in a mass ratio of 3:60:35:2, PVDF dissolved in isobutyl isobutyrate is added to prepare a slurry, wet-coated and then dried to obtain a positive electrode sheet; (2) Add the prepared positive electrode sheet, electrolyte membrane and lithium-indium alloy negative electrode into the mold in sequence, apply a manufacturing pressure of 3.5 tons to assemble into a battery cell, and finally use a battery shell or mold battery to encapsulate the battery cell to obtain an all-solid-state lithium battery.

[0039] Intrinsic conductivity testing: Electronic conductivity was measured using an ion-blocking cell. The sample was pressed into a PEEK mold, a DC voltage was applied, and the corresponding current response was recorded. Ionic conductivity was measured using a DC polarization method with the sample pressed into a PEEK mold using an electron-blocking cell. Table 1 below lists the intrinsic conductivity data for the positive electrodes prepared in these Examples and Comparative Examples.

[0040] Table 1 Intrinsic conductivity of positive electrodes prepared in Examples and Comparative Examples Table 2 shows the positive electrode lithium supplements and battery performance data of these examples and comparative examples.

[0041] Table 2 Performance table of examples and comparative examples It can be seen from the above description that the above embodiments of the present invention achieve the following technical effects: From Comparative Example 1 to Comparative Example 4, as the number of atomic layer deposition (ALD) cycles gradually increases, the thickness of the gradient composite layer LiBO2 gradually increases. Comparing the data of Example 1 of the present application with Comparative Examples 2 to 4, it can be seen that the thickness of the gradient composite layer of the lithium replenisher in the present application has a key influence on the lithium replenishment efficiency. When the thickness of the gradient composite layer LiBO2 is controlled at 1 to 2 nm, the lithium replenisher can exert a better lithium replenishment ability.

[0042] Compared with comparative examples 1 to 4, examples 1 to 4 are doped with transition metal elements with larger ion radius, such as Nb, Ta, Sc, and Ni, which effectively repair the intrinsic defects of the iron-based lithium supplement agent and improve its Li + The diffusion capacity and electronic conductivity of the solid-state battery are improved, thereby enhancing the first-cycle performance and cycling stability of the solid-state battery produced therefrom. Specifically, compared with Comparative Example 1, the solid-state battery in Example 1 has a 3.5% increase in first-cycle efficiency, a 20 mAh / g increase in first-cycle discharge capacity, and an 8% increase in capacity retention. The first-cycle efficiency (≥90%) and 100-cycle cycle retention (≥90%) of Examples 1-4 are significantly higher than those of Comparative Examples 1-4.

[0043] Compared with Comparative Example 5, Example 1 adds the lithium supplement agent prepared in this application to the composite positive electrode, and the first-cycle discharge capacity is increased by more than 20%, the first-cycle coulomb efficiency is increased by more than 6%, and the 100-cycle cycle retention rate is increased by more than 10%. This shows that the use of high-valence matching elements such as Nb and Ta for doping modification, and the effective control of the gradient interface layer thickness (1~2 nm) can improve the interface compatibility and lithium ion migration ability of the lithium supplement agent, improve the lithium supplement efficiency of the lithium supplement agent, and thus improve the long-cycle performance of the battery. By adjusting the type and content of the doping element and the low-temperature staged sintering process parameters, the defects of the iron-based lithium supplement agent can be controllably repaired, and by adjusting the fluorination treatment parameters and ALD process parameters, the interface can be controllably designed to achieve a higher lithium supplement efficiency.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An iron-based lithium supplement based on defect regulation, characterized in that: The iron-based lithium supplement agent includes a doped Li5FeO4 and a composite layer partially or completely coated on the surface of the doped Li5FeO4; the composite layer includes an inner LiF passivation layer and an outer LiBO2 layer; the molecular formula of the iron-based lithium supplement agent is Li x Fe y M z O4@LiF@LiBO2, wherein 4.95≤x≤5.05, 0.9≤y≤1, 0<z≤0.1, and M is one or more of Mg, Sc, Ti, V, Cr, Mn, Ni, Co, Cu, Zn, Zr, Nb, Mo, Ta, W, Al, Si, Sn, and Sb; the composite layer has a thickness of 2-10 nm, wherein the LiF passivation layer has a thickness of 1-5 nm, and the LiBO2 layer has a thickness of 1-5 nm; and the particle size of the iron-based lithium supplementer satisfies D10≥0.1 μm and D90≤30 μm.

2. A method for preparing an iron-based lithium supplement based on defect regulation according to claim 1, characterized in that: The following steps are involved: (1) Weighing a lithium source, a doped iron source or a lithium source, an iron source, and a dopant in proportion, and mixing and grinding the lithium source and the doped iron source or the lithium source, the iron source, and the dopant at high speed; (2) sintering the mixed raw material obtained in step (1) in an inert atmosphere at a low temperature in stages, and then crushing and sieving to obtain doped Li5FeO4; (3) dispersing the doped Li5FeO4 particles in an organic solvent and performing ultrasonic cleaning to remove impurities on the particle surface, then immersing them in a fluorine source solution for fluorination treatment and drying; (4) The thoroughly dried doped Li5FeO4 precursor is cyclically deposited under the atomic vapor deposition (ALD) process to achieve LiBO2 coating, and then screened and demagnetized to obtain the defect-controlled iron-based lithium supplement material Li x Fe y M z O4@LiF@LiBO2.

3. The preparation method according to claim 2, characterized in that In the step (1), the lithium source includes one or more of Li2O, Li2O2, Li2CO3, Li2C2O4, Li3CPO4, and LiOH; the iron source includes one or more of iron powder, Fe2O3, Fe3O4, FeC2O4, Fe(OH)3, and FeO(OH); the doped iron source includes one or more of Fe2O3, Fe3O4, Fe(OH)3, and FeO(OH) doped with M elements, and the M elements include Mg, Sc, Ti, V, Cr, Mn, Ni, Co, , Cu, Zn, Zr, Nb, Mo, Ta, W, Al, Si, Sn, Sb, and the dopant includes one or more of MgO, Sc2O3, TiO2, V2O5, VO2, Cr2O3, CrO3, MnO2, Mn3O4, NiO, LiNiO2, Co3O4, LiCoO2, CuO, Cu2O, ZnO, ZrO2, Nb2O5, MoO3, Ta2O5, WO3, Al2O3, SiO2, SnO2, Sb2O3, Sb2O5.

4. The preparation method according to claim 2, characterized in that In the step (1), the high-speed mixed grinding adopts one or more of high mixing, sand milling, dry ball milling or wet ball milling, wherein the high-speed mixing speed is 100-3000 rpm; the ball-to-material ratio during ball milling is 50-30:1, the ball milling time is 3-24 h, and the speed is 100-1000 rpm; the medium used in the high-speed mixed grinding is gas or organic medium, the gas is nitrogen and / or argon, and the organic medium includes one or more of decane, ethanol, ether, anisole, acetone, isobutyl isobutyrate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and xylene.

5. The preparation method according to claim 2, characterized in that In the step (2), the low-temperature segmented sintering includes: heating from room temperature to 300-500°C under an inert atmosphere at a heating rate of 1-10°C / min and keeping warm for 3-6 hours; continuing heating to 550-650°C in the second stage at a heating rate of 1-5°C / min and keeping warm for 2-18 hours; and a third annealing stage at a cooling rate of 1-5°C / min to room temperature, wherein the inert atmosphere is nitrogen and / or argon.

6. The preparation method according to claim 2, characterized in that In step (3), the organic solvent includes one or more of ethanol, acetonitrile, N-methylpyrrolidone, and isopropanol. The fluorine-containing source solution used in the fluorination treatment includes NH4F ethanol solution, LiPF6 acetonitrile solution, HF solution, and NaF acidic solution, with a molar concentration of 0.5 to 1 mol / L. The fluorination treatment temperature is 50 to 100°C, and the treatment time is 5 to 10 hours.

7. The preparation method according to claim 2, characterized in that In step (4), the boron source used in the ALD process includes one or more of trimethoxyborane, triethylborane, boron trichloride, and triisopropyl borate, and the lithium source used is lithium tert-butoxide or lithium hydroxide; the deposition temperature of the ALD process is 80-150°C, the number of cycles is 10-50 times, and the layer thickness is precisely controlled to 0.1 nm / time, so as to achieve a gradient distribution of the B element.

8. A positive electrode plate, characterized in that: The Li according to claim 1 or 2 x Fe y M z O4@LiF@LiBO2, positive electrode active material, solid electrolyte and conductive carbon are mixed evenly, a binder solution is added to prepare slurry, wet coating is performed and then dried to obtain the positive electrode sheet, wherein Li x Fe y M z The mass ratio of O4@LiF@LiBO2: positive electrode active material: solid electrolyte: conductive carbon is (1-6): (60-85): (10-40): (2-5), and the added amount of the binder is 1%-5%.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode active material includes one or more of lithium iron phosphate, lithium cobalt oxide, a ternary positive electrode material, a lithium-rich manganese-based positive electrode material and a sulfur-based positive electrode material; the solid electrolyte includes one or more of a polymer electrolyte, an oxide electrolyte, a sulfide electrolyte and a halide electrolyte; the conductive carbon includes one or more of Super P, Ketjen black, acetylene black, graphene, carbon nanotubes and carbon nanofibers; the binder includes one or more of PVDF, SEBS, SBR, SES, SEPS, EVA, CMC, PAA, PMMA, EP and PIB; and the solvent used for wet coating includes one or more of decane, ethanol, ethyl ether, anisole, acetone, isobutyl isobutyrate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and xylene.

10. An all-solid-state lithium-ion battery, characterized in that: The positive electrode sheet, electrolyte and negative electrode according to claim 8 are assembled together, and finally packaged with a battery shell to form the all-solid-state lithium-ion battery.

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