Pre-lithiation double-layer graphite negative electrode, and preparation method and application thereof

Abstract

The application provides a pre-lithiated double-layer graphite negative electrode and a preparation method and application thereof. An upper layer of the double-layer graphite negative electrode close to a separator side is constructed with straight-through channels along the thickness direction of the electrode by a plasma etching technology, which provides uniform lithium intercalation channels for lithium metal pre-lithiation; a lower layer close to a current collector side maintains a dense packing structure, which guarantees high surface capacity and high energy density. The straight-through channels effectively promote the uniform transmission of lithium ions in the electrode, and avoid the growth of lithium dendrites caused by local over-lithiation. When the double-layer graphite negative electrode is applied to a lithium ion battery, the pre-lithiation uniformity and initial coulomb efficiency can be significantly improved, while high energy density, long cycle life and use safety are also considered, and the process is compatible with the existing roll-to-roll production line, and has the feasibility of large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of battery anode manufacturing technology, specifically relating to a pre-lithiated bilayer graphite anode, its preparation method, and its application. Background Technology

[0002] With the rapid development of power batteries and energy storage batteries, there is an urgent need to develop lithium-ion batteries that combine high energy density, high power density, and long lifespan. Graphite anode is currently the most commonly used anode material in lithium-ion batteries. During the first charge and discharge of a lithium-ion battery, the surface of the anode reacts with the electrolyte to form a solid electrolyte interface (SEI) film. This process irreversibly consumes some active lithium. For graphite anodes, the initial coulombic efficiency (ICE) is typically only 85%–95%, meaning that 5%–15% of the active lithium is deactivated during the first cycle, leading to a decrease in the actual energy density of the battery. Pre-lithiation technology, by pre-supplementing the anode with an additional lithium source, can effectively compensate for the aforementioned loss of active lithium, improving the initial coulombic efficiency and energy density of the battery. Furthermore, the SEI film may repeatedly rupture and regenerate during subsequent cycles, continuously consuming active lithium and electrolyte, leading to battery capacity decay and shortened cycle life. Pre-lithiation technology, by stabilizing the electrode-electrolyte interface in advance, reduces the irreversible consumption of lithium during cycling, thereby effectively extending the battery's lifespan.

[0003] Currently, pre-lithiation methods mainly include direct lithium metal contact, electrochemical pre-lithiation, lithium powder addition, and lithium-rich compound doping. Among these, direct lithium metal contact pre-lithiation has attracted widespread attention due to its high lithium replenishment efficiency and relatively simple operation. However, during lithium metal pre-lithiation, the dense structure and uneven pore distribution of traditional graphite anodes lead to significant non-uniformity in lithium intercalation on the anode surface, easily resulting in localized over-lithiation or under-lithiation. Localized over-lithiation regions, exceeding the lithium intercalation capacity limit of graphite, can cause metallic lithium to precipitate on the anode surface, forming lithium dendrites, increasing the risk of short circuits within the battery, and posing serious safety hazards. Therefore, achieving uniform lithium distribution in the graphite anode while ensuring pre-lithiation efficiency is the core challenge currently facing pre-lithiation technology. Summary of the Invention

[0004] In view of this, the present invention provides a graphite anode structure that can achieve efficient and uniform pre-lithiation, which improves the initial coulombic efficiency and energy density of the battery while taking into account cycle life and safety of use, and meets the engineering requirements for large-scale production.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A pre-lithiated bilayer graphite anode, wherein the upper layer of the bilayer graphite anode near the separator side has a through-hole along the electrode thickness direction; and the lower layer near the current collector side has a close-packed structure. The upper and lower layers of the double-layer graphite negative electrode are both composed of graphite slurry, which is prepared by mixing graphite, thickener, binder, conductive agent and water.

[0006] Furthermore, the diameter of the through-holes in the upper layer is 1~100μm, and the areal density is 10~10000 per cm³. 2 The depth is 10% to 90% of the thickness of the double-layer graphite anode.

[0007] Preferably, the diameter of the through-holes in the upper layer is 5~50μm, and the areal density is 100~3000 per cm. 2 The depth is 30% to 80% of the thickness of the double-layer graphite anode.

[0008] In some specific embodiments, preferably, the diameter of the through-holes in the upper layer is 10 μm, and the areal density is 1000 per cm³. 2 The depth is 60% of the thickness of the double-layer graphite anode.

[0009] Furthermore, the graphite D50 is 15~20μm; The mass ratio of graphite, thickener, binder and conductive agent in the graphite slurry is (60-99):(0-10):(1-20):(1-20).

[0010] Preferably, the mass ratio of graphite, thickener, binder and conductive agent in the graphite slurry is (90~99):(0~2.5)(1~5):(1~5).

[0011] In some specific embodiments, preferably, the graphite D50 is 15 μm; The mass ratio of graphite, thickener, binder, and conductive agent in the graphite slurry is 96.3:1.35:1:1.

[0012] Furthermore, the graphite includes at least one of natural graphite and artificial graphite; The thickeners include sodium carboxymethyl cellulose, xanthan gum, guar gum, hydroxyethyl cellulose, starch, and carrageenan; The adhesives include water-based adhesives such as styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, and LA133, and oil-based adhesives such as polytetrafluoroethylene and polyvinylidene fluoride. The conductive agents include 0-dimensional, 1-dimensional, and 2-dimensional conductive agents such as carbon black, Ketjen black, carbon fiber, carbon nanotubes, and graphene.

[0013] A method for preparing the above-mentioned double-layer graphite anode includes the following steps: S1. Dissolve graphite, thickener, binder and conductive agent in deionized water and disperse evenly to obtain graphite slurry; S2. Using a slit coating equipment, graphite slurry is evenly coated onto the current collector to obtain a wet film, which is then dried and rolled to obtain a negative electrode sheet. S3. The upper layer of the negative electrode sheet is etched using a plasma etching device to form a through-hole, while the lower layer maintains its close-packed structure, thus obtaining the double-layer graphite negative electrode.

[0014] Furthermore, the solid content of the graphite slurry in step S1 is 30-60%.

[0015] In some specific embodiments, preferably, the solid content of the graphite slurry is 46-52%.

[0016] Furthermore, in step S2, the electrode loading during coating is 8~10 mg / cm³. -2 ; Drying conditions: temperature 50~100℃, time 1~24h; The compacted density of the electrode after roller pressing is 1.0~2.0 g / cm³. -3 .

[0017] Preferably, the drying conditions are: temperature 60~80℃, time 5~10h; the compacted density of the electrode after roller pressing is 1.4~1.7g / cm³. -3 .

[0018] In some specific embodiments, preferably, the electrode loading is 9 mg / cm³ during coating in step S2. -2 Drying conditions: temperature 80℃, time 8h; the compacted density of the electrode after roller pressing is 1.5g / cm³. -3 .

[0019] Furthermore, the etching gas source in step S3 includes at least one of Ar, O2, CF4, and SF6; Etching conditions: power 50~500W, time 10s~30min.

[0020] In some specific embodiments, the preferred etching conditions are: power 200W, time 5min.

[0021] The above-mentioned double-layer graphite anode is used in the preparation of power batteries and energy storage batteries that require lithium metal contact pre-lithiation treatment.

[0022] A lithium-ion battery comprising the aforementioned double-layer graphite anode.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The double-layer graphite anode design proposed in this invention uses plasma etching technology to directionally construct through-channels on the upper layer of the coated electrode, forming a gradient structure of "multi-porous conduction in the upper layer and dense energy storage in the lower layer". The through-channels in the upper layer significantly improve the transport efficiency of lithium ions in the electrode thickness direction, reduce the electrolyte wetting resistance, provide a uniform lithium intercalation channel for lithium metal pre-lithiation, effectively avoid local overlithiation and underlithiation, and fundamentally suppress the growth of lithium dendrites; the densely packed structure in the lower layer ensures the high compaction density and high areal capacity of the electrode, maintaining the overall energy density of the battery. Compared with low-torsion electrode preparation processes such as ice template method and magnetic template method, this invention uses plasma etching technology, which is mature, has controllable parameters, is compatible with existing roll-to-roll production lines, and has engineering feasibility for large-scale mass production.

[0024] (2) While improving the uniformity and efficiency of pre-lithiation, this invention also takes into account high energy density (0.1C capacity is 3.35~3.46mAh, 1C capacity is 2.7~2.87mAh, 2C capacity is 2.28~2.47mAh), long cycle life (first-cycle coulombic efficiency is 97.5~98.2%, and the capacity retention rate after 2000 cycles at 1C is 74.3~83.2%) and safety of use, providing a practical and feasible technical path for the development of the next generation of high-performance lithium-ion batteries. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the electrode slurry coating equipment and plasma etching method in Embodiment 1 of the present invention.

[0026] Figure 2 This is a schematic diagram of the cross-sectional structure of the pre-lithiated bilayer graphite anode prepared in Example 1 of the present invention.

[0027] Figure 3 This is a schematic diagram of the surface structure of the pre-lithiated bilayer graphite anode prepared in Example 1 of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art, and all reagents and consumables are commercially available products.

[0029] Example 1 This embodiment provides a pre-lithiated bilayer graphite anode, the specific preparation of which is as follows: S1. Active material natural graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber (SBR), and conductive agent carbon black (SP) are placed in deionized water at a mass ratio of 96.3:1.35:1.35:1 and dispersed evenly to prepare a graphite slurry (solid content 48%). The D50 of the artificial graphite material is 15 μm.

[0030] S2. Graphite slurry is uniformly coated onto the current collector (copper foil, 10 μm thick) using a slit-type coating device, with the electrode loading controlled at 9.0 mg / cm². -2 A wet film was prepared; the wet film was placed in a forced-air drying oven and dried at 80℃ for 8 hours to obtain a dry electrode sheet; the dry electrode sheet was then rolled to control the compaction density to 1.5 g / cm³. -3 This yields a negative electrode.

[0031] S3. The upper layer (near the separator side) of the negative electrode is etched using a plasma etching device (the etching gas source is a mixture of Ar and O2 (Ar:O2=3:1), the etching power is 200W, and the etching time is 5min). The etching depth is controlled to be 60% of the overall electrode thickness, forming a through-hole with a diameter of about 10μm and an areal density of about 1000 holes / cm². 2 The lower layer retains its close-packed structure, thus obtaining the double-layer graphite anode.

[0032] Example 2 This embodiment provides a pre-lithiated bilayer graphite anode, the preparation of which is basically the same as in Example 1, except that: in step S3, the etching power is adjusted to 300W, the etching time is adjusted to 3min, the diameter of the formed through-hole is about 30μm, and the areal density is about 800 pores / cm². 2 Everything else remains unchanged.

[0033] Example 3 This embodiment provides a pre-lithiated bilayer graphite anode, the preparation of which is basically the same as in Example 1, except that: in step S3, the etching power is adjusted to 100W, the etching time is adjusted to 10min, the etching depth is adjusted to 40% of the overall electrode thickness, the diameter of the formed through-hole is about 10μm, and the areal density is about 2000 / cm². 2 Everything else remains unchanged.

[0034] Example 4 This embodiment provides a pre-lithiated bilayer graphite anode, the preparation of which is basically the same as in Example 1, except that: in step S3, the etching gas source is replaced with CF4 gas, the etching power is 250W, the etching time is 4min, the etching depth is adjusted to 80% of the overall electrode thickness, the diameter of the formed through-hole is about 40μm, and the areal density is about 500 / cm². 2 Everything else remains unchanged.

[0035] Example 5 This embodiment provides a pre-lithiated bilayer graphite anode, which is prepared in basically the same way as in Example 1, except that in step S1, the natural graphite D50 is 20 μm, and the rest remain unchanged.

[0036] Comparative Example 1 This comparative example provides a graphite anode, which is prepared in basically the same way as in Example 1, except that step S3 (i.e., the etching of the upper through-hole is not performed) is omitted, while the rest remain unchanged.

[0037] Comparative Example 2 This comparative example provides a graphite negative electrode, which is prepared in basically the same way as in Example 1, except that: in step S3, a through-hole is formed along the electrode thickness direction, penetrating the entire electrode except for the copper current collector, while the rest remain unchanged.

[0038] Furthermore, to understand the performance of the various graphite anodes prepared above, the following tests were also conducted: The electrode sheets prepared in the above experimental example were punched into circular pieces with a diameter of 10 mm and assembled into lithium iron phosphate full cells in a vacuum glove box. The electrolyte consisted of 1 M LiPF6 dissolved in 1 L of organic solvent (EC:DEC volume ratio 3:7), with 5% FEC and 2% VC as additives. The positive electrode was lithium iron phosphate.

[0039] The assembled batteries were left to stand for 10 hours to allow the electrolyte to fully penetrate. Rate performance and long-cycle testing were then performed on the assembled batteries, and the results are shown in Table 1.

[0040] Table 1 Performance details of each graphite electrode

[0041] As shown in Table 1, Examples 1-5, which used plasma etching to construct the through-hole, significantly outperformed Comparative Examples 1 and 2 (which did not undergo plasma etching) in terms of first-cycle coulombic efficiency, rate performance, and cycle life. Specifically: The battery assembled in Example 1 (Ar / O2 mixed gas, etching power 200W, etching time 5min, through-hole depth ratio 60%, pore diameter approximately 20μm, areal density approximately 1000 pores per square centimeter) achieved a first-cycle coulombic efficiency of 98.2%, the highest among all samples; it still maintained an areal capacity of 2.47mAh at 2C, far exceeding other examples; and its capacity retention rate after 2000 cycles at 1C was 83.2%, also the highest among all samples.

[0042] The capacity retention rate of Comparative Example 1 (single-layer close packing, no etching) after 2000 cycles was only 43.2%, which is far lower than that of the embodiments of the present invention. In addition, the cycle retention rate of Comparative Example 2 (full-layer through-etching) was only 61.3%, which is also significantly lower than that of Example 1, which adopts a "top layer etching + bottom layer dense" two-layer gradient structure, verifying the necessity of retaining the bottom layer close packing structure for maintaining the mechanical strength and long-term cycle stability of the electrode.

[0043] Based on the above series of investigations, this invention provides a bilayer graphite anode material with high first-cycle coulombic efficiency, high areal capacity, and high cycle capacity retention. The optimal configuration is that the depth of the upper through-hole accounts for 60% of the overall electrode thickness, the hole diameter is about 20 μm, the areal density is about 1000 pores per square centimeter, the etching gas source is a mixture of Ar and O2, and the etching power is 200 W.

[0044] The double-layer graphite anode structure proposed in this invention can be used in lithium metal pre-lithiation scenarios, as well as other pre-lithiation processes such as electrochemical pre-lithiation and lithium powder pre-lithiation. In other words, the pre-lithiation method can be any feasible pre-lithiation technology.

[0045] The plasma etching process for constructing through-holes proposed in this invention can be used for graphite anodes, as well as silicon-based anodes, silicon-carbon composite anodes, and other anode material systems. In other words, the electrode active material can be any anode active material.

[0046] Unless otherwise specified, all raw materials used in this invention are existing substances that can be purchased directly from the market.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pre-lithiated bilayer graphite anode, characterized in that, The upper layer of the double-layer graphite anode, near the separator side, has a through-hole along the electrode thickness direction; the lower layer, near the current collector side, has a close-packed structure. The upper and lower layers of the double-layer graphite negative electrode are both composed of graphite slurry, which is prepared by mixing graphite, thickener, binder, conductive agent and water.

2. The double-layer graphite anode according to claim 1, characterized in that, The diameter of the through-holes in the upper layer is 1~100μm, and the areal density is 10~10000 per cm. 2 The depth is 10% to 90% of the thickness of the double-layer graphite anode.

3. The double-layer graphite anode according to claim 1, characterized in that, The graphite D50 is 15~20μm; The mass ratio of graphite, thickener, binder and conductive agent in the graphite slurry is (60-99):(0-10):(1-20):(1-20).

4. The double-layer graphite negative electrode according to claim 3, characterized in that, The graphite includes at least one of natural graphite and artificial graphite; The thickeners include sodium carboxymethyl cellulose, xanthan gum, guar gum, hydroxyethyl cellulose, starch, and carrageenan; The adhesive includes styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, LA133, polytetrafluoroethylene, and polyvinylidene fluoride; The conductive agent includes carbon black, Ketjen black, carbon fiber, carbon nanotubes, and graphene.

5. A method for preparing a bilayer graphite anode according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve graphite, thickener, binder and conductive agent in deionized water and disperse evenly to obtain graphite slurry; S2. Using a slit coating equipment, graphite slurry is evenly coated onto the current collector to obtain a wet film, which is then dried and rolled to obtain a negative electrode sheet. S3. The upper layer of the negative electrode sheet is etched using a plasma etching device to form a through-hole, while the lower layer maintains its close-packed structure, thus obtaining the double-layer graphite negative electrode.

6. The preparation method according to claim 5, characterized in that, The graphite slurry in step S1 has a solid content of 30-60%.

7. The preparation method according to claim 5, characterized in that, In step S2, the electrode loading during coating is 8~10 mg / cm³. -2 ; Drying conditions: temperature 50~100℃, time 1~24h; The compacted density of the electrode after roller pressing is 1.0~2.0 g / cm³. -3 .

8. The preparation method according to claim 5, characterized in that, The etching gas source in step S3 includes at least one of Ar, O2, CF4, and SF6; Etching conditions: power 50~500 W, time 10s~30min.

9. The application of the bilayer graphite anode according to any one of claims 1-4 in the preparation of power batteries and energy storage batteries that require lithium metal contact pre-lithiation treatment.

10. A lithium-ion battery, characterized in that, It includes the bilayer graphite anode as described in any one of claims 1-4.

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