A battery

Abstract

This invention provides a battery. The battery includes a negative electrode sheet and an electrolyte; the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material and a nitrogen-containing inorganic material; the negative electrode active material includes a silicon-carbon material, wherein the silicon element in the silicon-carbon material accounts for not less than 25 wt% of the mass of the negative electrode active material layer; the electrolyte includes a cyclic carbonate, which includes fluoroethylene carbonate, wherein the fluoroethylene carbonate accounts for not less than 50 wt% of the mass of the cyclic carbonate; the mass percentage 'a wt%' of nitrogen element in the negative electrode active material layer satisfies: 0.03 wt% ≤ a wt% ≤ 2.82 wt%. The battery of this invention combines high energy density, cycle performance, and thermal safety performance.

Description

Technical Field

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

[0002] As the global energy structure transformation continues, rechargeable batteries have become a core energy storage component in new energy vehicles, portable consumer electronics, and large-scale energy storage systems. Their comprehensive performance directly determines the level of technological iteration and industrial competitiveness in related fields. To meet the application demands of long driving range for new energy vehicles, lightweight and thin consumer electronics, and high-capacity grid energy storage, continuously improving the energy density of rechargeable batteries has become a core technology development direction for the industry.

[0003] However, as battery energy density continues to increase, its cycle performance and thermal safety performance generally show significant degradation, making it difficult to achieve synergistic optimization of energy density, cycle stability, and operational safety. This has become a key bottleneck restricting the commercial application of high-energy-density rechargeable batteries. Currently, to improve battery energy density, the industry generally adopts high-specific-capacity anode materials and high-voltage cathode material systems. Taking high-silicon anodes as an example, their theoretical specific capacity is much higher than that of traditional graphite anodes, which can significantly improve battery capacity and energy density. However, they exhibit severe volume effects during charge and discharge, easily causing electrode structure damage and instability of the solid electrolyte interface, leading to rapid degradation of battery cycle life. At the same time, to further improve energy density, the operating voltage of cathode materials continues to increase. However, conventional electrolytes are prone to oxidative decomposition under high-voltage conditions, producing gases and corrosive byproducts. This not only damages the electrode interface structure and exacerbates cycle performance degradation but also significantly increases the risk of thermal runaway, seriously threatening battery thermal safety performance.

[0004] Therefore, developing batteries that balance high energy density, cycle performance, and thermal safety has become a critical technical challenge that urgently needs to be addressed in the field of rechargeable batteries. Summary of the Invention

[0005] This invention provides a battery that combines high energy density, cycle performance, and thermal safety performance.

[0006] This invention provides a battery, including a negative electrode and an electrolyte;

[0007] The negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material and nitrogen-containing inorganic substances.

[0008] The negative electrode active material includes silicon-carbon material, and the mass percentage of silicon in the negative electrode active material layer is not less than 25 wt%.

[0009] The electrolyte comprises a cyclic carbonate, which includes fluoroethylene carbonate, wherein the fluoroethylene carbonate constitutes not less than 50 wt% of the cyclic carbonate.

[0010] The mass percentage of nitrogen in the negative electrode active material layer, a wt%, satisfies the following condition: 0.03wt%≤a wt%≤2.82wt%.

[0011] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0012] (1) 15wt%≤bwt%≤50wt%, where bwt% is the mass percentage of the cyclic carbonate in the electrolyte;

[0013] (2)0.05wt%≤a≤1.7wt%;

[0014] (3) The nitrogen-containing inorganic material includes one or more of boron nitride, silicon nitride, aluminum nitride, and titanium nitride;

[0015] (4) The cyclic carbonates also include one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate.

[0016] In some embodiments of the present invention, the battery satisfies: 0.001 ≤ a / b ≤ 0.1;

[0017] And / or, the nitrogen-containing inorganic material has a mass percentage of 0.05wt% to 5wt% in the negative electrode active material layer; preferably, the nitrogen-containing inorganic material has a mass percentage of 0.1wt% to 3wt% in the negative electrode active material layer.

[0018] In some embodiments of the present invention, the electrolyte further includes a carboxylic acid ester, which includes at least one of ethyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trimethylacetate, methyl trimethylacetate, propyl trimethylacetate, ethyl trifluoroacetate, difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, trifluoroethyl acetate, propyl difluoroacetate, and difluoropropyl acetate.

[0019] Preferably, the carboxylic acid ester includes ethyl propionate, and the mass of ethyl propionate accounts for 10% to 40% of the total mass of the cyclic carbonate and the carboxylic acid ester.

[0020] In some embodiments of the present invention, the electrolyte further includes compound D, which includes compounds represented by formula I:

[0021] Formula I

[0022] R1, R2, and R3 are each independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon groups with 1 to 8 carbon atoms, or fluorine-substituted or unsubstituted hydroxyl groups with 1 to 8 carbon atoms. At least one of R1, R2, and R3 includes a fluorine atom, and R2 and R3 can exist independently or be linked together to form a ring.

[0023] In some embodiments of the present invention, the mass percentage (dwt%) of compound D in the electrolyte satisfies 1 wt% ≤ dwt% ≤ 30 wt%.

[0024] And / or, the mass ratio e of the compound D to the fluoroethylene carbonate satisfies 0.1 ≤ e ≤ 3;

[0025] And / or, the compound D comprises one or more of the compounds shown in Formulas I-1 to I-6:

[0026] Formula I-1 Formula I-2 Formula I-3

[0027] Formula I-4 Formula I-5 Formula I-6.

[0028] In some embodiments of the present invention, the electrolyte comprises a sulfur-containing compound, which includes one or more of the following: 1,3-propanesulfonyl lactone, 5-methyloxathiapentane 2,2-dioxide, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,3-butanesulfonyl lactone, fluoro-1,3-propanesulfonyl lactone, mannitol carbonate sulfate, 4-methyl ethylene sulfate, and vinyl sulfate.

[0029] Preferably, the mass percentage (fwt%) of the sulfur-containing compound in the electrolyte satisfies 0.1 wt% ≤ f ≤ 5 wt%.

[0030] In some embodiments of the present invention, the electrolyte further includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide; the mass percentage of lithium hexafluorophosphate in the electrolyte is gwt%; the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is hwt%; and the battery satisfies at least one of the following conditions:

[0031] (1)9wt%≤g wt%≤16wt%;

[0032] (2)0.5wt%≤h wt%≤10wt%;

[0033] (3) 1 ≤ g / h ≤ 20.

[0034] In some embodiments of the present invention, the sphericity of the silicon-carbon material is 0.85 to 0.99.

[0035] In some embodiments of the present invention, the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide material; preferably, the charging cut-off voltage of the battery is ≥4.55V.

[0036] The present invention provides a battery that can effectively improve the cycle performance and thermal safety performance by adding nitrogen-containing inorganic substances to the negative electrode active material layer of the high silicon content negative electrode and adding fluoroethylene carbonate to the electrolyte, and controlling the content of both. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0038] Figure 1 The graphs show the cyclic performance test results of Embodiment 1 and Comparative Example 1 of the present invention.

[0039] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] How to balance interfacial stability and compatibility with high-voltage electrolytes in a high-silicon anode system has become an urgent technical problem to be solved.

[0042] To address the aforementioned issues, this invention provides a battery comprising a negative electrode and an electrolyte. The negative electrode includes a negative electrode active material layer, which comprises a negative electrode active material and a nitrogen-containing inorganic substance. The negative electrode active material comprises a silicon-carbon material, wherein the mass percentage of silicon in the negative electrode active material layer is not less than 25 wt%. The electrolyte comprises a cyclic carbonate, which includes fluoroethylene carbonate, wherein the mass percentage of fluoroethylene carbonate in the cyclic carbonate is not less than 50 wt%. The mass percentage of nitrogen, a wt%, in the negative electrode active material layer satisfies the following condition: 0.03 wt% ≤ a wt% ≤ 2.82 wt%.

[0043] The battery of this invention adopts a synergistic configuration of negative electrode sheet and electrolyte, which can enhance the interfacial stability of the negative electrode active material layer under high silicon negative electrode conditions, and improve the compatibility of electrolyte with negative electrode interface by combining cyclic carbonate system containing fluorinated ethylene carbonate, thereby providing a foundation for improving the cycle stability, thermal safety and high energy density application of the battery.

[0044] In detail, the battery of this invention achieves high energy density, cycle performance, and thermal safety performance because: the silicon content of the negative electrode active material layer is not less than 25 wt%, which can improve the overall energy density of the battery. However, the high silicon content of the negative electrode active material will cause drastic volume changes during the cycle of repeated intercalation and deintercalation of active metal ions, which can easily cause cracking and damage to the SEI film on the negative electrode surface, thereby inducing continuous side reactions between the electrolyte and the negative electrode. To address this, this invention limits the mass proportion of fluoroethylene carbonate in the cyclic carbonate component of the electrolyte to not less than 50 wt%. On the one hand, this ensures the stable dissolution effect of the electrolyte salt on the electrolyte, and on the other hand, it can continuously repair the SEI film of the damaged high silicon negative electrode, thereby weakening the adverse effects of side reactions. However, the heat generation of high silicon system batteries is higher than that of graphite system batteries. In this case, fluoroethylene carbonate is prone to defluorination reaction to generate HF. As the content of fluoroethylene carbonate in the electrolyte increases, the defluorination reaction becomes more intense, and the formed HF will corrode the negative electrode and other components of the battery, thereby deteriorating the battery cycle and thermal safety performance. This invention adds nitrogen-containing inorganic materials to the negative electrode active material layer, controlling the mass percentage of nitrogen in the negative electrode active material layer within the range of 0.03wt% to 2.82wt%. On the one hand, the nitrogen-containing inorganic materials can effectively adsorb active substances such as fluoride ions and oxygen ions in the electrolyte, reducing the HF concentration in the electrolyte. The nitrogen-containing inorganic materials promote the stable formation of low-impedance, high-mechanical-strength, and heat-resistant inorganic compounds such as LiF and Li2O at the negative electrode interface, reducing the interface corrosion problem caused by HF. On the other hand, the presence of nitrogen-containing inorganic materials can work synergistically with the inorganic protective layer at the interface to limit the volume expansion of silicon-carbon materials during charging and discharging, reducing the possibility of SEI film detachment and failure, while accelerating heat dissipation in the negative electrode area and avoiding the risk of local hot spot accumulation, thereby effectively improving the cycle stability and thermal safety performance of the battery.

[0045] Specifically, the nitrogen element in the negative electrode active material layer mainly comes from nitrogen-containing inorganic substances.

[0046] The embodiments of this invention can use conventional testing methods and instruments in the art to test the mass ratio of silicon in the negative electrode active material layer, for example, by ash content testing. Specific steps include: discharging the secondary battery to 0% SOC, disassembling and removing the negative electrode sheet, immersing it in dimethyl carbonate (DMC) solvent for 12 hours, then rinsing with DMC to remove lithium salts adhering to the negative electrode sheet, drying it, and then treating the electrode sheet at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer can then be peeled off from the negative electrode current collector, and the negative electrode active material can be collected. In the silicon content test, a thermogravimetric analyzer (e.g., a TGA550 thermogravimetric analyzer) is used. The sample amount is 5-15 mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes, allowing the non-silicon components in the negative electrode material active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire test process is the ash content of the negative electrode active layer. Ignoring the mass percentage of trace impurities that may exist in the ash, and treating all the ash as silicon dioxide, the mass of silicon in the negative electrode active material can be calculated using the following formula: Mass percentage of silicon in the negative electrode active material layer = 7 × mass of ash / (15 × mass of test sample).

[0047] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the mass ratio of fluoroethylene carbonate in cyclic carbonates, for example, quantitative detection can be performed by gas chromatography-mass spectrometry (GC-MS) or high performance liquid chromatography (HPLC) external standard method.

[0048] The embodiments of this invention can employ conventional testing methods and instruments in the art to determine the mass percentage 'a' of nitrogen in the negative electrode active material layer. For example, the following method can be used: testing using transmission electron microscopy (TEM) combined with EDS and X-ray photoelectron spectroscopy (XPS). Specifically, after the battery is fully discharged, it can be disassembled, the negative electrode sheet separated, and a suitable sample of the negative electrode active material layer placed under a transmission electron microscope. Corresponding detection conditions (such as adjusting the accelerating voltage and magnification) are set, and combined with EDS, the distribution of nitrogen in the negative electrode active material layer is detected, and the mass percentage of nitrogen in the negative electrode active material layer is calculated. Alternatively, the negative electrode active material layer sample can be placed under an X-ray photoelectron spectrometer, and corresponding detection conditions (such as adjusting the X-ray source power and detection pass) can be set to detect the chemical state of nitrogen-containing functional groups (such as -C≡N, -CN-) in the negative electrode active material layer to determine their specific types.

[0049] For example, the mass percentage of silicon in the negative electrode active material layer may be 25 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, or 70 wt%, but is not limited to this.

[0050] For example, the mass percentage of fluoroethylene carbonate in the cyclic carbonate is, for example, 50 wt%, 55 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, 100 wt%, or any combination thereof.

[0051] For example, the mass percentage (a wt%) of nitrogen in the negative electrode active material layer may be 0.03wt%, 0.15wt%, 0.5wt%, 1.0wt%, 1.65wt%, 2.0wt%, 2.5wt%, 2.82wt%, or any combination thereof.

[0052] In some embodiments of the present invention, the battery satisfies at least one of the following conditions: (1) 15wt%≤bwt%≤50wt%, where bwt% is the mass percentage of the cyclic carbonate in the electrolyte; (2) 0.05wt%≤a≤1.7wt%; (3) the nitrogen-containing inorganic material includes one or more of boron nitride, silicon nitride, aluminum nitride, and titanium nitride; (4) the cyclic carbonate also includes one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate.

[0053] In some embodiments, 15wt% ≤ bwt% ≤ 50wt%, where bwt% is the mass percentage of cyclic carbonate in the electrolyte. By limiting the mass percentage bwt% of cyclic carbonate in the electrolyte to 15wt% to 50wt%, this embodiment of the invention achieves a better balance between film-forming ability, ionic conductivity, and low-temperature fluidity. Within this range, cyclic carbonate provides more interfacial film-forming precursors and further mitigates the effects of excessively high content, such as increased viscosity, decreased wettability, or exacerbated high-pressure oxidation side reactions, thus promoting synergistic stability between the high-silicon anode and the high-voltage cathode. For example, the value of bwt% may be 15wt%, 20wt%, 28wt%, 35wt%, 42wt%, 48wt%, 50wt%, or any combination thereof.

[0054] In some embodiments, 0.05wt% ≤ a ≤ 1.7wt%. By controlling the nitrogen content (a) in the negative electrode active material layer to between 0.05wt% and 1.7wt%, this invention can further enhance the skeleton strength of the negative electrode, further buffer the volume change of the silicon-carbon material, and better suppress interfacial side reactions, thereby improving the cycle and thermal safety performance of the battery. For example, the value of awt% is, for instance, a range of 0.05wt%, 0.2wt%, 0.6wt%, 1.0wt%, 1.3wt%, 1.7wt%, or any combination thereof.

[0055] In some embodiments, when the nitrogen-containing inorganic material includes one or more of boron nitride, silicon nitride, aluminum nitride, and titanium nitride, it can further enhance the skeleton reinforcement and heat protection of the negative electrode active material layer, and can better induce the formation of a stable SEI film of fluoroethylene carbonate, further suppress the defluorination of FEC, better reduce the HF content, and thus further improve the interface integrity and thermal safety during battery cycling. Preferably, the nitrogen-containing inorganic material includes boron nitride, which includes at least one of hexagonal boron nitride, cubic boron nitride, rhombohedral boron nitride, and wurtzite boron nitride; preferably, the boron nitride includes hexagonal boron nitride.

[0056] In some embodiments, when the cyclic carbonate further includes one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate, a more stable electrolyte-electrode interface is formed under high silicon anode and high voltage conditions, thereby better improving the cycle life and safety of the battery.

[0057] In some embodiments of the present invention, the electrolyte further includes chain carbonates, including ethyl methyl carbonate (EMC) and diethyl carbonate (DEC).

[0058] In some embodiments of the present invention, the battery satisfies: 0.001 ≤ a / b ≤ 0.1, where awt% is the mass percentage of nitrogen in the negative electrode active material layer, and bwt% is the mass percentage of cyclic carbonate in the electrolyte. By limiting 0.001 ≤ a / b ≤ 0.1, the content of nitrogen-containing inorganic matter in the negative electrode and fluoroethylene carbonate in the cyclic carbonate are synergistically adjusted, improving the problems of insufficient nitrogen source leading to inadequate reduction of HF in the electrolyte and insufficient interface repair, or excessive nitrogen source causing increased electrode impedance, thereby further improving the cycle performance and thermal safety performance of the battery. For example, the value of a / b is, for example, a range of 0.001, 0.005, 0.01, 0.05, 0.1, or any combination thereof.

[0059] In some embodiments, the nitrogen-containing inorganic material accounts for 0.05 wt% to 5 wt% of the negative electrode active material layer. This can better buffer the volume expansion of silicon-carbon materials during charge and discharge, and better reduce the erosion of the negative electrode surface by electrolyte side reactions, further improving the cycle performance and thermal safety performance of the battery. Preferably, the nitrogen-containing inorganic material accounts for 0.1 wt% to 3 wt% of the negative electrode active material layer, which provides the above-mentioned better effects. For example, the mass percentage of nitrogen-containing inorganic material in the negative electrode active material layer is, for example, 0.05 wt%, 0.5 wt%, 1.2 wt%, 2.5 wt%, 3.8 wt%, 5 wt%, or any combination thereof.

[0060] In some embodiments of the present invention, the electrolyte further includes a carboxylic acid ester, which includes at least one of ethyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trimethylacetate, methyl trimethylacetate, propyl trimethylacetate, ethyl trifluoroacetate, difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, trifluoroethyl acetate, propyl difluoroacetate, and difluoropropyl acetate. This further improves the lithium-ion transport efficiency and is beneficial for improving the cycle performance of the battery. Preferably, the carboxylic acid ester includes ethyl propionate, and the mass of ethyl propionate accounts for 10% to 40% of the total mass of the cyclic carbonate and the carboxylic acid ester, which is even more effective. For example, the mass ratio of ethyl propionate to the total mass of the cyclic carbonate and the carboxylic acid ester is, for example, 10%, 15%, 22%, 28%, 35%, 40%, or any combination thereof. The embodiments of the present invention can use conventional testing methods and instruments in the art to test the types of carboxylic esters in the electrolyte and the mass ratio of ethyl propionate to the total mass of cyclic carbonates and carboxylic esters. For example, quantitative and qualitative detection can be performed by gas chromatography-mass spectrometry (GC-MS) or high performance liquid chromatography (HPLC) with external standard method.

[0061] In some embodiments of the present invention, the electrolyte further includes compound D, which includes compounds represented by formula I:

[0062] Formula I

[0063] Among them, R1, R2, and R3 are each independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon groups with 1 to 8 carbon atoms, and fluorine-substituted or unsubstituted hydroxyl groups with 1 to 8 carbon atoms. At least one of R1, R2, and R3 includes a fluorine atom. R2 and R3 can exist independently or be connected to each other to form a ring. The strong electron-withdrawing effect of fluorine atoms can reduce the highest occupied orbital energy level of the molecule, further improving its antioxidant capacity under high voltage. At the same time, the nitrogen-containing inorganic substances in the negative electrode can better induce fluoroethylene carbonate (FEC) and compound D in the electrolyte to form a protective film with good thermal conductivity and ion conduction properties at the negative electrode, and further inhibit the defluorination of FEC, thereby better improving the cycle life and thermal safety performance of the battery.

[0064] In some embodiments of the present invention, the mass percentage (dwt%) of compound D in the electrolyte satisfies 1 wt% ≤ dwt% ≤ 30 wt%. This ratio better ensures that compound D has sufficient interfacial participation in the electrolyte system, further maintaining reasonable electrolyte viscosity and ion conductivity, and is more conducive to suppressing the occurrence of side reactions within the electrolyte, thereby better improving the cycle performance and thermal safety performance of the battery. For example, the mass percentage (dwt%) is, for example, a range of 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or any combination thereof.

[0065] In some embodiments, the mass ratio e of compound D to fluoroethylene carbonate (FEC) satisfies 0.1≤e≤3, which can better improve the cycle performance and thermal safety performance of the battery.

[0066] In some embodiments, compound D includes one or more of the compounds shown in Formulas I-1 to I-6:

[0067] Formula I-1 Formula I-2 Formula I-3

[0068] Formula I-4 Formula I-5 Formula I-6.

[0069] Compound D in this embodiment of the invention includes one or more of the compounds shown in Formulas I-1 to I-6, which can better improve the cycle performance and thermal safety performance of the battery.

[0070] In some embodiments of the present invention, the electrolyte includes a sulfur-containing compound, which includes one or more of the following: 1,3-propanesulfonyl lactone, 5-methyloxathiapentane 2,2-dioxide, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,3-butanesulfonyl lactone, fluoro-1,3-propanesulfonyl lactone, mannitol carbonate sulfate, 4-methyl ethylene sulfate, and vinyl sulfate. This compound can form a dense SEI film rich in sulfur on the surface of the silicon-carbon anode, further reducing the reductive decomposition of the electrolyte and better suppressing repeated interfacial rupture caused by the volume expansion of silicon particles, thereby further improving the cycle life, thermal stability, and adaptability under high-voltage conditions of the battery. Preferably, the mass percentage (fwt%) of the sulfur-containing compound in the electrolyte satisfies 0.1 wt% ≤ f ≤ 5 wt%, which further enhances the above effects. For example, the mass percentage (fwt%) of sulfur-containing compounds in the electrolyte may be, for example, 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any combination thereof.

[0071] In some embodiments of the present invention, the electrolyte further includes lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the mass percentage of lithium hexafluorophosphate in the electrolyte is gwt%; the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is hwt%; and the battery satisfies at least one of the following conditions:

[0072] (1)9wt%≤g wt%≤16wt%;

[0073] (2)0.5wt%≤h wt%≤10wt%;

[0074] (3) 1 ≤ g / h ≤ 20.

[0075] In this embodiment of the invention, the electrolyte adopts a lithium salt system composed of lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide. Lithium hexafluorophosphate is used to provide basic lithium-ion conductivity, while lithium bis(trifluoromethanesulfonyl)imide is used to further improve the high voltage stability of the battery and the stable formation of the interface film, thereby helping to better improve the thermal safety performance of the battery.

[0076] In some embodiments, 9wt% ≤ g wt% ≤ 16wt% can address the issue of insufficient conductivity while ensuring sufficient ion carriers, although excessively high values ​​may lead to increased viscosity and polarization. Preferably, this range is advantageous for balancing rate performance and cycle stability. For example, gwt% values ​​may be, for instance, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, or any combination thereof.

[0077] In some embodiments, 0.5 wt% ≤ h wt% ≤ 10 wt% can leverage the high thermal stability and oxidation resistance of lithium bis(trifluoromethanesulfonyl)imide to enhance high-voltage compatibility, while further mitigating the increased cost and corrosion risk to the current collector caused by excessive use, thereby better improving the battery's cycle performance and thermal safety. For example, the value of hwt% can be, for instance, a range of 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, or any combination thereof.

[0078] In some embodiments, 1 ≤ g / h ≤ 20 allows for an appropriate ratio of lithium hexafluorophosphate to lithium bis(trifluoromethanesulfonyl)imide, thereby better regulating the electrolyte's dissociation capacity and interfacial film-forming characteristics, and further improving the battery's cycle performance and thermal safety. For example, the g / h value may be a range of 1, 3, 5, 7, 10, 12, 15, 18, 20, or any combination thereof.

[0079] In some embodiments of the present invention, the electrolyte comprises a nitrile compound, including one or more of the following: benzonitrile, p-toluenenitrile, 3,5-difluorobenzonitrile, adiponitrile, succinic acid, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, 1,2,4-butanetrionitrile, 1,2,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, ethylene glycol di(2-cyanoethyl) ether, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, ethylene glycol di(4-cyanobutyl) ether, and ethylene glycol (bis)propionitrile ether, 1,2,3-tris(2-cyanooxy)propane, tris(2-cyanoethyl)phosphine, and tris(2-cyanoethyl)phosphine oxide;

[0080] In some embodiments, the nitrile compound constitutes a mass percentage of 0.1 wt% to 6 wt% in the electrolyte, which can further improve the cycle performance and thermal safety performance of the battery. For example, the mass percentage of the nitrile compound in the electrolyte may be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, or any combination thereof.

[0081] In some embodiments of the present invention, the electrolyte includes lithium salt additives, which include one or more of lithium difluorophosphate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(oxalate) phosphate, which is beneficial to further improve the cycle performance of the battery.

[0082] In some embodiments, the lithium salt additive is present in the electrolyte at a mass percentage of 0.01 wt% to 3 wt%, which can further improve the cycle performance and thermal safety performance of the battery. For example, the mass percentage of the lithium salt additive in the electrolyte is, for instance, 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, or any combination thereof.

[0083] In some embodiments of the present invention, the sphericity of the silicon-carbon material is 0.85~0.99. Sphericity reflects the degree to which the particle shape is close to an ideal sphere; the higher the value, the more rounded the particles are. By limiting it to this range and adding nitrogen-containing inorganic materials, especially hexagonal boron nitride, to the negative electrode, the layered structure of hexagonal boron nitride is easier to achieve adhesion and uniform coating on the surface of silicon-carbon with high sphericity. This can better buffer the volume expansion of the silicon-carbon material, further suppress electrolyte decomposition, thereby constructing a more stable interface. It can also make the particles more uniformly stressed during electrode rolling and charge-discharge volume changes, further reducing stress concentration and local cracking at the corners, and thus better improving the cycle performance of the battery. The sphericity of silicon-carbon materials can be tested using conventional testing methods and instruments in the art. For example, after discharging a lithium-ion secondary battery to 0% SOC, the negative electrode is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours and rinsed with DMC to remove the lithium salt adhering to the electrode. The negative electrode active material layer is then rinsed off the electrode with deionized water. After ultrasonication, the filtrate is removed by centrifugation and then dried. The resulting powder is observed using a scanning electron microscope in backscatter mode. In this mode, the silicon-carbon particles have a brighter contrast, which can distinguish them from graphite and conductive carbon. By analyzing the images of brighter particles in an SEM image at a certain magnification (e.g., 2500x) using image processing software (such as Image Pro Plus), the perimeter and area of ​​each particle are obtained. The equivalent radius r1 of the perimeter and the equivalent radius r2 of the area of ​​each particle are calculated. Then, the sphericity of each particle is S = r2 / r1. Finally, the sphericity of each particle is weighted and averaged (at least 50) to obtain the average sphericity of the silicon-carbon material in the negative electrode.

[0084] In some embodiments of the present invention, the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide material, which is beneficial to further improve the energy density and high voltage performance of the battery.

[0085] In some embodiments, the charging cutoff voltage of the battery is greater than or equal to 4.55V, for example, it can be any one of 4.55V, 4.56V, 4.57V, 4.58V, 4.6V, or 4.65V.

[0086] In this embodiment of the invention, the battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell is a wound battery cell, meaning that the battery cell is formed by stacking and winding the positive electrode, separator, and negative electrode.

[0087] As mentioned above, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. Specifically, the positive active material layer can be provided on one side surface in the thickness direction of the positive current collector, or positive active material layers can be provided on both opposite sides surface in the thickness direction of the positive current collector.

[0088] The positive electrode active material layer includes positive electrode active material, positive electrode conductive agent and positive electrode binder. In the positive electrode active material layer, the mass percentage of positive electrode active material can be 80% to 99%, the mass fraction of positive electrode conductive agent can be 0.5% to 10%, and the mass fraction of positive electrode binder can be 0.5% to 10%.

[0089] In this embodiment of the invention, the positive electrode conductive agent in the positive electrode active layer can be a conventional conductive material in the art. For example, the positive electrode conductive agent in the positive electrode active layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0090] In this embodiment of the invention, the positive electrode binder in the positive electrode active layer can be a conventional bonding material in the art. For example, the positive electrode binder in the positive electrode active layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0091] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0092] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be provided on one side surface of the negative electrode current collector, or negative electrode active material layers can be provided on both opposite sides of the negative electrode current collector in the thickness direction.

[0093] Specifically, the negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. For example, the negative electrode active material may also include carbon-based materials, which may include at least one of graphite, hard carbon, soft carbon, etc. The negative electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber. The negative electrode binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0094] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0095] In this embodiment of the invention, the separator is used to separate the positive and negative electrode plates, preventing short circuits caused by contact between them. Conventional separators in the art can be used in this embodiment, and there are no particular limitations. For example, the separator material can be one or more of the following: high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0096] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0097] This invention also provides an electrical device including the battery described above. This electrical device has advantages corresponding to the electrolyte described above, which will not be elaborated further.

[0098] The electrical equipment used in the embodiments of this invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic devices (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations. The technical solution of this invention will be further described below with reference to specific embodiments.

[0099] Example 1

[0100] The battery in this embodiment is prepared by the following method:

[0101] 1) Preparation of positive electrode sheet: Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (superP) and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) is added and the mixture is stirred under vacuum until the mixture becomes a uniform and fluid positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of a 9μm aluminum foil. The coated aluminum foil is dried and then rolled and slit to obtain the desired positive electrode sheet.

[0102] 2) Negative electrode preparation: Artificial graphite (negative electrode active material), silicon carbide (sphericity 0.9), nitrogen-containing compound (specifically hexagonal boron nitride), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 20:74:0.5:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both surfaces of a copper foil. The coated copper foil was air-dried at room temperature, then transferred to an 80℃ oven for 10 hours. After cold pressing, slitting, cleaning, and sheet forming, the negative electrode sheet was obtained.

[0103] 3) Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 25 wt% of cyclic carbonates (including 60 wt% fluoroethylene carbonate and 40 wt% ethylene carbonate and propylene carbonate in a 1:1 mass ratio) and 59.5 wt% of carboxylic acid esters (ethyl propionate and propyl propionate) based on the total mass of the electrolyte were uniformly mixed. Then, 13 wt% of LiPF6 based on the total mass of the electrolyte was added and dissolved. Next, 2.5 wt% of a sulfur-containing additive (specifically mannitol sulfate) based on the total mass of the electrolyte was added. The specific types and amounts are shown in Table 1. After thorough mixing, the electrolyte was obtained after passing moisture and free acid tests. The content of ethyl propionate accounted for 15% of the total content of carboxylic acid esters and cyclic carbonates.

[0104] The differences between Examples 2-10, Comparative Examples 1-4 and Example 1 are as follows: the types of nitrogen-containing inorganic materials, the mass percentage of silicon in the negative electrode active material layer (referred to as silicon content in the table), the types of cyclic carbonates, the mass percentage of fluoroethylene carbonate in cyclic carbonates (referred to as FEC content in the table), the mass percentage of nitrogen in the negative electrode active material layer (a wt%), the mass percentage of cyclic carbonates in the electrolyte (b wt%), a / b, and the mass percentage of nitrogen-containing inorganic materials in the negative electrode active material layer (referred to as nitrogen-containing inorganic material percentage in the table). See Table 1 for details. " / " indicates that it does not exist.

[0105]

[0106] The differences between Examples 11-13 and Example 1 are as follows: the mass percentage of cyclic carbonates in the electrolyte (bwt%), a / b, the mass percentage of nitrogen-containing inorganic matter in the negative electrode active material layer (referred to as nitrogen-containing inorganic matter percentage in the table), the type of carboxylic acid ester, and the mass percentage of ethyl propionate in the total mass of cyclic carbonates and carboxylic acid esters (referred to as ethyl propionate content in the table). See Table 2 for details.

[0107]

[0108] The differences between Examples 14-26 and Example 1 are as follows: the type of compound D, the mass percentage of compound D in the electrolyte (dwt%), the mass ratio of compound D to fluoroethylene carbonate (e), the type of sulfur-containing compound, the mass percentage of sulfur-containing compound in the electrolyte (fwt%), the mass percentage of lithium hexafluorophosphate in the electrolyte (gwt%), the mass percentage of lithium bis(trifluoromethanesulfonylimide) in the electrolyte (hwt%), g / h, and the sphericity of the silicon-carbon material. See Table 3 for details.

[0109]

[0110] The differences between Examples 27-29 and Example 1 are detailed in Table 4.

[0111]

[0112] In Examples 2-26 and Comparative Examples 1-5, when the components in the electrolyte are increased or decreased, the increased or decreased portions are adjusted by deducting or adding the corresponding carboxylic acid esters.

[0113] Test case

[0114] Preparation of lithium-ion batteries: The positive electrode sheet from step 1) and the negative electrode sheet from step 2) of the above embodiments and comparative examples are stacked in the order of positive electrode sheet, separator, negative electrode sheet, and separator. The number of stacked negative electrode sheets is 26, resulting in a battery cell. The battery cell is then placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting processes, a lithium-ion battery is obtained. The charge / discharge range of the battery of this invention is 2.8-4.58V.

[0115] The lithium-ion batteries obtained in the examples and comparative examples were subjected to battery ED calibration, 45°C cycle performance test and hot box safety performance (thermal safety performance) test, respectively.

[0116] Battery ED (volume energy density) calibration: The batteries obtained in the examples and comparative examples were discharged at 25±3℃ at 0.2C to the cutoff voltage of 2.8V, allowed to stand for 5 minutes, and their volume was measured. They were then fully charged to 4.58V using the standard 0.5C charging method, with a cutoff current of 0.02C, and discharged at 0.2C to 2.8V. This constitutes one charge-discharge cycle. The ratio of the highest discharge energy to the volume after three cycles was recorded as the battery's ED. The test results are shown in Table 5.

[0117] 45℃ Cycling Performance Test: The batteries obtained in the examples and comparative examples were discharged to 2.8V at 0.5C at 45±3℃. Then, they were charged at a constant current of 2.5C to a voltage of 4.58V, and then charged at a constant voltage of 4.58V to a current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 2.5C to a voltage of 2.8V. This constitutes one charge-discharge cycle. The discharge capacity of the first week is recorded as x mAh, and the discharge capacity of the Nth week is recorded as y mAh. The capacity of the Nth week is divided by the capacity of the first week to obtain the cycle capacity retention rate R = y / x. The capacity retention rate of the battery after 500 cycles is recorded. The test results are shown in Table 5. The cycle performance test results of Example 1 and Comparative Example 1 are as follows: Figure 1 As shown, by Figure 1 It can be seen that Example 1 (Example-1#) has better cycle performance than Comparative Example 1 (Comparative Example-1#).

[0118] Hot Box Safety Performance Test: The batteries obtained in the examples and comparative examples were discharged to 2.8V at 0.2C at 25±3℃, charged to 4.58V at a constant current of 0.5C, and then charged to 0.02C at a constant voltage of 4.58V. After standing for 5 minutes, the batteries were placed in an oven and heated at a rate of 3±2℃ / min. When the temperature inside the oven reached 130℃±2℃, it was kept constant for 60 minutes. The number of batteries that caught fire / exploded / smoke was recorded. Batteries that did not catch fire / explode / smoke passed the test. Ten batteries were tested, and if none of the ten batteries caught fire / exploded / smoke, they all passed, recorded as 10Pass / 10Test, abbreviated as 10 / 10. The test results are shown in Table 5.

[0119]

[0120] As shown in Table 5, compared with the comparative example, the embodiments of the present invention can effectively improve the cycle performance and thermal safety performance of the battery by adding nitrogen-containing inorganic substances to the negative electrode active material layer of the high silicon content negative electrode and adding fluoroethylene carbonate to the electrolyte, and controlling the content of both.

[0121] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to what has been described above. Various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A battery, characterized by, Including negative electrode and electrolyte; The negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material and nitrogen-containing inorganic matter. The negative electrode active material includes silicon-carbon material, and the mass percentage of silicon in the negative electrode active material layer is not less than 25 wt%. The electrolyte comprises a cyclic carbonate, which includes fluoroethylene carbonate, wherein the fluoroethylene carbonate constitutes not less than 50 wt% of the cyclic carbonate. The mass percentage of nitrogen in the negative electrode active material layer, a wt%, satisfies the following condition: 0.03wt%≤a wt%≤2.82wt%.

2. The battery of claim 1, wherein, The battery satisfies at least one of the following conditions: (1) 15wt%≤bwt%≤50wt%, where bwt% is the mass percentage of the cyclic carbonate in the electrolyte; (2)0.05wt%≤a≤1.7wt%; (3) The nitrogen-containing inorganic material includes one or more of boron nitride, silicon nitride, aluminum nitride, and titanium nitride; (4) The cyclic carbonates also include one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate.

3. The battery of claim 2, wherein, The battery satisfies: 0.001 ≤ a / b ≤ 0.1; And / or, the nitrogen-containing inorganic material has a mass percentage of 0.05wt% to 5wt% in the negative electrode active material layer; preferably, the nitrogen-containing inorganic material has a mass percentage of 0.1wt% to 3wt% in the negative electrode active material layer.

4. The battery according to any one of claims 1-3, characterized in that, The electrolyte also includes carboxylic acid esters, which include at least one of ethyl propionate, propyl propionate, ethyl difluoroacetate, ethyl trimethylacetate, methyl trimethylacetate, propyl trimethylacetate, ethyl trifluoroacetate, difluoroethyl acetate, ethyl monofluoroacetate, monofluoroethyl acetate, trifluoroethyl acetate, propyl difluoroacetate, and difluoropropyl acetate. Preferably, the carboxylic acid ester includes ethyl propionate, and the mass of ethyl propionate accounts for 10% to 40% of the total mass of the cyclic carbonate and the carboxylic acid ester.

5. The battery according to any one of claims 1-4, characterized in that, The electrolyte further includes compound D, which includes the compound shown in Formula I: Equation I R1, R2, and R3 are each independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon groups with 1 to 8 carbon atoms, or fluorine-substituted or unsubstituted hydroxyl groups with 1 to 8 carbon atoms. At least one of R1, R2, and R3 includes a fluorine atom, and R2 and R3 can exist independently or be linked together to form a ring.

6. The battery according to claim 5, characterized in that, The mass percentage (dwt%) of compound D in the electrolyte satisfies 1 wt% ≤ dwt% ≤ 30 wt%. And / or, the mass ratio e of the compound D to the fluoroethylene carbonate satisfies 0.1 ≤ e ≤ 3; And / or, the compound D comprises one or more of the compounds shown in Formulas I-1 to I-6: Formula I-1 Formula I-2 Formula I-3 Formula I-4 Formula I-5 Formula I-6.

7. The battery according to any one of claims 1-6, characterized in that, The electrolyte comprises a sulfur-containing compound, which includes one or more of the following: 1,3-propanesulfonyl lactone, 5-methyloxathiapentane 2,2-dioxide, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,3-butanesulfonyl lactone, fluoro-1,3-propanesulfonyl lactone, mannitol carbonate sulfate, 4-methyl ethylene sulfate, and vinyl sulfate. Preferably, the mass percentage (fwt%) of the sulfur-containing compound in the electrolyte satisfies 0.1 wt% ≤ f ≤ 5 wt%.

8. The battery according to any one of claims 1-7, characterized in that, The electrolyte further includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide; the mass percentage of lithium hexafluorophosphate in the electrolyte is gwt%; the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is hwt%; the battery satisfies at least one of the following conditions: (1)9wt%≤g wt%≤16wt%; (2)0.5wt%≤h wt%≤10wt%; (3) 1 ≤ g / h ≤ 20.

9. The battery according to any one of claims 1-8, characterized in that, The sphericity of the silicon-carbon material is 0.85~0.

99.

10. The battery according to any one of claims 1-9, characterized in that, The battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium cobalt oxide material; preferably, the charging cut-off voltage of the battery is ≥4.55V.

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