A high-safety ternary hybrid lithium-ion battery cell and its preparation method

Abstract

This invention discloses a high-safety ternary lithium-ion battery cell and its preparation method, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a casing; the positive electrode comprises an aluminum foil and a positive electrode material layer coated on the aluminum foil, wherein the active material of the positive electrode material layer is a ternary material; the ternary material comprises the following materials by mass percentage: 85-95% high-voltage single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O2 co-doped polycrystalline LiNi with 5-15% zirconium and titanium gradient 0.6 Co 0.2 Mn 0.2 O2; The negative electrode includes a copper foil and a negative electrode material layer coated on the copper foil. The active material of the negative electrode material layer is artificial graphite with pure needle coke as a precursor. Through the design of zirconium and titanium gradient doping, functional partitioning is achieved. The internal zirconium doping acts like a pillar to stabilize the lattice, effectively suppressing the generation of harmful phase transitions and particle microcracks under high voltage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-safety blended ternary lithium-ion cell and its preparation method. Background Technology

[0002] High-nickel layered oxide cathode materials (such as LiNi) 0.6 Co 0.2 Mn 0.2 O2 (NCM622) has become a key material for improving the energy density of lithium-ion batteries due to its high specific capacity (≥180mAh / g) and high operating voltage platform. However, with the increase of nickel content, the thermal stability of the material in the deep delithiation state deteriorates significantly. Under conditions of overcharging, high temperature, or mechanical abuse (such as needle penetration or extrusion), oxygen in the material lattice is easily released, which reacts violently with the organic electrolyte, generating a large amount of heat and gas, thereby triggering a chain reaction of thermal runaway, leading to battery smoke, fire, or even explosion.

[0003] Existing technologies for improving the safety of ternary lithium batteries typically employ single or limited improvement measures, but all have significant limitations or side effects:

[0004] Regarding the modification of cathode materials: conventional bulk uniform doping (such as Al and Mg doping) can stabilize the structure to a certain extent, but it cannot specifically suppress the most severe side reactions and transition metal dissolution at the material surface and interface; traditional wet or solid coating (such as Al2O3 and ZrO2) often have uneven coating layers and weak bonding with the matrix, which are prone to failure during long-term cycling, and thicker coating layers can hinder lithium-ion conduction.

[0005] Regarding anode materials: their reactivity is rarely controlled at the source. Fine graphite particles (fine powder) have a larger specific surface area and higher surface energy, which can exacerbate side reactions with the electrolyte, leading to increased gas production and decreased initial efficiency. This is one of the causes of cell cycle expansion and poor high-temperature performance.

[0006] Regarding electrolytes: Adding a single flame retardant (such as phosphorus-based or fluorinated solvents) usually impairs the ionic conductivity and compatibility with the electrodes of the electrolyte to some extent, leading to increased battery internal resistance, reduced rate performance, and decreased cycle life.

[0007] Regarding the separator: simply increasing the thickness of the base film or the ceramic coating will reduce the energy density. Furthermore, ordinary ceramic coatings (containing only spherical particles) still have insufficient resistance to shrinkage and puncture at high temperatures, and cannot effectively prevent the expansion of internal short circuits caused by lithium dendrites or metal debris during thermal runaway.

[0008] The aforementioned point-based or isolated improvement schemes fail to systematically address each critical step in the thermal runaway chain reaction from the perspective of synergistic effects within the electrochemical system: localized internal short circuit → Joule heating and reaction heat accumulation → cathode material decomposition and oxygen release → violent reaction between electrolyte and oxygen → sudden temperature and pressure rise → separator melting leading to large-area short circuit → combustion and explosion. Therefore, a comprehensive solution integrating material intrinsic properties, multiphase interface stability, and macroscopic structural strength is urgently needed to maintain high energy density while constructing multiple reliable safety defenses, thus achieving inherent battery safety. Summary of the Invention

[0009] To address the needs and problems mentioned in the background above, this invention provides a high-safety mixed ternary lithium-ion battery cell and its preparation method, thereby at least partially solving the above-mentioned problems.

[0010] According to the technical solution of the present invention, a high-safety ternary lithium-ion battery cell is provided, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a casing;

[0011] The positive electrode includes an aluminum foil and a positive electrode material layer coated on the aluminum foil, wherein the active material of the positive electrode material layer is a ternary material; the ternary material comprises the following materials in mass percentage:

[0012] 85-95% high-voltage single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O2 co-doped polycrystalline LiNi with 5-15% zirconium and titanium gradient 0.6 Co 0.2 Mn 0.2 O2;

[0013] The negative electrode includes a copper foil and a negative electrode material layer coated on the copper foil. The active material of the negative electrode material layer is artificial graphite with pure needle coke as a precursor. The particle size distribution of the artificial graphite is: 8μm≥D10≥6μm, 16.5μm≥D50≥15.5μm, and the mass percentage of the artificial graphite with a particle size of less than 2μm is less than 5%.

[0014] Preferably, the electrolyte comprises a lithium salt, an organic solvent, and additives, wherein the lithium salt is LiPF6 with a concentration of 1.0-1.3 mol / L; the organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7; and the additives comprise the following materials in the total mass percentage of the electrolyte:

[0015] 1-3% fluoroethylene carbonate, 1-2% lithium difluorophosphate, 0.5-2% ionic liquid functionalized siloxane and 2-5% cyclic phosphononitrile flame retardants.

[0016] Preferably, the diaphragm comprises a porous polyethylene base membrane and a composite ceramic coating applied to both sides of the porous polyethylene base membrane;

[0017] The thickness of the polyethylene porous base film is 7-12 μm, and the thickness of the composite ceramic coating on one side is 1.5-3 μm.

[0018] The composite ceramic coating comprises nano-alumina, two-dimensional flaky vermiculite nanosheets, and nano-cellulose binder in a mass ratio of 4-6:4-6:1.

[0019] Preferably, the cathode material layer further includes a silane coupling agent comprising 1-2% of the mass percentage of the blended ternary material.

[0020] Preferably, the surface of the active material of the negative electrode is provided with a pre-formed film layer, which includes Li3PO4 and Li2SO3.

[0021] Preferably, the cation of the ionic liquid functionalized siloxane is 1-ethyl-3-methylimidazolium, and the anion is bis(fluorosulfonyl)imide;

[0022] The tabs of the battery cell meet the following conditions: the width of the tabs is 4.5-5.5mm, the exposed length of the tabs is 7-9mm, and the center distance between two tabs of the same polarity is 27-29mm.

[0023] On the other hand, the present invention also provides a method for preparing a high-safety mixed ternary lithium-ion battery cell, comprising the following steps:

[0024] Positive electrode preparation: Gradient co-doped polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 O2 and single-crystal LiNi with a surface coated with Li3PO4 layer 0.6 Co 0.2 Mn 0.2 O2 is mixed at a mass ratio of 5-15:85-95 to obtain the positive electrode active material;

[0025] The positive electrode active material, conductive agent, binder and silane coupling agent are mixed and slurried, and then coated onto the aluminum foil of the positive electrode. After drying and rolling, the positive electrode is subjected to gas phase fluorination treatment at 80-120℃ for 10-30 minutes in a nitrogen atmosphere containing 1-5% hexafluoroethane to obtain the positive electrode sheet.

[0026] Negative electrode preparation: Pure needle-shaped coke artificial graphite with a particle size distribution of 8μm≥D10≥6μm, 16.5μm≥D50≥15.5μm and a mass percentage of particles smaller than 2μm is less than 5% is impregnated in an ethanol solution containing trimethyl phosphate and vinyl sulfate. After treatment, it is heat-treated at 180-220℃ under an inert atmosphere, followed by slurry preparation, coating, drying and rolling to obtain the negative electrode.

[0027] Cell assembly: The positive electrode, composite ceramic separator, and negative electrode are stacked in sequence, and the tabs are welded and packaged.

[0028] Electrolyte injection and formation: Electrolyte is injected and allowed to stand for soaking. Formation is then carried out using a stepped current: First, the battery is charged at a constant current of 0.02C to 3.0-3.2V and allowed to stand. Then, it is charged at a constant current of 0.05C to 3.5-3.6V to obtain the battery cell.

[0029] Preferably, the gradient co-doped polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 The method for preparing O2 includes the following steps:

[0030] Preparation of gradient doped precursors:

[0031] (a) Before the theoretical reaction progress of the coprecipitation reaction reaches 40%, the nickel-cobalt-manganese main salt solution, the precipitant and all the zirconium salt solution are added to the reaction system in parallel flow.

[0032] (b) After the theoretical reaction progress reaches 40%, switch to adding nickel-cobalt-manganese main salt solution, precipitant and all titanium salt solution to the reaction system in parallel until the reaction is completed, and obtain hydroxide precursor with radial concentration gradient.

[0033] High-temperature solid-state sintering: The precursor and lithium source are mixed and sintered at 720-780℃ for 10-15 h in an oxygen atmosphere to obtain the gradient co-doped polycrystalline LiNi. 0.6 Co 0.2 Mn 0.2 O2.

[0034] Preferably, after the liquid injection and formation steps, an aging and screening step is also included: the cells are placed in an environment of 45°C and an environment of 25°C for 5-7 days each, and cells with voltage drop exceeding 10mV are monitored and removed.

[0035] Preferably, the method for preparing the composite ceramic diaphragm is as follows:

[0036] Nano-alumina, two-dimensional vermiculite nanosheets and nano-cellulose adhesive were mixed and dispersed at a mass ratio of 4-6:4-6:1 to prepare an aqueous slurry. The aqueous slurry was then coated on both sides of a polyethylene film using a microgravure coating method. After drying, a composite ceramic diaphragm was obtained. Beneficial effects

[0037] This invention achieves functional partitioning through a zirconium and titanium gradient doping design. The internal zirconium doping acts as a pillar to stabilize the crystal lattice, effectively suppressing harmful phase transitions and microcracks in particles under high voltage. The strong titanium-oxygen bonding on the surface significantly increases the oxygen vacancy formation energy, suppressing oxygen release under high temperature or abuse conditions from a thermodynamic source. Combined with a dense Li3PO4 coating layer constructed using atomic layer deposition technology, it provides a physical isolation barrier for the material, greatly enhancing the intrinsic safety of the positive electrode active material.

[0038] This invention, by strictly controlling the particle size distribution of artificial graphite, ensures an extremely low content of fine powder, directly and effectively reducing the total specific surface area of ​​the negative electrode material. This significantly reduces the active sites that can react with the electrolyte, fundamentally suppressing gas generation and abnormal heat generation, improving the thermal safety boundary of the battery, and significantly reducing irreversible capacity loss during the first charge and discharge cycle.

[0039] This invention forms an inorganic-organic composite layer rich in Li3PO4 and Li2SO3 on the graphite surface through pretreatment with phosphorus and sulfur compounds. The composite layer has a dense structure and high ionic conductivity, and is more stable than the SEI film formed by the in-situ decomposition of traditional electrolytes. It can effectively prevent the continuous decomposition of electrolytes and the growth of lithium dendrites during cycling, thereby improving the rate performance, low-temperature performance and high-temperature storage stability of the negative electrode.

[0040] This invention employs a synergistic design of four subsystems: gradient doping of the positive electrode (ALD coating + interfacial fluorination), particle size control and pre-film formation of the negative electrode, synergistic film formation of the electrolyte + vapor-phase flame retardancy, and a composite reinforced structure for the separator. This design incorporates effective suppression or blocking mechanisms at every critical node of the thermal runaway chain. This enables the cell to pass the most stringent nail penetration test, exhibiting only a slow temperature rise and limited smoke without ignition or explosion, fundamentally addressing the safety concerns of high-nickel ternary batteries. Detailed Implementation

[0041] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0042] The primary objective of this invention is to overcome the shortcomings of existing high-nickel ternary lithium-ion battery safety technologies and provide a high-safety cell design scheme with multi-level synergy from materials to the system, along with a method for large-scale production. This invention aims to construct an internal self-protection system through precise material design and process control, enabling the cell to withstand extreme abuse conditions such as needle penetration, external short circuits, and heavy object compression, achieving the highest safety goals of not catching fire, not exploding, and not burning. Simultaneously, this scheme must ensure that the cell possesses comprehensive superior performance characteristics such as high capacity, low internal resistance, long cycle life, and high production yield.

[0043] To achieve the above objectives, the core of this invention lies in constructing a four-in-one synergistic safety system composed of an intrinsically stable positive electrode, a low-activity negative electrode, a flame-retardant synergistic electrolyte, and a composite reinforced separator. This system is not a simple superposition of existing technologies, but rather a systematic blockade from the physicochemical source of thermal runaway to its propagation path through functional complementarity and synergistic enhancement among its components.

[0044] 1. Cathode system: A triple-protection structure of "core-shell-interface" through synergistic gradient doping and interface modification.

[0045] Technical solution: The positive electrode active material adopts a specially treated ternary material, which is composed of 85-95wt% high-voltage single crystal NCM622 and 5-15wt% polycrystalline NCM622 co-doped with zirconium and titanium gradient.

[0046] Gradient-doped polycrystalline material: In the polycrystalline NCM622, the atomic concentrations of Zr and Ti exhibit a predetermined continuous gradient distribution in the radial direction from the center to the surface of the particle. Specifically, based on the normalized radial position x (x=0 for the center, x=1 for the surface), the zirconium concentration C_Zr(x) monotonically decreases from 0.5-1.5 at.% in the interior (x≤0.3) to 0.1-0.4 at.% in the surface layer (x≥0.7); while the titanium concentration C_Ti(x) monotonically increases from 0-0.2 at.% in the interior (x≤0.3) to 0.8-2.0 at.% in the surface layer (x≥0.7).

[0047] Single-crystal material coating: The surface of the single-crystal NCM622 is coated with a layer of amorphous Li3PO4 with a thickness of 2-10nm using atomic layer deposition technology.

[0048] Electrode interface strengthening: Add 1-2% of silane coupling agent (such as KH-550) to the positive electrode slurry, and after the electrode is rolled, perform gas phase fluorination treatment at 80-120℃ for 10-30 min in a nitrogen atmosphere containing 1-5 vol% hexafluoroethane (C2F6).

[0049] Explanation of principles and effects:

[0050] Gradient doping functional partitioning effect: Zr with larger ionic radii 4+ (~0.72 Å) enriched within the particles, acting like pillars to support the interlayer spacing, effectively suppressing the drastic volume shrinkage during the H2 to H3 phase transition, thereby reducing the formation of microcracks within the particles and improving bulk structural stability. Ti with a small ionic radius but stronger oxygen binding energy... 4+ Enriched on the particle surface, it can strongly pin the surface lattice oxygen, significantly increasing the oxygen vacancy formation energy and suppressing oxygen release at high temperatures or high voltages from a thermodynamic source. This gradient design of internally stable lattice and externally locked oxygen achieves synergistic optimization of bulk and interfacial stability.

[0051] The physical barrier effect of atomic deposition (ALD) coating: The ultrathin, uniform, and dense Li3PO4 layer (preferably 5nm) can physically isolate the positive electrode active material from direct contact with the electrolyte, reducing interfacial side reactions. At the same time, its excellent lithium-ion conductivity and electrochemical stability ensure smooth lithium-ion transport at the interface. Combined with the gradient-doped Ti-rich surface region, it forms a dual interfacial protection of chemical anchoring and physical isolation.

[0052] Enhanced bonding and passivation effects at the electrode interface: Silane coupling agents strengthen the chemical bonding between the active material, conductive agent, and binder, reducing the risk of electrode swelling and pulverization in the electrolyte. Vapor-phase fluorination treatment can introduce lithium fluoride (LiF) or CF bonding layers onto the surfaces of the active material and conductive agent, pre-constructing a more stable cathode-electrolyte interface film (CEI) with lower impedance, significantly reducing interfacial impedance growth and transition metal catalytic decomposition effects during cycling.

[0053] 2. Negative Electrode System: Low Strain and High Stability SEI Pre-built Design

[0054] Technical Solution: The negative electrode active material is artificial graphite made from 100% pure needle-shaped coke source. Its particle size distribution is specially designed and strictly controlled: 8μm≥D10≥6μm, 16.5μm≥D50≥15.5μm, and the mass percentage of fine powder with a particle size less than 2μm is less than 0.5%. Before pulping, the graphite is pretreated by immersing it in an ethanol solution containing trimethyl phosphate and vinyl sulfate, followed by heat treatment at 180-220℃ under an inert atmosphere to form a pre-formed film on its surface.

[0055] Explanation of principles and effects:

[0056] The deactivation and side-effect reduction effects of particle size control: 8μm ≥ D10 ≥ 6μm means that the proportion of fine particles in the particle group is extremely low. The reduction in specific surface area directly reduces the active sites that react with the electrolyte, thereby significantly reducing the initial irreversible capacity loss, reducing gas generation, and improving the storage and cycle stability of the battery. Controlling D50 at around 16μm, while reducing the specific surface area, also takes into account the diffusion kinetics of lithium ions within the graphite particles and the compaction density of the electrode, which is beneficial to the performance of capacity and rate capability.

[0057] Interfacial stabilization effect of pre-formed film: Pretreatment pre-constructs an inorganic-organic composite layer rich in Li3PO4 and Li2SO3 on the graphite surface. This film exists before battery formation, and its composition is denser, more stable, and has better ionic conductivity than the SEI film formed by in-situ decomposition of the electrolyte. It can effectively inhibit the continuous decomposition of the electrolyte and the formation of lithium dendrites in subsequent cycles, while improving the anode's tolerance to high temperatures.

[0058] 3. Electrolyte system: Synergistic flame retardancy and interface regulation of multifunctional additives

[0059] Technical solution: The electrolyte base system consists of lithium salt, organic solvent, and additives. The lithium salt is LiPF6 with a concentration of 1.0-1.3 mol / L. The organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7. The additives comprise the following materials as a percentage of the total mass of the electrolyte:

[0060] 1-3% fluoroethylene carbonate, 1-2% lithium difluorophosphate, 0.5-2% ionic liquid functionalized siloxane and 2-5% cyclic phosphononitrile flame retardants.

[0061] Explanation of principles and effects:

[0062] Synergistic film formation and interface stabilization: Fluoroethylene carbonate is preferentially reduced at the negative electrode to form a stable SEI film rich in LiF; LiPO2F2 decomposes at both the positive and negative electrodes, participating in the construction of a robust interface film rich in Li3PO4 and LiF, especially inhibiting oxidative decomposition under high voltage at the positive electrode surface. The two work synergistically to construct low-impedance, high-stability CEI and SEI at the positive and negative electrodes, respectively.

[0063] In-situ polymerization and flame retardancy synergy: Ionic liquid functionalized siloxanes possess both flame retardancy and electrochemical activity. In the early stages of battery operation, the siloxane groups undergo slight electrochemical polymerization on the electrode surface, further enhancing the density and adhesion of the interfacial film. Under high-temperature abuse conditions, it decomposes to produce free radical quenchers, creating a synergistic flame retardant effect with phosphononitrile flame retardants. Phosphononitrile compounds decompose at approximately 120-150℃ to generate PO· free radicals, which can efficiently capture H· and OH· free radicals in combustion chain reactions, achieving gas-phase flame retardancy with minimal impact on battery electrochemical performance.

[0064] 4. Diaphragm system: A composite structure that combines mechanical strength and thermal stability.

[0065] Technical solution: A porous polyethylene (PE) membrane with a thickness of 7-12 μm is used as the substrate, and a composite ceramic coating is coated on both sides of the membrane, with a single-sided coating thickness of 1.5-3 μm by dry weight. The coating consists of nano-alumina, two-dimensional lamellar vermiculite nanosheets, and nano-cellulose binder in a mass ratio of (4-6):(4-6):1; wherein the nano-alumina has a particle size range of 100-400 nm, and the two-dimensional lamellar vermiculite nanosheets have a thickness of 10-50 nm and a sheet diameter of 1-3 μm.

[0066] Explanation of principles and effects:

[0067] The mechanical strengthening effect of the above structure: Two-dimensional lamellar vermiculite nanosheets and spherical Al2O3 particles are stacked alternately in the coating, forming a dense composite structure similar to brick and mortar. The lamellar vermiculite has an extremely high aspect ratio and rigidity, which can greatly improve the puncture resistance of the coating and effectively resist the penetration of lithium dendrites or metallic impurities. This structure can disperse stress when the diaphragm is subjected to local pressure or impact, preventing large-area peeling of the coating.

[0068] Thermal stability and wetting effect of nanocellulose binder: Nanocellulose possesses excellent heat resistance, flexibility, and strong bonding with ceramic particles, ensuring that the coating does not crack or peel off at high temperatures. Simultaneously, the hydrophilicity of nanocellulose helps improve the wetting rate and electrolyte retention capacity of the separator. During assembly, the ceramic coating surface is specified to face the positive electrode. This coating can physically adsorb transition metal ions that may dissolve from the positive electrode, delaying their damage to the SEI of the negative electrode.

[0069] The following describes the preparation of key materials (all examples and comparative examples used the same method to prepare the corresponding materials).

[0070] 1. Gradient-doped polycrystalline NCM622 (used in Examples 1-10, Comparative Examples 2-3)

[0071] Precursor preparation by coprecipitation:

[0072] Preparation of 2.0 mol / L Ni 0.6 Co 0.2 Mn 0.2 Mixed sulfate solution (main salt solution).

[0073] Prepare a 4.0 mol / L NaOH solution (precipitant) and a 10 g / L NH3·H2O solution (complexing agent).

[0074] Prepare a 0.1 mol / L ZrOCl2 aqueous solution (zirconium source) and a 0.1 mol / L TiOSO4 dilute sulfuric acid solution (titanium source).

[0075] 2L of deionized water and a certain amount of ammonia water were injected into a 10L continuous stirred reactor as a base solution. The temperature was controlled at 55℃, pH=11.0, and the stirring speed was 800rpm.

[0076] Timing-controlled feeding:

[0077] Stage I (first 40% of the reaction volume): The main salt solution, NaOH solution, ammonia, and all the zirconium salt solution are simultaneously pumped in parallel. By controlling the pump rate, the reaction in this stage generates Zr-rich (Ni,Co,Mn,Zr)(OH)2 nuclei.

[0078] Phase II (last 60% of the reaction volume): The process switches to simultaneous, parallel-flow pumping of the main salt solution, NaOH solution, ammonia, and all the titanium salt solution. During this phase, a Ti-rich shell is epitaxially grown on the Zr-rich core.

[0079] After the reaction was completed, the mixture was aged, filtered, and washed with deionized water until the conductivity of the filtrate was <50 μS / cm. The filtrate was then vacuum dried at 120℃ for 12 hours to obtain the gradient-doped precursor.

[0080] High-temperature sintering:

[0081] The dried precursor was mechanically mixed with LiOH·H2O (lithium source) at a total molar ratio of metal elements Li / (Ni+Co+Mn+Zr+Ti)=1.05.

[0082] The mixture was placed in an oxygen atmosphere furnace and heated to 500°C at a rate of 5°C / min for 5 hours for pre-firing; then heated to 750°C at a rate of 3°C / min for 12 hours for constant-temperature sintering.

[0083] After furnace cooling, the material was pulverized and sieved to obtain gradient-doped polycrystalline NCM622 material with a D50 of approximately 10 μm. EPMA analysis showed that its Zr / Ti concentration gradient met the design requirements.

[0084] 2. Uniformly doped polycrystalline NCM622 (used in Example 9)

[0085] The preparation process is similar to that of gradient-doped materials, with the only difference being the co-precipitation stage: all zirconium and titanium salt solutions are pre-mixed uniformly with the main salt solution, and then this mixed salt solution, NaOH, and ammonia are pumped in parallel throughout the reaction process. The final result is a polycrystalline NCM622 with uniformly distributed Zr and Ti elements, and the total doping amount is the same as that of the gradient material in Example 1.

[0086] 3. ALD coating treatment (used in Examples 1-4, 6-10, and Comparative Examples 2-3)

[0087] The cathode material to be coated (single-crystal NCM622 or a doped material) was loaded into the ALD reaction chamber. Tris(dimethylamino)phosphine (TDMP) and ozone (O3) were used as precursors. The chamber temperature was set to 200℃. The cycling process was as follows: TDMP pulse 0.1s → N2 purge 20s → O3 pulse 0.2s → N2 purge 30s. After 200 cycles, a Li3PO4 thin film with a thickness of approximately 5nm was deposited on the material surface.

[0088] 4. Negative electrode graphite pretreatment (used in all examples and comparative examples 1-3)

[0089] Artificial graphite meeting the corresponding particle size requirements (Examples 1-9, Comparative Examples 1-3 used a product with D50=16.2μm; Example 4 used a product with D50=13.0μm; Example 10 used a 16.2μm product containing 2% fine powder) was added to the pretreatment solution. The solution composition was: 1000ml ethanol, 10g trimethyl phosphate, and 10g vinyl sulfate. The mixture was stirred and impregnated at room temperature for 4 hours. After filtration, the filter cake was heat-treated at 180℃ for 2 hours under argon protection, and then cooled for later use.

[0090] 5. Composite ceramic diaphragm slurry and coating (used in Examples 1-8, 10, and Comparative Example 2)

[0091] Slurry preparation: The raw materials were weighed according to the dry weight ratio of nano-Al2O3:2-dimensional vermiculite nanosheets:nanocellulose (CNF) = 5:5:1. Using deionized water as the solvent, 0.5% sodium polyacrylate dispersant (by total dry powder mass) was added. The mixture was dispersed in a high-speed planetary mixer at 2000 rpm for 2 hours to prepare a homogeneous slurry with a solid content of 35%.

[0092] Coating: Using a 9μm thick PE base film as the substrate, the above slurry was applied once to each side using a microgravure coating machine. The wet film thickness was precisely controlled to 10μm. After drying in a 120℃ hot air circulating oven, the dry weight thickness of the coating on one side was measured to be approximately 2.2μm.

[0093] The following are the detailed preparation steps and parameters for Examples 1-3 and Comparative Examples 1-10. All operations were carried out in a glove box with dry air (dew point < -40°C) or an inert atmosphere, and the basic process equipment (coating machine, roller press, stacking machine, etc.) were industry-standard equipment.

[0094] Example 1: Positive electrode plate:

[0095] Ingredients: Take 96 kg of ALD-coated mixed cathode material (10% gradient doping + 90% single crystal NCM622), 2 kg of conductive carbon black (SP), and 2 kg of PVDF. Add 1.5% (by mass) of silane coupling agent KH-550 during dry mixing.

[0096] Homogenization and Coating: Add an appropriate amount of NMP and homogenize under vacuum in a planetary mixer until the viscosity reaches 3000 mPa·s. Coat the slurry evenly onto 12 μm aluminum foil, controlling the areal density to 21.5 mg / cm² (based on active material). Dry in an oven at 120℃.

[0097] Rolling and post-treatment: The electrode is cold-pressed to a compaction density of 3.5 g / cm³. The rolled electrode is then placed in a sealed chamber, and a nitrogen mixture containing 3 vol% C2F6 is introduced. The chamber is then treated at 100°C for 20 minutes to complete the gas-phase fluorination.

[0098] Negative electrode plate:

[0099] Ingredients: Take 96 kg of pretreated artificial graphite, 1 kg of SP, 1 kg of CMC, and 2 kg of SBR.

[0100] Homogenization and Coating: Add deionized water and homogenize to a viscosity of 4000 mPa·s. Coat onto 8 μm copper foil, with the areal density controlled at 11.8 mg / cm³. 2 After drying, it is rolled to a compacted density of 1.65 g / cm³. 3 .

[0101] Separator: Al2O3 / vermiculite / CNF composite ceramic separator prepared using the aforementioned method.

[0102] Electrolyte preparation: In an argon-filled glove box, mix EC and EMC at a volume ratio of 3:7. Dissolve LiPF6 to a concentration of 1.2 mol / L. Then add the following in sequence: FEC (2 wt%), LiPO2F2 (1.5 wt%), ionic liquid functionalized siloxane (1 wt%), and cyclic phosphononitrile flame retardant (3 wt%), and stir until homogeneous.

[0103] Cell assembly: Z-shaped stacking is performed in the order of positive electrode sheet → separator (ceramic surface facing positive electrode) → negative electrode sheet. Positive electrode aluminum tab dimensions: 5.0 mm wide, 8.0 mm exposed, center distance between the two tabs 28.0 mm; negative electrode nickel tab has the same dimensions.

[0104] Encapsulation, electrolyte injection, and formation: Aluminum-plastic film encapsulation was used. Vacuum heat sealing was performed at 85°C. Sufficient electrolyte was injected. The mixture was allowed to stand at 45°C for 24 hours. Then, step formation was performed: ① Charging to 3.0V at a constant current of 0.02C (200 mA) and standing for 1 hour; ② Charging to 3.5V at a constant current of 0.05C (500 mA) and standing for 2 hours. Following this, venting and secondary edge sealing were performed.

[0105] Aging screening: The cells were aged sequentially at 45℃ for 7 days, and then at 25℃ for 7 days. During this period, the voltage was monitored daily, and cells with a voltage drop exceeding 10mV were discarded.

[0106] Example 2: The difference from Example 1 is in the ratio of positive electrode active materials. 5% gradient-doped polycrystalline NCM622 and 95% single-crystal NCM622 are mixed and then coated with ALD.

[0107] Example 3: The difference from Example 1 is in the ratio of positive electrode active materials. 15% gradient-doped polycrystalline NCM622 and 85% single-crystal NCM622 are mixed and then coated with ALD.

[0108] Comparative Example 1: The difference from Example 1 is that pure needle-shaped coke artificial graphite with D50=13.0μm and D10>5.0μm was used for negative electrode pretreatment and electrode fabrication.

[0109] Comparative Example 2: The difference from Example 1 is that the positive electrode active material was not subjected to ALD coating treatment. 10% gradient-doped polycrystalline material was physically mixed with 90% single-crystal material and then directly used for slurry preparation.

[0110] Comparative Example 3: The difference from Example 1 is that no ionic liquid functionalized siloxane is added in the preparation of the electrolyte, while the types and proportions of other additives remain unchanged.

[0111] Comparative Example 4: The difference from Example 1 lies in the diaphragm. Its coating slurry uses only nano-Al2O3 and PVDF binder (mass ratio 95:5), without adding vermiculite or CNF. Double-sided coating is performed using the same process.

[0112] Comparative Example 5: The difference from Example 1 is that the positive electrode sheet skips the gas phase fluorination treatment step after rolling and is directly cut and assembled.

[0113] Comparative Example 6: The difference from Example 1 lies in the positive electrode active material. 10% uniformly doped polycrystalline NCM622 and 90% monocrystalline NCM622 were mixed and then coated with ALD.

[0114] Comparative Example 7: The difference from Example 1 lies in the negative electrode graphite raw material. Artificial graphite with a D50 of 16.2 μm but containing approximately 2% fine powder smaller than 2 μm was used, and no additional fine classification treatment was performed; it was directly pretreated.

[0115] Comparative Example 8: Positive electrode: Ordinary polycrystalline NCM622 (without any doping or coating) was used as the active material, and it was slurried and coated with SP and PVDF in a ratio of 96:2:2. No silane coupling agent was used, and no gas-phase fluorination treatment was performed.

[0116] Negative electrode: Commercially available artificial graphite (D50~18μm) is used, and coated according to a conventional formula (graphite:SP:CMC:SBR=96:1:1:2). No pretreatment is required.

[0117] Separator: A commercially available PE separator with Al2O3 coated on one side (coating thickness approximately 2μm) is used.

[0118] Electrolyte: Base solution (1.2M LiPF6 in EC:EMC=3:7), with only 2% FEC added.

[0119] Assembly and formation: Conventional wafer stacking, packaging, and electrolyte injection. The formation process involves constant current charging at 0.1C to 3.8V.

[0120] Comparative Example 9: The difference from Example 1 is that no cyclic phosphononitrile flame retardant and ionic liquid functionalized siloxane are added in the electrolyte preparation, and only 2% FEC and 1.5% LiPO2F2 are retained.

[0121] Comparative Example 10: The only difference from Example 1 is that a raw 9 μm thick PE base film without any coating is used as the separator.

[0122] Examples 1-3 and Comparative Examples 1-10 were tested respectively. In order to objectively and accurately evaluate the performance and safety of the battery cell of the present invention, all examples and comparative examples were tested according to the following unified testing methods and standards.

[0123] Capacity Test:

[0124] Testing standard: Refer to GB / T 18287-2013 "General Specification for Lithium-ion Batteries and Battery Packs for Mobile Phones".

[0125] Testing method: Place the battery cell in a constant temperature environment of 25±2℃. Using a battery testing system, first charge it to 4.2V with a constant current and constant voltage of 0.5C, and cut off the current at 0.05C. Let it stand for 5 minutes, and then discharge it to 2.75V with a constant current of 0.2C. Record the discharge capacity, which is the rated capacity of the battery cell.

[0126] DC Internal Resistance Test:

[0127] Testing standard: Refer to IEC 61960-2011.

[0128] Testing method: Charge the battery cell to 50% SOC (half-charge state) at 25℃. Using an internal resistance tester, apply a small AC current signal of 1000 Hz and measure its voltage response. The calculated AC internal resistance is the internal resistance value in the report. This method eliminates the influence of polarization impedance and reflects the ohmic internal resistance.

[0129] Open Circuit Voltage (OCV):

[0130] Testing standard: Industry-standard method.

[0131] Testing method: After the cell has been tested for capacity, it is left to stand in an open circuit at 25±2℃ for 24 hours. The potential difference between its positive and negative terminals is measured using a high-precision voltmeter (accuracy of at least 0.1mV) and recorded as the open circuit voltage.

[0132] Nail Penetration Test:

[0133] Testing standards: Strictly follow the nail penetration test clause in GB / T 31485-2015 "Safety Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0134] Testing method: Fix the battery cell on the fixture, and use a φ5mm tapered steel needle (taper angle recommended 45°) that has been treated with high temperature resistance to penetrate the battery cell from the direction perpendicular to the battery cell electrode (generally the thickness direction) at a speed of 25±5 mm / s. Hold the needle in place for 1 minute after penetration.

[0135] Judgment criteria: Observe and record whether the battery cell catches fire or explodes within 1 hour. At the same time, monitor the highest surface temperature of the battery cell using thermocouples.

[0136] External Short Circuit Test:

[0137] Testing standards: Comply with GB / T 31485-2015 requirements for medium and short circuit tests.

[0138] Detection method:

[0139] Using copper wires with a total resistance ≤5mΩ (including the resistance of connecting components), directly connect the positive and negative terminals of the battery cell externally, maintaining a short circuit for 10 minutes or until the current in the circuit drops below 1% of its initial value. Judgment criteria: Observe and record whether the battery cell catches fire or explodes during the test and within 1 hour after the test. Monitor the highest surface temperature of the battery cell.

[0140] Crush Test:

[0141] Testing standard: Follows the simplified procedure of the extrusion test in GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles".

[0142] Testing method: Place the battery cell between two parallel plates and squeeze it along the width direction of the battery cell (i.e., the direction perpendicular to the extrusion plate) at a speed of 2 mm / s until the extrusion force reaches 200 kN or the deformation of the battery cell reaches 30% of the initial size (whichever comes first). Then maintain the maximum pressure for 10 seconds.

[0143] Judgment criteria: Observe and record whether the battery cell catches fire or explodes during the test and within 1 hour after the test.

[0144] First Pass Yield:

[0145] Calculation method:

[0146] To count the number of battery cells in a continuous production batch (e.g., 1000 cells) that meet all factory specifications (voltage, internal resistance, capacity, appearance, insulation, etc.) without rework after completing all manufacturing processes (including formation, aging, and capacity testing).

[0147] First-pass yield (%) = (Number of qualified cells / Total number of cells put into use in this batch) × 100%.

[0148] The test results are shown in Table 1 below:

[0149]

[0150] It can be seen from the above table:

[0151] Examples 1-3 demonstrate that, under the core solution of this invention, with the proportion of gradient-doped polycrystalline material varying within the range of 5%-15%, all cells can pass 100% of the three extreme safety tests: nail penetration, short circuit, and extrusion, and the maximum temperature is controlled at a low level. All examples have a capacity exceeding 10000mAh, an internal resistance below 50mΩ, and a throughput exceeding 94%, fully achieving the preset targets.

[0152] Example 2: The optimal performance in terms of capacity and internal resistance indicates that a low proportion of gradient doped material is sufficient to form an effective security network in a single crystal host while minimizing impedance.

[0153] Example 3: The lowest safety test temperature indicates that a higher proportion of gradient doped material brings better thermal stability, but the capacity is slightly reduced, reflecting the balance between safety and energy.

[0154] The comparison between Example 1 and Comparative Example 2 demonstrates the necessity of ALD coating: Without Li3PO4, the ALD coating resulted in a needle-punching temperature of 135°C and increased smoke production. This indicates that the dense physical barrier layer formed by ALD coating is crucial for suppressing the intense exothermic reaction between the positive electrode and the electrolyte during needle-punching.

[0155] By comparing Comparative Examples 4 and 10 with Example 1, it can be seen that:

[0156] Comparative Example 4 used a pure Al2O3 coating, which showed slight splattering upon needle penetration, with the temperature reaching 150℃. This indicates that the lack of a brick-and-mortar reinforcement structure of two-dimensional vermiculite nanosheets reduces the coating's puncture resistance and fails to completely prevent localized thermal shock caused by internal short circuits.

[0157] Comparative Example 10, with no coating whatsoever, showed that the base film instantly melted upon needle puncture, leading to a large-area short circuit, violent combustion, and explosion. This strongly demonstrates that the sandwich composite ceramic coating of this invention is an irreplaceable physical barrier against thermal runaway.

[0158] A comparison between Comparative Example 9 and Example 1 shows that although Comparative Example 9 exhibits good basic electrical properties after removing all flame retardants, the electrolyte cannot self-extinguish in the event of thermal runaway, leading to continuous combustion. This demonstrates that the synergistic flame-retardant mechanism of phosphazenes and ionic liquid additives in the gas phase is the last chemical line of defense for achieving the goal of non-combustibility.

[0159] By comparing Comparative Examples 1 and 7 with Example 1, it can be seen that:

[0160] The higher short-circuit temperature and lower pass-through rate of Comparative Example 1 indicate that smaller particles lead to increased side reactions and poorer consistency.

[0161] Comparative Example 7 showed that the internal resistance increased to a critical value, and significant gas expansion occurred after high-temperature storage. This directly confirms that controlling the fine powder content below 0.5% plays a crucial role in reducing internal resistance and improving cycle and storage stability.

[0162] A comparison between Comparative Example 6 and Example 1 shows that: Comparative Example 6 replaced gradient doping with uniform doping of the same total dose, while other conditions were exactly the same as in Example 1. The results show:

[0163] Safety performance was a complete failure: both the needle penetration and crush tests resulted in fires. This is because uniform doping cannot form internally stable and externally locked functional zones, and the surface layer's ability to anchor oxygen is insufficient. Under abuse conditions, a large amount of oxygen is released, which reacts explosively with the electrolyte.

[0164] Cycling and storage performance deteriorated: both capacity retention and storage recovery rates were significantly lower than in Example 1, and thickness expansion was more severe. This indicates that gradient doping has an unparalleled advantage over uniform doping in improving long-term interface stability.

[0165] Comparative Example 7 represents a traditional high-nickel ternary battery that does not employ any of the key technologies of this invention. Its performance is poor across the board: low capacity, high internal resistance, all batteries exploded during safety tests, and the pass rate was only 85.3%. This highlights the significant advancement and necessity of the system-level solution of this invention compared to traditional technologies.

[0166] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-safety ternary lithium-ion battery cell, characterized in that, Includes positive electrode, negative electrode, separator, electrolyte and casing; The positive electrode includes an aluminum foil and a positive electrode material layer coated on the aluminum foil. The positive electrode material layer includes an active material and a silane coupling agent. The active material of the positive electrode material layer is a ternary material blend. The ternary material blend comprises the following materials in the indicated mass percentages: 85-95% high-voltage single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O2 co-doped polycrystalline LiNi with 5-15% zirconium and titanium gradient 0.6 Co 0.2 Mn 0.2 O2; among which, zirconium and titanium gradient co-doped polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 O2 is calculated with normalized radial position x, where x=0 is the center and x=1 is the surface. The zirconium concentration monotonically decreases from 0.5-1.5 at.% for x≤0.3 to 0.1-0.4 at.% for x≥0.7; the titanium concentration monotonically increases from 0-0.2 at.% for x≤0.3 to 0.8-2.0 at.% for x≥0.7; the high-voltage single-crystal LiNi... 0.6 Co 0.2 Mn 0.2 The surface of O2 is coated with a layer of amorphous Li3PO4 with a thickness of 2-10 nm; the positive electrode is subjected to gas phase fluorination treatment for 10-30 min in a nitrogen atmosphere containing 1-5 vol% hexafluoroethane and at 80-120 °C after the electrode sheet is rolled; The negative electrode includes a copper foil and a negative electrode material layer coated on the copper foil. The active material of the negative electrode material layer is artificial graphite with pure needle coke as a precursor. The particle size distribution of the artificial graphite is: 8μm≥D10≥6μm, 16.5μm≥D50≥15.5μm, and the mass percentage of particles with a diameter less than 2μm in the artificial graphite is less than 5%. Before slurry preparation, the graphite is impregnated in an ethanol solution containing trimethyl phosphate and vinyl sulfate, and then heat-treated at 180-220℃ under an inert atmosphere to form a pre-film on its surface. The electrolyte comprises a lithium salt, an organic solvent, and additives. The lithium salt is LiPF6 with a concentration of 1.0-1.3 mol / L. The organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:

7. The additives comprise the following materials in the total mass percentage of the electrolyte: 1-3% fluoroethylene carbonate, 1-2% lithium difluorophosphate, 0.5-2% ionic liquid functionalized siloxane and 2-5% cyclic phosphononitrile flame retardant; The diaphragm comprises a porous polyethylene base membrane and a composite ceramic coating applied to both sides of the porous polyethylene base membrane. The thickness of the polyethylene porous base film is 7-12 μm, and the thickness of the composite ceramic coating on one side is 1.5-3 μm. The composite ceramic coating comprises nano-alumina, two-dimensional flaky vermiculite nanosheets, and nano-cellulose binder in a mass ratio of 4-6:4-6:

1.

2. The high-safety blended ternary lithium-ion battery cell according to claim 1, characterized in that, The cathode material layer also includes a silane coupling agent comprising 1-2% of the mass percentage of the blended ternary material.

3. The high-safety ternary lithium-ion battery cell according to claim 1, characterized in that, The surface of the active material of the negative electrode is provided with a pre-formed film layer, which includes Li3PO4 and Li2SO3.

4. The high-safety ternary lithium-ion battery cell according to claim 1, characterized in that, The cation of the ionic liquid functionalized siloxane is 1-ethyl-3-methylimidazolium, and the anion is bis(fluorosulfonyl)imide; The tabs of the battery cell meet the following conditions: the width of the tabs is 4.5-5.5mm, the exposed length of the tabs is 7-9mm, and the center distance between two tabs of the same polarity is 27-29mm.

5. A method for preparing a high-safety ternary lithium-ion battery cell as described in any one of claims 1-4, characterized in that, Includes the following steps: Positive electrode preparation: Gradient co-doped polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 O2 and single-crystal LiNi with a surface coated with Li3PO4 layer 0.6 Co 0.2 Mn 0.2 O2 is mixed at a mass ratio of 5-15:85-95 to obtain the positive electrode active material; wherein, the gradient co-doped polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 The method for preparing O2 includes the following steps: Preparation of gradient doped precursors: (a) Before the theoretical reaction progress of the coprecipitation reaction reaches 40%, the nickel-cobalt-manganese main salt solution, the precipitant and all the zirconium salt solution are added to the reaction system in parallel. By controlling the pump speed, the reaction generates Zr-rich (Ni,Co,Mn,Zr)(OH)2 cores at this stage. (b) After the theoretical reaction progress reaches 40%, switch to adding nickel-cobalt-manganese main salt solution, precipitant and all titanium salt solution to the reaction system in parallel until the reaction is completed, and obtain hydroxide precursor with radial concentration gradient. High-temperature solid-state sintering: The precursor and lithium source are mixed and sintered at 720-780℃ for 10-15 h in an oxygen atmosphere to obtain the gradient co-doped polycrystalline LiNi. 0.6 Co 0.2 Mn 0.2 O2; The positive electrode active material, conductive agent, binder and silane coupling agent are mixed and slurried, and then coated onto the aluminum foil of the positive electrode. After drying and rolling, the positive electrode is subjected to gas phase fluorination treatment at 80-120℃ for 10-30 minutes in a nitrogen atmosphere containing 1-5% hexafluoroethane to obtain the positive electrode sheet. Negative electrode preparation: Pure needle-shaped coke artificial graphite with a particle size distribution of 8μm≥D10≥6μm, 16.5μm≥D50≥15.5μm and a mass percentage of particles smaller than 2μm is less than 5% is impregnated in an ethanol solution containing trimethyl phosphate and vinyl sulfate. After treatment, it is heat-treated at 180-220℃ under an inert atmosphere, followed by slurry preparation, coating, drying and rolling to obtain the negative electrode. Cell assembly: The positive electrode, composite ceramic separator, and negative electrode are stacked in sequence, and the tabs are welded and packaged. Electrolyte injection and formation: Electrolyte is injected and allowed to stand for soaking. Formation is then carried out using a stepped current: First, the battery is charged at a constant current of 0.02C to 3.0-3.2V and allowed to stand. Then, it is charged at a constant current of 0.05C to 3.5-3.6V to obtain the battery cell.

6. The preparation method according to claim 5, characterized in that, After the liquid injection and formation steps, an aging and screening step is also included: the cells are placed in an environment of 45°C and an environment of 25°C for 5-7 days each, and cells with voltage drop exceeding 10mV are monitored and removed.

7. The preparation method according to claim 5, characterized in that, The method for preparing the composite ceramic diaphragm is as follows: Nano-alumina, two-dimensional vermiculite nanosheets and nano-cellulose adhesive were mixed and dispersed at a mass ratio of 4-6:4-6:1 to prepare an aqueous slurry. The aqueous slurry was then coated on both sides of a polyethylene film using a microgravure coating method. After drying, a composite ceramic diaphragm was obtained.

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