Positive plate, lithium battery and preparation method thereof

Abstract

The invention provides a positive plate, a lithium battery and a preparation method thereof, the positive plate comprises a positive current collector and a positive active material layer, and the positive active material layer is attached to at least one side surface of the positive current collector through hot pressing; wherein the positive electrode active material layer comprises a positive electrode active material, a fiberizable binder, a conductive agent, a lithium supplement agent and a catalyst, the lithium supplement agent is an organic lithium supplement agent, and the catalyst is a transition metal oxide. The problems that the energy density of the lithium battery prepared by a dry-method electrode preparation process is reduced and the cycle life is shortened are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a positive electrode sheet, a lithium battery and a preparation method thereof. Background Art

[0002] With the rapid development of lithium batteries, the requirements for their energy density, cycle life, and rate performance are becoming increasingly higher. Electrodes are an important component of lithium batteries. In existing technologies, the wet electrode preparation process has always dominated the preparation of electrodes. However, with the increasing demand for environmental protection, people have gradually shifted their research focus to solvent-free dry electrode preparation processes. Compared with the wet electrode preparation process, the dry electrode preparation process does not introduce any organic solvents, avoiding the high pollution and high energy consumption processes in the wet electrode preparation process. It has the advantages of small equipment footprint, low investment, and low cost. Its overall cost can be reduced by more than 18% compared to the wet electrode preparation process.

[0003] While dry-electrode preparation offers numerous advantages, continuous film formation, lacking the dispersibility provided by solvents, presents a significant challenge in its development. Existing dry-electrode preparation processes, in an effort to improve electrode film formation, often result in reduced lithium battery energy density and cycle life. Pre-lithiation technology can eliminate this capacity loss and increase the energy density of lithium batteries. However, existing positive and negative electrode pre-lithiation technologies both have drawbacks. The decomposition voltage of binary and organic lithium supplements used in positive electrode pre-lithiation technology is as high as 4.7V, exceeding the normal charge and discharge voltage of existing lithium battery systems and the withstand voltage of the electrolyte, making it difficult to meet the requirements of commonly used positive electrode materials in lithium batteries. Lithium-rich supplements also have poor air stability and can leave residues in the battery after supplementation, impacting performance. Negative electrode pre-lithiation technology typically requires the use of metallic lithium, which presents significant challenges in mass production and carries high safety risks. Summary of the Invention

[0004] The present invention aims to provide a positive electrode sheet, a lithium battery and a preparation method thereof, so as to solve the problems of decreased energy density and shortened cycle life of lithium batteries prepared by a dry electrode preparation process.

[0005] To solve the above problems, the first aspect of the present invention provides a positive electrode sheet, comprising: a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is attached to at least one side surface of the positive electrode current collector by hot pressing;

[0006] The positive electrode active material layer includes a positive electrode active material, a fiberizable binder, a conductive agent, a lithium replenisher and a catalyst. The lithium replenisher is an organic lithium replenisher, and the catalyst is a transition metal oxide.

[0007] A second aspect of the present invention provides a method for preparing a positive electrode sheet, for preparing the positive electrode sheet as described in the first aspect, the preparation method comprising the following steps:

[0008] The conductive agent, the lithium supplement agent and the catalyst are mixed uniformly to prepare a first mixture; the positive electrode active material is added to the first mixture and mixed uniformly to prepare a second mixture; the fiberizable binder is added to the second mixture and mixed uniformly to prepare a third mixture;

[0009] performing a fiberization treatment on the third mixture to obtain a fiberized mixture, and heating and rolling the fiberized mixture into sheets to obtain a positive electrode active material layer;

[0010] The positive electrode active material layer is laminated to at least one surface of a positive electrode current collector by hot pressing to obtain a positive electrode sheet.

[0011] The third aspect of the present invention provides a lithium battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet described in the first aspect, or is a positive electrode sheet prepared by the preparation method of the positive electrode sheet described in the second aspect.

[0012] The positive electrode sheet of the present invention adds an organic lithium replenisher to the positive electrode active material layer. The organic lithium replenisher has good air stability and can effectively replenish the active lithium in the positive electrode active material layer to make up for the active lithium lost in the first charge and discharge, which is beneficial to improving the battery energy density and cycle life. After the lithium replenishment is completed, the reaction products other than lithium ions are mainly gas products. The gas products can be discharged from the positive electrode active material layer without remaining in the positive electrode active material layer, thereby avoiding damage to the structure of the positive electrode sheet. By adding a transition metal oxide as a catalyst to the positive electrode active material layer, the catalyst can reduce the decomposition potential of the organic lithium replenisher to within the normal charge and discharge voltage range of the lithium battery, and the transition metal oxide has high electrical conductivity and stability. Using the transition metal oxide as a catalyst can not only effectively reduce the decomposition potential of the organic lithium replenisher into active lithium, but also improve the electrical conductivity of the positive electrode active material layer, thereby improving the lithium in the dry-process positive electrode sheet. The ion transmission efficiency is improved; by adding a fibrillable binder to the positive electrode active material layer, the fibrillable binder forms a network structure after fibrillation, which can better fix the positive electrode active material, conductive agent, lithium supplement agent and catalyst, so that the various components in the positive electrode active material layer are more tightly bonded, thereby improving the structural stability of the positive electrode active material layer, and the network structure formed by the fibrillable binder can also provide an exhaust channel for the gas products of the organic lithium supplement agent, which is beneficial for the gas products to be removed from the positive electrode active material layer, avoiding affecting the structural strength of the positive electrode active material layer, and after lithium supplementation, these exhaust channels are filled with electrolyte, which can increase the liquid retention capacity of the electrolyte, reduce the diffusion distance of lithium ions, accelerate the transmission speed of lithium ions, and help improve the rate performance and power performance of the lithium battery; the conductive agent in the positive electrode active material layer can improve the conductivity of the positive electrode active material and the lithium supplement agent, and improve the electron transfer efficiency between the positive electrode current collector and the positive electrode active material layer. The positive electrode active material layer provided in this embodiment, through the combination of the above-mentioned substances, effectively replenishes the active lithium in the positive electrode active material layer while reducing the decomposition potential of the organic lithium supplement into active lithium, and can also improve the ion transfer rate and electron transfer rate in the positive electrode active material layer, which is beneficial to improving the energy density and cycle performance of the lithium battery.

[0013] The method for preparing the positive electrode sheet described in the present invention prepares the third mixture by adding each component step by step, which can more effectively reduce the decomposition reaction potential of the lithium supplement agent, reduce the agglomeration of each component, and is beneficial to improving the electrochemical performance of the positive electrode active material layer. After preparing the third mixture, fiberization treatment and hot rolling are carried out in sequence, which is beneficial to improving the structural strength of the positive electrode active material layer. Finally, the positive electrode active material layer is hot-pressed and bonded to at least one side surface of the positive electrode current collector. There is no need for coating, baking and solvent recovery processes, which can reduce energy consumption and reduce the cracking problem of the positive electrode active material layer during the baking process, which is beneficial to improving the quality of the positive electrode sheet. In addition, the present invention prepares the positive electrode sheet by a dry method, avoids the use of organic solvents, is environmentally friendly, can reduce production costs, improve production efficiency, and is suitable for industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A process flow chart for preparing a positive electrode sheet according to an embodiment of the present invention;

[0015] Figure 2 This is a graph showing the cycle performance test results provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0018] In addition, the terms "comprising", "including", "containing", and "having" are not restrictive, and other steps and other components that do not affect the results can be added. Unless otherwise specified, materials, equipment, and reagents are commercially available.

[0019] In addition, although the present invention describes the various steps in the preparation in the form of S110, S120 and S130, this description is only for ease of understanding. The form of S110, S120 and S130 does not limit the order of the steps.

[0020] To solve the above technical problems, a first aspect of an embodiment of the present application provides a positive electrode sheet, the positive electrode sheet comprising: a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is attached to at least one side surface of the positive electrode current collector by hot pressing;

[0021] The positive electrode active material layer includes a positive electrode active material, a fiberizable binder, a conductive agent, a lithium supplement agent and a catalyst. The lithium supplement agent is an organic lithium supplement agent and the catalyst is a transition metal oxide.

[0022] The positive electrode sheet provided in this embodiment is formed by adding an organic lithium replenisher to the positive electrode active material layer. The organic lithium replenisher has good air stability and can effectively replenish the active lithium in the positive electrode active material layer to make up for the active lithium lost during the first charge and discharge, which is beneficial to improving the battery energy density and cycle life. After the lithium replenishment is completed, the reaction products other than lithium ions are mainly gas products. The gas products can be discharged from the positive electrode active material layer without remaining in the positive electrode active material layer, thereby avoiding damage to the structure of the positive electrode sheet. By adding a transition metal oxide as a catalyst to the positive electrode active material layer, the catalyst can reduce the decomposition potential of the organic lithium replenisher to within the normal charge and discharge voltage range of the lithium battery, and the transition metal oxide has high electrical conductivity and stability. Using a transition metal oxide as a catalyst can not only effectively reduce the decomposition potential of the organic lithium replenisher into active lithium, but also improve the electrical conductivity of the positive electrode active material layer, thereby improving the lithium in the dry-process positive electrode sheet. The ion transmission efficiency is improved; by adding a fibrillable binder to the positive electrode active material layer, the fibrillable binder forms a network structure after fibrillation, which can better fix the positive electrode active material, conductive agent, lithium supplement agent and catalyst, so that the various components in the positive electrode active material layer are more tightly bonded, thereby improving the structural stability of the positive electrode active material layer, and the network structure formed by the fibrillable binder can also provide an exhaust channel for the gas products of the organic lithium supplement agent, which is beneficial for the gas products to be removed from the positive electrode active material layer, avoiding affecting the structural strength of the positive electrode active material layer, and after lithium supplementation, these exhaust channels are filled with electrolyte, which can increase the liquid retention capacity of the electrolyte, reduce the diffusion distance of lithium ions, accelerate the transmission speed of lithium ions, and help improve the rate performance and power performance of the lithium battery; the conductive agent in the positive electrode active material layer can improve the conductivity of the positive electrode active material and the lithium supplement agent, and improve the electron transfer efficiency between the positive electrode current collector and the positive electrode active material layer. The positive electrode active material layer provided in this embodiment, through the combination of the above-mentioned substances, effectively replenishes the active lithium in the positive electrode active material layer while reducing the decomposition potential of the organic lithium supplement into active lithium, and can also improve the ion transfer rate and electron transfer rate in the positive electrode active material layer, which is beneficial to improving the energy density and cycle performance of the lithium battery.

[0023] Based on the above embodiment, as an optional implementation, the lithium supplement agent is lithium oxalate (Li2C2O4) and / or lithium squarate (Li2C4O4). For example, the lithium supplement agent is lithium oxalate, lithium squarate, or a mixture of lithium oxalate and lithium squarate. If the lithium supplement agent is a mixture of lithium oxalate and lithium squarate, the lithium oxalate and lithium squarate can be mixed in any proportion. Selecting lithium oxalate and lithium squarate as lithium supplement agents not only has a high lithium content, which can increase the content of active lithium in the positive electrode active material layer, but also, after lithium supplementation, the reaction products of lithium oxalate and lithium squarate, in addition to lithium ions, are carbon dioxide and oxygen. These two gases can not only be discharged from the positive electrode active material layer, but also do not affect the catalytic activity of the transition metal oxide.

[0024] Based on the above embodiment, as an optional embodiment, the catalyst is nickel oxide and / or manganese dioxide. For example, the catalyst is a mixture of nickel oxide, manganese dioxide, or nickel oxide and manganese dioxide. If the catalyst is a mixture of nickel oxide and manganese dioxide, the nickel oxide and manganese dioxide can be mixed in any proportion. Nickel oxide and manganese dioxide are selected as catalysts. These two catalysts have high catalytic activity and stability, can effectively reduce the decomposition potential of the organic lithium supplement to active lithium, and have good electrical conductivity, which is beneficial for improving the lithium ion transmission efficiency in the dry-process positive electrode sheet. In addition, these two catalysts are simple to prepare and are relatively cheap, which helps reduce the production cost of the positive electrode sheet.

[0025] On the basis of the above embodiment, as an optional embodiment, the fiberizable binder is polytetrafluoroethylene. Although polytetrafluoroethylene (PTFE) will react with the free lithium ions after desolvation and consume the active lithium in the positive electrode active material layer, PTFE has excellent mechanical properties, high crystallinity and fiberization ability. PTFE powder particles can extend to form filamentous fibers when a shear load is applied. This fiberization process helps to form a stable electrode structure with stronger flexibility and less internal stress during the cycle, which is conducive to improving the cycle performance of the positive electrode sheet. The fiberization ability of PTFE enables the positive electrode active material layer to be self-supporting without the use of solvents, reducing the manufacturing cost of the positive electrode sheet. The high chemical stability and electrical insulation of PTFE also help to improve the safety and cycle stability of lithium batteries. In addition, PTFE can enhance the capillary adsorption of the positive electrode sheet for the electrolyte. In this embodiment, by dispersing the organic lithium replenisher in PTFE, the organic lithium replenisher can replenish the active lithium lost in the side reactions of PTFE, which is beneficial to improving the energy density and cycle life of the lithium battery. The network structure formed by PTFE is beneficial to the removal of gas products of the organic lithium replenisher from the positive electrode active material layer and enhances the absorption of the electrolyte by the positive electrode active material layer. The combination of the two can not only improve the energy density and cycle life of the lithium battery, but also avoid damaging the structure of the positive electrode sheet.

[0026] Based on the above embodiment, as an optional embodiment, the positive electrode active material is selected from lithium iron phosphate (LFP), nickel cobalt manganese ternary material (LiNi x Co y Mn z The conductive agent is one or a combination of conductive carbon black (SP), carbon nanotubes (CNT) and graphene.

[0027] Based on the above embodiment, as an optional implementation mode, the positive electrode active material layer includes, in parts by weight: 70 to 99 parts of positive electrode active material, 0.5 to 10 parts of fibrillable binder, 0.5 to 10 parts of conductive agent, 0.5 to 10 parts of lithium supplement agent and 0.5 to 10 parts of catalyst, for example: 94.5 parts of positive electrode active material, 2 parts of fibrillable binder, 1 part of conductive agent, 1.5 parts of lithium supplement agent and 1 part of catalyst. As a result, the positive electrode active material accounts for the highest proportion in the positive electrode active material layer, which increases the loading amount of the positive electrode active material and is beneficial to improving the energy density of the battery. The mass of the fibrillated binder is within the above range, which can improve the structural stability of the positive electrode active material layer while reducing the consumption of active lithium by the fibrillated binder. The mass of the conductive agent is within the above range, which is beneficial to further improve the conductive properties of the positive electrode active material and the lithium replenisher. The mass of the lithium replenisher is within the above range, which can better compensate for the active lithium lost in the formation of the SEI film and the PTFE side reaction during the first charge. The mass of the catalyst is within the above range, which can increase the reaction rate and reduce the occurrence of side reactions, and is more beneficial to reducing the decomposition potential of the organic lithium replenisher to within the normal charge and discharge voltage range of the lithium battery.

[0028] Based on the above embodiment, as an optional implementation, the weight ratio of the lithium supplement agent to the catalyst is N, where N≤1.6, i.e., the weight ratio of the lithium supplement agent to the catalyst is less than or equal to 1.6:1. For example, the weight ratio of the lithium supplement agent to the catalyst is 1.6:1, 1.5:1, 1.4:1, 1.3:1, or 1.2:1. Therefore, a weight ratio of the lithium supplement agent to the catalyst within the above range can not only further reduce the decomposition potential of the organic lithium supplement agent to active lithium, but also facilitate the utilization of the specific capacity of the organic lithium supplement agent, thereby providing more active lithium.

[0029] In this embodiment, the particle size of the lithium replenisher is smaller than the particle size of the positive electrode active material, the fiberizable binder and the conductive agent, and the particle size of the catalyst is smaller than the particle size of the positive electrode active material, the fiberizable binder and the conductive agent. On the basis of the above embodiment, as an optional embodiment, the particle size of the positive electrode active material, the fiberizable binder and the conductive agent are all in the micron order, and the particle size of the lithium replenisher and the catalyst is in the nanometer order. As a result, the particle size of the lithium replenisher and the catalyst is smaller, so that the lithium replenisher and the catalyst are evenly dispersed in the gaps between the positive electrode active material, the fiberizable binder and the conductive agent, which is beneficial for the lithium replenisher to make up for the lost active lithium in time, shorten the diffusion path of the active lithium, and accelerate the transmission speed of the active lithium. Moreover, the particle size of the lithium replenisher and the catalyst is smaller than the particle size of the positive electrode active material, the fiberizable binder and the conductive agent, so that the various components in the positive electrode active material layer are in closer contact, which can further improve the energy density of the positive electrode sheet and is beneficial to improving the structural stability of the positive electrode active material layer. As an optional embodiment, the particle size of the positive electrode active material is 5 μm to 80 μm, and the particle size of the fibrillable binder is 5 μm to 30 μm.

[0030] Based on the above embodiment, as an optional implementation, the particle size of the lithium supplement agent is less than or equal to 100 nm, and the particle size of the catalyst is less than or equal to 100 nm. For example, the particle size of the lithium supplement agent is 100 nm, 90 nm, 80 nm, 70 nm, or 60 nm, and the particle size of the catalyst is 90 nm, 80 nm, 70 nm, 60 nm, or 50 nm. Therefore, keeping the particle sizes of the lithium supplement agent and the catalyst within the above ranges is beneficial for further improving the electrochemical performance and structural stability of the positive electrode active material layer.

[0031] Based on the above embodiments, as an optional implementation manner, the positive electrode current collector can be selected from one or a combination of metal foils such as aluminum foil, copper foil, nickel foil, gold foil and platinum foil, and the positive electrode current collector can also be selected from one or a combination of composite aluminum foil, carbon-coated aluminum foil, glue-coated aluminum foil and electroplated aluminum foil.

[0032] A second aspect of the embodiments of the present application provides a method for preparing a positive electrode sheet, which is used to prepare the positive electrode sheet of the first aspect.

[0033] Figure 1 The process flow chart of preparing the positive electrode sheet in the embodiment of the present invention is shown in FIG. Figure 1 As shown, the preparation method of the positive electrode sheet includes the following steps:

[0034] Step S110: Mix the conductive agent, lithium supplement agent and catalyst uniformly to prepare a first mixture, add the positive electrode active material to the first mixture and mix uniformly to prepare a second mixture, add the fiberizable binder to the second mixture and mix uniformly to prepare a third mixture.

[0035] In this embodiment, the conductive agent, lithium supplement agent and catalyst are first mixed evenly, which is conducive to the full mixing of the conductive agent, lithium supplement agent and catalyst, so that the catalyst is evenly dispersed in the lithium supplement agent, which is conducive to improving the reaction activity of the catalyst and can more effectively reduce the decomposition reaction potential of the lithium supplement agent. The lithium supplement agent and catalyst can be coated on the surface of the conductive agent, which can reduce the agglomeration of the conductive agent and help improve the conductivity of the conductive agent; then, the positive electrode active material is added to the first mixture, which is conducive to full contact between the positive electrode active material and the conductive agent, lithium supplement agent and catalyst, reducing the diffusion distance of lithium ions and accelerating the transmission speed of lithium ions; finally, the fiberizable binder is added to the second mixture, which can prevent the fiberizable binder from entering fiberization too early, causing agglomeration between the powders, and affecting the uniformity of the third mixture.

[0036] Based on the above embodiment, as an optional implementation manner, the mixing speed for preparing the first mixture can be 500r / min to 1000r / min, and the mixing time is 20min to 40min; the mixing speed for preparing the second mixture can be 500r / min to 1000r / min, and the mixing time is 40min to 60min; the mixing speed for preparing the third mixture can be 100r / min to 500r / min, and the mixing time is 20min to 40min.

[0037] Step S120 , performing fiberization treatment on the third mixture to obtain a fiberized mixture, heating and rolling the fiberized mixture into sheets to obtain a positive electrode active material layer.

[0038] Specifically, the third mixture is poured into a jet mill for fiberization to produce a fiberized mixture. The fiberized mixture is then subjected to a hot roller to form a film, which is then thinned to produce the positive electrode active material layer. Thus, fiberization of the third mixture followed by hot roller processing is beneficial for improving the bonding strength between the various components and enhancing the structural strength of the positive electrode active material layer.

[0039] It should be noted that those skilled in the art can perform thinning treatment according to the surface density of the positive electrode active material layer, for example, thinning the positive electrode active material layer to a single-side surface density of 34 mg / cm2. Of course, those skilled in the art can also perform thinning treatment on the positive electrode active material layer according to actual needs.

[0040] Based on the above embodiment, as an optional implementation manner, the temperature of the hot roller is 80°C to 150°C.

[0041] Step S130 : hot-pressing the positive electrode active material layer onto at least one surface of the positive electrode current collector to produce a positive electrode sheet.

[0042] Based on the above embodiment, as an optional implementation manner, the hot pressing temperature is 150°C to 300°C.

[0043] The method for preparing the positive electrode sheet provided in this embodiment prepares the third mixture by adding each component step by step, which can more effectively reduce the decomposition reaction potential of the lithium supplement agent and reduce the agglomeration of each component, which is beneficial to improving the electrochemical performance of the positive electrode active material layer. After preparing the third mixture, fiberization treatment and hot rolling are carried out in sequence, which is beneficial to improving the structural strength of the positive electrode active material layer. Finally, the positive electrode active material layer is hot-pressed and bonded to at least one side surface of the positive electrode current collector. There is no need for coating, baking and solvent recovery processes, which can reduce energy consumption and reduce the cracking problem of the positive electrode active material layer during the baking process, which is beneficial to improving the quality of the positive electrode sheet. In addition, this embodiment prepares the positive electrode sheet by a dry method, avoiding the use of organic solvents, is environmentally friendly, can reduce production costs, improve production efficiency, and is suitable for industrial mass production.

[0044] The third aspect of the embodiment of the present application also provides a lithium battery, including a battery cell, the battery cell including a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet, the negative electrode sheet and the separator are stacked or wound to form the battery cell, the positive electrode sheet is the positive electrode sheet described in the first aspect, the battery also includes an electrolyte and a shell, and the battery cell and the electrolyte are encapsulated in the shell.

[0045] On the basis of the above embodiment, as an optional implementation, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is attached to at least one side surface of the negative electrode current collector by hot pressing. The negative electrode active material layer includes a negative electrode active material, a fiberizable binder and a conductive agent. Specifically, in parts by weight, the negative electrode active material layer includes: 70 to 99 parts of negative electrode active material, 0.5 to 10 parts of binder and 1 to 10 parts of conductive agent. Therefore, the content of each component of the negative electrode active material layer is within the above range, which is conducive to improving the discharge capacity of the lithium battery and improving the structural stability and safety of the negative electrode sheet. In addition, the use of a fiberizable binder in the negative electrode active material layer can realize the dry preparation of the negative electrode active material layer, which is conducive to improving the flexibility of the negative electrode active material layer, making the internal stress of the negative electrode active material layer smaller during the cycle and the cycle performance better.

[0046] The negative electrode active material is selected from one or a combination of artificial graphite, natural graphite, soft carbon, and hard carbon. The conductive agent is one or a combination of conductive carbon black (SP), carbon nanotubes (CNTs), and graphene. The fiberizable binder is polytetrafluoroethylene. The negative electrode current collector can be selected from one or a combination of metal foils such as aluminum foil, copper foil, nickel foil, gold foil, and platinum foil. The negative electrode current collector can also be selected from one or a combination of composite aluminum foil, carbon-coated aluminum foil, rubber-coated aluminum foil, and electroplated aluminum foil.

[0047] The negative electrode sheet in this embodiment is prepared by a dry method, specifically: a conductive agent and a negative electrode active material are mixed uniformly to obtain a fourth mixture, a fiberizable binder is added to the fourth mixture and mixed uniformly to obtain a fifth mixture; the fifth mixture is fiberized to obtain a fiberized mixture, the fiberized mixture is heated and rolled into a sheet to obtain a negative electrode active material layer; the negative electrode active material layer is hot-pressed and bonded to at least one side surface of the negative electrode current collector to obtain a negative electrode sheet.

[0048] The specific process parameters in the preparation process of the negative electrode sheet, such as mixing speed, mixing time and hot roller temperature, can refer to the process parameters in the preparation process of the positive electrode sheet and will not be repeated here. Of course, technicians in this field can also make adjustments according to actual conditions.

[0049] The lithium battery provided in this embodiment uses a dry method to prepare the positive and negative electrodes, which not only reduces the use of organic solvents and reduces pollution to the environment, but also reduces the internal stress of the positive and negative electrodes during the cycle process, which is beneficial to further improve the cycle performance of the lithium battery.

[0050] In this embodiment, the electrolyte includes a lithium salt and a non-aqueous organic solvent, and the lithium salt concentration of the electrolyte is 0.2 mol / L to 2.0 mol / L, for example, the lithium salt concentration of the electrolyte is 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L. The lithium salt includes one or a combination of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate and lithium chloroaluminate; the non-aqueous solvent is a mixed solution of chain acid esters and cyclic acid esters, wherein the chain acid esters include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methylpropyl carbonate (MPC), dipropyl carbonate (DPC) and other chain organic esters containing fluorine, sulfur or unsaturated bonds; the cyclic acid esters include at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), sultone and other cyclic organic esters containing fluorine, sulfur or unsaturated bonds.

[0051] In this embodiment, there is no specific restriction on the type of diaphragm and it can be selected according to actual needs. Specifically, the diaphragm can be selected from polypropylene film, polyethylene film, aramid film, polyimide film, non-woven fabric diaphragm or their multi-layer composite film, or a ceramic coated diaphragm with the above materials as the base material, or a glue-coated diaphragm; the thickness of the diaphragm is 5μm to 30μm, for example: the thickness of the diaphragm is 5μm, 10μm, 15μm, 20μm, 25μm or 30μm.

[0052] In order to further explain the present invention in detail, the present invention will be further described below with reference to specific examples. Unless otherwise specified, the experimental methods used in the examples of the present invention are conventional methods; unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention are all purchased from the market.

[0053] Example 1

[0054] This embodiment provides a method for preparing a lithium battery, comprising the following steps:

[0055] (1) Preparation of positive electrode sheet: 1.5 wt% of lithium oxalate (Li2C2O4) powder, 1 wt% of nickel oxide (NiO) powder and 1 wt% of conductive carbon black (SP) were added to a stirring tank and mixed at 700 r / min for 30 min to prepare a first mixture; 94.5 wt% of lithium cobalt oxide (LCO) was added to the first mixture and mixed at 700 r / min for 60 min to prepare a second mixture; 2 wt% of polytetrafluoroethylene (PTFE) was added to the second mixture and mixed at 300 r / min for 30 min to prepare a third mixture.

[0056] The third mixture was poured into a jet mill for fiberization to produce a fiberized mixture. The jet mill parameters were set as follows: air velocity of 150 m / s, feed rate of 10 kg / h, chamber pressure of 0.4 MPa, grinding disc speed of 10,000 rpm, and temperature of 45°C. The fiberized mixture was hot rolled to form a film, which was then thinned to a single-sided surface density of 34 mg / cm² to produce the positive electrode active material layer.

[0057] The positive electrode active material layer is placed on the surface of a 13 μm coated aluminum foil and rolled to a compaction density of 3.5 g / cm3. After slitting and die-cutting, the positive electrode sheet is obtained.

[0058] (2) Preparation of negative electrode sheet: 1 wt% conductive carbon black (SP) and 97 wt% graphite were added to a stirring tank and mixed at 700 rpm for 30 min to prepare a fourth mixture; 2 wt% polytetrafluoroethylene (PTFE) was added to the fourth mixture and mixed at 300 rpm for 30 min to prepare a fifth mixture;

[0059] The fifth mixture was poured into a jet mill for fiberization to produce a fiberized mixture. The jet mill parameters were set as follows: air velocity of 150 m / s, feed rate of 10 kg / h, chamber pressure of 0.4 MPa, grinding disc speed of 10,000 rpm, and temperature of 45°C. The fiberized mixture was then rolled onto a hot roller to form a film, which was then thinned to a single-sided density of 17 mg / cm² to produce the negative electrode active material layer.

[0060] The negative electrode active material layer is placed on the surface of a 7 μm coated copper foil and rolled to a compaction density of 1.5 g / cm3. After slitting and die-cutting, the negative electrode sheet is obtained.

[0061] (3) Preparation of lithium batteries: The positive electrode sheets, negative electrode sheets and PE diaphragms coated with alumina ceramics prepared above are stacked in sequence to prepare laminated cells. After the tabs of the laminated cells are welded, the laminated cells are welded into the shell and baked. After baking, the battery is disassembled and the moisture content is measured. When the moisture value is below 200 PPM, the battery is injected at a rate of 4 g / Ah. After injection, the battery is subjected to aging, formation exhaust, secondary injection, aging and volume separation processes to prepare a lithium battery.

[0062] Example 2

[0063] This embodiment provides a method for preparing a lithium battery. The preparation process of the lithium battery is the same as that of Example 1, except that:

[0064] When preparing the positive electrode sheet, 2wt% lithium oxalate (Li2C2O4) powder, 1.33wt% nickel oxide (NiO) powder, 1wt% conductive carbon black (SP), 93.67wt% lithium cobalt oxide (LCO) and 2wt% polytetrafluoroethylene (PTFE) were added to a stirring tank.

[0065] Example 3

[0066] This embodiment provides a method for preparing a lithium battery. The preparation process of the lithium battery is the same as that of Example 1, except that:

[0067] When preparing the positive electrode sheet, 10wt% lithium oxalate (Li2C2O4) powder, 10wt% nickel oxide (NiO) powder, 5wt% conductive carbon black (SP), 70wt% lithium cobalt oxide (LCO) and 5wt% polytetrafluoroethylene (PTFE) were added to a stirring tank.

[0068] Example 4

[0069] This embodiment provides a method for preparing a lithium battery. The preparation process of the lithium battery is the same as that of Example 1, except that:

[0070] When preparing the positive electrode sheet, 2wt% lithium oxalate (Li2C2O4) powder, 0.5wt% nickel oxide (NiO) powder, 0.5wt% conductive carbon black (SP), 96wt% lithium cobalt oxide (LCO) and 1wt% polytetrafluoroethylene (PTFE) were added to a stirring tank.

[0071] Comparative Example 1

[0072] This comparative example provides a method for preparing a lithium battery, which uses a wet process to prepare positive and negative electrode sheets, including the following steps:

[0073] (1) Preparation of positive electrode sheet: N-methylpyrrolidone (NMP) and 2 wt% binder polyvinylidene fluoride (PVDF) powder were added to a double planetary mixing tank, and slowly stirred at a revolution speed of 20 r / min and a dispersion speed of 200 r / min for 10 min. The mixing tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. Then, the mixture was quickly stirred at a revolution speed of 30 r / min and a dispersion speed of 2500 r / min under vacuum for 180 min to prepare a glue solution.

[0074] 1 wt% conductive carbon black (SP) was added to the adhesive solution, and the mixture was slowly stirred at a revolution speed of 20 r / min and a dispersion speed of 200 r / min for 10 minutes. The stirring tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The mixture was then rapidly stirred at a revolution speed of 30 r / min and a dispersion speed of 2500 r / min under vacuum for 90 minutes to prepare a first mixed solution.

[0075] 96.5 wt% of lithium cobalt oxide (LCO) was added to the first mixed solution, and the mixture was slowly stirred at a revolution speed of 20 r / min and a dispersion speed of 200 r / min for 10 minutes. The stirring tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The mixture was then vacuum stirred at a revolution speed of 30 r / min and a dispersion speed of 2500 r / min for 240 minutes to obtain a second mixed solution.

[0076] 0.5 wt% carbon nanotubes (CNTs) were added to the second mixed solution, and the mixture was stirred at a speed of 30 r / min and 2500 r / min under vacuum for 30 min. After degassing, the mixture was passed through a 150-mesh sieve to prepare a positive electrode slurry.

[0077] The positive electrode slurry was coated at a surface density of 34 mg / cm2 on both sides, roll-pressed at a compaction density of 3.5 g / cm3, and die-cut to form a positive electrode sheet.

[0078] (2) Preparation of negative electrode sheet: 100 wt% deionized water and 1.5 wt% thickener sodium carboxymethyl cellulose (CMC) powder were added to a double planetary mixing tank, and the mixture was slowly stirred at a speed of 20 r / min for revolution and 200 r / min for dispersion for 10 min. The mixing tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The mixture was then stirred at a speed of 20 r / min for revolution and 1800 r / min for dispersion for 120 min to obtain a glue solution.

[0079] 1 wt% conductive carbon black (SP) was added to the glue solution, and the mixture was slowly stirred at a revolution speed of 20 r / min and a dispersion speed of 200 r / min for 10 minutes. The stirring tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The mixture was then stirred at a revolution speed of 20 r / min and a dispersion speed of 1800 r / min for 90 minutes to prepare a third mixed solution.

[0080] 95 wt % of the negative electrode material was added to the third mixed solution in two additions. 50 wt % of the negative electrode material was added for the first time, and the mixture was slowly stirred at a revolution of 20 r / min and a dispersion speed of 200 r / min for 10 min. The stirring tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The remaining negative electrode material was then added and the mixture was slowly stirred at a revolution of 20 r / min and a dispersion speed of 200 r / min for 10 min. The stirring tank was lowered and the powder on the paddle was scraped clean with a silicone scraper. The mixture was then quickly stirred at a revolution of 20 r / min and a dispersion speed of 1800 r / min for 90 min to obtain a fourth mixed solution.

[0081] Add 2 wt% of the active substance in NMP to the fourth mixed solution, and stir at a speed of 20 rpm and 1800 rpm for 30 minutes to obtain a fifth mixed solution.

[0082] 2.5 wt% SBR was added to the fifth mixed solution, and the mixture was stirred at a speed of 20 r / min and 500 r / min for 30 min. After degassing, the mixture was passed through a 150-mesh sieve to obtain a negative electrode slurry.

[0083] The negative electrode slurry was coated at a surface density of 16.8 mg / cm2 on both sides, rolled at a compaction density of 1.5 g / cm3, and die-cut to form negative electrode sheets.

[0084] (3) Preparation of lithium batteries: The positive electrode sheets, negative electrode sheets and PE diaphragms coated with alumina ceramics prepared above are stacked in sequence to prepare laminated cells. After the tabs of the laminated cells are welded, the laminated cells are welded into the shell and baked. After baking, the battery is disassembled and the moisture content is measured. When the moisture value is below 200 PPM, the battery is injected at a rate of 4 g / Ah. After injection, the battery is subjected to aging, formation exhaust, secondary injection, aging and volume separation processes to prepare a lithium battery.

[0085] Comparative Example 2

[0086] This comparative example provides a method for preparing a positive electrode sheet. The preparation process of the positive electrode sheet is the same as that of Example 1, except that:

[0087] When preparing the positive electrode sheet, no lithium supplement and catalyst were added to the third mixture, that is, 1 wt% conductive carbon black (SP), 97 wt% lithium cobalt oxide (LCO) and 2 wt% polytetrafluoroethylene (PTFE) were added to the stirring tank.

[0088] Comparative Example 3

[0089] This comparative example provides a method for preparing a positive electrode sheet. The preparation process of the positive electrode sheet is the same as that of Example 1, except that:

[0090] When preparing the positive electrode sheet, no catalyst was added to the third mixture, that is, 2wt% of lithium oxalate (Li2C2O4) powder, 1wt% of conductive carbon black (SP), 95wt% of lithium cobalt oxide (LCO) and 2wt% of polytetrafluoroethylene (PTFE) were added to the stirring tank.

[0091] The lithium batteries prepared in Example 1, Example 2 and Comparative Examples 1 to 3 were subjected to constant capacity tests at room temperature 25°C, 0.2C / 0.2C, and a voltage range of 3.0V to 4.3V. The performance test results of each embodiment and comparative example are shown in Table 1. The lithium batteries prepared in Example 1, Example 2 and Comparative Examples 1 to 3 were subjected to 50-cycle tests at room temperature 25°C, 1C / 1C, and a voltage range of 3.0V to 4.3V. The performance test results of each embodiment and comparative example are shown in Table 1. Figure 2 shown.

[0092] Table 1

[0093]

[0094] The energy density of the positive electrode active material lithium cobalt oxide is generally 170Wh / kg to 200Wh / kg. As can be seen from Table 1, the energy density of the batteries prepared in Examples 1 to 4 is higher than 234Wh / kg, which shows that adding lithium supplements and catalysts to the positive electrode active material layer is beneficial to improving the energy density of the lithium battery. In addition, the energy density of Examples 1 to 4 is higher than that of Comparative Example 2, which shows that adding lithium supplements to the positive electrode active material layer can improve the capacity and energy density of the lithium battery, and the energy density of Example 2 is higher than that of Example 1, which shows that appropriately increasing the mass ratio of the lithium supplement in the positive electrode active material layer is beneficial to further improve the energy density of the lithium battery; Compared with Example 2, Example 4 has the same amount of lithium oxalate added, but the capacity of the battery of Example 4 is lower than that of Example 2, which shows that when the ratio of lithium oxalate to nickel oxide is greater than 1.6, the corresponding capacity cannot be exerted in the voltage range of 3.0V to 4.3V, and by Figure 2It can be seen that the cycle effect of Example 4 is also worse than that of Example 2, indicating that the electrical performance of the battery in Example 4 has declined to a certain extent. The energy density of Comparative Example 3 is lower than that of Comparative Example 2, indicating that when no catalyst is added to the positive electrode active material layer and only a lithium supplement is added, the lithium supplement cannot exert its capacity in the voltage range of 3.0V to 4.0V. This shows that adding a catalyst to the positive electrode active material layer can effectively reduce the decomposition potential of the lithium supplement into active lithium, thereby reducing the reaction voltage of the lithium supplement. In Example 2, a dry method is used to prepare the positive and negative electrode sheets. Compared with the wet method used in Comparative Example 1 to prepare the positive and negative electrode sheets, the energy density of the lithium battery of Example 2 is significantly higher than that of the lithium battery of Comparative Example 1. This shows that the use of a dry method to prepare electrodes can significantly improve the energy density of lithium batteries.

[0095] Depend on Figure 2 It can be seen that the cycle performance of Examples 1 to 4 of the present invention is higher than that of Comparative Examples 2 and 3, indicating that adding a lithium supplement and a catalyst to the positive electrode active material layer is beneficial to improving the cycle performance of the lithium battery, and the cycle performance of Examples 1 to 4 is higher than that of Comparative Example 1, indicating that the dry method for preparing electrodes is more beneficial to improving the cycle performance of the lithium battery than the wet method for preparing electrodes. Figure 2 It can be seen that the positive electrode sheet, lithium battery and preparation method thereof provided by the present invention can increase the energy density of the lithium battery and enhance the cycle performance of the lithium battery.

[0096] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: A positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is attached to at least one side surface of the positive electrode current collector by hot pressing; The positive electrode active material layer includes a positive electrode active material, a fiberizable binder, a conductive agent, a lithium replenisher and a catalyst. The lithium replenisher is an organic lithium replenisher, and the catalyst is a transition metal oxide.

2. The positive electrode sheet according to claim 1, characterized in that The lithium supplement agent is lithium oxalate and / or lithium squarate, and the catalyst is nickel oxide and / or manganese dioxide.

3. The positive electrode sheet according to claim 1, characterized in that The fiberizable binder is polytetrafluoroethylene.

4. The positive electrode sheet according to claim 1, characterized in that In parts by weight, the positive electrode active material layer includes: 70 to 99 parts of the positive electrode active material, 0.5 to 10 parts of the fibrillable binder, 0.5 to 10 parts of the conductive agent, 0.5 to 10 parts of the lithium supplement agent, and 0.5 to 10 parts of the catalyst.

5. The positive electrode sheet according to claim 4, characterized in that: The weight ratio of the lithium supplement agent to the catalyst is less than or equal to 1.

6.

6. The positive electrode sheet according to claim 1, characterized in that The particle size of the lithium supplement agent is less than 100 nm, and the particle size of the catalyst is less than 100 nm.

7. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active material is selected from one or a combination of lithium iron phosphate, nickel-cobalt-manganese ternary material and lithium cobalt oxide, and the conductive agent is one or a combination of conductive carbon black, carbon nanotubes and graphene.

8. A method for preparing a positive electrode sheet, characterized in that: For preparing the positive electrode sheet according to any one of claims 1 to 7, the preparation method comprises the following steps: The conductive agent, the lithium supplement agent and the catalyst are mixed uniformly to prepare a first mixture; the positive electrode active material is added to the first mixture and mixed uniformly to prepare a second mixture; the fiberizable binder is added to the second mixture and mixed uniformly to prepare a third mixture; performing a fiberization treatment on the third mixture to obtain a fiberized mixture, and heating and rolling the fiberized mixture into sheets to obtain a positive electrode active material layer; The positive electrode active material layer is laminated to at least one surface of a positive electrode current collector by hot pressing to obtain a positive electrode sheet.

9. A lithium battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 7, or the positive electrode sheet prepared by the preparation method of the positive electrode sheet according to claim 8.

10. The lithium battery according to claim 9, characterized in that The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is attached to at least one side surface of the negative electrode current collector by hot pressing. The negative electrode active material layer includes a negative electrode active material, a fiberizable binder and a conductive agent.

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