Coating material and lithium battery

Abstract

A coating material and a lithium battery, the coating material is used for coating of a negative electrode sheet, the coating material comprises a carbon material, a metal oxide and a binder, the carbon material, the metal oxide and the binder account for 30-60%, 30-60% and 0-5% (not including 0) of the whole coating material in turn in mass percentage. The coating material can reduce heat accumulation and improve lithium precipitation phenomenon at the tab of the lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to a coating material and a lithium battery. Background Technology

[0002] With the rapid development of new energy vehicles and smart wearable devices, the requirements for the energy density and safety of lithium batteries are constantly increasing. However, lithium batteries still face many challenges, especially under fast charging and high-temperature cycling conditions, where they are prone to safety hazards such as thermal runaway and lithium dendrite formation. During fast charging, the internal heat of the battery is difficult to dissipate in time, leading to a significant increase in the center temperature of the cell, which affects the battery's safety and performance.

[0003] Currently, the tabs of lithium batteries are a critical area for heat accumulation, with high current density, leading to severe lithium plating and heat buildup. These issues not only affect battery lifespan but may also pose safety hazards.

[0004] Therefore, how to improve the lithium plating phenomenon at the electrode tab and reduce heat accumulation has become a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a coating material and a lithium battery. The coating material can reduce heat accumulation and improve lithium plating at the electrode tabs of the lithium battery.

[0006] This invention provides a coating material for coating negative electrode sheets. The coating material includes carbon material, metal oxide and binder. By mass percentage, the carbon material, the metal oxide and the binder account for 30-60%, 30-60% and 0-5% (excluding 0%) of the total coating material, respectively.

[0007] Furthermore, the carbon material is one or more of carbon nanotubes, keratin black, graphene, and carbon black; the metal oxide is one or more of manganese, cobalt, nickel, and copper oxides; and the binder is one or more of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, cross-linked polyacrylate, polyimide, polythiophene derivative, and polyaniline.

[0008] Furthermore, the coating material also includes a dispersant, which accounts for 0-3% of the coating material by mass percentage.

[0009] Further, the dispersant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, polyethylene glycol, polycarboxylate, polyvinylpyrrolidone, block copolymers, polyurethanes, and polyamides.

[0010] Furthermore, the viscosity of the coating material is 2000-4500 mPa·s.

[0011] The present invention also provides a lithium battery, including a negative electrode sheet, wherein a first end connected to a negative electrode tab and a second end corresponding to the first end are formed on the negative electrode sheet, and the first end of the negative electrode sheet is coated with a coating material as described in any one of the above.

[0012] Furthermore, at the first end of the negative electrode sheet, the thickness of the coating material gradually decreases from the direction near the end face to the direction away from the first end.

[0013] Further, at the first end of the negative electrode sheet, the negative electrode sheet is divided into a first region and a second region according to the distance between the coating position of the negative electrode sheet and the end of the first end of the negative electrode sheet. The first region is located at the first end of the negative electrode sheet, and the second region is connected to the first region and located on the side of the first region away from the first end of the negative electrode sheet. The length of the first region accounts for more than 0% and less than 15% of the length of the entire negative electrode sheet in the first direction; the length of the second region accounts for more than 0% and less than 20% of the length of the entire negative electrode sheet in the first direction. The maximum thickness of the coating material in the first region does not exceed 20 μm, and the maximum thickness of the coating material in the second region does not exceed 10 μm.

[0014] Furthermore, a coating material is applied to the second end of the negative electrode sheet.

[0015] Furthermore, at the second end of the negative electrode sheet, the negative electrode sheet is divided into a third region and a fourth region according to the distance between the coating position and the end face of the second end of the negative electrode sheet. The third region is located at the second end of the negative electrode sheet, and the fourth region is connected to the third region and located on the side of the third region facing the first end of the negative electrode sheet. The length of the third region accounts for more than 0% and less than 15% of the length of the entire negative electrode sheet in the first direction; the length of the fourth region accounts for more than 0% and less than 20% of the length of the entire negative electrode sheet in the first direction. The maximum thickness of the coating material in the third region does not exceed 20 μm, and the maximum thickness of the coating material in the fourth region does not exceed 10 μm. In summary, in this invention, by coating the first end of the negative electrode sheet and optionally coating the second end of the negative electrode sheet, the carbon material can quickly conduct heat, thereby dissipating heat and rapidly heating the metal oxide. As the temperature increases, this can effectively reduce the resistivity of metal oxides, effectively improve kinetic conduction efficiency, reduce ohmic heat, slow down side reactions and metal precipitation at the tab location, and significantly improve the safety and stability of the battery.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The diagram shown is a front view of the structure when the coating material is applied to the negative electrode sheet in an embodiment of the present invention.

[0019] Figure 2 As shown Figure 1 A schematic diagram of the cross-sectional structure. Detailed Implementation

[0020] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. Based on the description of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0021] In the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0022] The terms “upper,” “lower,” “left,” “right,” “front,” “back,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use. They are only for the convenience of description and simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0023] The terms “first,” “second,” “third,” etc., are used merely to distinguish elements with similar properties, not to indicate or imply relative importance or a specific order.

[0024] The terms “include,” “comprising,” or any other variation thereof are intended to cover non-exclusive inclusion, which includes not only the elements listed but also other elements not expressly listed.

[0025] To address the aforementioned problems, this invention provides a coating material and a lithium battery. The coating material can reduce heat accumulation and improve lithium plating at the electrode tabs of the lithium battery.

[0026] The coating material provided in this embodiment of the invention is used for coating negative electrode sheets. The coating material includes carbon material, metal oxide and binder. By mass percentage, carbon material, metal oxide and binder account for 30-60%, 30-60% and 0-5% (excluding 0%) of the total coating material, respectively.

[0027] Furthermore, in this embodiment, the carbon material can be one or more of carbon nanotubes, kexane, graphene, and carbon black. The metal oxide can be one or more of manganese, cobalt, nickel, and copper oxides.

[0028] The adhesive can be one or more of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), cross-linked polyacrylate (CLPA), polyimide, polythiophene derivative and polyaniline.

[0029] Furthermore, to reduce interparticle forces in the dispersion system, prevent agglomeration, and ensure uniform and stable particle dispersion, a dispersant can be added to the coating material. This dispersant can be one or more of the following: sodium dodecylbenzenesulfonate (SDBS), hexadecyltrimethylammonium bromide (CTAB), polyethylene glycol (PEG), polycarboxylates, polyvinylpyrrolidone (PVP), block copolymers, polyurethanes, and polyamides. The dispersant accounts for 0-3% of the total coating material by weight.

[0030] The coating material can exist in the form of a slurry. During preparation, various materials are added to deionized water and stirred to prepare a slurry with good fluidity and a viscosity of 2000-4500 mPa·s. This slurry is then coated onto the end of the negative electrode sheet connected to the negative electrode tab (i.e.,...). Figure 1 (The left end of the negative electrode plate). For ease of understanding, in the following text, the part of the negative electrode tab that protrudes from the negative electrode plate will be called the first end of the negative electrode plate, and the end of the negative electrode plate opposite to the first end will be called the second end (i.e., the left end of the negative electrode plate). Figure 1 The right end of the negative electrode plate, that is, the end of the negative electrode plate that is farthest from the negative electrode tab, is called the second end.

[0031] In other embodiments, the coating material liquid can be simultaneously coated on the second end of the negative electrode sheet (i.e., Figure 1 On the right end of the negative electrode plate. Because the negative and positive electrodes are positioned opposite each other in the battery cell, therefore, as... Figure 1 As shown, the second end of the negative electrode plate corresponds to the end of the positive electrode plate facing the positive electrode tab (in... Figure 2 The dotted line at the right end of the negative electrode plate indicates the positive electrode tab.

[0032] In this coating material, carbon materials can form heat conduction channels, while metal oxides can regulate the lithium ion transport efficiency, and the binder can firmly adhere the carbon materials and metal oxides to the negative electrode sheet.

[0033] The tabs on both sides of the battery cell (also known as dual-ended tab leads) are a core structure that independently leads the positive and negative tabs from two opposite ends of the battery cell casing. They achieve conduction with external circuits through a conductive path of "tab-connecting piece-terminal".

[0034] During operation, due to the current convergence effect, electrode structure matching and electrochemical kinetic characteristics, a significant temperature rise concentration will occur at the end where the negative electrode tab is located and at the end of the negative electrode sheet away from the negative electrode tab, which in turn induces the risk of lithium plating.

[0035] The end containing the negative electrode tab is the "entry point" for electrons to enter the negative current collector from the external circuit, exhibiting a significant current-converging effect. The heat generation intensity and rate are higher than in other areas of the battery cell. The second end of the negative electrode, directly opposite the positive electrode tab, is a region where electrochemical heat generation and ion migration congestion overlap. Although this region lacks a significant current-converging effect, as the "primary landing zone" for lithium ions migrating from the positive to the negative electrode, the enhanced local polarization caused by electrochemical heat generation and ion migration congestion also leads to concentrated temperature rise.

[0036] Therefore, by coating the first end of the negative electrode sheet with this material, and optionally coating the second end, the carbon material can rapidly conduct heat, both dissipating heat and causing the metal oxide to heat up quickly. As the temperature rises, this effectively reduces the resistivity of the metal oxide, significantly improves kinetic conductivity, reduces ohmic heat, slows down side reactions and metal deposition at the tab location, and significantly improves the safety and stability of the battery.

[0037] The preparation of lithium batteries with this coating material can be carried out in the following manner.

[0038] The coating material 31 in the embodiments of the present invention is provided; The coating material 31 is applied to the first end 11 of the negative electrode sheet 10 (that is, the end connected to the negative electrode tab 21).

[0039] During coating, the thickness of the coating material 31 gradually decreases at the first end 11 of the negative electrode 10, from the direction close to the end face of the first end 11 to the direction away from the first end 11.

[0040] After coating is completed, the negative electrode sheet 10 coated with coating material 31 is dried and rolled.

[0041] The negative electrode 10 is combined with the positive electrode to form a lithium battery.

[0042] By varying the coating thickness of the coating material 31, the current density concentration and heat accumulation characteristics at the negative electrode tab 21 position during fast charging can be fully considered, effectively reducing the current density at the negative electrode tab 21 position and slowing down side reactions and metal dissolution.

[0043] The present invention also provides a lithium battery, which includes a negative electrode 10, a first end 11 connected to a negative electrode tab 21 and a second end 12 corresponding to the first end 11 are formed on the negative electrode 10, and a coating material 31 is coated on the first end 11 of the negative electrode 10. The coating material 31 includes carbon material, metal oxide and binder, and by mass percentage, carbon material, metal oxide and binder account for 30-60%, 30-60% and 0-5% (excluding 0) of the total coating material 31, respectively.

[0044] In this embodiment, at the first end 11 of the negative electrode 10, the negative electrode 10 is divided into a first region and a second region according to the distance between the coating position of the negative electrode 10 and the end of the first end 11 of the negative electrode 10. That is, the first region is in contact with the first end 11 of the negative electrode 10, and the second region is in contact with the first region and located on the side of the first region away from the first end 11. The first region is located between the first end 11 and the second region of the negative electrode 10. The length of the first region (i.e., Figure 1 L1), occupying the first direction of the entire negative electrode plate 10 (i.e. Figure 1 The length of the second region (in the left-right direction on the paper), that is, the distance from the first end 11 to the second end 12 of the negative electrode plate 10, is greater than 0 and less than or equal to 15%. Figure 1 The length of L2 in the first direction of the entire negative electrode plate 10 is greater than 0 and less than or equal to 20%.

[0045] Understandably, the thickness of the coating material 31 in the second region will be less than the thickness of the coating material 31 in the first region. The maximum thickness (H1) of the coating material 31 in the first region does not exceed 20 μm, while the maximum thickness (H2) of the coating material 31 in the second region does not exceed 10 μm.

[0046] Furthermore, a coating material 31 is also coated on the second end 12 of the negative electrode 10. For example... Figure 2 As shown, similarly, the coating thickness gradually decreases from the direction near the end face of the second end 12 to the direction away from the second end 12.

[0047] In this embodiment, at the second end 12 of the negative electrode 10, the negative electrode 10 can be divided into a third region and a fourth region according to the distance from the coating position of the negative electrode 10 to the end face of the second end 12 of the negative electrode 10. That is, the third region is located at the end of the second end 12 of the negative electrode 10, and the fourth region is in contact with the third region and is located on the side of the third region facing the first end 11 of the negative electrode 10.

[0048] The length of the third region (i.e.) Figure 1 The length of region L3 (in the first direction) of the entire negative electrode plate 10 is greater than 0 and less than or equal to 15%. The length of the fourth region (i.e.,...) Figure 1 The portion L4 (in the middle) occupies a length in the first direction of the entire negative electrode 10 that is greater than 0 and less than or equal to 20%. That is, when both the first end 11 and the second end 12 of the negative electrode 10 are coated with coating material 31, there is an uncoated area in the middle of the negative electrode 10. Please refer to... Figure 1 A first region, a second region, an uncoated region, a fourth region, and a third region are sequentially formed on the negative electrode sheet 10.

[0049] Understandably, the thickness of the coating material 31 in the fourth region will be less than the thickness of the coating material 31 in the third region. The maximum thickness (H3) of the coating material 31 in the third region does not exceed 20 μm, while the maximum thickness (H4) of the coating material 31 in the fourth region does not exceed 10 μm.

[0050] Preferably, the length and coating thickness of the third region are the same as those of the first region; the length and coating thickness of the fourth region are the same as those of the second region.

[0051] For ease of description, in this invention, when only the first end 11 of the negative electrode 10 is coated, it is called single-end coating. When both the first end 11 and the second end 12 of the negative electrode 10 are coated simultaneously, it is called double-end coating. Regardless of whether it is single-end or double-end coating, during coating, the coating material 31 will be present on both the upper and lower surfaces of the negative electrode 10.

[0052] The following specific examples illustrate the coating materials and coating process described above: Example 1: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1% and stirred to prepare a slurry with good fluidity at a viscosity of 3000 mPa·s.

[0053] 2. The slurry is coated onto the negative electrode sheet, with coating applied to both ends. The coating height and length are as follows: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0054] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0055] Example 2: 1. Carbon nanotubes, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1% and stirred to prepare a slurry with good fluidity at a viscosity of 3000 mPa·s.

[0056] 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0057] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0058] Example 3: 1. Graphene, cobalt oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0059] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0060] Example 4: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to one end, and the coating height and length are as follows: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0061] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0062] Example 5: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.2L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0063] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0064] Example 6: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1 = 0.15L, L2 = 0.1L; H1 = 10µm, H2 = 5µm. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0065] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0066] Example 7: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 36%:60%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0067] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0068] Example 8: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 60%:36%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0069] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0070] Example 9: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 4000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1 = 0.15L, L2 = 0.1L; H1 = 15µm, H2 = 5µm. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0071] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0072] Example 10: 1. Graphene, manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 48%:48%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 4500 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1 = 0.15L, L2 = 0.1L; H1 = 10µm, H2 = 3µm. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0073] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0074] Comparative Example 1: 1. Without applying any coating material, the battery was made directly using basic electrode sheets as a blank control to verify the core function of the coating; Comparative Example 2: 1. Graphene, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 96%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0075] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0076] Comparative Example 3: 1. Manganese oxide, SBR binder, CMC binder, and dispersant were added to deionized water in a ratio of 96%:2%:1%:1%, and stirred to prepare a slurry with good fluidity and a viscosity of 3000 mPa·s. 2. A slurry is prepared and coated onto the negative electrode slurry. The coating is applied to both ends, with the following coating heights and lengths: L1=0.1L, L2=0.1L; H1=10um, H2=5um. The length and coating thickness of L3 are the same as L1, and the length and coating thickness of L4 are the same as L2. After drying and rolling, the negative electrode sheet for lithium batteries is formed.

[0077] 3. A lithium battery is prepared by combining a conventional positive electrode and the negative electrode provided in this embodiment.

[0078] Table 1: Battery parameters for each embodiment and comparative example

[0079] Table 2: Temperature rise (ΔT) at different magnification ratios for each embodiment and comparative example

[0080] Table 3: Capacity retention and lithium plating of each example and comparative example after 800 cycles at 45°C 1C / 1C:

[0081] As can be seen from Table 2, compared with Comparative Example 1, the lithium batteries prepared in Examples 1 to 10 have lower temperature rise at different rates, indicating that the addition of coating materials can reduce the heat generation of lithium batteries under high-rate charging and discharging conditions and prevent the lithium battery temperature from becoming too high.

[0082] As can be seen from Table 3, compared with Comparative Examples 1, 2 and 3, the lithium batteries prepared in Examples 1 to 10 have a higher capacity retention rate at 45℃ and 1C / 1C cycling, and a relatively smaller lithium deposition area. This indicates that the lithium batteries prepared in Examples 1 to 10 can reduce heat generation by lowering resistivity under high-temperature cycling conditions, effectively solving the problem of heat accumulation in lithium batteries under high-temperature cycling conditions, and thus improving the lithium deposition problem at the tab position.

[0083] According to Examples 1, 2, and 3, changing the types of carbon materials and metal oxides affects the temperature rise, capacity retention, and lithium plating area of ​​the cell. According to Examples 1 and 4, single-end coated negative electrode sheets are less effective at reducing lithium plating compared to double-end coated negative electrode sheets. According to Examples 1, 5, and 6, by adjusting the length ratio of region L1 to region L2, the optimal L1 / L2 ratio can be found, thereby controlling the capacity retention and temperature change of the electrode within a certain range. According to Examples 1, 7, and 8, by adjusting the ratio of carbon materials to metal oxides, the optimal ratio can be found, thereby controlling the capacity retention and DCR growth rate of the electrode within a certain range. According to Examples 1, 9, and 10, by adjusting the height ratio of region L1 to region L2, the optimal values ​​of H1 and H2 can be found, thereby controlling the temperature rise and lithium plating of the electrode at different rate ratios within a certain range.

[0084] The test results above show that by using a 1:1 ratio of carbon material (thermally conductive structure) and metal oxide (ion conduction regulation), both temperature drop and ion distribution optimization can be achieved. Double-end coating enhances overall temperature control, and the gradient of the tab connection area and current diffusion area is set to match the current density distribution. This can effectively solve the problem of heat accumulation in lithium batteries under fast charging and high-temperature cycling conditions, as well as the side reactions and lithium plating problems at the tab position.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A coating material, characterized in that: For coating negative electrode sheets, the coating material includes carbon material, metal oxide and binder, and by mass percentage, the carbon material, the metal oxide and the binder account for 30-60%, 30-60% and 0-5% (excluding 0) of the total coating material, respectively.

2. The coating material according to claim 1, characterized in that: The carbon material is one or more of carbon nanotubes, kojel black, graphene, and carbon black; the metal oxide is one or more of manganese, cobalt, nickel, and copper oxides; and the binder is one or more of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, cross-linked polyacrylate, polyimide, polythiophene derivative, and polyaniline.

3. The coating material according to claim 1, characterized in that: The coating material also includes a dispersant, which accounts for 0-3% of the coating material by mass percentage.

4. The coating material according to claim 3, characterized in that: The dispersant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, polyethylene glycol, polycarboxylate, polyvinylpyrrolidone, block copolymers, polyurethanes, and polyamides.

5. The coating material according to claim 1, characterized in that: The viscosity of the coating material is 2000-4500 mPa·s.

6. A lithium battery, characterized in that: The device includes a negative electrode sheet, on which a first end connected to a negative electrode tab is formed, and a second end corresponding to the first end is formed. The first end of the negative electrode sheet is coated with a coating material as described in any one of claims 1 to 5.

7. The lithium battery according to claim 6, characterized in that: At the first end of the negative electrode sheet, the thickness of the coating material gradually decreases from the direction close to the end face to the direction away from the first end.

8. The lithium battery according to claim 6, characterized in that: At the first end of the negative electrode sheet, the negative electrode sheet is divided into a first region and a second region according to the distance between the coating position of the negative electrode sheet and the end of the first end of the negative electrode sheet. The first region is located at the first end of the negative electrode sheet, and the second region is connected to the first region and located on the side of the first region away from the first end of the negative electrode sheet. The length of the first region accounts for more than 0% and less than 15% of the length of the entire negative electrode sheet in the first direction; the length of the second region accounts for more than 0% and less than 20% of the length of the entire negative electrode sheet in the first direction. The maximum thickness of the coating material in the first region does not exceed 20 μm, and the maximum thickness of the coating material in the second region does not exceed 10 μm.

9. The lithium battery according to claim 7, characterized in that: A coating material is applied to the second end of the negative electrode sheet.

10. The lithium battery according to claim 8, characterized in that: At the second end of the negative electrode sheet, the negative electrode sheet is divided into a third region and a fourth region according to the distance between the coating position of the negative electrode sheet and the end face of the second end of the negative electrode sheet. The third region is located at the second end of the negative electrode sheet, and the fourth region is connected to the third region and located on the side of the third region facing the first end of the negative electrode sheet. The length of the third region accounts for more than 0% and less than 15% of the length of the entire negative electrode sheet in the first direction; the length of the fourth region accounts for more than 0% and less than 20% of the length of the entire negative electrode sheet in the first direction. The maximum thickness of the coating material in the third region does not exceed 20 μm, and the maximum thickness of the coating material in the fourth region does not exceed 10 μm.

Images