Electrolyte, alkali metal ion battery using same and preparation method

Abstract

The invention discloses an electrolyte, an alkali metal ion battery using the same and a preparation method, the electrolyte at least contains a first functional additive and a second functional additive, the first functional additive is at least one of nitrates of In, Ag, Mg, Al, Zn and Bi and / or bis (trifluoromethylsulfonyl) imide salt, and the second functional additive is at least one of nitrates of In, Ag, Mg, Al, Zn and Bi and / or bis (trifluoromethylsulfonyl) imide salt. The second functional additive is at least one of Cs, Rb, K nitrate and / or bis (trifluoromethylsulfonyl) imide. The preparation method of the battery comprises the following steps: preparing a positive plate and a negative composite current collector; assembling the positive plate, the diaphragm and the current collector into a dry cell; and injecting the electrolyte into a dry battery core, fully standing, charging to a first cut-off voltage by using a first current pulse, standing, charging to a second cut-off voltage by using a second current constant current, standing again, exhausting in vacuum, and packaging the battery. The prepared battery is high in energy density and good in cycle performance, and the preparation method can be used for preparing alkali metal ion batteries such as lithium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, in particular to an electrolyte, an alkali metal ion battery using the electrolyte and a preparation method thereof. Background Art

[0002] Among the numerous large-scale energy storage technologies, the negative electrode material used in lithium-ion power batteries is mostly layered graphite, which has a relatively low theoretical capacity limit. The energy density of traditional lithium-ion power batteries needs to be improved. Lithium metal batteries using lithium metal foil as the negative electrode have a much higher theoretical capacity than lithium-ion power batteries, but their practical application also has some limitations, such as safety issues, reduced energy density due to lithium metal redundancy, and higher requirements for the lithium metal battery assembly environment. Anode-free lithium batteries have attracted much attention due to their higher energy density, better safety, and lower production costs compared to traditional lithium metal batteries. However, their current cycling stability faces severe challenges, mainly due to significant lithium loss during the lithium metal deposition process.

[0003] In anode-free lithium batteries, the nucleation and growth of lithium metal at the anode interface determine the loss of active lithium, thereby affecting key performance indicators such as energy density and cycle stability. The nucleation of lithium metal is mainly affected by the current collector, while the subsequent growth is closely related to the interfacial properties and stability of the anode side. Future research and development of anode-free lithium batteries will prioritize achieving higher energy density, better cycle stability, higher safety, simpler assembly processes, and more advanced production technologies, while also focusing on material selection. Therefore, the design of current collectors and electrolytes remains a focus of current research.

[0004] Current current collector design strategies primarily involve material selection and optimization, as well as surface modification and interface engineering. While these approaches can significantly improve battery performance, they inevitably increase costs and complicate manufacturability. Therefore, efforts should be focused on reducing R&D costs, optimizing material synthesis and processing techniques, and ensuring that the modified current collectors are suitable for large-scale industrial applications.

[0005] In order to solve the above-mentioned various technical problems, the present invention is hereby provided. Summary of the Invention

[0006] In response to the above-mentioned deficiencies in the prior art, the present invention provides an electrolyte, an alkali metal ion battery using the same, and a preparation method. The battery prepared by the present invention has high energy density and good cycle performance. The preparation method is not only suitable for lithium-ion batteries, but can also be used to prepare other alkali metal ion batteries.

[0007] The technical solution of the present invention is:

[0008] The present invention relates to an electrolyte, comprising an alkali metal salt and a solvent, and further comprising at least a first functional additive and a second functional additive, wherein the first functional additive is at least one of nitrates and / or bis(trifluoromethylsulfonyl)imide salts of In, Ag, Mg, Al, Zn, and Bi, and the second functional additive is at least one of nitrates and / or bis(trifluoromethylsulfonyl)imide salts of Cs, Rb, and K.

[0009] Preferably, the concentration of the first functional additive in the electrolyte is 0.05-0.15M.

[0010] Preferably, the concentration of the second functional additive in the electrolyte is 0.01-0.1M.

[0011] Preferably, the solvent is at least one of ethylene glycol dimethyl ether, methanol dimethyl ether, ethylene dimethyl ether, methylene diethyl ether, 2,5-dimethyltetrahydrofuran, 1,3-dioxolane, ethylene carbonate, and propylene carbonate;

[0012] The concentration of the alkali metal salt is 1.0~3.5M.

[0013] Preferably, the electrolyte is used for a lithium-ion battery, the alkali metal salt is a lithium salt, and the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate.

[0014] The present invention also relates to a method for preparing an alkali metal ion battery, comprising the following steps:

[0015] S1, preparing a positive electrode sheet and a negative electrode composite current collector;

[0016] S2, assembling the positive electrode sheet, separator and negative electrode composite current collector into a dry battery cell;

[0017] S3. Inject the above electrolyte into the dry cell, let it stand for a long time, charge it with a first current pulse to a first cut-off voltage, let it stand for a long time, then charge it with a second constant current to a second cut-off voltage, let it stand for a long time, vacuum exhaust it, and package the battery.

[0018] This preparation method is not only applicable to lithium-ion batteries, but can also be used to prepare other alkali metal ion batteries. Taking lithium-ion batteries as an example, the present invention adopts a step-by-step charging formation method. First, uniform lithium-philic active sites are formed within the negative electrode composite current collector skeleton, while protective layers are formed on the positive and negative electrode surfaces. Then, continued charging strengthens the positive and negative electrode protective layers and activates the active materials in the battery to activate the battery. This can effectively reduce the irreversible capacity loss of lithium ions during the initial charging process and improve the coulombic efficiency.

[0019] Preferably, the alkali metal ion battery is a lithium ion battery, the alkali metal salt contained in the electrolyte in step S3 is a lithium salt, and the positive electrode sheet in step S1 can be made of a common positive electrode sheet material for a lithium ion battery without a negative electrode.

[0020] Preferably, in step S3, the first charging current is 2-50C, the first cut-off voltage is 0.5-1.5V, the pulse interval is 1-20s, and the pulse is repeated 5-15 times, so that the cations in the first functional additive are reduced and deposited inside the current collector skeleton to form lithium-philic active sites.

[0021] Preferably, in step S3, the second charging current is 0.1-2C, and the second cut-off voltage is 3.6-4.5V, so as to activate the active material in the battery and activate the battery.

[0022] Preferably, the negative electrode composite current collector is prepared by curing a composite film layer on a current collector substrate. The composite film layer is an electronic conductor with a three-dimensional porous structure, and a carbon nanofiber aerogel film is more preferably used. The negative electrode composite current collector of the present invention has the characteristics of high specific surface area, high electrical and thermal conductivity, and sufficient electrolyte infiltration. This ensures low internal resistance of the electrode sheet, rapid heat dissipation, uniform ion concentration distribution, low and uniform current density, uniform temperature, and uniform stress, facilitating ultra-high rate charging without dendrite formation.

[0023] Taking carbon nanofiber aerogel film as an example, the preparation method of the corresponding negative electrode composite current collector is: coating the carbon nanofiber dispersion on the surface of the current collector substrate, freeze-drying or supercritical drying, and then calendering and cutting to obtain the negative electrode composite current collector.

[0024] The prepared carbon nanofiber dispersion is made of solvent, carbon nanofiber, binder and stabilizer. The mass concentration of carbon nanofiber in the carbon nanofiber dispersion is 8% to 12%, and the mass ratio of carbon nanofiber to binder and stabilizer is 20 to 10:0.7:0.3.

[0025] The solvent is at least one of deionized water, alcohol, ethylene glycol, propanol, isopropanol, acetone, and N-methylpyrrolidone; the binder is at least one of polyvinyl pyrrolidone, polyvinyl alcohol, polytetrafluoroethylene, polyethylene terephthalate, polybutylene terephthalate, perfluorosulfonic acid polymer, lithium alginate, and lithium pectate; and the stabilizer is sodium carboxymethyl cellulose or sodium lithium carboxymethyl cellulose.

[0026] The current collector of the present invention can be fully infiltrated by the electrolyte. Under the action of the electric field, the anions and cations in the electrolyte migrate to the positive and negative electrode surfaces respectively. During the first current pulse charging process, the cations in the first functional additive first receive electrons on the surface of the nano-carbon fiber, forming nano-metal elements M1 and depositing on the surface of the carbon fiber. At the same time, the cations M2 in the second functional additive+ It plays an electrostatic shielding role, ensuring that the newly generated nano-metal elements are evenly deposited on the carbon fiber surface; the newly deposited nano-metal elements have good lithium affinity properties, show extremely low nucleation barriers to lithium, and can induce rapid and uniform nucleation of lithium ions in the later stage.

[0027] During the second current constant-current charging process, the newly deposited nanometal crystals on the surface of the nanocarbon fibers and the cations in the second functional additive synergistically induce the uniform nucleation of lithium ions and form a mechanically stable, lithium-ion conductive alloy layer. This alloy layer effectively prevents the subsequent generation of lithium metal from directly contacting the electrolyte, avoiding the occurrence of side reactions, thereby reducing the irreversible capacity loss of lithium ions during charging and improving coulombic efficiency. At the same time, the three-dimensional skeleton structure of the current collector can reduce the electrode current density and provide sufficient internal space to accommodate the deposited lithium metal. The alloy layer with good lithium affinity and ion conductivity works synergistically with the three-dimensional skeleton structure to effectively inhibit the growth of lithium dendrites and drastic changes in the electrode volume; the open network space of the 3D negative electrode composite current collector can store a large amount of lithium metal, exhibiting an ultra-high charging capacity.

[0028] The present invention also relates to an alkali metal ion battery produced using the above-mentioned preparation method. When the alkali metal ion battery is a lithium ion battery, the inner surface of the negative electrode composite current collector skeleton is loaded with M1 nanocrystals and a Li-M1 alloy layer formed therefrom, where M1 is at least one of In, Ag, Mg, Al, Zn, and Bi.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention combines the excellent electronic conductivity of the 3D negative electrode composite current collector with the lithium affinity sites and lithium ion conductive alloy layer formed during the first charging process to construct the Li-M1M2 + @CNTp composite electrode material (M1: lithium-philic nanometallic crystals formed by cation reduction of the first functional additive, M2 + : cations in the secondary functional additive). The inner surface of the anode composite current collector skeleton is loaded with M1 nanocrystals, which possess abundant lithiophilic sites, and the resulting Li-M1 alloy layer. This not only utilizes the 3D anode current collector's inherently well-developed pore structure and chemically stable skeleton to form fast ion transport channels, but also induces uniform and dense deposition of lithium ions at the lithiophilic sites. Furthermore, the highly electronically conductive 3D skeleton reduces local micro-field effects, slowing the growth of lithium dendrites during cycling. The open network of the 3D anode composite current collector allows for the storage of a large amount of lithium metal, demonstrating an exceptionally high charge capacity.

[0031] (2) Under the action of the electric field, the anions and cations in the electrolyte migrate to the positive and negative electrode surfaces respectively. During the pulse charging process, the cations in the first functional additive first receive electrons on the surface of the nanocarbon fiber, forming nanometallic element M1 and depositing on the surface of the carbon fiber. The cations M2 in the second functional additive then + It plays an electrostatic shielding role, ensuring that the newly generated nano-metallic element is evenly deposited on the carbon fiber surface; the newly deposited nano-metallic element M1 has good lithium affinity and shows an extremely low nucleation barrier to lithium. If charging continues, M1 and M2 + The synergistic effect induces lithium ions to uniformly nucleate on the carbon nanofiber surface and form a mechanically stable, lithium-ion conductive alloy layer, Li-M1. During the subsequent lithium deposition process, this alloy layer effectively prevents the subsequent lithium metal from directly contacting the electrolyte, avoiding side reactions, thereby reducing the irreversible loss of lithium ion capacity during charging and improving coulombic efficiency.

[0032] (3) Under the action of the electric field, the anions in the additives, especially the nitrate ions, are preferentially adsorbed at the positive electrode interface to form an "anion shield" effect, which can construct a solvent-poor / anion-rich double layer, reduce the contact between the free solvent molecules and the electrode, and effectively improve the oxidation tolerance voltage of the electrolyte. The positive electrode electrolyte interface (CEI) thus formed is a thin, uniform and dense protective layer with extremely high ionic conductivity and chemical stability. It not only protects the structural integrity of the positive electrode material, but also inhibits the erosion of the electrolyte on the electrode material, effectively inhibiting the dissolution of transition metals.

[0033] (4) The preparation method of the lithium-ion battery of the present invention can also be used to prepare other alkali metal ion batteries. The preparation method can use the existing battery assembly environment to assemble the battery. The preparation method is simple, the manufacturing cost is low, and the manufacturability is strong. The prepared battery has high energy density, good cycle performance and rate performance, which can meet market demand and is conducive to the promotion of the new energy vehicle and chemical energy storage battery market. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The charge and discharge curves of the full battery prepared in Example 1 at different current densities;

[0035] Figure 2 The rate performance of the full battery prepared in Example 1;

[0036] Figure 3 Comparison of the cycling performance of the full batteries prepared in Example 1 and Comparative Example 1 at 1.0 C;

[0037] Figure 4 SEM images of the surface of the negative electrode current collector materials used in Example 1 and Comparative Example 1 after cycling;

[0038] Figure 5 SEM images of the cross-section of the negative electrode current collector materials used in Example 1 and Comparative Example 1 after cycling;

[0039] Figure 6 The SEM (left) and TEM (right) images of the positive electrode materials of Example 2 and Comparative Example 2 after cycling. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] (1) Preparation of positive electrode sheet

[0043] The cathode active material lithium iron phosphate (LFP), lithium supplement agent Li2S, binder PVDF, conductive additive SP, and conductive additive CNTp (Suzhou First Element Nanotechnology Co., Ltd.) were dispersed in N-methylpyrrolidone (NMP) in a weight ratio of 95:0.5:2.2:1.8:1.5 and stirred to form a uniform slurry. The cathode slurry was then coated on a carbon-coated aluminum foil as the current collector substrate, vacuum-dried at 80°C for 12 h, and rolled and slit to obtain LFP cathode sheets. The single-side mass loading of LFP was approximately 29.4 mg / cm 2 , equivalent to 5mAh / cm 2 .

[0044] (2) Preparation of 3D negative electrode composite current collector

[0045] 10 kg of carbon nanofibers (Suzhou First Element Nanotechnology Co., Ltd., CNTp, diameter 50-200 nm, aspect ratio 50-400) were added to 90 kg of 50% alcohol solution by mass. After ultrasonic treatment, 7 kg of 10% polyvinyl alcohol solution and 3 kg of 10% sodium carboxymethyl cellulose solution were added to the mixture, and the mixture was stirred at 200 rpm for 30 min to fully mix the mixture to obtain a carbon nanofiber dispersion. The above dispersion was coated on both sides of a carbon-coated copper mesh, freeze-dried, calendered, and slit to obtain a negative electrode composite current collector.

[0046] (3) Electrolyte preparation

[0047] In(NO3)3 and CsNO3 powders were sequentially added to the basic electrolyte 3.5M LiFSI DME electrolyte, stirred and dissolved, and the electrolyte was prepared. The concentration of In(NO3)3 in the obtained electrolyte was 0.1M and the concentration of CsNO3 was 0.05M.

[0048] (4) Battery preparation

[0049] After stacking the positive electrode sheet\diaphragm\negative electrode composite current collector, place them in aluminum-plastic packaging film and vacuum bake at 85±5℃ for 24h to obtain the battery cell to be filled with liquid. Inject the prepared electrolyte into the battery cell, seal it and perform the formation according to the following steps: First, charge to 1.0V with a 5C current pulse, with an interval of 10s between each pulse, and pulse 10 times. Then, further charge to 4.2V with a constant current of 1C. After standing for 10min, vacuum exhaust and package the battery.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that:

[0052] 1. The electrolyte directly uses the basic electrolyte 3.5M LiFSI DME;

[0053] 2. Perform the following steps for the first charge: charge at 0.2C for 16 minutes, charge at 0.7C for 40 minutes, and then further charge at 0.5C constant current to 4.0V.

[0054] Figure 1 The charge and discharge curves of the full battery prepared in Example 1 are shown. It can be found that under the test conditions of 0.1 ~ 1.0 C, the battery shows the typical electrochemical behavior of LiFePO4, at about 3.4 V (relative to Li + / Li) shows a flat platform, and can maintain a relatively high discharge capacity (140.1mAh / g) even at 1.0 C. The rate performance test shows that ( Figure 2 ), the battery can still achieve a high specific capacity of 125.4 mAh / g at a high current density (2.0 C), showing excellent rate performance. Figure 3 As shown in the figure, under 1.0 C conditions, the full battery still has a capacity retention rate of 84.2% after 500 cycles, an average coulombic efficiency of 99.97%, and a battery energy density of 314.3wh / kg; while the full battery prepared in Comparative Example 1 has a capacity retention rate of only 60.8% due to the lack of functional additives, and its discharge specific capacity fluctuates continuously during the cycle, reflecting the instability of its interface. The excellent cycle stability performance of the battery prepared in Example 1 is attributed to the stable electrode structure, highly reversible lithium deposition / stripping process, and rapid electrochemical kinetics of the negative electrode. During the charge and discharge process of rapid lithium ion migration, there are no lithium dendrite protrusions in the entire battery, and the interface impedance remains stable.

[0055] In order to further explore the reasons for the cycle stability and rapid reaction kinetics of the prepared battery, the SEM images of the negative electrode current collector material after cycling were tested ( Figure 4 、 Figure 5 The results show that the negative electrode of Comparative Example 1 after cycling ( Figure 4 (a) ), lithium is unevenly deposited on the electrode surface, and granular deposits appear on the negative electrode surface. These particles vary in size, are unevenly distributed, and have a fluffy porous structure. This corresponds to the constant fluctuations in the performance of the full battery during the entire cycle. The uneven deposition of lithium ions leads to instability in the interface. The negative electrode of Example 1 after cycling is shown in its SEM image ( Figure 4 (b) It is clearly observed that the negative electrode surface presents a uniform, continuous coating with no visible particles or cracks. The surface layer formed by the deposited lithium is relatively smooth, with no obvious bumps or rough areas. The deposited layer is continuous across the entire surface, with no visible isolated particles or voids.

[0056] From the cross-sectional image of the negative electrode current collector of Comparative Example 1 ( Figure 5 (a) It can be clearly seen that the lithium is deposited loosely inside the current collector and some lithium is deposited on the "top" of the current collector, causing the volume of the negative electrode to expand. The uneven deposition of lithium ions will lead to instability at the interface. The cross-sectional image of the negative electrode current collector of Example 1 [ Figure 5 (b)] It can be seen that all the lithium is evenly deposited inside the current collector. The uniform deposition of lithium ions improves the battery cycle stability.

[0057] Example 2

[0058] The difference from Example 1 is that:

[0059] 1. The cathode active material is changed to lithium nickel cobalt manganese oxide, and the single-side mass loading of NCM 811 is about 30 mg / cm 2 , equivalent to 6 mAh / cm 2 ;

[0060] 2. Preparation of the electrolyte: Select the basic electrolyte 1M LiTFSI DME, add In(NO3)3 and CsTFSI powders to the basic electrolyte in turn, stir and dissolve, and prepare the electrolyte. The concentration of In(NO3)3 in the obtained electrolyte is 0.1M and the concentration of CsTFSI is 0.05M.

[0061] Comparative Example 2

[0062] The difference from Example 2 is that:

[0063] 1. Directly use the basic electrolyte 1M LiTFSI DME;

[0064] 2. The formation method is the same as that of Comparative Example 1.

[0065] The full battery prepared in Example 2 still had a capacity retention rate of 80.2% after 500 cycles at 1.0 C, an average coulombic efficiency of 99.96%, and a battery energy density of 419.7 Wh / kg; while the full battery prepared in Comparative Example 2 short-circuited in less than 100 cycles, and disassembly of the battery revealed that the diaphragm used was punctured.

[0066] In order to further explore the reasons why the prepared battery can maintain good cycle stability, the SEM and TEM images of its positive electrode material after cycling were tested respectively ( Figure 6 It can be clearly seen that the comparative example 2 using the basic electrolyte formed a thicker and non-uniform CEI ( Figure 6 b), and the positive electrode particles are obviously cracked ( Figure 6 a); while Example 2 uses an electrolyte containing a multifunctional additive to form a thinner, denser and more uniform CEI ( Figure 6 d), the cathode particles are intact ( Figure 6 c). Multifunctional additives can effectively protect the positive electrode material and improve the battery cycle stability.

[0067] Example 3

[0068] The difference from Example 1 is that:

[0069] 1. The positive electrode active material is changed to sodium ion battery material Na3V2O2(PO4)2F (NaVPOF), and the single-side mass loading of NaVPOF is about 19 mg / cm 2 , equivalent to 2.5 mAh / cm 2 ;

[0070] 2. Preparation of the electrolyte: Select the basic electrolyte 1.0 M NaClO4 EC / PC (volume ratio 1:1), add In(NO3)3 and CsNO3 powders to the basic electrolyte in turn, stir and dissolve, and prepare the electrolyte. The concentration of In(NO3)3 in the obtained electrolyte is 0.1M and the concentration of CsNO3 is 0.05M.

[0071] Comparative Example 3

[0072] The difference from Example 3 is that:

[0073] 1. Directly use the basic electrolyte 1.0M NaClO4 EC / PC (volume ratio 1:1);

[0074] 2. The formation method is the same as that of Comparative Example 1.

[0075] The full battery prepared in Example 3 still had a capacity retention rate of 90.4% and an average coulombic efficiency of 99.98% after 500 cycles at 1.0 C. However, the full battery prepared in Comparative Example 3 short-circuited in less than 100 cycles, and disassembly of the battery revealed that the diaphragm used was punctured.

[0076] This shows that this battery preparation method is also applicable to the preparation of other alkali metal ion batteries.

[0077] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An electrolyte comprising an alkali metal salt and a solvent, characterized in that: The electrolyte further contains at least a first functional additive and a second functional additive, wherein the first functional additive is at least one of nitrates and / or bis(trifluoromethylsulfonyl)imide salts of In, Ag, Mg, Al, Zn, and Bi, and the second functional additive is at least one of nitrates and / or bis(trifluoromethylsulfonyl)imide salts of Cs, Rb, and K.

2. The electrolyte according to claim 1, characterized in that The concentration of the first functional additive in the electrolyte is 0.05~0.15M.

3. The electrolyte according to claim 1, characterized in that The concentration of the second functional additive in the electrolyte is 0.01~0.1M.

4. The electrolyte according to claim 1, characterized in that The solvent is at least one of ethylene glycol dimethyl ether, methanol dimethyl ether, ethylene dimethyl ether, methylene diethyl ether, 2,5-dimethyltetrahydrofuran, 1,3-dioxolane, ethylene carbonate, and propylene carbonate; The concentration of the alkali metal salt is 1.0~3.5M.

5. The electrolyte according to claim 4, characterized in that The electrolyte is used for lithium-ion batteries, the alkali metal salt is a lithium salt, and the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate.

6. A method for preparing an alkali metal ion battery, characterized in that: The following steps are involved: S1, preparing a positive electrode sheet and a negative electrode composite current collector; S2, assembling the positive electrode sheet, separator and negative electrode composite current collector into a dry battery cell; S3. Inject the electrolyte described in any one of claims 1 to 5 into the dry battery cell. After sufficient rest, charge it with a first current pulse to a first cut-off voltage. After resting, charge it with a second constant current to a second cut-off voltage. After resting again, vacuum exhaust and package the battery.

7. The preparation method according to claim 6, characterized in that In step S3, the first charging current is 2-50C, the first cut-off voltage is 0.5-1.5V, the pulse interval is 1-20s, and the pulse is repeated 5-15 times.

8. The preparation method according to claim 6, characterized in that In step S3, the second charging current is 0.1-2C, and the second cut-off voltage is 3.6-4.5V.

9. The preparation method according to claim 6, characterized in that The negative electrode composite current collector is prepared by curing a composite film layer on a current collector substrate. The composite film layer is an electronic conductor with a three-dimensional porous structure, preferably a carbon nanofiber aerogel film.

10. An alkali metal ion battery, characterized in that: The method is prepared according to any one of claims 6 to 9.

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