Non-aqueous electrolyte of high-voltage lithium cobalt oxide secondary battery, and lithium secondary battery

Abstract

A non-aqueous electrolyte of a lithium secondary battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte lithium salt, and additives. The additives comprise a first additive and a second additive. The first additive comprises a sulfonimide compound, and the second additive comprises a nitrile compound. The combined use of the first additive and the second additive can effectively mitigate the gas generation problem caused by the first additive and the impedance increase problem caused by the second additive, thereby improving the long-cycle performance of high-voltage lithium cobalt oxide secondary batteries.

Description

A non-aqueous electrolyte for a high-voltage lithium cobalt oxide secondary battery and the lithium secondary battery itself.

[0001] This application claims priority to Chinese Patent Application No. 202411038314.0, filed on July 31, 2024, entitled "A Non-Aqueous Electrolyte for a High-Voltage Lithium Cobalt Oxide Secondary Battery and a Lithium Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium secondary battery technology, and in particular to a high-voltage lithium cobalt oxide lithium secondary battery non-aqueous electrolyte and a lithium secondary battery. Background Technology

[0003] Lithium-ion batteries are a type of battery that relies on lithium ions (Li... + Secondary batteries, which move between positive and negative electrodes to achieve charging and discharging, have been widely used in mobile phones, tablets, laptops, smartwatches, drones, electric bicycles, electric cars, and other power tools in recent years, permeating every corner of our lives. As consumer electronics demand increasingly longer battery life from lithium-ion batteries, there is an urgent need to further improve their volumetric energy density.

[0004] Lithium cobalt oxide (LiCoO2) is the most widely used positive electrode active material in consumer lithium-ion rechargeable batteries. For lithium cobalt oxide batteries, increasing the charging voltage is one of the most effective ways to improve the battery's energy density. A higher charging cutoff voltage (≥4.4V) results in more active Li₂ participating in the insertion / extraction process. + The higher the specific capacity of the positive electrode active material, the greater its actual specific capacity. High-voltage lithium cobalt oxide materials generally refer to lithium cobalt oxide materials with a charging voltage higher than 4.35V. Currently, high-voltage lithium cobalt oxide products on the market are divided into models such as 4.35V, 4.4V, 4.45V, 4.48V, and 4.5V. The volumetric energy density of 4.6V lithium cobalt oxide can reach as high as 3696.0Wh / L, far exceeding that of other positive electrode active materials. However, increasing the upper limit of the charging voltage of lithium secondary batteries brings a series of problems, such as material phase transitions, interfacial side reactions, cobalt metal dissolution, and oxygen evolution, leading to a rapid decline in material performance, especially cycle performance. Therefore, how to improve the cycle stability of lithium secondary batteries while increasing the charging cut-off voltage has become one of the difficulties and bottlenecks in lithium secondary battery design. Summary of the Invention

[0005] The purpose of this application is to provide a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery itself, so as to improve the cycle stability of high-voltage lithium cobalt oxide battery systems. The specific technical solution is as follows:

[0006] The first aspect of this application provides a non-aqueous electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent, an electrolyte lithium salt, and additives; the additives include a first additive and a second additive; the first additive includes a sulfonylimide compound, and the second additive includes a nitrile compound.

[0007] The first additive is selected from the compound shown in Formula A:

[0008] Wherein, R1 is selected from halogens, unsubstituted or halogen-substituted phenyl groups, unsubstituted or halogen-substituted pyridyl groups, and unsubstituted or halogen-substituted C1-C groups. 10 Hydrocarbon group, unsubstituted or halogenated C1-C 10 alkoxyalkyl, phosphate ester, sulfonate and C1-C 10 Any of the silane groups; R2 and R3 are each individually selected from halogens, unsubstituted or halogen-substituted phenyl groups, and unsubstituted or halogen-substituted C1-C groups. 10 Any of the alkyl groups.

[0009] This application combines a first additive with a second additive to synergistically improve the long-cycle performance of high-voltage lithium cobalt oxide secondary batteries. The first additive, rich in F and S elements, can construct a stable, highly ionicly conductive SEI (Solid electrolyte Interface) / CEI (Chemical-electrochemical Interface) interface on the surfaces of the negative and positive electrodes, effectively mitigating the decomposition of the lithium salt electrolyte during cycling, thereby improving the cycle stability of the lithium secondary battery. However, the first additive undergoes reductive decomposition after being attacked by electrons during cycling, and the decomposition products (e.g., It possesses a strong electron-donating ability, which can attack carbonate solvents, leading to solvent decomposition and gas production. This gas production is exacerbated at high temperatures. Furthermore, under high-temperature conditions, the decomposition products of electrolyte lithium salts readily form F... -This leads to HF erosion of the cathode material. Furthermore, a second additive is introduced. This second additive improves the overall oxidation resistance of the electrolyte. Its cyano group can coordinate with Co ions dissolved from the lithium cobalt oxide cathode and participate in the formation of the CEI, inhibiting electrolyte decomposition and reducing side reactions caused by voltage increases within the battery, further improving the battery's cycle stability. Moreover, the cyano group in the second additive has electron-withdrawing capabilities, interacting with the decomposition products generated by the electron attack of the first additive, thereby improving the situation where carbonate solvent is attacked and decomposes, producing gas. In addition, the cyano group can preferentially capture H protons, inhibiting HF formation. However, using nitrile compounds alone as additives results in high interfacial impedance, leading to larger battery electrodes, hindering lithium ion insertion / extraction, and negatively impacting cycle performance. The first additive, on the other hand, can suppress the increase in impedance during cycling. The synergistic effect of the two additives can form an interfacial film rich in inorganic components, optimizing the film composition and further reducing film impedance, thereby achieving long-cycle performance of high-voltage lithium cobalt oxide.

[0010] In summary, by adding the first additive and the second additive of this application to the electrolyte, the synergistic effect of the first additive and the second additive can effectively improve the gas generation phenomenon caused by the first additive and the impedance increase caused by nitrile compounds, while achieving long cycle performance of high-voltage lithium cobalt oxide secondary batteries.

[0011] In one embodiment of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 5%. For example, W1 can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two sets of values. If W1 is less than 0.1%, the content of the component participating in film formation is too low and it cannot improve the interface. If W1 is greater than 5%, it will lead to increased gas production and excessive HF formation, which will cause the battery performance to deteriorate. The content of W2 should be 0.1% ≤ W2 ≤ 8%, for example, W2 can be 0.1%, 0.5%, 1.0%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any two of these values. If W2 is less than 0.1%, the gas generation of the first additive and the effects of HF corrosion cannot be effectively suppressed, and the long-cycle performance of the battery cannot be guaranteed. If W2 is greater than 8%, it will lead to a significant increase in battery impedance, hindering the insertion / extraction of lithium ions and degrading the cycle performance. By adding the first additive and the second additive of this application to the electrolyte and controlling the content of the first additive and the second additive within the range of this application, the gas generation phenomenon caused by the first additive and the impedance increase caused by nitrile compounds can be effectively improved through the synergistic effect of the first additive and the second additive, while improving the long-cycle performance of the high-voltage lithium cobalt oxide secondary battery.

[0012] In one embodiment of this application, R2 and R3 in compound A are the same.

[0013] In one embodiment of this application, the second additive is selected from at least one of succinic anionyl nitrile (SN), glutaronitrile (GN), adiponitrile (ADN), trans-butenedionitrile, trans-hexenedionitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarbonyl nitrile (HTCN), and ethylene glycol (bis)propionitrile ether (DENE).

[0014] In one embodiment of this application, the first additive is selected from at least one of the following compounds:

[0015] In one embodiment of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 2%, 2% ≤ W2 ≤ 6%. Controlling the mass percentage content of the first additive and the second additive of this application within the above range can further improve the cycle stability of the lithium secondary battery and suppress the increase in impedance.

[0016] In one embodiment of this application, the non-aqueous electrolyte of the lithium secondary battery further includes other additives selected from at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylene carbonate (VC), 1,3-propenesulfonate lactone (PS), vinyl sulfate, and methanedisulfonate. Based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W3 of the other additives satisfies: 0.5% ≤ W3 ≤ 25%. Adding other additives to the electrolyte can enhance the interfacial film formation on the electrode surface, inhibit electrolyte decomposition, and improve the lithium-ion insertion rate during cycling, thereby giving the high-voltage lithium cobalt oxide secondary battery better cycle stability.

[0017] In one embodiment of this application, the non-aqueous organic solvent comprises a carbonate solvent, which is selected from at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate. Based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W4 of the non-aqueous organic solvent satisfies: 50% ≤ W4 ≤ 80%. The non-aqueous organic solvent is the main component of the non-aqueous electrolyte of the lithium secondary battery. By selecting the non-aqueous organic solvent of this application and controlling the mass percentage of the non-aqueous solvent within the range of this application, the lithium salt can have a higher solubility, thereby giving the electrolyte a higher ionic conductivity.

[0018] In one embodiment of this application, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W5 of the electrolyte lithium salt satisfies: 8% ≤ W5 ≤ 18%. Using at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the electrolyte lithium salt, and controlling the mass percentage of the electrolyte lithium salt within the range of this application, can improve the lithium ion transport capacity in the electrolyte, form a more stable SEI / CEI interface on the electrode surface, reduce the lithium ion transport impedance, and thus give the high-voltage lithium cobalt oxide secondary battery better cycle stability.

[0019] A second aspect of this application provides a lithium secondary battery, which includes a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte of the lithium secondary battery of this application.

[0020] In one embodiment of this application, the positive electrode includes a positive electrode active material, which is lithium cobalt oxide.

[0021] In one embodiment of this application, the charging cut-off voltage of the lithium secondary battery is ≥4.4V. For lithium cobalt oxide batteries, increasing the charging voltage is one of the most effective methods to improve battery energy density. The higher the charging cut-off voltage (≥4.4V), the more active Li₂ participating in the insertion / extraction process... + The more [amount], the higher the actual specific capacity of the positive electrode active material.

[0022] The beneficial effects of this application are:

[0023] This application provides a non-aqueous electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, an electrolyte lithium salt, and additives; the additives include a first additive and a second additive; the first additive comprises a sulfonylimide compound, and the second additive comprises a nitrile compound; the first additive is selected from compounds shown in Formula A. By using the first and second additives in combination, this application can effectively improve the gas generation phenomenon caused by the first additive and the impedance increase problem caused by the nitrile compound, thereby achieving long-cycle performance of high-voltage lithium cobalt oxide secondary batteries. By adding the first and second additives of this application to the electrolyte and controlling their contents within the range specified in this application, the synergistic effect of the first and second additives can improve the long-cycle performance of high-voltage lithium cobalt oxide secondary batteries and effectively improve the gas generation phenomenon caused by the first additive and the impedance increase problem caused by the nitrile compound.

[0024] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following embodiments are provided to further illustrate this application in detail. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] This application provides a non-aqueous electrolyte for lithium secondary batteries, comprising a non-aqueous organic solvent, an electrolyte lithium salt, and additives; the additives include a first additive and a second additive; the first additive comprises a sulfonylimide compound, and the second additive comprises a nitrile compound; the first additive is selected from compounds shown in Formula A:

[0027] Wherein, R1 is selected from halogens, unsubstituted or halogen-substituted phenyl groups, unsubstituted or halogen-substituted pyridyl groups, and unsubstituted or halogen-substituted C1-C groups. 10 Hydrocarbon group, unsubstituted or halogenated C1-C 10 alkoxyalkyl, phosphate ester, sulfonate and C1-C 10 Any of the silane groups; R2 and R3 are each individually selected from halogens, unsubstituted or halogen-substituted phenyl groups, and unsubstituted or halogen-substituted C1-C groups. 10 Any of the alkyl groups. This application uses the first additive and the second additive in combination to improve the cycle stability of lithium secondary batteries and suppress impedance increase. By adding the first additive and the second additive of this application to the electrolyte and controlling the content of the first additive and the second additive within the range of this application, the long-cycle performance of high-voltage lithium cobalt oxide secondary batteries can be improved through the synergistic effect of the first additive and the second additive.

[0028] In one embodiment of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 5%, 0.1% ≤ W2 ≤ 8%. By adding the first and second additives of this application to the electrolyte and controlling their contents within the range specified in this application, the synergistic effect of the first and second additives can effectively improve the gas generation phenomenon caused by the first additive and the impedance increase problem caused by nitrile compounds. Simultaneously, it achieves long-cycle performance of the high-voltage lithium cobalt oxide secondary battery.

[0029] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive can be 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 4.5%, 5%, or a range of any two values ​​therein, and the mass percentage content W2 of the second additive can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range of any two values ​​therein.

[0030] In some embodiments of this application, R2 and R3 in compound A are the same.

[0031] In some embodiments of this application, the second additive is selected from at least one of butadionitrile, glutaronitrile, adiponitrile, trans-butenedionitrile, trans-hexenedionitrile, 1,2-di(cyanoethoxy)ethane, 1,3,6-hexanetricarbonyl ether and ethylene glycol (bis)propionitrile ether.

[0032] In some embodiments of this application, the first additive is selected from at least one of the following compounds:

[0033] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 2%, 2% ≤ W2 ≤ 6%. Controlling the mass percentage content of the first additive and the second additive within the range of this application can promote the synergistic effect of the first additive and the second additive, significantly improve the cycle stability and suppress the increase of impedance during the cycling process of the lithium secondary battery.

[0034] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive can be 0.1%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values, and the mass percentage content W2 of the second additive can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range of any two of these values.

[0035] In some embodiments of this application, the non-aqueous electrolyte of the lithium secondary battery further includes other additives selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propenesulfonate lactone, vinyl sulfate, and methanedisulfonate. Based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W3 of the other additives satisfies: 0.5% ≤ W3 ≤ 25%. Adding other additives to the electrolyte can enhance the interfacial film formation on the electrode surface, inhibit electrolyte decomposition, and improve the lithium-ion insertion rate during cycling, thereby giving the high-voltage lithium cobalt oxide secondary battery better cycle stability.

[0036] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W3 of the other additives can be 0.5%, 1%, 5%, 8%, 10%, 15%, 20%, 23%, 25%, or a range of any two of these values.

[0037] In some embodiments of this application, the non-aqueous organic solvent comprises a carbonate solvent selected from at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate; based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W4 of the non-aqueous organic solvent satisfies: 50% ≤ W4 ≤ 80%.

[0038] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W4 of the non-aqueous organic solvent can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range of any two of these values.

[0039] In some embodiments of this application, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W5 of the electrolyte lithium salt satisfies: 8% ≤ W5 ≤ 18%. Using at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the electrolyte lithium salt, and controlling the mass percentage of the electrolyte lithium salt within the range of this application, can improve the lithium ion transport capacity in the electrolyte, form a more stable SEI / CEI interface on the electrode surface, reduce the lithium ion transport impedance, and thus give the high-voltage lithium cobalt oxide secondary battery better cycle stability.

[0040] In some embodiments of this application, based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W5 of the electrolyte lithium salt can be 8%, 10%, 12%, 14%, 15%, 16%, 18%, or a range of any two of these values.

[0041] A second aspect of this application provides a lithium secondary battery, the lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte for lithium secondary batteries.

[0042] In some embodiments of this application, the positive electrode includes a positive electrode active material, which is lithium cobalt oxide.

[0043] In some embodiments of this application, the charging cut-off voltage of the lithium secondary battery is ≥4.4V. For lithium cobalt oxide batteries, increasing the charging voltage is one of the most effective methods to improve battery energy density. The higher the charging cut-off voltage (≥4.4V), the more active Li₂ participating in the insertion / extraction process... + The more [amount], the higher the actual specific capacity of the positive electrode active material.

[0044] The lithium-ion secondary battery of this application also includes a positive electrode sheet. For example, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. This application does not have any particular limitation on the positive current collector, as long as it can achieve the purpose of this application. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil is aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer disposed on at least one surface of the polymer material base layer. For example, the material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. The polymer material base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, or polyethylene. This application does not have any particular limitation on the thickness of the positive current collector and the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the positive current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode material layer is 30 μm to 120 μm. In this application, the positive electrode material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or it can be disposed on two surfaces in the thickness direction of the positive electrode current collector.

[0045] The positive electrode material layer of this application may further include a conductive agent and a binder. This application does not impose any particular limitations on the conductive agent and binder, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder may include, but is not limited to, at least one of polyvinyl chloride, polyacryl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0046] The lithium-ion secondary battery of this application includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. This application does not impose any particular limitation on the negative electrode current collector; any negative electrode current collector known in the art can be used, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise at least one of aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, and copper foam. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 150 μm. In this application, the negative electrode material layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. Optionally, the negative electrode active material includes a thickener, which may include, but is not limited to, sodium carboxymethyl cellulose. The negative electrode material layer of this application may also include a conductive agent and a binder. This application does not impose any particular limitations on the conductive agent and the binder, as long as they can achieve the purpose of this application. For example, the binder and conductive agent may include, but are not limited to, at least one of the optional materials for the positive electrode material layer described above.

[0047] The negative electrode material layer of this application includes a negative electrode active material. This application does not impose any particular limitation on the type of negative electrode active material; any negative electrode active material known in the art can be used, as long as it achieves the purpose of this application. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate.

[0048] The lithium-ion secondary battery of this application also includes a separator to separate the positive electrode and the negative electrode, prevent internal short circuits, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the type of separator; any porous structure separator with good chemical and mechanical stability can be selected. For example, the separator material can include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator type can include, but is not limited to, at least one of woven membrane, nonwoven membrane (nonwoven fabric), microporous membrane, composite membrane, rolled membrane, or spun membrane. The separator can be a single-layer thin film or a multi-layer composite thin film. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness can be from 5 μm to 500 μm.

[0049] The lithium-ion secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art in the electrochemical device. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0050] The preparation process of the lithium-ion secondary battery of this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a lithium-ion secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a lithium-ion secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the lithium-ion secondary battery from rising and overcharging / discharging.

[0051] The battery of this application may be in the form of a single battery cell, a battery module, or a battery pack. A single battery cell can be assembled into a battery module, and a battery module may contain one or more battery cells; the specific number can be selected by those skilled in the art based on the application and capacity of the battery module. The battery modules of this application can also be assembled into a battery pack, and a battery pack may contain one or more battery modules; the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0052] A third aspect of this application provides an electrical device comprising the non-aqueous electrolyte for a lithium secondary battery provided in the first aspect of this application and the lithium secondary battery provided in the second aspect of this application. The electrical device provided in the third aspect of this application exhibits good cycle stability.

[0053] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. In some embodiments, the electrical device may include, 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, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0054] Example

[0055] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0056] Test methods and equipment:

[0057] ambient temperature cycling performance test

[0058] The lithium secondary battery was placed in a 25℃ environment and left to stand for 2 hours. It was then charged at a constant current of 1C to a voltage of 4.5V, and then charged at a constant voltage of 4.5V until the cutoff current reached 0.05C, thus achieving a fully charged state. The lithium secondary battery was then placed in a 25℃ environment for 5 minutes, and then discharged at a constant current of 1C to 3.0V. This constitutes one charge-discharge cycle, and the initial discharge capacity was recorded as C1. This charge-discharge cycle was repeated for 400 cycles, and the discharge capacity C1 in the 400th cycle was recorded. 400 Room temperature cycling capacity retention rate = (C 400 / C1)×100%.

[0059] High-temperature cycling performance test

[0060] The lithium secondary battery was placed in a 45℃ environment and left to stand for 2 hours. It was then charged at a constant current of 1C to a voltage of 4.5V, and then charged at a constant voltage of 4.5V until the cutoff current reached 0.05C, thus achieving a fully charged state. The lithium secondary battery was then placed in a 45℃ environment for 5 minutes, and then discharged at a constant current of 1C to 3.0V. This constitutes one charge-discharge cycle, and the initial discharge capacity was recorded as C1. This charge-discharge cycle was repeated for 400 cycles, and the discharge capacity C on the 400th cycle was recorded. 400 High-temperature cycling capacity retention rate = (C 400 / C1)×100%.

[0061] Thickness expansion rate test after 14 days of high temperature storage

[0062] The lithium-ion battery was placed in a constant temperature environment of 25℃ and charged at a constant current of 1C until the voltage reached 4.5V. It was then charged at a constant voltage of 4.5V until the cutoff current reached 0.05C. The thickness of the lithium-ion battery was recorded as D0. After storing the lithium-ion battery in a 60℃ explosion-proof oven for 14 days, the thickness of the lithium-ion battery was measured and recorded as D1. The thickness expansion rate of the lithium-ion battery was calculated as follows: Thickness expansion rate (%) = (D1 - D0) / D0 × 100%.

[0063] Battery impedance test

[0064] After formation, the battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. It was then charged at a constant current of 1C to 4.5V, charged at a constant voltage of 4.5V to the cutoff current of 0.05C, and discharged at a constant current of 1C to 3.0V. The initial discharge capacity of the battery was then measured.

[0065] Next, charge the battery at a constant current of 1C to 4.5V, then charge it at a constant voltage of 4.5V until the cutoff current is 0.05C. Discharge it at a constant current of 1C to 50% of its rated capacity, and record the battery voltage value as V1. After letting the battery rest for 1 hour, discharge it for 10 seconds using a current I0 corresponding to a 2C rate, and record the battery voltage value as V2. Calculate the battery's DC impedance DCIR: DCIR = (V1 - V2) / I0.

[0066] Example 1

[0067] <Preparation of Electrolyte>

[0068] In an argon-atmosphere glove box with moisture <10 ppm and oxygen <1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 20:20:20:40 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6), compound A-1, and succinic anionyl nitrile (SN) were added to the base solvent and stirred until homogeneous to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentages of LiPF6, A-1, and SN were 14%, 0.1%, and 4%, respectively.

[0069] <Preparation of the positive electrode>

[0070] Lithium cobalt oxide (LiCoO2), a positive electrode active material, polyvinylidene fluoride (PVDF), a positive electrode binder, and conductive carbon black, a conductive agent, were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 68 wt%. The positive electrode slurry was uniformly coated onto one surface of a 16 μm thick aluminum foil current collector. After drying at 85°C, a single-sided positive electrode sheet with a 96 μm coating thickness was obtained. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet. After drying under vacuum at 85°C, the sheet underwent cold pressing, edge trimming, cutting, slitting, sheet forming, and electrode tab welding and adhesive bonding processes to obtain a positive electrode sheet with dimensions of 558 mm × 55 mm. The compaction density of the positive electrode material layer was 4.15 g / cm³. 3 .

[0071] <Preparation of Negative Electrode Sheets>

[0072] A mixture of graphite (negative electrode active material), conductive carbon black (conductive agent), carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) was prepared at a mass ratio of 96.3:1:1.2:1.5. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 49 wt%. The negative electrode slurry was uniformly coated onto one surface of a 9 μm thick copper foil current collector. After drying at 85°C, a single-sided negative electrode sheet with a 92 μm coating thickness was obtained. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet. After drying under vacuum at 85°C, the sheet underwent cold pressing, edge trimming, cutting, slitting, sheet forming, and tab welding and adhesive bonding to obtain a negative electrode sheet with dimensions of 708 mm × 59 mm. The compaction density of the negative electrode material layer was 1.6 g / cm³. 3 .

[0073] <Preparation of the diaphragm>

[0074] The diaphragm is SP312J3020H diaphragm purchased from Xingyuan Material.

[0075] <Preparation of Lithium Secondary Batteries>

[0076] The separator, positive electrode, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to isolate them. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, thus obtaining the electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside of the bag to the outside. After drying at 85°C for 48 hours to remove moisture, it is heat-sealed to obtain the cell ready for electrolyte injection. The prepared electrolyte is then injected into the dried cell. Following vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion secondary battery is obtained.

[0077] Examples 2 to 6

[0078] Except for adjusting the mass percentage W1 of the first additive based on the total mass of the electrolyte according to Table 1 in the <Preparation of Electrolyte>, the rest is the same as in Example 1.

[0079] Examples 7 to 13

[0080] Except for adjusting the mass percentages W1 and W2 of the first and second additives based on the total mass of the electrolyte in Table 1 during the <Preparation of Electrolyte>, the rest is the same as in Example 1.

[0081] Examples 14 to 19

[0082] Except for adjusting the type of the second additive according to Table 1 in the <Preparation of Electrolyte>, and adjusting the mass percentages W1 and W2 of the first and second additives based on the total mass of the electrolyte, the rest is the same as in Example 1.

[0083] Examples 20 to 28

[0084] In the <Preparation of Electrolyte>, the types of the first and second additives were adjusted according to Table 1, and the mass percentages of the first and second additives, W1 and W2, based on the total mass of the electrolyte were adjusted, except that the rest were the same as in Example 1.

[0085] Examples 29 to 30

[0086] Except for adding other additives according to Table 2 in the <Preparation of Electrolyte> and adjusting the mass percentage content W3 of other additives based on the total mass of the electrolyte, the rest is the same as in Example 5.

[0087] Comparative Examples 1 to 4

[0088] Except for the fact that in the <Preparation of Electrolyte>, only one of the first additive and the second additive is added, and the types and contents of the first additive and the second additive are adjusted according to Table 1, the rest is the same as in Example 1.

[0089] Comparative Examples 5 to 8

[0090] In the <Preparation of Electrolyte>, the types of the first and second additives were adjusted according to Table 1, and the mass percentages W1 and W2 of the first and second additives based on the total mass of the electrolyte were adjusted, with the rest being the same as in Example 1.

[0091] In Tables 1 and 2, SN is succinate, HTCN is 1,3,6-hexanetricarbonate, ADN is adiponitrile, FEC is fluoroethylene carbonate, PS is 1,3-propenesulfonate lactone, and VC is vinylene carbonate. The preparation and performance parameters of each example and comparative example are shown in Tables 1 and 2.

[0092] Table 1

[0093] Table 2

[0094] As can be seen from the comparison between the examples and Comparative Examples 1 to 8, the non-aqueous electrolyte for lithium secondary batteries in this application includes a first additive and a second additive. The first additive includes sulfonylimide compounds, and the second additive includes nitrile compounds. The mass percentages W1 and W2 of the first and second additives are controlled within the scope of this application. However, the non-aqueous electrolyte for lithium secondary batteries in the comparative examples does not simultaneously meet the above characteristics and cannot achieve good room temperature cycle capacity retention and high temperature cycle capacity retention.

[0095] This application combines the first additive and the second additive to effectively improve the gas generation phenomenon caused by the first additive and the impedance increase caused by nitrile compounds. This significantly improves cycle stability and suppresses impedance increase during the cycling process of lithium secondary batteries. Examples 1 to 6, Comparative Examples 7 and 8 show that the thickness expansion rate of the lithium-ion battery increases with the increase of the first additive content. Examples 7 to 13, Comparative Examples 5 and 6 show that the battery impedance increases with the increase of the second additive content. Comparison shows that adding the first and second additives of this application to the electrolyte, and controlling their contents within the range of this application, through the synergistic effect of the first and second additives, can enable high-voltage lithium cobalt oxide secondary batteries to have high room-temperature cycle capacity retention and high-temperature cycle capacity retention, while also exhibiting low thickness expansion rate and low impedance.

[0096] As can be seen from Examples 29, 30 and 5, adding other additives to the electrolyte can enhance the interfacial film formation on the electrode surface, inhibit the decomposition of the electrolyte, and improve the lithium ion insertion rate during cycling, thereby giving the high-voltage lithium cobalt oxide secondary battery better cycle stability.

[0097] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A non-aqueous electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent, an electrolyte lithium salt, and additives; the additives comprising a first additive and a second additive; the first additive comprising a sulfonylimide compound, and the second additive comprising a nitrile compound; The first additive is selected from the compound shown in Formula A: in, R1 is selected from halogens, unsubstituted or halogenated phenyl groups, unsubstituted or halogenated pyridyl groups, and unsubstituted or halogenated C1-C groups. 10 Hydrocarbon group, unsubstituted or halogenated C1-C 10 alkoxyalkyl, phosphate ester, sulfonate and C1-C 10 Any of the silane groups; R2 and R3 are each individually selected from halogens, unsubstituted or halogen-substituted phenyl groups, and unsubstituted or halogen-substituted C1-C groups. 10 Any of the alkyl groups.

2. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, Based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 5%, 0.1% ≤ W2 ≤ 8%.

3. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, R2 and R3 are the same.

4. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, The second additive is selected from at least one of butadionitrile, glutaronitrile, adiponitrile, trans-butenedionitrile, trans-hexenedionitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarbonyl ether and ethylene glycol (bis)propionitrile ether.

5. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, The first additive is selected from at least one of the following compounds:

6. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, 0.1% ≤ W1 ≤ 2%, 2% ≤ W2 ≤ 6%.

7. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, The non-aqueous electrolyte for the lithium secondary battery also includes other additives, which are selected from at least one of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propenesulfonate lactone, vinyl sulfate, and methane disulfonate; based on the total mass of the non-aqueous electrolyte for the lithium secondary battery, the mass percentage W3 of the other additives satisfies: 0.5% ≤ W3 ≤ 25%.

8. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, The non-aqueous organic solvent includes carbonate solvents, which are selected from at least one of ethylene carbonate, propylene carbonate, and diethyl carbonate; based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W4 of the non-aqueous organic solvent satisfies: 50% ≤ W4 ≤ 80%.

9. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein, The electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide; based on the total mass of the non-aqueous electrolyte of the lithium secondary battery, the mass percentage W5 of the electrolyte lithium salt satisfies: 8% ≤ W5 ≤ 18%.

10. A lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary batteries according to any one of claims 1 to 9, wherein the lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte for lithium secondary batteries.

11. The lithium secondary battery according to claim 10, wherein, The positive electrode includes a positive electrode active material, which is lithium cobalt oxide.

12. The lithium secondary battery according to claim 10, wherein, The charging cutoff voltage of the lithium secondary battery is ≥4.4V.

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