Electrochemical device and preparation method therefor, and vehicle comprising electrochemical device

Abstract

An electrochemical device, comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer that are stacked; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer that are stacked; the electrolyte comprises a lithium salt, a non-aqueous solvent, and an additive; the positive electrode active material layer comprises a lithium supplementing agent; the non-aqueous solvent comprises carboxylate; and the additive comprises vinylene carbonate.

Description

An electrochemical device, its preparation method, and a vehicle including the electrochemical device.

[0001] Cross-references to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411857316.2, filed on December 16, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure pertains to the field of battery manufacturing technology, and relates to an electrochemical device, particularly an electrochemical device and its preparation method, and a vehicle including the electrochemical device. Background Technology

[0004] In recent years, the development trend of new energy vehicles has been continuously positive, electric vehicles have been rapidly popularized, and the shipment volume of lithium iron phosphate batteries and ternary batteries in the field of electrochemical devices has been increasing year by year. Summary of the Invention

[0005] The purpose of this disclosure is to provide an electrochemical device, its preparation method, and its application. Through the synergistic effect between lithium replenishment agent, carboxylic acid ester, and vinylene carbonate, the problem of battery swelling and cycle performance degradation under high temperature conditions is effectively solved, the service life of fast-charging batteries is extended, and it is conducive to large-scale promotion and application.

[0006] In a first aspect, embodiments of this disclosure provide an electrochemical device, including a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer stacked together, and the negative electrode includes a negative current collector and a negative active material layer stacked together. The electrolyte includes a lithium salt, a non-aqueous solvent, and an additive. The positive active material layer contains a lithium replenishing agent. The non-aqueous solvent includes a carboxylic acid ester, and the additive includes vinylene carbonate (VC).

[0007] The chemical formula of the lithium supplement is: Li x M y O z Wherein, M is selected from any one or at least two of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo or Sn, and 1≤x≤8, y>0, 0<z≤13.

[0008] This embodiment of the invention adds a carboxylic acid ester to a non-aqueous solvent. Due to its lower viscosity, this significantly improves the ionic conductivity of the electrolyte and reduces the desolvation energy, thereby improving electrolyte kinetics and enhancing the fast-charging capability of the battery cell. However, because the carboxylic acid ester is relatively reactive at both the positive and negative electrodes, it is prone to side reactions, causing the positive electrode metal to dissolve. The dissolved metal then deposits on the negative electrode, further degrading the negative electrode interface and negatively impacting high-temperature cycling performance. To address this, this embodiment introduces vinylene carbonate into the electrolyte, which can form a stable SEI (solid electrolyte interface) film at the negative electrode, thereby reducing the side reactions between the carboxylic acid ester and the negative electrode. Simultaneously, a specific type of lithium replenishing agent is added to the positive electrode active material layer to compensate for lithium loss caused by side reactions, thus ensuring no degradation during cycling. Ultimately, through the synergistic effect between the lithium replenishing agent, carboxylic acid ester, and vinylene carbonate, the problems of battery swelling and cycle performance degradation under high-temperature conditions are effectively solved, extending the lifespan of fast-charging batteries and facilitating large-scale application.

[0009] In some embodiments, the total mass of non-aqueous solvents is used as the calculation basis, and the content of the carboxylic acid ester is a%, where the value of a ranges from 5 to a ≤ 75.

[0010] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of vinylene carbonate is b%, where the value of b ranges from 0.1 to 5.

[0011] In some embodiments, the total mass of the positive electrode is used as the calculation basis, and the content of the lithium replenishing agent is c%, where the value of c ranges from 0.2 to 3.

[0012] In some embodiments, the content relationship of the carboxylic acid ester, vinylene carbonate and lithium supplement is: 0.03≤(b+c) / a≤0.75.

[0013] In some embodiments, the lithium supplement includes Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li6MnO4, Li6ZnO4, Li2CuO2, Li2CoO2, Li2MnO2, Li2C2O4, and Li2Ni 0.5 Mn 1.5 O4 or Li(Ni) 0.8 Co 0.1 Mn 0.1 ) 1.3 Any one or at least two of O2.

[0014] In some embodiments, the carboxylic acid ester includes any one or a combination of at least two of ethyl acetate (EA), propyl acetate (PA), ethyl propionate (EP), or propyl propionate (PP).

[0015] In some embodiments, the additive further includes sulfate esters and / or oxalate phosphates.

[0016] In some embodiments, the sulfate ester is selected from any one or a combination of at least two of the following compounds:

[0017] In some embodiments, the oxalate phosphate includes lithium difluorodioxalate phosphate (LiDODFP) and / or lithium tetrafluorooxalate phosphate (LiOTFP).

[0018] In some embodiments, the non-aqueous solvent further includes any one or a combination of at least two of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC).

[0019] In some embodiments, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethylsulfonyl)methyl.

[0020] In a second aspect, embodiments of this disclosure provide a method for preparing an electrochemical device as described in the first aspect, the method comprising the following steps:

[0021] (1) Prepare a positive electrode slurry containing lithium supplementation agent, coat the positive electrode slurry onto the surface of the positive electrode current collector, and then dry and post-process it to obtain the positive electrode;

[0022] (2) Prepare negative electrode slurry, coat the negative electrode slurry onto the surface of the negative electrode current collector, and then dry and post-process it to obtain the negative electrode;

[0023] (3) In a protective gas atmosphere, additives and lithium salts are added to a non-aqueous solvent in sequence, and the mixture is homogeneous to obtain an electrolyte.

[0024] (4) Preparation of the isolation membrane;

[0025] (5) Assemble the positive electrode, negative electrode, separator and battery cell housing, and inject electrolyte after forming to obtain an electrochemical device.

[0026] Steps (1)-(4) are not in any particular order.

[0027] In some embodiments, the positive current collector in step (1) comprises aluminum foil.

[0028] In some embodiments, the negative current collector in step (2) comprises copper foil.

[0029] In some embodiments, the drying temperatures in steps (1) and (2) are 85-120°C, respectively.

[0030] In some embodiments, the post-processing described in steps (1) and (2) includes sequential cold pressing, cutting, and slitting.

[0031] In some embodiments, the protective gas in step (3) includes any one or a combination of at least two of nitrogen, helium, or argon.

[0032] In some embodiments, the preparation of the isolation membrane in step (4) includes: coating a composite coating on the surface of a substrate.

[0033] In some embodiments, the substrate comprises a polyethylene film, and the composite coating comprises a polyvinylidene fluoride layer and / or a boehmite ceramic layer.

[0034] In some embodiments, the assembly of the electrochemical device in step (5) includes: stacking the positive electrode, the separator and the negative electrode in sequence, installing them into the battery cell housing, sealing and shaping them, injecting electrolyte, and activating the battery cell.

[0035] Thirdly, embodiments of this disclosure provide a vehicle that includes the electrochemical device as described in the first aspect.

[0036] This embodiment of the invention adds a carboxylic acid ester to a non-aqueous solvent. Due to its lower viscosity, this significantly improves the ionic conductivity of the electrolyte and reduces the desolvation energy, thereby improving electrolyte kinetics and enhancing the fast-charging capability of the battery cell. However, because the carboxylic acid ester is relatively reactive at both the positive and negative electrodes, it is prone to side reactions, causing the positive electrode metal to dissolve. The dissolved metal then deposits on the negative electrode, further degrading the negative electrode interface and negatively impacting high-temperature cycle performance. To address this, this embodiment introduces vinylene carbonate into the electrolyte, which can form a stable SEI film at the negative electrode, thereby reducing the side reactions between the carboxylic acid ester and the negative electrode. Simultaneously, a specific type of lithium replenishing agent is added to the positive electrode active material layer to compensate for lithium loss caused by side reactions, ensuring no degradation during cycling. Ultimately, through the synergistic effect between the lithium replenishing agent, carboxylic acid ester, and vinylene carbonate, the problems of battery swelling and cycle performance degradation under high-temperature conditions are effectively solved, extending the lifespan of fast-charging batteries and facilitating large-scale application. Attached Figure Description

[0037] Figure 1 is a photograph showing the determination of lithium plating during fast-charging performance evaluation of the electrochemical device provided in this embodiment of the present disclosure. Detailed Implementation

[0038] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0039] In recent years, the development trend of new energy vehicles has been continuously positive, and electric vehicles have been rapidly popularized. Shipments of lithium iron phosphate batteries and ternary lithium batteries in the electrochemical device field have increased year by year. However, people still experience travel anxiety when it comes to electric vehicles. This anxiety mainly stems from the long charging time of the batteries, which affects the convenience of using electric vehicles.

[0040] To address travel anxiety, fast charging technology has become a key factor in increasing the adoption rate of electric vehicles. While existing fast charging technologies can shorten charging time, they often come at the cost of battery life. During fast charging, high temperatures are generated inside the battery, leading to problems such as electrolyte decomposition and damage to electrode material structures, thus accelerating battery aging. Furthermore, increased internal battery temperatures can cause battery swelling and even trigger safety issues such as thermal runaway.

[0041] It is evident that existing fast charging technologies often lead to a decline in battery life, especially under high-temperature conditions where batteries swell and their cycle performance deteriorates, leaving considerable room for improvement.

[0042] Some embodiments of this disclosure provide an electrochemical device including a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer stacked together, and the negative electrode includes a negative current collector and a negative active material layer stacked together. The electrolyte includes a lithium salt, a non-aqueous solvent, and an additive. The positive active material layer contains a lithium replenishing agent. The non-aqueous solvent includes a carboxylic acid ester, and the additive includes vinylene carbonate.

[0043] The chemical formula of the lithium supplement is: Li x M y O z M is selected from any one or at least two combinations of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, or Sn. Typical but non-limiting combinations include combinations of Fe and Ni, Ni and Mn, Mn and Cu, Cu and Zn, Zn and Co, Co and Cr, Cr and Zr, Zr and Sb, Sb and Ti, Ti and V, V and Mo, or Mo and Sn.

[0044] In some embodiments, 1≤x≤8, for example, x = 1, 2, 3, 4, 5, 6, 7 or 8; y>0, for example, y = 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5; 0<z≤13, for example, z = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13, but not limited to the listed values, other unlisted values ​​within this range also apply.

[0045] This embodiment of the invention adds a carboxylic acid ester to a non-aqueous solvent. Due to its lower viscosity, this significantly improves the ionic conductivity of the electrolyte and reduces the desolvation energy, thereby improving electrolyte kinetics and enhancing the fast-charging capability of the battery cell. However, because the carboxylic acid ester is relatively reactive at both the positive and negative electrodes, it is prone to side reactions, causing the positive electrode metal to dissolve. The dissolved metal then deposits on the negative electrode, further degrading the negative electrode interface and negatively impacting high-temperature cycle performance. To address this, this embodiment introduces vinylene carbonate into the electrolyte, which can form a stable SEI film at the negative electrode, thereby reducing the side reactions between the carboxylic acid ester and the negative electrode. Simultaneously, a specific type of lithium replenishing agent is added to the positive electrode active material layer to compensate for lithium loss caused by side reactions, ensuring no degradation during cycling. Ultimately, through the synergistic effect between the lithium replenishing agent, carboxylic acid ester, and vinylene carbonate, the problems of battery swelling and cycle performance degradation under high-temperature conditions are effectively solved, extending the lifespan of fast-charging batteries and facilitating large-scale application.

[0046] In some embodiments, the total mass of non-aqueous solvents is used as the calculation basis, and the content of the carboxylic acid ester is a%, where the value of a ranges from 5 to 75. For example, a can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or 75, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of vinylene carbonate is b%, where the value of b is in the range of 0.1≤b≤5, for example, b can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0048] In some embodiments, the total mass of the positive electrode is used as the calculation basis, and the content of the lithium supplement is c%, where the value of c is in the range of 0.2≤c≤3, for example, c = 0.2, 0.5, 1, 1.5, 2, 2.5 or 3, and more preferably 0.3≤c≤3, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some embodiments, the content relationship of the carboxylic acid ester, vinylene carbonate, and lithium supplement is: 0.03 ≤ (b+c) / a ≤ 0.75, for example, (b+c) / a = 0.03, 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, or 0.75, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0050] This disclosure limits the content relationship of carboxylic acid ester, vinylene carbonate, and lithium replenisher to the above-mentioned range, which can balance the battery's charging window and fast-charging cycle performance. While carboxylic acid ester can significantly improve the battery's fast-charging capability, it is prone to side reactions at both the positive and negative electrodes, leading to poor cycle performance. Adding vinylene carbonate can form a stable interface at the negative electrode, reducing side reactions. However, a high content of vinylene carbonate results in a thicker film layer at the negative electrode, degrading fast-charging performance. The addition of a lithium replenisher can compensate for lithium loss during cycling. Excessive lithium replenisher can easily cause oxygen release from the positive electrode and reaction with the electrolyte, thus degrading battery performance. Therefore, this disclosure strictly limits the content relationship of the three substances to the above-mentioned range to fully improve fast-charging and cycle performance.

[0051] In some embodiments, the lithium supplement includes Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li6MnO4, Li6ZnO4, Li2CuO2, Li2CoO2, Li2MnO2, Li2C2O4, and Li2Ni 0.5 Mn 1.5 O4 or Li(Ni) 0.8 Co 0.1 Mn 0.1 ) 1.3 Any combination of one or at least two of the following: Li5FeO4 and Li5Fe5O8; Li5Fe5O8 and Li6CoO4; Li6CoO4 and Li2NiO2; Li2NiO2 and Li2O; Li2O and Li2O2; Li2O2 and Li6MnO4; Li6MnO4 and Li6ZnO4; Li6ZnO4 and Li2CuO2; Li2CuO2 and Li2CoO2; Li2CoO2 and Li2MnO2; Li2MnO2 and Li2C2O4; Li2C2O4 and Li2NiO2. 0.5 Mn 1.5 Combinations of O4, or Li2Ni 0.5 Mn 1.5 O4 and Li(Ni 0.8 Co0.1 Mn 0.1 ) 1.3 The combination of O2.

[0052] In some embodiments, the carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, propyl acetate, ethyl propionate, or propyl propionate. Typical but non-limiting combinations include combinations of ethyl acetate and propyl acetate, combinations of propyl acetate and ethyl propionate, or combinations of ethyl propionate and propyl propionate, with ethyl acetate being more preferred.

[0053] In some embodiments, the additive further includes sulfate esters and / or oxalate phosphates.

[0054] In this embodiment, the sulfate ester can suppress electrolyte oxidation caused by the addition of lithium supplementation agent, and can form a stable interface film at the negative electrode, thereby further improving cycle performance; the oxalate phosphate can also suppress the side reactions caused by lithium supplementation agent, thereby further improving the cycle performance of the battery.

[0055] In some embodiments, the sulfate ester is selected from any one or a combination of at least two of the following compounds:

[0056] In some embodiments, the oxalate phosphate includes lithium difluorodioxalate phosphate and / or lithium tetrafluorooxalate phosphate.

[0057] In some embodiments, the non-aqueous solvent further includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, or ethyl propyl carbonate. Typical but non-limiting combinations include combinations of ethylene carbonate and propylene carbonate, combinations of propylene carbonate and methyl ethyl carbonate, combinations of methyl ethyl carbonate and diethyl carbonate, combinations of diethyl carbonate and dimethyl carbonate, combinations of dimethyl carbonate and dipropyl carbonate, combinations of dipropyl carbonate and methyl propyl carbonate, or combinations of methyl propyl carbonate and ethyl propyl carbonate.

[0058] In some embodiments, the lithium salt comprises any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethanesulfonyl)methyl. Typical but non-limiting combinations include combinations of lithium hexafluorophosphate and lithium difluorophosphate, and combinations of lithium difluorophosphate and lithium difluorooxalate borate. Combinations of lithium difluorooxalate borate and lithium difluorosulfonyl imide, combinations of lithium difluorosulfonyl imide and lithium difluoromethanesulfonyl imide, combinations of lithium difluoromethanesulfonyl imide and lithium tetrafluoroborate, combinations of lithium tetrafluoroborate and lithium difluorooxalate borate, combinations of lithium difluorooxalate borate and lithium hexafluoroantimonylate, combinations of lithium hexafluoroantimonylate and lithium hexafluoroarsenate, combinations of lithium hexafluoroarsenate and lithium di(pentafluoroethylsulfonyl)imide, or combinations of lithium di(pentafluoroethylsulfonyl)imide and lithium tri(trifluoromethanesulfonyl)methyl lithium.

[0059] Some embodiments of this disclosure provide a method for preparing the above-described electrochemical device, the method comprising the following steps:

[0060] (1) Prepare a positive electrode slurry containing lithium supplementation agent, coat the positive electrode slurry onto the surface of the positive electrode current collector, and then dry and post-process it to obtain the positive electrode;

[0061] (2) Prepare negative electrode slurry, coat the negative electrode slurry onto the surface of the negative electrode current collector, and then dry and post-process it to obtain the negative electrode;

[0062] (3) In a protective gas atmosphere, additives and lithium salts are added to a non-aqueous solvent in sequence, and the mixture is homogeneous to obtain an electrolyte.

[0063] (4) Preparation of the isolation membrane;

[0064] (5) Assemble the positive electrode, negative electrode, separator and battery cell housing, and inject electrolyte after forming to obtain an electrochemical device.

[0065] Steps (1)-(4) are not in any particular order.

[0066] In some embodiments, the positive current collector in step (1) comprises aluminum foil.

[0067] In some embodiments, the negative current collector in step (2) comprises copper foil.

[0068] In some embodiments, the drying temperatures in steps (1) and (2) are 85-120°C, for example, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0069] In some embodiments, the post-processing described in steps (1) and (2) includes sequential cold pressing, cutting, and slitting.

[0070] In some embodiments, the protective gas in step (3) includes any one or a combination of at least two of nitrogen, helium, or argon. Typical but non-limiting combinations include a combination of nitrogen and helium, a combination of helium and argon, a combination of nitrogen and argon, or a combination of nitrogen, helium, and argon.

[0071] In some embodiments, the preparation of the isolation membrane in step (4) includes: coating a composite coating on the surface of a substrate.

[0072] In some embodiments, the substrate comprises a polyethylene film, and the composite coating comprises a polyvinylidene fluoride layer and / or a boehmite ceramic layer.

[0073] In some embodiments, the thickness of the polyethylene film is 6-8 μm, for example, it can be 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm or 8 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0074] In some embodiments, the thickness of the polyvinylidene fluoride layer is 4-6 μm, for example, it can be 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm or 6 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0075] In some embodiments, the thickness of the boehmite ceramic layer is 2-4 μm, for example, it can be 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm or 4 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0076] In some embodiments, the assembly of the electrochemical device in step (5) includes: stacking the positive electrode, the separator and the negative electrode in sequence, installing them into the battery cell housing, sealing and shaping them, injecting electrolyte, and activating the battery cell.

[0077] Some embodiments of this disclosure provide a vehicle that includes the above-described electrochemical device.

[0078] The numerical ranges described in this disclosure include not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this disclosure will not exhaustively list all the specific point values ​​included in the ranges.

[0079] Examples 1-17

[0080] This set of embodiments provides an electrochemical device and its preparation method. The electrochemical device includes a positive electrode, a negative electrode, and a separator and electrolyte located between the positive and negative electrodes. The positive electrode includes a positive current collector (aluminum foil) and a positive active material layer stacked together. The negative electrode includes a negative current collector (copper foil) and a negative active material layer stacked together. The electrolyte includes a lithium salt, a non-aqueous solvent, and an additive. The positive active material layer contains a lithium supplement agent. The non-aqueous solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and carboxylic acid esters. The additive is vinylene carbonate (VC).

[0081] In this set of embodiments, the lithium salt is LiPF6, and the specific types and contents of the lithium supplement, carboxylic acid ester and additives are shown in Table 1 below.

[0082] Table 1

[0083] In the table above, the non-aqueous solvent component ratio specifically refers to the mass ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and carboxylic acid esters (EA, PA, EP, or PP).

[0084] The electrochemical devices provided in this set of embodiments were prepared according to the following method:

[0085] (1) Preparation of positive electrode: Active material (lithium iron phosphate LiFePO4 + lithium supplement), conductive carbon (SP), carbon nanotubes (CNTs) and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone solvent at a mass ratio of 96.3:0.7:1:2 and stirred evenly to obtain positive electrode slurry; aluminum foil is used as positive electrode current collector, and the positive electrode current collector coated with positive electrode slurry is baked at 85°C for 1 hour, and then cold-pressed, cut and slit in sequence to obtain positive electrode.

[0086] (2) Anode preparation: Artificial graphite, conductive carbon, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are mixed in deionized water at a mass ratio of 96.4:1:1.2:1.4 and stirred evenly to obtain anode slurry; copper foil is used as anode current collector, and the anode current collector coated with anode slurry is baked at 120°C for 1 hour, and then cold-pressed, cut and slit in sequence to obtain anode.

[0087] (3) Electrolyte preparation: EC, EMC, DMC and carboxylic acid ester are mixed in an argon atmosphere to obtain an anhydrous solvent; then VC is added to the anhydrous solvent, followed by LiPF6, and the content of LiPF6 is 12.5% ​​based on the total mass of the electrolyte.

[0088] (4) Preparation of the isolation membrane: A polyethylene film with a thickness of 7 μm is used as the substrate, and a PVDF coating with a thickness of 5 μm is applied to both sides of the film, and then a boehm ceramic layer with a thickness of 3 μm is applied.

[0089] (5) Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes to play a role in isolation. The side coated with boehm ceramic layer is aligned with the positive electrode. Then the cells are stacked and placed in an aluminum-plastic film. After drying at 80°C, the obtained electrolyte is injected. The cells are then subjected to vacuum sealing, standing, formation and shaping processes to complete the preparation of the silicon-based lithium-ion battery.

[0090] Examples 18-26

[0091] The embodiments in this group provide an electrochemical device and its preparation method. Except for the addition of sulfate ester and / or oxalate phosphate (specific types and contents are shown in Table 2 below) to the addition of vinylene carbonate (VC) as the additive, the other steps and conditions are the same as those in Example 8, so they will not be described in detail here.

[0092] Table 2

[0093] In the table above, the contents of sulfate ester and oxalate phosphate are calculated based on the total mass of the electrolyte, and the chemical structural formulas of compounds 1-6 are shown in Table 3 below.

[0094] Table 3

[0095] The electrochemical device preparation method provided in this set of embodiments only requires adaptive adjustments to the types and contents of additives according to Table 2. The remaining steps and conditions are the same as in Example 8, so they will not be repeated here.

[0096] Examples 27-32

[0097] This set of embodiments provides an electrochemical device and its preparation method. The electrochemical device includes a positive electrode, a negative electrode, and a separator and electrolyte located between the positive and negative electrodes. The positive electrode includes a positive current collector (aluminum foil) and a positive active material layer stacked together. The negative electrode includes a negative current collector (copper foil) and a negative active material layer stacked together. The electrolyte includes a lithium salt, a non-aqueous solvent, and an additive. The positive active material layer contains a lithium supplement agent. The non-aqueous solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and carboxylic acid esters. The additive is vinylene carbonate (VC).

[0098] In this set of embodiments, the lithium salt is LiPF6, and the specific types and contents of the lithium supplement, carboxylic acid ester and additives are shown in Table 4 below.

[0099] Table 4

[0100] The electrochemical device preparation method provided in this set of embodiments only requires adaptive adjustment of the content of each material according to Table 4. The remaining steps and conditions are the same as in Example 8, so they will not be repeated here.

[0101] Comparative Example 1

[0102] This comparative example provides an electrochemical device and its preparation method. Except for the absence of a lithium supplement agent during the preparation of the positive electrode, the other steps and conditions are the same as in Example 8, and therefore will not be repeated here.

[0103] Comparative Example 2

[0104] This comparative example provides an electrochemical device and its preparation method. Except that no carboxylic acid ester is added during the preparation of the electrolyte, the other steps and conditions are the same as in Example 8, so they will not be described again here.

[0105] Comparative Example 3

[0106] This comparative example provides an electrochemical device and its preparation method. Except for the absence of adding vinylene carbonate during the preparation of the electrolyte, the other steps and conditions are the same as in Example 8, and therefore will not be repeated here.

[0107] Comparative Example 4

[0108] This comparative example provides an electrochemical device and its preparation method. Except that no lithium supplementation agent is added during the preparation of the positive electrode, and no carboxylic acid ester and vinylene carbonate are added during the preparation of the electrolyte, the other steps and conditions are the same as in Example 8, so they will not be described in detail here.

[0109] Performance testing

[0110] (1) Fast charging performance evaluation: The electrochemical device was placed in a constant temperature chamber at 25°C for 30 minutes, charged at a constant charging rate of 4C to 3.8V, then charged at a constant voltage to a charging rate of 0.05C, and left to stand for 5 minutes. Then it was discharged at a constant discharge rate of 1.0C to 2.5V. This process was repeated 100 times: left to stand for 5 minutes, charged at a constant charging rate of 4C to 3.8V, and then charged at a constant voltage to a charging rate of 0.05C. The cells were then disassembled, and the lithium plating was assessed according to the standards shown in Figure 1. In Figure 1, the leftmost photo shows no lithium plating on the surface of the cell, the middle photo shows lithium plating at the edge of the cell, and the rightmost photo shows severe lithium plating on the main body of the cell.

[0111] (2) Cyclic test: The electrochemical device was placed in a constant temperature chamber at 25°C and left to stand for 30 minutes. It was then charged at a constant charging rate of 4C to 3.8V, followed by constant voltage charging to a charging rate of 0.05C. After standing for 5 minutes, it was discharged at a constant discharge rate of 1.0C to 2.5V, and the capacity was recorded as D0. The cyclic test was performed according to the following steps:

[0112] (2.1) Let stand for 5 minutes;

[0113] (2.2) Charge at a constant charging rate of 4C to 3.8V, and then charge at a constant voltage to a charging rate of 0.05C;

[0114] (2.3) Let stand for 5 minutes;

[0115] (2.4) Discharge to 2.5V at a constant discharge rate of 1.0C;

[0116] (2.5) Repeat steps (2.1) to (2.4) 2000 times, with a recording capacity of D1.

[0117] Calculate the cycle capacity retention rate (%) of the electrochemical device = (D1-D0) / D0×100%.

[0118] The fast-charging performance evaluation and cycle test results of the electrochemical devices obtained in Examples 1-32 and Comparative Examples 1-4 are shown in Table 5 below.

[0119] Table 5

[0120] It can be seen from Table 5 above:

[0121] (1) In Examples 1-17, a specific type of lithium replenishing agent was added to the positive electrode active material layer, and a carboxylic acid ester was added to the non-aqueous solvent. Ethylene carbonate was introduced into the electrolyte, and the content relationship of the three was strictly limited. The fast charging performance and cycle performance of the final electrochemical device were maintained at a high level.

[0122] (2) Based on Example 8, Examples 18-23 added sulfate ester to the electrolyte, Examples 24-25 added oxalate phosphate to the electrolyte, and Example 26 added both sulfate ester and oxalate phosphate to the electrolyte. The cycle performance of the resulting electrochemical devices was further improved because: sulfate ester can inhibit electrolyte oxidation caused by the addition of lithium replenishment agent, and can form a stable interface film at the negative electrode, thereby further improving cycle performance; oxalate phosphate can also inhibit the side reactions caused by lithium replenishment agent, thereby further improving the cycle performance of the battery.

[0123] (3) Based on Example 8, Examples 27-32 respectively adjusted the contents of lithium replenishing agent, carboxylic acid ester and vinylene carbonate to outside the specified range, and adapted the components and ratio of non-aqueous solvents. Ultimately, the fast charging performance and cycle performance of the obtained electrochemical device were adversely affected to varying degrees.

[0124] (4) Based on Example 8, no lithium replenishing agent was added to Comparative Example 1, no carboxylic acid ester was added to Comparative Example 2, no vinylene carbonate was added to Comparative Example 3, and no lithium replenishing agent, carboxylic acid ester, and vinylene carbonate were added to Comparative Example 4. Ultimately, the fast charging performance and cycle performance of the obtained electrochemical device were significantly adversely affected.

[0125] Therefore, the addition of carboxylic acid esters to the non-aqueous solvent in this embodiment significantly improves the ionic conductivity of the electrolyte and reduces the desolvation energy due to their lower viscosity, thereby improving electrolyte kinetics and enhancing the fast-charging capability of the battery cell. However, because carboxylic acid esters are relatively reactive at both the positive and negative electrodes, they are prone to side reactions, leading to the dissolution of the positive electrode metal. The dissolved metal further degrades the negative electrode interface after deposition, which is detrimental to high-temperature cycle performance. To address this, the present embodiment introduces vinylene carbonate into the electrolyte, which can form a stable SEI film at the negative electrode, thereby reducing the side reactions between the carboxylic acid ester and the negative electrode. At the same time, a specific type of lithium replenishing agent is added to the positive electrode active material layer to compensate for the lithium loss caused by the side reactions, thus ensuring no degradation during cycling. Finally, through the synergistic effect between the lithium replenishing agent, carboxylic acid ester, and vinylene carbonate, the problems of battery swelling and cycle performance degradation under high-temperature conditions are effectively solved, extending the service life of fast-charging batteries and facilitating large-scale promotion and application.

[0126] The applicant declares that the above description is only a specific implementation of this disclosure, but the protection scope of this disclosure is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this disclosure fall within the protection and disclosure scope of this disclosure.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and a separating membrane and an electrolyte located between the positive and negative electrodes, wherein the positive electrode comprises a positive current collector and a positive active material layer stacked thereon, the negative electrode comprises a negative current collector and a negative active material layer stacked thereon, and the electrolyte comprises a lithium salt, a non-aqueous solvent, and an additive, wherein... The positive electrode active material layer contains a lithium replenishing agent, the non-aqueous solvent includes a carboxylic acid ester, and the additive includes vinylene carbonate; The chemical formula of the lithium supplement is: Li x M y O z Wherein, M is selected from any one or at least two of Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo or Sn, and 1≤x≤8, y>0, 0<z≤13.

2. The electrochemical device according to claim 1, wherein, Using the total mass of the non-aqueous solvent as the calculation basis, the content of the carboxylic acid ester is a%, where the value of a ranges from 5 to a ≤ 75; and / or Using the total mass of the electrolyte as the calculation basis, the content of vinylene carbonate is b%, where the value of b ranges from 0.1 to b ≤ 5; and / or Using the total mass of the positive electrode as the calculation basis, the content of the lithium replenishing agent is c%, where the value of c ranges from 0.2 to 3.

3. The electrochemical device according to claim 2, wherein, The content relationship of the carboxylic acid ester, the vinylene carbonate and the lithium supplement is: 0.03≤(b+c) / a≤0.

75.

4. The electrochemical device according to any one of claims 1-3, wherein, The lithium supplements include Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li6MnO4, Li6ZnO4, Li2CuO2, Li2CoO2, Li2MnO2, Li2C2O4, and Li2Ni 0.5 Mn 1.5 O4 or Li(Ni) 0.8 Co 0.1 Mn 0.1 ) 1.3 Any one or at least two of the following O2; and / or The carboxylic acid ester includes any one or a combination of at least two of ethyl acetate, propyl acetate, ethyl propionate, or propyl propionate.

5. The electrochemical device according to any one of claims 1-4, wherein, The additives also include sulfate esters and / or oxalate phosphates; and / or The sulfate ester is selected from any one or a combination of at least two of the following compounds: and / or The oxalate phosphate includes lithium difluorodioxalate phosphate and / or lithium tetrafluorooxalate phosphate.

6. The electrochemical device according to any one of claims 1-5, wherein, The non-aqueous solvent further includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, or ethyl propyl carbonate; and / or The lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorosulfonylimide, lithium bis(trifluoromethylsulfonylimide), lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethylsulfonyl)methyl.

7. A method for preparing an electrochemical device as described in any one of claims 1-6, comprising the following steps: (1) Prepare a positive electrode slurry containing lithium supplementation agent, coat the positive electrode slurry onto the surface of the positive electrode current collector, and then dry and post-process it to obtain the positive electrode; (2) Prepare negative electrode slurry, coat the negative electrode slurry onto the surface of the negative electrode current collector, and then dry and post-process it to obtain the negative electrode; (3) In a protective gas atmosphere, additives and lithium salts are added to a non-aqueous solvent in sequence, and the mixture is homogeneous to obtain an electrolyte. (4) Preparation of the isolation membrane; (5) Assemble the positive electrode, negative electrode, separator and battery cell housing, and inject electrolyte after molding to obtain an electrochemical device; Steps (1)-(4) are not in any particular order.

8. The preparation method according to claim 7, wherein, The positive current collector in step (1) includes aluminum foil; and / or The negative electrode current collector in step (2) includes copper foil; and / or The drying temperatures described in steps (1) and (2) are 85-120°C, respectively; and / or The post-processing described in steps (1) and (2) includes sequential cold pressing, cutting, and slitting.

9. The preparation method according to claim 7 or 8, wherein, The protective gas in step (3) includes any one or a combination of at least two of nitrogen, helium, or argon; and / or The preparation of the separator in step (4) includes: coating a composite coating on the surface of a substrate; and / or The substrate comprises a polyethylene film, and the composite coating comprises a polyvinylidene fluoride layer and / or a boehmite ceramic layer; and / or The assembly of the electrochemical device in step (5) includes: stacking the positive electrode, the separator and the negative electrode in sequence, installing them into the battery cell housing, sealing and shaping the battery, injecting electrolyte, and activating the battery cell.

10. A vehicle comprising the electrochemical device as described in any one of claims 1-6.

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