A semi-solid battery and a method of manufacturing the same

Abstract

The application discloses a novel semi-solid battery and a preparation method thereof, and belongs to the technical field of lithium ion batteries. A novel electrolyte is added with a sulfur-containing cyclic compound in a lithium ion battery electrolyte, and the semi-solid battery contains the novel electrolyte and a composite positive electrode containing a current collector layer, an active material layer and a solid-state electrolyte layer. The sulfur-containing cyclic compound in the novel electrolyte can form a nano-thickness sulfur-containing organic film on the surface of the solid-state electrolyte layer, effectively avoiding high-temperature side reactions between the solid-state electrolyte and the electrolyte, thereby greatly improving the service life of the battery under high-temperature conditions.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion batteries, and more specifically to the technical field of semi-solid-state lithium-ion batteries. Background Technology

[0002] With the rapid development of digital products, electric vehicles, and the energy storage industry, the requirements for the energy density, long cycle life, and safety of lithium-ion batteries have also increased accordingly. Liquid electrolyte-based lithium rechargeable batteries cannot meet these application demands and pose certain safety risks. Therefore, solid-state electrolyte lithium-ion batteries, which have significant advantages in energy density and safety, have experienced rapid development.

[0003] Solid electrolytes are classified into polymer solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, etc. There are many ways to prepare solid batteries, such as forming composite electrode sheets by mixing or coating with positive and negative electrode materials, or coating them on the surface of separators or positive and negative electrode sheets to form a thin electrolyte layer, or preparing an electrolyte separator alone to replace commercial separators.

[0004] A novel preparation method in the prior art involves directly coating a solid electrolyte layer onto the surface of the electrode active material layer. The coating layer is relatively thin, thus improving battery performance. For example, Chinese patent application CN116741942A discloses a lithium iron manganese phosphate (LFMP) composite cathode sheet, which coats the surface of the active material layer with a solid electrolyte layer, solving the problem of Mn leaching from manganese-containing cathode materials through physical barrier. Chinese patent application CN117727864A discloses a method for preparing a composite electrode sheet including a current collector, which has a lithium replenishment layer, an active layer, and an electrolyte layer including a solid electrolyte and a ceramic coating on the surface of the solid electrolyte on at least one side of the current collector. This method solves the problems of low safety at the positive and negative electrode interfaces and low energy density in existing batteries.

[0005] While the existing products or methods mentioned above can significantly improve battery energy density and safety performance, they cannot solve the problem of solid electrolyte coating layers easily reacting with battery electrolytes at high temperatures, leading to rapid battery life degradation. For example, the solid electrolyte LATP reacts with fluorine-containing components in the electrolyte at high temperatures to form TiF3, causing Ti... 3+ It dissolves into the electrolyte, causing serious side reactions that lead to a rapid decline in the high-temperature lifespan of semi-solid batteries, making them unable to meet application requirements. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a novel semi-solid battery and its preparation method. The semi-solid battery comprises a composite positive electrode sheet containing a solid electrolyte layer and an electrolyte containing sulfur-containing cyclic compound additives. During the first charge and discharge process, the sulfur-containing cyclic compound additives can form a sulfur-containing organic film with a thickness of nanometers on the surface of the solid electrolyte layer, effectively avoiding high-temperature side reactions between the solid electrolyte and the electrolyte during use, thereby greatly improving the battery's service life under high-temperature conditions.

[0007] The technical solution of the present invention is as follows: A semi-solid-state battery includes an electrolyte and a semi-solid-state battery cell. The semi-solid-state battery cell includes a negative electrode, a composite positive electrode, and a separator separating the negative electrode and the composite positive electrode. The composite positive electrode contains a current collector layer, an active material layer attached to the current collector layer, and a solid electrolyte layer attached to the active material layer. One or more of the following sulfur-containing cyclic compounds are added to the electrolyte:

[0008] The sulfur-containing cyclic compound in the electrolyte of this invention can form a sulfur-containing organic interface layer on the surface of the solid electrolyte through an electrochemical decomposition reaction. This layer can effectively isolate the solid electrolyte from direct contact with the electrolyte, effectively protect the electrode materials of the battery, and improve the high-temperature cycle performance of the battery.

[0009] Preferably, the added mass of the sulfur-containing cyclic compound is 0.1-8% of the total mass of the electrolyte, and more preferably, it is 0.5-3%.

[0010] Preferably, the lithium-ion battery electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), methyl propionate (MP), and propyl propionate (PP); and the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonate)imide (LiTFSI), lithium difluorooxalateborate (LiODFB), lithium dioxalateborate (LiBOB), and lithium tetrafluoroborate (LiBF4).

[0011] Preferably, the thickness of the solid electrolyte layer is 4-20 μm, and more preferably, it is 6-12 μm.

[0012] Preferably, the positive electrode active material included in the active material layer is selected from one or more of lithium nickel manganese oxide ternary (NCM), lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), lithium iron manganese phosphate (LiFe x Mn (1-x) PO4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), and lithium-rich manganese-based (LMR); the solid electrolyte included in the solid electrolyte layer is selected from one or more of lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), and lithium phosphorus oxynitride (LIPON); more preferably, the solid electrolyte is selected from lithium aluminum titanium phosphate with the molecular formula Li Y Al X Ti 2-X (PO4)3, wherein 0<X<1 and 1<Y.

[0013] Preferably, the negative electrode sheet contains one or more of the following negative electrode active materials: graphite, soft carbon, hard carbon, metallic lithium, nano-silicon, nano-tin, silicon-carbon, silicon-oxygen, tin-carbon and tin-oxygen.

[0014] The present invention further provides a method for preparing the above semi-solid battery, comprising: mixing the positive electrode active material, a first binder, a conductive agent and a first solvent uniformly to obtain a first slurry, coating the first slurry on at least one side surface of a current collector, followed by drying and rolling to obtain a basic positive electrode sheet; mixing the solid electrolyte, a second binder, a dispersant and a second solvent uniformly to obtain a second slurry, coating the second slurry on the basic positive electrode sheet by a doctor blade film-forming method, followed by drying and rolling to obtain the composite positive electrode sheet; assembling and encapsulating the composite positive electrode sheet, the separator and the negative electrode sheet to obtain the dry semi-solid battery cell; injecting the electrolyte into the dry semi-solid battery cell to obtain the semi-solid battery.

[0015] Preferably, the mass of the solid electrolyte is 65% to 90% of the total mass of the second slurry, more preferably 75% to 85%; the mass of the injected electrolyte is 5 to 25% of the total mass of the semi-solid battery, more preferably 10 to 15%.

[0016] Preferably, the first binder is selected from one or more of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) and polyacrylic acid (PAA).

[0017] Preferably, the conductive agent is selected from one or more of carbon black, Ketjen black, carbon nanotubes, carbon fibers, graphene, and conductive graphite.

[0018] Preferably, the second adhesive is selected from one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyethylene oxide (PEO), and polyacrylonitrile (PAN), wherein, more preferably, it is polyvinylidene fluoride (PVDF).

[0019] Preferably, the material of the diaphragm is selected from one or more of polyethylene (PE), polypropylene (PP), and polyimide (PI).

[0020] Preferably, the first solvent is selected from N-methyl-2-pyrrolidone (NMP).

[0021] Preferably, the second solvent is selected from propylene carbonate (PC).

[0022] In the semi-solid battery provided by this invention, the electrolyte containing sulfur cyclic compound additives can form a nanoscale protective film in situ on the surface of the composite positive electrode, effectively improving the high-temperature stability of the oxide solid electrolyte. Compared with conventional liquid lithium-ion batteries, the semi-solid battery of this invention can significantly improve the safety performance of lithium batteries, preventing fire and explosion when punctured, while also possessing excellent high-temperature cycle stability, thus promoting the application and development of high-safety, high-energy-density, and high-temperature lithium batteries. Attached Figure Description

[0023] Figure 1 Image of the battery after needle puncture in Example 1; Figure 2 Image of the battery after needle puncture in Example 2; Figure 3 The voltage-temperature change curve of the acupuncture process in Example 2; Figure 4 This is a comparison chart of the 60°C cycle life of Example 1 and Comparative Example 2. Detailed Implementation

[0024] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the scope of the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0025] Example 1 A semi-solid-state battery was prepared using the following steps: (1) The ternary active material lithium nickel manganese oxide (NCM622), PVDF, SP, and CNT were dispersed in NMP at a mass ratio of 97:1.2:1:0.8 to obtain the first slurry. This slurry was then coated on both sides of a 14 μm thick aluminum foil, followed by drying and rolling to obtain a double-sided areal density of 3.50 g / dm. 2 The positive electrode plate; (2) Solid electrolyte LATP, PVDF, and dispersant are dispersed in PC at a mass ratio of 90:9:1 and stirred evenly to obtain a second slurry. The slurry is then coated onto the positive electrode using a scraper film-forming method. After drying and rolling, a 4μm thick solid electrolyte layer is formed on the surface of the positive electrode to obtain a composite positive electrode. (3) The negative electrode active materials graphite, SBR, SP, and CMC were dispersed in water at a mass ratio of 96:2:1:1 to obtain a negative electrode slurry. This slurry was then coated on both sides of a 9μm thick copper foil, followed by drying and rolling to obtain a double-sided surface density of 1.84 g / dm. 2 The negative electrode plate; (4) Assemble the above composite positive electrode, commercial PE separator and negative electrode in a stacked manner, and seal them with aluminum-plastic film to form a 15Ah semi-solid battery dry cell ready for liquid injection. (5) Mix ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, add 12.8% of LiPF6 by mass of the total electrolyte, and then add 2% of the sulfur-containing cyclic compound additive shown in Formula 2 by mass of the total electrolyte to obtain electrolyte E1. (6) Electrolyte E1 is injected into the semi-solid battery dry cell, and then the finished semi-solid battery is obtained through aging, formation, aging, secondary sealing and capacity testing.

[0026] Example 2 The semi-solid battery was prepared according to the process in Example 1, except that the thickness of the solid electrolyte layer was 8 μm.

[0027] Example 3 The semi-solid battery was prepared according to the process in Example 1, except that the thickness of the solid electrolyte layer was 17 μm.

[0028] Example 4 The semi-solid battery was prepared according to the process in Example 1, except that the solid electrolyte was LLZO and the thickness of the solid electrolyte layer was 17 μm.

[0029] Example 5 The semi-solid battery was prepared according to the process in Example 1, except that the solid electrolyte was LLTO and the thickness of the solid electrolyte layer was 8 μm.

[0030] Example 6 The semi-solid battery was prepared according to the process in Example 2, except that the electrolyte used was prepared by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, then adding 12.8% of LiPF6 by mass of the total electrolyte, and then adding 2% of the sulfur-containing cyclic compound additive shown in Formula 6 by mass of the total electrolyte to obtain electrolyte E2.

[0031] Example 7 The semi-solid battery was prepared according to the process of Example 2, except that the electrolyte used was prepared by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, then adding 12.8% of LiPF6 by mass of the total electrolyte, and then adding 2% of the sulfur-containing cyclic compound additive shown in Formula 7 by mass of the total electrolyte to obtain electrolyte E3.

[0032] Example 8 The semi-solid battery was prepared according to the process of Example 2, except that the electrolyte used was prepared by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, then adding 12.8% of LiPF6 by mass of the total electrolyte, and then adding 2% of the sulfur-containing cyclic compound additive shown in Formula 8 by mass of the total electrolyte to obtain electrolyte E4.

[0033] Example 9 The semi-solid battery was prepared according to the process in Example 2, except that the electrolyte used was prepared by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, then adding 12.8% of LiPF6 by mass of the total electrolyte, and then adding 5% of the sulfur-containing cyclic compound additive shown in Formula 2 by mass of the total electrolyte to obtain electrolyte E5.

[0034] Comparative Example 1 A lithium-ion battery is prepared by the following steps: (1) The ternary active material lithium nickel manganese oxide (NCM622), PVDF, SP, and CNT were dispersed in NMP at a mass ratio of 97:1.2:1:0.8 to obtain the first slurry. This slurry was then coated on both sides of a 14 μm thick aluminum foil, followed by drying and rolling to obtain a double-sided areal density of 3.50 g / dm. 2 The positive electrode plate; (2) The negative electrode active materials graphite, SBR, SP, and CMC were dispersed in water at a mass ratio of 96:2:1:1 to obtain a negative electrode slurry. This slurry was then coated on both sides of a 9μm thick copper foil, followed by drying and rolling to obtain a double-sided surface density of 1.84 g / dm³. 2 The negative electrode plate; (3) The obtained positive electrode sheet, commercial PE separator and negative electrode sheet are assembled in a stacked form and sealed with aluminum-plastic film to form a 15Ah lithium battery dry cell ready for liquid injection. (4) Mix ethylene carbonate and dimethyl carbonate in a mass ratio of 3:7, and add 12.8% of the total mass of the electrolyte to obtain electrolyte E0; (5) The electrolyte E0 is injected into the semi-solid battery dry cell, and then the finished lithium-ion battery is obtained through aging, formation, aging, secondary sealing and capacity testing.

[0035] Comparative Example 2 The lithium-ion battery was prepared according to the process of Example 2, except that the electrolyte used was the same as that in Comparative Example 1, namely electrolyte E0.

[0036] Comparative Example 3 The lithium-ion battery was prepared according to the process of Comparative Example 1, the only difference being that the electrolyte used was the same as that in Example 1, namely electrolyte E1.

[0037] Performance tests were conducted on the semi-solid-state batteries or lithium-ion batteries prepared in the above embodiments and comparative examples, including: Impedance test: At room temperature, the battery was charged to 50% SOC at a current of 0.2C, and the cutoff current was 0.05C. After standing for 1 hour, the battery impedance was tested and fitted using an electrochemical workstation. 60℃ Cyclic Test: In a 60℃ constant temperature chamber, the battery is repeatedly charged and discharged within the capacity range of 0~100% SOC at a charge / discharge current of 1C / 1C. The charge / discharge capacity of each cycle is recorded. A 0.2C / 0.2C (0-100% SOC) charge / discharge test is performed every 100 cycles to monitor the battery capacity retention rate. The test is stopped when the capacity decays to 80% HOC.

[0038] Needle prick safety testing includes: Charge to full voltage at 0.2C, select CC-CV mode, cut-off current 0.01C, and let stand for 4 hours; At room temperature, place the battery in an explosion-proof box, aligning the center of the largest surface of the battery with the steel needle; At least one temperature testing device is installed 1 cm from the battery penetration point and 1 cm from the battery edge to test the battery temperature online. Connect to a voltage testing device for online voltage testing; A φ5mm high-temperature resistant steel needle with a cone angle of 45° at the tip, smooth surface, free of rust, oxide layer and oil stains, is used to penetrate the battery from a direction perpendicular to the largest surface of the battery at a speed of 25±5mm / s. The penetration position is the geometric center of the largest surface of the battery, and the steel needle stays in the battery. Observe for 1 hour and record the video of the test process and the data on the surface temperature and voltage changes of the battery.

[0039] The test results are shown in Table 1 below: Table 1 Battery performance test results

[0040] Some exemplary images from the above tests are attached. Figure 1-4 As shown, where, Figure 1 Image of the battery after needle puncture in Example 1; Figure 2 Image of the battery after needle puncture in Example 2; Figure 3 The voltage-temperature change curve of the acupuncture process in Example 2; Figure 4 This is a comparison chart of the 60°C cycle life of Example 1 and Comparative Example 2.

[0041] The test results above show that, based on the comparison between Example 2, Comparative Example 1 and Comparative Example 2, although the semi-solid battery assembled with LATP solid electrolyte layer and conventional electrolyte E0 improves the battery safety performance (no fire when punctured), it significantly degrades its high-temperature 60°C cycle life; while the semi-solid battery assembled with LATP solid electrolyte layer and sulfur-containing cyclic compound additive electrolyte E1 not only ensures the battery safety performance, but also significantly improves its high-temperature life.

[0042] Based on the comparison of Examples 1, 2, and 3, if the solid electrolyte layer is too thin, it cannot effectively physically isolate the positive and negative electrodes, and the safety cannot be guaranteed. If the solid electrolyte layer is too thick, it will increase the battery impedance and degrade its high-temperature 60°C cycle life. Therefore, the optimal coating thickness of the solid electrolyte layer should be around 6~12μm.

[0043] Based on the comparison of Examples 2, 4, and 5, the different oxide solid electrolytes and the sulfur-containing cyclic compound additive electrolyte E1 all showed good compatibility.

[0044] Based on the comparison of Examples 2, 6, 7, and 8, the same oxide solid electrolyte has good compatibility with sulfur-containing cyclic compound additives with different structures.

[0045] Based on the comparison of Examples 2 and 9, as the content of sulfur-containing cyclic compound additives increases, the effect of further improving the high-temperature cycle life of the battery is not obvious, but the battery impedance increases significantly.

[0046] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a semi-solid-state battery, characterized in that, It includes: (1) The positive electrode active material, the first binder, the conductive agent and the first solvent are mixed evenly to obtain the first slurry, which is coated on at least one side of the current collector, and then dried and rolled to obtain the basic positive electrode sheet; (2) Mix the solid electrolyte, the second binder, the dispersant and the second solvent evenly to obtain the second slurry, and coat it onto the base positive electrode sheet by the scraper film forming method, and then dry and roll it to obtain the composite positive electrode sheet; (3) The composite positive electrode sheet is assembled and encapsulated with the separator and the negative electrode sheet to obtain the semi-solid battery dry cell, wherein the separator separates the negative electrode sheet from the composite positive electrode sheet; (4) Inject the electrolyte into the semi-solid battery cell to obtain a semi-solid battery; The electrolyte contains one or more of the following sulfur-containing cyclic compounds: ； Wherein, the electrolyte includes a lithium salt and an organic solvent, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, ethyl propionate, methyl propionate and propyl propionate; the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate and lithium tetrafluoroborate; the mass percentage of the sulfur-containing cyclic compound added is 0.5~3% of the total mass of the electrolyte; the thickness of the solid electrolyte layer is 6-12μm; the solid electrolyte is selected from compounds with the molecular formula Li Y Al X Ti 2-X (PO4)3, which is lithium aluminum titanium phosphate satisfying 0<X<1 and 1<Y.

2. The preparation method according to claim 1, characterized in that, in, The positive electrode active material included in the active material layer is selected from one or more of the following: lithium nickel manganese oxide ternary materials, lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium iron manganese phosphate, lithium nickel manganese oxide, and lithium-rich manganese-based materials.

3. The preparation method according to claim 1, characterized in that, The negative electrode sheet contains one or more of the following negative electrode active materials: graphite, soft carbon, hard carbon, metallic lithium, nano silicon, nano tin, silicon-carbon, silicon-oxygen, tin-carbon, and tin-oxygen.

4. The preparation method according to claim 1, characterized in that, in, The mass of the solid electrolyte is 65% to 90% of the total mass of the second slurry; the mass of the injected electrolyte is 5% to 25% of the total mass of the semi-solid battery.

5. The preparation method according to claim 1, characterized in that, in, The mass of the solid electrolyte is 75% to 85% of the total mass of the second slurry; the mass of the injected electrolyte is 10% to 15% of the total mass of the semi-solid battery.

6. The preparation method according to claim 1, characterized in that, in, The first binder is selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; and / or, the conductive agent is selected from one or more of carbon black, carbon nanotubes, carbon fibers, graphene, and conductive graphite; and / or, the second binder is selected from one or more of polyvinylidene fluoride, polyacrylic acid, polyethylene oxide, and polyacrylonitrile; and / or, the membrane material is selected from one or more of polyethylene, polypropylene, and polyimide; and / or, the first solvent is selected from N-methyl-2-pyrrolidone; and / or, the second solvent is selected from propylene carbonate.

7. A semi-solid-state battery, characterized in that, It is prepared by the method according to any one of claims 1-6.

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