A high-energy-density lithium metal battery and a method of making the same

Abstract

This invention belongs to the field of electrochemical energy storage technology and discloses a high-energy-density lithium metal battery and its preparation method. The core of the method lies in controlling the microporous structure of the high areal loading cathode through differential stirring and coating processes, enabling it to synergistically interact with a specific fluorinated gel electrolyte precursor solution. During battery assembly and in-situ polymerization, the electrolyte can fully wet the optimized cathode pores and react on the surface of the cathode active material to form a stable interface layer containing Mn-F bonds. This method effectively solves the fundamental problem of compatibility between high areal loading cathodes and low electrolytes in high-energy-density lithium metal batteries. The resulting battery combines high energy density and long cycle life, achieving a mass energy density of over 550 Wh / kg at 2-4.8 V, and exhibiting excellent chemical stability at the cathode interface. This invention provides a systematic and industrially scalable high-energy-density battery solution.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology and relates to a high-energy-density lithium metal battery and its preparation method. Background Technology

[0002] Lithium metal batteries (LMBs) utilize a high theoretical specific capacity (3860 mAh·g). -1 Lithium metal, with its low oxidation potential (compared to -3.04 V for hydrogen electrode), has great potential as an anode in energy storage and transportation, and is widely used in battery systems. Commercial cathodes (LiFePO4 (LFP), LiCoO2, xLi2MnO3·(1-x)LiMO2 (LRMO), etc.) have good cycle stability and high material tap density, and are considered ideal choices for next-generation energy storage systems. However, transition metal cathode materials such as LFP have narrow intrinsic voltage ranges and low median discharge voltages, resulting in low energy density in lithium metal battery systems, which cannot alleviate the "range anxiety" problem caused by the widespread adoption of new energy vehicles. LRMO cathode materials not only have a wide voltage range (2-4.8 V) but also a higher theoretical discharge specific capacity (>300 mAh·g). -1 High-energy-density batteries have an advantage in energy density. However, high-energy-density batteries require high areal loading (bifacial loading > 50 mg·cm³). -2 High areal loading and low E / C ratios pose challenges to battery fabrication and operation. High areal loading, due to the increased proportion of active material in the electrode, often leads to cracking and powder shedding after drying, requiring improved electrode fabrication processes. A low E / C ratio implies electrolyte-poor conditions, under which the lithium deposition / stripping process with large areal loading poses a significant challenge to the stability of the electrolyte / cathode interface. Furthermore, a chemically stable electrolyte / cathode interface layer is crucial to reduce electrolyte consumption or gas generation caused by side reactions between the electrolyte and cathode materials. Chinese patent CN116314829A points out that during the fabrication of high areal loading electrodes, as the active material loading increases, the electrode material exhibits strong mechanical instability above a critical thickness, making the active material prone to cracking and even detachment. Simply increasing the amount of conductive agent and binder not only increases costs but also severely impairs the battery's rate performance. This indicates that cracking of high areal loading electrodes is a common technical challenge in this field. Therefore, employing appropriate fabrication processes and constructing an electrolyte system that is compatible with both positive and negative electrodes under high voltage is beneficial for preparing long-life, high-energy-density lithium metal batteries.

[0003] In electrode fabrication, it is essential to ensure good ion / electron transport channels under high loading conditions. Carbon nanotubes (CNTs), as conductive agents, can construct point-to-line structures between electrodes, improving electron transport. However, CNTs have poor dispersibility and tend to agglomerate in the slurry, leading to uneven CNT concentration distribution within the electrode and ultimately reducing overall battery performance. Similarly, during large-scale stirring of slurries containing polyvinylidene fluoride (PVDF) binders, a polymeric "pole-climbing effect" easily occurs, causing the inner layers of slurry to aggregate near the stirring paddle. The dispersibility issue of this slurry remains to be addressed.

[0004] Regarding electrolytes, classic ester-based liquid electrolytes not only suffer from dendrite growth on the negative electrode side, but the dissolution of transition metals on the positive electrode side also leads to severe lattice distortion, further reducing battery performance. Solid-state lithium metal batteries can fundamentally avoid the problem of transition metal dissolution, but the interface problem between the electrode and electrolyte caused by solid-solid contact hinders the development of solid-state lithium metal batteries. Gel electrolytes (GPEs) better balance the above relationships. Gel electrolytes (GPEs) use polymers to bind the electrolyte containing lithium salts and solvents within polymer chains, exhibiting high room-temperature ionic conductivity and improving battery safety. In GPEs, using weakly solvating solvents instead of classic strong solvating solvents can construct more anion-rich solvated structures in the system, thereby promoting the decomposition of film-forming solvents (such as FEC) and salt anions at the interface to form a more robust and stable interface layer. However, the weakly solvating solvents themselves are Li-phobic. + These characteristics will reduce the conductivity of GPE to some extent. Therefore, the aforementioned issues of transport dynamics and positive / negative electrode compatibility still need to be addressed.

[0005] Therefore, there is an urgent need to develop a systematic solution that can synergistically regulate the microstructure of the positive electrode and its interfacial chemistry with the electrolyte, thereby achieving long-cycle stability of the battery while ensuring high energy density. Summary of the Invention

[0006] This invention aims to overcome the aforementioned deficiencies of the prior art and provide a high-energy-density lithium metal battery and its preparation method. Through specific slurry preparation and coating processes, the micropore structure of the high areal loading cathode is precisely controlled to adapt it to efficient and uniform wetting under electrolyte-poor conditions. Furthermore, in synergy with a specific fluorinated gel electrolyte system, a stable interface layer reinforced by Mn-F chemical bonding is constructed in situ on the surface of the cathode active material on the basis of sufficient wetting. This simultaneously solves the dual challenges of interface wetting and interface stability faced by high-energy-density lithium metal batteries, thereby improving electrochemical performance.

[0007] The applicant has discovered that simply increasing the areal loading and decreasing the electrolyte content leads to a sharp deterioration in battery performance. The root cause is that the high-load electrode sheets prepared using conventional processes have a porous structure that hinders uniform wetting of the electrolyte-poor electrolyte, resulting in an unstable electrolyte / cathode solid-liquid interface, exacerbating side reactions and structural degradation. Therefore, the key to this invention lies in: controlling the formation of an electrode microstructure suitable for electrolyte-poor wetting through specific slurry preparation and coating processes, and enabling this structure to synergize with a specific fluorinated gel electrolyte to construct a stable interface layer (such as forming Mn-F bonds) on the cathode surface, thereby fundamentally resolving the aforementioned contradictions.

[0008] The present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a high-energy-density lithium metal battery, comprising the following steps: (1) A positive electrode active slurry is prepared by using a differential stirring process with lithium-rich manganese-based positive electrode active material, conductive agent and binder in proportion; (2) The positive electrode active slurry is coated on the current collector and dried to obtain a high surface loading positive electrode sheet with optimized pore structure; (3) Using lithium metal or lithium copper composite strip as negative electrode (the thickness of lithium metal in lithium copper composite strip is 20-100 μm), the positive electrode and negative electrode are stacked and assembled, and the positive electrode is impregnated with a fluorine-containing gel electrolyte precursor solution to form a stable interface layer containing Mn-F bonds on the surface of the positive electrode active material. The impregnated cell is subjected to in-situ polymerization and formation treatment to obtain the high energy density lithium metal battery.

[0009] Preferably, the conductive agent comprises carbon nanotubes and conductive carbon black, and the binder is polyvinylidene fluoride (PVDF); the mass ratio of the lithium-rich manganese-based positive electrode active material, the conductive agent, and the binder is 80-96.5:2.5-10:1-10.

[0010] Preferably, the differential stirring process includes: S1. Adhesive Dispersion Stage: Disperse the adhesive in the solvent. First, stir slowly at 25±5 rpm for 15-20 minutes to ensure the adhesive is completely wetted and there is no residue on the stirring paddle. Then, increase the speed to 40±5 rpm and continue stirring for 5-15 minutes. Finally, stir at high speed at 3000±200 rpm for 300-360 minutes to form a uniform adhesive solution. The mass ratio of adhesive to solvent is 0.05-0.08. S2, First conductive agent dispersion stage: Add carbon nanotube dispersion to the adhesive solution, stir slowly at 25±5 rpm for 5-15 min and scrape the material, stir at 30±5 rpm first, and then stir at 3000±200 rpm for 55-65 min to obtain an adhesive solution with uniformly dispersed carbon nanotubes. S3, Second conductive agent dispersion stage: Add conductive carbon black to the uniformly dispersed carbon nanotube solution, stir slowly at 25±5 rpm for 5-15 min and scrape the material, stir at 30±5 rpm for 10-20 min, and then stir at 3000±200 rpm for 80-100 min to obtain a uniformly dispersed carbon nanotube and conductive carbon black solution. S4. Active material mixing stage: Add the remaining solvent in portions to the uniformly dispersed carbon nanotubes and conductive carbon black slurry, then slowly add lithium-rich manganese-based positive electrode active material powder. Stir slowly at 25±5 rpm for 10-20 min and scrape the material, then stir at 30±5 rpm for 5-15 min, and then stir at 3000±200 rpm for 30-40 min to obtain a slurry with uniformly dispersed active materials. S5. Vacuum Degassing Stage: After completing steps S1 to S4, the mixture is slowly stirred at 15±5 rpm for 30-60 minutes under vacuum conditions to obtain the positive electrode active slurry. This method is simple and easy to operate, and can effectively eliminate the "pole climbing effect" caused by the polymer slurry during stirring.

[0011] Preferably, the coating process includes: coating the positive electrode active slurry onto the current collector with a wet film thickness of 300-560 μm, followed by vacuum drying at 110-130°C for 10-14 hours to obtain a single-sided areal loading of 16-36 mg / cm². 2 The positive electrode sheet.

[0012] Preferably, the fluorinated gel electrolyte precursor solution comprises a weakly solvated electrolyte, a polymerizing monomer, and an initiator; The mass ratio of the polymeric monomer to the weakly solvated electrolyte is 1:7.5-15. Specifically, the weakly solvated electrolyte comprises a mixed solvent of fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl acetate (TFEA), and lithium hexafluorophosphate and lithium difluorooxalate borate dissolved therein. The concentration of lithium hexafluorophosphate in the weakly solvated electrolyte is 0.8-1.1 mol / L, and the concentration of lithium difluorooxalate borate is 0.1-0.3 mol / L.

[0013] The polymerizing monomer is selected from at least one of acrylic monomers and epoxy monomers. The acrylic monomer is one or more of 2,2,3,4,4,4-hexafluorobutyl acrylate, trifluoroethyl acrylate, ethoxylated trimethylolpropane triacrylate, or pentaerythritol tetraacrylate; the epoxy monomer is one or more of vinyl ethylene carbonate, vinylene carbonate, or trimethylene carbonate. More preferably, the polymerizing monomer is two or more of 2,2,3,4,4,4-hexafluorobutyl acrylate, trifluoroethyl acrylate, ethoxylated trimethylolpropane triacrylate, and pentaerythritol tetraacrylate.

[0014] Preferably, lithium hexafluorophosphate (LiPF6) and lithium difluorooxalate phosphate (LiDFOB) are dissolved in a mixed solvent of fluoroethylene carbonate and 2,2,2-trifluoroethyl acetate to obtain a weakly solvated electrolyte. Polymer monomers and an initiator are added to the weakly solvated electrolyte to obtain a fluorinated gel electrolyte precursor solution. The polymer matrix in the fluorinated gel electrolyte precursor solution is a network polymer composed of 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) and ethoxylated trimethylolpropane triacrylate (ETPTA), or a linear or cross-linked polymer composed of acrylic monomers and / or epoxy monomers. In the precursor solution, based on 100% by weight of the weakly solvated electrolyte, the amount of 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) is 5-10%, and the amount of ETPTA is 2.5-5%. The initiator is azobisisobutyronitrile (AIBN), and the amount of initiator is 0.30-0.50% based on 100% of the weight of the mixed solution of the weakly solvated electrolyte and the polymerized monomer.

[0015] Preferably, the amount of the fluorinated gel electrolyte precursor solution added is 1.3-2.8 g / Ah, calculated as the ratio of the precursor solution mass to the positive electrode capacity.

[0016] Preferably, the in-situ polymerization process includes: pressing the battery cell containing the precursor solution in a fixture and letting it stand for 8-16 hours, followed by heating and polymerization at 45-55 °C for 2-6 hours.

[0017] A second aspect of the present invention provides a high-energy-density lithium metal battery, which is prepared by the above-described preparation method, wherein the surface of its positive electrode active material contains Mn-F bonds.

[0018] Preferably, the energy density of the battery when operating in the voltage range of 2-4.8 V is not less than 550 Wh / kg. The energy density (ED, Wh / kg) of the pouch battery of the present invention is calculated based on formula (1): (1) Where E is the discharge energy of the pouch battery (Wh), and m is the total mass of the battery (kg).

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. This invention is the first to systematically combine electrode microstructure control with electrolyte interface chemical design, and specifically solves the dual bottleneck problems of interface wetting and interface stability in high-energy-density lithium metal batteries under high load-lean electrolyte conditions. The technical path is non-obvious.

[0020] 2. This invention optimizes the pore structure of the positive electrode through differential stirring and coating processes, enabling it to synergistically interact with the fluorinated gel electrolyte precursor solution to form a stable interface layer characterized by Mn-F bonds in situ on the surface of the positive electrode active material. This interface layer effectively suppresses irreversible phase transitions of the positive electrode material and the dissolution of transition metal ions during charging and discharging, significantly improving the chemical stability of the electrode / electrolyte interface, which is the fundamental reason for the battery's ultra-long cycle life.

[0021] 3. This invention achieves a simultaneous breakthrough in energy density and cycle life. Example data shows that the pouch cell prepared using the method of this invention can provide an energy density exceeding 550 Wh / kg while operating within a voltage range of 2-4.8 V, and exhibits cycle stability far exceeding that of conventional liquid electrolyte batteries under harsh electrolyte-deficient conditions.

[0022] 4. The preparation method described in this invention has clear steps and well-defined parameters, making it easy to adapt and scale up on existing battery manufacturing lines, and has good prospects for industrial application.

[0023] This invention employs a differential stirring method for positive electrode coating, effectively mitigating the "pole-climbing effect" generated during polymer solution stirring and improving the dispersion uniformity of the conductive agent within the positive electrode sheet. For the electrolyte, an in-situ polymerization method is used; polymerization is initiated by heating the precursor solution after it is added to the battery, forming a gel electrolyte. A weak solvating solvent is used instead of a classic strong solvating solvent, resulting in an anion-rich solvating structure in the system. This promotes the decomposition of film-forming solvents (such as FEC) and salt anions at the interface, forming a more robust and stable interfacial layer, thus enabling stable operation of the pouch battery even under low electrolyte conditions. Through the synergy of process and formulation, this invention achieves stable operation of pouch batteries with high positive electrode loading and low electrolyte addition, and improves the energy density of lithium metal batteries, highlighting the advantages of lithium batteries in the energy storage field. Attached Figure Description

[0024] Figure 1 This is a test diagram of electrolyte leakage in a soft-pack battery, where a corresponds to Example 1 and b corresponds to Example 1. Figure 2The test diagrams show the contact angle of the positive electrode sheet in Comparative Example 2 and Example 1; Figure 3 Ultrasonic resolution transmission images of the pouch cells of Comparative Examples 2-3 and Example 1; Figure 4 The images show the morphology and cross-sectional view of the positive electrode sheet, where the left side of a corresponds to Example 2 and the right side corresponds to Example 1; and b corresponds to the cross-sectional view of Example 1. Figure 5 The images show the morphology of the negative and positive electrodes of the Li-LRMO pouch cell in Example 1 after two cycles at a rate of 0.1 C, where a corresponds to the negative electrode and b corresponds to the positive electrode. Figure 6 The above are characterization diagrams of the post-cycle cathodes of Comparative Examples 1-2 and Example 1 using time-of-flight secondary ion mass spectrometry (TOF-SIMS); where a represents MnF3. - Three-dimensional distribution map of fragment content, b represents BO2 - Three-dimensional distribution map of fragment content, where c represents LiF2. - Three-dimensional distribution map of fragment content; Figure 7 The graph shows the cycling performance of Li-LRMO pouch cells in Comparative Examples 1-3 at a rate of 0.1 C. Figure 8 The following graphs show the cycle performance and capacity-voltage of the Li-LRMO pouch cell in Comparative Example 4 at a rate of 0.1 C, where a is the cycle life graph of the pouch cell and b is the corresponding capacity-voltage graph. Figure 9 The following are the cycle performance and capacity-voltage diagrams of the Li-LRMO pouch cell in Example 1 at a rate of 0.1 C, where a is the cycle life diagram of the pouch cell and b is the corresponding capacity-voltage diagram. Figure 10 The following is a graph showing the cycle performance and capacity-voltage of the Li-LRMO pouch cell in Example 2 under 0.1 C charging and 0.33 C discharging conditions, where a is the cycle life graph of the pouch cell and b is the corresponding capacity-voltage graph. Figure 11 These are images of the soft-pack battery before and after needle puncture in Example 1, where a corresponds to before needle puncture, b corresponds to during needle puncture, and c corresponds to after needle puncture. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Example 1 A method for preparing a high-energy-density lithium metal battery includes the following steps: (1) Preparation of positive electrode active slurry A positive electrode active slurry was prepared by differential stirring at a mass ratio of 95:3:2 using lithium-rich manganese-based positive electrode active material (LRMO), conductive agent (SuperP), and binder (PVDF). The specific operation is as follows: S1. Adhesive dispersion stage: PVDF adhesive is dispersed in NMP solvent and slowly stirred at 25 rpm for 20 min to ensure that the PVDF adhesive is completely wetted and there is no residue on the stirring paddle; then the speed is increased to 40 rpm and stirring is continued for 10 min; finally, the speed is high-speed stirred at 3000 rpm for 320 min to form a uniform adhesive solution; wherein, the mass ratio of PVDF to NMP is 0.07:1. S2, First conductive agent dispersion stage: Add carbon nanotube (CNT) dispersion to the above adhesive solution, stir slowly at 25 rpm for 10 min and scrape the material, stir at 30 rpm for 10 min and then stir at 3000 rpm for 60 min to obtain an adhesive solution with uniform CNT dispersion. S3, Second conductive agent dispersion stage: Add conductive carbon black (Super P) to the uniformly dispersed CNT solution, stir slowly at 25 rpm for 10 min and scrape the material, stir at 30 rpm for 15 min, and then stir at 3000±200 rpm for 90 min to obtain a uniformly dispersed CNT and Super P solution. S4. Active material mixing stage: In the uniformly dispersed CNT and Super P slurry, the remaining NMP is added in two batches (the amount added in the two batches is equal, so that the solid content of the slurry is controlled at 35%), and stirred for 5 min after each addition; then lithium-rich manganese-based positive electrode active material powder is slowly added, stirred at 25 rpm for 15 min and scraped, then stirred at 30 rpm for 10 min, and then stirred at 3000 rpm for 35 min to obtain a slurry in which the active material is uniformly dispersed. S5. Vacuum degassing stage: Under vacuum conditions, the active material is slowly stirred at a speed of 15 rpm for 30 minutes to uniformly disperse the slurry, thus obtaining the positive electrode active slurry.

[0027] (2) Preparation of high areal loading positive electrode sheet: The coating thickness was adjusted to 560 μm, and the positive electrode active slurry was coated onto the current collector. After vacuum heating at 120 ℃ for 12 h, a single-sided areal loading of 35.2 mg / cm² was obtained. 2The positive electrode sheet.

[0028] (3) Preparation of fluorine-containing gel electrolyte precursor solution: A weakly solvated electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) and lithium difluorooxalate borate (LiDFOB) in a solvent of fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethyl acetate (TFEA) at a mass ratio of 3.46:1. The concentration of lithium hexafluorophosphate in the weakly solvated electrolyte was 0.9 mol / L, and the concentration of lithium difluorooxalate borate was 0.2 mol / L.

[0029] Polymerizing monomers and initiators were added to the above-mentioned weakly solvated electrolyte, wherein: based on 100% weight of the weakly solvated electrolyte, the amount of hexafluorobutyl acrylate (HFBA) was 5.0%, and the amount of ethoxylated trimethylolpropane triacrylate (ETPTA) was 2.5%; based on 100% weight of the mixed solution of the weakly solvated electrolyte and polymerizing monomers, the amount of initiator azobisisobutyronitrile (AIBN) was 0.30%. After stirring for 20 min, a fluorinated gel electrolyte precursor solution was obtained.

[0030] (4) Preparation of Li-LRMO pouch cell A lithium-copper composite strip with a thickness of 80 μm was used as the negative electrode. The positive and negative electrodes were stacked to form a cell, and tabs were welded on. The cell was then sealed with a 76 μm aluminum-plastic film. A fluorinated gel electrolyte precursor solution was added to the cell. The ratio of the precursor solution mass to the positive electrode capacity (E / C) was 1.41 g / Ah. During battery assembly, the precursor solution was dropped onto both sides of the Celgard separator and the sides were sealed. The assembled pouch cell was pressed in a fixture and placed for 12 h. Then, it was heated and polymerized at 50 °C in a forced-air oven for 4 h. After cooling to room temperature, it was formed.

[0031] Example 2 A method for preparing a high-energy-density battery differs from Example 1 only in that: in step (3), when adding polymer monomers to the weakly solvated electrolyte, the amount of trifluoroethyl acrylate used is 3.0% and the amount of pentaerythritol tetraacrylate is 1.5% based on 100% of the weight of the weakly solvated electrolyte. After stacking and assembling according to the method and materials in Example 1, a fluorinated gel electrolyte precursor solution is added to the packaged cell. The ratio of the precursor solution mass to the positive electrode capacity (E / C) is 1.43 g / Ah. When assembling the battery, the precursor solution is dropped onto both sides of the Celgard separator and side-sealed. The assembled soft-pack battery is pressed in a fixture and placed for 12 h, then heated and polymerized at 50 °C in a forced-air oven for 4 h. After cooling to room temperature, it is then formed.

[0032] Comparative Example 1 A method for preparing a high-energy-density battery differs from Example 1 only in that: step (3) does not involve preparing a fluorinated gel electrolyte precursor solution. Step (4) directly uses commercially available LB-012 electrolyte with a solute concentration of 1.15 mol·L⁻¹. -1 The LiPF6 was used as the solvent, a mixture of DMC, EC, and EMC in a volume ratio of 2:1:2. An 80 μm thick lithium-copper composite strip was used as the negative electrode. The positive and negative electrodes were stacked to form a battery cell, which was then welded with tabs. A 76 μm aluminum-plastic film was used for top sealing to obtain the encapsulated battery cell. Commercial LB-012 electrolyte was then added to the encapsulated cell. The mass ratio (E / C) of the commercial LB-012 electrolyte to the positive electrode capacity was 1.41 g·Ah. -1 During battery assembly, the precursor solution is added dropwise to both sides of the Celgard separator, side-sealed for formation, and left to stand for 12 hours.

[0033] Comparative Example 2 A method for preparing a high-energy-density battery differs from Example 1 only in that: step (1) involves preparing a positive electrode active slurry using a classic process with lithium-rich manganese-based positive electrode active material (LRMO), conductive agent (SuperP), and binder (PVDF) in a mass ratio of 95:3:2; the specific operation is as follows: (1) Preparation of positive electrode active slurry S1. Adhesive dispersion stage: PVDF adhesive is dispersed in NMP solvent and slowly stirred at 30 rpm for 20 min, followed by high-speed stirring at 3000 rpm for 330 min to form a uniform adhesive solution; wherein, the mass ratio of PVDF to NMP is 0.05:1. S2, Conductive agent dispersion stage: Add conductive carbon black (Super P) to the uniformly dispersed PVDF solution, stir slowly at 25 rpm for 10 min and scrape the material, then stir at 3000 rpm for 90 min to obtain a uniformly dispersed PVDF and Super P solution. S4. Active material mixing stage: Add the remaining NMP to the PVDF and Super P uniformly dispersed slurry (to control the solid content of the slurry at 35%), and stir for 10 min after adding; then slowly add lithium-rich manganese-based positive electrode active material powder, stir at 25 rpm for 15 min and scrape the material, and then stir at 3000 rpm for 45 min to obtain a slurry with uniformly dispersed active materials. S5. Vacuum degassing stage: Under vacuum conditions, the active material is slowly stirred at a speed of 15 rpm for 30 minutes to uniformly disperse the slurry, thus obtaining the positive electrode active slurry.

[0034] (2) Preparation of high areal loading positive electrode sheet: The coating thickness was adjusted to 560 μm, and the positive electrode active slurry was coated onto the current collector. After vacuum heating at 120 ℃ for 12 h, a single-sided areal loading of 35.1 mg cm⁻¹ was obtained. -2 The positive electrode sheet.

[0035] Comparative Example 3 A method for preparing a high-energy-density battery differs from Example 1 only in that the ratio of the precursor solution mass to the positive electrode capacity (E / C) is 1.25 g·Ah. -1 .

[0036] Comparative Example 4 A method for preparing a high-energy-density battery includes the following steps: (1) Preparation of positive electrode active slurry A positive electrode active slurry was prepared using the same classic process as Comparative Example 2, with lithium-rich manganese-based positive electrode active material (LRMO), conductive agent (SuperP), and binder (PVDF) in a mass ratio of 95:3:2. (2) Preparation of high areal loading positive electrode sheet: The coating thickness was adjusted to 560 μm, and the positive electrode active slurry was coated onto the current collector. After vacuum heating at 120 ℃ for 12 h, an areal loading of 35.2 mg / cm² was obtained. -2 The positive electrode sheet.

[0037] (3) Preparation of electrolyte precursor solution Using fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) as solvents (FEC / EMC = 1 / 4, w / w), 1 M LiPF6 was dissolved in the solvent to obtain the electrolyte. Based on 100% by weight of the electrolyte, 0.5 wt% tris(trimethylsilyl)borate (TMSB) was added as an electrolyte additive, and the mixture was stirred for 10 min to obtain the electrolyte precursor solution. It should be noted that this electrolyte formulation is the optimal electrolyte used in existing literature for Li-LRMO pouch cells in the 2-4.8 V cycling range.

[0038] (4) Preparation of soft-pack batteries An 80 μm thick lithium-copper composite strip was used as the negative electrode. The positive and negative electrodes were stacked to form a battery cell, which was then welded with tabs. A 76 μm aluminum-plastic film was used for top sealing to obtain the encapsulated battery cell. A fluorinated gel electrolyte precursor solution was then added to the encapsulated cell. The ratio of the precursor solution mass to the positive electrode capacity (E / C) was 1.41 g·Ah. -1 The electrolyte was added dropwise to both sides of the Celgard diaphragm, which was then side-sealed and formed.

[0039] Performance testing and analysis The materials prepared in the examples and comparative examples were characterized and their electrochemical performance was tested.

[0040] Figure 1 The diagram shows the electrolyte leakage test results for the pouch cell, where a corresponds to Comparative Example 1 and b corresponds to Example 1. Two pouch cells were cut open and inverted for 15 minutes, and the mass change before and after was measured. Comparative Example 1 showed a 14.2% electrolyte leakage, while Example 1 showed no leakage, indicating that the precursor solution completely wetted the interior of the separator and polymerized upon heating to form a gel electrolyte.

[0041] Figure 2 The test diagrams of the positive electrode contact angles of Comparative Example 2 and Example 1 show that the positive electrode prepared by the differential stirring process of the present invention has a smaller contact angle and better wettability with electrolyte.

[0042] Figure 3 The images show ultrasonically resolved transmission images of the pouch cells from Comparative Examples 2-3 and Example 1. A redder color indicates better wettability. Comparative Example 2, due to the use of a classic process, exhibits uneven electrolyte distribution within the cell. Comparative Example 3, with its low E / C ratio, did not fully wet the cell with added electrolyte. In contrast, Example 1, using the differential stirring process of this invention, produces a positive electrode sheet with suitable porosity, resulting in better electrolyte wettability throughout the pouch cell.

[0043] Figure 4 The images show the morphology and cross-sectional view of the positive electrode sheet. In example a, the left side corresponds to Example 2, and the right side corresponds to Example 1. It can be seen that the electrode sheet prepared by the differential stirring process of the present invention has a smoother surface and fewer cracks. Figure 4 Figure b is a cross-sectional view of the positive electrode sheet prepared in Example 1. It can be seen that its internal structure is relatively uniform and its thickness is appropriate.

[0044] Figure 5 Figure 1 shows the morphology of the negative and positive electrodes of the Li-LRMO pouch cell from Example 1 after two cycles at 0.1 C. Figure 1a corresponds to the negative electrode, and Figure 2b corresponds to the positive electrode. It can be seen that the positive electrode prepared in this invention maintains a good conductive network after cycling, with CNTs distributed around the LRMO spherical particles, ensuring full utilization of the electrode capacity in the thick positive electrode. Figure 2a shows that the deposition on the negative electrode surface is relatively uniform. Due to the lower clamping pressure compared to coin cells, the lithium morphology is close to a blocky stack, with no obvious dead lithium formation, proving that the in-situ polymerized gel electrolyte has good compatibility with the negative electrode.

[0045] Figure 6 The following are characterization diagrams of the post-cycle cathodes of Comparative Examples 1-2 and Example 1 using time-of-flight secondary ion mass spectrometry (TOF-SIMS), where a represents MnF3.- Three-dimensional distribution map of fragment content, b represents BO2 - Three-dimensional distribution map of fragment content, where c represents LiF2. - The three-dimensional distribution map of fragment content shows that there is no obvious MnF3 on the surface of the cathode in Comparative Example 1. - This demonstrates that the vast majority of its interfacial layer is bonded by Mn-O bonds, making it prone to reaction at the cathode / electrolyte interface under high pressure. Structural distortion causes oxygen to escape as oxygen gas and leads to the migration of transition metal ions. Furthermore, its BO2... - and LiF2 - When fragment ions are present in low concentrations and shallowly distributed, the resulting interface layer is unstable. Comparative Example 2 showed a weak MnF3 concentration. - The signal indicates that a partial exchange reaction (F replacing O) has occurred in the electrolyte, but the degree is weak and insufficient to form a stable and robust interface layer. In Example 1, significant MnF3 was detected on the surface. - The signal indicates that the exchange reaction can occur fully at the interface, and the Mn-F bond can better stabilize the structure within LRMO during cycling, while its BO2 - and LiF2 - The abundance of fragment ions indicates the formation of a stable fluorine-rich / boron-rich interface layer on the LRMO surface, which effectively improves the cycle life of Li-LRMO batteries.

[0046] Figure 7 The graphs show the cycling performance of Li-LRMO pouch cells (Comparative Examples 1-3) at a 0.1 C rate. It can be seen that Comparative Example 3, with the least electrolyte, is easily depleted and overcharged during cycling, only managing 4 cycles. While Comparative Example 1 can also cycle, the unstable interface layer formed by the commercial electrolyte results in a lower number of cycles. Comparative Example 2 has the longest cycle life, achieving 26 cycles. However, due to the poor internal wetting of the electrodes caused by the classic process, uniform electron / ion conduction cannot be achieved, resulting in a lower battery capacity.

[0047] Figure 8 The graph shows the cycling performance of the Li-LRMO pouch cell in Comparative Example 4 at a rate of 0.1 C. In the graph, a is the cycle life of the pouch cell, and b is the corresponding capacity-voltage graph. Comparative Example 4 is the optimal electrolyte used in the Li-LRMO pouch cell in the literature for cycling from 2 to 4.8 V, with a capacity retention of 80.58% after 19 cycles.

[0048] Figure 9The graph shows the cycle performance of the Li-LRMO pouch cell in Example 1 at a 0.1 C rate, where a is the cycle life graph of the pouch cell and b is the corresponding capacity-voltage graph. It can be seen that the capacity retention rate after 67 cycles is 90.42%. The pouch cell has a first-cycle discharge capacity of 4.79 Ah, a first-cycle discharge energy of 16.574 Wh, and a total battery mass of 29.987 g, resulting in a total energy density of 552.71 Wh / kg. Furthermore, the cycle life of Example 1 is significantly better than that of Comparative Example 4, indicating that the process and formulation of this invention can synergistically achieve excellent battery performance. The energy density (ED, Wh / kg) is calculated based on formula (1): (1) Where E is the discharge energy of the pouch battery (Wh), and m is the total mass of the battery (kg).

[0049] Figure 10 The graph shows the cycle performance of the Li-LRMO pouch cell in Example 2 under 0.1 C charging and 0.33 C discharging conditions. In the graph, a is the cycle life of the pouch cell and b is the corresponding capacity-voltage graph. The capacity retention rate after 90 cycles is 84.68%, which shows that the process and formulation of the present invention are still applicable to the battery system in the voltage range of 2-4.6 V and exhibit excellent cycle stability.

[0050] Figure 11 The images shown are of the soft-pack battery in Example 1 before and after being punctured. It can be seen that no fire or other phenomena occurred after being punctured and left in place for 30 seconds, demonstrating that the soft-pack battery of the present invention has high safety.

[0051] Based on the above embodiments, this invention provides a method for preparing a high-energy-density lithium metal battery. The method includes: mixing lithium-rich manganese-based positive electrode active material, conductive agent, and binder in a specific ratio to prepare a positive electrode active slurry, which is then coated onto an aluminum foil current collector to obtain a positive electrode sheet. A lithium-copper composite strip is used as the negative electrode sheet. The positive and negative electrode sheets are then combined using a stacking method to obtain a high-energy-density battery. The differential stirring method optimizes the slurry preparation process, resulting in a better electrode surface loading and a suitable ratio of conductive agent and binder, ensuring normal positive electrode capacity while improving the overall energy density of the battery. Furthermore, optimizing various parameters in the pouch battery (such as the thickness of lithium in the negative electrode sheet and the amount of electrolyte added to the battery) effectively improves the battery's energy density and cycle stability. This optimization of electrode preparation processes and battery parameters yields a high-energy-density lithium battery. This method is easy to operate and has the potential for large-scale application. The embodiments of this invention do not exhaust all options in the technical solutions of this invention. Technical solutions composed of other options not included in the embodiments have the same technical effects as the disclosed embodiments. Further comparisons have verified that the modifications made in this invention regarding cathode process, pouch parameters, and electrolyte engineering are quite effective, resulting in Li-LRMO pouch batteries exhibiting high energy density and good cycle stability.

[0052] It should be further noted that the above embodiments are merely for understanding the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Any obvious adjustments and modifications made to the inventive concept should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-energy-density lithium metal battery, characterized in that, Includes the following steps: (1) A lithium-rich manganese-based positive electrode active material, a conductive agent, and a binder are prepared into a positive electrode active slurry by a differential stirring process in a certain proportion; the differential stirring process includes a binder dispersion stage, a conductive agent dispersion stage, an active material mixing stage, and a vacuum degassing stage performed sequentially. (2) The positive electrode active slurry is coated on the current collector and dried to obtain a high surface loading positive electrode sheet with optimized pore structure; (3) Using lithium metal or lithium copper composite strip as negative electrode, the positive electrode and negative electrode are stacked and assembled, and the positive electrode is impregnated with a fluorine-containing gel electrolyte precursor solution to form a stable interface layer containing Mn-F bonds on the surface of the positive electrode active material. The impregnated cell is subjected to in-situ polymerization and formation treatment to obtain the high energy density lithium metal battery.

2. The preparation method according to claim 1, characterized in that, The conductive agent includes carbon nanotubes and conductive carbon black, and the binder is polyvinylidene fluoride; the mass ratio of the lithium-rich manganese-based positive electrode active material, the conductive agent, and the binder is 80-96.5:2.5-10:1-10.

3. The preparation method according to claim 2, characterized in that, The differential stirring process includes: S1. Adhesive Dispersion Stage: Disperse the adhesive in the solvent. First, stir slowly at 25±5 rpm for 15-20 minutes to ensure the adhesive is completely wetted and there is no residue on the stirring paddle. Then, increase the speed to 40±5 rpm and continue stirring for 5-15 minutes. Finally, stir at high speed at 3000±200 rpm for 300-360 minutes to form a uniform adhesive solution. The mass ratio of adhesive to solvent is 0.05-0.

08. S2, First conductive agent dispersion stage: Add carbon nanotube dispersion to the adhesive solution, stir slowly at 25±5 rpm for 5-15 min and scrape the material, stir at 30±5 rpm first, and then stir at 3000±200 rpm for 55-65 min to obtain an adhesive solution with uniformly dispersed carbon nanotubes. S3, Second conductive agent dispersion stage: Add conductive carbon black to the uniformly dispersed carbon nanotube solution, stir slowly at 25±5 rpm for 5-15 min and scrape the material, stir at 30±5 rpm for 10-20 min, and then stir at 3000±200 rpm for 80-100 min to obtain a uniformly dispersed carbon nanotube and conductive carbon black solution. S4. Active material mixing stage: Add the remaining solvent in portions to the uniformly dispersed carbon nanotubes and conductive carbon black slurry, then slowly add lithium-rich manganese-based positive electrode active material powder. Stir slowly at 25±5 rpm for 10-20 min and scrape the material, then stir at 30±5 rpm for 5-15 min, and then stir at 3000±200 rpm for 30-40 min to obtain a slurry with uniformly dispersed active materials. S5. Vacuum degassing stage: After completing steps S1 to S4, stir slowly at a speed of 15±5 rpm for 30-60 minutes under vacuum conditions to obtain the positive electrode active slurry.

4. The preparation method according to claim 1, characterized in that, The coating process includes: coating the positive electrode active slurry onto the current collector with a wet film thickness of 300-560 μm, followed by vacuum drying at 110-130℃ for 10-14 hours to obtain a single-sided areal loading of 16-36 mg / cm². 2 The positive electrode sheet.

5. The preparation method according to claim 1, characterized in that, The fluorinated gel electrolyte precursor solution comprises a weakly solvated electrolyte, a polymerizing monomer, and an initiator. The mass ratio of the polymeric monomer to the weakly solvated electrolyte is 1:(7.5-15). The weakly solvated electrolyte contains a mixed solvent of fluoroethylene carbonate and 2,2,2-trifluoroethyl acetate, as well as lithium hexafluorophosphate and lithium difluorooxalate borate dissolved therein. The polymerizing monomer is selected from at least one of acrylic monomers and epoxy monomers.

6. The preparation method according to claim 5, characterized in that, The polymer monomers include one or more of 2,2,3,4,4,4-hexafluorobutyl acrylate, ethoxylated trimethylolpropane triacrylate, trifluoroethyl acrylate, and pentaerythritol tetraacrylate. Wherein, based on the weight of the weakly solvated electrolyte as 100%, the amount of hexafluorobutyl 2,2,3,4,4,4-acrylate is 5-10%, and the amount of ethoxylated trimethylolpropane triacrylate is 2.5-5%; The initiator is azobisisobutyronitrile, and its amount is 0.30-0.50% of the total weight of the weakly solvated electrolyte and the polymerizing monomer.

7. The preparation method according to claim 1, characterized in that, The amount of the fluorinated gel electrolyte precursor solution added is 1.3-2.8 g / Ah, calculated as the ratio of the precursor solution mass to the positive electrode capacity.

8. The preparation method according to claim 1, characterized in that, The in-situ polymerization process includes: pressing the battery cell containing the precursor solution in a fixture and letting it stand for 8-16 hours, followed by heating and polymerization at 45-55 °C for 2-6 hours.

9. A high-energy-density lithium metal battery, characterized in that, The positive electrode active material is prepared by any one of the preparation methods described in claims 1-8, and its surface contains Mn-F bonds.

10. The high-energy-density lithium metal battery according to claim 9, characterized in that, The energy density of the battery is not less than 550 Wh / kg when operating in a voltage range of 2-4.8 V.

Images