Lithium ion battery, method for manufacturing the same, and electric device

Abstract

This invention relates to a lithium-ion battery and its preparation method. A lithium-ion battery includes a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode comprises a highly moisture-sensitive positive electrode active material with a specific surface area of ​​5 m² / g to 80 m² / g, and the residual moisture content of the positive electrode after drying is 200 ppm to 400 ppm. The electrolyte comprises a lithium salt, a solvent, a film-forming agent, an auxiliary agent, and a hydrogen scavenging agent. The film-forming agent includes 1,3-propanesulfonate lactone and 0.3% to 1.0% ethylene sulfate. The auxiliary agent is tris(trimethylsilane)phosphate. The hydrogen scavenging agent is ammonium p-nitrobenzoate. This lithium-ion battery is compatible with positive electrode sheets with high residual moisture content and, through a specially formulated electrolyte system, effectively suppresses the side reactions caused by this moisture, thereby achieving excellent electrochemical performance and safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery, a preparation method thereof and an electric device. BACKGROUND

[0002] As an important energy storage device, lithium ion batteries have been widely used in portable electronic devices, electric vehicles and large-scale energy storage systems. In order to improve the energy density, the research on positive electrode materials is continuously deepened, and high-voltage platform, low-cost positive electrode materials such as lithium iron manganese phosphate (LFMP) and lithium manganese phosphate (LMP) show great potential. However, such materials usually have a large specific surface area (for example, 5 80 m² / g), and there are a large number of active sites on the surface, which have a strong adsorption capacity for moisture, resulting in a high moisture sensitivity, which brings serious challenges to battery manufacturing and long-term reliability.

[0003] In the existing lithium ion battery manufacturing process, the removal of moisture mainly depends on the long-time high-temperature baking of the positive and negative electrode materials and the electrode sheets. However, this physical dehumidification method has a fundamental defect: first, the energy consumption is extremely high, and for materials with a large specific surface area, it is difficult to completely remove the trace moisture (such as 200 400 ppm level) physically adsorbed; secondly, and more importantly, this method mainly targets the moisture introduced at the initial stage of manufacturing, but it lacks effective response mechanisms for the trace moisture that may be continuously generated during the long-term charge and discharge cycles of the battery and the cumulative hazards caused thereby.

[0004] The moisture remaining in the battery system will trigger a series of harmful chain reactions: 1) reacting with the mainstream lithium salt lithium hexafluorophosphate (LiPF6) in the electrolyte to generate strong corrosive hydrofluoric acid (HF), which continuously corrodes the surface of the positive electrode material, causing the dissolution of transition metal ions, the destruction of the crystal structure, the irreversible capacity decay and the sharp rise of the interface impedance; 2) when charged to high potential, water molecules on the surface of the positive electrode are electrochemically decomposed to directly produce hydrogen gas. The accumulation of hydrogen gas will cause the internal pressure of the battery to rise, leading to battery swelling, and in extreme cases, it may cause the safety valve to fail or the shell to break, posing a serious safety hazard.

[0005] Therefore, the existing technical route faces a key bottleneck: the traditional physical water removal method cannot dynamically and completely eliminate moisture, especially lacking effective inhibition means for the key hazard of continuous decomposition of moisture to produce hydrogen gas (H2) in the electrochemical cycle. This leads to the battery using high moisture-sensitive positive electrode materials to always face the performance degradation and safety concerns caused by moisture, which limits its reliability and widespread application. SUMMARY

[0006] Therefore, it is necessary to provide a lithium ion battery, a preparation method thereof and an electric device, which can be compatible with a positive electrode sheet with high residual moisture, and effectively inhibit side reactions caused by the residual moisture through a special formula of electrolyte system, so as to obtain excellent electrochemical performance and safety.

[0007] The first aspect of the present application provides a lithium ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a high moisture sensitive positive active material, the specific surface area of the positive active material is 5 m² / g-80 m² / g, and the residual moisture content of the positive electrode sheet after drying is 200 ppm-400 ppm.

[0008] The electrolyte comprises a lithium salt, a solvent, a film forming agent, an auxiliary agent and a hydrogen elimination agent.

[0009] The film forming agent comprises 1,3 propane sulfone lactone and vinyl sulfate.

[0010] The auxiliary agent is tris (trimethylsilyl) phosphate.

[0011] The hydrogen elimination agent is ammonium p-nitrobenzoate.

[0012] In one of the embodiments, the mass percentage of 1,3 propane sulfone lactone is 0.5%-1.0%, the mass percentage of vinyl sulfate is 0.3%-1.0%, the mass percentage of the auxiliary agent tris (trimethylsilyl) phosphate is 0.3%-1.0%, and the mass percentage of the hydrogen elimination agent ammonium p-nitrobenzoate is 0.1%-0.5%.

[0013] In one of the embodiments, the high moisture sensitive positive active material is lithium manganese iron phosphate or lithium manganese phosphate.

[0014] In one of the embodiments, the moisture content of the electrolyte is 5 ppm-100 ppm.

[0015] In one of the embodiments, the solvent comprises at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC), propylene carbonate (PC), methyl propyl carbonate (MPC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA), methyl butyrate (MB) and ethyl propionate (EP).

[0016] In one of the embodiments, the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2).

[0017] The second aspect provides a preparation method of the lithium ion battery of the first aspect, comprising the following steps:

[0018] The positive electrode sheet, the separator and the negative electrode sheet are made into an electric core;

[0019] The lithium salt, the solvent, the film-forming agent, the auxiliary agent and the hydrogen elimination agent are uniformly mixed to obtain an electrolyte; and

[0020] The electric core is placed into a packaging shell, the electrolyte is injected to obtain the lithium ion battery;

[0021] The positive electrode sheet comprises a high-moisture-sensitive positive electrode active material, the specific surface area of the positive electrode active material is 5m 2 / g~80m 2 / g, and the residual moisture content of the positive electrode sheet after drying is 200ppm~400ppm; in the electrolyte, the film-forming agent comprises 1,3-propane sulfone lactone and ethylene sulfate, the auxiliary agent is tris(trimethylsilyl) phosphate, and the hydrogen elimination agent is ammonium p-nitrobenzoate.

[0022] In one of the embodiments, the preparation of the electrolyte comprises the following steps:

[0023] The selected solvents are uniformly mixed according to the volume ratio to obtain a mixed solvent;

[0024] The lithium salt is added into the mixed solvent, and the base electrolyte is obtained after uniform mixing;

[0025] The film-forming agent, the auxiliary agent and the hydrogen elimination agent are sequentially added into the base electrolyte, and the electrolyte is obtained after uniform mixing and vacuum degassing treatment.

[0026] In one of the embodiments, the degassing treatment is carried out at a temperature of 80℃~100℃ and a vacuum degree of not less than 0.05MPa for 2h~4h.

[0027] The third aspect provides a power utilization device comprising the lithium ion battery of the first aspect.

[0028] The present application has the following beneficial effects:

[0029] The lithium ion battery, the preparation method thereof and the electric device provided by the application achieve significant technical effects by applying a synergistic electrolyte system containing specific film-forming agents (PS, DTD), auxiliary agents (TMSP) and hydrogen elimination agents in a high-moisture positive electrode sheet (200 ppm-400 ppm residual water) system.

[0030] (1) Efficient hydrogen elimination and safety improvement: TMSP passivates the electrode surface through Si-O bonds to inhibit gas generation; the synergistic hydrogen elimination agent ammonium p-nitrobenzoate can reduce the hydrogen evolution reaction, effectively inhibit the battery swelling, reduce the risk of thermal runaway, and improve the safety.

[0031] (2) Significant reduction in interface impedance: PS and DTD synergistically construct a low-impedance SEI film with a "dense inner layer and flexible outer layer", combined with the cleaning effect of TMSP on HF, the battery direct current resistance (DCR) is reduced from >11.6 mΩ in the comparative example to <8.6 mΩ in the embodiment, and the rate performance is improved.

[0032] (3) Significant extension of cycle life: Benefiting from the effective inhibition of harmful side reactions caused by moisture and HF, the battery capacity retention rate at room temperature after 1000 cycles is significantly improved from <72.1% in the comparative example to >83.1% in the embodiment (the preferred embodiment can reach 98.7%).

[0033] The above effects synergistically solve the contradiction between "high interface impedance" and "high gas production" in the application of high-moisture sensitive positive electrode materials, and provide an effective solution for the development of high electrochemical performance and high safety batteries. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The flowchart of the preparation method of the lithium ion battery according to an embodiment of the application is shown in the figure.

[0035] Figure 2 The flowchart of the preparation method of the electrolyte according to an embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth in order to provide a thorough understanding of the application. However, the application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the scope of the application, so the application is not limited to the specific embodiments disclosed below.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0038] The lithium ion battery of an embodiment includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte.

[0039] The positive electrode sheet contains a high moisture-sensitive positive electrode active material, the specific surface area of the positive electrode active material is 5 m² / g to 80 m² / g, and the residual moisture content of the positive electrode sheet after drying is 200 ppm to 400 ppm. The high moisture-sensitive positive electrode active material refers to a positive electrode material with a specific surface area in the range of 5 m² / g to 80 m² / g and which is prone to remaining 200 ppm to 400 ppm of moisture after drying of the electrode sheet, such as lithium iron manganese phosphate, lithium manganese phosphate, etc. The greater the specific surface area of the material, the greater the number of active sites on the surface, and the more likely it is to combine with polar water molecules (H2O) through van der Waals forces or hydrogen bonds.

[0040] The specific surface area of the positive electrode active material is determined by nitrogen adsorption-desorption BET (Brunauer-Emmett-Teller), and the test standard can refer to GB / T 19587-2017. The residual moisture content of the positive electrode sheet after drying is determined by Karl Fischer Coulommetric Titration, and the test standard can refer to GB / T 45330-2025. The dew point temperature of the environment during testing should be no more than -20℃, the ambient temperature is 15℃ to 30℃, 0.1 g to 0.2 g of the sample is taken, the electrode sheet sample is quickly transferred to a glass bottle, the sample bottle is placed on the Karl Fischer Coulommetric moisture meter for measurement, the heating temperature is 120 to 150℃, and the mass of the moisture in the sample bottle is recorded after the test is completed.

[0041] Further, the specific surface area of the positive electrode active material can be, but is not limited to, 5 m² / g, 10 m² / g, 15 m² / g, 20 m² / g, 25 m² / g, 30 m² / g, 35 m² / g, 40 m² / g, 45 m² / g, 50 m² / g, 55 m² / g, 60 m² / g, 65 m² / g, 70 m² / g, 75 m² / g, or 80 m² / g, and the residual moisture content of the positive electrode sheet after drying can be, but is not limited to, 200 ppm, 250 ppm, 300 ppm, 350 ppm, or 400 ppm.

[0042] The electrolyte contains a lithium salt, a solvent, a film-forming agent, an auxiliary agent, and a hydrogen elimination agent.

[0043] Among them, the film-forming agent includes 1,3 Propane sulfonate lactone (PS) and vinyl sulfate (DTD); the auxiliary agent is tris(trimethylsilane) phosphate (TMSP); the hydrogen scavenger is ammonium p-nitrobenzoate.

[0044] In this embodiment, PS and DTD jointly construct an SEI film with a "dense inner layer and flexible outer layer." The film-forming effect reduces the direct contact between the electrolyte and the electrode, lowering the rate of side reactions. TMSP further optimizes the ion conductivity and structural stability of the film. The three work synergistically to reduce the impedance of the SEI film. At the same time, TMSP further inhibits LiPF6 hydrolysis by removing HF and H2O, and the hydrogen scavenger can consume H2O. + TMSP works synergistically with hydrogen scavengers to eliminate hydrogen, suppress hydrogen evolution reaction, inhibit gas generation and reduce interfacial side reactions, improve the rate performance and cycle life of the battery, and solve the contradiction of "high impedance + high gas production" in traditional electrolytes.

[0045] In this embodiment, the hydrogen scavenger is ammonium p-nitrobenzoate. Ammonium p-nitrobenzoate can preferentially bind H+ through the electron-withdrawing effect of the nitro group. + It inhibits hydrogen evolution and neutralizes corrosive HF through alkaline ammonium ions, thereby synergizing with the auxiliary agent TMSP to achieve hydrogen removal and acid scavenging effects far exceeding those of ordinary hydrogen scavengers or single-mechanism agents, precisely curbing gas generation and interface corrosion from the source.

[0046] In this embodiment, the hydrogen scavenger is ammonium p-nitrobenzoate, and its core mechanism of action is as follows:

[0047] The specific chemical reactions that lead to hydrogen production include the hydrolysis of water from the electrode itself, the electrolyte, and water impurities generated by side reactions during battery cycling.

[0048] 2H2O+2e →H₂↑+2OH

[0049] Ammonium p-nitrobenzoate, as a hydrogen scavenger in lithium battery electrolytes, has a core mechanism of action revolving around the electron-withdrawing effect of the nitro group, the alkaline neutralization of the ammonium group, and the regulation of the interfacial film.

[0050] 1. Electron-withdrawing effect of nitro groups: inhibits hydrogen evolution reaction.

[0051] The nitro group (-NO2) in ammonium p-nitrobenzoate is a strong electron-withdrawing group, which adsorbs free H+. + It can preferentially adsorb free hydrogen ions in the electrolyte, reducing H+ ions. + The reduction reaction (2H) on the negative electrode surface + +2e - →H2↑), thereby reducing the amount of hydrogen produced.

[0052] 2. Ammonium ion neutralization: removal of harmful acid (HF)

[0053] The ammonium ion (NH4+) generated by the dissociation of ammonium p-nitrobenzoate + It has a certain alkalinity and can undergo a neutralization reaction with hydrofluoric acid (HF) in the electrolyte:

[0054] NH4 + + HF →NH3·H2O+F

[0055] This reaction not only directly consumes HF (HF is the most corrosive impurity in the electrolyte, which can damage the SEI film and corrode the electrode), but also can complex F - (e.g., forming NH4F) reduces F - Concentration, to inhibit the excessive formation of LiF (LiF is a high-impedance product, which will increase the interfacial impedance).

[0056] Meanwhile, the synergistic effect of ammonium p-nitrobenzene and TMSP further enhances the hydrogen removal effect:

[0057] TMSP adsorbs H through Si-O bonds + It catalyzes the recombination of H2 and O2 (2H2 + O2 → 2H2O), adsorbs moisture to reduce hydrogen production, and uses the hydrogen scavenger ammonium p-nitrobenzene to consume H2 through nitro reduction. + The two work together to inhibit the hydrogen evolution reaction, reducing the concentration of H2 produced to 50 ppm.

[0058] The SEI film formed by 1,3-propanesulfonyl lactone (PS) and vinyl sulfate (DTD) can reduce the contact area between the electrolyte and the electrode, reduce the side reaction rate, and provide interfacial environment support for the hydrogen removal effect of ammonium p-nitrobenzoate.

[0059] Based on the foregoing embodiments, and assuming the total mass of the lithium salt and the solvent is 100%, the film-forming agent contains 0.5%~1.0% 1,3-propanesulfonate lactone (PS) and 0.3%~1.0% ethylene sulfate (DTD); the auxiliary agent tris(trimethylsilane) phosphate (TMSP) contains 0.3%~1.0% 1,3-propanesulfonate lactone (PS) by mass. Propane sulfonate lactone (PS) accounts for 0.5% to 1.0% of the total mass of the solvent and lithium salt, and vinyl sulfate (DTD) accounts for 0.3% to 1.0% of the total mass of the solvent and lithium salt. Further, 1,3 The mass fraction of propane sulfonate lactone may be, but is not limited to, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%, and the mass fraction of vinyl sulfate may be, but is not limited to, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%.

[0060] Similarly, tris(trimethylsilane) phosphate (TMSP) accounts for 0.3% to 1.0% of the total mass of the solvent and lithium salt. Further, the mass fraction of tris(trimethylsilane) phosphate may be, but is not limited to, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%.

[0061] The hydrogen scavenger, ammonium p-nitrobenzene, comprises 0.1% to 0.5% of the total mass of the solvent and lithium salt. Similarly, the hydrogen scavenger, ammonium p-nitrobenzene, comprises 0.1% to 0.5% of the total mass of the solvent and lithium salt. Further, the mass percentage of the hydrogen scavenger, ammonium p-nitrobenzene, may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0062] Based on the aforementioned embodiments, the high moisture-sensitive cathode active material is lithium iron manganese phosphate (LFMP) or lithium manganese phosphate (LMP). The solution of this invention best addresses the extreme moisture management and gas generation challenges posed by high-voltage, high-specific-surface-area cathode materials such as LFMP / LMP, demonstrating the outstanding value and targeted application of this invention in improving the reliability of specific high-performance material batteries.

[0063] Based on the aforementioned implementation method, the water content of the electrolyte is 5ppm to 100ppm. The water content of the electrolyte is determined using the Karl Fischer coulometric method. Appropriate amounts of Karl Fischer reagent are added to the titration cell and cathode chamber, respectively. The electrolyte sample to be analyzed is repeatedly drawn using a 2.50mL syringe, and the syringe is rinsed 5-8 times. Then, 1-2mL of the electrolyte sample to be tested is drawn and rapidly added to the titration cell through the injection port. The instrument automatically performs the titration. At the endpoint, the instrument display shows the water content of the sample. This ensures that the electrolyte injected into the battery itself introduces very little water, reducing the overall water load of the system from the source. This allows the additive system to focus more on treating the limited water remaining on the electrodes and generated during circulation, thus providing more efficient and stable synergistic protection and improving the feasibility of the entire technical solution.

[0064] Based on the foregoing embodiments, the solvent includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), propylene carbonate (PC), methyl propyl carbonate (MPC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA), methyl butyrate (MB), and ethyl propionate (EP).

[0065] Preferably, the solvent comprises ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC), wherein the volume ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) is (30... 35): (35) 40): (20 25): (5 10) The solvent accounts for 85%~90% of the total mass of the solvent and lithium salt. This embodiment constructs an optimized solvent environment that balances high dielectric constant (facilitating lithium salt dissociation), suitable viscosity (facilitating wetting and ion migration), and low freezing point (non-freezing at -40℃). This specific solvent system provides an ideal platform for the interaction of lithium salt and various additives, ensuring the normal operation of the battery over a wide temperature range, especially at low temperatures, and is an important prerequisite for obtaining excellent overall performance.

[0066] Based on the aforementioned embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium dioxolaneborate (LiBOB), and lithium difluorophosphate (LiPO2F2).

[0067] Preferably, the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the concentration of lithium hexafluorophosphate is 1.0 mol / L to 1.5 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide is 0.3 mol / L to 0.5 mol / L; the mass fraction of the lithium salt in the total mass of the solvent and lithium salt is 10% to 15%. In this embodiment, lithium hexafluorophosphate is the main salt and lithium bis(fluorosulfonyl)imide is the auxiliary salt. By limiting the use of a double lithium salt system of LiPF6 and LiFSI and a specific concentration, the high-temperature stability of LiPF6 and the excellent ionic conductivity and low-temperature performance of LiFSI are combined. This compounding scheme not only ensures the basic electrochemical stability window of the electrolyte, but also significantly improves the ion migration rate at low temperatures, thereby effectively reducing the overall impedance of the battery. It is particularly helpful in improving high-power output and low-temperature discharge performance, and together with functional additives, achieves the goal of low impedance.

[0068] The lithium-ion battery provided by this invention achieves significant technical effects by applying a synergistic electrolyte system containing specific film-forming agents (PS, DTD), auxiliary agents (TMSP), and hydrogen scavenging agents in a high-moisture positive electrode system (200ppm~400ppm residual water).

[0069] (1) High efficiency hydrogen elimination and safety improvement: TMSP passivates the electrode surface through Si-O bonds to suppress gas generation; the synergistic hydrogen elimination agent ammonium nitrate can reduce hydrogen evolution reaction, effectively suppress battery swelling, reduce the risk of thermal runaway, and improve safety.

[0070] (2) Significantly reduced interface impedance: PS and DTD synergistically constructed a low-impedance SEI film with "dense inner layer and flexible outer layer". Combined with the HF removal effect of TMSP, the DC internal resistance (DCR) of the battery was reduced from >11.6 mΩ in the comparative example to <8.6 mΩ in the example, thus improving the rate performance.

[0071] (3) Significantly extended cycle life: Thanks to the effective suppression of harmful side reactions caused by moisture and HF, the capacity retention rate of the battery after 1000 cycles at room temperature has been greatly improved from <72.1% in the comparative example to >83.1% in the example (98.7% in the preferred example).

[0072] The synergistic effect of these factors fundamentally resolves the contradiction between "high interfacial impedance" and "high gas production" in the application of high moisture-sensitive cathode materials, providing an effective solution for the development of batteries with high electrochemical performance and high safety.

[0073] Please see Figure 1 The method for preparing the lithium-ion battery according to one embodiment of the present invention includes the following steps:

[0074] S10. The positive electrode, separator, and negative electrode are made into a battery cell.

[0075] In step S10, the positive electrode, separator, and negative electrode can be stacked or wound to form a battery cell.

[0076] In one embodiment, the preparation of the positive electrode sheet includes: mixing the positive active material, conductive agent, and binder in a mass ratio of (96%). 98): (1 3): (1 2) The materials are mixed in a specific ratio to form a slurry, which is then coated, dried, and rolled to obtain a positive electrode sheet. The drying temperature is 80℃~90℃, and the time is 36 hours~50 hours, so that the residual moisture content of the positive electrode sheet after drying is 200ppm~400ppm. This embodiment clarifies a practical method for stably controlling the residual moisture content of high specific surface area positive electrode materials within the target range of 200ppm~400ppm. This process achieves a balance between moisture control and production energy consumption and efficiency without excessively damaging the material structure, making the technical solution feasible for industrial implementation.

[0077] S20. Mix lithium salt, solvent, film-forming agent, auxiliary agent and hydrogen scavenger evenly to obtain electrolyte.

[0078] In step S20, the selection of lithium salt, solvent, film-forming agent, auxiliary agent and hydrogen scavenger is as described above.

[0079] Please see Figure 2 In one embodiment, the preparation of the electrolyte includes the following steps:

[0080] S21. Mix the selected solvents evenly according to the volume ratio to obtain a mixed solvent;

[0081] S22. Add lithium salt to the mixed solvent obtained in step S21, and mix evenly to obtain the basic electrolyte.

[0082] S23. Add film-forming agent, auxiliary agent and hydrogen scavenger to the basic electrolyte obtained in step S22 in sequence, mix evenly and then degas under vacuum to obtain electrolyte.

[0083] Further, step S21 can be performed by mixing ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and fluoroethylene carbonate in a volume ratio of (30...) 35): (35) 40): (20 25): (5 10) Mix thoroughly to obtain a mixed solvent.

[0084] Further, step S22 can be performed by adding lithium hexafluorophosphate and lithium difluorosulfonylimide to the mixed solvent obtained in step S21, mixing them evenly to obtain a basic electrolyte; wherein the concentration of lithium hexafluorophosphate is 1.0 mol / L to 1.5 mol / L, and the concentration of lithium difluorosulfonylimide is 0.3 mol / L to 0.5 mol / L.

[0085] Furthermore, the mixing process in steps S21 and S22 can be, but is not limited to, stirring at 200 rpm to 500 rpm for 1 h to 4 h at 25℃ to 50℃; the vacuum degassing process in step S23 can be, but is not limited to, vacuum degassing at 80℃ to 100℃ and -0.2 MPa to -0.05 MPa for 2 h to 4 h.

[0086] The electrolyte preparation method described above ensures that all components, especially water- and oxygen-sensitive lithium salts and additives, can form a homogeneous solution uniformly and stably in a controlled environment. This process avoids localized failures or decompositions that may result from improper mixing, and is crucial for ensuring the consistency and reproducibility of the final electrolyte performance, providing a reliable process foundation for the large-scale production of batteries.

[0087] S30. Place the battery cell obtained in step S10 into a packaging shell and inject the electrolyte obtained in step S20 to obtain a lithium-ion battery; wherein, the positive electrode sheet contains a highly moisture-sensitive positive electrode active material, and the specific surface area of ​​the positive electrode active material is 5m². 2 / g~80m 2 / g, and the residual moisture content of the positive electrode sheet after drying is 200ppm~400ppm; in the electrolyte, the film-forming agent includes 1,3-propanesulfonate lactone and vinyl sulfate, the auxiliary agent is tris(trimethylsilane) phosphate, and the hydrogen scavenging agent is ammonium p-nitrobenzene.

[0088] In step S30, conventional methods in the art can be used to place the battery cell into the packaging shell and inject electrolyte to obtain a lithium-ion battery.

[0089] In some embodiments, the packaging shell of the lithium-ion battery involved in this invention can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The packaging shell of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0090] In one embodiment, the active material of the negative electrode is graphite, the separator is a polyolefin porous separator, and the lithium-ion battery is a pouch battery. In other words, the synergistic electrolyte system of this invention can be seamlessly adapted to existing mature battery material systems and manufacturing platforms. It can significantly improve the performance of batteries using high-moisture-sensitive positive electrode materials without changing core raw materials or disrupting existing production lines, greatly reducing the barriers to technological upgrades and industrialization.

[0091] It should be noted that the order of steps S10 and S20 in the preparation method of the lithium-ion battery of the present invention is not limited.

[0092] One embodiment of the electrical device includes any of the lithium-ion batteries described above.

[0093] Wherein, "electrical device" refers to any device or system that uses any of the aforementioned lithium-ion batteries as its power source or a component of its power source. Electrical devices may include, but are not limited to: portable electronic devices, such as mobile phones, laptops, tablets, digital cameras, and wearable devices; electric vehicles, such as electric cars, electric bicycles, electric scooters, and power utility vehicles; energy storage systems, such as home energy storage units, grid-side energy storage power stations, and backup power supplies for communication base stations; and other power or backup power equipment.

[0094] Because the lithium-ion battery of the present invention has advantages such as low impedance, long cycle life, high safety and low gas production, and is particularly compatible with high moisture-sensitive cathode materials, it can significantly improve the overall performance of the electrical device, including but not limited to: longer battery life, faster charging capability, wider operating temperature range, higher safety and longer service life.

[0095] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0096] Example 1

[0097] (1) Preparation of electrolyte:

[0098] 1. Solvent mixing: EC, DMC, EMC and FEC are added in sequence at a volume ratio of 30:40:20:10. Stir at 300 rpm for 2 hours at 25°C until transparent. The mass fraction of the mixed solvent is 85% of the total mass of the solvent and lithium salt.

[0099] 2. Lithium salt dissolution: Slowly add LiPF6 and LiFSI to the above solvent, controlling the final concentration of LiPF6 to be 1.2 mol / L and the final concentration of LiFSI to be 0.3 mol / L. Stir at 40℃ and 500 rpm for 2 hours until completely dissolved to obtain the basic electrolyte. The mass fraction of lithium salt is approximately 15% of the total mass of solvent and lithium salt.

[0100] 3. Additive addition: Film-forming agent PS (addition amount is 0.8%), DTD (0.5%), auxiliary agent TMSP (0.5%) and hydrogen scavenging agent ammonium p-nitrobenzoate (0.2%) were added to the above basic electrolyte in sequence (the addition amount is calculated based on the total mass of solvent and lithium salt in the system after steps 1 and 2 being 100%), and ultrasonic treatment was carried out at room temperature for 45 min.

[0101] 4. Vacuum degassing: Vacuum degassing at 80℃ and -0.095MPa for 2 hours, followed by cooling to obtain the electrolyte.

[0102] (2) Preparation of positive electrode sheet:

[0103] LMFP, conductive agent, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:2:1, and N-methylpyrrolidone (NMP) was added. The mixture was stirred to prepare a uniform slurry with a viscosity of approximately 6500 mPa·s. The slurry was coated onto an aluminum foil current collector, and after coating and staged drying, an electrode sheet with a dry film thickness of approximately 150 μm was obtained. The electrode sheet was then compacted by roller pressing to a density of 2.3 g / cm³, and then dried at 85°C for 48 hours. The final positive electrode sheet had a residual moisture content of approximately 300 ppm.

[0104] (3) Preparation of negative electrode sheet:

[0105] Graphite, sodium carboxymethyl cellulose (CMC) binder, styrene-butadiene rubber (SBR) (with a CMC to SBR mass ratio of 1:1), and conductive agent Super P were mixed at a mass ratio of 96:3:1, and deionized water was added to prepare a slurry with a viscosity of approximately 4000 mPa·s. The slurry was coated onto copper foil, and after coating and drying, an electrode sheet with a dry film thickness of 93 μm was obtained. The electrode sheet was then rolled and compacted to a density of 1.6 g / cm³.

[0106] (4) Battery assembly:

[0107] The positive electrode, separator, and negative electrode prepared above are stacked to form a battery cell. There are 29 positive electrode sheets in total. The stacked body is placed in an aluminum-plastic film for encapsulation, and finally the electrolyte is added to form a soft-pack battery.

[0108] Example 2

[0109] The difference from Example 1 is that the film-forming agent PS (0.5%) and DTD (0.3%) are used.

[0110] Example 3

[0111] The difference from Example 1 is the addition of the adjuvant TMSP (0.3%).

[0112] Example 4

[0113] The difference from Example 1 is that the hydrogen scavenger is ammonium p-nitrobenzoate (0.1%).

[0114] Example 5

[0115] The difference from Example 1 is that film-forming agent PS (0.8%), DTD (0.7%), auxiliary agent TMSP (0.6%), and hydrogen scavenger ammonium p-nitrobenzene (0.3%) were added sequentially.

[0116] Example 6

[0117] The difference from Example 1 is that film-forming agent PS (0.5%), DTD (0.3%), auxiliary agent TMSP (0.3%), and hydrogen scavenger ammonium p-nitrobenzene (0.1%) were added in sequence.

[0118] Example 7

[0119] The difference from Example 1 is that film-forming agent PS (1%), DTD (1%), auxiliary agent TMSP (1%), and hydrogen scavenger ammonium p-nitrobenzene (0.5%) were added in sequence.

[0120] Example 8

[0121] The difference from Example 1 is that film-forming agent PS (0.2%), DTD (0.2%), auxiliary agent TMSP (0.2%), and hydrogen scavenger ammonium p-nitrobenzoate (0.05%) were added in sequence.

[0122] Example 9

[0123] The difference from Example 1 is that film-forming agent PS (1.3%), DTD (1.2%), auxiliary agent TMSP (1%), and hydrogen scavenger ammonium p-nitrobenzene (1%) were added in sequence.

[0124] Comparative Example 1

[0125] Compared with Example 1, the difference is that a conventional electrolyte is used, without the addition of any PS, DTD, TMSP and hydrogen scavenging agent, containing only solvent and lithium salt (LiPF6 1.2 mol / L, LiFSI 0.3 mol / L).

[0126] Comparative Example 2

[0127] Compared with Example 1, the difference is that PS (0.8%), DTD (0.5%), and ammonium p-nitrobenzoate (0.2%) were added, but the auxiliary agent TMSP was not added.

[0128] Comparative Example 3

[0129] Compared with Example 1, the difference is that PS (0.8%), DTD (0.5%), and TMSP (0.5%) were added, but the hydrogen scavenger ammonium p-nitrobenzene was not added.

[0130] Performance testing:

[0131] The performance of the lithium-ion batteries of Examples 1-9 and Comparative Examples 1-5 was tested. The test methods are as follows, and the test results are shown in Table 1.

[0132] Low-temperature capacity retention: At 25℃, constant volume at 1C; after temperature equalization at -20℃ for 6 hours, discharge at 1C to 2.5V, and let stand for 30 minutes; record the discharge capacity.

[0133] DC impedance DCR: At an ambient temperature of 25±2℃, charge at 1C constant current to the upper limit voltage of 4.3V, cut off current to 0.05C, and let stand for 1h; discharge at 1Cn constant current to 50% SOC and let stand for 1h; discharge at 3C0 for 10s and let stand for 10min. Calculate the discharge DCR at 50% SOC.

[0134] Moisture content test: The Karl Fischer coulometric method was used to test the electrolyte in the battery after the low-temperature test.

[0135] Cycle life: At an ambient temperature of 25±2℃, the system is charged at 0.33C constant current and constant voltage to the upper limit voltage of 4.4V, and the cutoff current is reduced to 0.05C; then left to stand for 30 minutes; discharged at 1C constant current to 2.5V; left to stand for 30 minutes; and the charge-discharge cycle is repeated 1000 times while the data is recorded and the capacity retention rate is calculated.

[0136] Gas chromatography-mass spectrometry: Collect gas samples after battery cycling (10 mL of gas is drawn with a syringe); inject into the GC-MS instrument and test the H2 concentration.

[0137] Table 1 Performance test results of lithium-ion batteries in the examples and comparative examples

[0138]

[0139] As can be seen from the data in Table 1:

[0140] The key performance indicators (DCR < 6.1 mΩ, H2 concentration < 63 ppm, cycle retention > 86.2%) of the lithium-ion batteries in Examples 1 to 7 of this invention are all maintained at an excellent level. Among them, Example 1 represents the complete additive system under the preferred ratio of this invention, and its performance indicators are all optimal: the lowest residual water content in the electrolyte (20 ppm), the lowest interfacial impedance (DCR 2.6 mΩ), the highest low temperature performance (capacity retention of 86.5% at -20℃) and cycle life (capacity retention of 98.7% after 1000 cycles), and extremely low gas production (H2 concentration 50 ppm).

[0141] Example 8 shows that the dosage was insufficient, indicating that when the dosage of each additive is close to or lower than the lower limit of the preferred range of the claims, the battery performance is better than the comparison of no / missing components, but significantly inferior to the preferred embodiment, indicating that insufficient dosage will not have a good effect.

[0142] Example 9 showed an excessive dosage, indicating that when the additive dosage exceeded the upper limit of the preferred range, the performance (especially the DCR increased to 8.6 mΩ, and the cycle retention decreased to 83.1%) was worse than that of Examples 1-7. This suggests that excessive addition may introduce new side reactions or have a negative impact on the electrode interface, and more is not necessarily better.

[0143] Comparative Example 1 (without any additives) had the worst performance in all aspects, especially with a DCR as high as 15.6 mΩ, an H2 concentration of 90 ppm, and a cycle retention rate of only 65%.

[0144] For Comparative Examples 2 (lacking TMSP) and 3 (lacking hydrogen scavenger), although the performance was better than Comparative Example 1, the DCR, H2 concentration, and cycle retention were significantly worse than in Example 1. This strongly demonstrates that PS, DTD, TMSP, and the hydrogen scavenger ammonium p-nitrobenzene constitute a synergistic whole, and the absence of any core component will lead to a significant decline in overall performance. Therefore, although single or partial additive combinations may bring certain improvements, only when the specific types and proportions of film-forming agents, auxiliary agents, and hydrogen scavengers described in this invention work together can the optimal balance between low impedance, high cycle retention, and extremely low gas production, as shown in Example 1, be achieved, thereby systematically solving the fundamental contradiction in the application of high-moisture cathode materials.

[0145] In summary, this invention, through the synergistic effect of specific types and ratios of film-forming agents (PS, DTD), auxiliary agents (TMSP), and hydrogen scavengers, can be compatible with positive electrode sheets with high residual moisture content, effectively suppressing the side reactions caused by this, thereby obtaining excellent electrochemical performance and safety.

[0146] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0147] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, characterized in that, The positive electrode sheet contains a high moisture-sensitive positive electrode active material, the specific surface area of ​​which is 5m² / g to 80m² / g, and the residual moisture content of the positive electrode sheet after drying is 200ppm to 400ppm. The electrolyte contains lithium salt, solvent, film-forming agent, auxiliary agent and hydrogen scavenger; The film-forming agent comprises 1,3 Propane sulfonate lactone and vinyl sulfate; The auxiliary agent is tris(trimethylsilane) phosphate; The hydrogen scavenging agent is ammonium p-nitrobenzoate; Based on a total mass of 100% for the lithium salt and the solvent, the film-forming agent contains 1,3... The mass percentage of propane sulfonate lactone is 0.5%~1.0%, and the mass percentage of vinyl sulfate is 0.3%~1.0%; the mass percentage of the auxiliary agent tris(trimethylsilane) phosphate is 0.3%~1.0%; and the mass percentage of the hydrogen scavenger ammonium p-nitrobenzene is 0.1%~0.5%.

2. The lithium-ion battery according to claim 1, characterized in that, The high moisture-sensitive positive electrode active material is lithium manganese iron phosphate or lithium manganese phosphate.

3. The lithium-ion battery according to claim 1, characterized in that, The electrolyte has a water content of 5ppm to 100ppm.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, methyl propyl carbonate, diethyl carbonate, methyl formate, methyl acetate, methyl butyrate, and ethyl propionate.

5. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium dioxaborate, and lithium difluorophosphate.

6. A method for preparing a lithium-ion battery as described in any one of claims 1 to 5, characterized in that, Includes the following steps: The positive electrode, separator, and negative electrode are used to make the battery cell; The lithium salt, solvent, film-forming agent, auxiliary agent and hydrogen scavenger are mixed evenly to obtain the electrolyte; as well as The battery cell is placed into a casing, and the electrolyte is injected to obtain a lithium-ion battery. The positive electrode sheet contains a high moisture-sensitive positive electrode active material, and the specific surface area of ​​the positive electrode active material is 5m². 2 / g~80m 2 / g, and the residual moisture content of the positive electrode sheet after drying is 200ppm~400ppm; in the electrolyte, the film-forming agent includes 1,3-propanesulfonate lactone and vinyl sulfate, the auxiliary agent is tris(trimethylsilane) phosphate, and the hydrogen scavenging agent is ammonium p-nitrobenzoate.

7. The method for preparing a lithium-ion battery according to claim 6, characterized in that, The preparation of the electrolyte includes the following steps: The selected solvents are mixed evenly according to the volume ratio to obtain a mixed solvent; Lithium salt is added to the mixed solvent and mixed evenly to obtain the basic electrolyte; A film-forming agent, an auxiliary agent, and a hydrogen scavenger are added sequentially to the basic electrolyte, mixed evenly, and then degassed under vacuum conditions to obtain the electrolyte.

8. The method for preparing a lithium-ion battery according to claim 7, characterized in that, The degassing treatment is carried out at a temperature of 80℃~100℃ and a vacuum degree of not less than 0.05MPa for 2h~4h.

9. An electrical device, characterized in that, Including the lithium-ion battery as described in any one of claims 1 to 5.

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