Lithium ion battery liquid injection method and lithium ion battery

Abstract

The invention provides a lithium ion battery liquid injection method and a lithium ion battery, the liquid injection method comprises the following steps: primary liquid injection, injection of a first electrolyte into a to-be-injected lithium ion battery, and preparation of a pre-lithiated lithium ion battery, the first electrolyte comprises a first phenolic compound, the molecular structure of the first phenolic compound comprises pyrogallol, and the molecular structure of the first phenolic compound comprises pyrogallol; the mass ratio of the first phenolic compound in the first electrolyte is 2%-3%; and secondary liquid injection is conducted, specifically, a second electrolyte is injected into the pre-lithiated battery, the second electrolyte comprises a second phenolic compound, the molecular structure of the second phenolic compound comprises pyrogallol groups, and the mass ratio of the second phenolic compound in the second electrolyte is 0.5%-1.5%. The liquid injection method can effectively reduce decomposition gas production of the electrolyte, reduce deposition of transition metal on a negative electrode interface, and improve the cycle performance of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for injecting electrolyte into a lithium-ion battery and a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles, energy storage systems, and other fields, the market is placing increasingly stringent demands on the energy density, safety, and cycle life of lithium-ion batteries. Lithium iron phosphate (LiFePO4, LFP) batteries, due to their advantages such as high safety, low cost, and good cycle stability, have become one of the mainstream choices for long-life battery systems. However, in the pursuit of even longer cycle life, how to further suppress capacity decay during long-term cycling remains a key challenge in current research and development.

[0003] Currently, the industry commonly uses the addition of lithium replenishing agents (such as lithium-rich compounds) during the cathode slurry preparation process to compensate for the loss of active lithium during cycling, thereby improving the overall cycle life of the battery. However, this technical approach has significant drawbacks: lithium replenishing agents typically require high voltages (usually higher than the conventional charging cutoff voltage) to decompose and release active lithium. This high-voltage process easily triggers the oxidative decomposition of the electrolyte. Simultaneously, the decomposition of lithium replenishing agents is often accompanied by the release of reactive oxygen species, which have extremely strong oxidizing properties and further exacerbate the decomposition of solvents and lithium salts in the electrolyte. These side reactions not only consume limited active lithium and electrolyte but also cause the battery to generate a large amount of gas during formation and the early stages of cycling. Gas accumulation causes cell swelling, hindering the uniform transport of lithium ions at the electrode interface, resulting in localized interface deterioration (such as the formation of "black spots"), severely impairing the battery's later cycle performance and safety.

[0004] To address the reactive oxygen species (ROS) problem caused by lithium supplementation agents, existing technologies attempt to introduce specific functional additives into the electrolyte to capture ROS and inhibit their destructive effects. For example, patent document CN119050477A discloses the use of boronate pinacol esters as additives to scavenge ROS and reduce electrolyte decomposition. However, such boron-containing additives may introduce new risks in practical applications: on the one hand, their decomposition products may corrode the current collector, affecting the long-term reliability of the battery; on the other hand, these substances may have poor thermal stability, posing safety hazards under extreme conditions such as battery thermal abuse, thus limiting their widespread application.

[0005] Therefore, developing a solution that can effectively accommodate lithium replenishment processes, suppress gas generation and interfacial side reactions, while also possessing good electrochemical stability and safety, is of great significance for further improving the cycle life of lithium iron phosphate batteries and other systems. Summary of the Invention

[0006] To address at least one problem in the prior art, this invention provides a method for electrolyte injection into a lithium-ion battery and a lithium-ion battery itself. The electrolyte injection method provided by this invention can effectively reduce electrolyte decomposition and gas generation, decrease transition metal deposition at the negative electrode interface, and improve the cycle performance of the lithium-ion battery.

[0007] According to a first aspect of the present invention, a method for injecting electrolyte into a lithium-ion battery is provided, comprising the following steps: a first electrolyte injection, wherein a first electrolyte is injected into the lithium-ion battery to be injected to prepare a pre-lithiated lithium-ion battery, the first electrolyte comprising a first phenolic compound, the molecular structure of the first phenolic compound comprising a pyrogallol group, and the mass percentage of the first phenolic compound in the first electrolyte being 2% to 3%; and a second electrolyte injection, wherein a second electrolyte is injected into the pre-lithiated battery, the second electrolyte comprising a second phenolic compound, the molecular structure of the second phenolic compound comprising a pyrogallol group, and the mass percentage of the second phenolic compound in the second electrolyte being 0.5% to 1.5%.

[0008] Preferably, the mass ratio of the first electrolyte to the second electrolyte is 8-10:1. More preferably, it is 9:1.

[0009] Preferably, the total electrolyte filling coefficient of the lithium-ion battery is 2.5 to 3.5.

[0010] Preferably, after the lithium-ion battery has undergone one electrolyte filling, it is left to stand at 40-50°C for 20-36 hours. More preferably, it is left to stand at 45°C. The preferred standing time is 24 hours.

[0011] Preferably, after the lithium-ion battery completes one electrolyte injection, the lithium-ion battery is subjected to formation and aging treatments in sequence.

[0012] Preferably, after the lithium-ion battery completes one liquid injection, it is left to stand at 40~50℃ for 20~36 hours, and then undergoes formation and aging treatments in sequence.

[0013] Preferably, the molecular structure of the first phenolic compound contains an ester group, and / or the molecular structure of the second phenolic compound contains an ester group.

[0014] Preferably, the first phenolic compound includes methyl gallate, and / or the second phenolic compound includes methyl gallate.

[0015] Preferably, the first electrolyte further includes a boron compound and / or a first additive.

[0016] Preferably, the boron compound includes at least one of LiDFOB and LiBOB; and the mass percentage of the boron compound in the electrolyte is 0.8% to 1.875%.

[0017] Preferably, the first additive includes vinylene carbonate and fluoroethylene carbonate, with a mass ratio of vinylene carbonate to fluoroethylene carbonate of (1~10):1, preferably 2:1; and the mass percentage of the first additive in the electrolyte is 1.5%~5%. Preferably, the first additive includes vinylene carbonate and fluoroethylene carbonate, with the mass percentages of vinylene carbonate and fluoroethylene carbonate in the electrolyte being 2% and 1%, respectively.

[0018] Preferably, the first electrolyte further includes a first lithium salt, which includes LiPF6. Preferably, the first lithium salt accounts for 7% to 14% of the first electrolyte.

[0019] Preferably, in the first electrolyte, the mass ratio of boron compound to first lithium salt is (8~10):1, more preferably 9:1.

[0020] Preferably, the total mass of the boron compound and the first lithium salt in the first electrolyte is 12.8%.

[0021] Preferably, the first electrolyte further includes a first solvent, which includes at least one selected from ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. Preferably, the first solvent includes ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate. Preferably, the first solvent accounts for 80% to 85% of the mass of the first electrolyte.

[0022] Preferably, the second electrolyte further includes vinylene carbonate, and the mass ratio of vinylene carbonate to the electrolyte is 2% to 6%.

[0023] Preferably, the second electrolyte further includes a second lithium salt, which includes LiPF6. Preferably, the second lithium salt accounts for 10% to 15% of the mass of the second electrolyte. Preferably, the second lithium salt accounts for 12.8% of the mass of the second electrolyte.

[0024] Preferably, the second electrolyte further includes a second solvent, which includes at least one selected from ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Preferably, the second solvent includes ethylene carbonate or ethyl methyl carbonate. Preferably, the second solvent accounts for 80% to 85% of the mass of the second electrolyte.

[0025] According to a second aspect of the present invention, a lithium-ion battery is provided, which is prepared by any of the above-described methods for liquid injection of lithium-ion batteries.

[0026] Preferably, the positive electrode of the lithium-ion battery contains a lithium replenishing agent; the lithium replenishing agent includes at least one of lithium iron phosphate and lithium nickel phosphate.

[0027] Compared with the prior art, the injection method provided by the present invention has the following beneficial effects: (1) A two-step gradient electrolyte injection method was adopted, and the concentration of phenolic compounds containing pyrogallol groups was precisely controlled in the two electrolytes (2%~3% in the first injection and 0.5%~1.5% in the second injection). This method specifically solved the two core problems of concentrated release of active oxygen during the formation stage and continuous dissolution of transition metal ions at the positive electrode during the cycling stage. The first high-concentration addition effectively captured active oxygen, significantly inhibited gas production during formation, and improved the initial electrode interface. The second lower-concentration addition continuously chelated transition metal ions, inhibited their catalytic decomposition of the negative electrode SEI film, stabilized the long-term cycling interface, and further enhanced the advantages of the lithium supplement in improving cycling performance.

[0028] (2) Phenolic compounds and boron compounds are compounded in the electrolyte. The boron compounds can participate in the formation of a dense CEI film at the positive electrode, which not only protects the positive electrode, but also reduces the oxidative decomposition of phenolic additives under high voltage, thus greatly improving their utilization efficiency and durability.

[0029] (3) The injection volume ratio and high-temperature settling process were optimized, which promoted the full wetting of the electrolyte and the controllable pre-reaction, laying the foundation for the formation of a uniform and stable SEI / CEI film. The specific ratios of VC / FEC film-forming additives, LiPF6 lithium salt and other components were also clarified, ensuring the best synergy of the functions of each component, and taking into account cost control and production feasibility while achieving performance targets. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] According to a first aspect of the present invention, a method for injecting electrolyte into a lithium-ion battery is provided, comprising the following steps: a first electrolyte injection, wherein a first electrolyte is injected into the lithium-ion battery to be injected to prepare a pre-lithiated lithium-ion battery, the first electrolyte comprising a first phenolic compound, the molecular structure of the first phenolic compound comprising a pyrogallol group, and the mass percentage of the first phenolic compound in the first electrolyte being 2% to 3%; and a second electrolyte injection, wherein a second electrolyte is injected into the pre-lithiated battery, the second electrolyte comprising a second phenolic compound, the molecular structure of the second phenolic compound comprising a pyrogallol group, and the mass percentage of the second phenolic compound in the second electrolyte being 0.5% to 1.5%.

[0032] In the electrolyte injection method for lithium-ion batteries provided by this invention, a multi-level, synergistic battery interface and electrolyte stabilization system is constructed through a phased and differentiated electrolyte formulation design and compounding of additives with specific functions. This effectively suppresses gas generation, stabilizes the electrode interface, improves the utilization rate of active materials, and extends the battery cycle life.

[0033] Specifically, phenolic compounds containing pyrogallol groups in their molecular structure are selected as core additives, and a special injection method is set up where a higher concentration (2%~3%) of the first phenolic compound is used in the first injection and a lower concentration (0.5%~1.5%) of the second phenolic compound is used in the second injection. First, active oxygen is mainly released during the formation stage (especially the decomposition of lithium supplementation agent, which releases a large amount of active oxygen). The higher concentration of phenolic compounds can efficiently capture these active oxygens (phenolic compounds have strong reducing properties and can preferentially react with active oxygen, effectively capturing active oxygen that would originally attack electrolyte solvent molecules, trigger chain decomposition reactions and generate a large amount of gas). This significantly reduces gas production caused by electrolyte oxidation and decomposition, improves the initial electrode interface morphology, and avoids defects such as "black spots".

[0034] Secondly, during the long-term cycling phase, the main issue shifts to the dissolution of transition metal ions at the positive electrode and their catalytic decomposition at the negative electrode. Maintaining a low concentration of phenolic compounds effectively chelates the dissolved transition metal ions (the pyrogallol group in phenolic compounds has a strong complexing ability for transition metal ions (such as iron and manganese ions). During cycling, it effectively chelates transition metal ions dissolved from the positive electrode, preventing their migration to the negative electrode and their reduction and deposition on the surface), suppressing their deposition and catalytic effects on the negative electrode surface, thus optimizing the battery's long-term stability and capacity retention. This strategy of "heavy protection in the early stages and stable maintenance in the later stages" ensures the effectiveness of core functions while avoiding the overuse of additives, reducing costs and minimizing potential side effects.

[0035] Therefore, by using the aforementioned specific additives and specific secondary injection methods, this invention can effectively solve the two core problems of gas generation during formation and cycle degradation, significantly improving the cycle life, safety, and production economy of batteries, especially lithium iron phosphate batteries. It also effectively improves the problems of excessive gas, poor interface, corrosion risk, or insufficient thermal stability caused by simply using lithium replenishing agents or single-type additives in the prior art.

[0036] Preferably, the mass ratio of the first electrolyte to the second electrolyte is 8-10:1, more preferably 9:1. This ratio range ensures that the first electrolyte injection contains more phenolic compounds, fully meeting the needs of efficiently removing large amounts of reactive oxygen species, suppressing gas generation, and building an initial stable interface during the formation stage. Simultaneously, a small amount of secondary electrolyte injection precisely replenishes the lower concentration of phenolic compounds required for long-term protection, used to chelate trace amounts of transition metals continuously dissolved during cycling. Therefore, the aforementioned mass ratio of the first and second electrolytes not only forms a more stable and denser electrode interface, optimizing battery performance, but also reduces overall material costs, achieving optimal synergy in functional realization, cost control, and final electrochemical performance improvement.

[0037] Preferably, the total electrolyte filling coefficient of the lithium-ion battery is 2.5 to 3.5.

[0038] Preferably, after the lithium-ion battery completes one electrolyte filling, it is left to stand at 40-50°C for 20-36 hours. More preferably, it is left to stand at 45°C. The preferred standing time is 24 hours. Allowing the lithium-ion battery to stand at a high temperature of 40-50°C for 20-36 hours after one electrolyte filling optimizes the electrolyte wetting process and initial interfacial reaction within a safe range, resulting in a more uniform and stable initial interfacial film (SEI / CEI). This effectively reduces local differences in interfacial side reactions during subsequent formation and cycling, lowers the battery's internal resistance, and improves the consistency of its long-term cycle performance, thus contributing to the acquisition of high-performance, high-reliability batteries.

[0039] Preferably, after the lithium-ion battery completes one electrolyte injection, the lithium-ion battery is subjected to formation and aging treatments in sequence.

[0040] Preferably, after the lithium-ion battery completes one liquid injection, it is left to stand at 40~50℃ for 20~36 hours, and then undergoes formation and aging treatments in sequence.

[0041] Preferably, the molecular structure of the first phenolic compound contains an ester group, and / or the molecular structure of the second phenolic compound contains an ester group. The introduction of the ester group enhances the solubility and compatibility of the phenolic compound in organic electrolyte solvents such as carbonates. This ensures that the additive can be uniformly dispersed throughout the electrolyte system, avoiding localized precipitation or uneven concentration, thereby ensuring its stable and effective function throughout the battery. Furthermore, combining the strongly reducing pyrogallol group with the ester group within a single molecule may improve the molecular structural stability to some extent. This can reduce the self-decomposition of the additive during storage or early cycling, allowing it to act more persistently on the target side reactions (capturing reactive oxygen species, chelating metal ions), thereby extending its effective protection cycle and improving utilization efficiency.

[0042] Preferably, the first phenolic compound includes methyl gallate, and / or the second phenolic compound includes methyl gallate. Using methyl gallate as both the first and second phenolic compounds is more conducive to achieving efficient reactive oxygen species capture and transition metal ion chelation capabilities. Simultaneously, its good solubility in the electrolyte facilitates the formation of a stable and dense interfacial film, thereby optimizing the long-term cycle stability of the battery.

[0043] Preferably, the first electrolyte further includes a boron compound and / or a first additive.

[0044] Preferably, the boron compound includes at least one of LiDFOB and LiBOB; and the boron compound accounts for 0.8% to 1.875% of the electrolyte by mass. Preferably, the first additive includes vinylene carbonate and fluoroethylene carbonate, with a mass ratio of vinylene carbonate to fluoroethylene carbonate of (1 to 10):1, preferably 2:1; and the first additive accounts for 1.5% to 5% of the electrolyte by mass. Preferably, the first additive includes vinylene carbonate and fluoroethylene carbonate, with vinylene carbonate and fluoroethylene carbonate accounting for 2% and 1% of the electrolyte by mass, respectively.

[0045] Boron compounds, acting as synergistic additives, can participate in the formation of a dense CEI film on the positive electrode, reducing the oxidative decomposition of phenolic compounds on the positive electrode and improving the utilization rate of phenolic compounds. The selected mass percentage range ensures the formation of a complete and sufficiently protective CEI film with minimal side effects (such as impact on conductivity).

[0046] The first additive is a compound of vinylene carbonate (VC) and fluoroethylene carbonate (FEC), which synergistically constructs a more stable, dense, and lithium-ion conductive SEI film on the negative electrode surface. The specific mass ratio of VC to FEC achieves optimal synergy between the two additives, ensuring excellent film formation while avoiding problems such as increased gas production or excessive impedance that might arise from an excessive amount of a single component. Simultaneously, the specific proportions of VC and FEC in the electrolyte help to coordinate with the total amount of phenolic compounds and boron-based additives, resulting in a better synergistic effect and providing more comprehensive synergistic protection for the positive and negative electrode interfaces, thus improving the overall battery performance.

[0047] Preferably, the first electrolyte further includes a first lithium salt, which includes LiPF6. Preferably, the proportion of the first lithium salt in the first electrolyte is 7% to 14%. Selecting LiPF6 as the first lithium salt and controlling its concentration within this range ensures that the electrolyte has high ionic conductivity to meet the battery power requirements, while simultaneously providing a stable and efficient ion transport environment for the synergistic effect of various functional additives. This is beneficial for optimizing interfacial film quality and improving the battery's cycle stability and other electrochemical performance.

[0048] Preferably, in the first electrolyte, the mass ratio of boron compound to first lithium salt is (8~10):1, more preferably 9:1. Within this range, the boron compound and first lithium salt can exert a better synergistic effect, which is more conducive to the stability and efficiency of the overall electrolyte system, and thus more beneficial to the performance improvement of the battery.

[0049] Preferably, the total mass of the boron compound and the first lithium salt in the first electrolyte is 12.8%.

[0050] Preferably, the first electrolyte further includes a first solvent, which includes at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Preferably, the first solvent includes ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Preferably, the first solvent accounts for 80% to 85% of the mass of the first electrolyte.

[0051] Preferably, the second electrolyte further includes vinylene carbonate, and the mass ratio of vinylene carbonate to the electrolyte is 2% to 6%.

[0052] Preferably, the second electrolyte further includes a second lithium salt, which includes LiPF6. Preferably, the second lithium salt accounts for 10% to 15% of the mass of the second electrolyte. Preferably, the second lithium salt accounts for 12.8% of the mass of the second electrolyte.

[0053] Preferably, the second electrolyte further includes a second solvent, which includes at least one selected from ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Preferably, the second solvent includes ethylene carbonate or ethyl methyl carbonate. Preferably, the second solvent accounts for 80% to 85% of the mass of the second electrolyte.

[0054] According to a second aspect of the present invention, a lithium-ion battery is provided, which is prepared by any of the above-described methods for liquid injection of lithium-ion batteries.

[0055] Preferably, the positive electrode of the lithium-ion battery contains a lithium replenishing agent; the lithium replenishing agent includes at least one of lithium-rich lithium iron phosphate and lithium-rich lithium nickel phosphate. The selected lithium replenishing agent (lithium-rich lithium iron phosphate or lithium-rich lithium nickel phosphate) can decompose and release active lithium when the battery is first charged to a higher voltage, directly compensating for irreversible lithium loss in subsequent cycles. This is a key technical measure to improve the overall cycle life of batteries, especially silicon-containing anode battery systems such as lithium iron phosphate. However, the decomposition of the lithium replenishing agent inevitably involves the release of active oxygen. The liquid injection method provided by this invention effectively solves the core problem of "manufacturing" (active oxygen) while increasing capacity, and converts some byproducts into beneficial interface components, greatly reducing gas production. Therefore, it effectively improves the cycle stability and first-efficiency electrochemical performance of the battery, especially lithium iron phosphate batteries. Moreover, lithium-rich lithium iron phosphate and lithium-rich lithium nickel phosphate, as lithium replenishing agents, can better ensure the controllability of the lithium replenishment process, which is more conducive to the final improvement of battery performance.

[0056] Compared with the prior art, the injection method provided by the present invention has the following beneficial effects: (1) A two-step gradient electrolyte injection method was adopted, and the concentration of phenolic compounds containing pyrogallol groups was precisely controlled in the two electrolytes (2%~3% in the first injection and 0.5%~1.5% in the second injection). This method specifically solved the two core problems of concentrated release of active oxygen during the formation stage and dissolution of transition metal ions at the positive electrode in the later stage of cycling. The first high-concentration addition effectively captured active oxygen, significantly inhibited gas production during formation, and improved the initial electrode interface. The second lower-concentration addition continuously chelated transition metal ions, inhibited their catalytic decomposition of the SEI film on the negative electrode surface, stabilized the long-term cycling interface, and further enhanced the advantage of the lithium supplement in improving cycle performance.

[0057] (2) Phenolic compounds and boron compounds are compounded in the electrolyte. The boron compounds can participate in the formation of a dense CEI film at the positive electrode, which not only protects the positive electrode, but also reduces the oxidative decomposition of phenolic additives under high voltage, thus greatly improving their utilization efficiency and durability.

[0058] (3) The injection volume ratio and high-temperature settling process were optimized, which promoted the full wetting of the electrolyte and the controllable pre-reaction, laying the foundation for the formation of a uniform and stable SEI / CEI film. The specific ratios of VC / FEC film-forming additives, LiPF6 lithium salt and other components were also clarified, ensuring the best synergy of the functions of each component, and taking into account cost control and production feasibility while achieving performance targets.

[0059] To further illustrate the present invention, the following embodiments will be described in detail.

[0060] Example 1 1. Preparation of electrolyte The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:33:2:1:2:11.5:1.3 (mass ratio).

[0061] The second electrolyte (used for secondary injection) has the following formula: EC:DMC:VC:MG:LiPF6 = 35:48.2:3:1:12.8 (mass ratio).

[0062] The electrolyte injection coefficient is 3.0 (i.e., the injection volume is 3*70=210g). The ratio of the first injection volume to the second injection volume is 9:1, and the settling temperature and time after the first injection are 45℃ and 24h.

[0063] 2. Battery manufacturing The battery manufactured in this embodiment is a 70Ah aluminum-cased battery. 2.1 Preparation of the positive electrode sheet 2.1.1 Positive Electrode Mixture The lithium iron phosphate (LFP), binder (HSV900), lithium supplementer (LFC), and conductive agent (SP) were mixed using a dry slurry method in the following proportions: LFP:LFC:HSV900:SP = (93.3%-96.8%):1.7%:(0.5%-4%):1%.

[0064] The lithium supplement agent is lithium iron ferrite (Li5FeO4, which corresponds to the above-mentioned abbreviation "LFC"), and the preferred lithium supplement agent content is 2%.

[0065] 2.1.2 Positive electrode coating The positive electrode is coated on both sides, and the surface density of the positive electrode coating on one side is set to 178 g / m². 2 The baseband uses a coated aluminum foil of (12+1+1)μm*214mm with a coating width of 179±0.5mm.

[0066] 2.1.3 Positive electrode crushing Rolling is performed in a single rolling process. The compaction range of the positive electrode sheet is 2.35-2.5 g / cm³, preferably 2.45 g / cm³, and the compaction thickness is 160±2μm.

[0067] 2.2 Preparation of negative electrode sheet 2.2.1 Negative Electrode Slurry Graphite (Gr), binder (CMC+SBR), and conductive agent (SP) were mixed in a ratio of Gr:CMC:SBR:SP = 96.7%:0.8%:1.5%:1% using a dry mixing method.

[0068] 2.2.2 Negative electrode coating The negative electrode undergoes double-sided coating. The areal density of the coating on one side is determined by the N / P ratio, which ranges from 1.1 to 1.25, with a preferred N / P ratio of 1.19, corresponding to an areal density of 89 g / m³. 2 The coating width is 190±0.5mm, where the baseband uses 4.5μm*216mm copper foil.

[0069] 2.2.3 Crushing of negative electrode sheet Rolling is performed in a single rolling process. The compaction range of the negative electrode sheet is 1.4-1.65 g / cm³, with 1.55 being preferred, and the compaction thickness is 124±2μm.

[0070] 2.3 Die-cutting and winding The positive and negative electrode sheets are die-cut according to the design dimensions, and the separator is (7+3+3+3)*98mm in size and is wound using a winding machine.

[0071] 2.4 Hi-pot1 & Hot Press Hi-pot1 & Hot Press Parameters: Voltage 200V, Internal Resistance ≥20MΩ, Test Time 10±1S (Hot Press 10±1S, Short Circuit Discharge Test 5±1S), Hot Press Temperature 90±5℃, Pressure 5000±300Kg, Time 65±5s.

[0072] 2.5 Assembly The assembly process includes ultrasonic welding, laser welding, Marly packaging, shell insertion, peripheral welding, shell insertion, helium testing, and Hipot testing.

[0073] 2.6 Cell Baking Vacuum baking is performed in an oven at a temperature of 100±5℃ and a vacuum degree of <1200Pa for 42h±3h. After baking, the water content of the electrodes should be <200ppm for the positive electrode and <200ppm for the negative electrode.

[0074] 2.7 One injection The injection is performed according to the design parameters.

[0075] 2.8 High-temperature storage After injection, the solution is placed at a high temperature of 45°C for 24 hours.

[0076] 2.9 Formation The abandoned battery cells are then processed according to the set program.

[0077] 2.10 Aging, secondary replenishment, sealing, and volume division. After formation, the battery cells undergo aging and resting, secondary electrolyte replenishment, sealing nail welding, and capacity testing.

[0078] Example 2 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:32.5:2:1:2.5:11.5:1.3 (mass ratio).

[0079] The rest is the same as in Example 1.

[0080] 2. Battery manufacturing Consistent with Example 1.

[0081] Example 3 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:32.2:2:1:2.8:11.5:1.3 (mass ratio).

[0082] The rest is the same as in Example 1.

[0083] 2. Battery manufacturing Consistent with Example 1.

[0084] Example 4 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:32:2:1:3:11.5:1.3 (mass ratio).

[0085] The rest is the same as in Example 1.

[0086] 2. Battery manufacturing Consistent with Example 1.

[0087] Example 5 1. Preparation of electrolyte The difference from Example 2 is that: The second electrolyte (used for secondary injection) has the following formula: EC:DMC:VC:MG:LiPF6 = 35:48.7:3:0.5:12.8 (mass ratio).

[0088] The rest is the same as in Example 2.

[0089] 2. Battery manufacturing Consistent with Example 2.

[0090] Example 6 1. Preparation of electrolyte The difference from Example 2 is that: The second electrolyte (used for secondary injection) has the following formula: EC:DMC:VC:MG:LiPF6 = 35:47.7:3:1.5:12.8 (mass ratio).

[0091] The rest is the same as in Example 2.

[0092] 2. Battery manufacturing Consistent with Example 2.

[0093] Example 7 1. Preparation of electrolyte The difference from Example 2 is that the ratio of the injection volume of the first injection to the second injection is 7:1. The rest is the same as in Example 1.

[0094] 2. Battery manufacturing Consistent with Example 2.

[0095] Example 8 1. Preparation of electrolyte The difference from Example 2 is that the ratio of the injection volume of the first injection to the second injection is 11:1. The rest is the same as in Example 1.

[0096] 2. Battery manufacturing Consistent with Example 2.

[0097] Example 9 1. Preparation of electrolyte The difference from Example 2 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:32.5:2:1:2.5:10.8:2 (mass ratio).

[0098] The rest is the same as in Example 2.

[0099] 2. Battery manufacturing Consistent with Example 2.

[0100] Example 10 1. Preparation of electrolyte The difference from Example 2 is that: Methyl gallate (MG) in the first and second electrolytes was replaced with pyrogallol (pyrogallol).

[0101] 2. Battery manufacturing Consistent with Example 2.

[0102] Example 11 1. Preparation of electrolyte The difference from Example 2 is that: The methyl gallate (MG) in the first electrolyte and the second electrolyte was changed to propyl gallate.

[0103] 2. Battery manufacturing Consistent with Example 2.

[0104] Comparative Example 1 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (used for primary injection) has the following formula: EC:EMC:DMC:VC:FEC:LiPF6 = 26:25.2:33:2:1:12.8 (mass ratio).

[0105] The second electrolyte (used for secondary injection) has the following formula: EC:DMC:VC:LiPF6 = 35:49.2:3:12.8 (mass ratio).

[0106] The rest is the same as in Example 1.

[0107] 2. Battery manufacturing Consistent with Example 1.

[0108] Comparative Example 2 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:LiPF6:LiDFOB = 24:25.2:35:2:1:11.5:1.3 (mass ratio).

[0109] The rest is the same as in Example 1.

[0110] 2. Battery manufacturing Consistent with Example 1.

[0111] Comparative Example 3 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:34:2:1:1:11.5:1.3 (mass ratio).

[0112] The rest is the same as in Example 1.

[0113] 2. Battery manufacturing Consistent with Example 1.

[0114] Comparative Example 4 1. Preparation of electrolyte The difference from Example 1 is that: The first electrolyte (for primary injection) formulation is EC:EMC:DMC:VC:FEC:MG:LiPF6:LiDFOB = 24:25.2:34:2:1:1:11.5:1.3 (mass ratio).

[0115] The second electrolyte (used for secondary injection) has the following formula: EC:DMC:VC:MG:LiPF6 = 35:49.2:3:2:12.8 (mass ratio).

[0116] The rest is the same as in Example 1.

[0117] 2. Battery manufacturing Consistent with Example 1.

[0118] Comparative Example 5 1. Preparation of electrolyte The difference from Example 1 is that: Methyl gallate (MG) in the first and second electrolytes was replaced with hydroquinone methyl ester.

[0119] The rest is the same as in Example 1.

[0120] 2. Battery manufacturing Consistent with Example 1.

[0121] Test case 1. Experimental Construction Method The batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests: (1) Gas production after formation: Negative pressure formation is used during the formation process. The gas generated during formation is extracted from the battery. The other end of the hose of negative pressure formation is connected to the gas bag to collect the gas produced during formation.

[0122] (2) DC internal resistance after capacity testing: The battery internal resistance was tested using a battery charging and discharging device. At room temperature of 25°C, the battery was charged to 3.65V using 1C constant current and constant voltage, with a cutoff current of 0.05C. Then, the battery was discharged to 50% SOC using 1C for 0.5h. After resting for 1h, the battery was discharged to 30s using 2C.

[0123] Discharge DC internal resistance = (V1 before discharge - V2 at the end of discharge) / Discharge current I (3) Cyclic performance test: The battery cycle performance was tested using a battery cycle test device at a test temperature of 60℃ and a test rate of 1C / 1C cycle. The relevant values ​​were recorded, and the first efficiency and 800-cycle retention rate were calculated.

[0124] 2. Experimental Results The test results of the relevant performance of the batteries prepared in the above embodiments and comparative examples are shown in Table 1.

[0125] Table 1. Test results of relevant performance of the batteries prepared in the examples and comparative examples.

[0126] As shown in Table 1, the liquid injection method for lithium-ion batteries provided by this invention effectively reduces gas production, has a high initial efficiency and a cycle retention rate of 800 cycles, and also has a low DC resistance after capacity grading. For details, please refer to the data in the embodiments.

[0127] The electrolyte in Comparative Example 1 lacked phenolic and boron compounds, while the electrolyte in Comparative Example 2 lacked phenolic compounds. This resulted in a deficiency of the free radical scavenger in the lithium supplementation agent, leading to a higher formation gas production. Furthermore, Comparative Example 2 had a slightly lower gas production than Comparative Example 1. This is because the boron additive formed a dense CEI film at the positive electrode, reducing solvent oxidation at the positive electrode during the formation process and thus lowering the gas production.

[0128] In Comparative Example 3, the first electrolyte contained too few phenolic compounds, and in Comparative Example 4, the first electrolyte contained even fewer phenolic compounds than the second electrolyte. This resulted in insufficient free radical scavengers during the formation stage, leading to increased formation gas production and increased internal resistance. Furthermore, it was observed that the cycling performance of Comparative Example 4 deteriorated. This is because phenolic additives and free radicals combine to form relatively stable structures. While pure phenolic additives themselves have a probability of cyclic decomposition, excessive phenolic additives may increase the probability of phenolic substances decomposing themselves, thus worsening the cycling process.

[0129] In Comparative Example 5, the methyl gallate (MG) in the electrolyte was replaced with hydroquinone methyl ester, which increased the amount of gas produced during formation. This is because hydroquinone has a weaker ability to bind with free radicals than o-phenyltrihydroxyl, resulting in increased solvent decomposition and thus increased gas production.

[0130] Further comparison of Examples 1 and 2-4 shows that as the content of phenolic compounds in the primary electrode increases, the amount of gas produced gradually decreases, and at 2.0%, reactive oxygen species are almost completely captured. Increasing the content of phenolic compounds from 2% to 3% significantly increases the DC internal resistance. This is because the decomposed reactive oxygen species also participate in SEI formation. An appropriate amount of reactive oxygen species is beneficial for forming a low-resistance SEI film. Therefore, adding 2.0% phenolic compounds can significantly reduce the amount of gas produced while also regulating the reactive oxygen species content, thereby promoting the formation of a low-resistance SEI film on the negative electrode. The lower impedance also significantly improves the cycle retention rate.

[0131] Comparing Examples 2 and 5-6, the addition of phenolic compounds increased from 0.5% to 1.5%. In Example 2, with a phenolic compound content of 1.5%, the cycle life retention rate was the highest, at 94.8%. Lower contents resulted in insufficient chelation of transition metals, while higher contents led to higher battery impedance, greater polarization, and reduced cycle life retention.

[0132] Comparing Examples 2 and 7-8, the ratio of the first and second injection volumes in Examples 7 and 8 was too small and too large, respectively. A ratio that was too small resulted in insufficient wetting of the electrode before formation, leading to increased impedance. A ratio that was too large resulted in insufficient phenol content in the second injection, reducing the ability to chelate transition metals and decreasing cycle retention.

[0133] Comparing Example 2 and Example 9, in Example 9, the mass ratio of boron compounds in the first electrolyte was too large, resulting in a decrease in cycle retention rate and an increase in impedance. This is because boron salts participate in the formation of the CEI film. Excessive boron salts lead to a thicker and looser CEI film, making the solvent more prone to oxidation at the positive electrode, resulting in an increase in initial impedance and a decrease in cycle retention rate.

[0134] Comparing Examples 2 and 10 and 11, the phenolic compound in Example 10 was pyrogallol, while in Example 11 it was propyl gallate, resulting in increased formation gas production and decreased cycle retention. This is because the solubility of both pyrogallol and propyl gallate is lower than that of methyl gallate, thus reducing their ability to capture free radicals and chelate transition metals.

[0135] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for injecting electrolyte into a lithium-ion battery, characterized in that, Includes the following steps: A first electrolyte is injected into the lithium-ion battery to be injected to prepare a pre-lithiated lithium-ion battery. The first electrolyte includes a first phenolic compound, the molecular structure of which includes a pyrogallol group, and the mass percentage of the first phenolic compound in the first electrolyte is 2% to 3%. Secondary electrolyte injection involves injecting a second electrolyte into the pre-lithiated battery. The second electrolyte includes a second phenolic compound, the molecular structure of which includes a pyrogallol group. The mass percentage of the second phenolic compound in the second electrolyte is 0.5% to 1.5%.

2. The injection method as described in claim 1, characterized in that: The mass ratio of the first electrolyte to the second electrolyte is 8~10:

1.

3. The injection method as described in claim 1, characterized in that: The first phenolic compound contains an ester group in its molecular structure, and / or the second phenolic compound contains an ester group in its molecular structure.

4. The injection method as described in claim 1, characterized in that: The first phenolic compound includes methyl gallate, and / or the second phenolic compound includes methyl gallate.

5. The injection method as described in claim 1, characterized in that: The first electrolyte also includes boron compounds and / or a first additive.

6. The injection method as described in claim 5, characterized in that: The boron compound includes at least one of LiDFOB and LiBOB; and the boron compound accounts for 0.8% to 1.875% of the mass of the electrolyte.

7. The injection method as described in claim 5, characterized in that: The first additive includes vinylene carbonate and fluoroethylene carbonate, wherein the mass ratio of vinylene carbonate to fluoroethylene carbonate is (1~10):1; The first additive accounts for 1.5% to 5% of the mass of the electrolyte.

8. The injection method as described in claim 1, characterized in that: The second electrolyte also includes vinylene carbonate, and the vinylene carbonate accounts for 2% to 6% of the mass of the electrolyte.

9. A lithium-ion battery, characterized in that: The lithium-ion battery is prepared by the liquid injection method of the lithium-ion battery as described in any one of claims 1 to 8.

10. The lithium-ion battery as described in claim 9, characterized in that: The positive electrode of the lithium-ion battery contains a lithium replenishing agent; the lithium replenishing agent includes at least one of lithium iron phosphate and lithium nickel phosphate.

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