An electrolyte, a battery

Abstract

This invention provides an electrolyte and a battery. The electrolyte comprises a haloalkane and a polycyclic sulfate, wherein the haloalkane includes at least one fluorine atom, and the polycyclic sulfate includes at least two cyclic structures. The electrolyte exhibits good stability and low-temperature ionic conductivity, thus improving both the battery's cycle performance and thermal safety at high and low temperatures.

Description

Technical Field

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

[0002] With the increasing range of electric vehicles and the pursuit of energy density in energy storage systems, high-voltage lithium-ion batteries have become a research hotspot.

[0003] High-voltage systems (e.g., above 4.5V) can significantly improve battery energy density, but they place higher demands on electrolyte stability. In high-voltage cathode systems, electrolyte oxidation and decomposition, as well as interfacial side reactions, further exacerbate battery capacity decay. Furthermore, the performance bottleneck of the electrolyte is particularly pronounced in high-voltage batteries under extreme temperature conditions (e.g., 0°C or 45°C): at low temperatures, electrolyte viscosity increases and ionic conductivity decreases, hindering lithium-ion transport; at high temperatures, the electrolyte is prone to oxidation and decomposition, accelerating the rupture and reconstruction of the SEI film, leading to continuous consumption of active lithium.

[0004] Therefore, developing a high-voltage silicon-carbon lithium-ion battery that can balance long cycle life and safety over a wide temperature range is a technical challenge that urgently needs to be solved in the current new energy field. Summary of the Invention

[0005] This invention provides an electrolyte and a battery. The electrolyte has good stability and low-temperature ionic conductivity, which can improve the battery's cycle performance and thermal safety performance at both high and low temperatures.

[0006] This invention provides an electrolyte comprising a haloalkane and a polycyclic sulfate, wherein the haloalkane comprises at least one fluorine atom and the polycyclic sulfate comprises at least two cyclic structures.

[0007] In some embodiments of the present invention, the electrolyte satisfies at least one of the following conditions:

[0008] (1) The mass percentage (Awt%) of the haloalkane in the electrolyte satisfies: 1wt%≤Awt%≤50wt%; preferably, 3wt%≤Awt%≤30wt%;

[0009] (2) The mass percentage of the polycyclic sulfate in the electrolyte is Bwt% and satisfies: 0.1wt%≤Bwt%≤5wt%; preferably, 0.5wt%≤Bwt%≤5wt%;

[0010] (3) The number of carbon atoms in the haloalkane is 3 to 6;

[0011] (4) The polycyclic sulfate includes at least one of bicyclic sulfate compounds and tricyclic sulfate compounds.

[0012] In some embodiments of the present invention, the haloalkane includes one or more of the following: 1-fluoropropane, 1-fluorobutane, 1-fluoropentane, 1-fluorohexane, 1,3-difluoropropane, 1,4-difluorobutane, 1,5-difluoropentane, 1,6-difluorohexane, 1-fluoro-3-chlorobutane, 1-fluoro-4-chlorobutane, 1-fluoro-3-bromobutane, and 1-fluoro-4-bromobutane.

[0013] And / or, the polycyclic sulfate comprises one or more compounds represented by formulas I to IX:

[0014] Formula I Formula II Formula III Formula IV

[0015] Formula V Formula VI Formula VII Formula VIII

[0016] Formula IX;

[0017] And / or, 1≤A / B≤50.

[0018] In some embodiments of the present invention, the electrolyte further includes a non-fluorinated cyclic carbonate, wherein the non-fluorinated cyclic carbonate accounts for a mass percentage (Cwt) in the electrolyte; and the electrolyte satisfies at least one of the following conditions:

[0019] (1) 0.5 ≤ C / A ≤ 25;

[0020] (2) 3wt%≤C wt%≤50wt%; preferably, 10wt%≤C wt%≤40wt%.

[0021] In some embodiments of the present invention, the electrolyte further includes a first additive, which includes one or more of lithium difluorophosphate, lithium tetrafluoroborate, vinyl sulfate, methyl vinyl sulfate, 1-propylphosphonic anhydride, and 1-butylphosphonic anhydride; preferably, the mass percentage of the first additive in the electrolyte is 0.05wt% to 5wt%.

[0022] In some embodiments of the present invention, the electrolyte further includes fluorocarboxylic acid esters, which include at least one of ethyl fluoroacetate, ethyl fluorobutyrate, methyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, and propyl fluoropropionate, wherein the ethyl fluoroacetate includes 2,2-difluoroethyl acetate; preferably, the mass percentage of fluorocarboxylic acid esters in the electrolyte is 5wt% to 55wt%.

[0023] This invention also provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises the electrolyte described above.

[0024] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon material, and the battery satisfies at least one of the following conditions:

[0025] (1) The average sphericity of the silicon-carbon material is 0.8~0.99;

[0026] (2) The particle size Dv50 of the silicon carbide material is 1μm~15μm;

[0027] (3) The mass percentage of silicon in the negative electrode active material layer is 2wt%~50wt%;

[0028] (4) The silicon-carbon material includes a porous carbon matrix and silicon material deposited in the carbon matrix.

[0029] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0030] (1) The silicon-carbon material includes nitrogen, and the mass percentage of nitrogen in the silicon-carbon material is 0.01 wt% to 5 wt%;

[0031] (2) The silicon-carbon material includes a coating layer, which includes at least one of amorphous carbon, carbon nanotubes, and conductive polymers.

[0032] In some embodiments of the present invention, the areal density of the negative electrode active material layer on one side is 3 mg / cm³. 2 ~16mg / cm 2 .

[0033] The present invention provides an electrolyte and a battery by adding haloalkanes and polycyclic sulfates to the electrolyte. The haloalkanes include at least one fluorine atom, and the polycyclic sulfates include at least two cyclic structures. The two work together to enable the electrolyte to maintain good ionic conductivity at low temperatures and good stability at high temperatures, thereby helping to improve the cycle performance and thermal safety performance of the battery at both high and low temperatures. Detailed Implementation

[0034] 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.

[0035] In high-voltage charge-discharge systems, to further improve range, operating time, and energy storage efficiency within limited volume or weight, batteries typically employ high-voltage positive electrodes or high-specific-capacity negative electrodes. Among these, silicon-carbon negative electrodes have become a key application area due to their high theoretical capacity. For new energy vehicles, batteries need to remain stable under conditions such as low-temperature vehicle starting in winter, long-term operation in high-temperature summer, fast charging and discharging, and long-cycle operation. For consumer electronics, batteries need to balance charging efficiency and lifespan while maintaining high energy density and a slim design. Therefore, electrolytes suitable for high-voltage silicon-carbon systems must not only maintain good ion migration capabilities at low temperatures but also maintain high oxidation and interfacial stability at high temperatures, thereby supporting the reliable operation of the entire battery under complex operating conditions.

[0036] However, in high-voltage silicon-carbon systems, the silicon-carbon anode undergoes significant volume changes during charge and discharge, causing the interface film already formed on its surface to easily crack, detach, and repeatedly reconstruct. This continuously consumes electrolyte and active lithium, increasing battery internal resistance, decreasing reversible capacity, and accelerating cycle life decay. On the other hand, the higher potential at the positive electrode under high-voltage conditions makes the electrolyte more susceptible to oxidative decomposition. The resulting byproducts not only worsen the interfacial chemical environment but also further affect the overall battery's thermal stability and safety. Meanwhile, the demand for wide-temperature applications amplifies these problems. In low-temperature environments, the viscosity of traditional organic electrolytes increases significantly, lithium-ion diffusion and migration rates decrease, and electrode interface reaction kinetics deteriorate, easily leading to increased polarization, decreased discharge capacity, and even increased risk of lithium plating. In high-temperature environments, electrolyte decomposition reactions and interfacial side reactions are significantly exacerbated, resulting in a loose, unstable, or even failed interfacial film structure. More critically, existing solutions often struggle to simultaneously achieve both low-temperature (e.g., around 0°C) transport performance and high-temperature (e.g., around 45°C) stability. If the focus is on reducing viscosity to improve low-temperature performance, oxidation stability and interfacial stability at high temperatures are often sacrificed. Conversely, if the focus is on enhancing film formation and high-temperature protection, higher interfacial impedance is easily introduced, which is detrimental to ion transport under low-temperature conditions. Therefore, existing high-voltage silicon-carbon battery electrolyte technologies generally suffer from the problem of balancing ion transport and interfacial stability over a wide temperature range, making it difficult to meet the practical requirements for long-term stable operation of high-energy-density batteries.

[0037] In view of this, how to balance the ion transport capability over a wide temperature range and the stability of the electrolyte in a high-voltage silicon-carbon system in order to improve the cycle performance and thermal safety of the battery under high and low temperature conditions has become an urgent technical problem to be solved.

[0038] To address the aforementioned problems, embodiments of the present invention provide an electrolyte comprising a haloalkane and a polycyclic sulfate, wherein the haloalkane comprises at least one fluorine atom and the polycyclic sulfate comprises at least two cyclic structures.

[0039] This invention provides an electrolyte comprising a haloalkane and a polycyclic sulfate, wherein the haloalkane comprises at least one fluorine atom and the polycyclic sulfate comprises at least two cyclic structures.

[0040] When the electrolyte of the present invention includes the above-mentioned components, it can simultaneously improve the ion transport capability and stability of the electrolyte over a wide temperature range, thereby improving the high-temperature cycle performance, low-temperature cycle performance and thermal safety performance of the battery.

[0041] Specifically, the electrolyte of this invention comprises a haloalkane containing at least one fluorine atom and a polycyclic sulfate containing at least two cyclic structures. The fluorinated haloalkane molecule possesses high-energy carbon-fluorine bonds, exhibiting excellent chemical stability in high-voltage electrochemical environments. It can also reduce electrolyte viscosity at low temperatures and increase ionic conductivity, enhancing the transport capacity of lithium ions in the liquid phase. Compared to monocyclic sulfates, the polycyclic sulfate with at least two cyclic structures exhibits stronger spatial rigidity, higher interfacial adsorption capacity, and better film-forming stability. Its multi-cyclic structure enables multi-site interactions between the molecule and the electrode surface, adapting to the volume expansion and contraction during the charging and discharging process of the silicon-carbon anode, facilitating... It can form an interface film with higher coverage and better continuity. When haloalkanes and polycyclic sulfates are used together, haloalkanes first wet the electrode surface and form a loose and porous basic SEI framework, which ensures the rapid transport of lithium ions at the interface under low temperature conditions. However, the film layer formed by it has micro-defects and poor stability at high temperature. In contrast, polycyclic sulfates preferentially adsorb onto the electrode surface during charge and discharge, accurately fill and passivate the micro-defects of the haloalkan film layer, and can construct a gradient composite interface film with a loose and low impedance inner layer and a dense and highly stable outer layer. This not only further improves the low temperature cycle of the battery, but also improves the high temperature cycle and thermal safety performance of the battery.

[0042] In this embodiment of the invention, the electrolyte is preferably used in lithium-ion batteries, and is particularly suitable for high-voltage silicon-carbon lithium-ion batteries.

[0043] The components and content of the electrolyte described above can be tested using conventional testing methods and instruments in the art, such as gas chromatography-mass spectrometry (GC-MS). Furthermore, the above tests can also be performed on batteries containing the electrolyte of this invention; the results from both methods are similar and within acceptable error ranges.

[0044] In some embodiments of the present invention, the electrolyte satisfies at least one of the following conditions:

[0045] (1) The mass percentage (Awt%) of haloalkanes in the electrolyte satisfies: 1wt%≤Awt%≤50wt%; preferably, 3wt%≤Awt%≤30wt%;

[0046] (2) The mass percentage of polycyclic sulfate in the electrolyte is Bwt% satisfying: 0.1wt%≤Bwt%≤5wt%; preferably, 0.5wt%≤Bwt%≤5wt%;

[0047] (3) Haloalkanes have 3 to 6 carbon atoms;

[0048] (4) Polycyclic sulfates include at least one of bicyclic sulfate compounds and tricyclic sulfate compounds.

[0049] In some embodiments, the mass percentage (Awt%) of haloalkanes in the electrolyte satisfies: 1wt% ≤ Awt% ≤ 50wt%. By controlling the haloalkanes between 1wt% and 50wt%, this embodiment of the invention can better balance low-temperature fluidity and interfacial film formation ability while ensuring the system's ability to dissolve lithium salts and wet the electrode, thereby further improving the battery's high-temperature cycle performance, low-temperature cycle performance, and thermal safety performance. For example, the mass percentage (Awt%) of haloalkanes in the electrolyte may be, for example, 1 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, or any combination thereof.

[0050] In some embodiments, the mass percentage of polycyclic sulfates in the electrolyte, Bwt%, satisfies the condition: 0.1wt% ≤ Bwt% ≤ 5wt%. This allows them to preferentially participate in the negative electrode interface reaction as a highly active film-forming component. While ensuring low system impedance, this better promotes the formation of a dense and stable interface film, thereby better suppressing film rupture and side reactions caused by volume changes in the silicon-carbon negative electrode, and ultimately improving battery safety. For example, the mass percentage of polycyclic sulfates in the electrolyte, Bwt%, may be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any combination thereof. Preferably, 0.5 wt% ≤ Bwt% ≤ 5 wt% provides even better results.

[0051] In some embodiments, the number of carbon atoms in the haloalkane is 3 to 6, which allows for a better balance between volatility, viscosity, and interfacial adsorption capacity. This enables the electrolyte to maintain a more compact solvation structure while retaining lower ion transport resistance, thereby improving the battery's low-temperature cycling performance. For example, the number of carbon atoms in the haloalkane may be 3, 4, 5, 6, or any combination thereof.

[0052] In some embodiments, polycyclic sulfates include at least one of bicyclic sulfate compounds and tricyclic sulfate compounds, wherein the bicyclic or tricyclic structure further enhances the molecular rigidity and preferential adsorption capacity of the polycyclic sulfate, making it easier to form an oxidation-resistant and heat-resistant protective layer under high voltage conditions, thereby better improving the high-temperature cycle performance and thermal safety performance of the battery.

[0053] In some embodiments of the present invention, the halogenated alkanes include one or more of 1-fluoropropane, 1-fluorobutane, 1-fluoropentane, 1-fluorohexane, 1,3-difluoropropane, 1,4-difluorobutane, 1,5-difluoropentane, 1,6-difluorohexane, 1-fluoro-3-chlorobutane, 1-fluoro-4-chlorobutane, 1-fluoro-3-bromobutane, and 1-fluoro-4-bromobutane, which can further balance the low-temperature fluidity and interfacial film-forming activity of the electrolyte, thereby better improving the low-temperature cycle performance of the battery.

[0054] In some embodiments, polycyclic sulfates include one or more compounds represented by formulas I to IX:

[0055] Formula I Formula II Formula III Formula IV

[0056] Formula V Formula VI Formula VII Formula VIII

[0057] Formula IX.

[0058] The aforementioned polycyclic sulfates are more likely to participate in the construction of the interfacial film under high voltage, thereby further inhibiting the continuous oxidative decomposition of the electrolyte, better mitigating the film cracking and reconstruction caused by the volume change of the silicon-carbon anode, and thus better improving the thermal safety performance of the battery.

[0059] In some embodiments, 1 ≤ A / B ≤ 50 is beneficial for balancing the interfacial film formation effect and the ion transport capability of the electrolytic liquid phase, better achieving a synergistic balance between ion conduction, interfacial protection, and wide temperature adaptability, and further improving the cycle life and safety of the battery over a wide temperature range. For example, the value of A / B may be 1, 2, 5, 7, 10, 15, 20, 25, 30, 40, 50, or any combination thereof.

[0060] In some embodiments of the present invention, the electrolyte further includes a non-fluorinated cyclic carbonate, wherein the non-fluorinated cyclic carbonate accounts for a mass percentage (Cwt) in the electrolyte; the electrolyte satisfies at least one of the following conditions:

[0061] (1) 0.5 ≤ C / A ≤ 25;

[0062] (2) 3wt%≤C wt%≤50wt%; preferably, 10wt%≤C wt%≤40wt%.

[0063] In some embodiments, 0.5 ≤ C / A ≤ 25. If the proportion of cyclic carbonates is too high, the system viscosity increases dramatically, hindering ion migration and leading to a decrease in kinetics. If the proportion of haloalkanes is too high, although low viscosity is maintained, insufficient lithium salt dissociation results in a low concentration of free lithium ions, which similarly decreases conductivity and increases interfacial impedance, preventing the realization of kinetic advantages. Therefore, only when the ratio of the two is controlled within this range can the optimal balance between dissociation capacity and transport performance be achieved, thereby further improving cycle life and thermal safety over a wide temperature range. For example, the value of C / A can be 0.5, 1, 3, 6, 10, 15, 20, 25, or any combination thereof.

[0064] In some embodiments, 3wt% ≤ C wt% ≤ 50wt%. For example, the value of C wt% is, for instance, a range of 3wt%, 8wt%, 15wt%, 22wt%, 30wt%, 42wt%, 50wt%, or any combination thereof. Preferably, 10wt% ≤ C wt% ≤ 40wt%, the above effect is better.

[0065] In some embodiments of the present invention, the electrolyte further includes a first additive, which includes one or more of lithium difluorophosphate, lithium tetrafluoroborate, vinyl sulfate, methyl vinyl sulfate, 1-propylphosphonic anhydride, and 1-butylphosphonic anhydride, which can further improve the cycle life and thermal safety of the battery over a wide temperature range. The addition of 1-propylphosphonic anhydride and / or 1-butylphosphonic anhydride can, on the one hand, increase the activity of 1-propylphosphonic anhydride and / or 1-butylphosphonic anhydride in the electrolyte, promote their film formation on the positive electrode, and thus improve the protection of the positive electrode. On the other hand, 1-propylphosphonic anhydride and / or 1-butylphosphonic anhydride can inhibit the defluorination reaction of halogenated alkanes and consume the HF generated after the defluorination of halogenated alkanes, which can further improve the mechanical toughness and thermal stability of the negative electrode film, further slow down the film pyrolysis caused by the volume change of the silicon-carbon negative electrode, and thus better improve the low-temperature cycle performance and thermal safety performance of the battery.

[0066] In some embodiments, the first additive has a mass percentage of 0.05 wt% to 5 wt% in the electrolyte. For example, the mass percentage of the first additive is, for example, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2.5 wt%, 4 wt%, 5 wt%, or any combination thereof.

[0067] In some embodiments, the electrolyte further includes fluorocarboxylic acid esters, including at least one selected from ethyl fluoroacetate, ethyl fluorobutyrate, methyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, and propyl fluoropropionate. Ethyl fluoroacetate includes 2,2-difluoroethyl acetate, which can further improve the low-temperature and high-temperature cycle performance of the battery. Preferably, the mass percentage of fluorocarboxylic acid esters in the electrolyte is 5wt% to 55wt%, which enhances the above-mentioned effects.

[0068] The present invention also provides a method for preparing the above-mentioned electrolyte, comprising the following steps: in a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm), the electrolyte components including haloalkanes and polycyclic sulfates are mixed evenly to obtain the electrolyte.

[0069] In some embodiments of the present invention, the electrolyte preparation method may further include adding lithium salt, additives, solvents and other components to the electrolyte components, stirring evenly, and then obtaining the desired electrolyte after passing the tests for moisture and free acid.

[0070] This invention also provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes the electrolyte described above. The battery provided by this invention has advantages corresponding to the electrolyte described above, which will not be elaborated upon here.

[0071] In some embodiments, the charging cutoff voltage of the battery is ≥4.5V.

[0072] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-carbon material, and the battery satisfies at least one of the following conditions:

[0073] (1) The average sphericity of silicon-carbon materials is 0.8~0.99;

[0074] (2) The particle size Dv50 of silicon carbide materials is 1μm~15μm;

[0075] (3) The mass percentage of silicon in the negative electrode active material layer is 2wt%~50wt%;

[0076] (4) Silicon-carbon materials include porous carbon matrix and silicon materials deposited in carbon matrix.

[0077] In some embodiments, the average sphericity of the silicon-carbon material is 0.8~0.99, which is beneficial for further balancing the interfacial reactivity and processing dispersibility of the negative electrode active material, making the electrolyte easier to wet and reducing local polarization, thus better improving the cycle performance of the battery. The embodiments of the present invention can use conventional testing methods and instruments in the art to test the average sphericity of the silicon-carbon material. For example, the test can be performed as follows: Analyze the images of each particle in the SEM image of the silicon-carbon material at a certain magnification (e.g., 2500x) using image processing software (e.g., Image ProPlus) to obtain the perimeter and area of ​​each particle. Calculate the equivalent radius r1 of the perimeter and the equivalent radius r2 of the area of ​​each particle. Then, the sphericity S of each particle is S = r2 / r1. Finally, the sphericity of each particle is weighted and averaged (at least 50 particles) to obtain the average sphericity of the silicon-carbon material.

[0078] In some embodiments, the Dv50 of the silicon-carbon material is 1μm to 15μm, which is beneficial for further reducing the side reactions between the negative electrode active material and the electrolyte, thereby improving the cycle performance of the battery. The Dv50 of the silicon-carbon material is, for example, a range of 1μm, 2μm, 3μm, 4μm, 5μm, 8μm, 10μm, 12μm, 15μm, or any combination thereof. The embodiments of the present invention can use conventional testing methods and instruments in the art to test the Dv50 (referring to the volume median particle size, i.e., the particle size corresponding to 50% of the cumulative volume distribution of the particles) of the silicon-carbon material, such as a laser particle size analyzer.

[0079] In some embodiments, the silicon content in the negative electrode active material layer is 2wt%~50wt%, which can achieve a better balance between capacity improvement and volume change control of the negative electrode sheet, thereby further reducing repeated rupture of the interface film during cycling. The embodiments of the present invention can use conventional testing methods and instruments to test the silicon content in the negative electrode active material layer, for example, through ash content testing. Specifically, the steps include: after discharging the battery to 0% SOC, disassembling and removing the negative electrode sheet, immersing it in dimethyl carbonate (DMC) solvent for 12 hours, then rinsing it with DMC to remove the lithium salt adhering to the 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), so that the negative electrode active material layer can be peeled off from the current collector. In silicon content testing, a thermogravimetric analyzer (such as a TGA 550 thermogravimetric analyzer) is used. The mass of the test sample 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 min. This allows the non-silicon components in the active layer of the negative electrode material 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 be present in the ash, and treating all ash as silicon dioxide, the mass percentage 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). Preferably, the mass percentage of silicon in the negative electrode active material layer is ≤30 wt%, which improves the above results.

[0080] In some embodiments, the silicon-carbon material includes a porous carbon matrix and silicon material deposited in the carbon matrix, which can better buffer and confine the expansion of the silicon material. Therefore, it is more helpful for the battery to maintain the stability of the negative electrode interface under high voltage and wide temperature conditions, and to work with the electrolyte to improve cycle life and safety.

[0081] In some embodiments, the porous carbon matrix may include at least one of graphite, hard carbon, and soft carbon.

[0082] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0083] (1) Silicon-carbon materials contain nitrogen, and the mass percentage of nitrogen in silicon-carbon materials is 0.01wt%~5wt%;

[0084] (2) Silicon carbon materials include a coating layer, which includes at least one of amorphous carbon, carbon nanotubes, and conductive polymers.

[0085] In some embodiments of the present invention, when the silicon-carbon material includes nitrogen, the SEI film formed by haloalkanes can be further optimized, and the microscopic defects of the film layer can be reduced, thereby further improving the cycle life and thermal safety of the battery over a wide temperature range. The above effects are better when the mass percentage of nitrogen in the silicon-carbon material is 0.01 wt% to 5 wt%. For example, the mass percentage of nitrogen in the silicon-carbon material may be 0.01 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, or any combination thereof. The mass percentage of nitrogen in the silicon-carbon material can be tested using conventional testing methods and instruments in the art. For example, the test can be performed using energy dispersive spectroscopy (EDS) by scanning electron microscopy or transmission electron microscopy. The specific steps include: disassembling the battery after it is fully discharged, separating the negative electrode sheet, taking an appropriate amount of sample of the negative electrode active material layer and placing it under a transmission electron microscope, setting the corresponding detection conditions (such as adjusting the accelerating voltage and magnification) and combining it with EDS to detect the distribution of nitrogen in the negative electrode active material layer. The mass of silicon-carbon material can be obtained by converting the mass ratio of silicon in the negative electrode active material layer, thereby calculating the mass ratio of nitrogen in the negative electrode active material layer.

[0086] Nitrogen doping in silicon-carbon materials can be achieved using conventional doping methods for anode materials in this field, such as chemical vapor deposition (CVD). CVD uses silane (SiH4) as the silicon source and introduces nitrogen-containing gases (such as ammonia (NH3) and nitrogen (N2)) as the nitrogen source. A vapor deposition reaction is carried out on the surface and inside of a porous carbon matrix to obtain nitrogen-doped silicon-carbon materials.

[0087] In some embodiments, the silicon-carbon material includes a coating layer comprising at least one of amorphous carbon, carbon nanotubes, and a conductive polymer. This coating layer can form a conductive and buffering protective layer on the surface of the silicon-carbon particles, further reducing the damage to the interface film caused by volume changes, thereby improving the thermal safety performance of the battery. In some specific embodiments, the conductive polymer includes one or more of polypyrrole, polythiophene, and polyaniline.

[0088] In some embodiments, when the porous carbon matrix includes nitrogen, the conductivity, structural stability, and bonding strength with the deposited silicon-carbon material are further improved.

[0089] In some embodiments of the present invention, the areal density of the negative electrode active material layer on one side is 3 mg / cm³. 2 ~16mg / cm 2 This approach can further balance the specific capacity of the negative electrode with the electrolyte wetting and ion transport of the electrode, enabling the battery to maintain good capacity performance, cycle stability, and safety under high voltage and wide temperature range conditions. For example, the areal density of the negative electrode active material layer on one side is, for instance, 3 mg / cm³.2 5mg / cm 2 8mg / cm 2 12mg / cm 2 16mg / cm 2 Or a range consisting of any two of them. Embodiments of the present invention can use conventional testing methods and instruments in the art to test the areal density of the negative electrode sheet. For example, it can be tested by the following method: Take a negative electrode sheet sample, test the total mass m1 of the negative electrode sheet sample, and the surface area S of one side of the negative electrode sheet sample in the thickness direction; then scrape off the negative electrode active material layer on the negative electrode sheet sample, and test the mass m2 of the obtained negative electrode current collector. Then, the areal density of one side of the negative electrode active material layer = (m1 - m2) / S.

[0090] In some embodiments of the present invention, the positive electrode active material includes lithium cobalt oxide or doped and coated modified lithium cobalt oxide.

[0091] In some embodiments of the present invention, the electrolyte may contain lithium salts, which may include one or more of lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium perchlorate (LiClO4).

[0092] In some embodiments, the electrolyte includes at least one of linear carbonates and linear carboxylic acid esters, including but not limited to one or more of diethyl carbonate, methyl ethyl carbonate, propyl propionate, ethyl propionate, and ethyl butyrate.

[0093] In some embodiments of the present invention, the electrolyte further includes additives, including fluoroethylene carbonate (FEC), boron-containing positive electrode protection additives (including but not limited to lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate (LiBOB)), etc.), and nitrile positive electrode protection additives (including but not limited to one or more of succinic anionyl (SN), adiponitrile (ADN), and 1,3,6-hexanetrionitrile (HTCN).

[0094] 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.

[0095] In this embodiment of the invention, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. In the positive electrode active material layer, the positive electrode active material accounts for 80% to 99.8% by mass percentage, the conductive agent accounts for 0.1% to 10%, and the binder accounts for 0.1% to 10%.

[0096] In this embodiment of the invention, the conductive agent in the positive electrode active material layer can be a conventional conductive material in the art. For example, the positive electrode conductive agent in the positive electrode active material layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0097] In this embodiment of the invention, the binder in the positive electrode active material layer can be a conventional binder in the art. For example, the positive electrode binder in the positive electrode active material 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.

[0098] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0099] In this embodiment of the invention, the negative electrode active material layer may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, 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.

[0100] In the negative electrode active material layer, by mass percentage, the negative electrode active material is 80wt%~98.5wt%, the conductive agent is 0.1%~10wt%, and the binder is 0.1%~10wt%.

[0101] 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.

[0102] This invention also provides a battery pack comprising at least two of the aforementioned batteries, which has advantages corresponding to the aforementioned batteries, and will not be described in detail hereafter.

[0103] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0104] Example 1

[0105] The battery in this embodiment is prepared by the following method:

[0106] 1) Preparation of positive electrode sheet: Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), superP (SP), and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5 and added to the solvent N-methylpyrrolidone (NMP). The mixture is stirred under vacuum until it becomes a uniform and fluid positive electrode slurry. The positive electrode slurry is uniformly coated on both surfaces of an aluminum foil. The coated aluminum foil is dried and then rolled and slit to obtain the desired positive electrode sheet.

[0107] 2) Negative Electrode Preparation: Artificial graphite, silicon carbide, 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 74.5:20:2.5:1.5:1:0.5. Deionized water was added, and a negative electrode active slurry was obtained under vacuum stirring. The negative electrode active 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 and slitting, the negative electrode sheet was obtained. The silicon carbide had an average sphericity of 0.92, a particle size Dv50 of 7.5 μm, a silicon content of 15 wt% in the negative electrode active material layer, and a single-sided areal density of 8 mg / cm³. 2 .

[0108] 3) Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the solvents ethylene carbonate (EC) / propylene carbonate (PC) / propyl propionate (PP) were mixed thoroughly, and then 15 wt% of a haloalkane (specifically 1,4-difluorobutane) was added based on the electrolyte mass. Then, 12 wt% of fully dried lithium hexafluorophosphate (LiPF6), 10 wt% of FEC (fluoroethylene carbonate), and 2.5 wt% of polycyclic sulfate (as shown in Formula I) based on the total electrolyte mass were rapidly added. Specific substances and amounts are shown in Table 1. Subsequently, 1 wt% LiDFOB, 2 wt% HTCN, 1 wt% ADN, and 1 wt% SN were added based on the total electrolyte mass. After being stirred evenly and passing the tests for moisture and free acid, the desired electrolyte is obtained, in which the ratio of ethylene carbonate to propylene carbonate is 1:2, accounting for 10% of the electrolyte mass (C%), and the remainder is propyl propionate.

[0109] 4) Preparation of lithium-ion batteries: The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, standing, formation, shaping and sorting, lithium-ion batteries are obtained.

[0110] The differences between Examples 2-18, Comparative Examples 1-4 and Example 1 are as follows: the mass percentage of haloalkanes in the electrolyte A (wt%), the mass percentage of polycyclic sulfate B (wt%) in the electrolyte B, the number of carbon atoms in the haloalkanes, the type of haloalkanes, the type of polycyclic sulfate, the A / B ratio, the mass percentage of non-fluorinated cyclic carbonates in the electrolyte C (wt%), and the C / A ratio are different. See Table 1 for details.

[0111]

[0112] The differences between Examples 19-29 and Example 1 lie in the type of the first additive, the mass percentage of the first additive in the electrolyte (hereinafter referred to as the mass percentage of the first additive in the table), the type of fluorocarboxylic acid ester, the mass percentage of fluorocarboxylic acid ester in the electrolyte (hereinafter referred to as the mass percentage of fluorocarboxylic acid ester in the table), the average sphericity of the silicon-carbon material, the particle size Dv50 of the silicon-carbon material, the mass percentage of silicon in the negative electrode active material layer (hereinafter referred to as the mass percentage of silicon element in the table), the mass percentage of nitrogen in the silicon-carbon material (hereinafter referred to as the mass percentage of nitrogen element in the silicon-carbon material in the table), and the category parameters of the coating layer material, as detailed in Table 2. In Example 10, the areal density of the negative electrode active material layer was 3 mg / cm³. 2 The areal density of the negative electrode active material layer in Example 10 is 16 mg / cm³. 2 .

[0113]

[0114] In Examples 23-25, nitrogen-doped silicon-carbon materials were used.

[0115] The differences between Examples 30-31 and Example 1 are detailed in Table 3.

[0116]

[0117] Test case

[0118] 1) Low-temperature 0℃ cycling performance test

[0119] The batteries obtained from the above embodiments and comparative examples were subjected to charge-discharge cycles at 0°C at a rate of 1C within the charge-discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1mAh, and the discharge capacity of the Nth cycle was measured as y1mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1. The number of cycles of the battery when the cycle capacity retention rate R1 was 80% was recorded. The results are shown in Table 4.

[0120] 2) High-temperature 45℃ cycle performance test

[0121] The batteries obtained from the above embodiments and comparative examples were subjected to charge-discharge cycles at 45°C within the charge-discharge cutoff voltage range at a 2C rate. The discharge capacity of the first cycle was measured as x2mAh, and the discharge capacity of the Nth cycle was measured as y2mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = y2 / x2. The number of cycles when the cycle capacity retention rate R2 was 80% was recorded. The results are shown in Table 4.

[0122] 3) Hot box safety performance test:

[0123] The batteries obtained in the examples and comparative examples were discharged to 3V at 0.2C at 25±3℃, charged to 4.53V at a constant current of 0.5C, and then charged to 0.02C at a constant voltage of 4.53V. 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 at that temperature for 60 minutes. Whether the battery caught fire / exploded / smoke was recorded. If the battery did not catch fire / explode / smoke, it was considered to have passed the test. The test results are shown in Table 4.

[0124]

[0125] As shown in Table 4, compared with the comparative example, the embodiments of the present invention, by adding haloalkanes and polycyclic sulfates to the electrolyte, wherein the haloalkanes include at least one fluorine atom and the polycyclic sulfates include at least two cyclic structures, the two can work together to enable the electrolyte to maintain good ionic conductivity at low temperature and good stability at high temperature, thereby helping to improve the cycle performance and thermal safety performance of the battery at both high and low temperatures.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises haloalkanes and polycyclic sulfates, wherein the haloalkanes comprise at least one fluorine atom and the polycyclic sulfates comprise at least two cyclic structures.

2. The electrolyte according to claim 1, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The mass percentage (Awt%) of the haloalkane in the electrolyte satisfies: 1wt%≤Awt%≤50wt%; preferably, 3wt%≤Awt%≤30wt%; (2) The mass percentage of the polycyclic sulfate in the electrolyte is Bwt% and satisfies: 0.1wt%≤Bwt%≤5wt%; preferably, 0.5wt%≤Bwt%≤5wt%; (3) The number of carbon atoms in the haloalkane is 3 to 6; (4) The polycyclic sulfate includes at least one of bicyclic sulfate compounds and tricyclic sulfate compounds.

3. The electrolyte according to claim 1 or 2, characterized in that, The haloalkane includes one or more of the following: 1-fluoropropane, 1-fluorobutane, 1-fluoropentane, 1-fluorohexane, 1,3-difluoropropane, 1,4-difluorobutane, 1,5-difluoropentane, 1,6-difluorohexane, 1-fluoro-3-chlorobutane, 1-fluoro-4-chlorobutane, 1-fluoro-3-bromobutane, and 1-fluoro-4-bromobutane. And / or, the polycyclic sulfate comprises one or more compounds represented by formulas I to IX: Formula I Formula II Formula III Formula IV Formula V Formula VI Formula VII Formula VIII Formula IX; And / or, 1≤A / B≤50.

4. The electrolyte according to any one of claims 1-3, characterized in that, The electrolyte further includes a non-fluorinated cyclic carbonate, wherein the non-fluorinated cyclic carbonate accounts for a mass percentage (Cwt) in the electrolyte; the electrolyte satisfies at least one of the following conditions: (1) 0.5 ≤ C / A ≤ 25; (2) 3wt%≤C wt%≤50wt%; preferably, 10wt%≤C wt%≤40wt%.

5. The electrolyte according to any one of claims 1-4, characterized in that, The electrolyte further includes a first additive, which includes one or more of lithium difluorophosphate, lithium tetrafluoroborate, vinyl sulfate (DTD), methyl vinyl sulfate, 1-propylphosphonic anhydride, and 1-butylphosphonic anhydride; preferably, the first additive accounts for 0.05wt% to 5wt% of the mass of the electrolyte.

6. The electrolyte according to any one of claims 1-5, characterized in that, The electrolyte further includes fluorocarboxylic acid esters, which include at least one of ethyl fluoroacetate, ethyl fluorobutyrate, methyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, and propyl fluoropropionate. The ethyl fluoroacetate includes 2,2-difluoroethyl acetate. Preferably, the mass percentage of fluorocarboxylic acid esters in the electrolyte is 5 wt% to 55 wt%.

7. A battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte includes the electrolyte according to any one of claims 1-6.

8. The battery according to claim 7, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-carbon material. The battery satisfies at least one of the following conditions: (1) The average sphericity of the silicon-carbon material is 0.8~0.99; (2) The particle size Dv50 of the silicon carbide material is 1μm~15μm; (3) The mass percentage of silicon in the negative electrode active material layer is 2wt%~50wt%; (4) The silicon-carbon material includes a porous carbon matrix and silicon material deposited in the carbon matrix.

9. The battery according to claim 8, characterized in that, The battery satisfies at least one of the following conditions: (1) The silicon-carbon material includes nitrogen, and the mass percentage of nitrogen in the silicon-carbon material is 0.01 wt% to 5 wt%; (2) The silicon-carbon material includes a coating layer, which includes at least one of amorphous carbon, carbon nanotubes, and conductive polymers.

10. The battery according to claim 8 or 9, characterized in that, The single-sided area density of the negative electrode active material layer is 3 mg / cm 2 16 mg / cm 2 .

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