An electrochemical device and an electrical device comprising the same.

Abstract

This application relates to an electrochemical device comprising a positive electrode, a negative electrode, a separating membrane, and an electrolyte, wherein the electrolyte comprises fluoroethylene carbonate, and the content a of the fluoroethylene carbonate is 0.01% to 5% based on the mass of the electrolyte; the positive electrode comprises a positive electrode active material, the positive electrode active material containing Mn element, and the content of the Mn element is greater than or equal to 15% based on the mass of the positive electrode active material; the unit reaction area of ​​the positive electrode active material is c, expressed in m 2 / cm 2 It is calculated that a and c satisfy the following relationship: 0.0006 ≤ a / c ≤ 6.25; wherein the unit reaction area is the product of the weight W of the positive electrode active material per unit area and the specific surface area BET of the positive electrode active material. The electrochemical device of the present invention ensures the performance requirements of the battery after the manganese content in the positive electrode material is increased, thereby achieving a balance between battery product cost and performance.

Description

[0001] This application is a divisional application of patent application No. 202210335359.9, filed on March 31, 2022, entitled "An electrochemical device and an electrical appliance comprising the same". Technical Field

[0002] This application relates to the field of energy storage technology, and more specifically to an electrochemical device and an electrical appliance comprising the same. Background Technology

[0003] Currently, the concepts of carbon neutrality and carbon peaking are accelerating the development of the new energy industry, and lithium batteries are a crucial component of this industry. With the increasing demand for lithium batteries, the demand for transition metal elements such as cobalt, nickel, and manganese is also rising, leading to price increases for cobalt and nickel-related resources. Therefore, the industry has been seeking to reduce costs by increasing the manganese (Mn) content in cathode materials. However, high manganese content in cathode active materials is prone to leaching problems. The leached manganese deposits on the anode, damaging the solid electrolyte interphase (SEI) layer, resulting in poor cycle performance and storage performance of the lithium battery. Summary of the Invention

[0004] This application is made in view of the problems existing in the prior art, and its purpose is to provide an electrochemical device and an electrical appliance containing the same, so as to solve the above problems, namely, to eliminate or at least mitigate the problem of poor cycle performance and storage performance of lithium batteries caused by the use of high manganese content in the positive electrode active material.

[0005] To achieve the above objectives, this application provides an electrochemical device and an electrical appliance comprising the same.

[0006] On one hand, the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, a separating membrane, and an electrolyte, wherein...

[0007] The electrolyte comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate a is from 0.01% to 5%, based on the mass of the electrolyte;

[0008] The positive electrode includes a positive electrode active material, which contains Mn element, and the content of Mn element is greater than or equal to 15%, based on the mass of the positive electrode active material;

[0009] The unit reaction area of ​​the positive electrode active material is c, and m 2 / cm 2 It is assumed that a and c satisfy the following relationship: 0.0006 ≤ a / c ≤ 6.25; where the unit reaction area is the unit area (cm²). 2The weight W (g) of the positive electrode active material and the specific surface area BET (m²) of the positive electrode active material 2 The product of / g).

[0010] In any embodiment, the electrochemical device satisfies at least one of the following conditions:

[0011] 0.0006≤a / c≤2.5;

[0012] The content of the fluoroethylene carbonate is 0.05% to 5%, based on the mass of the electrolyte;

[0013] The range of W is 8 mg / cm³ 2 Up to 35 mg / cm 2 The range of BET is 1m 2 / g to 5m 2 / g.

[0014] In any embodiment, the Dv10 / Dv99 of the positive electrode active material is z, and a / z is 0.01 to 1.

[0015] In any embodiment, the electrolyte further includes vinylene carbonate (VC), the content of which b is 0.01% to 5% based on the mass of the electrolyte.

[0016] In any implementation, b and a satisfy the following relationship: 0.11a - 0.05%. <b<5.1a+0.45%。

[0017] In any embodiment, the content of Mn element in the positive electrode active material is x, and b / x ≥ 10. -3 .

[0018] In any embodiment, the electrolyte further includes additive A, which is selected from at least one of methylene methane disulfonate (MMDS), 1,3-propenesulfonate lactone (PES), 1,3-propanesulfonate lactone (PS), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), 2-fluoropyridine (2-PY), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0019] In any embodiment, the content of additive A is 0.01 to 10%, based on the mass of the electrolyte.

[0020] In any embodiment, the electrolyte further contains dimethyl carbonate (DMC), the content of which is less than or equal to 5% based on the mass of the electrolyte.

[0021] In any embodiment, the positive electrode active material includes at least one of lithium manganese oxide and lithium nickel cobalt manganese oxide.

[0022] In any embodiment, the electrochemical device satisfies at least one of the following conditions:

[0023] The content of the fluoroethylene carbonate is 0.05% to 3%, based on the mass of the electrolyte;

[0024] The range of W is 13 mg / cm² 2 Up to 30 mg / cm 2 The range of BET is 1.2m. 2 / g to 3.5m 2 / g;

[0025] The electrolyte also includes vinylene carbonate (VC), the content of which is 0.01% to 2% based on the mass of the electrolyte;

[0026] The electrolyte also includes dimethyl carbonate, the content of which is less than or equal to 1%, based on the mass of the electrolyte;

[0027] The content of Mn element in the positive electrode active material is less than or equal to 60%;

[0028] The positive electrode active material has a Dv10 / Dv99 ratio of z and an a / z ratio of 0.05 to 0.3.

[0029] On the other hand, this application also provides an electrical appliance that includes the above-described electrochemical device.

[0030] Surprisingly, it was found that by increasing the manganese content in the positive electrode active material, controlling the ratio of fluoroethylene carbonate content in the electrolyte to the unit reaction area of ​​the positive electrode active material within the range of this invention can significantly improve the battery's cycle performance and storage performance. This ensures the battery's performance requirements are met even with increased manganese content in the positive electrode material, thus achieving a balance between battery product cost and performance. Detailed Implementation

[0031] The following detailed description discloses embodiments of the electrochemical device and its manufacturing method, positive and negative electrode plates, electrolyte, and electrical components of the present invention. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0032] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] The terms “above” and “below” used in this application include the number itself. For example, “above one” means one or more, and “above one of A and B” means “A”, “B” or “A and B”.

[0038] The term "at least one" as used in this application means one or more, such as "at least one of A, B or C" means "A", "B", "C", "A and B", "A and C", "B and C" or "A, B and C".

[0039] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] Fluoroethylene carbonate, also known as 4-fluoro-1,3-dioxolan-2-one.

[0041] Unless otherwise stated, all contents and percentages in the context of this application are based on weight.

[0042] Unless otherwise stated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0043] Because the high manganese content in the positive electrode active material easily leads to leaching, the leached manganese deposits on the negative electrode, damaging the negative electrode interface protective film (SEI), which in turn results in poor cycle performance and storage performance of lithium batteries. Through extensive experimentation, the inventors discovered that using the electrochemical device of this invention can significantly improve the above-mentioned problems.

[0044] Therefore, the first aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separating membrane, and an electrolyte, wherein...

[0045] The electrolyte comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate a is from 0.01% to 5%, based on the mass of the electrolyte;

[0046] The positive electrode includes a positive electrode active material, which contains Mn element, and the content of Mn element x is greater than or equal to 15%, preferably greater than or equal to 25%, even more preferably greater than or equal to 30%, and more preferably less than or equal to 60%, based on the mass of the positive electrode active material;

[0047] The unit reaction area of ​​the positive electrode active material is c, and m 2 / cm 2 It is calculated that a and c satisfy the following relationship: 0.0006≤a / c≤6.25; wherein the unit reaction area is the product of the weight W of the positive electrode active material per unit area and the specific surface area BET of the positive electrode active material.

[0048] Unbound by any particular theory, the inventors believe that fluoroethylene carbonate (FEC) can undergo oxidative decomposition on the positive electrode surface to form a protective layer with lithium salts in the electrolyte, reducing manganese dissolution. Simultaneously, it can form a stable protective layer on the negative electrode, reducing the damage caused by the reduction of manganese dissolved from the positive electrode. However, FEC itself has poor thermal stability and sometimes decomposes to produce HF, which can actually accelerate the dissolution of manganese from the positive electrode. Through research, the inventors discovered that when using high manganese content in the positive electrode active material, controlling the ratio of FEC content (a, based on the mass of the electrolyte) to the unit reaction area of ​​the positive electrode active material (c, which is the product of the weight W of the positive electrode active material per unit area and the specific surface area BET of the positive electrode active material) within the range of this invention can fully guarantee the protective effect of FEC film formation on both the positive and negative electrodes, while also reducing the adverse effects of decomposition caused by excessively high content.

[0049] electrolyte

[0050] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte comprises an electrolyte lithium salt and a solvent.

[0051] In some embodiments, the electrolyte lithium salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, lithium aluminate, lithium fluoride, lithium tetrachloroaluminate, lithium chloride, lithium fluoride, lithium perfluorobutyl sulfonate, and lithium tetrafluorooxalate phosphate.

[0052] In some embodiments, the content of the electrolyte lithium salt can be from 1% to 30% by mass, preferably from 5% to 20% by mass, and more preferably from 8% to 15% by mass, based on the mass of the electrolyte.

[0053] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dioxolane, dimethyl ether, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0054] In some embodiments, the solvent content may be 20% by mass or more, preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, based on the mass of the electrolyte.

[0055] In some embodiments, the electrolyte comprises fluoroethylene carbonate, wherein the content a of the fluoroethylene carbonate is 0.01% to 5%, preferably 0.05% to 3%, more preferably 0.05% to 2%, based on the mass of the electrolyte.

[0056] In some embodiments, the electrolyte further includes vinylene carbonate (VC), the content of which is 0.01% to 5%, preferably 0.01% to 4%, and even more preferably 0.01% to 2%, based on the mass of the electrolyte.

[0057] In some implementations, b and a satisfy the following relationship: 0.11a - 0.05%. <b<5.1a+0.45%。

[0058] In some embodiments, the electrolyte further includes additive A, which is selected from at least one of methylene methane disulfonate (MMDS), 1,3-propenesulfonate lactone (PES), 1,3-propanesulfonate lactone (PS), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), 2-fluoropyridine (2-PY), or lithium bisfluorosulfonylimide (LiFSI).

[0059] In some embodiments, additive A is selected from at least one of 1,3-propanesulfonic acid lactone and 2-fluoropyridine.

[0060] The content of additive A is 0.01% to 10%, preferably 0.01% to 6%, based on the mass of the electrolyte.

[0061] In some embodiments, the electrolyte further contains dimethyl carbonate (DMC) in a content of less than or equal to 5% based on the mass of the electrolyte.

[0062] In some embodiments, the content of dimethyl carbonate is less than or equal to 1%, based on the mass of the electrolyte.

[0063] In some embodiments, the electrolyte further includes other additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0064] positive electrode

[0065] In this application, the positive electrode is a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0066] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0067] The positive electrode film layer includes a positive electrode active material, which contains Mn element, and the Mn element content x is 15% to 60% based on the mass of the positive electrode active material; the unit reaction area of ​​the positive electrode active material is c, expressed in m. 2 / cm 2 It is calculated that a and c satisfy the following relationship: 0.0006≤a / c≤6.25, preferably 0.001≤a / c≤4.5, and more preferably 0.001≤a / c≤2.5; wherein the unit reaction area is the product of the weight W of the positive electrode active material per unit area and the specific surface area BET of the positive electrode active material.

[0068] In some embodiments, W ranges from 8 mg / cm³. 2 Up to 35 mg / cm 2 The range of BET is 1m 2 / g to 5m 2 / g. More preferably, W is in the range of 13 mg / cm³. 2 Up to 30 mg / cm 2 The range of BET is 1.2m. 2 / g to 3.5m 2 / g.

[0069] In some implementations, b / x ≥ 10 -3 Preferably, b / x ≤ 0.1, where b is the content of vinylene carbonate and x is the content of Mn element.

[0070] In some implementations, x and a satisfy x×e a The value of e is 0.1 to 1.2, preferably 0.15 to 0.7, where e is the base of the natural logarithm.

[0071] In this application, the BET surface area is tested using the nitrogen adsorption method (GB / T19587-2017). For example, the sample is baked in a vacuum oven at 120°C for 2 hours before testing; the six-point BET method (i.e., P / P0 = 0.05 / 0.10 / 0.15 / 0.2 / 0.25 / 0.3) is used; the purity of the nitrogen gas used is 99.999%, and the liquid nitrogen temperature is -196°C.

[0072] The weight W of the positive electrode active material layer per unit area is determined as follows: Take a positive electrode sheet with a certain area S and both surfaces of the current collector having the positive electrode active material layer, scrape the positive electrode active material layer off the positive electrode current collector (scrape off the material other than the current collector), weigh the powder, and the weight m of the powder is calculated. The weight per unit area W = m / (S×2); or

[0073] Take a positive electrode with a certain area S1 and an active material layer on one surface of the current collector. Scrape off the active material layer of the positive electrode from the current collector (scrape off the material other than the current collector). Weigh the powder m1. The weight per unit area is W = m1 / S1.

[0074] Then, the weight W (g / cm³) of the above-mentioned positive electrode active material layer per unit area is... 2 Multiply by the specific surface area BET(m) of the above positive electrode active material layer 2 / g), to obtain the unit reaction area c(m) of the positive electrode active material layer. 2 / cm 2 ).

[0075] In some embodiments, the positive electrode active material may further include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0076] In some embodiments, the positive electrode active material contains not less than 80% by weight, optionally not less than 90% by weight, and more preferably not less than 95% by weight, based on the total weight of the positive electrode film.

[0077] In some embodiments, the Dv99 of the positive electrode active material is y μm, where y ranges from 20 to 60, preferably from 25 to 55, and more preferably from 30 to 53.

[0078] In this application, when the particles of the positive electrode active material are too small, the reaction contact area is large and there are many side reactions. When the particles of the positive electrode active material are too large, the ion transport path inside the particles is long, which affects the performance.

[0079] In this application, the Dv10 and Dv99 of the positive electrode active material can be determined using a laser particle size analyzer (such as a Malvern Master Size 3000) according to standard GB / T19077.1-2016. The physical definitions of Dv10 and Dv99 are as follows:

[0080] Dv10: The particle size corresponding to a cumulative volume distribution percentage of 10% for the positive electrode active material;

[0081] Dv99: The particle size corresponding to a cumulative volume distribution percentage of 99% for the positive electrode active material.

[0082] In some implementations, y and a satisfy the following relationship: (π×y) 2 The value of ) / (10000×a) is 0.01 to 115, preferably 0.01 to 20, and even more preferably 0.01 to 10.

[0083] In some embodiments, the Dv10 of the positive electrode active material is 3 μm to 10 μm, preferably 3.2 μm to 8 μm.

[0084] In some embodiments, the positive electrode active material Dv10 / Dv99 is z, ranging from 0.01 to 0.5, preferably from 0.05 to 0.4; and the value of a / z is from 0.01 to 1, preferably from 0.05 to 0.3.

[0085] In some embodiments, the positive electrode active material includes lithium manganese oxide (LiMn2O4) and optionally lithium nickel cobalt manganese oxide (Li). x Ni m Co n Mn p O2, where 0.95≤x≤1.05, 0.98≤m+n+p≤1.02, and where 0≤m<1, 0≤n<1, 0<p≤1 (e.g., LiNi). 0.8 Co 0.1 Mn 0.1 O2), and optionally LiFeO4.

[0086] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil; the composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, polyethylene (PE), etc.).

[0087] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0088] In some embodiments, the binder content in the positive electrode film layer may be from 0.1% to 6% by weight, optionally from 0.5% to 5% by weight, and even more preferably from 0.8% to 3% by weight, based on the total weight of the positive electrode film layer.

[0089] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the conductive agent may be present in the positive electrode film layer at a content of 0.1% to 6% by weight, optionally 0.5% to 5% by weight, and more preferably 0.8% to 3% by weight, based on the total weight of the positive electrode film layer.

[0091] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0092] negative electrode

[0093] In this application, the negative electrode is a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0094] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, polyethylene (PE), etc.).

[0096] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0097] In some embodiments, the negative electrode active material comprises at least 80% by weight in the negative electrode film layer, optionally at least 90%, and more preferably at least 95%. In some embodiments, the negative electrode film layer may also optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the binder may have a weight fraction of 0.1% to 6% by weight in the negative electrode film layer, optionally 0.5% to 5% by weight.

[0099] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the conductive agent may have a weight fraction of 0.1% to 6% by weight in the negative electrode film layer, optionally 0.5% to 5% by weight.

[0101] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners (e.g., carboxymethyl cellulose (CMC)).

[0102] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0103] Separating membrane

[0104] In this application, there are no particular restrictions on the type of separator; any known separator with good chemical and mechanical stability can be selected. The material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular restrictions.

[0105] In this application, the positive electrode sheet, negative electrode sheet, and separator can be fabricated into an electrode assembly through a winding process or a stacking process.

[0106] In this application, the lithium metal battery may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0107] In this application, the outer packaging of the lithium metal battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the lithium metal battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0108] In this application, there are no particular restrictions on the shape of the lithium metal battery; it can be cylindrical, square, or any other arbitrary shape.

[0109] Another aspect of this application provides an electrical appliance that includes the above-described electrochemical device.

[0110] Example

[0111] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application.

[0112] The manufacturing process of lithium-ion batteries is as follows:

[0113] (1) Preparation of positive electrode sheet

[0114] The positive electrode active material (single or mixed positive electrode material), conductive agent Super P, and binder polyvinylidene fluoride are mixed in a weight ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 72% by weight. The positive electrode slurry is then uniformly coated onto a positive electrode current collector aluminum foil. The coated aluminum foil is dried at 100°C, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with a specification of 74mm×867mm. The tabs are then welded on for later use.

[0115] (2) Preparation of negative electrode sheet

[0116] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC-Na) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a weight ratio of 96:2:0.8:1.2. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a cathode slurry with a solid content of 54% by weight. The cathode slurry was uniformly coated onto a copper foil current collector. The coated copper foil was dried at 85°C, and then cold-pressed, cut, and slit to obtain a cathode sheet with a size of 79mm × 872mm. The tabs were then welded on for later use.

[0117] (3) Electrolyte preparation

[0118] In a dry argon-atmospheric glove box, solvents were mixed in a ratio of ethylene carbonate (EC): diethyl carbonate (DEC): ethyl methyl carbonate (EMC) = 3:5:2 (mass ratio). Lithium hexafluorophosphate (12.5 wt%, based on the mass of the base electrolyte) was then added to obtain the base electrolyte. Additives were added to the base electrolyte according to the types and mass contents listed in the table below. The mixture was dissolved and thoroughly stirred to obtain the final electrolyte. All additive contents listed in the tables are based on the mass of the electrolyte.

[0119] (4) Preparation of the separating membrane

[0120] A 9μm thick polyethylene (PE) substrate layer was selected. A polyvinylidene fluoride (PVDF) slurry and an inorganic particle slurry (a ratio of 70:30 of flake boehmite and Al2O3) were applied to one side of the polyethylene substrate layer. After drying, the final isolation film was obtained with a coating thickness of 3μm and a porosity of 55%.

[0121] (5) Preparation of lithium-ion batteries

[0122] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrode assembly is wound up. After welding the tabs, the electrode assembly is placed in the outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried electrode assembly. After vacuum sealing, standing, formation (0.02C constant current charging to 3.3V, then 0.1C constant current charging to 3.6V), shaping, and capacity testing (0.5C constant current and constant voltage charging to 4.2V, 0.5C discharging to 3.0V), a soft-pack lithium-ion battery is obtained.

[0123] It should be noted here that in Example 1-1 below, the positive electrode active material is composed of 90% LiMn2O4 and 10% LiNi by mass. 0.8 Co 0.1 Mn 0.1 The positive electrode active material is obtained by mixing O2 particles. The positive electrode active material has a Dv99 of 45 μm and a Dv10 of 10 μm.

[0124] Unless otherwise specified, the batteries in Examples 1-1 and other examples in Table 1 were prepared using essentially the same method, differing only in the adjustment of the FEC content and related parameters of the positive electrode active material as recorded in Table 1. Similarly, in Table 2, the batteries in Examples 2-1 to 2-10 were prepared using essentially the same method as those in Examples 1-4, except that different contents of FEC and different positive electrode active materials and particle sizes were used. It is understood that different Dv99 and Dv10 materials can be obtained by adjusting the sintering temperature and time of the preparation process, and the Mn content can be fine-tuned by elemental doping as needed. In Table 3, the batteries in Examples 3-1 to 3-8 were prepared using essentially the same method as those in Examples 1-4, except that different contents of FEC and different contents of vinylene carbonate were used. In Table 4, the batteries in Examples 4-1 to 4-15 were prepared using essentially the same method as those in Examples 1-4, except that different types and contents of additives were added. In Table 5, the preparation methods of the batteries in Examples 5-1 to 5-4 are basically the same as those in Examples 1-4, except that different amounts of dimethyl carbonate are added.

[0125] Performance testing:

[0126] Cyclic testing and cyclic thickness variation

[0127] The battery cell was placed in a 45°C high-temperature chamber and charged to 4.2V with a constant voltage and constant current of 0.5C. The thickness was measured as h1. After standing for 15 minutes, it was discharged to 3.0V with a constant current of 0.5C and stood for 15 minutes, which constituted one cycle. The capacity of the first cycle was recorded as C1. After 100 cycles, the discharge capacity of the 100th cycle was recorded as C. 100Thickness h 100 The cycle capacity retention rate is [C] 100 / C1]×100%, thickness change rate is [(h 100 / h1)-1]×100%

[0128] Low temperature discharge test

[0129] The battery cell was placed in a high-low temperature chamber and the temperature was adjusted to 25℃. It was then charged at a constant current and constant voltage of 0.2C to 4.2V, and then discharged at 0.2C to 3.0V. The discharge capacity at this point was recorded as C. 25 (mAh); then charge at a constant current and constant voltage of 0.2C to 4.2V, then adjust the temperature of the high and low temperature chamber to -20℃, and then discharge at a constant current of 0.2C to 3.0V. Record the discharge capacity at this time as C. -20 (mAh), low-temperature discharge capacity retention rate [C] -20 / C 25 ]×100%

[0130] High-temperature full-charge storage

[0131] First, the battery cell was charged at 25℃ with a constant current and constant voltage of 0.5C to 4.35V, then discharged at 0.2C to 3.0V (discharge capacity denoted as C0). Then, it was charged again at 0.5C with a constant current and constant voltage to 4.35V. The initial thickness d1 was measured. Next, the battery cell was placed in a 60℃ high-temperature furnace and stored for 30 days. After storage, the thickness d2 was measured. After storage, the battery cell was discharged at 25℃ with a constant current and constant voltage of 0.2C to 3.0V, then charged again at 0.5C with a constant current and constant voltage to 4.35V, and then discharged again at 0.2C to 3.0V (discharge capacity denoted as C0). 30 ).

[0132] The thickness change rate of high-temperature full-charge storage is: [(d2 / d1)-1]×100%.

[0133] The recoverable capacity after 30 days of storage at 60℃ is: [(C0 / C 30 )-1]×100%.

[0134] The preparation parameters and performance tests for each embodiment and comparative example are shown in Tables 1 to 5.

[0135] Table 1. Effects of fluoroethylene carbonate (FEC) content and unit reaction area (c) of the positive electrode active material on cycle and storage performance.

[0136]

[0137]

[0138] As can be seen from Examples 1-1 to 1-12 and Comparative Examples 1-1 and 1-2 in Table 1, the ratio of the content of fluoroethylene carbonate in the positive electrode material to the unit reaction area c of the positive electrode active material improves both the battery cycle and high-temperature storage performance within a certain range. This is mainly because fluoroethylene carbonate can undergo oxidative decomposition on the surface of the positive electrode to form a protective layer with the lithium salt in the electrolyte on the surface of the positive electrode. Based on the appropriate unit reaction area of the positive electrode active material, an appropriate content of FEC can protect the positive electrode active material while reducing the adverse effects of HF generated by the decomposition of FEC on the positive electrode, and at the same time improve the stability of the negative electrode interface during cycling and storage.

[0139] Table 2 Effects of Different Positive Electrode Active Materials and Their Particle Sizes on Cycling Performance and Low-Temperature Discharge Performance

[0140]

[0141] Table 2 shows the Dv10, Dv99, cycling performance, and low-temperature discharge performance data corresponding to different lithium manganate materials and mixed materials. Among them, when the value of a / z is from 0.01 to 1, the electrochemical device can maintain better comprehensive performance. In particular, when the value of a / z is from 0.05 to 0.3, the discharge capacity retention rate of the electrochemical device under low-temperature conditions is significantly improved. This may be because when a / z is maintained within an appropriate range, local side reaction phenomena caused by particle size distribution do not occur, and the interface between the positive electrode active material and the electrolyte has overall consistency, which has a relatively positive impact on ion transport performance.

[0142] Table 3 Effects of the Addition of Vinylene Carbonate (VC) on Cycling Performance

[0143]

[0144] As can be seen from Examples 3-1 to 3-8 in Table 3, the addition of VC can further improve the cycling capacity retention rate and reduce the thickness change during cycling. In particular, when the contents of VC and FEC satisfy 0.11a - 0.05% < b < 5.1a + 0.45%, while the cycling retention rate of the electrochemical device is further improved, the high-temperature thickness expansion is significantly improved. This may be because VC and FEC copolymerize to form an organic polymer component. When 0.11a - 0.05% < b < 5.1a + 0.45% is satisfied, the stability of the SEI is improved, reducing the degree of damage to the SEI by the reduction on the negative electrode and the thickness increase caused by side reactions. 2+ The reduction on the negative electrode reduces the degree of damage to the SEI and the thickness increase caused by side reactions.

[0145] Table 4 Effects of Various Additives on Storage Performance

[0146]

[0147]

[0148] Table 4 shows the effect of adding additive A on storage stability. On the one hand, it can improve gas generation during high-temperature storage; on the other hand, it can improve capacity recovery after storage. This is mainly because the combined use of this type of additive with FEC can reduce side reactions in the system under high-temperature storage conditions and reduce the consumption of active lithium by the electrolyte during long-term storage. In particular, the overall performance of the electrochemical device is significantly improved when at least one of LiFSI, LiPO2F2, and 2-PY is further added to the electrolyte.

[0149] Table 5. Effects of dimethyl carbonate (DMC) addition on cycling performance and storage performance.

[0150]

[0151] As can be seen from Examples 5-1 to 5-4 and Examples 1-4 in Table 5, adding a certain amount of DMC can improve the cycle and storage performance. This is mainly because the presence of a small amount of DMC can inhibit EMC decomposition and reduce the deterioration of cycle life caused by side reactions. However, when the DMC content is too high, the insufficient oxidation resistance of DMC will lead to gas generation and cycle decay during storage.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separating membrane, and an electrolyte. The electrolyte comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate, a, is 0.01% to 5% based on the mass of the electrolyte; The electrolyte also includes vinylene carbonate, the content of which b is 0.01% to 5% based on the mass of the electrolyte; The positive electrode includes a positive electrode active material, which contains Mn element, and the content of Mn element is greater than or equal to 15%, based on the mass of the positive electrode active material; The unit reaction area of ​​the positive electrode active material is c, and m 2 / cm 2 It is calculated that a and c satisfy the following relationship: 0.0006≤a / c≤6.25; wherein the unit reaction area is the product of the weight W of the positive electrode active material per unit area and the specific surface area BET of the positive electrode active material; The positive electrode active material has a Dv10 / Dv99 ratio of z and an a / z ratio of 0.01 to 1.

2. The electrochemical device according to claim 1, wherein at least one of the following conditions is met: a) 0.0006 ≤ a / c ≤ 2.5; b) The content of the fluoroethylene carbonate is 0.05% to 5%, based on the mass of the electrolyte; c) The range of W is 8 mg / cm² 2 Up to 35 mg / cm 2 The range of BET is 1m 2 / g to 5m 2 / g.

3. The electrochemical device according to claim 1, wherein at least one of the following conditions is met: a) 0.11a - 0.05% <b<5.1a+0.45%; b) In the positive electrode active material, the content of manganese is x, satisfying b / x≥10 -3 .

4. The electrochemical device according to claim 1 or 2, wherein the electrolyte further comprises additive A, said additive A being selected from at least one of methylene methane disulfonate, 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, succinic anhydride, lithium difluorophosphate, 2-fluoropyridine, and lithium difluorosulfonylimide, said additive A being present in a content of 0.01 to 10% based on the mass of said electrolyte.

5. The electrochemical device according to claim 1 or 2, wherein the electrolyte further comprises dimethyl carbonate, the content of which is less than or equal to 5% based on the mass of the electrolyte.

6. The electrochemical device according to claim 1 or 2, wherein the positive electrode active material comprises at least one of lithium manganese oxide and lithium nickel cobalt manganese oxide.

7. The electrochemical device according to claim 1 or 2, wherein it satisfies at least one of the following conditions: a) The content of the fluoroethylene carbonate is 0.05% to 3%, based on the mass of the electrolyte; b) The range of W is 13 mg / cm² 2 Up to 30 mg / cm 2 The range of BET is 1.2m. 2 / g to 3.5m 2 / g; c) The electrolyte further includes vinylene carbonate, the content of which is 0.01% to 2% based on the mass of the electrolyte; d) The electrolyte further includes dimethyl carbonate, wherein the content of dimethyl carbonate is less than or equal to 1%, based on the mass of the electrolyte; e) The content of Mn element in the positive electrode active material is less than or equal to 60%; f) The Dv10 / Dv99 of the positive electrode active material is z, and a / z is 0.05 to 0.

3.

8. An electrical appliance comprising the electrochemical device according to any one of claims 1-7.

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