Wood-plastic lightweight porous copper foil, preparation method thereof and application of wood-plastic lightweight porous copper foil in secondary battery

Abstract

The invention discloses a wood-plastic lightweight porous copper foil, a preparation method thereof and an application of the wood-plastic lightweight porous copper foil in a secondary battery. Firstly, lignin and cellulose obtained from wood are used as base materials, a suspension is prepared, and a lignocellulose membrane is prepared through film casting; then the lignocellulose membrane is subjected to coupling or cross-linking treatment, and the mechanical strength and chemical stability of the lignocellulose membrane are improved; and finally carrying out sensitization, activation and chemical copper plating treatment to obtain the wood-plastic lightweight porous copper foil current collector. The wood-plastic light porous copper foil is rough in surface and porous, so that the adhesive force between an active substance and a current collector is increased, the adhesive force and electric contact between active particles and the current collector are improved, and the rate capability of the battery is further improved; meanwhile, a larger internal space is provided for accommodating the volume change of the active substance, and the cycle life of the battery is prolonged. The problems that a current collector is large in mass, the adhesive force between an active substance and an electrode coating is weak, and a copper foil current collector preparation process is complex in equipment and too high in cost are solved.

Description

Technical Field

[0001] The present invention belongs to the field of the negative electrode of secondary batteries, and particularly relates to a copper foil current collector and its preparation and application. Background Art

[0002] In the past three decades, lithium-ion batteries (LIBs) and zinc-ion batteries (ZIBs) have been widely used in fields such as electronic devices. Among them, the negative electrode current collector is a key component of the battery, which plays the role of supporting the negative electrode active material and conducting electrons, and has a great impact on the battery performance. Copper foil is mainly used as the current collector in existing batteries.

[0003] However, the copper foil current collector has two problems: large mass and weak contact adhesion force with the electrode coating. First of all, copper has a relatively large density (8.96 g / cm 3 ), and the areal density of the commonly used 8 μm copper foil is about ~70 g / m 2 . As a non-active component of the battery, the heavier copper current collector limits the improvement of the battery energy density; secondly, the contact between the copper foil and the electrode material is a planar contact and the adhesion force is weak, resulting in a large contact resistance between the two, which affects the rate performance of the battery; thirdly, China is short of copper resources, and the current import dependence has exceeded 80%. At present, the copper used in new energy batteries has reached millions of tons per year, and the situation of tight copper resource supply and rising prices will exist for a long time.

[0004] The composite current collector prepared by using a polymer as a matrix (such as PEI, PP, and PI, etc.) and forming a metal coating on its surface has been developed rapidly, which can greatly reduce the weight of the current collector to meet the needs of high energy density batteries. Generally, vacuum coating technologies such as magnetron sputtering are used to metallize the substrate, and then the process of electroplating with water is combined to thicken the coating. However, the process equipment is complex and the cost is too high, and it is still difficult to solve the problems of small contact area and weak adhesion force between the copper coating and the active substance. Therefore, developing new composite current collector materials, solving the problems of reducing the weight of the current collector and the adhesion of the active substance at the same time, and greatly reducing the consumption of copper and the production cost, has broad practical application value. Summary of the Invention

[0005] The purpose of the present invention is to provide a wood-plastic lightweight porous copper foil and its preparation method and application in secondary batteries in view of the deficiencies of the prior art, and solve the problems of large mass of the current collector, weak adhesion force between the active substance and the electrode coating, and complex process equipment and high cost of the copper foil current collector preparation process.

[0006] The present invention first uses lignin and cellulose obtained from wood as substrates, prepares a suspension and casts a film to prepare a wood cellulose film; then performs coupling or cross-linking treatment on the wood cellulose film to improve its mechanical strength and chemical stability; finally, performs sensitization, activation and electroless copper plating treatment to obtain a wood-plastic lightweight porous copper foil current collector The preparation method of the wood-plastic lightweight porous copper foil provided by the present invention includes the following contents: (1) Preparation of a lignocellulose membrane: Dissolve lignin and cellulose in a mixed solution of LiOH and urea in a certain proportion, centrifuge to remove air bubbles, obtain a light yellow lignocellulose solution, place it under low temperature conditions, add a certain amount of cross-linking agent, after reacting for 1-2 h, use a film scraper to scrape into a film with a certain thickness, then wash with deionized water and air dry at room temperature to obtain a lignocellulose membrane.

[0007] (2) Strengthening or dehydroxylation modification of the lignocellulose membrane: In order to enhance the mechanical properties of the current collector, immerse the lignocellulose membrane in a hydrogel strengthening solution for 10-60 min to strengthen the lignocellulose membrane. The hydrogel strengthening solution is a mixed solution of acrylamide, cross-linking agent and initiator, and vacuum dry to obtain the strengthened lignocellulose membrane; Or, in order to reduce the hydroxyl groups on the lignocellulose membrane and reduce the capture reaction of lithium ions during charging, immerse the lignocellulose membrane in a dehydroxylation modifier solution at 40-80 °C, after soaking for 1-10 h, wash with deionized water and absolute ethanol, and vacuum dry to obtain a dehydroxylated modified lignocellulose membrane; The dehydroxylation modifier is at least one of epichlorohydrin, glutaraldehyde, and diglycidyl ether.

[0008] For the copper foil used in zinc ion batteries, the treatment method of polymer-strengthened lignocellulose membrane is preferably adopted. This is because a large number of hydroxyl groups in polyacrylamide can be coupled with lignocellulose, which can improve the wettability of the electrolyte, accelerate ion transport and diffusion, and thus effectively improve the rate performance of the battery. For the copper foil used in lithium ion batteries, the method of cross-linking the lignocellulose membrane with a dehydroxylation modifier is preferably adopted, and one or more treatment agents such as epichlorohydrin, glutaraldehyde, and diglycidyl ether are used to react to remove the hydroxyl groups on the lignocellulose, reduce the side reactions on the surface of the negative electrode current collector during the first charge and discharge of the battery, and improve the first efficiency of the battery. Polyacrylamide is not used in lithium ion batteries because a large number of hydroxyl groups and amino groups in polyacrylamide are prone to capture reactions with lithium ion batteries, increasing the loss of active lithium and reducing the first efficiency of the battery.

[0009] (3) Electroless copper plating on the lignocellulose membrane: Place the modified lignocellulose membrane obtained in step (2) in a sensitizer solution and an activator solution in sequence, and finally place it in a copper plating solution for electroless copper deposition treatment.

[0010] (4) Densification treatment of the copper foil: The copper foil after copper deposition treatment in step (3) is hot-pressed in a hot press into a uniform and flat modified wood-plastic lightweight porous copper foil, a composite copper foil current collector with a thickness of about 25-35 μm and an areal density of about 30-33 g / m 2, so the weight of the current collector is greatly reduced.

[0011] In the above method, further, the mass ratio of lignin to cellulose in step (1) is (1~5):10.

[0012] In the above method, further, in the mixed solution of LiOH and urea in step (1), the mass concentration of LiOH is 5~10% LiOH, and the mass concentration of urea is 10~15%; the crosslinking agent is a boric acid solution with a mass concentration of 0.5~2%, and the mass ratio of the boric acid solution to the lignocellulose solution is (0.5~5):100.

[0013] In the above method, further, the low temperature condition in step (1) is under the condition of -20~0 °C.

[0014] In the above method, further, in step (2), the hydrogel strengthening solution is a mixed solution of acrylamide, a crosslinking agent and an initiator. The concentration of acrylamide is 1~5 mol / L. The crosslinking agent is N,N′-methylenebisacrylamide, and its concentration is 2~8×10 -4 mol / L. The initiator is ammonium persulfate, and its concentration is 2~8×10 -4 mol / L. The amount of the hydrogel strengthening solution is based on the fact that the lignocellulose membrane can be completely and fully immersed.

[0015] In the above method, further, the dehydroxylation modifier solution in step (2) is prepared by the following method: Dissolve 2~8 parts by mass of NaOH in 100 parts by mass of deionized water to prepare a NaOH solution, and then add at least one of 5~15 parts by mass of epichlorohydrin, glutaraldehyde, and diglycidyl ether as a crosslinking agent, and stir evenly. The amount of the epichlorohydrin crosslinking solution is based on the fact that the lignocellulose membrane can be completely and fully immersed.

[0016] In the above method, further, the specific method for electroless copper plating of the lignocellulose membrane in step (3) is: at room temperature, immerse the modified lignocellulose membrane in the sensitizer solution for 2~20 min, and wash with water; at room temperature, immerse the sensitized lignocellulose membrane in the activator solution for 1~10 min, and wash with water; immerse the activated lignocellulose membrane in the copper plating solution, the reaction temperature is 30~50 °C, and the reaction time is 5~60 min. The denseness of the copper plating is controlled by controlling the copper plating reaction time.

[0017] In the above method, further, the sensitizer solution in step (3) is a mixed solution of SnCl2 and HCl, where the concentration of SnCl2 is 10~30 g / L, and the concentration of HCl is 0.1~0.5 mol / L.

[0018] In the above method, further, the chemical solution of the activator in step (3) is a PdCl2 solution with a concentration of 0.1 - 0.8 g / L.

[0019] In the above method, further, the copper plating solution in step (3) is a mixed solution of CuSO4 and NaKC4H4O6, where the concentration of CuSO4 is 10 - 40 g / L and the concentration of NaKC4H4O6 is 10 - 80 g / L.

[0020] In the above method, further, the hot pressing temperature in step (4) is 100 - 180 °C, and the pressure holding time is 1 - 10 min.

[0021] The present invention also provides a wood-plastic lightweight porous copper foil prepared by the above method, with a thickness of about 25 - 35 μm and an areal density of about 30 - 33 g / m 2 , greatly reducing the weight of the current collector.

[0022] The present invention also provides the application of the above wood-plastic lightweight porous copper foil in secondary batteries, and further in the field of negative current collectors for zinc-ion and / or lithium-ion batteries.

[0023] In the above application, further, the negative electrode active material, conductive agent, and binder are mixed uniformly in a certain proportion (refer to the conventional preparation methods in the art) to obtain a slurry, the slurry is uniformly coated on the wood-plastic lightweight porous copper foil of the present invention, and then dried to obtain an electrode sheet material. It can be cut into the required shape during use.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The wood-plastic lightweight porous copper foil of the present invention can replace the commonly used rolled or electrolytic copper foil. The density of copper is 8.96 g / cm 3 , while the density of cellulose is much lower than that of copper, only 0.26 - 0.28 g / cm 3 , so it can greatly reduce the weight of the copper current collector and improve the energy density of the battery, and is particularly suitable for use as a current collector in zinc-ion or lithium-ion batteries.

[0025] (2) The wood-plastic lightweight porous copper foil of the present invention has a porous structure, which is beneficial to the transmission and diffusion of zinc / lithium ions and improves the rate performance of zinc / lithium-ion batteries.

[0026] (3) The wood-plastic lightweight porous copper foil of the present invention has a rough and porous surface, which is very beneficial to increasing the adhesion between the active material and the current collector. It can form a good interfacial bond with the electrode active material, enhance the adhesion and electrical contact between the active particles and the current collector, and prevent the shedding of the active material during the cycling process. At the same time, it provides a larger internal space to accommodate the volume change of the active material, thus improving the cycle life of the battery.

[0027] (4) Compared with pure copper foil, lignin and cellulose have wide sources and low costs, which can reduce the battery cost and alleviate the consumption of national copper resources. Description of the Drawings

[0028] Figure 1 It is the surface scanning electron microscope picture of the wood-plastic lightweight porous copper foil obtained in Example 1.

[0029] Figure 2 It is the contact angle diagram of the wood-plastic lightweight porous copper foil (HCP-Cu) in Example 1 and the ordinary 8 μm copper foil (Cu) in Comparative Example 1 with 2 mol / L ZnSO4 electrolyte.

[0030] Figure 3 It is the X-ray diffraction pattern of the wood-plastic lightweight porous copper foil (HCP-Cu) obtained in Example 1.

[0031] Figure 4 It is the digital photo of the wood-plastic lightweight porous copper foil (HCP-Cu) obtained in Example 1.

[0032] Figure 5 It is the surface conductivity of the wood-plastic lightweight porous copper foil (HCP-Cu) in Example 1 and the copper foil (Cu) in Comparative Example 1.

[0033] Figure 6 It is the mass per unit area of the wood-plastic lightweight porous copper foil (HCP-Cu) in Example 1 and the copper foil (Cu) in Comparative Example 1.

[0034] Figure 7 It is the constant current charge-discharge cycle stability of the zinc ion battery in Example 1 and Comparative Example 1.

[0035] Figure 8 It is the rate performance diagram of the I2@AC electrode prepared in Example 1 and Comparative Example 1.

[0036] Figure 9 It is the capacity-voltage curve of Example 2 (ECP-Cu) and Comparative Example 2 (Cu), Comparative Example 3 (HCP-Cu), Comparative Example 4 (CP-Cu). Detailed Embodiments

[0037] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the invention.

[0038] Example 1 (1) Preparation of lignocellulose membrane: Lignin and cellulose were dissolved in a 12 wt% urea solution containing 7 wt% LiOH at a mass ratio of 1:10, centrifuged to remove air bubbles to obtain a light yellow lignocellulose solution. Under ice bath conditions, a crosslinking agent solution, i.e., a 1 wt% boric acid solution, was added. The mass ratio of the boric acid solution to the lignocellulose solution was 1:100, and the reaction was carried out for 1 h. Then it was poured on a glass plate and scraped into a film of a certain thickness using a film scraper, washed with deionized water, and air-dried at room temperature to obtain the lignocellulose membrane.

[0039] (2) Strengthening of the lignocellulose membrane: The lignocellulose membrane was immersed in a hydrogel strengthening solution for 20 min to strengthen the lignocellulose. The hydrogel strengthening solution was a mixed solution of acrylamide, a crosslinking agent, and an initiator. The concentration of acrylamide was 2 mol / L, the crosslinking agent was N,N′-methylenebisacrylamide with a concentration of 4×10 -4 mol / L, and the initiator was ammonium persulfate with a concentration of 4×10 -4 mol / L. The wet lignocellulose membrane was transferred to a glass plate and vacuum-dried at 80 °C for 12 h to obtain a polymer-strengthened lignocellulose membrane. The weight of the strengthened lignocellulose membrane was about 2.0 mg / cm 2 (3) Electroless copper plating on the lignocellulose membrane: At room temperature, the strengthened lignocellulose membrane was immersed in a sensitizer solution (10 g / L SnCl2, 0.15 mol / L HCl) for 8 min to adsorb Sn 2+ ; then it was transferred to an activator solution (0.2 g / L PdCl2) for 2 min. Through the redox reaction between Sn 2+ and Pd 2+ (Pd 2+ + Sn 2+ → Pd + Sn 4+ ), tiny Pd nanoparticles were loaded on the membrane as copper deposition sites; after the reaction, the treated lignocellulose membrane was immersed in a solution containing Cu 2+ (15 g / L CuSO4, 40 g / L NaKC4H4O6) for 20 min at a temperature of 40 °C.

[0040] (4)Densify the wood-plastic lightweight porous copper foil: After rinsing and drying the wood-plastic lightweight porous copper foil obtained in step (3), place it in a hot press and hot press at 130 °C for 2 min to obtain a uniform and flat modified wood-plastic lightweight porous copper foil.

[0041] The preparation method of the zinc-ion battery includes the following steps: (1)Use an electrochemical workstation to perform constant-current deposition on the surface of the current collector, deposit a certain amount of zinc, and prepare a negative electrode sheet; (2)Weigh iodine and activated carbon according to a mass ratio of 1:1, ball-mill and mix them evenly, place them in a reaction kettle, react at 120 °C for 6 h to obtain a composite material of iodine and activated carbon (I2@AC). Weigh 80 parts of I2@AC, 10 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 150 parts of N-methylpyrrolidone by mass, stir and prepare an I2@AC positive electrode slurry; coat the I2@AC positive electrode slurry evenly on the surface of a 20-μm-thick titanium foil, roll and cut to prepare a positive electrode sheet; (3)Assemble a button battery in air: First, place the negative electrode shell of the button battery on the platform, then sequentially add the negative electrode sheet, separator, electrolyte, and positive electrode sheet. The amount of electrolyte should be sufficient to completely wet the separator and the electrode sheet. Cover with a gasket, a spring piece, and a positive electrode shell, use an automatic sealer to seal the battery, wipe off the electrolyte remaining on the battery shell, and let it stand for 24 hours before testing.

[0042] Example 2 (1)Prepare a lignocellulose membrane: Dissolve lignin and cellulose in a 12 wt% urea solution containing 7 wt% LiOH according to a mass ratio of 1:10, centrifuge to remove air bubbles to obtain a light yellow lignocellulose solution. Place it under low-temperature conditions and add a certain amount of cross-linking agent solution. The cross-linking agent solution is a 1 wt% boric acid solution, and the mass ratio of the boric acid solution to the lignocellulose solution is 1:100. React for 1 h, pour it on a glass plate and use a film scraper to scrape it into a film of a certain thickness, wash it with deionized water, and air-dry at room temperature to obtain a lignocellulose membrane.

[0043] (2)Dehydroxylation of the lignocellulose membrane: Weigh 100 parts by mass of deionized water and 4 parts by mass of NaOH, stir at room temperature for 30 min, and then add 10 parts by mass of epichlorohydrin as a cross-linking agent to the solution and stir for 5 min to obtain an epichlorohydrin cross-linking solution. Immerse the lignocellulose membrane in the epichlorohydrin cross-linking solution at 50 °C for 6 h; transfer the wet lignocellulose membrane to a glass plate, wash it with deionized water and absolute ethanol, and then vacuum-dry at 80 °C for 12 h to obtain a dehydroxylated modified lignocellulose membrane. The weight of the dehydroxylated modified lignocellulose membrane is about 1.7 mg / cm 2 。

[0044] (3) Electroless copper plating on the lignocellulose membrane: At room temperature, immerse the crosslinked lignocellulose membrane in the sensitizer solution (10 g / L SnCl2, 0.15 mol / L HCl) for 8 min to adsorb Sn 2+ ; transfer it to the activator solution (0.2 g / L PdCl2) for 2 min. Through the redox reaction between Sn 2+ and Pd 2+ (Pd 2+ + Sn 2+ → Pd + Sn 4+ ), tiny Pd nanoparticles are loaded on the membrane. After the reaction, immerse the treated membrane in the solution containing Cu 2+ (15 g / L CuSO4, 40 g / L NaKC4H4O6) for 20 min at a temperature of 40 °C. After rinsing and drying, hot press it at 130 °C for 2 min on a hot press to finally obtain a flat dehydroxylated modified wood-plastic lightweight porous copper foil.

[0045] The preparation method of the lithium-ion battery includes the following steps: (1) Weigh 93 parts of graphite, 3 parts of conductive carbon black, 1.5 parts of carboxymethyl cellulose, 2.5 parts of styrene-butadiene rubber, and 280 parts of deionized water by mass, and stir to prepare the graphite negative electrode slurry; coat the graphite negative electrode slurry evenly on the current collector, roll and cut it to obtain the negative electrode sheet; (2) Weigh 94.5 parts of lithium cobalt nickel manganate, 3 parts of conductive carbon black, 2.5 parts of polyvinylidene fluoride, and 150 parts of N-methylpyrrolidone by mass, and stir to prepare the lithium cobalt nickel manganate positive electrode slurry; coat the lithium cobalt nickel manganate positive electrode slurry evenly on the surface of a 12-μm-thick aluminum foil, roll and cut it to obtain the positive electrode sheet; (3) Conduct battery assembly in a glove box filled with an argon atmosphere and with the water and oxygen content lower than 0.01 ppm. Wind the positive (or lithium sheet), negative electrode sheet and the separator, and inject the electrolyte to obtain the lithium-ion battery.

[0046] Example 3 On the basis of Example 1, adjust the immersion time in the electroless copper plating solution to 10 min, and keep the remaining preparation process parameters and process steps the same as those in Example 1 to prepare the negative electrode current collector of the zinc-ion battery and the zinc-ion button battery.

[0047] Example 4 On the basis of Example 1, adjust the immersion time in the electroless copper plating solution to 30 min, and keep the remaining preparation process parameters and process steps the same as those in Example 1 to prepare the negative electrode current collector of the zinc-ion battery and the zinc-ion button battery.

[0048] Example 5 On the basis of Example 1, the time of immersion in the electroless copper plating solution was adjusted to 50 min, and the remaining preparation process parameters and process steps were the same as those in Example 1, and the negative electrode current collector of the zinc ion battery and the zinc ion button battery were prepared.

[0049] Comparative Example 1 Using copper foil as the current collector, the remaining preparation process parameters and process steps were the same as those in Example 1 respectively. Correspondingly, the negative electrode current collector of the zinc ion battery and the zinc ion button battery were prepared respectively.

[0050] Comparative Example 2 Using copper foil as the current collector, the remaining preparation process parameters and process steps were the same as those in Example 2 respectively. Correspondingly, the negative electrode current collector of the lithium ion battery and the lithium ion button battery were prepared respectively.

[0051] Comparative Example 3 Using the wood-plastic lightweight porous copper foil obtained in Example 1 as the current collector, the remaining electrode and battery preparation process parameters and process steps were the same as those in Example 2 respectively. Correspondingly, the negative electrode current collector of the lithium ion battery and the lithium ion button battery were prepared respectively.

[0052] Comparative Example 4 The wood cellulose membrane was not enhanced and dehydroxylated modified to prepare an unmodified wood-plastic lightweight porous copper foil. Using the unmodified wood-plastic lightweight porous copper foil as the current collector, the remaining preparation process parameters and process steps were the same as those in Example 2, and the negative electrode current collector of the lithium ion battery and the lithium ion button battery were prepared respectively. The following makes a detailed description of Example 1 and Example 2 with the best electrical properties to further understand the excellent performance of the present invention.

[0053] From the surface scanning electron microscope picture of Example 1 Figure 1 It can be seen that Cu is uniformly and densely deposited on the surface of the wood cellulose. This rough surface structure greatly increases the adhesion force between the active material and the current collector.

[0054] The electrolyte contact angle test was carried out on Example 1 and Comparative Example 1, and the electrolyte was 2 mol / L ZnSO4, and the results were as Figure 2 . From Figure 2 It can be known that compared with Comparative Example 1 in Example 1, due to the presence of the wood cellulose membrane, the wettability of the wood-plastic lightweight porous copper foil to the electrolyte is significantly improved. The hydrophilic surface can promote the uniform coating of the slurry, reduce the interface defects, and thus reduce the contact resistance. The good wettability enables the electrolyte to more efficiently penetrate the electrode surface, accelerate the ion transport and diffusion, and thus effectively improve the rate performance of the battery, highlighting the advantages of the present invention in improving the battery performance.

[0055] The present invention can realize the large-area preparation of the wood-plastic lightweight porous copper foil (Figure 4 ), this characteristic is of great significance for industrial scale production, which is conducive to reducing production costs and improving production efficiency, and is a major advantage of the present invention.

[0056] Figure 5 shows the area mass comparison between Example 1 (HCP-Cu) and Comparative Example 1 (Cu). Figure 5 It can be seen that compared with the 8 μm copper foil, the area mass of the wood-plastic lightweight porous copper foil prepared by us is greatly reduced, which is very crucial for improving the battery energy density. For Example 1 and Comparative Example 1, four-probe conductivity tests were carried out, and the results are as Figure 6 . From Figure 6 it can be seen that Example 1 has a high surface conductivity, indicating that the wood-plastic lightweight porous copper foil obtained in Example 1 has good electrical conductivity. Although non-conductive materials such as lignin and cellulose are used, after electroless copper plating, its electrical conductivity can still meet the requirements of the battery current collector. Compared with the 8 μm copper foil, while reducing the battery weight, it does not affect the electrical conductivity, effectively improving the battery energy density.

[0057] For the zinc-ion batteries assembled with Example 1 and Comparative Example 1, constant current charge-discharge tests were carried out, and the results are as Figure 7 . From Figure 7 it can be seen that the battery with the porous copper foil of the present invention as the current collector has excellent cycle stability. After 2000 charge-discharge cycles, it can still maintain 82.6% of the initial capacity. This is due to the good interfacial adhesion between the porous copper foil and the electrode active material, and the accommodation of the volume change of the active material by the porous structure, effectively reducing the shedding of the active material and greatly improving the battery cycle life, highlighting the technical advantages of the present invention. Figure 8 The rate performance graph of shows that the electrode prepared in Example 1 has good performance at different charge-discharge rates, fully verifying that the wood-plastic lightweight porous copper foil in the present invention improves the electrical contact between the active particles and the current collector and promotes ion diffusion to improve the battery rate performance.

[0058] Example 2 changed the surface chemical properties of the lignocellulose membrane through dehydroxylation modification. Comparing the first charge-discharge cycle data of the lithium-ion batteries of Example 2 (ECP-Cu) and Comparative Examples 2 (Cu), 3 (HCP-Cu), and 4 (CP-Cu) ( Figure 9It can be seen that when the polymer-reinforced wood-plastic lightweight porous copper foil (Comparative Example 2) is applied to a lithium-ion battery, the initial efficiency is lower than that of the wood-plastic lightweight porous copper foil without any modification in Comparative Example 4 (81.4% vs. 89.1%). This is because a large amount of amino and hydroxyl groups in polyacrylamide will react with lithium ions, increasing the loss of active lithium and resulting in a decrease in the initial efficiency of the battery. The initial charge-discharge efficiency of Example 2 reaches 93.6%, which is much higher than 89.1% of Comparative Example 4. This is because the dehydroxylation modification reduces the presence of hydroxyl groups, reduces the side reaction between hydroxyl groups and lithium ions in the electrolyte (such as excessive growth of the SEI layer), reduces the loss of active lithium, and effectively improves the initial efficiency of the battery, which is of great significance for improving the energy density of the battery and reflects the key role of dehydroxylation modification. The initial efficiency of Example 2 is basically the same as that of Comparative Example 2 (93.6% vs. 94.2%), but the areal mass density of the wood-plastic lightweight porous copper foil is half as light as that of the commonly used 8-μm copper foil (3.3 vs. 7.3 mg / cm 2 ). Therefore, the dehydroxylated modified wood-plastic lightweight porous copper foil takes into account both the initial efficiency and the collective weight, and can greatly improve the energy density of the battery.

[0059] Comparative Example 1 uses a traditional copper foil as the current collector, which is inferior to Example 1 in terms of electrolyte wettability, battery weight, energy density, cycle life, and rate performance, fully demonstrating the advantages of the wood-plastic lightweight porous copper foil of the present invention.

[0060] In Comparative Example 4, the lignocellulose membrane was not modified. Compared with Example 2, the initial charge-discharge efficiency was lower, indicating that the dehydroxylation modification plays an important role in improving battery performance.

[0061] In Examples 3, 4, and 5, only the immersion time in the electroless copper plating solution was changed, and the other conditions were the same. As the copper plating time prolonged, the compactness of the copper plating changed. A relatively short copper plating time (such as 10 min in Example 3) may make the copper coating relatively thin with more pores. Although it is beneficial for ion diffusion, it may lead to slightly insufficient conductivity; a longer copper plating time (such as 50 min in Example 5) will make the copper coating denser and the conductivity stronger, but excessive copper deposition may lead to an increase in weight and fail to achieve the ideal effect of increasing the energy density of the battery. Therefore, by controlling the copper plating time, a balance can be found between conductivity and electrode weight to achieve the best battery performance, which is also a key control point in the preparation process of the present invention.

[0062] Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and it is obvious that relevant personnel can make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

Claims

1. Preparation method of wood-plastic lightweight porous copper foil, characterized in that, It includes the following contents: (1) Preparation of lignocellulose membrane: Dissolve lignin and cellulose in a mixed solution of LiOH and urea according to a certain ratio, centrifuge to remove air bubbles to obtain a lignocellulose solution. Place it under low-temperature conditions, add a crosslinking agent, react for 1 - 2 h, then use a film scraper to scrape into a film, wash with deionized water, and air-dry at room temperature to obtain a lignocellulose membrane; (2) Strengthening or dehydroxylation modification of the lignocellulose membrane: Immerse the lignocellulose membrane in a hydrogel strengthening solution for 10 - 60 min to strengthen the lignocellulose membrane. The hydrogel strengthening solution is a mixed solution of acrylamide, a crosslinking agent, and an initiator. After soaking, vacuum dry to obtain the strengthened lignocellulose membrane; Or, immerse the lignocellulose membrane in a dehydroxylation modifier solution at 40 - 80 °C for 1 - 10 h, then wash with deionized water and absolute ethanol, and vacuum dry to obtain a dehydroxylated modified lignocellulose membrane; The dehydroxylation modifier is at least one of epichlorohydrin, glutaraldehyde, and diglycidyl ether; (3) Electroless copper plating on the lignocellulose membrane: Place the modified lignocellulose membrane obtained in step (2) successively in a sensitizer solution and an activator solution, and finally place it in a copper plating solution for electroless copper deposition treatment; (4) Densify the copper foil: The copper foil after electroless copper plating in step (3) is hot-pressed in a hot press into a uniform and flat modified wood-plastic lightweight porous copper foil, which is a composite copper foil current collector with a thickness of about 25-35 μm and an areal density of about 30-33 g / m 2 , so the weight of the current collector is greatly reduced.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of lignin to cellulose is (1 - 5):

10.

3. The method according to claim 1, characterized in that In the mixed solution of LiOH and urea in step (1), the mass concentration of LiOH is 5 - 10% LiOH, and the mass concentration of urea is 10 - 15%; The crosslinking agent is a boric acid solution with a mass concentration of 0.5 - 2%, and the mass ratio of the boric acid solution to the lignocellulose solution is (0.5 - 5):100; The low-temperature condition in step (1) is at -20 - 0 °C.

4. The method according to claim 1, wherein In step (2), the hydrogel strengthening liquid is a mixed liquid of acrylamide, a crosslinking agent and an initiator. The concentration of acrylamide is 1 to 5 mol / L. The crosslinking agent is N,N'-methylenebisacrylamide, and its concentration is (2 to 8)×10 -4 mol / L. The initiator is ammonium persulfate, and its concentration is (2 to 8)×10 -4 mol / L.

5. According to the method described in claim 1, characterized in that, The dehydroxylation modifier solution in step (2) is prepared by the following method: Dissolve 2 - 8 parts by mass of NaOH in 100 parts by mass of deionized water to prepare a NaOH solution, then add 5 - 15 parts by mass of at least one of epichlorohydrin, glutaraldehyde, and diglycidyl ether as a crosslinking agent, and stir evenly.

6. The method according to claim 1, wherein The specific method for electroless copper plating on the lignocellulose membrane in step (3) is: At room temperature, immerse the modified lignocellulose membrane in the sensitizer solution for 2 - 20 min, wash with water, then immerse it in the activator solution for 1 - 10 min, wash with water, and finally immerse it in the copper plating solution and react at 30 - 50 °C for 5 - 60 min.

7. The method according to claim 6, wherein The sensitizer solution in step (3) is a mixed solution of SnCl2 and HCl, where the concentration of SnCl2 is 10 - 30 g / L and the concentration of HCl is 0.1 - 0.5 mol / L; The chemical solution of the activator in step (3) is a PdCl2 solution with a concentration of 0.1 - 0.8 g / L; The copper plating solution in step (3) is a mixed solution of CuSO4 and NaKC4H4O6, where the concentration of CuSO4 is 10 - 40 g / L CuSO4 and the concentration of NaKC4H4O6 is 10 - 80 g / L.

8. The method according to claim 1, characterized in that The hot pressing temperature described in step (4) is 100~180 °C, and the pressure holding time is 1~10 min.

9. The wood-plastic lightweight porous copper foil prepared by the method according to claims 1 to 8 has a thickness of about 25 to 35 μm and an areal density of about 30 to 33 g / m 2 .

10. Application of the wood-plastic lightweight porous copper foil described in claim 9 in secondary batteries.

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