Negative electrode sheet, and electrochemical device and electronic device comprising same
By constructing a multi-layer lithium intercalation potential gradient structure on the negative electrode of a lithium-ion battery, the lithium intercalation reaction is preferentially carried out in the outer layer, which solves the lithium plating problem in the fast charging process of lithium-ion batteries, improves safety and energy density, and enhances cycle life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG LIWINON ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-03-31
- Publication Date
- 2026-06-05
AI Technical Summary
The negative electrode materials of existing lithium-ion batteries are prone to lithium plating during fast charging, resulting in insufficient safety and energy density. Existing designs cannot simultaneously achieve fast charging, high energy density, and high safety.
By employing a multilayer anode active material structure and controlling the lithium intercalation potential and silicon content gradient of different layers, a gradient structure is constructed in which "the delithiation potential of the outer layer is higher than that of the inner layer". This allows for preferential lithium intercalation reaction in the outer layer, preventing lithium from being deposited in the inner layer.
It improves the fast-charging performance and safety of lithium-ion batteries, while also increasing energy density and cycle life, and provides a systematic design methodology for optimizing silicon-based anodes.
Smart Images
Figure SMS_1 
Figure SMS_2 
Figure SMS_3
Abstract
Description
Technical Field
[0001] This application relates to the field of electrochemical energy storage technology, and more specifically, to a negative electrode and an electrochemical and electronic device comprising the same. Background Technology
[0002] With the increasing popularity of electric vehicles and portable electronic devices, the requirements for the fast charging performance, energy density, and safety of electrochemical devices (especially lithium-ion batteries) are becoming increasingly stringent.
[0003] During fast charging, the negative electrode of lithium-ion batteries, especially the widely used graphite negative electrode, faces a severe challenge. When lithium-ion intercalation is too slow, the surface potential of the negative electrode can rapidly drop to 0V (relative to Li / Li). + Below this point, lithium metal is deposited (lithium plating). Lithium plating not only consumes active lithium, reducing the capacity and cycle life of lithium-ion batteries, but it can also puncture the separator, causing internal short circuits. Currently, to improve the fast-charging performance or energy density of electrochemical devices, lithium titanate (LTO) materials are generally used in the negative electrode to improve safety, or silicon-based materials are introduced to improve capacity. However, these single materials often cannot simultaneously achieve fast charging, high energy density, and high safety. Alternatively, the negative electrode may adopt a multi-layer gradient structure, but its design focuses more on physical structure (such as porosity gradient) or conductive network optimization, failing to fundamentally and actively and precisely control the sequence of lithium ion insertion behavior through the intrinsic electrochemical properties of the material (lithium intercalation potential). The potential gradient design of its multi-layer gradient structure cannot effectively eliminate the risk of lithium plating. Summary of the Invention
[0004] The purpose of this application is to overcome the shortcomings of existing technologies and provide a negative electrode sheet and an electrochemical device and electronic device comprising the same. This application achieves a synergistic improvement in the energy density, fast-charging capability, and cycle life of the electrochemical device by introducing materials with different lithium intercalation potentials to construct a better potential gradient and functional partitioning.
[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: The first aspect of this application provides a negative electrode sheet, including a negative electrode current collector and n negative electrode active material layers disposed sequentially on at least one surface of the negative electrode current collector, where n≥2, and the layer furthest from the negative electrode current collector is the nth negative electrode active material layer. The nth negative electrode active material layer includes an nth negative electrode active material, which comprises graphite and an nth silicon-carbon material, wherein the mass percentage of silicon in the nth silicon-carbon material is X. n The average delithiation potential of the nth negative electrode active material is V. n ; The (n-1)th negative electrode active material layer includes an (n-1)th negative electrode active material, which comprises graphite and an (n-1)th silicon-carbon material, wherein the mass percentage of silicon in the (n-1)th silicon-carbon material is X. n-1 The average delithiation potential of the (n-1)th negative electrode active material is V. n-1 ; The X n X n-1 Satisfy: X n >X n-1 ; The V n V n-1 Satisfy: V n -V n-1 ≥0.1V.
[0006] In some implementations, the X n-1 X n Satisfy: 0≤X n-1 ≤6%, 7.5% < X n ≤45%.
[0007] In some implementations, the V n V n-1 Satisfies: 0.2V ≤ V n ≤0.6V, 0.1V≤V n-1 ≤0.5V.
[0008] In some implementations, the V n V n-1 Satisfies: 0.1V ≤ V n -V n-1 ≤0.35V.
[0009] In some implementations, the V n V n-1 Satisfies: 0.12V ≤ V n -V n-1 ≤0.15V.
[0010] In some embodiments, the thickness ratio of the nth negative electrode active material layer to the (n-1)th negative electrode active material layer is (20~50):(50~80).
[0011] In some embodiments, the mass ratio of graphite to silicon carbide in the nth negative electrode active material is (10~85):(15~90).
[0012] In some embodiments, the mass ratio of graphite to silicon carbide in the (n-1)th negative electrode active material is (85~100):(0~15).
[0013] In some embodiments, the Dv90 particle size of graphite in the nth negative electrode active material is a, and the Dv90 particle size of graphite in the (n-1)th negative electrode active material is b, wherein a and b satisfy: a < b.
[0014] In some embodiments, the sphericity of the silicon-carbon material in the nth negative electrode active material is φ(n), and the sphericity of the silicon-carbon material in the (n-1)th negative electrode active material is φ(n-1), wherein φ(n) and φ(n-1) satisfy: φ(n)≥φ(n-1).
[0015] A second aspect of this application provides an electrochemical device comprising the negative electrode sheet described above.
[0016] A third aspect of this application provides an electronic device including the electrochemical device described above.
[0017] The beneficial effects of this application are as follows: 1. This application constructs a gradient structure where the outer layer has a higher delithiation potential than the inner layer. During charging of the electrochemical device, this structure provides a strong driving force for lithium-ion migration due to the higher thermodynamic lithium intercalation potential of the outer layer, thus preferentially causing the lithium intercalation reaction to occur in the outer layer. This active control over the reaction sequence fundamentally avoids the accumulation and precipitation of lithium ions in the inner layer and on the current collector surface, greatly improving the fast-charging safety of the electrochemical device.
[0018] 2. The preferential lithium intercalation mechanism of this application is essentially a kinetic optimization. It allows the electrochemical device to operate safely under higher external currents (fast charging). Simultaneously, the gradient structure constructed in this application, where the outer layer delithiation potential is higher than the inner layer delithiation potential, places a high-capacity silicon-based material with high reactivity and large volume change in the outer layer. Its volume expansion is physically constrained by the more stable graphite or low-silicon material in the inner layer, alleviating the overall plastic deformation of the electrochemical device. This achieves high energy density while improving the cycle life of the electrochemical device.
[0019] 3. Based on the design principles of lithium removal potential and silicon content gradient, this application provides a new and systematic design methodology for developing next-generation silicon-based anodes that meet different fast charging and energy density requirements. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0021] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.
[0022] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.
[0023] In this application, there are no particular restrictions on the specific dispersion and mixing methods.
[0024] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available.
[0025] General definition Negative electrode active material: As used herein and in the claims, the term "negative electrode active material" (also known as anodic active material) is defined as a material that is electrochemically active in a negative electrode or anode. Active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.
[0026] I. Negative electrode This application provides a negative electrode sheet, including a negative electrode current collector and n negative electrode active material layers sequentially disposed on at least one surface of the negative electrode current collector, where n≥2, and the nth negative electrode active material layer is the one furthest away from the negative electrode current collector. The nth negative electrode active material layer includes an nth negative electrode active material, which comprises graphite and an nth silicon-carbon material, wherein the mass percentage of silicon in the nth silicon-carbon material is X. n The average delithiation potential of the nth negative electrode active material is V. n ; The (n-1)th negative electrode active material layer includes an (n-1)th negative electrode active material, which comprises graphite and an (n-1)th silicon-carbon material, wherein the mass percentage of silicon in the (n-1)th silicon-carbon material is X. n-1 The average delithiation potential of the (n-1)th negative electrode active material is V. n-1 ; The X n X n-1 Satisfy: X n >X n-1 ; The V n V n-1 Satisfy: V n -V n-1 ≥0.1V.
[0027] The inventors of this application have discovered that the fast-charging performance (rate performance), fast-charging safety, and cycle life of a negative electrode sheet with a multilayer negative electrode active material structure are significantly correlated with the average delithiation potential and silicon content of the negative electrode active material in the negative electrode active material layer. This application utilizes control: X n >X n-1 V n -V n-1 With a potential ≥0.1V, the lithium storage mechanism of the (n-1)th anode active material is primarily a lithium-ion intercalation reaction, which has a low and flat potential plateau. In contrast, the lithium storage mechanism of the nth anode active material is an alloying reaction, which generates thermodynamically more stable crystalline Li. 15 Intermetallic compounds such as Si4 release lithium ions from these stable alloy phases, systematically guiding their electrochemical mechanism towards alloying reactions, thereby actively guiding lithium ions to preferentially intercalate into the outer layer during charging. Therefore, this application effectively improves the energy density of the electrochemical device by controlling the priority of lithium ion intercalation, effectively mitigates lithium plating during fast charging, and enhances the fast charging performance (rate performance), fast charging safety, and cycle life of the electrochemical device.
[0028] The "average delithiation potential" mentioned in this application refers to the constant current discharge (lithium insertion) at 25°C and a rate of 0.05C down to 0.005 V (vs. Li). + / Li), after standing, recharge (delithiate) to 1.5 V (vs. Li). + The voltage-capacity curve for the first discharge (lithium intercalation) is recorded ( / Li). The average operating potential is defined as the ratio of reversible energy during charging to reversible capacity during charging.
[0029] The method for testing the mass percentage of silicon described in this application is as follows: 1. Layered Sampling: The finished negative electrode sheet is placed in a low-temperature environment (-50℃ to -30℃) for freeze-embrittlement treatment for 10-30 minutes to reduce the bonding force between the layers. Then, using a scalpel or a special delamination tool, the nth negative electrode active material layer (outermost layer) is carefully peeled off from the electrode sheet surface in a direction parallel to the current collector to obtain the outer layer sample. The remaining part is the composite layer from the 1st to the (n-1)th layers.
[0030] 2. Further separation (if it is necessary to determine the individual components of layer n-1): The remaining composite layers are subjected to freeze-embrittlement again. Layer n-1 is then peeled off sequentially following the method in step 1 until individual samples of each layer are obtained. To ensure testing accuracy, the sample size for each layer should be no less than 50 mg.
[0031] 3. Silicon content test: The obtained samples from each layer were processed as follows: 1) The sample was fully calcined at 800℃ to constant weight to remove carbon materials and organic binders, and ash (mainly SiO2) was obtained.
[0032] 2) The ash is digested with a mixture of hydrofluoric acid and nitric acid to convert it into a soluble silicate solution.
[0033] 3) The concentration of silicon in the solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the total silicon content in the sample was calculated based on the standard curve.
[0034] The percentage of silicon by mass is calculated using the following formula: Xn (%) = (mass of silicon element / total mass of sample) × 100%.
[0035] 4) Verification method: As an alternative or verification method, energy dispersive X-ray spectroscopy (EDS) combined with scanning electron microscopy (SEM) can be used to perform line or surface scanning analysis on the cross-section of the electrode. By observing the distribution changes of the characteristic X-ray intensity of silicon, it can be qualitatively confirmed whether the silicon content gradient of each layer conforms to the relationship Xn>Xn-1.
[0036] In some implementations, the V n Satisfies: 0.2V ≤ V n ≤0.6V, for example, it can be 0.2V, 0.25V, 0.3V, 0.35V, 0.4V, 0.45V, 0.5V, 0.55V, 0.6V or any two of these values.
[0037] In some implementations, the V n-1 Satisfies: 0.1V ≤ V n-1 ≤0.5V, for example, it can be a range of 0.1V, 0.2V, 0.3V, 0.4V, 0.5V or any two of these values.
[0038] In some implementations, the following condition is satisfied: 0.1V ≤ V n -V n-1 ≤0.35V, for example, can be a range of 0.1V, 0.15V, 0.2V, 0.25V, 0.3V, 0.35V, or any two of these values, especially by controlling V. n -V n-1Within this range, it is possible to further improve lithium plating during fast charging, thereby enhancing the fast charging performance (rate performance), fast charging safety, and cycle life of electrochemical devices.
[0039] In some implementations, the following condition is satisfied: 0.1V ≤ V n -V n-1 ≤0.15V. By controlling V n -V n-1 Within this range, it can effectively guide the flow of lithium ions while avoiding excessive loss of operating voltage and energy density of the all-electrochemical device due to excessively high outer layer potential, thus achieving the goal of balancing capacity, rate performance and cycle stability.
[0040] In some embodiments, the thickness ratio of the nth negative electrode active material layer to the (n-1)th negative electrode active material layer is (20~50):(50~80), for example, it can be 20:80, 30:70, 40:60, 50:50, or any two of these values. By controlling the thickness ratio of the nth negative electrode active material layer to the (n-1)th negative electrode active material layer, it is possible to ensure that the outer layer effectively performs the "preferential lithium intercalation" function while maintaining the overall structural stability and cycle life of the electrochemical device.
[0041] In some embodiments, the thickness of the nth negative electrode active material layer is 50~100μm, for example, it can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm or any two of these values.
[0042] In some embodiments, the thickness of the (n-1)th negative electrode active material layer is 10~50μm, for example, it can be 10μm, 20μm, 30μm, 40μm, 50μm or any two of these values.
[0043] In some implementations, the X n-1 Satisfy: 0%≤X n-1 ≤6%, for example, can be 1%, 2%, 3%, 4%, 5%, 6% or any two of these values.
[0044] In some implementations, the X n Satisfy: 7.5% < X n ≤45%, for example, can be 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or any two of these values.
[0045] In some embodiments, the mass ratio of graphite to silicon carbide in the nth negative electrode active material is (10~85):(15~90), for example, it can be 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 85:15 or any two of these values.
[0046] In some embodiments, the mass ratio of graphite to silicon-carbon material in the (n-1)th negative electrode active material is (85~100):(0~15), for example, it can be 85:15, 86:14, 88:12, 90:10, 92:8, 94:6, 95:5, 96:4, 98:2, 99:1, 100:0 or any two of these values.
[0047] In some embodiments, the Dv90 particle size of graphite in the nth negative electrode active material is a, and the Dv90 particle size of graphite in the (n-1)th negative electrode active material is b, wherein a and b satisfy: a < b.
[0048] Dv90 particle size testing method: 1. Sample preparation: Separate each layer of active material from the negative electrode sheet (separation method is the same as the "layer sampling" step above), and gently grind and disperse them in an agate mortar to avoid damaging the original morphology of the particles. Take an appropriate amount of powder sample for later use.
[0049] 2. Test conditions: 1) Reference standard (Measurement criteria): GB-T 19077-2016; 2) Testing device: Laser particle size analyzer (LPS); 3) Instrument model: Malvern, Master Size 3000; 4) Sample weight: ~0.06 g; 5) Dispersant: Deionized water (DIW) & 1% hand sanitizer aqueous solution; 6) Pump speed: 3000 r / min; Shading degree: 8%-14%.
[0050] 3. Data Processing: Analysis is performed using the instrument's software, outputting a particle size distribution curve based on volume distribution. Dv90 is defined as the particle size value corresponding to 90% of the cumulative volume distribution, meaning that 90% of the particles have a volume smaller than this particle size value. Each sample is tested at least three times, and the average value is taken as the final result.
[0051] In some implementations, b satisfies: b ≥ 15 μm, for example, it can be 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm.
[0052] In some embodiments, the sphericity of the silicon-carbon material in the nth negative electrode active material is φ(n), and the sphericity of the silicon-carbon material in the (n-1)th negative electrode active material is φ(n-1), wherein φ(n) and φ(n-1) satisfy: φ(n)≥φ(n-1).
[0053] The sphericity φ of silicon-based materials was determined by static image analysis, and the specific steps are as follows: (1) Sample preparation and image acquisition: After the sample is dispersed, clear images of multiple fields of view are randomly acquired by scanning electron microscope (SEM); (2) Image analysis: Import the SEM image into ImageJ software, randomly select no less than 200 independent particles, and measure their projected area A and projected perimeter P; (3) Calculation: According to the formula φ=4πA / P 2 Calculate the sphericity of each particle, and take the arithmetic mean of all measurements as the sphericity φ of the batch of materials.
[0054] In some implementations, φ(n) satisfies: φ(n) ≥ 0.7, for example, it can be 0.7, 0.75, 0.8, 0.9, or 0.95.
[0055] In some embodiments, the negative electrode active material layer further includes a negative electrode binder, a negative electrode conductive agent, and a thickener.
[0056] In some embodiments, the negative electrode binder includes at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. This application is not limited to the above materials and also includes other materials that can be used as battery negative electrode binders.
[0057] In some embodiments, the negative electrode conductive agent includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon. This application is not limited to the above materials, but also includes other materials that can be used as negative electrode conductive agents in batteries.
[0058] In some embodiments, the thickener includes at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, polyacrylic acid, sodium polyacrylate, sodium alginate, guar gum, xanthan gum, carrageenan, gellan gum, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, and acrylic copolymers.
[0059] In this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector, etc.
[0060] II. Electrochemical Device This application provides an electrochemical device comprising the aforementioned negative electrode. In some embodiments, the electrochemical device further includes a positive electrode, a membrane, and an electrolyte, wherein the membrane is located between the positive and negative electrodes.
[0061] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.
[0062] positive electrode The electrochemical device of this application includes a positive electrode, wherein the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.
[0063] In some implementations, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.
[0064] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.
[0065] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.
[0066] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.
[0067] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4 and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2.
[0068] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.
[0069] In some embodiments, the positive electrode active material has the general formula Li 1+x Ni a Mn b Co c Al (1-a-b-c)O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.
[0070] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof.
[0071] In some embodiments, the positive electrode active material includes LiNi. 0.33 Mn 0.33 Co 0.33 O2(NMC333), LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2(NMC532), LiNi 0.6 Mn 0.2 Co 0.2 O2(NMC622), LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2(NMC811), LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2 (NCA) and LiNiO2 (LNO).
[0072] In some embodiments, the positive electrode binder includes binder materials comprising at least one of the following: polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. This application is not limited to the above materials and also includes other materials that can be used as battery positive electrode binders.
[0073] In some embodiments, the positive electrode conductive agent includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon. This application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.
[0074] diaphragm The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.
[0075] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.
[0076] electrolytes The electrochemical device of this application also includes an electrolyte.
[0077] In some embodiments, the electrolyte includes at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.
[0078] In some embodiments, the liquid electrolyte includes a non-aqueous solvent and a lithium salt.
[0079] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.
[0080] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.
[0081] In some embodiments, the carbonate compound includes at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.
[0082] In some embodiments, the chain carbonate compound includes diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorinated carbonate compounds are at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.
[0083] In some embodiments, examples of carboxylic acid ester compounds are at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.
[0084] In some embodiments, examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
[0085] In some embodiments, the non-aqueous solvent also includes at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.
[0086] III. Electronic Devices This application also provides an electronic device, including the electrochemical device described in this application.
[0087] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.
[0088] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.
[0089] Example 1 The method for preparing a lithium-ion battery includes the following steps: 1. Preparation of negative electrode sheet: Preparation of the first negative electrode active slurry: The first negative electrode active material includes 95 wt% artificial graphite (average delithiation potential 0.14 V vs. Li). + Li) and 5 wt% silicon-carbon material (average delithiation potential 0.19V vs. Li) + / Li). The silicon content X1 in the silicon-carbon material is 2.5wt%. The first negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are mixed in deionized water at a mass ratio of 96.5:1.0:1.5:1.0 and stirred at high speed to prepare a uniformly mixed first negative electrode active slurry.
[0090] Preparation of the second negative electrode active slurry: The second negative electrode active material includes 50 wt% artificial graphite (average delithiation potential 0.14 V vs. Li). + Li) and 50 wt% silicon-carbon material (average delithiation potential 0.39 V vs. Li) + / Li). The silicon content X2 in the silicon-carbon material is 25wt%. The second negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) are mixed in deionized water at a mass ratio of 91.0:1.0:7.0:1.0 and stirred at high speed to prepare a uniformly mixed second negative electrode active slurry.
[0091] Negative electrode preparation: The first negative electrode active slurry is coated on the negative electrode current collector copper foil with a thickness of 8μm. After drying, a first negative electrode active material layer with a thickness of 42μm is formed. Then, the second negative electrode active slurry is coated on the first negative electrode active material layer. After drying, a second negative electrode active material layer with a thickness of 18μm is formed. After drying, cold pressing and slitting, the negative electrode is obtained.
[0092] The areal density of the first negative electrode active material layer is 63 mg / 1540.25 mm. 2 The areal density of the second negative electrode active material layer is 27 mg / 1540.25 mm². 2 The thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer is 30:70. The delithiation potential difference between the first negative electrode active material layer and the second negative electrode active material layer is 0.20V.
[0093] 2. Preparation of the positive electrode sheet The active material LiCoO2, conductive agent acetylene black, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were fully dispersed and uniformly dispersed in an N-methylpyrrolidone solvent system at a weight ratio of 98.2:0.3:0.5:1.0. The mixture was then coated onto an aluminum current collector and cold-pressed into slits to obtain the positive electrode sheet.
[0094] 3. Preparation of the diaphragm The surface is coated with a ceramic mixture, and a 7μm thick PE membrane is used as the separator.
[0095] 4. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a volume ratio of 1:1:4:4 to obtain a mixed organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.
[0096] 5. Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation, and then wound to form the electrode assembly. The electrode assembly is placed in a packaging shell, injected with electrolyte, and sealed. After standing, hot and cold pressing, formation, and capacity testing, a lithium-ion battery is obtained.
[0097] The parameters of the negative electrode are shown in Table 1.
[0098] Examples 2-5 The difference between Examples 2-5 and Example 1 is that the contents of graphite, silicon carbide, and X1 in the first negative electrode active material are changed.
[0099] Examples 6-9 The difference between Examples 6-9 and Example 1 is that the contents of graphite, silicon carbide, and X2 in the second negative electrode active material are changed.
[0100] Examples 10-13 The difference between Examples 10-13 and Example 1 is that the thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer is changed.
[0101] Examples 14-17 Examples 14-17 differ from Example 1 in that the difference in average delithiation potential between the second negative electrode active material layer and the first negative electrode active material layer is changed, i.e., V n -V n-1 .
[0102] Example 18 Example 18 differs from Example 1 in that the Dv90 particle sizes a and b of graphite in the first and second negative electrode active materials are changed, with a < b.
[0103] Example 19 Example 19 differs from Example 1 in that the Dv90 particle sizes a and b of graphite in the first and second negative electrode active materials are changed, with a > b.
[0104] Example 20 Example 20 differs from Example 1 in that the sphericity φ1 and φ2 of the silicon-carbon material in the first and second negative electrode active materials are changed, with φ1 < φ2.
[0105] Example 21 Example 21 differs from Example 1 in that the sphericity φ1 and φ2 of the silicon-carbon material in the first and second negative electrode active materials are changed, with φ2 < φ1.
[0106] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that X2 < X1.
[0107] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that V2-V1=0.
[0108] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that V2-V1=0.07V.
[0109] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that n=1.
[0110] Table 1 Test methods The lithium-ion batteries prepared in the above examples and comparative examples were subjected to the following performance tests, and the results are recorded in the table below.
[0111] 1. Lithium plating test: At 25℃, charge at a constant current rate of 3C and 3.5C to the cutoff voltage of 4.53V, and discharge at a constant current rate of 0.7C to the cutoff voltage of 3V. Cycle for 50cls. After completion, disassemble the lithium-ion battery and observe whether there is metallic lithium plating on the surface of the negative electrode.
[0112] Table 2. Evaluation Description of Lithium Plating Area Percentage by Grade
[0113] 2. Cycle Life: At 25℃, the lithium-ion battery was charged and discharged according to the following method: Charged at a 2.5C rate to 4.10V, then charged at a 2.5C rate to 4.20V, then at a 1.5C rate to 4.30V, then at a 1.0C rate to 4.53V, and finally discharged at a 0.7C rate to 3.0V, for a total of 500 cycles. Cycle capacity retention = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.
[0114] The test results are shown in Table 3.
[0115] Table 3 As shown in Table 3, this application constructs a bilayer anode structure with a high outer layer delithiation potential based on a silicon content gradient (X2>X1). By introducing a delithiation potential difference of not less than 0.1V and controlling the outer layer thickness ratio within the range of 20%-50%, lithium ions are actively guided to preferentially embed in the outer layer during fast charging, thereby fundamentally solving the lithium plating problem of high silicon anodes and synergistically achieving a significant improvement in battery energy density, fast charging performance, and cycle life.
[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.
Claims
1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and n negative electrode active material layers arranged sequentially on at least one surface of the negative electrode current collector, where n≥2, and the layer furthest from the negative electrode current collector is the nth negative electrode active material layer. The nth negative electrode active material layer includes an nth negative electrode active material, which comprises graphite and an nth silicon-carbon material, wherein the mass percentage of silicon in the nth silicon-carbon material is X. n The average delithiation potential of the nth negative electrode active material is V. n ; The (n-1)th negative electrode active material layer includes an (n-1)th negative electrode active material, which comprises graphite and an (n-1)th silicon-carbon material, wherein the mass percentage of silicon in the (n-1)th silicon-carbon material is X. n-1 The average delithiation potential of the (n-1)th negative electrode active material is V. n-1 ; The X n X n-1 Satisfy: X n >X n-1 ; The V n V n-1 Satisfy: V n -V n-1 ≥0.1V.
2. The negative electrode sheet according to claim 1, characterized in that, The X n-1 X n Satisfy: 0≤X n-1 ≤6%, 7.5% < X n ≤45%.
3. The negative electrode sheet according to claim 1, characterized in that, The V n V n-1 Satisfies: 0.2V ≤ V n ≤0.6V, 0.1V≤V n-1 ≤0.5V.
4. The negative electrode sheet according to claim 3, characterized in that, The V n V n-1 Satisfies: 0.1V ≤ V n -V n-1 ≤0.35V.
5. The negative electrode sheet according to claim 1, characterized in that, The thickness ratio of the nth negative electrode active material layer to the (n-1)th negative electrode active material layer is (20~50):(50~80).
6. The negative electrode sheet according to claim 1, characterized in that, The mass ratio of graphite to silicon-carbon material in the nth negative electrode active material is (10~85):(15~90). And / or, the mass ratio of graphite to silicon carbide in the (n-1)th negative electrode active material is (85~100):(0~15).
7. The negative electrode sheet according to claim 1, characterized in that, The Dv90 particle size of graphite in the nth negative electrode active material is a, and the Dv90 particle size of graphite in the (n-1)th negative electrode active material is b, wherein a and b satisfy: a < b.
8. The negative electrode sheet according to claim 1, characterized in that, The sphericity of the silicon-carbon material in the nth negative electrode active material is φ(n), and the sphericity of the silicon-carbon material in the (n-1)th negative electrode active material is φ(n-1). The φ(n) and φ(n-1) satisfy: φ(n)≥φ(n-1).
9. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-8.
10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.