Electrolytes and batteries

Abstract

This invention discloses an electrolyte and a battery, belonging to the field of secondary battery technology. Based on the total mass of the electrolyte, the electrolyte comprises the following components in the following mass percentages: 20%~30% ethylene carbonate, 24.5%~35% diethyl carbonate, 25%~35% methyl ethyl carbonate, 2%~8% fluoroethylene carbonate, 8%~12% lithium hexafluorophosphate, 0.5%~2.5% lithium difluorooxalate borate, 1%~4% vinylene carbonate, 0.5%~2% 1,3-propanesulfonate lactone, and 0.5%~2% lithium difluorophosphate. The battery containing the electrolyte proposed in this invention can achieve a balance between high-frequency charging and discharging, wide temperature range operation, long lifespan, and high safety.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to an electrolyte and a battery. Background Technology

[0002] With the continuous advancement of energy conservation and emission reduction policies in the automotive industry and the continuous improvement of vehicle electrification and intelligence, automatic start-stop systems have been widely applied in traditional fuel vehicles and hybrid vehicles, effectively reducing idling fuel consumption and exhaust emissions. As the core power unit of the start-stop system, the start-stop battery faces extremely stringent requirements regarding high-frequency, high-rate charging and discharging, wide-temperature range adaptability, long cycle life, and high safety. Currently, most automotive start-stop batteries use lithium-ion battery systems. The electrolyte, as a key component affecting battery performance, directly determines its rate response, interface stability, temperature range adaptability, and safety characteristics. The negative electrode, as the core carrier for lithium-ion insertion and extraction, directly affects interface reaction efficiency, SEI film stability, and high-current conductivity. The matching degree between the electrolyte and the negative electrode material is the core key to determining the overall battery performance.

[0003] Most electrolytes used in current start-stop batteries follow conventional power battery formulations, such as using ternary solvents (EC+DEC+EMC), lithium salts (e.g., lithium hexafluorophosphate), and VC additives. These systems have prominent problems under battery start-stop conditions: at low temperatures, the electrolyte viscosity is high and the ionic conductivity decreases significantly, making cold starts difficult; at high temperatures, the solvent is easily decomposed, and LiPF6 is easily hydrolyzed to produce HF that corrodes the electrode, damages the SEI film structure, and causes battery swelling and rapid capacity decay.

[0004] In summary, existing technologies struggle to simultaneously meet multiple requirements, including wide temperature range adaptability from -40℃ to 85℃, 300A-level high-current start-up response, 3C high-rate long-cycle operation, and high-temperature safety and stability. In actual automotive start-stop scenarios, the minimum voltage of conventional batteries during 300A high-current discharge often drops to around 2.0V or even lower, resulting in insufficient start-up power stability and significant shortcomings in cycle life and high-temperature storage performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose an electrolyte and battery that aims to solve the technical problem of the inability to simultaneously achieve high-frequency charging and discharging, wide temperature range, long lifespan operation, and high safety.

[0006] To achieve the above-mentioned technical objectives, a first aspect of the present invention provides an electrolyte comprising, based on the total mass of the electrolyte, the following components in the indicated mass percentages: 20%~30% ethylene carbonate, 24.5%~35% diethyl carbonate, 25%~35% methyl ethyl carbonate, 2%~8% fluoroethylene carbonate, 8%~12% lithium hexafluorophosphate, 0.5%~2.5% lithium difluorooxalate borate, 1%~4% vinylene carbonate, 0.5%~2% 1,3-propanesulfonate lactone, and 0.5%~2% lithium difluorophosphate.

[0007] In some embodiments, based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is 22% to 28%; and / or, based on the total mass of the electrolyte, the mass percentage of diethyl carbonate is 28% to 32%; and / or, based on the total mass of the electrolyte, the mass percentage of methyl ethyl carbonate is 28% to 32%; and / or, based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate is 4% to 6%.

[0008] In some embodiments, the lithium hexafluorophosphate accounts for 9% to 11% of the total mass of the electrolyte; and / or, the lithium difluorooxalate borate accounts for 1% to 2% of the total mass of the electrolyte; and / or, the vinylene carbonate accounts for 2% to 3% of the total mass of the electrolyte; and / or, the 1,3-propanesulfonate lactone accounts for 1% to 1.5% of the total mass of the electrolyte; and / or, the lithium difluorophosphate accounts for 1% to 1.5% of the total mass of the electrolyte.

[0009] In a second aspect, the present invention provides a battery comprising the electrolyte described in the first aspect of the present invention.

[0010] In some embodiments, the battery includes a negative electrode sheet, which includes artificial graphite secondary particles.

[0011] In some embodiments, the median particle size D of the artificial graphite 50 The particle size distribution range is 6µm to 18µm; and / or, the particle size distribution span factor (D) of the artificial graphite is... 90 -D 10 ) / D 50 ≤1.2, where D 90 D of the artificial graphite 90 Particle size, D 10 D of the artificial graphite 10 Particle size, D 50 The median particle size of the artificial graphite is given.

[0012] In some embodiments, the artificial graphite comprises a first artificial graphite and a second artificial graphite, wherein the median particle size D of the first artificial graphite is... 50 The median particle size D of the second artificial graphite is 14µm~18µm. 50 The value is 6µm to 8µm.

[0013] In some embodiments, the mass ratio of the first artificial graphite to the second artificial graphite is (3~6):(4~7).

[0014] In some embodiments, the OI value of the artificial graphite is ≤3.

[0015] In some embodiments, the battery is a start-stop battery; and / or, the battery is a 12V or 48V automotive start-stop battery.

[0016] Compared with the prior art, the beneficial effects of the present invention include: The electrolyte proposed in this invention addresses the requirements of start-stop batteries for high-frequency, high-rate charge / discharge, wide-temperature range adaptability, long cycle life, and high safety. Regarding the solvent, by controlling the types and ratios of four solvents, it overcomes the problems of performance imbalance in a wide temperature range, excessively high impedance in high-FEC systems, and severe gas generation associated with conventional three-solvent systems, achieving a dual improvement in low-temperature fluidity and high-temperature stability. Regarding the lithium salt, the LiPF6 and LiDFOB composite lithium salt used exhibits good compatibility with the aforementioned quaternary solvent system, ensuring basic ion conduction efficiency while LiDFOB can suppress HF production from LiPF6 hydrolysis in situ, reducing high-temperature gas generation and lowering interface degradation. Impedance; Regarding additives, a ternary synergistic additive of VC-PS-LiPO2F2 is used, avoiding the shortcomings of poor interfacial film toughness and easy breakage formed by single VC or simple binary additives. During battery charging and discharging, vinylene carbonate (VC), as the core additive, can quickly form a basic SEI film on the negative electrode. 1,3-propanesulfonyl lactone (PS) can improve the flexibility and thermal stability of the SEI film, while LiPO2F2 can achieve film repair and corrosion prevention, realizing "film formation-toughening-repair" interfacial protection, solving the problems of rapid battery capacity decay, soaring internal resistance, and excessively low discharge voltage under high-frequency cycling. Experiments show that the electrolyte proposed in this invention can stabilize the minimum voltage of 300A high-current discharge at about 2.2-2.3V, which is 200-300mV higher than conventional formulations. It can simultaneously meet the requirements of minimum discharge voltage ≥2.2V at 300A, cycle life ≥3000 times at 80% SOH, and high-temperature storage recovery rate ≥94%. It has strong stability and applicability when applied to start-stop batteries. Attached Figure Description

[0017] Figure 1 These are comparison graphs of the 300A discharge curves of Embodiment 1, Embodiment 10, Comparative Example 1, and Comparative Example 3 of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] In a first aspect, the present invention provides an electrolyte comprising, based on the total mass of the electrolyte, the following components in the indicated mass percentages: 20%–30% ethylene carbonate (EC), 24.5%–35% diethyl carbonate (DEC), 25%–35% methyl ethyl carbonate (EMC), 2%–8% fluoroethylene carbonate (FEC), 8%–12% lithium hexafluorophosphate (LiPF6), 0.5%–2.5% lithium difluorooxalate borate (LiDFOB), 1%–4% vinylene carbonate (VC), 0.5%–2% 1,3-propanesulfonate lactone (PS), and 0.5%–2% lithium difluorophosphate (LiPO2F2).

[0020] In some embodiments, the electrolyte contains 20% to 30% ethylene carbonate (EC) based on its total mass. For example, the mass percentage of EC based on the total mass of the electrolyte can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any combination of two of the above values. In other embodiments, the mass percentage of ethylene carbonate based on the total mass of the electrolyte is 22% to 28%. EC has a high dielectric constant, which can promote lithium salt dissociation and participate in the formation of the SEI film. Controlling the EC content in the electrolyte within the above range, and adapting it to other components, can improve the dielectric constant and ionic conductivity of the electrolyte, and enhance the electrolyte's adaptability and stability to sudden changes in rate and temperature.

[0021] In some embodiments, the electrolyte contains 24.5% to 35% diethyl carbonate (DEC) based on its total mass. For example, the mass percentage of DEC based on the total mass of the electrolyte can be 24.5%, 25%, 27%, 29%, 30%, 32%, 34%, 35%, or any combination of two of these values. In other embodiments, the mass percentage of diethyl carbonate based on the total mass of the electrolyte is 28% to 32%. DEC has low viscosity, which can improve the low-temperature fluidity and thermal stability of the electrolyte, further improving the fluidity of the battery at extreme temperatures, especially low temperatures, and enhancing cycle performance.

[0022] In some embodiments, the electrolyte contains 25% to 35% ethyl methyl carbonate (EMC) based on its total mass. For example, the mass percentage of EMC based on the total mass of the electrolyte can be 25%, 27%, 29%, 30%, 32%, 34%, 35%, or any combination of two of these values. In other embodiments, the mass percentage of diethyl carbonate based on the total mass of the electrolyte is 28% to 32%. EMC in the electrolyte can balance the dielectric constant and viscosity, improve the battery's rate capability and low-temperature performance, and contribute to a minimum discharge voltage of ≥2.2V at 300A.

[0023] In some embodiments, the electrolyte contains 2% to 8% fluoroethylene carbonate based on its total mass. For example, the mass percentage of FEC based on the total mass of the electrolyte can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination of two of these values. In other embodiments, the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte is 4% to 6%. FEC can assist in film formation, improve the density of the SEI film, suppress high-temperature decomposition, and further enhance the stability of the battery at high temperatures.

[0024] In some embodiments, the electrolyte contains 8% to 12% lithium hexafluorophosphate based on its total mass. For example, the mass percentage of LiPF6 based on the total mass of the electrolyte can be 8%, 9%, 10%, 11%, 12%, or any combination of two of these values. In other embodiments, the mass percentage of lithium hexafluorophosphate based on the total mass of the electrolyte is 9% to 11%. As the main lithium salt in the electrolyte, the above-mentioned lithium salt can provide high ionic conductivity, is compatible with other components, further improves the migration rate of lithium ions, and enhances the rate performance of the battery.

[0025] In some embodiments, the electrolyte contains 0.5% to 2.5% lithium difluorooxalate borate based on its total mass. For example, the mass percentage of LiDFOB in the electrolyte can be 0.5%, 1%, 1.5%, 2%, 2.5%, or any combination of two of these values. In other embodiments, the mass percentage of lithium difluorooxalate borate is 1% to 2% based on the total mass of the electrolyte. Thus, LiDFOB, as a co-lithium salt, can suppress the hydrolysis of LiPF6 and form a stable, low-resistance CEI film at the battery cathode, adapting to other components and further improving the battery's cycle stability and rate performance.

[0026] In some embodiments, the electrolyte contains 1% to 4% vinylene carbonate (VC) based on its total mass. For example, the mass percentage of VC based on the total mass of the electrolyte can be 1%, 2%, 3%, 4%, or any two of these values. In other embodiments, the mass percentage of vinylene carbonate based on the total mass of the electrolyte is 2% to 3%. Thus, VC, as a core film-forming agent in the electrolyte, can rapidly form a basic SEI film during battery cycling, inhibiting electrolyte decomposition and adapting to other components, further improving the battery's cycle stability.

[0027] In some embodiments, the electrolyte contains 0.5% to 2% 1,3-propanesulfonate lactone (PS) based on its total mass. For example, the mass percentage of PS based on the total mass of the electrolyte can be 0.5%, 1%, 1.5%, 2%, or any two of the above values. In other embodiments, the mass percentage of 1,3-propanesulfonate lactone based on the total mass of the electrolyte is 1% to 1.5%. PS can improve the flexibility and thermal stability of the SEI membrane, suppress high-temperature gas generation, achieve interfacial protection of "film formation-toughening-repair," and, in combination with other components, solve the core problems of rapid capacity decay, soaring internal resistance, and excessively low voltage during high-current discharge under high-frequency cycling.

[0028] In some embodiments, the electrolyte contains 0.5% to 2% lithium difluorophosphate based on its total mass. For example, the mass percentage of LiPO2F2 based on the total mass of the electrolyte can be 0.5%, 1%, 1.5%, 2%, or any combination of two of the above values. Thus, LiPO2F2 has membrane repair and corrosion protection functions, continuously repairing damaged SEI / CEI membranes, and working with other components to achieve "film formation-toughening-repair" interface protection, solving the problems of rapid capacity decay, soaring internal resistance, and excessively low discharge voltage under high-frequency cycling.

[0029] In summary, the electrolyte proposed in this invention addresses the requirements of start-stop batteries for high-frequency, high-rate charging and discharging, wide-temperature range adaptability, long cycle life, and high safety. Regarding the solvent, by precisely controlling the types and ratios of four solvents, it solves the problems of performance imbalance in the wide temperature range, excessively high impedance in high-FEC systems, and severe gas generation associated with conventional three solvents, achieving a dual improvement in low-temperature fluidity and high-temperature stability. Regarding the lithium salt, a composite lithium salt of LiPF6 and LiDFOB is used, which has good compatibility with the aforementioned quaternary solvent system. This ensures basic ion conduction efficiency while suppressing HF production from LiPF6 hydrolysis in situ, reducing high-temperature gas generation, and lowering interfacial resistance. Regarding additives, a ternary synergistic additive system of VC-PS-LiPO2F2 is adopted, avoiding the shortcomings of poor interfacial film toughness and easy breakage formed by single VC or simple binary additives. During battery charging and discharging, vinylene carbonate (VC), as the core additive, can quickly form a basic SEI film on the negative electrode. 1,3-propanesulfonate lactone (PS) can improve the flexibility and thermal stability of the SEI film, while LiPO2F2 can achieve film repair and corrosion prevention, realizing "film formation-toughening-repair" interfacial protection, solving the problems of rapid capacity decay, soaring internal resistance, and excessively low discharge voltage under high-frequency cycling. Experiments show that the electrolyte proposed in this invention can stabilize the minimum discharge voltage of 300A high current at around 2.2-2.3V, which is 200-300mV higher than conventional formulations. It can simultaneously meet the requirements of minimum discharge voltage of 300A ≥2.2V, cycle life of 80% SOH ≥3000 cycles, and high-temperature storage recovery rate ≥94%. It has strong stability and applicability when applied to start-stop batteries.

[0030] As an example, the electrolyte can be prepared using the following method: (1) Dehydrate ethylene carbonate, diethyl carbonate, methyl ethyl carbonate and fluoroethylene carbonate to a water content of ≤10ppm; dry lithium hexafluorophosphate, lithium difluorooxalate phosphate, vinylene carbonate, 1,3-propanesulfonyl lactone and lithium difluorophosphate to a water content of ≤5ppm. (2) Add ethylene carbonate, diethyl carbonate and methyl ethyl carbonate in sequence according to the proportion, stir at 25℃~30℃ for 30min~60min, add fluoroethylene carbonate, and continue stirring for 15min to obtain a mixed solvent. (3) Control the system temperature to 20℃~25℃, add lithium hexafluorophosphate and lithium difluorooxalate phosphate while stirring, and stir at 500r / min~800r / min for 60min~90min until completely dissolved; (4) Keep the temperature at 25℃~30℃, add vinylene carbonate, 1,3-propanesulfonate lactone and lithium difluorophosphate in sequence, and stir at 300r / min~500r / min for 30min~45min. (5) After filtration through a 0.22μm filter membrane, the water content is tested to be ≤10ppm and the free acid content is ≤50ppm, and then the product is sealed and packaged. The entire process was carried out in an environment where the H2O content was <1ppm and the O2 content was <1ppm.

[0031] In some embodiments, a step of high-temperature aging-low-temperature standing treatment is added between step (4) and step (5): the mixed electrolyte is aged in a sealed environment at 40℃~50℃ for 12h~24h, and then stood at -20℃~-10℃ for 6h~12h.

[0032] In a second aspect, the present invention provides a battery comprising the electrolyte described in the first aspect of the present invention.

[0033] Therefore, the battery proposed in this invention possesses all the beneficial effects of the electrolyte mentioned above, which will not be elaborated upon here.

[0034] In some embodiments, the battery includes a negative electrode sheet comprising artificial graphite secondary particles. Thus, the negative electrode active material has a rich porous structure, which can significantly improve electrolyte wettability and reduce interfacial impedance.

[0035] In some embodiments, the median particle size D of the artificial graphite 50 The particle size ranges from 6µm to 18µm. As an example, the median particle size D of synthetic graphite... 50 The particle size can be 6µm, 8µm, 10µm, 12µm, 14µm, 16µm, 18µm, or any combination of two of the above values. Within the above median particle size range of artificial graphite, the interaction with the electrolyte ensures that the lithium ion transport path in the negative electrode active material is short enough, while the median particle size is not too small, resulting in an excessively large contact area with the electrolyte, thus reducing the occurrence of side reactions between artificial graphite and the electrolyte.

[0036] In some embodiments, the particle size distribution span factor (D) of the artificial graphite 90 -D 10 ) / D 50 ≤1.2, where D 90 D of the artificial graphite 90 Particle size, D 10 D of the artificial graphite 10 Particle size, D 50The median particle size of the artificial graphite is given. As an example, the particle size distribution range coefficient of the artificial graphite can be 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or any combination of two of the above values. Therefore, the artificial graphite exhibits excellent particle size uniformity, constructing a continuous and smooth lithium-ion transport channel. Combined with the high ionic conductivity of the electrolyte, it is suitable for the instantaneous discharge requirements of ultra-high currents up to 300A.

[0037] It can be understood that the particle size distribution span coefficient (Span) is a dimensionless index characterizing the width of the particle size distribution in a particle system. 10 This refers to the particle size corresponding to a cumulative volume fraction of 10%, i.e., the "effective particle size"—10% of the particles in the system are smaller than this value; D 50 This refers to the median diameter, where the cumulative volume fraction reaches 50%, with half of the particles smaller than this value and half larger than this value; D 90 This refers to the particle size corresponding to a cumulative volume fraction of 90%, i.e., the "dominant particle size"—90% of the particles in the system are smaller than this value. If Span=0, theoretically all particles have the same size; a smaller Span (e.g., <1) results in a narrower distribution and better particle size uniformity; a larger Span (e.g., >2) results in a wider distribution, greater particle size variation, and a less homogeneous system. D 90 D 10 D 50 The particle size distribution can be determined using a laser particle size analyzer, referring to the standard GB / T19077-2016 "Laser Diffraction Method for Particle Size Distribution".

[0038] In some embodiments, the artificial graphite comprises a first artificial graphite and a second artificial graphite, wherein the median particle size D of the first artificial graphite is... 50 The median particle size D of the second artificial graphite is 14µm~18µm. 50 The particle size ranges from 6µm to 8µm. As an example, the median particle size D of the first type of artificial graphite... 50 It can be 14µm, 15µm, 16µm, 17µm, 18µm, or any combination of two of these values; the median particle size D of the second type of artificial graphite. 50The particle size can be 6µm, 6.5µm, 7µm, 7.5µm, 8µm, or any combination of two of these values. Therefore, by using two particle sizes of artificial graphite, adapted to both the large and small sizes and the electrolyte, the large-particle-size (14µm~18µm) artificial graphite forms the conductive framework of the negative electrode, ensuring that the solid-phase diffusion path of lithium ions is not too long and reducing concentration polarization during high-current charging and discharging. The small-particle-size (6µm~8µm) artificial graphite fills the gaps between the large particles, increasing the negative electrode compaction density and interparticle contact area, forming a continuous, low-torsion lithium-ion transport network, thereby significantly improving the wetting and retention capabilities of the electrolyte. On the other hand, the abundant active sites on the surface of the small particles can preferentially react with additives such as VC, PS, and LiPO2F2 in the electrolyte to form a uniform, dense SEI film rich in inorganic components; the large particles provide stable volume support, inhibiting particle cracking and peeling during cycling. The coupling of the two enables the negative electrode and the electrolyte of the present invention (containing FEC, LiDFOB and ternary additives) to achieve a synergistic effect of rapid wetting, low-resistance film formation and long-term structural stability, ultimately reducing interfacial impedance, improving rate performance and cycle life.

[0039] In some embodiments, the mass ratio of the first artificial graphite to the second artificial graphite is (3~6):(4~7). As an example, the mass ratio can be 3:7, 4:6, 5:5, 6:4, or any range of two of these values. Thus, by controlling the mass ratio of large and small graphite particles, the densest packing structure can be formed in the negative electrode. When the proportion of large particles is too low (<30%), the skeleton support is insufficient, and the compaction density decreases; when the proportion of large particles is too high (>60%), the small particles are not fully filled, the interparticle porosity increases, and local enrichment of the electrolyte easily triggers side reactions. Under this preferred ratio, the porosity and tortuosity of the negative electrode are balanced. Combined with the high ionic conductivity (≥10.5 mS / cm at 25℃) of the electrolyte of this invention and the rapid film-forming characteristics of the ternary additives VC, PS, and LiPO2F2, rapid and uniform wetting of the electrode by the electrolyte can be achieved. Simultaneously, the stable SEI film formed on the surface of the small particles covers the active sites at the edges of the large particles, synergistically reducing interfacial impedance and improving high-current discharge capability and cycle stability.

[0040] In some embodiments, the OI value of the artificial graphite is ≤3. As an example, the OI value of the artificial graphite can be 3, 2.5, 2, 1.5, 1, 0.5, or any two of the above values. Thus, on the one hand, the LiDFOB auxiliary lithium salt in the electrolyte can generate an ultra-thin, low-resistance stable SEI film in situ on the surface of the artificial graphite with low OI value secondary granulation. Combined with the film-forming characteristics of VC and the self-healing effect of LiPO2F2 interface, the problem of easy cracking and easy shedding of conventional negative electrode SEI films is solved from the root. On the other hand, the graphite sheet height is isotropic, which can significantly suppress graphite layer peeling under high rate charge and discharge. Combined with the strong SEI toughening effect of PS additives, the battery's long cycle stability and high frequency stress resistance are synergistically improved.

[0041] In some embodiments, the battery is a start-stop battery. Taking vehicle start-stop as an example, a start-stop battery is a high-performance battery capable of withstanding frequent engine shutdown and restart cycles during vehicle operation. Its design goal is to meet the stringent requirements of automatic start-stop systems for deep cycle capability, high charge acceptance rate, and long service life. As the core power unit of the start-stop system, the start-stop battery places extremely stringent requirements on high-frequency, high-rate charging and discharging, wide-temperature range environmental adaptability, long cycle life, and high safety. This application recognizes that the electrolyte, as a key component affecting battery performance, directly determines its rate response, interface stability, temperature range adaptability, and safety characteristics; while the negative electrode active material, as the core carrier for lithium-ion intercalation and deintercalation, directly affects the interface reaction efficiency, SEI film stability, and high current conduction capability due to its structure, particle size uniformity, and crystal orientation. The matching degree between the electrolyte and the negative electrode active material is the core key to determining the overall performance of the battery. By matching the electrolyte and negative electrode active material of this application, the components of both work together to further enable the battery to adapt to high-frequency charging and discharging, 300A-level high current, wide temperature range (-40℃ to 85℃), 3C high-rate long-life operation and high safety.

[0042] In some embodiments, the battery is a 12V or 48V automotive start-stop battery. Experiments show that the above-mentioned battery voltage can adapt to the harsh automotive operating conditions of high frequency, high current, and wide temperature range alternation.

[0043] In some embodiments, the binder used in the negative electrode sheet is an acrylate-modified styrene-butadiene rubber latex, wherein the crosslinking density of the modified styrene-butadiene rubber latex is ≤0.4%, the swelling ratio in the electrolyte is ≤15%, and the glass transition temperature is ≤-30℃.

[0044] In some embodiments, the electrolyte exhibits an ionic conductivity ≥10.5 mS / cm at 25°C and ≥0.8 mS / cm at -40°C. Therefore, the electrolyte maintains high ionic conductivity at different temperatures, which can improve the migration rate of lithium ions in the electrolyte.

[0045] In some embodiments, the start-stop battery has a minimum voltage ≥2.2V when discharged at 10C / 300A for 10s. Therefore, the battery exhibits good performance under high-frequency, high-rate charge / discharge conditions.

[0046] In some embodiments, the start-stop battery has a cycle life of ≥3000 cycles at 3C / 100% DOD to 80% SOH; and a storage capacity recovery rate of ≥94% at 60℃ / 28 days. Therefore, the start-stop battery has a good cycle life.

[0047] In some embodiments, the start-stop battery operates within a SOC range of 35% to 85%, has a maximum pulse discharge current ≥300A, and operates for at least 20,000 start-stop cycles per year. Thus, the start-stop battery can balance high-frequency charging and discharging, wide temperature range operation, long lifespan, and high safety.

[0048] In summary, compared with existing technologies, this invention achieves directional coupling and synergy between electrolyte formulation and the microstructure of secondary granulated artificial graphite anode, rather than a conventional improvement of a single material. 1. Fast start-stop response and significant low voltage drop advantages: Quaternary solvent improves ion migration rate, composite lithium salt optimizes interface conductivity, and ternary additives stabilize electrode interface; when combined with the low OI and narrow particle size range customized negative electrode active material of this invention, the minimum voltage stabilizes at 2.28V~2.32V after 10s of 300A high current discharge, which is significantly improved compared to the existing 1.98~2.08V, and the phenomenon of voltage drop and insufficient start-up power during start-stop is significantly improved.

[0049] 2. Significantly improved cycle and high-temperature storage performance: Conventional start-stop batteries generally have a cycle life of less than 2000 cycles. This invention uses a ternary functional additive system of VC film formation, PS toughening, and LiPO2F2 repair, combined with the low orientation and high uniformity structure of the negative electrode active material. The SEI film remains intact and stable under hundreds of thousands of high-frequency stresses, with an 80% SOH cycle life of ≥3000 cycles and a capacity recovery rate of ≥94% at 60℃ / 28 days.

[0050] 3. Balanced performance over a wide temperature range: The electrolyte composition is well-matched with the porosity and crystal structure of the negative electrode active material. The ionic conductivity at -40℃ is ≥0.8mS / cm, which can stably achieve cold start in extremely cold environments. There is no gas expansion or significant capacity decay when stored at 85℃, which can be applied to vehicle use scenarios in extreme climates such as high cold and high temperature.

[0051] 4. Good safety and industrial compatibility: Using LiDFOB instead of the commonly used LiFSI as an auxiliary lithium salt can significantly reduce the risk of high-temperature gas generation, suppress the generation of HF by LiPF6 hydrolysis, and reduce electrode corrosion; it is fully compatible with existing lithium battery production lines, requires no equipment modification, and has high feasibility for mass production.

[0052] In some embodiments, the battery may include the aforementioned negative electrode, positive electrode, electrolyte, and separator. The positive electrode, negative electrode, and separator are all immersed in the electrolyte. During the charging and discharging process of the battery, active lithium ions are inserted and extracted back and forth between the positive and negative electrode. The electrolyte plays the role of conducting ions between the positive and negative electrode. The separator is disposed between the positive and negative electrode and mainly plays the role of preventing short circuits between the positive and negative electrode, while allowing active lithium ions to pass through.

[0053] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode sheet. The negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0054] In some embodiments, the negative current collector includes copper foil, composite copper foil, etc.

[0055] In some embodiments, the negative electrode active material may include carbon-based materials (such as artificial graphite), silicon-based materials, tin-based materials, etc.

[0056] In some embodiments, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0057] In some embodiments, the negative electrode conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0058] Typically, a positive electrode sheet includes a positive current collector and a positive active material layer formed on at least one side of the positive current collector, wherein the positive active material layer includes a positive active material, a positive conductive agent, and a positive binder.

[0059] In some embodiments, the positive electrode active material may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0060] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. Metal current collectors include at least one of aluminum foil current collectors and carbon-coated aluminum foil current collectors; composite current collectors may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. Composite current collectors can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or vinylidene fluoride. Tetrafluoroethylene propylene terpolymer, vinylidene fluoride hexafluoropropylene Tetrafluoroethylene terpolymer, tetrafluoroethylene At least one of hexafluoropropylene copolymer and fluorinated acrylate resin. As a specific example, this application uses polyvinylidene fluoride.

[0062] In some embodiments, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0063] In some embodiments, the diaphragm includes a polyethylene diaphragm, a polypropylene diaphragm, a polyethylene / polypropylene composite diaphragm, etc.

[0064] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0065] Example 1 I. Electrolyte Preparation The electrolytes for all examples and comparative examples were prepared according to the following steps: In an anhydrous and oxygen-free glove box (H2O < 1 ppm, O2 < 1 ppm), the four solvents EC, DEC, EMC, and FEC were dehydrated using molecular sieves until the water content was ≤ 10 ppm; LiPF6, LiDFOB, VC, PS, and LiPO2F2 were vacuum dried until the water content was ≤ 5 ppm, and set aside for later use. EC, DEC, and EMC were added sequentially in proportion, and stirred at 400 rpm for 45 min at 25°C until completely homogeneous; then FEC was added, and stirring was continued for 15 min to obtain a homogeneous mixed solvent. The reactor temperature was controlled at 25°C, and LiPF6 and LiDFOB were slowly added while stirring at low speed, and stirred at 650 rpm for 75 min until the lithium salt was completely dissolved and the solution was clear and transparent. While maintaining the system temperature at 25°C, VC, PS, and LiPO2F2 were added sequentially, and stirred at 400 rpm for 40 min to ensure uniform dispersion of each functional additive. Precision filtration is performed using a 0.22µm organic filter membrane. The finished electrolyte is tested to ensure that the water content is ≤10ppm and the free acid (HF meter) is ≤50ppm. After passing the test, it is sealed and packaged in a light-proof environment. The entire process is strictly operated in a low-water and low-oxygen environment.

[0066] II. Preparation of Negative Electrode Sheets Negative electrode active material: artificial graphite secondary particles, D 50 The first artificial graphite with a particle size of 12µm, D 50 =16µm, second artificial graphite D 50 =7µm, mass ratio of 5:5, artificial graphite (D 90 -D 10 ) / D 50 =1.05, OI value=2.6.

[0067] The above-mentioned negative electrode active material, conductive agent (conductive carbon black), and binder (styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 1:1) are added to water in a mass ratio of 95:2:3 and stirred to form a negative electrode slurry. The negative electrode slurry is then uniformly coated onto a copper foil current collector and dried to form a negative electrode sheet.

[0068] III. Preparation of Positive Electrode Sheets Positive electrode active material: NCM811, chemical formula LiNi 0.8 Co 0.1 Mn 0.1 O2, D 50 The particle size is 10µm.

[0069] The above-mentioned positive electrode active material, conductive agent (conductive carbon black), and binder (polyvinylidene fluoride) are added to NMP in a mass ratio of 96:2:2 and stirred to form a positive electrode slurry. The solid content of the slurry is controlled to be 70%. The positive electrode slurry is uniformly coated on an aluminum foil current collector and dried to form a positive electrode sheet.

[0070] IV. Separator: Polypropylene membrane is used as the separator, with a thickness of 20 micrometers.

[0071] Battery assembly The positive electrode, separator, and negative electrode are stacked or wound into a cell in the order of "positive electrode-separator-negative electrode," installed in a casing, and then injected with electrolyte. After sealing, formation (initial charge-discharge activation), and capacity testing, the finished battery is obtained. The battery has a rated capacity of 30Ah.

[0072] Examples 2-8 The difference between Examples 2-8 and Example 1 is that the electrolyte formulation is different, as shown in Table 1 below.

[0073] Table 1

[0074] Examples 9-11 The difference from Example 1 is as follows: The negative electrode active material in Example 9 is narrowly distributed single-particle-size artificial graphite, with secondary artificial graphite particles, D... 50 =12µm, (D 90 -D 10 ) / D 50 =1.10, OI value=2.8, the preparation method of the negative electrode sheet is as described in Example 1.

[0075] Example 10: The negative electrode active material is artificial graphite primary particles, D 50 =20µm, (D 90 -D 10 ) / D 50 =1.55, OI value=12, the preparation method of the negative electrode sheet is as described in Example 1.

[0076] Example 11: The negative electrode active material is natural graphite, D 50 =18µm, (D 90 -D 10 ) / D 50 =1.68, OI value=26, the preparation method of the negative electrode sheet is as described in Example 1.

[0077] Comparative Examples 1-3 The difference between Comparative Examples 1 and 2 and Example 1 is that the electrolyte formulation is different.

[0078] Comparative Example 1 Electrolyte formulation: EC 25%, DEC 30%, EMC 32.5%, LiPF6 10%, VC 2.5%; free of FEC, LiDFOB, PS, and LiPO2F2.

[0079] Comparative Example 2 Electrolyte formulation: EC 20%, PC 5%, EMC 33.5%, DMC 25%, LiPF6 12%, LiFSI 2%, VC 1.5%, LiPO2F 21%.

[0080] The electrolyte formulation for Comparative Example 3 is the same as that for Comparative Example 1, and the negative electrode active material is the same as that for Example 10.

[0081] Comparative Examples 4-11 The difference between Comparative Example 4 and Example 1 is that the content of lithium salt LiDFOB is 0 and the content of LiPF6 is 11%.

[0082] The difference between Comparative Example 5 and Example 1 is that the content of additive VC is 0, and the content of PS and LiPO2F2 is 2.5%.

[0083] The difference between Comparative Example 6 and Example 1 is that the content of additive PS is 0, the content of VC is 3.1%, and the content of LiPO2F2 is 1.9%.

[0084] The difference between Comparative Example 7 and Example 1 is that the content of additive LiPO2F2 is 0, the content of PS is 3.1, and the content of VC is 1.9%.

[0085] The difference between Comparative Example 8 and Example 1 is that the FEC content is 10% and the EMC content is 25%.

[0086] The difference between Comparative Example 9 and Example 1 is that the VC content of the additive is 5% and the EMC content is 27.5%.

[0087] The difference between Comparative Example 10 and Example 1 is that the content of additive PS is 2.5% and the content of VC is 1.2%.

[0088] The difference between Comparative Example 11 and Example 1 is that the content of additive LiPO2F2 is 2.5% and the content of VC is 1.3%.

[0089] The batteries corresponding to the examples and comparative examples were tested according to the following methods for the following indicators: low-temperature ionic conductivity, initial charge-discharge efficiency, 300A high-current discharge voltage drop, 3C cycle life, 60℃ high-temperature storage capacity recovery rate, and DCR internal resistance growth rate after 3000 cycles. The test results are shown in Table 2.

[0090] Low-temperature ionic conductivity test: The electrolyte is injected into the conductivity cell (electrode spacing is known) using the AC impedance method. The impedance spectrum of the electrolyte is measured in a constant temperature environment of -40℃. The ionic conductivity is calculated by the formula σ=L / (R·S), where L is the electrode spacing, S is the electrode area, and R is the ohmic resistance.

[0091] First charge / discharge efficiency: At 25℃, the battery is charged at a constant current of 0.2C to the upper limit voltage (4.2V), then charged at a constant voltage until the current is ≤0.05C, and then discharged at a constant current of 0.2C to the lower limit voltage (2.5V). The first discharge capacity and the first charge capacity are recorded. The first charge / discharge efficiency is calculated as follows: First charge / discharge efficiency = (first discharge capacity / first charge capacity) × 100%.

[0092] 300A high current discharge voltage drop test: Adjust the battery to 50% SOC at 25℃, and then discharge at a constant current of 300A for 10 seconds. Record the lowest voltage value that appears during the discharge process (usually the voltage at the end of 10 seconds), which is the lowest voltage of 300A discharge. The sampling interval is 0.1s.

[0093] 3C cycle life test: At 25℃, charge the battery at 3C constant current and constant voltage to the upper limit voltage (cutoff current 0.05C), then discharge it at 3C constant current to the lower limit voltage. Repeat this cycle and record the total number of cycles completed when the battery capacity decays to 80% of the initial capacity (i.e., 80% SOH).

[0094] 60℃ High Temperature Storage Capacity Recovery Rate Test: The battery is fully charged at 25℃, and its initial capacity (0.2C discharge) is tested; then the battery is placed in a 60℃ constant temperature chamber for 28 days; after being taken out, it is discharged at 25℃ at 0.2C to the lower limit voltage, and then charged and discharged at 0.2C 3 times. The capacity of the third discharge is taken as the recovery capacity; recovery rate = (recovery capacity / initial capacity) × 100%.

[0095] DCR (Discharge Rate of Return) Growth Rate Test After 3000 Cycles: Before the cycle test, adjust the battery to 50% SOC and measure the initial DC internal resistance (DCR) using a pulse method (e.g., discharging at 1C current for 10ms). After the battery completes 3000 cycles (if the battery has not failed), measure the DCR again under the same conditions. Growth Rate = (DCR after Cycles - Initial DCR) / Initial DCR × 100%.

[0096] Comparison of 300A discharge curves (50% SOC, 10C / 300A discharge for 10s) of Examples 1, 10, 1, and 3 of this invention, as shown in the figure. Figure 1 As shown, the electrolyte-containing battery of the present invention exhibits stronger stability during high-current discharge.

[0097] Table 2

[0098] As shown in Table 2, under the same electrolyte system, replacing the electrolyte with the customized anode of this invention, which features low OI and narrow particle size range, significantly improves high-current discharge voltage, cycle life, and low-temperature performance. Under the premise of the same anode material, the electrolyte of this invention, which is PC-free and contains LiDFOB and ternary additives, exhibits significantly better overall performance than existing similar formulations containing PC and LiFSI, as well as ordinary commercial electrolytes. Only the combination of the electrolyte and the proprietary secondary granulated graphite anode of this invention can simultaneously meet the stringent requirements of a minimum discharge voltage of ≥2.2V at 300A, a cycle life of ≥3000 cycles at 80% SOH, and a high-temperature storage recovery rate of ≥94%, demonstrating irreplaceable system synergistic advantages.

[0099] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An electrolyte, characterized in that, Based on the total mass of the electrolyte, the electrolyte comprises the following components by mass percentage: 20%~30% ethylene carbonate, 24.5%~35% diethyl carbonate, 25%~35% methyl ethyl carbonate, 2%~8% fluoroethylene carbonate, 8%~12% lithium hexafluorophosphate, 0.5%~2.5% lithium difluorooxalate borate, 1%~4% vinylene carbonate, 0.5%~2% 1,3-propanesulfonate lactone, and 0.5%~2% lithium difluorophosphate.

2. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is 22% to 28%; and / or, Based on the total mass of the electrolyte, the mass percentage of diethyl carbonate is 28% to 32%; and / or, Based on the total mass of the electrolyte, the mass percentage of methyl ethyl carbonate is 28% to 32%; and / or, Based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 4% to 6%.

3. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the lithium hexafluorophosphate accounts for 9% to 11% of the total mass; and / or, Based on the total mass of the electrolyte, the lithium difluorooxalate borate accounts for 1% to 2% of the total mass; and / or, Based on the total mass of the electrolyte, the mass percentage of vinylene carbonate is 2% to 3%; and / or, Based on the total mass of the electrolyte, the mass percentage of the 1,3-propanesulfonate lactone is 1% to 1.5%; and / or, Based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is 1% to 1.5%.

4. A battery, characterized in that, The battery comprises the electrolyte according to any one of claims 1 to 3.

5. The battery according to claim 4, characterized in that, The battery includes a negative electrode sheet, which comprises artificial graphite secondary particles.

6. The battery according to claim 5, characterized in that, The median particle size D of the artificial graphite 50 The thickness is 6µm to 18µm; and / or, The particle size distribution span factor (D) of the artificial graphite 90 -D 10 ) / D 50 ≤1.2, where D 90 D of the artificial graphite 90 Particle size, D 10 D of the artificial graphite 10 Particle size, D 50 The median particle size of the artificial graphite is given.

7. The battery according to claim 5, characterized in that, The artificial graphite includes a first artificial graphite and a second artificial graphite, wherein the median particle size D of the first artificial graphite is... 50 The median particle size D of the second artificial graphite is 14µm~18µm. 50 The value is 6µm to 8µm.

8. The battery according to claim 7, characterized in that, The mass ratio of the first artificial graphite to the second artificial graphite is (3~6):(4~7).

9. The battery according to claim 5, characterized in that, The OI value of the artificial graphite is ≤3.

10. The battery according to claim 4, characterized in that, The battery is a start-stop battery; and / or, The battery is a 12V or 48V automotive start-stop battery.

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