Pre-lithiated negative electrode sheet and lithium-ion battery and preparation method

Abstract

The application belongs to the field of lithium ion batteries, and particularly relates to a pre-lithiated negative electrode sheet and a lithium ion battery and a preparation method. The method comprises the following steps: dispersing a negative electrode active material, a conductive agent and a binder in a solvent to obtain a negative electrode slurry; coating the obtained negative electrode slurry on a negative electrode current collector, drying and rolling to obtain a rolled negative electrode sheet; and rolling the rolled negative electrode sheet, an ultrathin lithium film and a heat-conducting material again to obtain a pre-lithiated negative electrode. The technical scheme of the application can effectively absorb a large amount of heat generated in the pre-lithiation process by covering the heat-conducting material on the surface of the ultrathin lithium film, can significantly improve the pre-lithiation effect, ensure the activity of the lithium film, improve the initial efficiency and energy density of the battery, and greatly reduce the heat generation in the pre-lithiation process, thereby improving the safety of the battery preparation process.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a pre-lithiated negative electrode, a lithium-ion battery, and a preparation method thereof. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, wide operating temperature range, and long cycle life, have been widely used in aerospace, electronic equipment, computers, and new energy vehicles. However, with social development and technological progress, especially the widespread adoption of new energy vehicles in recent years, people have increasingly higher requirements for the energy density of lithium batteries, and the range anxiety problem urgently needs to be addressed. Traditional graphite anode lithium-ion batteries are insufficient to meet the expectations of social development, so there is an urgent need to develop positive and negative electrode materials with higher specific capacity.

[0003] Silicon-based anode materials have extremely high specific capacity. When silicon is alloyed with lithium at room temperature, the theoretical specific capacity can reach as high as 4200 mAh / g. However, silicon-based anodes have poor initial efficiency and cycle performance, resulting in low initial efficiency of the full cell, which in turn damages the capacity and energy density of the battery.

[0004] Currently, the pre-lithiation method for the negative electrode involves attaching lithium foil to the surface of the negative electrode sheet by rolling. Since lithium metal is relatively reactive, the pre-lithiation process generates a lot of heat, which affects the lithium replenishment effect, thereby degrading the battery performance and causing safety issues.

[0005] For the negative electrode, pre-lithiation can improve the first-efficiency of the entire battery, thereby increasing the battery capacity and energy density. This invention first addresses the problem of low first-efficiency of silicon-oxygen or silicon-carbon negative electrodes in existing high-energy-density systems. Secondly, the current method of negative electrode pre-lithiation involves attaching lithium foil to the surface of the negative electrode sheet by rolling. Because lithium metal is relatively reactive, the pre-lithiation process generates a lot of heat, affecting the lithium replenishment effect and thus degrading battery performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a pre-lithiated negative electrode, a lithium-ion battery, and a method for their preparation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a pre-lithiated anode includes the following steps:

[0009] Step (1): Disperse the negative electrode active material, conductive agent, and binder in a solvent to obtain a negative electrode slurry;

[0010] Step (2): The negative electrode slurry obtained in step (1) is coated onto the negative electrode current collector, dried, and rolled to obtain the rolled negative electrode sheet;

[0011] Step (3) involves rolling the rolled negative electrode sheet, ultrathin lithium film, and thermally conductive material obtained in step (2) again to obtain a pre-lithiated negative electrode.

[0012] Step (4) Roll up the pre-lithiated negative electrode together; after letting it stand for a period of time, extract the thermally conductive material and complete the negative electrode slicing. Preferably, the standing time is set to 3-24h, and preferably, the standing time is ≥6h.

[0013] Preferably, the thickness of the ultrathin lithium film in step (3) is 0.5-10 micrometers.

[0014] Preferably, the thermally conductive material in step (3) is one or a mixture of thermally conductive silicone, thermally conductive insulating adhesive, heat dissipation gel, thermally conductive graphite sheet, thermally conductive carbon nanotubes, thermally conductive graphene, or phase change material.

[0015] For the full-area heat dissipation method using thermally conductive materials, in step (3), the thermally conductive material is placed in the middle of the surface of the ultrathin lithium film, with the extension direction of the negative electrode sheet as the length direction; the width of the negative electrode sheet coating area is W. q1 60mm≤W q1 ≤340mm, width W of thermally conductive material q2 ,20mm≤W q2 ≤340mm; Width W of ultrathin lithium film q3 , for 60mm≤W q3 ≤340mm; preferably, W q2 =1 / 3-2 / 3W q3 .

[0016] For the strip-shaped heat dissipation method, in step (3), the heat-conducting material is placed in a strip shape on the surface of the full-area ultrathin lithium film; the extension direction of the negative electrode sheet is taken as the length direction; the width of the negative electrode sheet coating area is W. t1 60mm≤W t1 ≤340mm, width W of thermally conductive material t2 5mm≤W t2 ≤20mm; Width W of ultra-thin lithium film t3 60mm≤W t3 ≤340mm, the width W between adjacent thermally conductive materials t4 5mm≤W t4 ≤20mm; preferably, 10mm≤W t2 ≤20mm; 5mm≤W t4 ≤10mm.

[0017] The negative electrode active material mentioned in step (1) includes one or a mixture of graphite, silicon oxide, and silicon carbon.

[0018] The present invention also includes a pre-lithiated negative electrode sheet obtained by the preparation method described above, comprising a negative electrode current collector, a negative electrode active layer disposed on both sides of the negative electrode current collector, an ultrathin lithium film disposed on the outside of the negative electrode active layer, and a thermally conductive material layer disposed on the outside of the ultrathin lithium film.

[0019] The present invention also includes a lithium-ion battery comprising the aforementioned pre-lithiated negative electrode.

[0020] The present invention also includes a method for preparing the lithium-ion battery, comprising the following steps:

[0021] In a dry environment, the positive electrode sheet, the pre-lithiated negative electrode sheet, and the separator are wound or stacked into an electrode assembly in a certain order; the obtained electrode assembly is then welded with tabs, packaged, and short-circuited tested; and the liquid injection, formation, and aging processes are completed.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] The technical solution of this application effectively absorbs the large amount of heat dissipated during the pre-lithiation process by covering the surface of the ultra-thin lithium film with thermally conductive material. This significantly improves the pre-lithiation effect, ensures the activity of the lithium film, and enhances the battery's initial efficiency and energy density. Simultaneously, it drastically reduces heat generation during the pre-lithiation process, improving the safety of the battery manufacturing process. In a preferred embodiment, the pre-lithiated negative electrode is rolled up after being rolled; after a period of rest, the thermally conductive material is extracted, allowing for reuse. Furthermore, the application area of ​​the thermally conductive material can be optimized for both full-area and strip-shaped heat dissipation methods. This approach effectively absorbs the large amount of heat dissipated while conserving the area of ​​the thermally conductive material used, thus reducing costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the heat dissipation method of the full-area thermally conductive material in Example 1;

[0025] Figure 2 This is a schematic diagram of the heat dissipation method of the strip-shaped thermal conductive material in Example 2;

[0026] Figure 3 This is a schematic diagram of the pre-lithiated negative electrode sheet in the embodiment;

[0027] Figure 4 The graph shows the capacity retention rate during room temperature cycling for Examples 1, 2, and the comparative examples. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0029] Example 1

[0030] The preparation of a lithium-ion battery includes the following steps: Step (1), preparation of the positive electrode sheet: NCM is used as the positive electrode active material, and it is dispersed in NMP solution according to the ratio of active material: conductive agent: single-walled carbon nanotubes: glue = 97.4:0.6:0.8:1.2, and stirred and dispersed thoroughly. The positive electrode slurry obtained above is uniformly coated on aluminum foil (thickness 10μm) in a certain order and with a certain thickness, and the coating surface density is 43mg / cm. 2 The positive electrode sheet is completely dried at 110-115℃, and then rolled under a certain pressure to a density of 3.5 g / cm³. 3 Then, the processes of slicing, dust removal, and baking are completed to obtain the positive electrode sheet.

[0031] Step (2), Preparation of the pre-lithiated negative electrode: Commercial graphite and silicon suboxide were used as the negative electrode active materials, with silicon suboxide accounting for 20% of the total active material mass. The active material: multi-walled carbon nanotubes: single-walled carbon nanotubes: gel = 96.9:0.5:0.1:2.5 were dispersed in an aqueous solution and thoroughly stirred. The obtained slurry was then uniformly coated onto a copper foil (6 μm thick) in a specific order and with a coating surface density of 15.6 mg / cm². 2 The negative electrode sheet is completely dried at 110-115℃, and then rolled under a certain pressure to a density of 1.65 g / cm³. 3 The rolled negative electrode sheet (coating area width W) q1 (140mm), ultra-thin lithium film (5μm thickness, W width) q3 The 140mm thick thermally conductive phase change film material (which uses PET polyethylene terephthalate as the base film on both sides, with a microcapsule containing a phase change material in the middle, the outer shell being silica and the core material being disodium hydrogen phosphate dodecahydrate, a commercially available product) is rolled and wound together again (e.g.) Figure 3 (As shown) full-area pre-lithiation is performed, ( Figure 1 (A schematic diagram is shown), the pre-lithiation length is in the direction of the negative electrode, and the width W of the thermally conductive material is... q2 The diameters are 70mm, 90mm, 110mm, and 140mm; after resting for 12 hours, the negative electrode sheets are stamped and dust removed under a dry atmosphere to obtain a pre-lithiated negative electrode sheet with a full-area thermal conductive material heat dissipation method; the pre-lithiated negative electrode sheet includes a negative electrode sheet 1, an ultra-thin lithium film 2 disposed on the outside of the negative electrode sheet 1, and a thermal conductive material layer 3 disposed on the outside of the ultra-thin lithium film. The negative electrode sheet 1 includes a negative electrode current collector and negative electrode active layers disposed on both sides of the negative electrode current collector; after testing, the width W of the thermal conductive material is... q2The microcapsule phase change film of this embodiment with a width of 70 mm or greater can complete the heat dissipation function, improve the pre-lithiation effect, ensure the activity of the lithium film, and improve the battery's first efficiency and energy density. However, different thermally conductive materials, such as thermally conductive silicone, thermally conductive insulating adhesive, heat dissipation gel, thermally conductive graphite sheet, thermally conductive nano-carbon, thermally conductive graphene, etc., have different thermal conductivity and heat dissipation efficiency. The width of the thermally conductive material can be adjusted according to the type of thermally conductive material. In this application, the width of 70 mm in Example 1 is used as an example for illustration. As a preferred form, the thermally conductive material is placed in the middle of the negative electrode sheet, which is conducive to the completion of heat dissipation.

[0032] Meanwhile, due to the varying widths of the coating area on the negative electrode, typically 60mm≤W q1 ≤340mm, width W of ultra-thin lithium film q3 Adjustments can be made simultaneously; and the width W of the thermally conductive material q2 Typically, the width W of an ultrathin lithium film q3 One-third to two-thirds of the volume is sufficient to complete the heat dissipation function.

[0033] Step (3): In a dry environment, the positive electrode, the pre-lithiated negative electrode, and the separator are wound or stacked into an electrode assembly in a certain order; the obtained electrode assembly is welded with tabs, packaged, and short-circuited; the liquid injection, formation, and aging processes are completed to obtain a soft-pack battery.

[0034] Example 2

[0035] The preparation of a lithium-ion battery includes the following steps: step (1) preparation of the positive electrode and step (3) assembly of the pouch cell are the same as in Example 1.

[0036] Step (2), Preparation of the pre-lithiated negative electrode: Commercial graphite and silicon suboxide were used as the negative electrode active materials, with silicon suboxide accounting for 20% of the total active material mass. The active material: multi-walled carbon nanotubes: single-walled carbon nanotubes: gel = 96.9:0.5:0.1:2.5 were dispersed in an aqueous solution and thoroughly stirred. The obtained slurry was then uniformly coated onto a copper foil (6 μm thick) in a specific order and with a coating surface density of 15.6 mg / cm². 2 The negative electrode sheet is completely dried at 110-115℃, and then rolled under a certain pressure to a density of 1.65 g / cm³. 3 The rolled negative electrode sheet, ultrathin lithium film, and thermally conductive phase change film material are rolled again and wound together, wherein the width of the electrode coating area is W. t1 =140mm, ultra-thin lithium film thickness 5μm, width is W t2 =140mm, strip-shaped phase change thin film material (the phase change thin film material is the same as in Example 1), width W t3The widths W between adjacent phase change thin film materials are 5mm, 10mm, 15mm, and 20mm. t4 The thickness is 10mm. After resting for 12 hours, the negative electrode sheet is stamped and dusted under a dry atmosphere.

[0037] After testing, for heat dissipation using strip-shaped thermal conductive materials, the width W of the strip-shaped thermal conductive material... t2 An ultrathin lithium film with a width of W can be achieved using a 10mm microcapsule phase change film. t1 The negative electrode sheet with a diameter of 140 mm and a thickness of 5 μm has the function of heat dissipation, improving the pre-lithiation effect, ensuring the activity of the lithium film, and improving the battery's first efficiency and energy density. Therefore, it is illustrated by way of example. However, for different thermally conductive materials, such as thermally conductive silicone, thermally conductive insulating adhesive, heat dissipation gel, thermally conductive graphite sheet, thermally conductive carbon nanotubes, thermally conductive graphene, etc., their thermal conductivity and heat dissipation efficiency are different. The width and distribution of the thermally conductive material can be adjusted according to the type of thermally conductive material. In this application, the width of 10 mm in Example 2 is used as an example for illustration.

[0038] Meanwhile, due to the width W of the negative electrode coating area t1 Different, usually 60mm≤W t1 ≤340mm, width W of ultra-thin lithium film t3 Different, usually 60mm≤W t3 ≤340mm, width W of thermally conductive material t2 Simultaneous adjustments are possible, such as the width W of the thermally conductive material. t2， 5mm≤W t2 ≤20mm; Width W between adjacent thermally conductive materials t4 5mm≤W t4 ≤20mm; typically, the width of thermally conductive materials is 10mm ≤W t2 ≤20mm, width between adjacent thermally conductive materials 5mm≤W t4 A thickness of ≤10mm is sufficient to achieve better heat dissipation.

[0039] Comparative Example

[0040] Step (1) is the same as in Example 1;

[0041] Step (2): The negative electrode sheet is prepared in the same way as in Example 1. Then, the rolled negative electrode sheet and the ultrathin lithium film (thickness 5μm, width 140mm) are rolled together and left to stand for 12h.

[0042] Step (3) is the same as in Example 1;

[0043] The improved lithium film replenishment method is significantly more effective than the traditional lithium film replenishment method, and it effectively solves the heat generation problem of pre-lithiation. Figure 4As shown, compared with the comparative example, when the pouch battery prepared by the improved lithium film replenishment method achieves a room temperature cycle capacity retention rate of 80%, the number of cycles in Examples 1 and 2 is increased by 34.8% and 40.6% respectively compared with the comparative example.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a pre-lithiated negative electrode, characterized in that, Includes the following steps: Step (1): Disperse the negative electrode active material, conductive agent, and binder in a solvent to obtain a negative electrode slurry; Step (2): The negative electrode slurry obtained in step (1) is coated onto the negative electrode current collector, dried, and rolled to obtain the rolled negative electrode sheet; Step (3): The rolled negative electrode sheet obtained in step (2), the ultrathin lithium film set on both sides of the negative electrode sheet, and the thermally conductive material set on both sides of the ultrathin lithium film away from the negative electrode sheet are rolled again to obtain a pre-lithiated negative electrode; the thermally conductive material is one or a mixture of thermally conductive silicone, thermally conductive insulating adhesive, thermally conductive graphite sheet, thermally conductive nano carbon, and thermally conductive graphene. For the full-area heat dissipation method using thermally conductive materials, in step (3), the thermally conductive material is placed in the middle of the surface of the ultrathin lithium film, with the extension direction of the negative electrode sheet as the length direction; the width of the negative electrode sheet coating area is W. q1 60 mm≤W q1 ≤340mm, width W of ultra-thin lithium film q3 60mm≤W q3 ≤340mm; Width W of thermally conductive material q2 ,20mm≤W q2 ≤340mm; For the strip-shaped heat dissipation method, in step (3), the heat-conducting material is placed in a strip shape on the surface of the full-area ultrathin lithium film; the extension direction of the negative electrode sheet is taken as the length direction; the width of the negative electrode sheet coating area is W. t1 60 mm≤W t1 ≤340mm, width W of thermally conductive material t2 5mm≤W t2 ≤20mm; Width W of ultra-thin lithium film t3 60mm≤W t3 ≤340mm, the width W between adjacent thermally conductive materials t4 5mm≤W t4 ≤20mm; Step (4): The pre-lithiated negative electrode obtained in step (3) is rolled up together; after being left to stand for a period of time, the thermally conductive material is extracted and the negative electrode is sliced. The standing time is set to 3-24h.

2. The method for preparing the pre-lithiated negative electrode according to claim 1, characterized in that, In step (4), the resting time is ≥6h.

3. The method for preparing the pre-lithiated negative electrode according to claim 1, characterized in that, The thickness of the ultrathin lithium film mentioned in step (3) is 0.5-10 micrometers.

4. The method for preparing the pre-lithiated negative electrode according to claim 1, characterized in that, IN q2 =1 / 3-2 / 3 W q3 。 5. The method for preparing the pre-lithiated negative electrode according to claim 1, characterized in that, 10mm≤W t2 ≤20mm ;5mm≤W t4 ≤10mm。 6. The method for preparing the pre-lithiated negative electrode according to claim 1, characterized in that, The negative electrode active material mentioned in step (1) includes one or a mixture of graphite, silicon oxide, and silicon carbon.

7. A pre-lithiated negative electrode sheet obtained by the preparation method according to any one of claims 1-6, characterized in that, It includes a negative electrode sheet, an ultrathin lithium film disposed on the outer side of the negative electrode sheet, and a thermally conductive material layer disposed on the outer side of the ultrathin lithium film; the negative electrode sheet includes a current collector and a negative electrode active layer disposed on both sides of the negative electrode current collector.

8. A lithium-ion battery, characterized in that, Including the pre-lithiated negative electrode sheet as described in claim 7.

9. A method for preparing a lithium-ion battery according to claim 8, characterized in that, The process includes the following steps: In a dry environment, the positive electrode sheet, the pre-lithiated negative electrode sheet, and the separator are wound or stacked into an electrode assembly in a certain order; the obtained electrode assembly is welded with tabs, packaged, and short-circuited tested; and the liquid injection, formation, and aging processes are completed.

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