Secondary battery and electronic device including the same

Abstract

The application belongs to the technical field of electrochemistry and relates to a secondary battery and an electronic device comprising the secondary battery. The secondary battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; the negative electrode active material of the negative electrode comprises a silicon-carbon material; the electrolyte comprises ethyl propionate and propyl propionate, the mass percentage content of the ethyl propionate is a% and the mass percentage content of the propyl propionate is b% based on the total mass of the electrolyte, wherein 1.7<=a / b<=5.7; the electrolyte further comprises at least one of vinylene carbonate, a boron-containing lithium salt and a compound comprising a structure shown in Formula I; wherein A in Formula I is selected from C2 to C5 alkylene. The secondary battery, by improving the used electrolyte system, reduces the gas generated by the secondary battery containing the electrolyte system at high temperature, and further improves the high-rate discharge performance of the secondary battery.

Description

[0001] This application is a divisional application of application number 202410561295.3, application date 2024.05.08, application type 'invention', and application title 'secondary battery and electronic device comprising the secondary battery'. Technical Field

[0002] This application belongs to the field of electrochemical technology and relates to a secondary battery and an electronic device containing the secondary battery. Background Technology

[0003] Secondary batteries, such as lithium-ion batteries, offer advantages like environmental friendliness, high energy density, and long cycle life, and are widely used in mobile phones, computers, wearable devices, consumer drones, power tools, electric motorcycles, electric vehicles, and large energy storage devices. As the consumer market continues to expand, the performance requirements for batteries are becoming increasingly stringent. For example, secondary batteries need to maintain good performance under conditions such as high and low temperatures or high rates. Currently, carbonate compounds are commonly used as solvent systems for secondary battery electrolytes. However, these electrolytes are unstable under high-rate conditions, easily leading to a decrease in the performance of the secondary battery. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electrical device containing the secondary battery. In the secondary battery provided by this application, by improving the electrolyte system used, the gas generated by the secondary battery containing the electrolyte system at high temperature is reduced, and the high-rate discharge performance of the secondary battery is further improved.

[0005] According to a first aspect of this application, this application provides a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte;

[0006] The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, which includes silicon-carbon material.

[0007] The electrolyte contains ethyl propionate and propyl propionate. Based on the total mass of the electrolyte, the mass percentage of ethyl propionate is a%, and the mass percentage of propyl propionate is b%, wherein 1.7 ≤ a / b ≤ 5.7.

[0008] The electrolyte also contains at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structural formula shown in Formula I.

[0009]

[0010] In Formula I, A is selected from C2 to C5 alkylene groups.

[0011] This application has found that the presence of a specific ratio of ethyl propionate and propyl propionate in the electrolyte of a secondary battery can improve its low-temperature performance. However, under high-temperature conditions, the defective structure on the surface of silicon-carbon material in a secondary battery using silicon-carbon material as the negative electrode active material can easily cause damage and unevenness of the surface solid electrolyte membrane (SEI), leading to increased gas production inside the battery. Furthermore, when the secondary battery is discharged at a high rate, the internal impedance increases, further increasing gas production and reducing the discharge capacity.

[0012] Based on this, this application has found that, in the electrolyte of a secondary battery using silicon-carbon material as the negative electrode active material, when the mass percentage ratio a / b of ethyl propionate and propyl propionate is controlled to be in the range of 1.7 to 5.7, and when used in combination with at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structure shown in Formula I, the surface wettability of the negative electrode silicon-carbon material under high temperature and high rate conditions can be significantly improved, a uniform SEI film can be formed on the surface of the silicon-carbon material, promoting uniform electrode reaction on the negative electrode, reducing the gas generated under high temperature and high rate conditions, significantly improving the cycle characteristics and high-speed discharge characteristics of the secondary battery, enabling the lithium insertion / extraction on the negative electrode to proceed uniformly, effectively controlling the decrease in discharge capacity during high-rate discharge, and improving the high-rate discharge performance of the secondary battery.

[0013] In some embodiments of this application, the silicon-carbon material is prepared by mixing elemental silicon and graphite materials or by silicon deposition using porous carbon materials as a framework; preferably, the silicon-carbon material is obtained by silane deposition using porous carbon materials as a framework; preferably, the preparation of the silicon-carbon material includes the following steps: subjecting the porous carbon framework to a silane deposition reaction to obtain a precursor material, and micro-oxidizing the precursor material to obtain the silicon-carbon material.

[0014] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage ratio of ethyl propionate to propyl propionate ranges from 3.1 ≤ a / b ≤ 4.9. This application has found that when the mass percentage ratio of ethyl propionate to propyl propionate is further controlled within the above range, the amount of gas generated under high temperature and high rate conditions can be significantly reduced, and the cycle characteristics and high-speed discharge characteristics of the secondary battery can be significantly improved.

[0015] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges as follows: 20% ≤ a ≤ 70%, and the mass percentage of propyl propionate ranges as follows: 11% ≤ b ≤ 20%. Preferably, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges as follows: 36% ≤ a ≤ 54%, and the mass percentage of propyl propionate ranges as follows: 11% ≤ b ≤ 15%. When the mass percentages of ethyl propionate and propyl propionate meet the above-mentioned range characteristics, the combined action of propyl propionate and ethyl propionate results in a lower viscosity of the electrolyte, improves the flexibility of the SEI film at high temperatures, forms a more uniform SEI film on the surface of the silicon-carbon material, reduces the occurrence of side reactions, reduces gas production in the secondary battery at high temperatures, and improves the high-rate discharge performance of the secondary battery.

[0016] In some embodiments of this application, based on the total mass of the electrolyte, the sum of the mass percentages of ethyl propionate and propyl propionate ranges from 32% ≤ a + b ≤ 84%; preferably, based on the total mass of the electrolyte, the sum of the mass percentages of ethyl propionate and propyl propionate ranges from 47% ≤ a + b ≤ 65%. When the sum of the mass percentages of ethyl propionate and propyl propionate meets the above-mentioned range characteristics, the electrolyte can be guaranteed to have a low viscosity, improving the kinetic performance inside the secondary battery, reducing the active ion transport impedance inside the secondary battery, reducing the gas generated by the secondary battery at high temperatures, and improving the high-rate discharge performance of the secondary battery.

[0017] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 20% ≤ a ≤ 70%, and the mass percentage of propyl propionate ranges from 11% ≤ b ≤ 20%, while the sum of the mass percentages of ethyl propionate and propyl propionate satisfies 32% ≤ a + b ≤ 84%; preferably, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 36% ≤ a ≤ 54%, and the mass percentage of propyl propionate ranges from 11% ≤ b ≤ 15%, while the sum of the mass percentages of ethyl propionate and propyl propionate ranges 47% ≤ a + b ≤ 65%.

[0018] In some embodiments of this application, the mass percentage of the compound containing the structure shown in Formula I is from 0.11% to 4.9% based on the total mass of the electrolyte; preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.12% to 1.5% based on the total mass of the electrolyte; more preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.4% to 1.0% based on the total mass of the electrolyte. Even more preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.4% to 0.8% based on the total mass of the electrolyte.

[0019] In some embodiments of this application, the compound containing the structure shown in Formula I includes the compound shown in Formula II;

[0020]

[0021] When the mass percentage of the compound containing the structure shown in Formula I is controlled within the above range, the compound containing the structure shown in Formula I can make the SEI film have a lower impedance, improve the insertion and extraction rate of active ions, and further improve the discharge performance of the secondary battery at high rates.

[0022] In some embodiments of this application, the mass percentage of vinylene carbonate is 0.01% to 0.3% based on the total mass of the electrolyte; preferably, the mass percentage of vinylene carbonate is 0.01% to 0.1% based on the total mass of the electrolyte; preferably, the mass percentage of vinylene carbonate is 0.01% to 0.06% based on the total mass of the electrolyte.

[0023] In some embodiments of this application, the electrolyte comprises vinylene carbonate and boron-containing lithium salt, wherein the sum of the mass percentages of the vinylene carbonate and boron-containing lithium salt is 0.04% to 0.2% based on the total mass of the electrolyte; preferably, the sum of the mass percentages of the vinylene carbonate and boron-containing lithium salt is 0.1% to 0.2% based on the total mass of the electrolyte; preferably, the sum of the mass percentages of the vinylene carbonate and boron-containing lithium salt is 0.1% to 0.16% based on the total mass of the electrolyte.

[0024] In some embodiments of this application, controlling the mass percentage of the vinylene carbonate within the aforementioned range can further promote the formation of a uniform, low-resistance SEI film on the surface of the silicon-carbon material, reduce the gas generated inside the secondary battery, and improve the high-rate discharge performance of the secondary battery. Controlling the sum of the mass percentages of the vinylene carbonate and the boron-containing lithium salt within the aforementioned range can further promote the formation of a uniform SEI film on the surface of the silicon-carbon material, promote uniform electrode reactions on the negative electrode, reduce the occurrence of side reactions, reduce gas generation inside the secondary battery, and ensure appropriate electrolyte viscosity, thereby improving the cycle performance and high-rate discharge performance of the secondary battery.

[0025] In some embodiments of this application, the boron-containing lithium salt has a mass percentage content of 0.01% to 0.25% based on the total mass of the electrolyte; preferably, the boron-containing lithium salt has a mass percentage content of 0.05% to 0.15% based on the total mass of the electrolyte; more preferably, the boron-containing lithium salt has a mass percentage content of 0.07% to 0.12% based on the total mass of the electrolyte.

[0026] In some embodiments of this application, the boron-containing lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium borate.

[0027] In the technical solution provided in this application, a boron-containing lithium salt is added to the electrolyte. When the mass percentage of the boron-containing lithium salt is within the aforementioned range, it further promotes the formation of a uniform SEI film on the surface of the silicon-carbon material, reduces the impedance of the secondary battery, reduces the gas generated inside the secondary battery, and improves the cycle performance and high-rate discharge performance of the secondary battery. In particular, when lithium tetrafluoroborate is selected as the boron-containing lithium salt, the elasticity of the SEI film can be further improved, the active ion transport impedance can be reduced, and the cycle performance and high-rate discharge performance of the secondary battery can be further improved.

[0028] In some embodiments of this application, the electrolyte further comprises at least one of fluoroethylene carbonate, propylene carbonate, and ethylene carbonate. This application has found that when the electrolyte contains at least one of fluoroethylene carbonate, propylene carbonate, and ethylene carbonate, it can further improve the internal kinetics of the secondary battery, promote active ion transport, and enhance the high-rate performance of the secondary battery.

[0029] In some embodiments of this application, the mass percentage of the fluoroethylene carbonate is 2% to 7% based on the total mass of the electrolyte; preferably, the mass percentage of the fluoroethylene carbonate is 2.1% to 4.6% based on the total mass of the electrolyte. Adjusting the mass percentage of the fluoroethylene carbonate within the above range can further improve the high-rate performance of the secondary battery.

[0030] In some embodiments of this application, the mass percentage of propylene carbonate is 20% to 40% based on the total mass of the electrolyte; preferably, the mass percentage of propylene carbonate is 20% to 35% based on the total mass of the electrolyte; more preferably, the mass percentage of propylene carbonate is 20% to 25% based on the total mass of the electrolyte. Adjusting the mass percentage of propylene carbonate within the above range can further improve the high-rate performance of the secondary battery.

[0031] In some embodiments of this application, the mass percentage of ethylene carbonate is 4% to 18% based on the total mass of the electrolyte; preferably, the mass percentage of ethylene carbonate is 11% to 16% based on the total mass of the electrolyte; more preferably, the mass percentage of ethylene carbonate is 11% to 14% based on the total mass of the electrolyte. Adjusting the mass percentage of ethylene carbonate within the above range can further improve the high-rate performance of the secondary battery.

[0032] In some embodiments of this application, the electrolyte further comprises at least two of 1,3-propanesulfonate lactone, succinate, ethylene glycol bis(propionitrile) ether, and 1,3,6-hexanetrionitrile. This application has found that the above additives can improve the flexibility of the SEI, and together with propyl propionate and ethyl propionate, improve the uniformity of the SEI film formation on the silicon-carbon material surface, reduce the occurrence of internal side reactions in the battery, reduce gas generation at high temperatures, lower the internal impedance of the secondary battery, and further improve the high-rate discharge performance of the secondary battery.

[0033] In some embodiments of this application, the mass percentage of 1,3-propanesulfonate lactone is 0.1% to 4% based on the total mass of the electrolyte; preferably, the mass percentage of 1,3-propanesulfonate lactone is 1.2% to 3.6% based on the total mass of the electrolyte; more preferably, the mass percentage of 1,3-propanesulfonate lactone is 2.0% to 3.0% based on the total mass of the electrolyte. When the mass percentage of 1,3-propanesulfonate lactone is within the above range, the SEI film distribution on the surface of the silicon-carbon material is more uniform, which can further reduce gas generation at high temperatures and improve the high-rate discharge performance of the secondary battery.

[0034] In some embodiments of this application, the mass percentage of succinic anionylene is 0.1% to 4% based on the total mass of the electrolyte; preferably, the mass percentage of succinic anionylene is 1.6% to 2.4% based on the total mass of the electrolyte; more preferably, the mass percentage of succinic anionylene is 1.8% to 2.4% based on the total mass of the electrolyte. When the mass percentage of succinic anionylene is controlled within the above range, the SEI film on the surface of the silicon-carbon material has better flexibility, which can further reduce gas generation at high temperatures and improve the high-rate discharge performance of the secondary battery.

[0035] In some embodiments of this application, the mass percentage of ethylene glycol bis(propionitrile) ether is 0.01% to 1% based on the total mass of the electrolyte; preferably, the mass percentage of ethylene glycol bis(propionitrile) ether is 0.4% to 0.8% based on the total mass of the electrolyte; more preferably, the mass percentage of ethylene glycol bis(propionitrile) ether is 0.5% to 0.8% based on the total mass of the electrolyte. The SEI film on the surface of the silicon-carbon material has better uniformity, which can further reduce gas generation at high temperatures and improve the high-rate discharge performance of the secondary battery.

[0036] In some embodiments of this application, the mass percentage of 1,3,6-hexanetrionitrile is from 0.1% to 3.5% based on the total mass of the electrolyte; preferably, the mass percentage of 1,3,6-hexanetrionitrile is from 1.3% to 2.8% based on the total mass of the electrolyte; more preferably, the mass percentage of 1,3,6-hexanetrionitrile is from 1.8% to 2.5% based on the total mass of the electrolyte. Regulating the mass percentage of 1,3,6-hexanetrionitrile within the above range promotes the transport of active ions, further reduces gas generation at high temperatures, and improves the high-rate discharge performance of the secondary battery.

[0037] In some embodiments of this application, the silicon-carbon material accounts for 1% to 15% of the mass of the negative electrode active material; preferably, the silicon-carbon material accounts for 2% to 10% of the mass of the negative electrode active material.

[0038] In some embodiments of this application, based on the total mass of the electrolyte, when the mass percentage of ethyl propionate is a%, the mass percentage of propyl propionate is b%, 1.7 ≤ a / b ≤ 2.5, and the mass percentage range of ethyl propionate is 20% ≤ a ≤ 30%, the mass percentage range of propyl propionate is 11% ≤ b ≤ 15%, the mass percentage of the compound containing the structure shown in Formula I is 0.11% to 4.9%, and the mass percentage of vinylene carbonate is 0.01% to 0.3%; or the boron-containing lithium salt... The mass percentage content is 0.01% to 0.25%; or the mass percentage content of the fluoroethylene carbonate is 2% to 5%; or the mass percentage content of the propylene carbonate is 30% to 40%; or the mass percentage content of the ethylene carbonate is 8% to 14%; or the mass percentage content of the 1,3-propanesulfonate lactone is 1.1% to 3.5%; or the mass percentage content of the succinic anion is 1% to 4%; or the mass percentage content of the ethylene glycol bis(propionitrile) ether is 0.1% to 1%; or the mass percentage content of the 1,3,6-hexanetrionitrile is 0.5% to 3%.

[0039] In some embodiments of this application, based on the total mass of the electrolyte, when the mass percentage of ethyl propionate is a%, the mass percentage of propyl propionate is b%, 1.9 ≤ a / b ≤ 2.2, and the mass percentage range of ethyl propionate is 20% ≤ a ≤ 30%, the mass percentage range of propyl propionate is 11% ≤ b ≤ 15%, the mass percentage of the compound containing the structure shown in Formula I is 0.11% to 1.0%, and the mass percentage of vinylene carbonate is 0.01% to 0.1%; or the mass percentage of the boron-containing lithium salt is... The content is 0.05% to 0.2% by mass; or the content of the fluoroethylene carbonate is 2% to 5% by mass; or the content of the propylene carbonate is 30% to 40% by mass; or the content of the ethylene carbonate is 8% to 14% by mass; or the content of the 1,3-propanesulfonate lactone is 1.1% to 3% by mass; or the content of the succinic anion is 1.1% to 3% by mass; or the content of the ethylene glycol bis(propionitrile) ether is 0.1% to 0.8% by mass; or the content of the 1,3,6-hexanetrionitrile is 0.7% to 2.5% by mass.

[0040] In some embodiments of this application, the negative electrode active material further comprises graphite, a conductive agent, and a binder.

[0041] According to a second aspect of this application, this application provides an electronic device comprising a secondary battery as described in any one of the first aspects of this application.

[0042] Compared with the prior art, this application has the following beneficial effects:

[0043] This application provides a secondary battery. In the electrolyte of a secondary battery using silicon-carbon material as the negative electrode active material, by controlling the mass percentage ratio of ethyl propionate and propyl propionate (a / b) to be within the range of 1.7 to 5.7, and using it in combination with at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structure shown in Formula I, under high temperature and high rate conditions, it can improve the surface wettability of the silicon-carbon negative electrode material, form a uniform SEI film on the surface of the silicon-carbon material, promote uniform electrode reaction on the negative electrode, reduce the gas generated under high temperature and high rate conditions, significantly improve the cycle characteristics and high-speed discharge characteristics of the secondary battery, enable the lithium insertion / extraction on the negative electrode to proceed uniformly, effectively control the decrease in discharge capacity during high-rate discharge, and improve the high-rate discharge performance of the secondary battery. Detailed Implementation

[0044] The technical solutions of this application are further illustrated below through specific embodiments. These specific embodiments do not represent a limitation on the scope of protection of this application. Any non-essential modifications and adjustments made by others based on the concept of this application still fall within the scope of protection of this application.

[0045] It should be noted that, in the following explanation, lithium-ion batteries are used as an example of secondary batteries to illustrate this application. However, the secondary batteries in this application are not limited to lithium-ion batteries, but can be any other suitable secondary batteries, such as lithium metal secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0046] According to a first aspect of this application, this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon material; the electrolyte comprises a non-aqueous solvent and a boron-containing lithium salt, the non-aqueous solvent comprises ethyl propionate and propyl propionate, and based on the total mass of the electrolyte, the mass percentage of ethyl propionate is a%, and the mass percentage of propyl propionate is b%, wherein 1.7 ≤ a / b ≤ 5.7;

[0047] The electrolyte also contains at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structural formula shown in Formula I;

[0048]

[0049] In Formula I, A is selected from C2 to C5 alkylene groups.

[0050] This application has found that the presence of a specific ratio of ethyl propionate and propyl propionate in the electrolyte of a secondary battery can improve its low-temperature performance. However, under high-temperature conditions, the defective structure on the surface of silicon-carbon material in a secondary battery using silicon-carbon material as the negative electrode active material can easily cause damage and unevenness of the surface solid electrolyte membrane (SEI), leading to increased gas production inside the battery. Furthermore, when the secondary battery is discharged at a high rate, the internal impedance increases, further increasing gas production and reducing the discharge capacity.

[0051] Therefore, in the electrolyte of a secondary battery using silicon-carbon material as the negative electrode active material, controlling the mass percentage ratio of ethyl propionate to propyl propionate (a / b) in the range of 1.7 to 5.7, and combining it with at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structure shown in Formula I, can significantly improve the surface wettability of the silicon-carbon negative electrode material under high temperature and high rate conditions, form a uniform SEI film on the surface of the silicon-carbon material, promote uniform electrode reaction on the negative electrode, reduce the gas generated under high temperature and high rate conditions, significantly improve the cycle characteristics and high-speed discharge characteristics of the secondary battery, enable the lithium insertion / extraction on the negative electrode to proceed uniformly, effectively control the decrease in discharge capacity during high-rate discharge, and improve the high-rate discharge performance of the secondary battery.

[0052] In some embodiments of this application, the silicon-carbon material can be prepared by mixing elemental silicon material and graphite material or by preparing a porous carbon material as a framework after silicon deposition; preferably, the silicon-carbon material is prepared by silane deposition using a porous carbon material as a framework. Preferably, the preparation of the silicon-carbon material includes the following steps: subjecting the porous carbon framework to a silane deposition reaction to obtain a precursor material, and subjecting the precursor material to micro-oxidation to obtain the silicon-carbon material.

[0053] Specifically, in some embodiments of this application, based on the total mass of the electrolyte, the mass percentage ratio of ethyl propionate to propyl propionate can be 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, or a range consisting of any two of the above values. In some embodiments of this application, the mass percentage ratio of ethyl propionate to propyl propionate, based on the total mass of the electrolyte, can be 1.9 to 5.4, 2.1 to 5.6, 2.5 to 5.0, 3.2 to 5.4, or 2.3 to 4.8. In some embodiments of this application, the preferred range for the mass percentage ratio of ethyl propionate to propyl propionate, based on the total mass of the electrolyte, is 3.1 ≤ a / b ≤ 4.9. This application has found that when the mass percentage ratio of ethyl propionate to propyl propionate is further controlled within the above range, the gas generated under high temperature and high rate conditions can be significantly reduced, and the cycle characteristics and high-speed discharge characteristics of the secondary battery can be significantly improved.

[0054] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 20% to a to 70%; preferably, the mass percentage of ethyl propionate can range from 36% to a to 54%. Specifically, the mass percentage of ethyl propionate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 65%, 66%, 67%, 68%, 69%, 70%, or a range of any two of the above values. In some embodiments of this application, the mass percentage of ethyl propionate can range from 25% to 57%, 28% to 62%, 30% to 55%, 32% to 58%, or 34% to 56%, based on the total mass of the electrolyte.

[0055] In some embodiments of this application, the mass percentage of propyl propionate, based on the total mass of the electrolyte, ranges from 11% ≤ b ≤ 20%; preferably, the mass percentage of propyl propionate, based on the total mass of the electrolyte, can range from 11% ≤ b ≤ 15%. Specifically, the mass percentage of propyl propionate can be 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of the above values. In some embodiments of this application, the mass percentage of propyl propionate, based on the total mass of the electrolyte, can be 12% to 18%, 13% to 19%, or 14% to 18%.

[0056] When the mass percentages of ethyl propionate and propyl propionate meet the above-mentioned range characteristics, the combined action of propyl propionate and ethyl propionate can further reduce the viscosity of the electrolyte, further improve the flexibility of the SEI film at high temperatures, form a more uniform SEI film on the surface of silicon-carbon materials, further reduce the occurrence of side reactions, reduce gas production in secondary batteries at high temperatures, and further improve the high-rate discharge performance of secondary batteries.

[0057] In some embodiments of this application, the sum of the mass percentages of ethyl propionate and propyl propionate, based on the total mass of the electrolyte, ranges from 32% to 84% (a + b). Preferably, the sum of the mass percentages of ethyl propionate and propyl propionate, based on the total mass of the electrolyte, ranges from 47% to 65% (a + b). In some embodiments of this application, the sum of the mass percentages of ethyl propionate and propyl propionate, based on the total mass of the electrolyte, can be 35% to 70%, 38% to 73%, 41% to 75%, or 44% to 64%. When the sum of the mass percentages of ethyl propionate and propyl propionate further satisfies the above-mentioned range characteristics, it can further ensure that the electrolyte has a lower viscosity, improve the kinetic performance inside the secondary battery, reduce the active ion transport impedance inside the secondary battery, more significantly reduce the gas generated by the secondary battery at high temperatures, and improve the high-rate discharge performance of the secondary battery.

[0058] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentages of ethyl propionate and propyl propionate satisfy the following ranges: 20% ≤ a ≤ 70% and 11% ≤ b ≤ 20%, while the sum of the mass percentages of ethyl propionate and propyl propionate satisfies: 32% ≤ a + b ≤ 84%. Preferably, based on the total mass of the electrolyte, the mass percentages of ethyl propionate and propyl propionate respectively satisfy the following ranges: 36% ≤ a ≤ 54% and 11% ≤ b ≤ 15%, while the sum of the mass percentages of ethyl propionate and propyl propionate satisfies: 47% ≤ a + b ≤ 65%.

[0059] In some embodiments of this application, the mass percentage of the compound containing the structure shown in Formula I is from 0.11% to 4.9% based on the total mass of the electrolyte. Preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.12% to 1.5% based on the total mass of the electrolyte; more preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.4% to 1.0% based on the total mass of the electrolyte. Even more preferably, the mass percentage of the compound containing the structure shown in Formula I is from 0.4% to 0.8% based on the total mass of the electrolyte. Specifically, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I can be 0.11%, 0.15%, 0.17%, 0.19%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or a range of any two of the above values. In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I can be from 0.2% to 0.9%, from 0.15% to 1.2%, or from 0.3% to 0.8%.

[0060] In some embodiments of this application, compounds containing the structure shown in Formula I include compounds shown in Formula II;

[0061]

[0062] In particular, by controlling the mass percentage of the compound containing the structure shown in Formula I within the above range, the compound containing the structure shown in Formula I can further make the SEI film have a lower impedance, increase the insertion and extraction rate of active ions, and further improve the discharge performance of the secondary battery at high rates.

[0063] In some embodiments of this application, the mass percentage of vinylene carbonate is 0.01% to 0.3% based on the total mass of the electrolyte; preferably, the mass percentage of vinylene carbonate is 0.01% to 0.1% based on the total mass of the electrolyte; more preferably, the mass percentage of vinylene carbonate is 0.01% to 0.06% based on the total mass of the electrolyte. Specifically, the mass percentage of vinylene carbonate, based on the total mass of the electrolyte, can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, or a range consisting of any two of the above values. In some embodiments of this application, the mass percentage of vinylene carbonate can be 0.02% to 0.11%, 0.03% to 0.14%, or 0.01% to 0.09% based on the total mass of the electrolyte. When the mass percentage of vinylene carbonate is within the above range, it can further promote the formation of a uniform SEI film on the surface of the silicon-carbon material, more significantly reduce the gas generated inside the secondary battery, and improve the high-rate discharge performance of the secondary battery.

[0064] In some embodiments of this application, the electrolyte comprises vinylene carbonate and boron-containing lithium salt, wherein the sum of the mass percentages of vinylene carbonate and boron-containing lithium salt is 0.04% to 0.2% based on the total mass of the electrolyte; preferably, the sum of the mass percentages of vinylene carbonate and boron-containing lithium salt is 0.1% to 0.2% based on the total mass of the electrolyte; and preferably, the sum of the mass percentages of vinylene carbonate and boron-containing lithium salt is 0.1% to 0.16% based on the total mass of the electrolyte. Specifically, based on the total mass of the electrolyte, the sum of the mass percentages of vinylene carbonate and boron-containing lithium salt can be 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, or a range of any two of the above values. In some embodiments of this application, based on the total mass of the electrolyte, the sum of the mass percentages of vinylene carbonate and boron-containing lithium salt can be from 0.08% to 0.18%, 0.06% to 0.15%, or 0.05% to 0.17%. When the electrolyte simultaneously contains vinylene carbonate and boron-containing lithium salt, and the sum of the mass percentages of vinylene carbonate and lithium tetrafluoroborate satisfies the above relationship, it can further promote the formation of a uniform SEI film on the surface of silicon-carbon materials, promote the uniform electrode reaction on the negative electrode, reduce the occurrence of side reactions, reduce gas production inside the secondary battery, and make the electrolyte viscosity appropriate, thus significantly improving the high-rate discharge performance of the secondary battery.

[0065] In some embodiments of this application, the boron-containing lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium borate. Preferably, the boron-containing lithium salt is selected from lithium tetrafluoroborate. In some embodiments of this application, the mass percentage of the boron-containing lithium salt is 0.01% to 0.25% based on the total mass of the electrolyte; preferably, the mass percentage of the boron-containing lithium salt is 0.05% to 0.15% based on the total mass of the electrolyte; more preferably, the mass percentage of the boron-containing lithium salt is 0.07% to 0.12% based on the total mass of the electrolyte. Specifically, based on the total mass of the electrolyte, the mass percentage of boron-containing lithium salt can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, or a range of any two of the above values. In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of boron-containing lithium salt can be from 0.03% to 0.13% or from 0.06% to 0.14%. Adding boron-containing lithium salt to the electrolyte, and when the mass percentage of boron-containing lithium salt is within the above range, further promotes the formation of a uniform SEI film on the surface of the silicon-carbon material, reduces the impedance of the secondary battery, significantly reduces the gas generated inside the secondary battery, and improves the high-rate discharge performance of the secondary battery.

[0066] In some embodiments of this application, the electrolyte further comprises at least one of fluoroethylene carbonate, propylene carbonate, and ethylene carbonate. When the electrolyte contains at least one of fluoroethylene carbonate, propylene carbonate, and ethylene carbonate, the internal kinetics of the secondary battery can be further improved, the transport of active ions can be promoted, and the high-rate performance of the secondary battery can be significantly enhanced.

[0067] In some embodiments of this application, the mass percentage of fluoroethylene carbonate is 2% to 7% based on the total mass of the electrolyte; preferably, the mass percentage of fluoroethylene carbonate is 2.1% to 4.6% based on the total mass of the electrolyte. Specifically, the mass percentage of fluoroethylene carbonate can be 2%, 3%, 4%, 5%, 6%, 7%, or a range of any two of the above values ​​based on the total mass of the electrolyte. In some embodiments of this application, the mass percentage of fluoroethylene carbonate can be 2.4% to 5.2%, 2.7% to 5.6%, 2.3% to 6.0%, or 2.2% to 5.4% based on the total mass of the electrolyte. When the mass percentage of fluoroethylene carbonate is within the above ranges, the high-rate performance of the secondary battery can be further improved.

[0068] In some embodiments of this application, the mass percentage of propylene carbonate is 20% to 40% based on the total mass of the electrolyte; preferably, the mass percentage of propylene carbonate is 20% to 35% based on the total mass of the electrolyte; more preferably, the mass percentage of propylene carbonate is 20% to 25% based on the total mass of the electrolyte. Specifically, the mass percentage of propylene carbonate based on the total mass of the electrolyte can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or a range of any two of the above values. In some embodiments of this application, the mass percentage of propylene carbonate based on the total mass of the electrolyte can be 22% to 37%, 21% to 33%, or 20% to 31%. When the mass percentage of propylene carbonate is within the above ranges, the high-rate performance of the secondary battery can be further improved.

[0069] In some embodiments of this application, the mass percentage of ethylene carbonate is 4% to 18% based on the total mass of the electrolyte; preferably, the mass percentage of ethylene carbonate is 11% to 16% based on the total mass of the electrolyte; more preferably, the mass percentage of ethylene carbonate is 11% to 14% based on the total mass of the electrolyte. Specifically, the mass percentage of ethylene carbonate, based on the total mass of the electrolyte, can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or a range of any two of the above values. In some embodiments of this application, the mass percentage of ethylene carbonate, based on the total mass of the electrolyte, can be 5% to 15% or 7% to 17%. When the mass percentage of ethylene carbonate is within the above ranges, the high-rate performance of the secondary battery can be further improved.

[0070] In some embodiments of this application, the electrolyte further comprises at least two of 1,3-propanesulfonate lactone, succinate, ethylene glycol bis(propionitrile) ether, and 1,3,6-hexanetrionitrile. These additives can improve the flexibility of the SEI, and together with propyl propionate and ethyl propionate, improve the uniformity of the SEI film formation on the silicon-carbon material surface, reduce the occurrence of internal side reactions in the battery, reduce gas generation at high temperatures, lower the internal impedance of the secondary battery, and further improve the high-rate discharge performance of the secondary battery.

[0071] In some embodiments of this application, the mass percentage of 1,3-propanesulfonate lactone is 0.1% to 4% based on the total mass of the electrolyte; preferably, the mass percentage of 1,3-propanesulfonate lactone is 1.2% to 3.6% based on the total mass of the electrolyte; more preferably, the mass percentage of 1,3-propanesulfonate lactone is 2.0% to 3.0% based on the total mass of the electrolyte. Specifically, the mass percentage of 1,3-propanesulfonate lactone, based on the total mass of the electrolyte, can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of the above values. In some embodiments of this application, the mass percentage of 1,3-propanesulfonate lactone can be 0.4% to 3.3%, 0.8% to 3.1%, or 1.4% to 3.4% based on the total mass of the electrolyte. When the mass percentage of 1,3-propanesulfonate lactone is within the above range, the generation of gas at high temperatures can be further reduced and the high-rate discharge performance of the secondary battery can be improved.

[0072] In some embodiments of this application, the mass percentage of succinic anionylene is 0.1% to 4% based on the total mass of the electrolyte; preferably, the mass percentage of succinic anionylene is 1.6% to 2.4% based on the total mass of the electrolyte. Specifically, the mass percentage of succinic anionylene can be 0.1%, 0.15%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range of any two of the above values, based on the total mass of the electrolyte. In some embodiments of this application, the mass percentage of 1,3,6-hexanetrionitrile can be 0.2% to 2.5%, 0.5% to 2.7%, 0.8% to 2.9%, 1.1% to 3.4%, or 0.9% to 2.8% based on the total mass of the electrolyte. When the mass percentage of succinic anionylene is within the above ranges, the generation of gas at high temperatures can be further reduced and the high-rate discharge performance of the secondary battery can be improved.

[0073] In some embodiments of this application, the mass percentage of ethylene glycol bis(propionitrile) ether is 0.01% to 1% based on the total mass of the electrolyte; preferably, the mass percentage of ethylene glycol bis(propionitrile) ether can be 0.4% to 0.8% based on the total mass of the electrolyte. Specifically, the mass percentage of ethylene glycol bis(propionitrile) ether can be 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or a range consisting of any two of the above values, based on the total mass of the electrolyte. In some embodiments of this application, the mass percentage of ethylene glycol bis(propionitrile) ether can be 0.15% to 1.5%, 0.2% to 1.2%, or 0.3% to 1.0% based on the total mass of the electrolyte. When the mass percentage of ethylene glycol bis(propionitrile) ether is within the above range, the generation of gas at high temperatures can be further reduced and the high-rate discharge performance of the secondary battery can be improved.

[0074] In some embodiments of this application, the mass percentage of 1,3,6-hexanetrionitrile is 0.1% to 3.5% based on the total mass of the electrolyte; preferably, the mass percentage of 1,3,6-hexanetrionitrile is 1.3% to 2.8% based on the total mass of the electrolyte; more preferably, the mass percentage of 1,3,6-hexanetrionitrile is 1.8% to 2.5% based on the total mass of the electrolyte. Specifically, the mass percentage of 1,3,6-hexanetrionitrile can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or a range consisting of any two of the above values. In some embodiments of this application, the mass percentage of 1,3,6-hexanetrionitrile can be 0.2% to 2.5%, 0.5% to 2.7%, 0.8% to 2.9%, 1.1% to 3.4%, or 0.9% to 2.8% based on the total mass of the electrolyte. When the mass percentage of 1,3,6-hexanetrionitrile is within the above range, the generation of gas at high temperatures can be further reduced and the high-rate discharge performance of the secondary battery can be improved.

[0075] In some embodiments of this application, based on the total mass of the electrolyte, when the mass percentage of ethyl propionate is a%, the mass percentage of propyl propionate is b%, 1.7 ≤ a / b ≤ 2.5, and the mass percentage range of ethyl propionate is 20% ≤ a ≤ 30%, the mass percentage range of propyl propionate is 11% ≤ b ≤ 15%, the mass percentage of the compound containing the structure shown in Formula I is 0.11% to 4.9%, and the mass percentage of vinylene carbonate is 0.01% to 0.3%; or the mass percentage of boron-containing lithium salt is... The content is 0.01% to 0.25% by mass; or 2% to 5% by mass of fluoroethylene carbonate; or 30% to 40% by mass of propylene carbonate; or 8% to 14% by mass of ethylene carbonate; or 1.1% to 3.5% by mass of 1,3-propanesulfonate lactone; or 1% to 4% by mass of succinic anionyl; or 0.1% to 1% by mass of ethylene glycol bis(propionitrile) ether; or 0.5% to 3% by mass of 1,3,6-hexanetrionitrile.

[0076] In some embodiments of this application, based on the total mass of the electrolyte, when the mass percentage of ethyl propionate is a%, the mass percentage of propyl propionate is b%, 1.9 ≤ a / b ≤ 2.2, and the mass percentage range of ethyl propionate is 20% ≤ a ≤ 30%, the mass percentage range of propyl propionate is 11% ≤ b ≤ 15%, the mass percentage of the compound containing the structure shown in Formula I is 0.11% to 1.0%, and the mass percentage of vinylene carbonate is 0.01% to 0.1%; or the mass percentage of boron-containing lithium salt is... When the content is 0.05% to 0.2%; or the mass percentage of fluoroethylene carbonate is 2% to 5%; or the mass percentage of propylene carbonate is 30% to 40%; or the mass percentage of ethylene carbonate is 8% to 14%; or the mass percentage of 1,3-propanesulfonate lactone is 1.1% to 3%; or the mass percentage of succinic anionyl is 1.1% to 3%; or the mass percentage of ethylene glycol bis(propionitrile) ether is 0.1% to 0.8%; or the mass percentage of 1,3,6-hexanetrionitrile is 0.7% to 2.5%.

[0077] In some embodiments of this application, the electrolyte provided may also contain other components, including but not limited to: diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC). In some embodiments of this application, other components may include ether solvents, including but not limited to: at least one of 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME).

[0078] In some embodiments of this application, the electrolyte provided may further include a lithium salt as the electrolyte. The lithium salt in the electrolyte includes, but is not limited to: LiClO4, LiAsF6, LiPF6, LiSbF6, LiSO3F, LiN(FSO2)2, LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bis(oxalate)borate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, or lithium tetrafluoro(oxalate)phosphate. Furthermore, one of the above lithium salts may be used alone, or two or more may be used simultaneously. In some embodiments, the lithium salt includes LiPF6. In some embodiments, the mass percentage of lithium salt in the electrolyte is 10% to 20% based on the total mass of the electrolyte. Specifically, based on the total mass of the electrolyte, the mass percentage of lithium salt in the electrolyte is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of the above values.

[0079] In some embodiments of this application, the preparation method of the electrolyte provided in this application is not limited and can be prepared in accordance with conventional electrolyte preparation methods. In some embodiments, the electrolyte of this application can be prepared by mixing the components.

[0080] In some embodiments of this application, the silicon-carbon material in the negative electrode active material accounts for 1% to 15% of the total mass of the negative electrode active material; preferably, the silicon-carbon material in the negative electrode active material accounts for 2% to 10% of the total mass of the negative electrode active material. Specifically, the silicon-carbon material in the negative electrode active material accounts for 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% of the total mass of the negative electrode active material, or a range consisting of any two of the above values.

[0081] In some embodiments of this application, the negative electrode active material further comprises graphite, including at least one of artificial graphite or natural graphite.

[0082] In some embodiments of this application, the negative electrode active material further includes an adhesive, which may include various adhesive polymers such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0083] In some embodiments of this application, the negative electrode active material further comprises a conductive agent to improve electrode conductivity. Any conductive material can be used as the conductive material, as long as it does not cause a chemical change. Examples of conductive agents include, but are not limited to: carbon-based materials, such as carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials, such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof.

[0084] In some embodiments of this application, the weight ratio of silicon-carbon material to graphite, conductive agent and binder in the negative electrode active material is 1-15:80-95:0.5-2:1-3.

[0085] In some embodiments of this application, the negative electrode further includes a negative electrode current collector, which includes, but is not limited to: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative electrode current collector is copper foil.

[0086] In some embodiments of this application, the structure of the negative electrode can be a negative electrode structure known in the art that can be used in electrochemical devices.

[0087] In some embodiments of this application, the method for preparing the negative electrode is a method known in the art for preparing negative electrodes that can be used in electrochemical devices. Exemplarily, the negative electrode can be obtained by mixing a negative electrode active material, a conductive agent, and a binder in a solvent, and heating a thickener as needed to prepare a negative electrode active material slurry, coating the negative electrode active material slurry onto a negative electrode current collector, drying, and cold pressing to form a negative electrode active material layer. In some embodiments, the solvent may include, but is not limited to, water and N-methylpyrrolidone.

[0088] In some embodiments of this application, the positive electrode of the secondary battery includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The specific type of positive electrode active material in the positive electrode active material layer is not specifically limited and can be selected according to requirements. In some embodiments of this application, the positive electrode active material includes a lithium transition metal composite oxide. In some embodiments, the positive electrode active material is selected from at least one of the following: lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 (O4) or lithium iron phosphate (LiFePO4).

[0089] In some embodiments of this application, the positive electrode active material layer further includes an adhesive, and optionally, a conductive material. The adhesive can improve the bonding between the positive electrode active material particles and the bonding between the positive electrode active material and the positive electrode current collector. In some embodiments, the adhesive includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, etc.

[0090] In some embodiments of this application, the positive electrode active material layer further includes a conductive material to impart conductivity to the electrode. This conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., carbon black, acetylene black, Ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0091] In some embodiments of this application, the positive current collector is a metal, such as aluminum foil.

[0092] In some embodiments of this application, the structure of the positive electrode is a positive electrode structure known in the art that can be used in secondary batteries.

[0093] In some embodiments of this application, the method for preparing the positive electrode is a well-known method in the art for preparing positive electrodes for secondary batteries. For example, the positive electrode can be obtained by mixing a positive electrode active material, a conductive material, and a binder in a solvent to prepare a positive electrode active material slurry, coating the positive electrode active material slurry onto a positive electrode current collector, drying, and cold pressing to form a positive electrode active material layer. In some embodiments, the solvent may include water, N-methylpyrrolidone, etc., but is not limited thereto.

[0094] In some embodiments of this application, the separator of the secondary battery is used to prevent short circuits. The material and shape of the separator are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. For example, in some embodiments, the separator includes a substrate layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure. The material of the substrate layer can be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from at least one of polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane. At least one surface of the substrate layer is provided with a surface treatment layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by a mixture of polymers and inorganic materials. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles may be selected from one or a combination of several of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder may be selected from one or a combination of several of the following: polyvinylidene fluoride, a polymer of polyvinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0095] In some embodiments of this application, the secondary battery includes, but is not limited to, lithium-ion batteries or sodium-ion batteries. In some embodiments of this application, the secondary battery includes a lithium-ion battery.

[0096] According to a second aspect of this application, an electronic device is provided, comprising a secondary battery as described in any embodiment of the first aspect of this application. In some embodiments, the application does not particularly limit the use of the secondary battery, which can be used in any electrical device or equipment known in the prior art. For example, the electronic device includes, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc. Furthermore, the secondary battery provided in this application is applicable not only to the electronic devices exemplified above, but also to energy storage power stations, maritime transport vehicles, and air transport vehicles, including air transport vehicles within and outside the atmosphere.

[0097] Example

[0098] The following describes the implementation of this application in more detail through specific embodiments and comparative examples.

[0099] The test methods used in the following examples and comparative examples are as follows:

[0100] 1. Electrolyte testing

[0101] The components and their contents in the electrolyte can be determined using methods conventional in the art. For example, the components and their contents in the electrolyte can be detected by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0102] 2. Performance testing of lithium-ion batteries

[0103] 2.1 Gas production

[0104] The lithium-ion battery was charged at 25°C with a constant current and constant voltage of 1C until the termination voltage of 4.4V was reached, followed by constant voltage charging at 4.4V for 5 hours. Then, it was discharged at 0.3C to the termination voltage of 3.0V, and this charge-discharge cycle was repeated five times. The battery was then charged at 70°C with a constant current of 0.3C to 4.4V and held at 4.4V for 5 days. The amount of gas produced after 5 days of storage was determined using the Archimedes method. The relative gas production was calculated based on the gas production of Comparative Example 1-1, which was set to 100%.

[0105] 2.2 High-rate discharge capacity ratio

[0106] Test procedure: The lithium-ion battery was charged to 4.4V at 500mA, and then discharged to 3.0V at 500mA to obtain the discharge capacity C0 of the lithium-ion battery; Additionally, the lithium-ion battery was charged to 4.4V at 500mA, and then discharged to 3.0V at 3A to obtain the discharge capacity C1 of the lithium-ion battery. High-rate discharge capacity ratio = C1 / C2.

[0107] Example 1-1

[0108] 1. Preparation of the negative electrode

[0109] Preparation of silicon-carbon materials:

[0110] A porous carbon framework was prepared: the pore volume of the porous carbon framework was 0.65 g / cc, of which 80% was micropores and mesopores. The porous carbon framework was subjected to a silane deposition reaction. The conditions for the silane deposition reaction included: at 650°C, 22% silane gas was introduced by volume, and nitrogen was introduced as the other gas component, and the reaction time was 9 h to obtain the precursor material. The precursor material was then subjected to a reaction at 100°C, 20% oxygen gas was introduced by volume, and nitrogen was introduced as the other gas component, and the reaction time was 14 h to obtain the silicon-carbon material.

[0111] The silicon-carbon material, artificial graphite, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) prepared above were added to deionized water at a mass ratio of 5:90:1.5:2:1.5 and thoroughly mixed to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the negative electrode current collector copper foil, dried, and cold-pressed to form a negative electrode active material layer. After cutting and welding the tabs, the negative electrode was obtained.

[0112] 2. Preparation of the positive electrode

[0113] Lithium cobalt oxide (CCO), acetylene black (CMO), and polyvinylidene fluoride (PVDF) (PVDF) were mixed in a mass ratio of 96.3:2.2:1.5 in N-methylpyrrolidone (NMP) solvent and stirred thoroughly under vacuum to obtain a CCO slurry. This CCO slurry was then coated onto an aluminum foil current collector, dried, and cold-pressed to form a CCO active material layer. After cutting and welding the tabs, the CCO was obtained.

[0114] 3. Preparation of electrolyte

[0115] In a dry argon-atmospheric glove box, propyl propionate (PP), ethyl propionate (EP), and diethyl carbonate (DEC) were mixed evenly, dissolved, and thoroughly stirred. Then, lithium salt LiPF6, lithium tetrafluoroborate, vinylene carbonate, and compound of formula II were added and mixed evenly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentages were: ethyl propionate 49%, propyl propionate 12.0%, vinylene carbonate 0.03%, lithium tetrafluoroborate 0.1%, compound of formula II 0.65%, lithium salt LiPF6 12%, and the balance being diethyl carbonate.

[0116] 4. Preparation of the separating membrane

[0117] Polyethylene (PE) porous polymer film is used as the separator.

[0118] 5. Preparation of lithium-ion batteries

[0119] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare battery. The bare battery is placed in an outer packaging foil aluminum-plastic film, and electrolyte is injected. After vacuum sealing, standing, formation and other processes, a lithium-ion battery is obtained.

[0120] Examples 1-2 to 1-33, Comparative Examples 1-1 to 1-7

[0121] The electrolyte and lithium-ion battery preparation method of Example 1-1 are compared with those of Example 1-1. The differences are detailed in Table 1.

[0122] Examples 1-34

[0123] This embodiment is based on Embodiment 1-1, except that lithium tetrafluoroborate in the electrolyte is replaced with lithium difluorooxalate borate, and the rest is the same as in Embodiment 1-1.

[0124] Comparative Examples 1-8

[0125] This comparative example is based on Example 1-1, but differs from Example 1-1 in that the preparation method of the negative electrode is changed. The silicon-carbon material in the negative electrode preparation step of Example 1-1 is replaced with artificial graphite. The specific steps for preparing the negative electrode are as follows:

[0126] Artificial graphite, conductive carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are added to deionized water in a mass ratio of 95:1.5:2:1.5 and thoroughly mixed to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto a copper foil current collector, dried, and cold-pressed to form a negative electrode active material layer. After cutting and welding the tabs, the negative electrode is obtained.

[0127] In Table 1, the mass percentage of ethyl propionate is a%, the mass percentage of propyl propionate is b%, the mass percentage of vinylene carbonate is c%, the mass percentage of lithium tetrafluoroborate (or lithium difluorooxalate borate) is d%, the mass percentage of compound II is e%, the mass percentage ratio of ethyl propionate to propyl propionate in the electrolyte is a / b, the sum of the mass percentages of ethyl propionate and propyl propionate in the electrolyte is (a+b)%, and the sum of the mass percentages of vinylene carbonate and lithium tetrafluoroborate in the electrolyte is (c+d)%.

[0128] Table 1

[0129]

[0130]

[0131] According to the results presented in Table 1 above, in the electrolyte of a secondary battery using silicon-carbon material as the negative electrode active material, when the mass percentage ratio of ethyl propionate to propyl propionate (a / b) is controlled within a certain range, and when it is used in combination with at least one of vinylene carbonate, boron-containing lithium salt, or compound of formula II, the high-rate discharge capacity ratio under high temperature and high rate conditions can be significantly improved, and the gas generated under high temperature and high rate conditions can be reduced.

[0132] Based on the results in Table 1 above, the effects of other components and their dosages on the high-temperature gas generation and high-rate discharge capacity ratio of lithium-ion batteries were further investigated, as shown in Table 2:

[0133] Table 2

[0134]

[0135]

[0136]

[0137] As shown in Table 2, when the electrolyte contains at least one of fluoroethylene carbonate, propylene carbonate, or ethylene carbonate, the gas generation of the lithium-ion battery at high temperatures is further reduced, and the high-rate discharge performance is further improved. When the electrolyte contains at least two of 1,3-propanesulfonate lactone, succinate, ethylene glycol bis(propionitrile) ether, or 1,3,6-hexanetrionitrile, the gas generation of the lithium-ion battery at high temperatures is further reduced, and the high-rate discharge performance is further improved.

[0138] It is understood that this application has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this application. Furthermore, based on the teachings of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, which includes silicon-carbon material. The electrolyte contains ethyl propionate and propyl propionate. Based on the total mass of the electrolyte, the mass percentage of ethyl propionate is a%, and the mass percentage of propyl propionate is b%, wherein 1.7 ≤ a / b ≤ 5.

7. The electrolyte also contains at least one of vinylene carbonate, boron-containing lithium salt, and a compound containing the structural formula shown in Formula I. (Formula I); In Formula I, A is selected from C2 to C5 alkylene groups; The electrolyte further comprises at least one of fluoroethylene carbonate, propylene carbonate, and ethylene carbonate. Based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 20% to a and from 70%; the mass percentage of propyl propionate ranges from 11% to b and from 20%; the mass percentage of vinylene carbonate ranges from 0.01% to 0.3%; the mass percentage of boron-containing lithium salt ranges from 0.01% to 0.25%; and the mass percentage of the compound containing the structure shown in Formula I ranges from 0.11% to 4.9%.

2. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage ratio of ethyl propionate to propyl propionate is in the range of 3.1 ≤ a / b ≤ 4.

9.

3. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 36% to a to 54%; or, based on the total mass of the electrolyte, the mass percentage of ethyl propionate ranges from 20% to a to 30%.

4. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of propyl propionate is in the range of 11% ≤ b ≤ 15%.

5. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the sum of the mass percentages of ethyl propionate and propyl propionate is in the range of 32% ≤ a + b ≤ 84%; or, based on the total mass of the electrolyte, the sum of the mass percentages of ethyl propionate and propyl propionate is in the range of 47% ≤ a + b ≤ 65%.

6. The secondary battery according to claim 1, characterized in that, The electrolyte comprises a compound with the structural formula shown in Formula I, wherein the compound containing the structural formula shown in Formula I satisfies at least one of conditions (1) to (2): (1) Based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.15% to 4.9%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.15% to 4.5%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.15% to 3.5%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.11% to 2.5%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 2.0% to 2.5%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.15% to 1.5%; or, based on the total mass of the electrolyte, the mass percentage of the compound containing the structure shown in Formula I is 0.6% to 1.0%. (2) The compound containing the structure shown in Formula I is selected from the compound with the structure shown in Formula II: (Formula II).

7. The secondary battery according to claim 1, characterized in that, The electrolyte satisfies at least one of conditions (3) to (4): (3) The electrolyte contains vinylene carbonate, and the mass percentage of vinylene carbonate is 0.03% to 0.29%; or, the electrolyte contains vinylene carbonate, and the mass percentage of vinylene carbonate is 0.03% to 0.25% based on the total mass of the electrolyte; or, the mass percentage of vinylene carbonate is 0.03% to 0.2% based on the total mass of the electrolyte; or, the mass percentage of vinylene carbonate is 0.03% to 0.15% based on the total mass of the electrolyte; or, the mass percentage of vinylene carbonate is 0.03% to 0.1% based on the total mass of the electrolyte. (4) The electrolyte contains vinylene carbonate and boron-containing lithium salt, and the total mass percentage of the vinylene carbonate and boron-containing lithium salt is 0.04% to 0.2% based on the total mass of the electrolyte.

8. The secondary battery according to claim 1, characterized in that, The electrolyte contains a boron-containing lithium salt, which satisfies at least one of conditions (5) to (6): (5) The boron-containing lithium salt content is 0.05% to 0.25% by mass based on the total mass of the electrolyte; or, the boron-containing lithium salt content is 0.07% to 0.25% by mass based on the total mass of the electrolyte; or, the boron-containing lithium salt content is 0.06% to 0.2% by mass based on the total mass of the electrolyte. (6) The boron-containing lithium salt is selected from at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium borate.

9. The secondary battery according to claim 1, characterized in that, The electrolyte satisfies at least one of conditions (7) to (9): (7) The electrolyte contains fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate is 2% to 7% based on the total mass of the electrolyte; or, the mass percentage of the fluoroethylene carbonate is 2% to 5% based on the total mass of the electrolyte; (8) The electrolyte contains propylene carbonate, and the mass percentage of propylene carbonate is 20% to 40% based on the total mass of the electrolyte; or, the mass percentage of propylene carbonate is 20% to 30% based on the total mass of the electrolyte. (9) The electrolyte contains ethylene carbonate, and the mass percentage of ethylene carbonate is 4% to 18% based on the total mass of the electrolyte; or, the mass percentage of ethylene carbonate is 5% to 18% based on the total mass of the electrolyte; or, the mass percentage of ethylene carbonate is 10% to 18% based on the total mass of the electrolyte.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The electrolyte further comprises at least two of 1,3-propanesulfonate lactone, succinate, ethylene glycol bis(propionitrile) ether, and 1,3,6-hexanetrionitrile.

11. The secondary battery according to claim 10, characterized in that, The electrolyte satisfies at least one of conditions (10) to (13): (10) The electrolyte contains 1,3-propanesulfonate lactone, and the mass percentage of 1,3-propanesulfonate lactone is 0.1% to 4% based on the total mass of the electrolyte; or, the mass percentage of 1,3-propanesulfonate lactone is 0.8% to 3.1% based on the total mass of the electrolyte; (11) The electrolyte contains succinate, and the succinate content by mass is 0.1% to 4% based on the total mass of the electrolyte; or, the succinate content by mass is 0.2% to 2.5% based on the total mass of the electrolyte. (12) The electrolyte contains ethylene glycol bis(propionitrile) ether, and the mass percentage of the ethylene glycol bis(propionitrile) ether is 0.01% to 1% based on the total mass of the electrolyte; or, the mass percentage of the ethylene glycol bis(propionitrile) ether is 0.1% to 0.8% based on the total mass of the electrolyte; (13) The electrolyte contains 1,3,6-hexanetrionitrile, and the mass percentage of the 1,3,6-hexanetrionitrile is 0.1% to 3.5% based on the total mass of the electrolyte; or, the mass percentage of the 1,3,6-hexanetrionitrile is 0.2% to 2.5% based on the total mass of the electrolyte.

12. The secondary battery according to claim 1, characterized in that, The silicon-carbon material accounts for 1% to 15% of the mass of the negative electrode active material.

13. An electronic device, characterized in that, The electronic device comprises a secondary battery as described in any one of claims 1 to 12.

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