Electrode plate, preparation method thereof and electrochemical device

Abstract

The invention discloses an electrode plate, a preparation method thereof and an electrochemical device. The preparation method of the electrode plate comprises the following steps: mixing an electrode active material, a solvent and a dispersing agent to obtain a first mixture; a first monomer, an initiator and a conductive agent are added into the first mixture, a second mixture is obtained, the first monomer is used for polymerization to form a high polymer material, and the first monomer contains a polar group; stirring and heating the second mixture, so that the first monomer is subjected to in-situ polymerization on the surface of the electrode active material to form a polymer material layer containing a polar group, and the conductive agent is dispersed in the polymer material layer to obtain an electrode material; mixing an electrode material and a binder to obtain electrode slurry; and coating a current collector with the electrode slurry, and carrying out drying and rolling to obtain the electrode plate. According to the preparation method provided by the invention, the conductivity of the electrode plate can be improved, and the dissolution of transition metal ions in the electrode plate is inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, in particular to an electrode tab, a preparation method thereof and an electrochemical device. BACKGROUND

[0002] Lithium ion batteries have become one of the most promising energy storage media due to their high energy density, high working voltage, long cycle life, environmental friendliness and other advantages.

[0003] However, in the lithium ion battery system, there is a common problem of insufficient conductivity, which will cause electron transmission to be blocked and energy efficiency and rate performance to be reduced. At the same time, at high voltage, side reactions will occur between the electrolyte and the surface of the positive electrode material, and the dissolution of transition metal ions in the positive electrode material will increase, and the dissolved transition metal ions will migrate and deposit on the negative electrode surface during charging, catalyzing the decomposition and reconstruction of the solid electrolyte interface film (SEI) of the negative electrode, resulting in loss of active lithium, capacity decay and deterioration of high-temperature cycle performance. SUMMARY

[0004] In view of this, in order to solve at least one of the above technical problems, the embodiments of the present application provide a preparation method of a new type of electrode tab.

[0005] In addition, the embodiments of the present application also provide an electrode tab prepared by the above-mentioned preparation method of an electrode tab and an electrochemical device using the electrode tab.

[0006] The embodiments of the present application provide a preparation method of an electrode tab, which comprises the following steps: mixing an electrode active material, a solvent and a dispersing agent to obtain a first mixture; adding a first monomer, an initiator and a conductive agent to the first mixture to obtain a second mixture, wherein the first monomer is used to polymerize to form a high molecular material, and the first monomer contains a polar group; stirring and heating the second mixture to make the first monomer in-situ polymerize on the surface of the electrode active material to form a high molecular material layer containing a polar group, and the conductive agent is dispersed in the high molecular material layer to obtain an electrode material; mixing the electrode material and a binder to obtain an electrode slurry; and coating the electrode slurry on a current collector and performing drying and rolling to obtain the electrode tab.

[0007] In some possible embodiments, in the second mixture, the mass ratio of the electrode active material, the first monomer and the conductive agent is (80-95):(2.5-17.5):(0.5-4); the thickness of the high molecular material layer is 0.2 μm-3.0 μm; and the median particle size D50 of the particles of the electrode active material is 0.5 μm-8.0 μm.

[0008] In some possible embodiments, the conductive agent includes at least one of conductive carbon black and carbon nanotubes.

[0009] In some possible embodiments, the first monomer includes at least one of acrylonitrile, methacrylonitrile, cyanoacrylate, and m-cyanostyrene.

[0010] In some possible embodiments, the second mixture further includes a second monomer, which is a nonpolar monomer.

[0011] In some possible embodiments, the second monomer includes at least one of butadiene and halobutadiene; and / or in the second mixture, the mass ratio of the first monomer to the second monomer is 1:(0.1~1).

[0012] In some possible embodiments, the conductive agent, the first monomer, and the initiator are added sequentially in the order of preparing the second mixture.

[0013] In some possible embodiments, the step of stirring and heating the second mixture includes: stirring the second mixture and heating it until the viscosity of the second mixture is 2000 cp to 8000 cp, wherein the heating temperature is 55°C to 80°C and the heating rate is 5°C / min to 20°C / min; and cooling the heated second mixture to room temperature, precipitating, removing part of the upper layer solution, and the remaining part being the electrode material, wherein the viscosity of the electrode material is 5000 cp to 15000 cp and the solid content of the electrode material is 40% to 60%.

[0014] This application embodiment also provides an electrode sheet, which is prepared by the aforementioned electrode sheet preparation method. The electrode sheet includes an electrode material, which includes an electrode active substance and a polymer material layer containing polar groups located on the surface of the electrode active substance. A conductive agent is dispersed in the polymer material layer.

[0015] Additionally, this application also provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode are electrode plates as described above.

[0016] Compared to existing technologies, the electrode sheet and its preparation method provided in this application mix the electrode active material with a monomer containing polar groups and a conductive agent. After heating, the monomer containing polar groups polymerizes in situ on the surface of the electrode active material to form a polymer material layer containing polar groups. At the same time, the conductive agent is uniformly dispersed in the polymer material layer, thereby constructing a continuous three-dimensional conductive network on the surface of the active material. This is beneficial to improving the conductivity of the electrode sheet and inhibiting the dissolution or complexation of transition metal ions, thereby effectively improving the capacity, rate performance and high-temperature cycling performance of the electrochemical device. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the method for preparing an electrode sheet according to an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of an electrode material provided in an embodiment of this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; where there is no conflict, the embodiments and features of the embodiments of this application may be combined with each other; many specific details are set forth in the following description in order to provide a full understanding of this application, and the described embodiments are only a part of the embodiments of this application, and not all of them.

[0021] Please see Figure 1 As shown in the figure, this application provides a method for preparing an electrode sheet, which specifically includes the following steps: Step S1: Mix the electrode active material, solvent and dispersant to obtain a first mixture.

[0022] Specifically, at room temperature, the electrode active material and dispersant are first added to the solvent and stirred until homogeneous to obtain the first mixture.

[0023] Step S2: Add a first monomer, an initiator, and a conductive agent to the first mixture to obtain a second mixture, wherein the first monomer is used to polymerize and form a polymer material, and the first monomer contains polar groups.

[0024] Specifically, at room temperature, a first monomer, an initiator, and a conductive agent are added to a first mixture, and the mixture is mixed again to obtain a second mixture, wherein the first monomer is used to polymerize and form a polymer material, and the first monomer contains polar groups.

[0025] In some embodiments, the mass ratio of the electrode active material, the first monomer, and the conductive agent in the second mixture can be (80~95):(2.5~17.5):(0.5~4), which is beneficial for providing good electrochemical activity and conductivity to the electrode sheet.

[0026] In some embodiments, the mass ratio of electrode active material to dispersant in the second mixture can be (80~95):(0.1~0.4), which is beneficial to the full dispersion of electrode active material and reduces agglomeration.

[0027] In some embodiments, the mass ratio of the first monomer to the initiator in the second mixture can be (2.5~17.5):(0.1~0.4), which is beneficial for fully initiating the polymerization of the first monomer. In some embodiments, the solid content of the second mixture can be 10%~40%. By controlling the solid content of the second mixture within the above range, it is beneficial to balance the viscosity of the second mixture and the production efficiency, and to facilitate subsequent stirring and heating treatment of the second mixture.

[0028] In some embodiments, the first monomer, initiator, and conductive agent may be added in the order of conductive agent, first monomer, and initiator. Adding the conductive agent first promotes its uniform dispersion; adding the first monomer then ensures it is fully and uniformly dispersed on the surface of the electrode active material and mixes evenly with the conductive agent; adding the initiator last reduces premature polymerization of the monomer, thus improving the uniformity of subsequent polymerization reactions.

[0029] The first monomer can form a polymer material through free radical polymerization. Understandably, a monomer that can form a polymer material through free radical polymerization and contains a polar group can be used as the first monomer. For example, the first monomer can be a monomer containing a polar cyano group (-C≡N).

[0030] Specifically, the first monomer may include at least one of acrylonitrile (AN), methacrylonitrile, cyanoacrylate, and m-cyanostyrene. The first monomer has a polar cyano group (-C≡N) and undergoes polymerization under the action of an initiator and certain reaction conditions to form a polymer material containing polar groups. The cyano group is not easily hydrolyzed in the electrolyte environment and has good chemical stability. In addition, the first monomer also has a rigid molecular chain, which helps to enhance the density and mechanical strength of the polymer material formed by polymerization.

[0031] The second mixture may also include a second monomer, which is a nonpolar monomer, typically possessing flexible chain segments. The nonpolar monomer can copolymerize with monomers containing polar groups to form a polymer material, providing flexible polymer chain segments to the polymer material, thus giving the polymer material both polarity and flexibility, and improving the interfacial compatibility between the polymer material and the electrode active material. For example, the nonpolar monomer may include at least one of butadiene (BD) and halobutadiene, wherein halobutadiene may include at least one of fluorobutadiene, chlorobutadiene, bromobutadiene, and iodobutadiene. It is understood that the nonpolar monomer includes, but is not limited to, butadiene and halobutadiene; any nonpolar monomer capable of copolymerizing with monomers containing polar groups to form a polymer material and providing flexible polymer chain segments to the polymer material is acceptable.

[0032] In the second mixture, the mass ratio of the first monomer to the second monomer can be 1:(0.1~1), which can further improve the polarity, mechanical properties, and flexibility of the polymer material. This mass ratio can, for example, be any value within the range of 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, or any two of the above values. The mass ratio can further be 1:(0.4~1).

[0033] The initiator may include at least one of benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), and methyl ethyl ketone peroxide (MEKP), and the above initiators may be used in the free radical polymerization reaction of the first monomer and the second monomer.

[0034] The added conductive agent will be uniformly dispersed in the formed polymer material layer during the subsequent monomer polymerization reaction, forming a three-dimensional conductive network and improving the conductivity of the positive electrode. Such conductive agents can include at least one of conductive carbon black (SP) and carbon nanotubes (CNTs), which can enhance the conductivity of the electrode. CNTs can also adsorb transition metal ions dissolved from the positive electrode side.

[0035] Electrode active materials can include positive electrode active materials or negative electrode active materials. Positive electrode active materials can include, but are not limited to, at least one of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), nickel-cobalt-manganese ternary cathode materials (NCM), and nickel-cobalt-aluminum ternary cathode materials (NCA). Negative electrode active materials can include, but are not limited to, at least one of graphite, silicon, silicon oxide, silicon-carbon composite materials, and metallic lithium.

[0036] Solvents may include N-methylpyrrolidone (NMP), which can dissolve dispersants, monomers and other materials, adjust the solid content and viscosity of the second mixture, and facilitate subsequent stirring and heating of the second mixture.

[0037] The dispersant may include polyvinylpyrrolidone (PVP). The polar groups of PVP adsorb onto the surface of the electrode active material and the conductive agent, forming steric hindrance, preventing agglomeration, and making the material uniformly dispersed, thereby improving the uniformity of the second mixture.

[0038] Step S3: The second mixture is stirred and heated to allow the first monomer to polymerize in situ on the surface of the electrode active material to form a polymer material layer containing polar groups. The conductive agent is dispersed in the polymer material layer to obtain the electrode material.

[0039] Specifically, the second mixture is stirred and heated. Under heating conditions, the monomers polymerize in situ under the action of an initiator to form a polymer material layer, while a conductive agent is dispersed within the polymer material layer. The polymer material layer and the conductive agent dispersed within it essentially form a composite coating layer on the surface of the electrode active material, thereby modifying the surface of the electrode active material. This in-situ polymerization to form the polymer material layer improves the uniformity and controllability of the polymer material layer thickness, and simultaneously achieves surface polarity modification of the electrode active material and precise construction of a three-dimensional conductive network.

[0040] like Figure 2 The diagram illustrates one embodiment of an electrode material 100 formed using the method described in this application. The electrode material 100 includes an electrode active material 10 and a composite coating layer 20 located on the surface of the electrode active material 10. The composite coating layer 20 includes a polymer material 21 containing polar groups and a conductive agent 22. The polymer material 21 has polar groups, enabling surface polar modification of the electrode active material 10. The conductive agent 22 is uniformly dispersed in the polymer material 21, forming a through-hole electron transport channel, i.e., a three-dimensional conductive network. The conductive agent 22 may include short-chain CNTs and particulate SPs. It is understood that... Figure 2 Only one structural schematic diagram of electrode material 100 is given. In actual applications, the morphology of electrode material 100 is not limited to this.

[0041] First, the polymer material layer contains polar groups, which can interact with transition metal ions (such as Ni) through the lone pair electrons of the polar groups. 2+ Co 2+ Mn 2+(e.g., forming coordination bonds) to adsorb transition metal ions dissolved from the positive electrode side. Secondly, the polymer material layer is polymerized from monomers containing polar groups, exhibiting good density and acting as a physical barrier. When the polymer material layer contains the aforementioned non-polar monomers, it possesses a certain degree of toughness, which can alleviate the volume change stress of the electrode active material during charging and discharging, reducing the risk of secondary dissolution of transition metal ions due to polymer material layer breakage. The synergistic effect of monomers containing polar groups and non-polar monomers balances the polarity, mechanical strength, and flexibility of the polymer material layer. In addition, the conductive agent simultaneously forms a conductive network in the polymer material layer, thereby improving the charge transport efficiency of the electrode plate.

[0042] The specific mechanisms by which the polymer material layer inhibits the dissolution of transition metal ions include: when the electrode active material is the positive electrode active material, the polar groups in the polymer material layer directly adsorb and anchor the dissolved transition metal ions in the positive electrode active material through chemisorption, inhibiting the migration of transition metal ions to the electrolyte and their subsequent deposition on the negative electrode surface; the polymer material layer can also reduce the direct contact between the electrolyte and the positive electrode active material and the resulting side reactions through physical isolation, thereby reducing the dissolution of transition metal ions in the positive electrode active material. The reduction in the dissolution of transition metal ions in the positive electrode active material helps to reduce the structural collapse of the positive electrode active material, reduce the catalytic decomposition of the electrolyte by transition metal ions, and reduce the increase in the positive electrode interface impedance caused by the dissolution of transition metal ions, thereby improving the volume retention rate of the positive electrode, delaying capacity decay, and improving rate performance.

[0043] When the electrode active material is the negative electrode active material, the polar groups in the polymer material layer can chemically adsorb and complex transition metal ions that migrate with the electrolyte to the negative electrode side, preventing direct contact between the transition metal ions and the negative electrode active material and reducing direct deposition of transition metals on the surface of the negative electrode active material. Transition metal ions catalyze the decomposition and reconstruction of the solid electrolyte interphase (SEI) film at the negative electrode, leading to the loss of active lithium, capacity decay, and deterioration of high-temperature cycling performance. Forming this polymer material layer on the surface of the negative electrode active material can improve the capacity of the negative electrode and enhance its high-temperature cycling performance.

[0044] In some embodiments, the thickness of the polymer material layer can be 0.2 μm to 3 μm. The thickness of the polymer material layer can be precisely controlled by adjusting the monomer addition ratio through the in-situ polymerization reaction. Within the above thickness range, the polymer material layer effectively provides physical isolation and sufficient chemical adsorption, without affecting the energy density of the electrode material. The thickness of the polymer material layer can, exemplarily, be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 1.2 μm, 3 μm, or any value within the range of any two of these values. The thickness of the polymer material layer can further be 0.2 μm to 1.2 μm. It is understood that the thickness of the composite coating layer is the same as the thickness of the polymer material layer.

[0045] In some embodiments, the median particle size D50 of the electrode active material can be 0.5 μm to 8 μm, and exemplaryly can be any value within the range of 0.5 μm, 0.8 μm, 1.0 μm, 1.5 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, or any two of the above values. The median particle size D50 of the electrode active material can further be 0.5 μm to 6 μm.

[0046] Furthermore, step S3 may specifically include: Step S31: The second mixture is stirred and heated until its viscosity reaches 2000 cp to 8000 cp. While stirring and heating the second mixture, the monomers undergo a polymerization reaction to form a polymer layer. The viscosity of the second mixture gradually increases until it reaches 2000 cp to 8000 cp, at which point heating is stopped, and the polymerization reaction ends. This facilitates further control over the thickness of the polymer layer. The viscosity of the second mixture can, for example, be any value within the range of 2000 cp, 3000 cp, 3500 cp, 4500 cp, 5000 cp, 6000 cp, 7000 cp, 8000 cp, or any two of these values. The viscosity of the second mixture can further be between 2000 cp and 6000 cp.

[0047] In some embodiments, the heating temperature can be 55°C to 80°C. Within this temperature range, the polymerization reaction is facilitated to proceed uniformly and rapidly, resulting in polymer materials with uniform and high molecular weights. This further improves the uniformity and density of the polymer material layer, while also increasing production efficiency and reducing energy consumption. The heating temperature can, exemplarily, be any value within the range of 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any two of these values. The heating temperature can further be 60°C to 75°C.

[0048] In some embodiments, the heating rate can be 5°C / min to 20°C / min. Within this heating range, it is beneficial for uniform temperature increase, better control of the stable reaction, generation of polymer materials with uniform and high molecular weight, and further improvement of the controllability of polymer material layer thickness. It also facilitates rapid initiation of the polymerization reaction, shortens reaction time, improves production efficiency, and reduces production energy consumption. The heating rate can exemplary be 5°C / min, 7°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, 20°C / min, or any value within the range of any two of the above. The heating rate can further be 5°C / min to 15°C / min.

[0049] Step S22: Cool the heated second mixture to room temperature, precipitate, remove part of the upper solution, and the remaining part is electrode material.

[0050] Specifically, the second mixture after heating and reaction is cooled to room temperature, and after precipitation for 12 to 48 hours, part of the upper solution (about 5% to 30% of the volume of the upper solution) is removed. This can effectively remove low molecular weight polymers, unreacted impurities and residual solvents, resulting in a relatively pure electrode material.

[0051] In some embodiments, the viscosity of the electrode material can be 5000 cp to 15000 cp, and the viscosity of the electrode material obtained after removing the solvent is higher than the viscosity of the heated mixed slurry described above. The viscosity of the electrode material can, exemplarily, be any value within the range of 5000 cp, 6000 cp, 7000 cp, 8000 cp, 10000 cp, 15000 cp, or any two of the above values. The viscosity of the electrode material can further be 6000 cp to 12000 cp.

[0052] In some embodiments, the solid content of the electrode material can be 40% to 60%, and the solid content of the electrode material can be, for example, any value within the range of any two values ​​of 40%, 45%, 50%, 55%, 60% or more, and the solid content of the electrode material can be further 45% to 55%.

[0053] Step S4: Mix the electrode material and binder to obtain the electrode slurry.

[0054] Specifically, the binder solution can be prepared first, and the binder can be added to a solvent and stirred. The solvent can be NMP. The solid content of the binder solution is 5%~9%. After stirring evenly, it is filtered twice through a 200-mesh filter to obtain a uniform binder solution. Then the binder solution is added to the electrode material prepared in step S2 to obtain the electrode slurry.

[0055] In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0056] In some embodiments, the viscosity of the electrode paste can be 3000 cp to 6000 cp. Adding a binder can adjust the viscosity of the electrode paste. A viscosity within this range is beneficial for maintaining appropriate flowability and viscosity during subsequent coating processes, facilitating uniform coating. The viscosity of the electrode paste can, exemplarily, be any value within the range of 3000 cp, 4000 cp, 5000 cp, 6000 cp, or any two of these values. The viscosity of the electrode paste can further be 4000 cp to 6000 cp.

[0057] In some embodiments, the solid content of the electrode paste can be 40% to 60%, which is beneficial for the electrode paste to be well coated onto the current collector and to have sufficient electrode material capacity. The solid content of the electrode paste can, exemplarily, be any value within the range of any two values ​​consisting of 40%, 45%, 50%, 55%, 60%, or more. The solid content of the electrode paste can further be 45% to 60%.

[0058] Step S5: The electrode slurry is coated onto the current collector, and then dried and rolled to obtain the electrode sheet.

[0059] Specifically, the electrode slurry is uniformly coated onto the current collector and then subjected to conventional processes such as drying, rolling, and cutting to obtain the electrode sheet. The electrode sheet mainly consists of the current collector and an active material layer (formed after the electrode slurry is dried), and the active material layer includes the aforementioned electrode material.

[0060] In some embodiments, the areal density of the coating can be 120 g / m². 2 ~480g / m 2 The areal density of the coating affects the thickness and compaction density of the resulting electrode sheet. Coating areal densities within the aforementioned range can provide higher capacity and energy density. An exemplary areal density of 120 g / m² is possible. 2 180g / m 2 220g / m 2 300g / m 2 400g / m 2 480g / m 2 Or any value within the range of any two of the above values. The areal density of the coating can further be 120 g / m². 2 ~420g / m 2 .

[0061] In some embodiments, the compaction density of the electrode sheet can be 1.5 g / cm³. 3 ~3.5g / cm 3 At the same electrode thickness, a higher compaction density is beneficial for reducing the internal resistance of the positive electrode and increasing its energy density. An exemplary compaction density for an electrode sheet could be 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 3.5g / cm 3 Or any value within the range of any two of the above values. The compaction density of the electrode sheet can further be 1.55 g / cm³. 3 ~3.43g / cm 3 , Compared with the prior art, the electrode preparation method provided in this application has the following advantages: 1. Using polar monomers and conductive agents as coating materials, and then through in-situ polymerization, the monomers are polymerized on the surface of the electrode active material to form a polymer material layer containing polar groups. At the same time, the conductive agent is uniformly dispersed in the polymer material layer, forming a composite coating layer. This simultaneously realizes the precise construction of polar modification of the electrode active material surface and three-dimensional conductive network, and has the following synergistic effects: (1) Improve the conductivity of the electrode sheet. The conductive agent is uniformly dispersed in the polymer material layer, forming a through electron transport channel, which significantly reduces the interfacial contact resistance; (2) Inhibit the dissolution of transition metal ions. The polymer material layer containing polar groups can anchor the transition metal ions on the surface of the electrode active material through coordination. At the same time, the dense polymer material layer can physically block the electrolyte from eroding the electrode active material, thereby effectively inhibiting the dissolution or complexation of the dissolved transition metal ions. The above synergistic effects effectively improve the capacity, rate performance and high-temperature cycling stability of the electrode sheet.

[0062] 2. By adding non-polar monomers to the coating material, the non-polar monomers can copolymerize with monomers containing polar groups to form a polymer material. The synergistic effect balances the polarity, mechanical strength and flexibility of the polymer material layer, which can alleviate the volume change stress of the electrode active material during charging and discharging, and reduce the risk of secondary dissolution of transition metal ions caused by the rupture of the polymer material layer.

[0063] 3. This preparation method is simple and efficient, and achieves interface modification and conductivity enhancement of electrode materials in one step. It has the advantages of high efficiency and scalability, and has excellent commercial prospects.

[0064] This application embodiment also provides an electrode sheet, which is prepared by the aforementioned electrode sheet preparation method. The electrode sheet includes an electrode material, which includes an electrode active substance and a polymer material layer containing polar groups located on the surface of the electrode active substance, and a conductive agent is dispersed in the polymer material layer.

[0065] Compared with existing technologies, this electrode has higher conductivity, capacity, rate performance and high-temperature cycling stability.

[0066] This application also provides an electrochemical device (e.g., a battery) comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive and negative electrodes uses the aforementioned electrode. Electrochemical devices prepared using the aforementioned electrode have advantages such as high conductivity, high capacity, good rate performance, and good high-temperature cycle stability. It is understood that both the positive and negative electrodes can use the aforementioned electrode, and they can be used synergistically to minimize the risk of transition metal ion dissolution, effectively improving the high-temperature storage performance and cycle life of the electrochemical device.

[0067] The following specific examples further illustrate the aforementioned electrode plates, their preparation methods, and electrochemical devices.

[0068] Example 1 Step S1: Mix the electrode active material LMFP, solvent NMP and dispersant PVP to obtain a first mixture.

[0069] Step S2: Add the conductive agent CNT solution, the polar monomer AN and the non-polar monomer BD, and the initiator BPO to the first mixture in sequence, mix evenly to obtain the second mixture. The mass ratio of LMFP:AN:BD:CNT:BPO:PVP in the second mixture is 90:3.9:3.9:2:0.1:0.1. The solid content of the second mixture is 30%, the solid content of the CNT solution is 0.5%, and the median particle size D50 of the electrode active material LMFP particles is 0.8 μm.

[0070] Step S3: Stir the second mixture and heat it to 60°C at a heating rate of 5°C / min to allow the monomers (AN and BD) and conductive agent CNT to polymerize in situ on the surface of the electrode active material LMFP to form a polymer material layer containing polar groups. The conductive agent CNT is dispersed in the polymer material layer. Stop the reaction when the viscosity of the second mixture is 5000cp. Cool to room temperature and precipitate for 24 hours. Remove 20% of the upper solution. The remaining part is the electrode material. The viscosity of the electrode material is about 8000cp and the solid content is about 50%.

[0071] Step S4: Mix the above electrode material and PVDF adhesive to obtain an electrode slurry with a viscosity of 4000 cp and a solid content of approximately 48%. The PVDF adhesive is obtained by adding PVDF to NMP and stirring, with a solid content of 7%. After stirring evenly, the mixture is filtered twice through a 200-mesh filter.

[0072] Step S5: Coat the electrode paste onto the surface of the current collector aluminum foil, with a coating areal density of 400 g / m². 2 The material is then subjected to conventional processes such as drying, rolling, and cutting to obtain a positive electrode sheet. This positive electrode sheet comprises the aforementioned electrode material, and its compaction density is 2.4 g / cm³. 3 .

[0073] The prepared positive electrode, separator, and graphite electrode are stacked to prepare a soft-pack battery.

[0074] Example 2: The difference from Example 1 is that in step S2, the mass ratio of LMFP:AN:BD:CNT:BPO:PVP in the second mixture is 80:7.9:7.9:4:0.1:0.1. The preparation methods of the remaining positive electrode sheets and the soft-pack battery are basically the same as in Example 1.

[0075] Example 3: The difference from Example 1 is that in step S2, the mass ratio of LMFP:AN:BD:CNT:BPO:PVP in the second mixture is 91.5:3.9:3.9:0.5:0.1:0.1. The preparation methods of the remaining positive electrode sheets and the soft-pack battery are basically the same as in Example 1.

[0076] Example 4: The difference from Example 1 is that in step S2, the mass ratio of LMFP:AN:BD:CNT:BPO:PVP in the second mixture is 90:5.2:2.6:2:0.1:0.1, and the electrode active material LMFP is secondary particles with a median particle size D50 of 3 μm. The preparation methods of the remaining positive electrode sheets and the soft-pack battery are basically the same as in Example 1.

[0077] Example 5: The difference from Example 1 is that in step S2, the mass ratio of LMFP:AN:BD:CNT:BPO:PVP in the second mixture is 90:7:0.8:2:0.1:0.1. The preparation methods of the remaining positive electrode sheets and the soft-pack battery are basically the same as in Example 1.

[0078] Example 6: The difference from Example 1 is that in step S2, the nonpolar monomer BD is not added; the mass ratio of LMFP:AN:CNT:BPO:PVP in the second mixture is 80:17.5:2:0.4:0.1; the electrode active material LMFP is secondary particles with a median particle size D50 of 3 μm. The preparation methods of the remaining positive electrode sheet and the soft-pack battery are basically the same as in Example 1.

[0079] Example 7: The difference from Example 1 is that in step S2, the nonpolar monomer BD is not added; the mass ratio of LMFP:AN:CNT:BPO:PVP in the second mixture is 95:2.5:2:0.1:0.4; the electrode active material LMFP is secondary particles with a median particle size D50 of 3 μm. The preparation methods of the remaining positive electrode sheet and the soft-pack battery are basically the same as in Example 1.

[0080] Example 8: The difference from Example 1 is that in step S2, the non-polar monomer BD is not added, and the mass ratio of LMFP:AN:CNT:BPO:PVP in the second mixture is 90:7.8:2:0.1:0.1. The preparation methods of the remaining positive electrode sheets and the soft-pack battery are basically the same as in Example 1, and will not be described in detail here.

[0081] Example 9: The difference from Example 1 is that in step S2, the nonpolar monomer BD is not added, and the mass ratio of LMFP:AN:CNT:BPO:PVP in the second mixture is 96:1.8:2:0.1:0.1. The electrode active material LMFP is a secondary particle with a median particle size D50 of 3 μm. The preparation methods of the remaining positive electrode sheet and the soft-pack battery are basically the same as in Example 1, and will not be described in detail here.

[0082] Example 10: The difference from Example 1 is that in step S2, the nonpolar monomer BD is not added, and the mass ratio of LMFP:AN:CNT:BPO:PVP in the second mixture is 77.5:20:2:0.4:0.1. The electrode active material LMFP is secondary particles with a median particle size D50 of 3 μm. The preparation methods of the remaining positive electrode sheet and the soft-pack battery are basically the same as in Example 1, and will not be described in detail here.

[0083] Comparative Example 1 Step S1: Mix the electrode active material LMFP and PVDF adhesive in a mass ratio of 95.9:2.0:2.0:0.1 to obtain the electrode slurry. The PVDF adhesive is obtained by adding PVDF to NMP and stirring. The solid content is 7%. After stirring evenly, the mixture is filtered twice through a 200-mesh filter. The viscosity of the electrode slurry is 4000 cp and the solid content is about 48%.

[0084] Step S4: Coat the electrode paste onto the surface of the current collector aluminum foil, with a coating areal density of 400 g / m². 2 The material is then subjected to conventional processes such as drying, rolling, and cutting to obtain a positive electrode sheet. This positive electrode sheet comprises the aforementioned electrode material, and its compaction density is 2.4 g / cm³. 3 .

[0085] The prepared positive electrode, separator, and graphite electrode are stacked to prepare a soft-pack battery.

[0086] Details of Examples 1-10 and Comparative Example 1 can be found in Table 1.

[0087] The electrode plates and electrochemical devices (pouch cells) obtained in Examples 1-10 and Comparative Example 1 were subjected to the following performance tests, and the test results are shown in Table 2.

[0088] (1) Electrode film resistivity test: The test instrument is GDW3-KDY-2 two-probe film resistivity tester (Beijing Zhonghui Tiancheng Technology). Use a micrometer to select 5 points (center + four corners) evenly on the surface of the electrode sample to measure the thickness, and take the average value as D (unit: cm). Place the sample flat on the four-probe test platform with the film side facing up (if directly testing the coated electrode, an insulating sheet should be placed on the back of the aluminum foil to prevent current from passing through the aluminum foil); adjust the probe pressure (0.2~0.3N / needle) to ensure good contact between the probe and the film (avoid breaking down the film layer); start the constant current source and apply the current I (usually 1~10mA, adjusted according to the film conductivity to avoid overheating); record the voltage V between the inner probes (unit: mV), and the electrode film resistivity ρ=2πD*V / I; repeat the test at different positions (at least 5 points) on the sample surface and take the average value.

[0089] (2) Particle size test: A scanning electron microscope (SEM) is used to scan the sample surface by focusing an electron beam and collect reflected electron or secondary electron signals to form a high-resolution surface image, which shows the particle size.

[0090] Particle size was measured using Mastersizer 3000 laser diffraction technology. After internal ultrasonic dispersion for 5 minutes, the particle size distribution was tested. Particle size was measured by measuring the intensity of the scattered light as the laser beam passed through the dispersed particle sample. The data was then used to analyze and calculate the particle size distribution that formed the scattering spectrum. D50: median particle size, the particle size corresponding to a cumulative particle size distribution percentage of 50% for a sample.

[0091] (3) Coating thickness test: The electrode material was dried and sampled using a scanning electron microscope (SEM). The sample was frozen in liquid nitrogen and then fractured to keep the fracture surface flat. The coating thickness was measured by SEM imaging.

[0092] (4) Fast charging performance test: Use different charging rates to monitor the negative parameter potential to formulate a fast charging strategy. The test working voltage range is 2.5V-4.3V. First, use 0.33C to charge and discharge to obtain the calibrated capacity. Through different charging rate tests, monitor the changes in battery temperature rise and avoid high temperature (the temperature rise value is required to be <10℃). Formulate the optimal fast charging strategy. First, put the sample-cell in a standard environment (23℃, 50%RH) with SOC=10%. Then charge it to 80% SOC with constant current at 1C, 2C, 3C, 4C and 5C respectively (record the time). At the same time, monitor the changes in battery temperature and formulate a multi-stage variable rate fast charging strategy. Record the fast charging time from 10% to 80% SOC.

[0093] (5) High temperature cycle performance test: Before the test, the sample cell was charged to SOC=100% by constant current at 0.33C in a standard environment (23℃, 50%RH) and left to stand for 1 hour. Then it was sent to a 45℃ oven for high temperature cycle test. The test system is as follows: charging is 1C constant current (CC) charging to 4.35V, followed by constant voltage (CV) charging until the current drops to 0.05C cutoff; discharging is 1C constant current discharge to 2.0V, cycled 1000 times, and the capacity retention rate of the battery was tested.

[0094] The above results show that: As shown in Table 2, compared to Comparative Example 1 which lacks a polymer material layer, Examples 1-10 exhibit significantly higher resistivity due to the formation of a polymer material layer containing polar groups on the surface of the electrode active material, with a conductive agent uniformly dispersed within this layer. Firstly, the resistivity of the electrode films in Examples 1-10 is significantly lower than that in Comparative Example 1. Specifically, the resistivity of Example 1 is only 0.15 Ω·m, while that of Comparative Example 1 is as high as 0.41 Ω·m. This is because the conductive agent is uniformly dispersed within the polymer material layer, forming a penetrating electron transport channel, significantly reducing interfacial contact resistance, effectively lowering the resistivity of the electrode film, and improving its conductivity. Furthermore, the polymer material layer in Examples 1-10 has polar groups capable of adsorbing transition metal ions, and the conductive agent CNT also has adsorption properties. The synergistic effect of these two components further effectively adsorbs transition metal ions, suppressing their dissolution from the positive electrode side under high temperature and pressure, and reducing their deposition on the negative electrode side. This reduces capacity decay and interfacial impedance on the positive electrode side, and avoids repeated decomposition and reconstruction of the SEI on the negative electrode side, effectively delaying battery capacity decay and improving battery rate performance and high-temperature cycling performance. Therefore, the 10%-80% fast charging time of the batteries in Examples 1-10 is shortened by 3-8 minutes compared to Comparative Example 1. Furthermore, Examples 1-10 can stably cycle 1000 times at 45°C with a capacity retention rate of 82%-85%, while Comparative Example 1 has a capacity retention rate of 81%.

[0095] Comparing Example 1 and Example 2, it can be found that the method of forming a composite coating layer by in-situ polymerization can precisely control the thickness of the composite coating layer (i.e., the thickness of the polymer material layer). The thickness of the composite coating layer can be adjusted by adjusting the amount of monomers containing polar groups and non-polar monomers added.

[0096] Comparing Examples 1-3, it can be found that adjusting the amount of conductive agent in the composite coating layer is beneficial to the formation of the conductive network and further improves the charge transport efficiency of the electrode sheet.

[0097] Comparing Examples 1 and 4-5 reveals that by adjusting the ratio of polar monomers to non-polar monomers in the monomer composition, the polarity, mechanical strength, and flexibility of the composite coating layer can be further adjusted to accommodate electrode active materials of different particle sizes. In Example 1, the electrode active material LMFP is a primary particle, while in Example 4, the electrode active material LMFP is a secondary particle with a larger particle size; both examples demonstrate that the polymer material layer uniformly encapsulates the electrode active material.

[0098] Building upon Examples 9-10, Examples 6-8 further controlled the mass ratio of the electrode active material LMFP, the first monomer AN, and the conductive agent CNT within a preset range. This facilitated the adjustment of the polymer material layer thickness, reduced the dissolution of transition metal ions, and further provided the electrode sheet with good electrochemical activity and conductivity. Based on Examples 6-8, Examples 1-5 further added a non-polar monomer to the second mixture, which improved the flexibility of the polymer material layer and enhanced the interfacial compatibility between the polymer material and the electrode active material. Therefore, the batteries in Examples 1-5 exhibited better cycle performance.

[0099] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing an electrode sheet, characterized in that, include: The electrode active material, solvent, and dispersant are mixed to obtain a first mixture; A first monomer, an initiator, and a conductive agent are added to the first mixture to obtain a second mixture, wherein the first monomer is used to polymerize and form a polymer material, and the first monomer contains polar groups; The second mixture is stirred and heated to allow the first monomer to polymerize in situ on the surface of the electrode active material to form a polymer material layer containing polar groups. The conductive agent is dispersed in the polymer material layer to obtain the electrode material. The electrode material and binder are mixed to obtain an electrode slurry; and The electrode slurry is coated onto the current collector, and then dried and rolled to obtain the electrode sheet.

2. The method for preparing the electrode sheet according to claim 1, characterized in that, In the second mixture, the mass ratio of the electrode active material, the first monomer, and the conductive agent is (80~95):(2.5~17.5):(0.5~4). The thickness of the polymer material layer is 0.2 μm to 3.0 μm; The median particle size D50 of the electrode active material is 0.5 μm to 8.0 μm.

3. The method for preparing the electrode sheet according to claim 1, characterized in that, The conductive agent includes at least one of conductive carbon black and carbon nanotubes.

4. The method for preparing the electrode sheet according to claim 3, characterized in that, The first monomer includes at least one of acrylonitrile, methacrylonitrile, cyanoacrylate, and m-cyanostyrene.

5. The method for preparing the electrode sheet according to claim 1, characterized in that, The second mixture also includes a second monomer, which is a nonpolar monomer.

6. The method for preparing the electrode sheet according to claim 5, characterized in that, The second monomer includes at least one of butadiene and halobutadiene; and / or In the second mixture, the mass ratio of the first monomer to the second monomer is 1:(0.1~1).

7. The method for preparing the electrode sheet according to claim 1, characterized in that, In the step of preparing the second mixture, the conductive agent, the first monomer, and the initiator are added in sequence.

8. The method for preparing the electrode sheet according to claim 1, characterized in that, The step of stirring and heating the second mixture includes: The second mixture is stirred and heated until its viscosity reaches 2000 cp to 8000 cp, wherein the heating temperature is 55°C to 80°C and the heating rate is 5°C / min to 20°C / min; and The heated second mixture is cooled to room temperature, precipitated, and part of the upper solution is removed, leaving the electrode material, wherein the viscosity of the electrode material is 5000cp~15000cp, and the solid content of the electrode material is 40%~60%.

9. An electrode sheet, characterized in that, The electrode sheet is prepared by the method for preparing the electrode sheet according to any one of claims 1 to 8. The electrode sheet includes an electrode material, the electrode material includes an electrode active substance and a polymer material layer containing polar groups located on the surface of the electrode active substance, and a conductive agent is dispersed in the polymer material layer.

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and / or the negative electrode are electrode plates as described in claim 9.

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