Electrochemical device and electrolyte

Abstract

The present disclosure relates to an electrochemical device and an electrolyte. The electrochemical device comprises an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector. The negative electrode film layer comprises an active material. The active material comprises graphite and hard carbon. The electrolyte comprises a first additive and a second additive. The first additive has a lithium reduction potential of greater than or equal to 1.3 V, and the mass fraction of the first addictive in the electrolyte ranges from 0.1% to 1%. The second additive has a lithium reduction potential of less than 1.3 V.

Description

An electrochemical device and electrolyte

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202411854890.2, filed on December 16, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure belongs to the field of electrochemical technology, and particularly relates to an electrochemical device and an electrolyte. Background Technology

[0004] Electric vehicles have seen significant development in recent years as a crucial means of achieving global carbon emission reduction. Lithium-ion batteries, as a common electrochemical device, have become the most popular energy storage system due to their high operating voltage, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. Summary of the Invention

[0005] The main objective of this disclosure is to provide an electrochemical device and an electrolyte. This electrochemical device can achieve both fast charging performance and cycling performance.

[0006] The first aspect of this disclosure provides an electrochemical device comprising an electrolyte, a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, comprising graphite and hard carbon. The electrolyte includes a first additive and a second additive. The first additive has a lithium reduction potential ≥1.3V and a mass fraction of 0.1% to 1% in the electrolyte. The second additive has a lithium reduction potential <1.3V.

[0007] In some embodiments, the volumetric particle size distribution (Dv50) of the hard carbon is from 1.5 μm to 6.0 μm.

[0008] In some embodiments, the mass fraction of hard carbon in the negative electrode active material is 1% to 10%.

[0009] In some embodiments, the first additive includes lithium bis(oxalato)borate and / or lithium difluoro(oxalato)borate.

[0010] In some embodiments, the ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of hard carbon in the negative electrode active material is 0.02 to 0.8.

[0011] In some embodiments, the second additive includes one or more of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate.

[0012] In some embodiments, the second additive includes vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate.

[0013] In some embodiments, the mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate is (0.3-2.0):(1.0-2.0):(1.0-2.0):(0.5-2.0).

[0014] In some embodiments, the second additive has a mass fraction of 0.1% to 8% in the electrolyte.

[0015] In some embodiments, the mass ratio of the first additive to the second additive is 0.03 to 0.29.

[0016] In some embodiments, the volumetric particle size distribution (Dv50) of graphite is 8 to 17 μm.

[0017] In some embodiments, the negative electrode film layer has at least one of the following characteristics:

[0018] (1) The thickness of the negative electrode film is 70 μm to 150 μm;

[0019] (2) The areal density of the negative electrode film is 100 g / m³. 2 Up to 200g / m 2 ;

[0020] (3) The compaction density of the negative electrode film is 1.4 g / cm³. 2 Up to 1.7 g / cm 2 .

[0021] Another aspect of this disclosure provides an electrolyte comprising a first additive and a second additive, wherein the first additive has a lithium reduction potential ≥1.3V, the second additive has a lithium reduction potential <1.3V, and the mass fraction of the first additive in the electrolyte is 0.1% to 1%.

[0022] In some embodiments, the first additive includes lithium bis(oxalato)borate and / or lithium difluoro(oxalato)borate.

[0023] In some embodiments, the second additive includes one or more of fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, and vinylene carbonate.

[0024] In some embodiments, the second additive includes fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, and vinylene carbonate.

[0025] In some embodiments, the mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate is (0.3-2.0):(1.0-2.0):(1.0-2.0):(0.5-2.0).

[0026] In some embodiments, the second additive has a mass fraction of 0.1% to 8% in the electrolyte.

[0027] In some embodiments, the mass ratio of the first additive to the second additive is 0.03 to 0.29.

[0028] The electrochemical device disclosed herein uses a negative electrode active material that includes both graphite and hard carbon. Hard carbon has a low lithium intercalation energy barrier, which can improve the fast charging performance of the electrochemical device. Furthermore, by adding a first additive and a second additive to the electrolyte, the two work together to generate a stable SEI film on the negative electrode active film layer, thereby improving the cycle performance of the electrochemical device.

[0029] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 shows a schematic diagram of a negative electrode sheet with severe lithium plating;

[0032] Figure 2 shows a schematic diagram of the negative electrode sheet with edge lithium plating;

[0033] Figure 3 shows a schematic diagram of a negative electrode sheet that does not deposit lithium. Detailed Implementation

[0034] The technical solutions of this disclosure will be clearly and completely described below with reference to the accompanying drawings and exemplary embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this disclosure, not all embodiments, and are only used to illustrate this disclosure, and should not be regarded as limiting the scope of this disclosure. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure 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.

[0036] Unless otherwise specified, the term "or" is inclusive in this disclosure. 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).

[0037] Unless otherwise specified, in this disclosure, "one or more" or "at least one" refers to any one, two, or more of the listed items. "Several" refers to any two or more.

[0038] Electric vehicles have seen significant development in recent years as a crucial means of achieving global carbon emission reduction. Lithium-ion batteries, as a common electrochemical device, have become the most popular energy storage system due to their high operating voltage, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields.

[0039] In recent years, the market has placed higher demands on electrochemical devices, such as requiring them to balance fast charging capabilities and cycle performance. Improving fast charging performance typically requires increasing the conductivity of materials, but this may sacrifice structural stability. During rapid charging and discharging, significant volume expansion and contraction occur within the electrochemical device; insufficient structural stability can lead to material fracture, thus affecting cycle performance. Therefore, balancing battery cycle performance and fast charging performance remains a challenging technical hurdle for those skilled in the art.

[0040] The first aspect of this disclosure provides an electrochemical device. This electrochemical device can be a lithium-ion battery, a sodium-ion battery, a lithium metal battery, or a sodium metal battery, and the embodiments of this disclosure are not limited thereto.

[0041] Typically, an electrochemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte. During battery charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0042] The electrochemical device disclosed herein includes an electrolyte, a positive electrode, a negative electrode, and a separator between the positive and negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0043] The negative electrode film layer includes a negative electrode active material, which includes graphite and hard carbon. The electrolyte includes a first additive and a second additive. The first additive has a lithium reduction potential ≥1.3V and the mass fraction of the first additive in the electrolyte is 0.1% to 1%. The second additive has a lithium reduction potential <1.3V.

[0044] In the above technical solution, the negative electrode active material includes graphite and hard carbon. Compared to graphite, hard carbon has a lower lithium intercalation energy barrier. Therefore, adding hard carbon to the negative electrode active material can improve the fast charging performance of the electrochemical device. Based on this, a first additive with a lithium reduction potential ≥1.3V is added to the electrolyte. This first additive undergoes a reduction reaction before lithium intercalation on the hard carbon, forming an SEI film. This prevents the electrolyte from entering the hard carbon, thereby preventing side reactions at the hard carbon / electrolyte interface under low reduction potentials and improving the cycle stability of the electrochemical device. In addition, the electrolyte also includes a second additive with a lithium reduction potential <1.3V. This second additive reacts after lithium intercalation on the hard carbon to further form an SEI film, improving the overall stability of the SEI film, reducing side reactions at the overall negative electrode / electrolyte interface, and further improving the cycle performance of the electrochemical device. Furthermore, when the mass fraction of the first additive in the electrolyte is within the aforementioned range, a moderately thick and uniform SEI film can be formed. Such an SEI film not only provides a stable transport channel for lithium ions but also prevents the electrolyte solvent from directly contacting the hard carbon, reducing unnecessary side reactions and thus further improving the cycle stability of the electrochemical device. Therefore, the electrochemical device disclosed in this disclosure can achieve both fast charging performance and cycle performance.

[0045] In this disclosure, the mass fraction of the first additive in the electrolyte is any value within the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, or any combination thereof.

[0046] In this disclosure, the lithium reduction potential of the first additive can be any value within the range of 1.3V, 1.4V, 1.5V, 1.6V, 1.7V, 1.8V, 1.9V, 2V, or any combination thereof. Optionally, the lithium reduction potential of the first additive can be greater than or equal to 1.3V and less than 2.0V.

[0047] In this disclosure, the lithium reduction potential of the second additive can be any value within the range of 1.3V, 1.2V, 1.1V, 1.0V, 0.9V, 0.8V, 0.7V, 0.6V, or any combination thereof.

[0048] In this disclosure, the lithium reduction potential of the additive refers to the potential of the additive during the reduction reaction relative to a lithium standard electrode. The lithium reduction potential of the additive can be measured by cyclic voltammetry (CV), potentiostatic step method, electrochemical impedance spectroscopy (EIS), or potentiometric titration. The measurement steps may include: 1) assembling an electrolyte containing the additive with a lithium metal electrode and a reference electrode (typically a lithium reference electrode) into a test cell; 2) setting an appropriate test program (such as cyclic voltammetry or electrochemical impedance spectroscopy) on the battery testing system; 3) performing the test, recording the corresponding data, and determining the lithium reduction potential of the additive by analyzing the data.

[0049] The following is a further explanation of the components of the electrochemical device:

[0050] In this disclosure, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material. The negative electrode active material includes hard carbon and graphite.

[0051] In some embodiments, the volumetric particle size distribution (Dv50) of the hard carbon is from 1.5 μm to 6.0 μm. By setting the volumetric particle size distribution (Dv50) of the hard carbon within this range, the hard carbon can have a suitable specific surface area, resulting in a negative electrode film with a rich porous structure when the hard carbon material is used as a negative electrode active material. This provides abundant transport channels for lithium ions, thereby helping to improve the performance of the electrochemical device during fast charging. Exemplarily, the volumetric particle size distribution (Dv50) of the hard carbon can be any value within the range of 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or any combination thereof.

[0052] In this disclosure, the term "Dv50" (volume distribution particle size) has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0053] In some embodiments, the mass fraction of hard carbon in the negative electrode active material is 1% to 10%. By setting the mass fraction of hard carbon within the above range, the fast charging performance of the electrochemical device can be improved while simultaneously maintaining the capacity and cycle performance of the electrochemical device. Exemplarily, the mass fraction of hard carbon in the negative electrode active material can be any value within the range of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination thereof.

[0054] In some embodiments, the volumetric particle size distribution (Dv50) of graphite is between 8 μm and 17 μm. When the Dv50 of graphite is within this range, a reasonable particle size distribution can be formed between graphite and hard carbon, resulting in better porosity in the negative electrode film layer. This is beneficial for improving the transport performance of ions and electrons, and further enhancing fast charging performance. For example, the Dv50 of graphite can be any value within the range of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or any combination thereof.

[0055] In some embodiments, the negative electrode film layer has at least one of the following characteristics:

[0056] (1) The thickness of the negative electrode film is 70 μm to 150 μm;

[0057] (2) The areal density of the negative electrode film is 100 g / m³. 2 Up to 200g / m 2 ;

[0058] (3) The compaction density of the negative electrode film is 1.4 g / cm³. 2 Up to 1.7 g / cm 2 .

[0059] This will help to further improve the fast charging performance and cycle performance of electrochemical devices.

[0060] In some implementations, the negative electrode current collector can be a metal foil or a composite current collector.

[0061] In some embodiments, the negative electrode film layer may optionally include a binder. 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).

[0062] In some embodiments, the negative electrode film may optionally include a conductive agent. 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.

[0063] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0064] 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.

[0065] electrolytes

[0066] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0067] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0068] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethylsulfonyl)methyl, or lithium bis(trifluoromethylsulfonyl)imide.

[0069] In some embodiments, the solvent comprises a carbonate, wherein the carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The solvent may also comprise a carboxylic acid ester, wherein the carboxylic acid ester includes one or more of propyl propionate (PP), ethyl propionate (EP), propyl acetate (PA), and ethyl acetate (EA).

[0070] In this disclosure, the electrolyte further includes a first additive having a lithium reduction potential ≥1.3V. In some embodiments, the first additive includes lithium bis(oxalato)borate (LiBOB) and / or lithium difluorooxalato)borate (LiDFOB). Since the first additive has a lithium reduction potential ≥1.3V, it can react with lithium ions before lithium intercalation into the hard carbon material, thereby forming an SEI film on the surface of the negative electrode film. The SEI film prevents solvent from entering the hard carbon, thereby reducing side reactions at the interface between the negative electrode film and the electrolyte, and thus improving the cycle performance of the electrochemical device.

[0071] In some embodiments, the ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of hard carbon in the negative electrode active material is 0.02 to 0.8. By controlling the ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of hard carbon in the negative electrode active material within the above range, the fast charging performance of the battery can be improved while a moderately thick and uniform SEI film is formed at the interface between the negative electrode film and the electrolyte, thereby improving the cycle performance of the electrochemical device. Exemplarily, the ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of hard carbon in the negative electrode active material can be any value within the range of 0.02, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any combination thereof.

[0072] In this disclosure, the electrolyte further includes a second additive having a lithium reduction potential of <1.3V. In some embodiments, the second additive includes one or more of vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (1,3-PS), and fluoroethylene carbonate (FEC). The aforementioned second additive can react to form an SEI film after lithium intercalation on hard carbon, reducing damage to the SEI film during the hard carbon lithium intercalation process, improving the overall stability of the SEI film, and further enhancing the cycle performance of the electrochemical device.

[0073] In some embodiments, the second additive includes vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate. Using these second additives can further improve the cycle performance of the electrochemical device.

[0074] In some embodiments, the mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate is (0.3-2.0):(1.0-2.0):(1.0-2.0):(0.5-2.0). By selecting the above second additive, the cycle performance of the electrochemical device can be further improved. Exemplarily, the mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate can be any value within the range of 0.3:1:1:0.5, 0.3:1.5:1.5:0.5, 0.5:1.5:1.5:1, 0.5:2:1.5:1, 1:2:2:2, 2:2:2:2, or any combination thereof.

[0075] In some embodiments, the second additive has a mass fraction of 0.1% to 8% in the electrolyte. By keeping the added mass fraction within the above range, an SEI film of moderate thickness can be formed, which can reduce side reactions between the electrolyte and the active material and improve the cycle performance of the electrochemical device. Exemplarily, the mass fraction of the second additive in the electrolyte is any value within the range of 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any combination thereof.

[0076] In some embodiments, the mass ratio of the first additive to the second additive is from 0.03 to 0.29. The first additive functions before lithium intercalation in the hard carbon material, responsible for forming the initial layer of the SEI film, while the second additive further forms the SEI film before lithium intercalation in the graphite, thereby further enhancing the structure of the SEI film. By controlling the mass ratio of the first additive to the second additive within the above range, it is beneficial to form a uniform and stable SEI film, reduce SEI film damage and consumption during charge and discharge processes, and optimize the cycle performance of the electrochemical device. Exemplarily, the mass ratio of the first additive to the second additive can be any value within the range of 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24, 0.29, or any combination thereof.

[0077] Positive electrode sheet

[0078] In this disclosure, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this disclosure.

[0079] 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.

[0080] In some implementations, 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.

[0081] When the battery cell is a lithium-ion battery, the positive electrode active material can be any positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this disclosure 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. Exemplarily, lithium transition metal oxides include LiNi. 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 At least one of the following.

[0082] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0083] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] 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.

[0085] Separating membrane

[0086] In this disclosure, the electrochemical device also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0087] In some embodiments, 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 limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0088] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0089] Numerous details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this disclosure, and not all embodiments.

[0090] Example 1

[0091] The preparation method of the electrochemical device is as follows:

[0092] (1) Preparation of negative electrode sheet

[0093] A negative electrode active material (artificial graphite with a Dv50 of 12.6 μm and hard carbon with a Dv50 of 3.4 μm), conductive carbon (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in deionized water at a weight ratio of 96.4:1:1.2:1.4 and stirred until homogeneous to obtain a negative electrode slurry. The mass fraction of hard carbon in the negative electrode active material was 5%. Copper foil was used as the negative electrode current collector. The negative electrode slurry was coated on one side of the negative electrode current collector and baked at 120°C for 1 hour. Subsequently, it was cold-pressed, cut, and slit to prepare the negative electrode, wherein the thickness of the negative electrode active layer was 100 μm. The mass fraction of hard carbon in the negative electrode active material was 5%.

[0094] (2) Preparation of positive electrode sheet

[0095] LiNi 0.8 Co 0.1 Mn 0.1(NCM811), conductive carbon (SP), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96:1:0.5:2.5 in the solvent N-methylpyrrolidone and stirred until homogeneous to obtain a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated onto one side of the current collector. The foil was baked at 120°C for 1 hour, followed by cold pressing, cutting, and slitting to prepare the positive electrode, wherein the thickness of the positive electrode active layer was 143 μm.

[0096] (3) Preparation of electrolytes

[0097] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 3:7. Then, 0.3% by mass of a first additive, lithium bis(oxalato)borate (LiBOB, with a lithium reduction potential ≥1.3V), and a second additive were added. The second additive comprised vinylene carbonate (VC, with a lithium reduction potential <1.3V), 1,3-propanesulfonate lactone (PS, with a lithium reduction potential <1.3V), and fluoroethylene carbonate (FEC, with a lithium reduction potential <1.3V). Subsequently, lithium hexafluorophosphate (LiPF6) was added, with a mass fraction of 12.5%. Finally, vinyl sulfate (DTD, with a lithium reduction potential <1.3V) was added and mixed thoroughly to obtain the electrolyte. The mass ratio of VC, DTD, PS, and FEC was 0.3:1:1:0.5. The mass fraction of the second additive in the electrolyte was 2.8%.

[0098] (4) Preparation of the separating membrane

[0099] A polyethylene film with a thickness of 7 μm is used as the substrate. A PVDF coating with a thickness of 5 μm is applied to both sides of the substrate. A boehmite ceramic layer with a thickness of 3 μm is applied to one of the PVDF coated surfaces to obtain the isolation membrane.

[0100] (5) Assembly of electrochemical devices

[0101] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The side of the separator coated with boehmite ceramic layer is aligned with the positive electrode. The positive electrode, separator, and negative electrode are then stacked, placed in an aluminum-plastic film, dried at 80°C, and then injected with the prepared electrolyte. After vacuum sealing, settling, formation, and shaping, the electrochemical device is obtained.

[0102] The performance of the obtained electrochemical device was tested using the following methods:

[0103] Fast charging performance test:

[0104] 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 4.25V, 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 3.0V. This cycle was repeated 100 times, with each cycle followed by a 5-minute rest, charging at a constant charging rate of 4C to 4.25V, and then constant voltage charging to a charging rate of 0.05C. The electrochemical device was then disassembled to obtain the negative electrode. The lithium deposition on the surface of the negative electrode was observed.

[0105] Basis for judgment:

[0106] As shown in Figure 1, the presence of metallic lithium deposition on a large surface of the negative electrode indicates severe lithium deposition on the negative electrode, resulting in poor fast charging performance of the battery.

[0107] As shown in Figure 2, lithium metal is deposited at the edge of the negative electrode, indicating that lithium deposition at the edge of the negative electrode improves the battery's fast charging performance.

[0108] As shown in Figure 3, no metallic lithium is deposited on the surface of the negative electrode, indicating that the negative electrode does not deposit lithium, and the fast charging performance of the battery is further improved.

[0109] Cyclic performance test:

[0110] The electrochemical device was placed in a constant temperature chamber at 25°C and allowed to stand for 30 minutes. It was then charged at a constant charging rate of 4C to 4.25V, 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 3.0V, and the capacity was recorded as D0. Cyclic testing was then performed according to the following steps:

[0111] 1) Let stand for 5 minutes;

[0112] 2) Charge at a constant charging rate of 4C to 4.25V; then charge at a constant voltage to a charging rate of 0.05C;

[0113] 3) Let stand for 5 minutes;

[0114] 4) Discharge to 3.0V at a constant discharge rate of 1.0C;

[0115] 5) Repeat steps 1) to 4) 1500 times; the recording capacity is D1;

[0116] Cyclic capacity retention (%) = (D1-D0) / D0 × 100%.

[0117] Example 2

[0118] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction of the first additive, LiBOB, in Example 2 was 0.1%.

[0119] Example 3

[0120] The electrochemical device was prepared using the same method as in Example 1, except that the mass fraction of the first additive, LiBOB, in Example 3 was 0.5%.

[0121] Example 4

[0122] The electrochemical device was prepared using the same method as in Example 1, except that in Example 4, lithium difluorooxalate borate (LiDFOB, with a lithium reduction potential ≥1.3V) was used instead of LiBOB as the first additive, and the mass fraction of LiDFOB in the electrolyte was 1.0%.

[0123] Comparative Example 1

[0124] The electrochemical device was prepared using the same method as in Example 1, except that, in Comparative Example 1, hard carbon was not included in the negative electrode active material.

[0125] Comparative Example 2

[0126] The electrochemical device was prepared using the same method as in Example 1, except that no second additive was added to the electrolyte in Comparative Example 2.

[0127] Comparative Example 3

[0128] The electrochemical device was prepared using the same method as in Example 1, except that, in Comparative Example 3, the first additive was not added to the electrolyte.

[0129] Comparative Example 4

[0130] The electrochemical device was prepared using the same method as in Example 1, except that in Comparative Example 3, the mass fraction of the first additive in the electrolyte was 1.02%.

[0131] The electrochemical devices obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were tested using the same test methods as in Example 1. The test results are shown in Table 1 below. In Table 1, " / " indicates that no relevant items were set.

[0132] Table 1

[0133] As shown in Table 1, compared with Comparative Examples 1 to 4, the electrochemical devices of Examples 1 to 4 can achieve both fast charging performance and cycle performance.

[0134] Example 5

[0135] The electrochemical device was prepared using the same method as in Example 1, except that in Example 5, the Dv50 of the hard carbon in the negative electrode active material was 1.5 μm.

[0136] Example 6

[0137] The electrochemical device was prepared using the same method as in Example 1, except that in Example 6, the Dv50 of the hard carbon in the negative electrode active material was 6.0 μm.

[0138] The electrochemical devices obtained in Examples 5 and 6 were tested using the same test methods as in Example 1. Table 2 shows the test results for Examples 5, 6, and related examples.

[0139] Table 2: In Table 2, the mass fraction of hard carbon relative to the total mass of the negative electrode active material is represented by c.

[0140] Table 2

[0141] As shown in Table 2, when the hard carbon Dv50 is between 1.5 μm and 6 μm, the electrochemical device can achieve both fast charging performance and cycling performance.

[0142] Example 7

[0143] The electrochemical device was prepared using the same method as in Example 1, except that in Example 7, the mass fraction of hard carbon in the negative electrode active material was 1%, and the mass fraction of the first additive LiBOB was 0.8%.

[0144] Example 8

[0145] The electrochemical device was prepared using the same method as in Example 1, except that in Example 8, the mass fraction of hard carbon in the negative electrode active material was 3%, and the mass fraction of the first additive LiBOB was 0.8%.

[0146] Example 9

[0147] The electrochemical device was prepared using the same method as in Example 1, except that in Example 9, the mass fraction of hard carbon in the negative electrode active material was 8%, and the mass fraction of the first additive LiBOB was 0.8%.

[0148] Example 10

[0149] The electrochemical device was prepared using the same method as in Example 1, except that in Example 10, the mass fraction of hard carbon in the negative electrode active material was 10%, and the mass fraction of the first additive LiBOB was 0.8%.

[0150] Example 11

[0151] The electrochemical device was prepared using the same method as in Example 1, except that in Example 11, the first additive was 0.3% LiDFOB by mass.

[0152] The electrochemical devices obtained in Examples 7 to 11 were tested using the same test methods as in Example 1. Table 3 shows the test results for Examples 7 to 11 and related examples.

[0153] Table 3

[0154] As shown in Table 3, when the mass fraction of hard carbon in the negative electrode active material is 1% to 10%, the mass fraction of the first additive in the electrolyte is 0.1% to 0.8%, and the ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of hard carbon in the negative electrode active material is 0.02 to 0.8, the obtained electrochemical device can take into account both charging performance and cycle performance.

[0155] Example 12

[0156] The electrochemical device was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 12 was as follows:

[0157] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 3:7. Then, 0.3% by mass of the first additive LiBOB and the second additive VC are added, followed by lithium hexafluorophosphate (LiPF6) at a mass fraction of 12.5%. Finally, the second additive DTD is added and mixed thoroughly to obtain an electrolyte. The second additive has a mass fraction of 1.3% in the electrolyte, and the mass ratio of VC to DTD in the second additive is 0.3:1.

[0158] Example 13

[0159] The electrochemical device was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 13 was as follows:

[0160] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 3:7. Then, 0.3% by mass of the first additive LiBOB and the second additives VC and FEC are added. Subsequently, lithium hexafluorophosphate (LiPF6) with a mass fraction of 12.5% ​​is added, followed by the addition of the second additive DTD. The mixture is then thoroughly mixed to obtain an electrolyte with a mass fraction of 1.8% in the electrolyte. The mass ratio of VC, DTD, and FEC in the second additive is 0.3:1:0.5.

[0161] Example 14

[0162] The electrochemical device was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 14 was as follows:

[0163] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 3:7. Then, 0.3% by mass of the first additive LiBOB and the second additives VC and PS were added. Subsequently, lithium hexafluorophosphate (LiPF6) with a mass fraction of 12.5% ​​was added, followed by the addition of the second additive DTD. The mixture was then thoroughly mixed to obtain an electrolyte with a mass fraction of 2.3% in the electrolyte. The mass ratio of VC, DTD, and PS in the second additive was 0.3:1:1.

[0164] Example 15

[0165] The electrochemical device was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 15 was as follows:

[0166] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 3:7. Then, 0.3% by mass of the first additive LiBOB and the second additives PS and FEC were added. Subsequently, lithium hexafluorophosphate (LiPF6) with a mass fraction of 12.5% ​​was added. Then, the second additive DTD was added and mixed evenly to obtain an electrolyte. The mass fraction of the second additive in the electrolyte was 2.5%, and the mass ratio of DTD, PS and FEC in the second additive was 1:1:0.5.

[0167] Example 16

[0168] The electrochemical device was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 16 was as follows:

[0169] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 3:7. Then, 0.1% by mass of the first additive LiBOB and 0.1% by mass of the second additive VC are added, followed by the addition of lithium hexafluorophosphate (LiPF6) at a mass fraction of 12.5%. The mixture is then homogeneous to obtain the electrolyte.

[0170] Example 17

[0171] The lithium-ion battery was prepared using the same method as in Example 1, except that the electrolyte preparation process in Example 17 was as follows:

[0172] In an argon atmosphere, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 3:7. Then, 0.24% by mass of the first additive LiBOB and the second additives VC, PS, and FEC were added. Subsequently, lithium hexafluorophosphate (LiPF6) with a mass fraction of 12.5% ​​was added, followed by the addition of the second additive DTD. The mixture was then thoroughly mixed to obtain an electrolyte. The second additive had a mass fraction of 8% in the electrolyte, and the mass ratio of VC, DTD, PS, and FEC in the second additive was 2:2:2:2.

[0173] The electrochemical devices obtained in Examples 12 to 17 were tested using the same test methods as in Example 1. Table 4 shows the test results for Examples 12 to 17 and related examples.

[0174] Table 4

[0175] As can be seen from the results in Table 4, when the second additive of this disclosure is selected from one or more of VC, DTD, PS and FEC, and the mass fraction of the second additive in the electrolyte is 0.1% to 8%, the obtained electrochemical device can take into account both charging performance and cycling performance.

[0176] Example 18

[0177] The electrochemical device was prepared using the same method as in Example 1, except that in Example 18, the mass fraction of the second additive in the electrolyte was 3.8%, and the mass ratio of VC, DTD, PS and FEC in the second additive was 0.3:1.5:1.5:0.5.

[0178] Example 19

[0179] The electrochemical device was prepared using the same method as in Example 1, except that in Example 19, the mass fraction of the second additive in the electrolyte was 4.5%, and the mass ratio of VC, DTD, PS and FEC in the second additive was 0.5:1.5:1.5:1.

[0180] Example 20

[0181] The electrochemical device was prepared using the same method as in Example 1, except that in Example 20, the second additive had a mass fraction of 5% in the electrolyte and the mass ratio of VC, DTD, PS and FEC in the second additive was 0.5:2:1.5:1.

[0182] Example 21

[0183] The electrochemical device was prepared using the same method as in Example 1, except that in Example 21, the mass fraction of the second additive in the electrolyte was 7%, wherein the mass ratio of VC, DTD, PS and FEC in the second additive was 1:2:2:2.

[0184] The electrochemical devices obtained in Examples 18 to 21 were tested using the same test methods as in Example 1. Table 5 shows the test results for Examples 18 to 21 and related examples.

[0185] Table 5

[0186] As shown in Table 5, when the mass fraction of the second additive is 0.1% to 8% and the mass ratio of the first additive to the second additive is 0.03 to 0.29, the electrochemical device can achieve both charging performance and cycling performance.

[0187] Example 22

[0188] The electrochemical device was prepared using the same method as in Example 1, except that in Example 22, the graphite in the negative electrode active material had a Dv50 of 8 μm.

[0189] Example 23

[0190] The electrochemical device was prepared using the same method as in Example 1, except that in Example 23, the Dv50 of the graphite in the negative electrode active material was 17 μm.

[0191] The electrochemical devices obtained in Examples 22 and 23 were tested using the same test methods as in Example 1. Table 6 shows the test results for Examples 22 and 23 and related examples.

[0192] Table 6

[0193] As shown in Table 6, when the graphite Dv50 is between 8 μm and 17 μm, the electrochemical device can achieve both fast charging performance and cycle performance.

[0194] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. An electrochemical device, wherein, The electrochemical device includes an electrolyte, a positive electrode, a negative electrode, and a separator between the positive and negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes graphite and hard carbon. The electrolyte includes a first additive and a second additive. The first additive has a lithium reduction potential ≥1.3V and the mass fraction of the first additive in the electrolyte is 0.1% to 1%. The second additive has a lithium reduction potential <1.3V.

2. The electrochemical device of claim 1, wherein, The volumetric particle size Dv50 of the hard carbon is 1.5 μm to 6.0 μm.

3. The electrochemical device according to claim 1 or 2, wherein The hard carbon in the negative electrode active material has a mass fraction of 1% to 10%.

4. The electrochemical device according to any one of claims 1 to 3, wherein, The first additive includes lithium dioxaborate and / or lithium difluorooxaborate.

5. The electrochemical device according to any one of claims 1 to 4, wherein, The ratio of the mass fraction of the first additive in the electrolyte to the mass fraction of the hard carbon in the negative electrode active material is 0.02 to 0.

8.

6. The electrochemical device of any one of claims 1 to 5, wherein, The second additive includes one or more of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate.

7. The electrochemical device of claim 6, wherein, The second additive includes vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate.

8. The electrochemical device of claim 7, wherein, The mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate is (0.3-2.0):(1.0-2.0):(1.0-2.0):(0.5-2.0).

9. The electrochemical device according to any one of claims 1 to 8, wherein, The second additive has a mass fraction of 0.1% to 8% in the electrolyte.

10. The electrochemical device according to any one of claims 1 to 9, wherein, The mass ratio of the first additive to the second additive is 0.03 to 0.

29.

11. The electrochemical device according to any one of claims 1 to 10, wherein, The volumetric particle size distribution (Dv50) of the graphite is 8 μm to 17 μm.

12. The electrochemical device according to any one of claims 1 to 11, wherein, The negative electrode film layer has at least one of the following characteristics: (1) The thickness of the negative electrode film is 70 μm to 150 μm; (2) the double-sided density of the negative electrode film layer is 100 g / m 2 to 200 g / m 2 ; (3) the compaction density of the negative electrode film layer is 1.4 g / cm 2 to 1.7 g / cm 2 .

13. An electrolyte, wherein, The electrolyte includes a first additive and a second additive, wherein the first additive has a lithium reduction potential ≥1.3V, the second additive has a lithium reduction potential <1.3V, and the mass fraction of the first additive in the electrolyte is 0.1% to 1%.

14. The electrolyte of claim 13, wherein, The first additive includes lithium dioxaborate and / or lithium difluorooxaborate.

15. The electrolyte of claim 13 or 14, wherein, The second additive includes one or more of fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, and vinylene carbonate.

16. The electrolyte of claim 15, wherein, The second additive also includes fluoroethylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, and vinylene carbonate.

17. The electrolyte of claim 16, wherein, The mass ratio of vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, and fluorovinyl carbonate is (0.3-2.0):(1.0-2.0):(1.0-2.0):(0.5-2.0).

18. The electrolyte of any one of claims 13, wherein, The second additive has a mass fraction of 0.1% to 8% in the electrolyte.

19. The electrolyte of any one of claims 13, wherein the electrolyte is characterized by, The mass ratio of the first additive to the second additive is 0.03 to 0.29.

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