A high-safety nickel cobalt manganese lithium oxide semi-solid-state battery and its preparation method

Abstract

The present invention relates to the technical field of lithium-ion batteries, and specifically to a high-safety nickel cobalt manganese lithium semi-solid battery and a preparation method thereof, including a positive electrode, a negative electrode, a double-gradient functional layer composite separator, and a high-safety electrolyte; the positive electrode includes a positive electrode current collector and a modified nickel cobalt manganese lithium positive electrode material on its surface, and the modified nickel cobalt manganese lithium positive electrode material includes a modified nickel cobalt manganese lithium active material, a positive electrode conductive agent, a positive electrode binder, and an inorganic solid electrolyte. The modified nickel cobalt manganese lithium active material includes a core and a shell layer. The core is a NCM core doped with Ti and F gradients, and the shell layer is a Li2TiO3 / LiAl X B 1‑x O2 composite double-layer coating structure; the double-gradient functional layer composite separator is a sandwich double-gradient structure, including a basic layer in the middle, a negative electrode side gradient layer and a positive electrode side gradient layer respectively attached to both sides of the basic layer. This semi-solid battery has high energy density, long cycle stability, and high safety.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically to a high-safety nickel cobalt manganese lithium semi-solid battery and a preparation method thereof. Background Art

[0002] With the rapid development of electric vehicles and energy storage systems, higher requirements are put forward for the energy density, safety and cycle life of batteries. Traditional liquid lithium batteries have risks of flammability and thermal runaway, and their cycle life is limited. Although all-solid-state batteries have high safety, the impedance of the solid-solid contact interface is large and the ionic conductivity is low, and they have not been commercialized on a large scale due to technical complexity and cost issues. As a transitional solution, semi-solid batteries reduce the proportion of liquid electrolytes and introduce solid electrolytes, combining the advantages of high ionic conductivity of liquid electrolytes (ionic conductivity > 1×10 -3 S / cm) and high mechanical stability of solid electrolytes, and having advantages such as high safety and long cycle life.

[0003] At present, semi-solid batteries have attracted wide attention in the industry, academia and research. However, the following problems still exist in the prior art: (1) Poor stability of the cathode material: The commonly used nickel cobalt manganese lithium (NCM) cathode material has a high voltage platform and specific capacity, and can provide a high energy density. However, with the increase in the Ni content, the highly reactive Ni formed in the later stage of material charging 4+ will cause a decrease in the stability of the cathode / electrolyte interface, resulting in the oxidation and decomposition of the electrolyte. At the same time, the structure, chemistry and mechanical stability of the material itself gradually deteriorate, and the cycle performance decays rapidly, seriously restricting its industrialized and safe application. In addition, due to lithium-nickel mixing and residual lithium on the material surface, etc., the chemical and electrochemical stability of the cathode material becomes poor, and cracks appear in the particles, thereby leading to poor cycle stability of the battery; (2) Poor interface contact: The solid-solid contact between the solid electrolyte and the cathode particles has a high interface impedance, affecting the ion transport efficiency; (3) Energy density bottleneck: The energy density of traditional semi-solid batteries is generally lower than 350 Wh / kg, making it difficult to meet the requirements of high-end applications; (4) Poor battery safety: It is difficult to balance the high safety of the battery while ensuring the electrochemical performance of the battery.

[0004] Prior art attempts to improve the interfacial stability of ternary cathodes by optimizing the structure of cathode materials. Chinese Patent CN119170763A discloses a lithium nickel manganese oxide cathode material, its preparation method and application, using a coral-shaped coating layer (the coating layer material includes Al, Ti, Zr) to modify the cathode. Although it inhibits the dissolution of transition metals, it does not optimize the ion transport path at the cathode interface; US Patent US20220173101A1 discloses a fin field-effect transistor with a merged drift region, using a gradient compaction process to optimize the electrode structure. However, it does not involve material chemical modification and does not solve the cathode interface problem from the material itself; Chinese Patent CN113745455A discloses a ternary cathode sheet for a lithium battery, its preparation method and use. The main method is to add an oxide solid electrolyte with a specific particle size to the cathode sheet. Although this method can improve the high safety of the battery, the added oxide electrolyte is prone to agglomeration during ball milling, and the prepared battery is comparable to the existing liquid battery (260-300 Wh / kg), with a low energy density and does not demonstrate the advantages of a semi-solid battery, making it difficult to meet the requirements for high energy density of batteries in fields such as drones; Chinese Patent CN 118752738A discloses a solid electrolyte separator and a lithium-ion battery. The solid electrolyte separator includes a base film and a coating layer coated on at least one surface of the base film. The coating layer includes a solid electrolyte layer, where the solid electrolyte is reduced during formation to form a uniform and dense interphase layer, avoiding internal short circuits caused by direct contact between the aluminum current collector and the negative electrode, and can pass the battery heavy object impact test under a fully charged state. Although this electrolyte separator improves the safety performance of the battery, the cycle and rate performance of the battery are poor.

[0005] In summary, the existing improvement schemes (such as single-element doping, single-oxide coating) can only partially improve the above problems, and the processes are complex and costly. Summary of the Invention

[0006] To solve the above problems, the purpose of the present invention is to provide a high-safety lithium nickel cobalt manganese oxide semi-solid battery and its preparation method. The present invention proposes a triple composite modification strategy for the cathode, achieving synergistic optimization of the bulk-phase - interface - ion transport of the cathode material through element gradient doping, heterogeneous coating layer, and pre-mixing with solid electrolyte. Based on this, by optimizing the structure of the lithium nickel cobalt manganese oxide cathode and the design of the double-gradient functional layer composite separator, the present invention can obtain a semi-solid battery with high safety, high energy density (>360 Wh / kg), and long cycle life.

[0007] The high-safety lithium nickel cobalt manganese oxide semi-solid battery provided by the present invention includes a cathode, an anode, a double-gradient functional layer composite separator, and a high-safety electrolyte.

[0008] The positive electrode includes a positive current collector and a modified lithium nickel cobalt manganese oxide positive electrode material provided on the surface of the positive current collector.

[0009] Furthermore, the modified lithium nickel cobalt manganese oxide positive electrode material includes a modified lithium nickel cobalt manganese oxide active material, a positive electrode conductive agent, a positive electrode binder, and an inorganic solid electrolyte.

[0010] Furthermore, when preparing the modified lithium nickel cobalt manganese oxide positive electrode material, the inorganic solid electrolyte is prepared into a slurry as one of the raw materials. Specifically, the inorganic solid electrolyte is prepared into a slurry by mixing inorganic solid electrolyte powder with a solvent.

[0011] Furthermore, the chemical formula of the modified lithium nickel cobalt manganese oxide active material is LiNi x Co y Mn 1-x-y O2, where 0 ≤ x ≤ 1, and the active material includes a core and a shell layer. The core is a Ti- and F-gradient doped NCM core, and the shell layer is a Li2TiO3 / LiAl X B 1-x O2 composite double-layer coating structure;

[0012] Furthermore, the core is a gradient-doped NCM inner core, and Ti 4+ forms a doping concentration gradient from the center (concentration of 0.5 at%) to the surface (concentration of 1.5 at%), and F - forms a doping concentration gradient from the center (concentration of 2 at%) to the surface (concentration of 1 at%). Among them, Ti occupies the transition metal site, and the doping concentration is 0.5 - 1.5 at%. F partially replaces the O site to inhibit the loss of lattice oxygen, and the doping concentration is 1 - 2 at%.

[0013] Furthermore, the shell layer is a composite double-layer coating structure, where the inner layer is a 0.5 - 2 nm thick Li2TiO3 (lithium ion conductor), and the outer layer is a 1 - 3 nm thick LiAl 0.7 B 0.3 O2 glass phase (with both lithium ion conduction and mechanical toughness).

[0014] Furthermore, the positive electrode conductive agent includes one or more of conductive carbon black (Super P), multi-walled carbon nanotubes (SWCNT), vapor-grown carbon fibers (VGCF), and graphene.

[0015] Furthermore, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene (PVDF-HFP), and polytetrafluoroethylene (PTFE).

[0016] Further, the solvent includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetonitrile (ACN).

[0017] Further, the inorganic solid electrolyte is one or more of an NASICON-structured electrolyte, a LISICON-structured electrolyte, a thio-LISICON-structured electrolyte, a perovskite-type electrolyte, a garnet-structured oxide electrolyte, a sulfide electrolyte, and a halide electrolyte.

[0018] Further, the NASICON-structured electrolyte includes one of LATP and LAGP, the garnet-structured oxide electrolyte includes one of LLZO and LLZTO, the perovskite-type electrolyte includes LLTO, the sulfide electrolyte includes one of Li7P3S 7.5 O 3.5 and Li6PS5Cl, and the halide electrolyte includes one of Li3InCl6, Li3InBr6, and Li3InI6.

[0019] Further, the particle size D50 of the inorganic solid electrolyte particles is 5 nm to 90 nm.

[0020] Further, the mass ratio of the modified lithium nickel cobalt manganese oxide active material, the inorganic solid electrolyte, the positive electrode conductive agent, and the positive electrode binder is (85 to 98):(0.5 to 10):(0.5 to 5):(0.5 to 5).

[0021] Further, the modified lithium nickel cobalt manganese oxide active material is a high-nickel NCM positive electrode, including one or more of NCM8 series and NCM9 series active materials.

[0022] Further, among the modified lithium nickel cobalt manganese oxide active materials, the NCM8 series active material includes NCM811; the NCM9 series active material includes NCM90.

[0023] The double-gradient functional layer composite separator provided by the present invention has a sandwich double-gradient structure, including a base layer in the middle, a negative electrode side gradient layer and a positive electrode side gradient layer respectively attached to both side surfaces of the base layer.

[0024] Further, the base layer of the double-gradient functional layer composite separator is: a polyarylethersulfone (PAES) porous membrane is used as the base material, the thickness of the polyarylethersulfone (PAES) porous membrane is 5 - 10 μm, the porosity is 60 - 75%, the decomposition temperature > 450 °C, and the tensile strength ≥ 200 Mpa, having both high temperature resistance and dendrite puncture resistance strength.

[0025] Furthermore, the negative electrode side gradient layer of the double-gradient functional layer composite separator is an in-situ grown titanium nitride / polyvinylidene fluoride (TiN@PVDF) hybrid coating with a thickness of 2-3 μm. In this hybrid coating, TiN is nanowires with a diameter of 10-50 nm, which are vertically arranged to form an ion rapid channel. At the same time, PVDF provides a flexible buffer layer to reduce the interfacial stress.

[0026] Furthermore, the negative electrode side gradient layer of the double-gradient functional layer composite separator is prepared by the following method: Mix TiN nanowire powder and PVDF (Mw = 1,000,000) in a mass ratio of 7:3, then add NMP to adjust the solid content to 25 wt%, and then add carbon nanotubes (CNT) so that the mass fraction of CNT is 0.2 wt%. CNT serves as a conductive agent, and then ball mill for 4 hours at a rotation speed of 300 rpm. The viscosity of the slurry obtained after ball milling reaches 4500 ± 200 mPa·s. Then, using the magnetic field-assisted doctor blade coating method, coat the above slurry on the negative electrode side of the PAES base film. The thickness of the obtained wet film is 30 μm. Immediately apply a vertical magnetic field with an intensity of 0.5 T to align the TiN nanowires along the magnetic field direction, then preheat at 80 °C for 1 minute, and then transfer to a 120 °C vacuum oven for curing for 2 hours to form an oriented porous layer with a thickness of 2.5 μm. The surface resistance of the oriented porous layer < 10 Ω / sq. The above-mentioned oriented porous layer is the negative electrode side gradient layer.

[0027] Furthermore, the positive electrode side gradient layer of the double-gradient functional layer composite separator is a porous polyvinyl alcohol (PVA) coating loaded with a solid electrolyte with a thickness of 1-2 μm. The mass fraction of the solid electrolyte increases from 30% to 60% in a gradient manner from the inside (adjacent to the PAES base film) to the outside (contacting the positive electrode), realizing the synergistic optimization of ion conduction and oxidation resistance.

[0028] Furthermore, the solid electrolyte includes at least one of sulfide solid electrolytes, garnet-type solid electrolytes, LISICON-type solid electrolytes, NASICON-type solid electrolytes, perovskite-type solid electrolytes, and inorganic halide electrolytes;

[0029] Furthermore, the solid electrolyte is selected from Li 1+x Al x Ti 2-x (PO4)3(0.1 < x < 0.6), Li 3x La (2 / 3)-x TiO3(0.04 < x < 0.15), Li7La3M2O 12 (M is one or more of Zr, Ta, Nb), Li 7-m PS 6-m X n(X = Cl, Br, I; 0 ≤ m ≤ 2), xLi2S(100 - x)P2S5(50 < x ≤ 75), Li7P3S 7.5 O 3.5 、Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (LAGP), Li3MX6 (M = trivalent metal; X = Cl, Br, and I), Li x+5 La3Zr y A z O 12 (A is at least one element among Al, Ga, Sc, Yb, Dy, Ta, Ti, V, Y, Nb, hf, Si, Ge, Sn, 1.4 ≤ x ≤ 2, 0 < y < 2.0, 0 < z < 2.0); wherein the particle size D50 of the solid electrolyte particles is 10 nm - 200 nm;

[0030] Furthermore, in the solid electrolyte, the NASICON - type solid electrolyte includes one of LATP and LAGP, the garnet - type solid electrolyte includes one of LLZO (Li7La3Zr2O 12 ), LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ), the perovskite - type solid electrolyte includes LLTO (Li 0.33 La 0.56 TiO3), the sulfide solid electrolyte includes Li7P3S 7.5 O 3.5 、Li6PS5Cl, and the inorganic halide electrolyte includes one of Li3InCl6, Li3InBr6, and Li3InI6.

[0031] Furthermore, the positive - electrode - side gradient layer of the double - gradient functional - layer composite separator is prepared by the following method:

[0032] First, prepare the modified LATP electrolyte powder: Disperse the LATP solid electrolyte powder with a particle size of 100 nm and a silane coupling agent (KH-550) in ethanol at a mass ratio of 1:0.02, and dry at 60 °C for standby; then, prepare the inner layer, middle layer, and outer layer slurries respectively: The inner layer slurry (i.e., the positive electrode side in contact with the PAES base film) uses 70 g of an aqueous solution of polyvinyl alcohol (PVA) with a mass fraction of 5 wt% as the matrix, adds 30 g of the modified LATP electrolyte powder and 0.1 g of polyacrylic acid (PAA) dispersant, and the viscosity is controlled to 2500 mPa·s after ball milling; the middle layer slurry uses 70 g of an aqueous solution of PVA with a mass fraction of 5 wt%, adds 45 g of the modified LATP electrolyte powder and 0.05 g of PAA, and the viscosity is controlled to 2100 mPa·s after ball milling; the outer layer slurry uses 70 g of an aqueous solution of PVA with a mass fraction of 5 wt%, adds 60 g of the modified LATP electrolyte powder, and the viscosity is controlled to 1800 mPa·s after ball milling; then coat the inner layer slurry, middle layer slurry, and outer layer slurry in sequence: First, scrape and coat the inner layer slurry (wet film thickness 15 μm) on the positive electrode side of the PAES base film, and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3 - 5 μm) for 20 seconds to form a semi-dry base layer; then superpose and coat the middle layer slurry (wet film thickness 15 μm), and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3 - 5 μm) for 20 seconds; finally, coat the outer layer slurry (wet film thickness 15 μm), and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3 - 5 μm) for 20 seconds to form a dense surface layer with a high LATP content, and then dry it in a hot air circulation at 80 °C for 4 hours to obtain a composite coating with a total thickness of 1.8 μm and the LATP content continuously increasing from 30% to 60% in a gradient manner, and the interlayer thickness deviation monitored online by optics < 5%, that is, the gradient layer on the positive electrode side is obtained.

[0033] Further, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder;

[0034] Further, the negative electrode satisfies the following conditions:

[0035] (1) The negative electrode active material includes one or more of graphite, hard carbon, silicon-carbon composite material, and silicon-oxygen composite material;

[0036] (2) The negative electrode conductive agent includes one or more of conductive carbon black (Super P, i.e., SP), multi-walled carbon nanotubes (SWCNT), carbon fiber, and graphene;

[0037] (3) The negative electrode binder includes one or more of polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA);

[0038] (4) The mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (93 - 98.5):(1.0 - 3.0):(0.5 - 4.0);

[0039] (5) The negative electrode current collector is copper foil or carbon-coated copper foil;

[0040] Further, the high-safety electrolyte includes an electrolyte solvent and a solute;

[0041] Further, the electrolyte solvent in the high-safety electrolyte includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC);

[0042] Further, the solute in the high-safety electrolyte includes a lithium salt and an additive. The lithium salt includes one or more of LiPF6, LiDFOB, LiBF4, LiTFSI, LiBOB, and LiFSI, and the additive includes one or more of a film-forming additive, a flame retardant additive, an overcharge additive, and a high-temperature or low-temperature additive;

[0043] Further, the film-forming additive includes one or more of vinylene carbonate (VC), propylene carbonate (PC), and fluoroethylene carbonate (FEC);

[0044] Further, the flame retardant additive includes one or more of trimethyl phosphate (TMP), ethyl hexafluorophosphate (FEP), and propyl pentafluorophosphate (FPP);

[0045] The present invention also provides a preparation method of the above high-safety nickel cobalt manganese lithium oxide semi-solid battery, which is specifically as follows:

[0046] The positive electrode, the negative electrode, the dual-gradient functional layer composite separator, and the high-safety electrolyte are respectively prepared, and then the positive electrode, the dual-gradient functional layer composite separator, and the negative electrode are sequentially placed at intervals and wound, and then encapsulated with an aluminum-plastic film. After baking to remove moisture, the high-safety electrolyte is injected, and it is left standing at room temperature, formed, aged, and then capacity-fractionated to obtain the semi-solid battery.

[0047] The semi-solid battery is a nickel cobalt manganese lithium oxide semi-solid battery with high energy density, long cycle life, and high safety.

[0048] In the semi-solid battery provided by the present invention, the modified lithium nickel cobalt manganese oxide cathode material can not only improve the structural stability and interfacial stability of the cathode material, but also expand the lithium ion transport channels and improve the interfacial ion and electron transport rates. In the semi-solid battery provided by the present invention, the double-gradient functional layer composite separator can enhance the ion mobility between the positive and negative electrodes and the separator interface, improve the interfacial stability, and achieve the safe dynamic protection of the battery. The semi-solid battery assembled with the cathode sheet prepared from the cathode material of the above semi-solid battery, the anode sheet prepared from the anode material, and the double-gradient functional layer composite separator and the high-safety electrolyte has high cycle stability and high safety.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1). The modified cathode active material adopted by the present invention can achieve the synergistic effect of gradient doping + double coating: among them, Ti 4+ stabilizes the layered structure, and F − reduces the oxygen activity; Li2TiO3 improves the Li + diffusion rate, and LiAl x B 1-x O2 glass inhibits the corrosion of the electrolyte; it is prepared by the low-temperature atomic layer deposition (ALD) process: it can avoid the material decomposition caused by the high-temperature treatment of the traditional coating;

[0051] (2). During the battery cycling process, when lithium in the cathode is deintercalated and inserted into the anode, an SEI film will be formed, resulting in irreversible loss of lithium, reducing the capacity and initial efficiency of the battery. When the nickel content in the modified lithium nickel cobalt manganese oxide cathode material is relatively high, the lithium-nickel mixing and oxygen loss in the cathode cause the structural stability of the cathode to deteriorate. The doped solid electrolyte can provide lithium ions to relithiate the charged lithium nickel cobalt manganese oxide cathode, reduce the charged state of the cathode, delay its structural decomposition and oxygen release at high temperatures, and improve the thermal stability of the material and the safety of the battery;

[0052] (3). The double-gradient functional layer composite separator adopted by the present invention has high ionic conductivity (>1.5 mS / cm): the metal-like electron conductivity of TiN can assist the desolvation of lithium ions, and the solid electrolyte in the positive electrode side gradient layer can provide a three-dimensional lithium ion migration network, and the composite conductivity is increased by 300% compared with the traditional PE separator. In addition, it can achieve the control of the electrode / separator interface impedance: the TiN array on the negative electrode side can reduce the disordered growth of the SEI film, and the solid electrolyte in the positive electrode side gradient layer can inhibit the oxidative decomposition of the electrolyte on the positive electrode side. Finally, the double-gradient functional layer composite separator adopted by the present invention can provide dynamic safety protection: the pore shrinkage rate of the PAES substrate at 150 °C is <5% (superior to 80% of the traditional PE / PP), combined with the flame retardant characteristics of the solid electrolyte, it does not burn or explode through the 187 °C hot box experiment, which can significantly improve the safety of the battery;

[0053] (4) The high-energy density, long-cycle and high-safety nickel cobalt manganese lithium oxide semi-solid battery provided by the present invention uses the modified nickel cobalt manganese lithium oxide cathode material, double-gradient functional layer composite separator and electrolyte of the above nickel cobalt manganese lithium oxide semi-solid battery. During the 2040-cycle process, the battery capacity retention rate always remains above 80%, it will not catch fire or explode when punctured, and the thermal runaway temperature is increased to 187°C, having good cycle stability and high safety;

[0054] (5) The preparation method of a nickel cobalt manganese lithium oxide semi-solid battery provided by the present invention has simple process, is compatible with existing equipment, has low energy consumption, is environmentally friendly and has low cost. Description of the Drawings

[0055] Figure 1 It is the SEM image of the gradient precursor obtained in step a of step (1) in Example 1;

[0056] Figure 2 It is the SEM image of the gradient core-shell structure precursor obtained in step c of step (1) in Example 1;

[0057] Figure 3 It is the SEM image of the cross-section of the double-gradient functional layer composite separator in Example 3;

[0058] Figure 4 It is the impedance comparison diagram after the first cycle of the semi-solid batteries prepared in Example 3 and Comparative Example 2 respectively;

[0059] Figure 5 It is the first-efficiency comparison diagram of the semi-solid batteries prepared in Example 3 and Comparative Example 2 respectively;

[0060] Figure 6 It is the cycle performance comparison diagram of the semi-solid batteries prepared in Example 3 and Comparative Example 2 respectively at room temperature of 25°C and a rate of 0.33C;

[0061] Figure 7 It is the capacity retention rate comparison diagram of the semi-solid batteries prepared in Example 3 and Comparative Example 2 respectively after storage at 55°C for 7 days;

[0062] Figure 8 It is the thermal runaway critical temperature comparison diagram of the semi-solid batteries prepared in Example 3 and Comparative Example 2 respectively;

[0063] Figure 9 It is the gas production comparison diagram of the two types of batteries in Example 3 and Comparative Example 2 after storage at 70°C for 7 days. Detailed Embodiments

[0064] To better understand the content of the present invention, the present invention will be further elaborated below in conjunction with specific embodiments and drawings. The following embodiments are implemented based on the technology of the present invention, and detailed implementation manners and operation steps are given, but the protection scope of the present invention is not limited to the following embodiments.

[0065] Example 1:

[0066] (1) Preparation of modified lithium nickel cobalt manganese oxide (LiNi 0.8 Mn 0.1 Co 0.1 O2, i.e., NCM811) active material, realizing the formation of a doping concentration gradient of Ti 4+ from the center (concentration about 0.5 at%) to the surface (concentration about 1.5 at%), and F - forming a doping concentration gradient from the center (concentration about 1 at%) to the surface (concentration about 2 at%). A Li2TiO3 / LiAl x B 1−x O2 composite coating layer is formed on the surface of the Ti / F gradient-doped NCM811 core by a low-temperature ALD deposition process. The specific preparation process is as follows:

[0067] a. Core preparation: Using microfluidic co-precipitation technology to prepare Ni doped with high F (2.0 at%) and low Ti (0.5 at%) 0.8 Mn 0.1 Co 0.10Precursor: First, dissolve NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O in deionized water and mix them evenly to obtain the main salt solution a. The concentration of NiSO4·6H2O is 0.8 M, the concentration of MnSO4·H2O is 0.1 M, and the concentration of CoSO4·7H2O is 0.1 M. Add tetrabutyl titanate (TBOT) and citric acid to deionized water and stir well to obtain the citric acid chelating solution a containing TBOT. The concentration of TBOT is 0.05 M, and the molar ratio of TBOT to citric acid is 1:3. Add NH4F to deionized water and mix evenly to obtain the NH4F solution a. The concentration of NH4F is 0.2 M. Then, pump the above main salt solution a, the citric acid chelating solution a containing tetrabutyl titanate, and the NH4F solution a into the reactor simultaneously. The flow rate of the main salt solution a is 10 mL / min, the flow rate of the citric acid chelating solution a containing TBOT is 0.5 mL / min, and the flow rate of the NH4F solution a is 2.0 mL / min. At the same time, inject the NaOH / NH3 composite precipitant into the reactor at a flow rate of 8 mL / min. Carry out the coprecipitation reaction at 55 °C with a stirring speed of 800 rpm. The NaOH / NH3 composite precipitant is a solution with a pH of 11.0 prepared by adding NaOH and NH3 to deionized water; maintain a highly alkaline environment to promote rapid nucleation, Ti 4+ Due to chelation, it is uniformly incorporated into the bulk phase with delayed release, F - Is preferentially adsorbed on the particle surface to form a highly doped region; after the coprecipitation reaction starts to add each reactant until 40 minutes later, centrifuge the reaction mixture solution at a rate of 3000 rpm to collect the precipitate, wash it 3 times with an ethanol-water mixture (the volume ratio of ethanol to deionized water in this mixture is 3:1) to remove free ions, and finally vacuum dry it at 60 °C for 12 hours to obtain a gradient precursor with a D50 particle size diameter of 120 nm, a surface F content of about 2.0 at%, and a bulk phase Ti content of about 0.5 at%.

[0068] b. Preparation of the intermediate transition layer:

[0069] The gradient precursor obtained in step a is used as the matrix, and a dynamic linear adjustment process is used to achieve continuous change of Ti / F in the transition zone of the matrix surface: NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O are dissolved in deionized water and mixed evenly to obtain a main salt solution b, wherein the concentration of NiSO4·6H2O is 8M, the concentration of MnSO4·H2O is 1.0M, and the concentration of CoSO4·7H2O is 1.0M. Tetrabutyl titanate (TBOT) and citric acid are added to deionized water. After sufficient stirring, a citric acid chelating solution b containing TBOT is obtained, wherein the concentration of TBOT is 0.10M and the molar ratio of TBOT to citric acid is 1:3. NH4F is added to deionized water and mixed evenly to obtain NH4F solution b, wherein the concentration of NH4F is 0.15M; then the main salt solution b, the citric acid chelating solution b containing TBOT and the NH4F solution b are synchronously pumped into the reactor, wherein the flow rate of the main salt solution b is 10mL / min, the flow rate of the citric acid chelating solution b containing TBOT is 1.0 mL / min, and the flow rate of the NH4F solution b is 1.5mL / min (that is, relative to step a, the concentration of the citric acid chelating solution containing TBOT is increased from 0.05M to 0.10M, corresponding to Ti doping 0.5→1.0at%, and its flow rate is linearly increased from 0.5mL / min to 1.0mL / min, with a gradient slope of 0.017mL / min 2 ; The concentration of NH4F solution decreased from 0.2M to 0.15M, corresponding to F 2.0→1.5at%, and the flow rate decreased from 2.0mL / min to 1.5mL / min, with a slope of 0.017mL / min 2 ); At the same time, NaOH / NH3 composite precipitant was injected into the reactor at a flow rate of 6 mL / min, wherein the NaOH / NH3 composite precipitant was a solution of pH = 10.0 prepared by adding NaOH and NH3 into deionized water, and the temperature was set to 60 ° C. The laminar shear effect of the microfluidic reaction chamber was used to guide the Ti 4+ Preferentially doped into the granular epitaxial layer, F - Due to NH4 + The adsorption amount decreased with decreasing concentration. After 60 minutes of reaction, the mixed solution obtained by the reaction was collected by centrifugation and washed three times with anhydrous ethanol to obtain a transition layer precursor with a continuous Ti / F gradient (Ti 0.5 (pointing to the center) → 1.0 at%, F 2.0 (pointing to the center) → 1.5 at%) and a particle size D50 of 160 nm.

[0070] c. Preparation of surface layer: Using the transition layer precursor obtained in step b as the matrix, a surface layer structure is formed on its surface: NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O are dissolved in deionized water and mixed evenly to obtain a main salt solution c, wherein the concentration of NiSO4·6H2O is 8M, the concentration of MnSO4·H2O is 1.0M, and the concentration of CoSO4·7H2O is 1.0M. Tetrabutyl titanate (TBOT) and citric acid are added to deionized water and stirred thoroughly. After stirring, a citric acid chelating solution c containing TBOT was obtained, wherein the concentration of TBOT was 0.15 M, and the molar ratio of TBOT to citric acid was 1:3. NH4F was added to deionized water and mixed evenly to obtain an NH4F solution c, wherein the concentration of NH4F was 0.10 M. Then, the main salt solution c, the citric acid chelating solution c containing TBOT, and the NH4F solution c were simultaneously pumped into the reactor, wherein the flow rate of the main salt solution c was 10 mL / min, and the flow rate of the citric acid chelating solution c containing TBOT was 1.5 mL / min, the flow rate of NH4F solution c is 1.0 mL / min (that is, relative to step b, the concentration of the citric acid chelating solution containing TBOT is increased from 0.10 M to 0.15 M, corresponding to Ti doping 1.0→1.5 at%, and its flow rate is 1.5 mL / min; the concentration of NH4F solution is reduced from 0.15 M to 0.10 M, corresponding to F 1.5→1.0 at%, and the flow rate is 1.0 mL / min), and at the same time, the composite precipitant c is injected into the reactor at a flow rate of 4 mL / min. The composite precipitant c is a mixed solution prepared by mixing 0.2 M NaOH aqueous solution and 0.05 M NH3 aqueous solution, and the pH is stabilized at 9.5. The composite precipitant c also adds polyacrylic acid (PAA) dispersant to inhibit particle agglomeration, wherein the mass ratio of PAA to the mass of the mixed solution with a pH of 9.5 is 0.1 wt%; the reactor is kept at 65 ° C and stirred at a high intensity of 1000 rpm (shear rate> 500 s -1 ) Enhance mass transfer and promote Ti + The citric acid preferentially occupies the octahedral lattice sites on the particle surface through the citric acid chelation-dissociation mechanism. - The competitive adsorption of PAA reduces the surface residue; after the reaction, the mixture is centrifuged at 4000 rpm for 10 minutes, washed three times with an ethanol-acetone mixture (the volume ratio of ethanol to acetone is 3:1) to remove free Ti / F ions, and then freeze-dried (specifically pre-frozen at -50°C for 4 hours and vacuum dried for 12 hours) to fix the surface components, and finally annealed at 300°C for 30 minutes in an Ar / 5% CF4 atmosphere to compensate for the surface F loss to 0.8 at%, forming a gradient core-shell structure precursor with a particle size D50 of 200 nm, a surface Ti content of approximately 1.5 at%, and a F content of approximately 0.8 at%.

[0071] d. High-temperature lithiation and gradient doping locking

[0072] Mixing Lithium and Pre-sintering: Mix the core-shell structure precursor obtained in step c above with LiOH•H2O at a molar ratio of Li / (Ni + Mn + Co) = 1.05 (where Ni:Mn:Co = 8:1:1). Then, pre-sinter at 450 °C for 4 h in an oxygen atmosphere to form an Li2O intermediate phase, which promotes the solid solution of Ti / F elements in the lattice, and obtain the pre-sintered product.

[0073] Gradient Sintering Process: First, heat the product obtained after the above pre-sintering from room temperature to 800 °C and hold for 6 h for crystallization. During sintering, introduce oxygen with an oxygen flow rate of 2 L / min and a heating rate of 5 °C / min to make Ti 4+ occupy the Ni site (the Ti-rich central region inhibits Li / Ni mixing), and F - partially replaces the O site (the low-F surface region retains oxygen activity). Then, anneal at 500 °C for 2 h. During annealing, introduce Ar gas containing 5% CF4, and use the F radicals generated by the decomposition of CF4 to compensate for the surface F content, forming a concentration gradient from the center (F concentration is about 2 at%) to the surface (F concentration is about 1 at%); promote the diffusion of Ti / F elements along the grain boundaries to lock the gradient distribution, and finally obtain Ti / F gradient-doped NMC811 particles;

[0074] e. Using the above Ti / F gradient-doped NMC811 particles as the matrix, form an Li2TiO3 / LiAl x B 1-x O2 composite coating layer on its surface by the low-temperature atomic layer deposition (ALD) method: First, alternately pulse-deposit the precursor tetrakis(dimethylamino)titanium (TDMAT) and ozone under nitrogen protection, and complete 50 cycles at 100 °C (one cycle means first pulse-deposit TDMAT and then pulse-deposit ozone) to form an amorphous TiO2 layer with a thickness of 1.5 nm. Subsequently, introduce lithium tert-butoxide (LiOtBu) vapor for in-situ lithiation reaction at 120 °C to generate an inner layer of ionic conductor Li2TiO3 with a thickness of about 2 nm. Then, switch the precursor to trimethylaluminum and triethylborane (the mass ratio of the two is 1:1), and alternately pulse-deposit water vapor and ozone for 15 cycles (1 cycle means first pulse-deposit water vapor and then pulse-deposit ozone) to deposit an Al2O3 / B2O3 composite layer to a thickness of about 2.5 nm. Finally, introduce LiOtBu vapor to lithiate the Al2O3 / B2O3 composite layer at 80 °C, and anneal in nitrogen at 150 °C for 1 h to convert it into an LiAl 0.7 B 0.3The outer layer of O2 glass phase finally forms a continuous and dense Li2TiO3 / LiAlBO double-layer heterogeneous coating structure. The interlayer interface achieves atomic-level matching through the ALD self-limiting reaction, and finally the modified lithium nickel cobalt manganese oxide active material is obtained.

[0075] (2) Preparation of the modified lithium nickel cobalt manganese oxide positive electrode sheet: First, weigh 2.5 kg of the modified lithium nickel cobalt manganese oxide active material obtained in step (1) and add it to a slurry mixing kettle. Then add 0.028 kg of polyvinylidene fluoride (PVDF) binder and stir evenly. After that, add 0.3 kg of lithium titanium aluminum phosphate (LATP) electrolyte slurry with a solid content of 15%. The LATP electrolyte slurry is obtained by mixing LATP powder with a particle size of 50 nm and NMP in a mass ratio of 16:84. Immediately add 0.04 kg of conductive carbon black to the slurry mixing kettle and stir evenly. Then add 0.8 kg of NMP to the slurry mixing kettle and adjust the slurry viscosity to 3600 mPa•s. Finally, obtain the modified lithium nickel cobalt manganese oxide positive electrode slurry with a solid content of 72%. Then coat the slurry on the aluminum foil and dry it to obtain the positive electrode roll. The surface density of the unrolled positive electrode sheet is 340 g / m 2 , and the rolled compaction density is 3.2 g / cm 3 . Cut it into a roll with a width of 80 mm, a dressing length of 100 m, and then cut it into positive electrode sheets with length and width dimensions of 70 mm×80 mm respectively;

[0076] (3) Preparation of the negative electrode sheet: First, mix 1.0 kg of graphite and 0.17 kg of silicon-carbon composite material evenly. Then add 0.024 kg of Spuer P conductive agent and 1.0 kg of deionized water respectively and stir for dispersion. After that, add 0.05 kg of CMC slurry with a solid content of 20%, 0.05 kg of SBR slurry with a solid content of 20%, and 0.1 kg of PAA slurry with a solid content of 20% (the above CMC slurry, SBR slurry, and PAA slurry are obtained by mixing CMC, SBR, and PAA with deionized water respectively) and mix and stir. Add 0.8 kg of deionized water according to the slurry viscosity and adjust the slurry viscosity to 3600 / mpas. Finally, obtain the negative electrode slurry with a solid content of 54%.

[0077] Perform negative electrode coating through a coater. Using copper foil as the negative electrode current collector, coat the above negative electrode slurry on the copper foil, dry it in an oven, and wind it to obtain the negative electrode roll. The surface density of the negative electrode sheet before rolling is 160 g / m 2 , and then roll it through a rolling machine. Set the rolling compaction density to 1.6 g / cm 3 . Cut it into a roll with a width of 82 mm and a length of 100 m, and then cut it into negative electrode sheets with length and width dimensions of 72 mm×82 mm respectively.

[0078] (4) Preparation of double-gradient functional layer composite separator:

[0079] f. Preparation of the base layer (PAES porous membrane): First, 0.12 kg of polyarylethersulfone (PAES, Mw = 50,000 - 80,000) was dissolved in 0.88 kg of N-methylpyrrolidone (NMP). After stirring, the concentration of the resulting solution was 12 wt%. Then, 0.053 kg of polyethylene glycol (PEG-4000) was added as a pore former, so that the mass fraction of PEG-4000 was 0.5 wt%. After that, it was magnetically stirred at 60 °C for 6 h to completely dissolve, and vacuum degassed for 30 minutes. Then, the above vacuum degassed solution was uniformly coated on a PET release film by the slot extrusion method, with an initial wet film thickness of 200 μm. Then, it entered the first-stage gradient humidity coagulation bath. Specifically, it stayed at 25 °C and a humidity of 70% for 30 seconds to initially form surface micropores. Then, it was the second stage. Specifically, it stayed at 50 °C and a humidity of 40% for 2 minutes to induce an internal through-hole structure. Finally, it was washed with water to remove residual solvents and vacuum dried at 60 °C for 6 h to obtain a PAES base film with a porosity of 65 ± 3% and a thickness of 8 μm.

[0080] g. Preparation of the negative electrode side gradient layer (TiN@PVDF vertical array coating):

[0081] Preparation of TiN nanowires: First, using a copper foil as the substrate, TiCl4 as the titanium source, NH3 as the nitrogen source, and an Ar / H2 mixed gas (where the volume ratio of Ar to H2 is 9:1) as the carrier, TiN nanowires were synthesized by chemical vapor deposition (CVD) method, and the reaction temperature was set at 800 °C. The obtained nanowires were peeled off to obtain TiN nanowire powder (the diameter of TiN nanowires in this powder was 50 ± 5 nm, and the length was 3 - 5 μm). Then, 0.7 kg of the above TiN nanowire powder was mixed with PVDF (Mw = 1,000,000) at a mass ratio of 7:3, and then NMP was added to adjust the solid content to 25 wt%. After that, carbon nanotubes (CNT) were added so that the mass fraction of CNT was 0.2 wt%. CNT was used as a conductive agent, and then it was ball milled at a rotation speed of 300 rpm for 4 h, and the slurry viscosity reached 4500 ± 200 mPa·s.

[0082] Vertical array coating: Using the magnetic field-assisted doctor blade coating method, the above slurry was coated on the negative electrode side of the PAES base film. The obtained wet film thickness was 30 μm. Then, a vertical magnetic field with an intensity of 0.5 T was immediately applied to align the TiN nanowires along the magnetic field direction. Then, it was preheated at 80 °C for 1 minute, and then transferred to a 120 °C vacuum oven for curing for 2 h to form an oriented porous layer with a thickness of 2.5 μm, and the surface resistance of the oriented porous layer was <10 Ω / sq.

[0083] h. Preparation of the positive electrode side gradient layer (LATP@PVA gradient coating):

[0084] First, prepare the modified LATP electrolyte powder: Disperse the LATP solid electrolyte powder with a particle size of 100 nm and the silane coupling agent (KH-550) in ethanol at a mass ratio of 1:0.02, and dry at 60 °C for later use. Then, prepare the three-layer LATP@PVA slurries for the inner layer, middle layer, and outer layer respectively: The inner layer slurry (i.e., the positive electrode side in contact with the PAES base film) uses 70 g of an aqueous solution of polyvinyl alcohol (PVA) with a mass fraction of 5 wt% as the matrix, adds 30 g of the modified LATP electrolyte powder and 0.1 g of polyacrylic acid (PAA) dispersant, and controls the viscosity to 2500 mPa·s after ball milling; the middle layer slurry uses 70 g of an aqueous solution of PVA with a mass fraction of 5 wt%, adds 45 g of the modified LATP electrolyte powder and 0.05 g of PAA, and controls the viscosity to 2100 mPa·s after ball milling; the outer layer slurry uses 70 g of an aqueous solution of PVA with a mass fraction of 5 wt%, adds 60 g of the modified LATP electrolyte powder (without adding a dispersant), and controls the viscosity to 1800 mPa·s to promote dense packing; Subsequently, use a multi-channel slot coater to coat the inner layer slurry, middle layer slurry, and outer layer slurry in sequence: First, scrape the inner layer slurry (wet film thickness 15 μm) on the positive electrode side of the PAES base film, and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3-5 μm) for 20 seconds to form a semi-dry base layer; then stack and coat the middle layer slurry (wet film thickness 15 μm), and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3-5 μm) for 20 seconds to ensure no mixing between layers; finally, coat the outer layer slurry (wet film thickness 15 μm), and immediately pre-cure it with infrared radiation at 3 W / cm² (wavelength 3-5 μm) for 20 seconds to form a dense surface layer with a high LATP content. Then, dry it in a hot air circulation at 80 °C for 4 hours to obtain a composite coating with a total thickness of 1.8 μm and the LATP content continuously increasing from 30% to 60% in a gradient manner. The online optical monitoring shows that the interlayer thickness deviation < 5%, realizing the synergistic optimization of ion conduction and antioxidant properties.

[0085] (5) Electrolyte preparation: Mix ethylene methyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) evenly according to a mass ratio of 3:1:1 to obtain 84.5 g of a non-aqueous organic solvent. Then, add 0.2 g of propane sultone (PS) and 0.3 g of methylene methane disulfonate (MMDS) as additives to the above non-aqueous organic solvent respectively. After that, add 0.5 g of fluoroethylene carbonate (FEC) and 0.5 g of vinylene sulfate (DTD) as negative electrode film-forming aids and mix evenly. The resulting solution is the electrolyte.

[0086] (6) Cell assembly: Stack 20 positive electrode sheets prepared in step (2), 21 negative electrode sheets prepared in step (3), and the double-gradient functional layer composite separator prepared in step (4) to form a 10 Ah soft-pack cell (wherein the positive electrode sheet and the negative electrode sheet are respectively located on both sides of the double-gradient functional layer composite separator), then weld the electrode tabs, encapsulate the aluminum-plastic film, bake at 55 °C for 48 h, inject the electrolyte prepared in step (5), with a fixture pressure of 4 N•m, stand at room temperature for 24 h, perform formation, aging, and then grading to obtain a high-safety lithium nickel cobalt manganate semi-solid battery.

[0087] Example 2:

[0088] (1) Preparation of modified lithium nickel cobalt manganate (LiNi 0.9 Mn 0.05 Co 0.05 O2, i.e., NCM90) active material: According to the preparation method in step (1) of Example 1, in step a of Example 1, replace "prepare Ni doped with high F (2.0 at%) and low Ti (0.5 at%)" 0.8 Mn 0.1 Co 0.10 "precursor" with "prepare Ni doped with high F (2.0 at%) and low Ti (0.5 at%)" 0.90 Mn 0.05 Co 0.05 "precursor", and replace the concentration of NiSO4·6H2O in the main salt solution a with 0.90 M, the concentration of MnSO4·H2O with 0.05 M, and the concentration of CoSO4·7H2O with 0.05 M, and the others are the same as in Example 1;

[0089] (2) Preparation of positive electrode sheet: This step is the same as in Example 1; According to the preparation method in step (2) of Example 1, replace the LATP electrolyte in Example 1 with LAGP, and replace NCM811 with NCM90, and the others are the same as in Example 1;

[0090] (3) Preparation of negative electrode sheet: This step is the same as in Example 1;

[0091] (4) Preparation of double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with LAGP, and the others are the same as in Example 1;

[0092] (5) Electrolyte configuration: This step is the same as in Example 1;

[0093] (6) Cell assembly: This step is the same as in Example 1.

[0094] Example 3:

[0095] (1) Modified lithium nickel cobalt manganate (LiNi0.9 Mn 0.05 Co 0.05 O2, namely NCM90) active material preparation: This step is the same as in Example 2;

[0096] (2) Positive electrode sheet preparation: According to the preparation method in step (2) of Example 2, replace the LAGP electrolyte in Example 2 with LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ), and the others are the same as in Example 2;

[0097] (3) Negative electrode sheet preparation: This step is the same as in Example 1;

[0098] (4) Preparation of double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with LLZTO, and the others are the same as in Example 1;

[0099] (5) Electrolyte configuration: This step is the same as in Example 1;

[0100] (6) Cell assembly: This step is the same as in Example 1.

[0101] Example 4:

[0102] (1) Preparation of modified lithium nickel cobalt manganate (LiNi 0.9 Mn 0.05 Co 0.05 O2, namely NCM90) active material: This step is the same as in Example 2;

[0103] (2) Positive electrode sheet preparation: According to the preparation method in step (2) of Example 2, replace the LAGP electrolyte in Example 2 with LLTO (Li 0.33 La 0.56 TiO3), and the others are the same as in Example 2;

[0104] (3) Negative electrode sheet preparation: This step is the same as in Example 1;

[0105] (4) Preparation of double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with LLTO, and the others are the same as in Example 1;

[0106] (5) Electrolyte configuration: This step is the same as in Example 1;

[0107] (6) Cell assembly: This step is the same as in Example 1.

[0108] Example 5:

[0109] (1) Modified lithium nickel cobalt manganate (LiNi0.9 Mn 0.05 Co 0.05 Preparation of the active material of LiNi

[0110] (2) Preparation of the positive electrode sheet: According to the preparation method in step (2) of Example 2, replace the LAGP electrolyte in Example 2 with LLZO (Li7La3Zr2O 12 ), and the others are the same as in Example 2;

[0111] (3) Preparation of the negative electrode sheet: This step is the same as in Example 1;

[0112] (4) Preparation of the double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with LLZO, and the others are the same as in Example 1;

[0113] (5) Preparation of the electrolyte: This step is the same as in Example 1;

[0114] (6) Cell assembly: This step is the same as in Example 1.

[0115] Example 6:

[0116] (1) Preparation of the modified lithium nickel cobalt manganese oxide (LiNi 0.9 Mn 0.05 Co 0.05 O2, i.e., NCM90) active material: This step is the same as in Example 2;

[0117] (2) Preparation of the positive electrode sheet: According to the preparation method in step (2) of Example 2, replace the LAGP electrolyte in Example 2 with Li7P3S 7.5 O 3.5 , and the others are the same as in Example 2;

[0118] (3) Preparation of the negative electrode sheet: This step is the same as in Example 1;

[0119] (4) Preparation of the double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with Li7P3S 7.5 O 3.5 , and the others are the same as in Example 1;

[0120] (5) Preparation of the electrolyte: This step is the same as in Example 1;

[0121] (6) Cell assembly: This step is the same as in Example 1.

[0122] Example 7:

[0123] (1) Modified lithium nickel cobalt manganese oxide (LiNi 0.9 Mn0.05 Co 0.05 Preparation of active material of CoO2 (i.e., NCM90): This step is the same as that in Example 2;

[0124] (2) Preparation of positive electrode sheet: According to the preparation method in step (2) of Example 2, replace the LAGP electrolyte in Example 2 with Li6PS5Cl, and the others are the same as in Example 2;

[0125] (3) Preparation of negative electrode sheet: This step is the same as that in Example 1;

[0126] (4) Preparation of double-gradient functional layer composite separator: According to the preparation method in step (4) of Example 1, replace the LATP electrolyte in Example 1 with Li6PS5Cl, and the others are the same as in Example 1;

[0127] (5) Preparation of electrolyte solution: This step is the same as that in Example 1;

[0128] (6) Cell assembly: This step is the same as that in Example 1.

[0129] Comparative Example 1:

[0130] (1) Preparation of positive electrode paste: Select un-doped and un-coated high-nickel NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) as the positive electrode active material: Weigh 2.5 kg of the positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 and add it to the slurry mixing kettle, then add 0.028 kg of the binder PVDF and mix, stir evenly, then add 0.04 kg of conductive carbon black to make a slurry, set the revolution speed of the stirrer to 80 rpm and the dispersion speed to 1000 rpm, stir evenly, then add 0.5 kg of NMP, adjust the slurry viscosity to 3600 mPa•s, and finally obtain a high-nickel 8-series (LiNi 0.8 Co 0.1 Mn 0.1 O2) positive electrode paste.

[0131] (2) Preparation of positive electrode sheet: This step is the same as that in Example 1;

[0132] (3) Preparation of negative electrode sheet: This step is the same as that in Example 1;

[0133] (4) Preparation of ordinary electrolyte separator:

[0134] a. Add 0.3 kg of Al2O3 particles with a D50 particle size of 50 nm to 0.5 kg of NMP and stir evenly to obtain a slurry. Then, add dispersant PVA, surfactant CTAB, and binder PVDF-HFP to the above slurry in the mass ratio of Al2O3:PVA:PVDF-HFP:CTAB = 96%:2.5%:1%:0.5% in sequence and mix evenly; prepare Al2O3 coating slurry. The solid content of the Al2O3 coating slurry is 36.9% and the viscosity is 100 mPa•s. Coat the Al2O3 coating slurry on one side of a PE base film with a thickness of 9 μm through a coater, and after drying the slurry, obtain a base film with a 3-μm-thick Al2O3 layer coated on one surface;

[0135] b. Dissolve 0.2 kg of PVDF-HFP in 0.8 kg of NMP and stir to form a uniform colloidal slurry. Coat the obtained colloidal slurry on the other side of the base film to obtain a PVDF-HFP coating with a thickness of about 2 μm, and finally obtain a common electrolyte separator. Cut the obtained separator into a width of 86 mm for standby.

[0136] (5)Electrolyte preparation: This step is the same as that in Example 1;

[0137] (6)Cell assembly: This step is the same as that in Example 1.

[0138] Comparative Example 2:

[0139] (1)Preparation of positive electrode slurry: Weigh 2.5 kg of positive electrode material LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM90) and add it to a mixing kettle. Then, add 0.028 kg of binder PVDF and mix, stir evenly. Set the revolution speed of the stirrer to 100 rpm. Immediately add 0.04 kg of graphene to make a slurry, set the revolution speed of the stirrer to 80 rpm, the dispersion speed to 1000 rpm, and stir evenly. Then, add 0.5 kg of NMP and adjust the viscosity of the slurry to 3300 mPa•s. Finally, obtain a high-nickel 9-series (LiNi 0.9 Co 0.05 Mn 0.05 O2) positive electrode slurry;

[0140] (2)Preparation of positive electrode sheet: This step is the same as that in Example 1;

[0141] (3)Preparation of negative electrode sheet: This step is the same as that in Example 1;

[0142] (4)Preparation of common electrolyte separator: This step is the same as that in Comparative Example 1;

[0143] (5)Electrolyte preparation: This step is the same as that in Example 1;

[0144] (6) Cell assembly: This step is the same as that in Example 1.

[0145] Figure 1 It is the SEM image of the gradient precursor obtained in step a of step (1) in Example 1. The measured values of the core diameters of the gradient precursors are shown in Table 1.

[0146] Table 1

[0147]

[0148] Figure 2 It is the SEM image of the gradient core-shell structure precursor obtained in step c of step (1) in Example 1. The measured values of the diameters of the gradient core-shell structure precursors are shown in Table 2.

[0149] Table 2

[0150]

[0151] Figure 3 It is the SEM image of the cross-section of the dual-gradient functional layer composite separator in Example 3; after testing, the ionic conductivity of this separator is 1.8 mS / cm: among which, the metalloid electron conductivity of TiN assists in the desolvation of lithium ions, the LLZTO electrolyte provides a three-dimensional lithium ion migration network, and the composite conductivity is increased by 300% compared with the traditional PE separator. The electrode / separator interface impedance is 1.5 Ω·cm². Among them, the TiN array on the negative electrode side can reduce the disordered growth of the SEI film, and the gradient LLZTO electrolyte on the positive electrode side inhibits the oxidation and decomposition of the positive electrode electrolyte. In terms of dynamic safety protection: the pore shrinkage rate of the PAES substrate at 150 °C is <5% (superior to 80% of the traditional PE / PP), combined with the flame retardant characteristics of the LLZTO electrolyte, it does not catch fire or explode through the 185 °C hot box experiment.

[0152] Figure 4 It is the impedance comparison diagram after the first cycle of the batteries prepared in Example 3 and Comparative Example 2 respectively; Figure 4 It can be seen that the impedance of Example 3 is significantly smaller than that of Comparative Example 2, indicating that the modified lithium nickel cobalt manganese oxide cathode material and the dual-gradient functional layer composite separator can significantly reduce the interface impedance of the battery.

[0153] Figure 5 It is the first efficiency comparison diagram of the batteries prepared in Example 3 and Comparative Example 2 respectively; Figure 5 It can be seen that for Example 3, that is, the semi-solid battery using the modified lithium nickel cobalt manganese oxide cathode material and the dual-gradient functional layer composite separator, the first-cycle Coulombic efficiency is 99.8%, which is significantly higher than that of Comparative Example 2, that is, the battery with the unmodified lithium nickel cobalt manganese oxide cathode material and the ordinary separator (96.5%).

[0154] Figure 6It is a comparison chart of the cycling performance of the batteries prepared in Example 3 and Comparative Example 2 at room temperature of 25 °C and a rate of 0.33C. From Figure 6 It can be seen that after 2040 cycles, the capacity retention rate of Example 3 is 80%. However, after 500 cycles, the capacity of Comparative Example 2 rapidly decays, and the capacity retention rate decays to 80% after 960 cycles. The results show that the modified lithium nickel cobalt manganese oxide cathode material and the double-gradient functional layer composite separator can significantly improve the cycling stability of the battery.

[0155] Figure 7 It is a comparison chart of the capacity retention rate of the batteries prepared in Example 3 and Comparative Example 2 after storage at 55 °C for 7 days; from Figure 7 It can be seen that the capacity retention rate of the semi-solid battery prepared in Example 3 after storage at 55 °C for 7 days is 96.5%, which is significantly higher than that of Comparative Example 2, indicating that the modified lithium nickel cobalt manganese oxide cathode material and the double-gradient functional layer composite separator can significantly improve the high-temperature storage performance of the battery.

[0156] Figure 8 It is a comparison chart of the thermal runaway temperature of the batteries prepared in Example 3 and Comparative Example 2; from Figure 8 It can be seen that the thermal runaway temperature of Example 3 is 187 °C, and that of Comparative Example 2 is 131 °C. Example 3 is significantly higher than Comparative Example 2, indicating that the modified lithium nickel cobalt manganese oxide cathode material and the double-gradient functional layer composite separator can significantly improve the thermal stability of the battery.

[0157] Figure 9 It is a comparison chart of the gas production of the two types of batteries, Example 3 and Comparative Example 2, after storage at 70 °C for 7 days; from Figure 9 It can be seen that the gas production of Example 3 is 0.4 mL, while that of Comparative Example 2 is 4.6 mL. Example 3 is significantly less than Comparative Example 2, indicating that the modified lithium nickel cobalt manganese oxide cathode material and the double-gradient functional layer composite separator can significantly reduce the side reactions inside the battery.

[0158] Table 3 Comparison of the performance of the electrolyte separators prepared in Example 3 and Comparative Example 2

[0159]

[0160] It can be seen from Table 3 that the ionic conductivity of the separator in Example 3 is 1.8 mS / cm, which is significantly higher than that of Comparative Example 2. The thermal stability and mechanical strength of the separator in Example 3 are better than those of Comparative Example 2, indicating that the electrolyte-coated separator has excellent puncture strength, tensile strength and heat shrinkage, and can improve the puncture and thermal safety of the battery.

[0161] The semi-solid batteries prepared by assembling the battery cores of Examples 1-7 and the batteries prepared by assembling the battery cores of Comparative Examples 1-2 were subjected to relevant electrical performance and other performance tests, and the results are shown in Table 4.

[0162] Table 4

[0163]

[0164] As can be seen from Table 4, after constant volume of Examples 1-7, the DCR is lower than that of Comparative Examples 1 and 2, the capacities are higher than those of Comparative Examples 1 and 2, and the boundary heating temperatures are higher than those of Comparative Examples 1 and 2. After the batteries of Examples 1-7 are fully charged, they can all pass the nail penetration test, while Comparative Examples 1 and 2 fail. After 2000 cycles, the capacity retention rates of the batteries are also higher than those of Comparative Examples 1 and 2. The results show that the modified lithium nickel cobalt manganese oxide cathode material and the double-gradient functional layer composite separator can not only reduce the battery impedance and improve the battery capacity retention rate, but also significantly improve the nail penetration and thermal safety of the battery.

[0165] The above are only the embodiments of the present invention, and do not impose any form of limitation on the present invention. The present invention may also have other forms of embodiments based on the above structures and functions, which will not be listed one by one. Therefore, any person skilled in the art, without departing from the scope of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A nickel-cobalt-manganese-oxide lithium semi-solid battery, characterized in that: It includes a positive electrode, a negative electrode, a double gradient functional layer composite diaphragm and an electrolyte; The positive electrode comprises a positive electrode current collector and a modified lithium nickel cobalt manganese oxide positive electrode material disposed on the surface of the positive electrode current collector; The modified nickel cobalt lithium manganese oxide positive electrode material comprises a modified nickel cobalt lithium manganese oxide active material, a positive electrode conductor, a positive electrode binder and an inorganic solid electrolyte; The modified lithium nickel cobalt manganese oxide active material is a high nickel NCM positive electrode, including one or more of NCM8 series and NCM9 series active materials, and the active material includes a core body and a shell layer, the core body is a Ti and F gradient doped NCM core body, and the shell layer is Li2TiO3 / LiAl X B 1-x O2 composite double-layer coating structure; The core body is a gradient doped NCM core with Ti 4+ Forming a doping concentration gradient from the center to the surface, F - A doping concentration gradient is formed from the center to the surface, wherein Ti occupies the transition metal position, the doping concentration is 0.5-1.5at%, and the concentration at the center is 0.5at%, and the concentration at the surface is 1.5at%; F partially replaces the O position to inhibit the loss of lattice oxygen, the doping concentration is 1-2at%, and the concentration at the center is 2at%, and the concentration at the surface is 1at%; the shell layer is a composite double-layer coating structure, wherein the inner layer is a 0.5-2nm thick Li2TiO3 ion conductor, and the outer layer is a 1-3nm thick LiAl 0.7 B 0.3 O2 glass phase; The dual-gradient functional layer composite diaphragm is a sandwich dual-gradient structure, including a base layer in the middle, a negative electrode side gradient layer and a positive electrode side gradient layer respectively attached to the two sides of the base layer; The base layer of the dual gradient functional layer composite diaphragm is: a polyarylethersulfone porous membrane is used as a substrate, the polyarylethersulfone porous membrane has a thickness of 5-10μm, a porosity of 60-75%, a decomposition temperature>450°C, and a tensile strength of ≥200Mpa; the negative electrode side gradient layer is an in-situ grown titanium nitride / polyvinylidene fluoride mixed coating, the thickness of the mixed coating is 2-3μm, wherein TiN is a nanowire with a diameter of 10-50nm and is vertically arranged to form an ion fast channel; the positive electrode side gradient layer is a porous polyvinyl alcohol coating with a thickness of 1-2μm loaded with a solid electrolyte, and the mass fraction of the solid electrolyte increases from 30% to 60% from the inside to the outside; the solid electrolyte includes at least one of a sulfide solid electrolyte, a garnet solid electrolyte, a LISICON solid electrolyte, a NASICON solid electrolyte, a perovskite solid electrolyte, and an inorganic halide electrolyte.

2. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The mass ratio of the modified nickel cobalt lithium manganese oxide active material, inorganic solid electrolyte, positive electrode conductor and positive electrode binder is (85~98): (0.5~10): (0.5~5): (0.5~5); the positive electrode conductor includes one or more of conductive carbon black, multi-walled carbon nanotubes, vapor-grown carbon fibers and graphene; the positive electrode binder includes one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and polytetrafluoroethylene; the particle size D50 of the inorganic solid electrolyte particles is 5nm~90nm, and the inorganic solid electrolyte is one or more of a NASICON structure electrolyte, a LISICON structure electrolyte, a perovskite electrolyte, a garnet structure oxide electrolyte, a sulfide electrolyte and a halide electrolyte.

3. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 2, characterized in that: Among the modified nickel cobalt manganese oxide active materials, the NCM8 series active materials include NCM811; the NCM9 series active materials include NCM90; among the inorganic solid electrolytes, the NASICON structure electrolyte includes one of LATP and LAGP, the garnet structure oxide electrolyte includes one of LLZO and LLZTO, the perovskite electrolyte includes LLTO, and the sulfide electrolyte includes Li7P3S 7.5 O 3.5 , Li6PS5Cl, and the halide electrolyte includes one of Li3InCl6, Li3InBr6, and Li3InI6.

4. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The particle size D50 of the solid electrolyte particles is 10nm-200nm; Among the solid electrolytes, the NASICON type solid electrolyte includes one of LATP and LAGP, the garnet type solid electrolyte includes one of LLZO and LLZTO, the perovskite type solid electrolyte includes LLTO, and the sulfide solid electrolyte includes Li7P3S 7.5 O 3.5 , one of Li6PS5Cl, and the inorganic halide electrolyte includes one of Li3InCl6, Li3InBr6, and Li3InI6.

5. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The negative electrode side gradient layer of the dual gradient functional layer composite diaphragm is prepared by the following method: TiN nanowire powder and PVDF are mixed in a mass ratio of 7:3, wherein the Mw of PVDF is 1,000,000, and then NMP is added to adjust the solid content to 25wt%, and then CNT is added to make the mass fraction of CNT 0.2wt%, and then ball milled at a speed of 300rpm for 4 hours. The viscosity of the slurry obtained after ball milling reaches 4500±200mPa·s, and then the magnetic field assisted scraping method is used to apply the above slurry on the negative electrode side of the PAES base membrane. The obtained wet film thickness is 30μm, and then a vertical magnetic field with a strength of 0.5T is immediately applied, and then preheated at 80℃ for 1 minute, and then transferred to a 120℃ vacuum oven for curing for 2 hours to form a directional porous layer with a thickness of 2.5μm, and the surface resistance of the directional porous layer is <10Ω / sq. The above directional porous layer is the negative electrode side gradient layer.

6. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The positive electrode side gradient layer of the dual gradient functional layer composite diaphragm is prepared by the following method: First, the modified LATP electrolyte powder was prepared: LATP solid electrolyte powder with a particle size of 100 nm and silane coupling agent KH-550 were dispersed in ethanol at a mass ratio of 1:0.02, dried at 60°C and set aside; then, the inner layer, middle layer and outer layer slurries were prepared respectively: the inner layer slurry, i.e., the positive electrode side contacting the PAES base membrane, used 70g of a polyvinyl alcohol aqueous solution with a mass fraction of 5wt% as the matrix, added 30g of the modified LATP electrolyte powder and 0.1g of a polyacrylic acid dispersant, and the viscosity was controlled to be 2500mPa·s after ball milling; the middle layer slurry used 70g of a PVA aqueous solution with a mass fraction of 5wt%, added 45g of the modified LATP electrolyte powder and 0.05g of PAA, and the viscosity was controlled to be 2100mPa·s after ball milling; the outer layer slurry used 70g of a PVA aqueous solution with a mass fraction of 5wt%, added 60g of the modified LATP electrolyte powder, and ball milled The viscosity is controlled at 1800mPa·s; then the inner layer slurry, the middle layer slurry and the outer layer slurry are applied in sequence: the inner layer slurry is first applied on the positive side of the PAES base film, the inner layer slurry has a wet film thickness of 15μm, and it is immediately pre-cured with infrared radiation at 3W / cm² and a wavelength of 3-5μm for 20 seconds to form a semi-dry base layer; then the middle layer slurry is superimposed and applied, the wet film thickness of the middle layer slurry is 15μm, and it is immediately pre-cured with infrared radiation at 3W / cm² and a wavelength of 3-5μm for 20 seconds Pre-curing for 20 seconds; finally, apply the outer layer slurry with a wet film thickness of 15μm. Immediately pre-curing with infrared radiation at 3W / cm² and a wavelength of 3-5μm for 20 seconds forms a dense surface layer with a high LATP content. Then, dry it in a hot air cycle at 80℃ for 4 hours to obtain a composite coating with a total thickness of 1.8μm and a LATP content continuously increasing from 30% to 60%. The online optical monitoring of the interlayer thickness deviation is less than 5%, that is, the positive side gradient layer is obtained.

7. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a negative electrode conductive agent and a negative electrode binder; The negative electrode meets the following conditions: (1) The negative electrode active material includes one or more of graphite, hard carbon, silicon-carbon composite material, and silicon-oxygen composite material; (2) The negative electrode conductive agent includes one or more of conductive carbon black, multi-walled carbon nanotubes, carbon fibers and graphene; (3) The negative electrode binder includes one or more of polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; (4) The mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (93-98.5): (1.0-3.0): (0.5-4.0); (5) The negative electrode current collector is copper foil or carbon-coated copper foil.

8. The nickel-cobalt-manganese-oxide lithium semi-solid battery according to claim 1, characterized in that: The electrolyte includes an electrolyte solvent and a solute, the electrolyte solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and vinyl carbonate; the solute includes a lithium salt and an additive, the lithium salt includes one or more of LiPF6, LiDFOB, LiBF4, LiTFSI, LiBOB, LiFSI, the additive includes one or more of a film-forming additive, a flame retardant additive, an overcharge additive, a high temperature or low temperature additive; the film-forming additive includes one or more of vinylene carbonate, propylene carbonate and fluoroethylene carbonate; the flame retardant additive includes one or more of trimethyl phosphate, ethyl hexafluorophosphate and propyl pentafluorophosphate.

9. A method for preparing a nickel-cobalt-manganese-oxide lithium semi-solid battery according to any one of claims 1 to 8, characterized in that: The positive electrode, negative electrode, dual-gradient functional layer composite membrane and electrolyte are prepared respectively, and then the positive electrode, dual-gradient functional layer composite membrane and negative electrode are placed in sequence and then wound, and then packaged with aluminum-plastic film, baked to remove moisture, and then injected with the electrolyte, left to stand at room temperature, formed, aged, and then divided to obtain the semi-solid battery.

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