Negative electrode sheet for battery without negative electrode active material, preparation method thereof, and battery

Abstract

The present invention proposes a negative electrode sheet for a battery without negative electrode active material, a preparation method thereof, and a battery. Through the synergistic effect of the negative electrode current collector, nano-carbon fluoride, and a binder in the protective layer, a stable fluoride-rich lithium (sodium) SEI is formed during charging. This prevents lithium (sodium) from directly contacting other components of the battery and causing side reactions, thereby improving the battery's high-temperature performance and suppressing high-temperature flatulence. Furthermore, the sheet can induce uniform deposition of lithium (sodium), suppressing the formation of dendrites and dead lithium (sodium), thereby improving the battery's coulombic efficiency and cycle performance. Because the present invention does not use a negative electrode active material, it can significantly increase the battery's energy density compared to conventional lithium (sodium) ion batteries using carbon materials as the negative electrode active material.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode sheet of a battery without negative electrode active material, a preparation method thereof, and a battery. Background Art

[0002] In recent years, a new "negative active material-free" battery technology has emerged for lithium-ion and sodium-ion batteries. By eliminating the use of negative active material, the battery's energy density has been significantly improved. This technology works by depositing lithium from the positive electrode material onto the negative electrode current collector through formation charging. However, the lithium (sodium) deposition process causes significant volume expansion and uneven deposition, leading to the following problems:

[0003] 1) Poor high-temperature performance: Due to the severe volume expansion during lithium (sodium) deposition, it is difficult to form a stable SEI on the negative electrode surface. The highly active lithium (sodium) will directly come into contact with other components of the battery to produce side reactions. Especially at high temperatures, severe side reactions will cause battery bloating and lead to battery failure.

[0004] 2) Poor cycle performance: Due to uneven lithium (sodium) deposition, dendrites and dead lithium (sodium) are easily formed during the battery charge and discharge process, resulting in low battery coulombic efficiency, rapid cycle decay, and increased internal resistance;

[0005] In order to solve the above technical problems, researchers have done a lot of work. Among them, effective methods include coating a protective layer on the negative electrode current collector and performing surface treatment on the current collector.

[0006] An existing technology suppresses the formation of dendritic lithium by coating AgCl on the current collector, making the deposited lithium layer more uniform, reducing dead lithium, and improving the reversible capacity and cycle performance of the battery.

[0007] However, AgCl is expensive and difficult to use in industrial production. It also has poor stability and easily decomposes when exposed to light or heat, and has limited effect on improving the high-temperature performance of batteries. Summary of the Invention

[0008] In view of this, the present invention proposes a negative electrode sheet for a battery without negative electrode active material, a preparation method thereof, and a battery. Through the synergistic effect of the negative electrode current collector and the nano-carbon fluoride and binder in the protective layer, a complete and stable fluoride-rich lithium (sodium) SEI can be formed during the charging process, preventing lithium (sodium) from directly contacting other components of the battery to produce side reactions, thereby improving the high-temperature performance of the battery and inhibiting high-temperature flatulence of the battery; and it can induce uniform deposition of lithium (sodium), inhibit the formation of dendrites and dead lithium (sodium), thereby improving the coulombic efficiency and cycle performance of the battery.

[0009] The technical solution of the present invention is achieved as follows:

[0010] In one aspect, the present invention provides a negative electrode sheet for a battery without negative electrode active material, comprising a negative electrode current collector and a protective layer attached to the negative electrode current collector, wherein the protective layer components include nano-carbon fluoride and a binder.

[0011] The main reason for the poor high-temperature performance and flatulence of batteries without negative electrode active material is the inability to form a complete and stable SEI. Bare metallic lithium (sodium) is highly reactive and easily undergoes side reactions with other components within the battery at high temperatures. Therefore, the present invention provides a negative electrode sheet for a battery without negative electrode active material. Through the synergistic effect of the negative electrode current collector, nano-carbon fluoride, and binder in the protective layer, a complete and stable lithium (sodium) fluoride-rich SEI is generated. This SEI encapsulates the metallic lithium (sodium) deposited at the negative electrode and prevents the occurrence of side reactions at high temperatures. The negative electrode sheet has the following characteristics:

[0012] (1) The negative electrode sheet of the battery without negative active material is composed of a negative electrode current collector and a protective layer attached to the negative electrode current collector. In addition, the protective layer must be tightly attached to the negative electrode current collector and cannot be attached to other components of the battery, such as the separator, solid electrolyte, positive electrode sheet, or casing. Because if the protective layer is attached to other components of the battery, a gap will inevitably be generated between the protective layer and the current collector during the assembly process, resulting in the inability to generate a complete and stable SEI, which in turn leads to the occurrence of side reactions at high temperatures.

[0013] (2) The protective layer is composed of nano-carbon fluoride and a binder, and both must be present at the same time. Without nano-carbon fluoride, a lithium (sodium) fluoride-rich SEI cannot be formed on the negative electrode surface; without a binder, the protective layer is prone to cracking and falling off, resulting in the inability to form a complete and stable SEI, which in turn leads to the occurrence of side reactions at high temperatures.

[0014] (3) Nano-carbon fluoride must be used, and other specifications of carbon fluoride (such as micron carbon fluoride) cannot be used. Because the micron carbon fluoride particles are larger in size, the protective layer they form is thicker, and a large volume expansion will occur during the charging process, causing the protective layer to fall off and crack, resulting in the inability to form a complete and stable SEI, which in turn leads to the occurrence of side reactions at high temperatures.

[0015] (4) The protective layer may contain a small amount of electrochemically inert substances or substances that do not expand in volume during charging, but the nano-carbon fluoride content cannot be less than 90wt%. This is because if the nano-carbon fluoride content is too low, the nano-carbon fluoride particles cannot be in continuous and close contact, and a large number of defects will be formed on the protective layer. The defects in the protective layer cannot form a complete and stable SEI rich in lithium (sodium) fluoride, which will lead to the occurrence of side reactions at high temperatures. If the protective layer contains a large amount of substances that expand in volume during charging, the protective layer will crack and fall off, resulting in the inability to form a complete and stable SEI, which will lead to the occurrence of side reactions at high temperatures.

[0016] (5) The technical solution of the present invention must exist as a whole to produce a synergistic effect, thereby achieving the technical effect of improving the high-temperature performance of the battery and suppressing the high-temperature flatulence of the battery. If the technical solution of the present invention is split into several sub-solutions and used separately, the synergistic effect cannot be produced, the high-temperature performance of the battery cannot be effectively improved, and the high-temperature flatulence of the battery cannot be effectively suppressed.

[0017] In summary, the high-temperature performance of a battery is directly related to the morphology of the protective layer. Only a complete and stable protective layer can generate a complete and stable lithium (sodium) fluoride-rich SEI, enabling the battery to exhibit good high-temperature performance. If the protective layer is incomplete and unstable, or if it contains defects or cracks, the resulting SEI will contain defects or cracks, resulting in poor high-temperature performance.

[0018] On the basis of the above technical solution, preferably, the mass ratio of nano-carbon fluoride to binder in the protective layer is (90-99): (10-1).

[0019] Further preferably, the mass ratio of nano-carbon fluoride to the binder in the protective layer is (92-98): (8-2).

[0020] Based on the above technical solution, preferably, the thickness of the protective layer is 0.5 to 4 μm.

[0021] On the basis of the above technical solution, preferably, the chemical formula of the nano-carbon fluoride is CF x , wherein 0.35≤x≤1. More preferably, 0.5≤x≤0.9.

[0022] Further preferably, the nano-carbon fluoride is one or a combination of nano-graphite fluoride, nano-hard carbon fluoride, nano-soft carbon fluoride, nano-activated carbon fluoride, fluorinated carbon nanotubes, fluorinated graphene, and fluorinated carbon fibers.

[0023] Based on the above technical solution, preferably, the particle size D50 of the nano-carbon fluoride is 40 to 400 nm. Further preferably, the particle size D50 of the nano-carbon fluoride is 40 to 200 nm.

[0024] On the basis of the above technical solution, preferably, the binder is one or a combination of PVDF, PTFE, SBR, CMC, PAA, and LA133.

[0025] On the basis of the above technical solution, preferably, the negative electrode current collector is a metal foil, specifically one of copper foil, aluminum foil, tin foil, nickel foil, zinc foil or an alloy foil with the above metals as the main component.

[0026] On the basis of the above technical solution, preferably, the thickness of the negative electrode current collector is 4 to 100 um.

[0027] In a second aspect, the present invention provides a method for preparing a negative electrode sheet for a battery without negative electrode active material according to the first aspect of the present invention, comprising the following steps:

[0028] Weigh nano-carbon fluoride and binder in proportion, add them to the solvent respectively, stir and mix them evenly to prepare a slurry;

[0029] Coating the slurry on the negative electrode current collector and drying it to form a protective layer;

[0030] The negative electrode current collector coated with the protective layer is die-cut to form a negative electrode sheet.

[0031] Specifically, the slurry solvent may be deionized water or NMP.

[0032] In a third aspect, the present invention provides a battery comprising the negative electrode sheet described in the first aspect of the present invention.

[0033] On the basis of the above technical solution, preferably, it further includes a positive electrode sheet and a shell, the negative electrode sheet and the positive electrode sheet are arranged opposite to each other, the shell encapsulates the negative electrode sheet and the positive electrode sheet, the positive electrode sheet is coated with a positive electrode active material, and the protective layer is coated on the area where the negative electrode current collector faces the positive electrode active material.

[0034] Specifically, the positive electrode sheet is composed of a positive electrode active material, a positive electrode conductor, a positive electrode binder and a positive electrode current collector.

[0035] The positive electrode active material contains lithium and / or sodium. During charging, the lithium and / or sodium can be released to form lithium ions and / or sodium ions, which migrate to the negative electrode through the electrolyte and are reduced to metallic lithium or metallic sodium. There are no restrictions on the type and composition of the positive electrode active material, as long as it meets the above principles. It can be a lithium battery positive electrode active material such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide; or a sodium battery positive electrode active material such as sodium nickel iron manganese oxide, sodium copper iron manganese oxide, sodium iron phosphate, sodium vanadium phosphate, and Prussian blue (white) compounds.

[0036] The positive electrode conductive agent is one or more of conductive graphite, conductive carbon black, carbon nanotubes, graphene or carbon fiber.

[0037] Specifically, if a liquid electrolyte is used, it also includes an isolation membrane and an electrolyte. The isolation membrane is arranged between the negative electrode sheet and the positive electrode sheet, the shell encapsulates the negative electrode sheet, the positive electrode sheet and the isolation membrane, and the electrolyte is poured into the shell; if a solid electrolyte is used, the solid electrolyte is arranged between the negative electrode sheet and the positive electrode sheet 3, and the shell encapsulates the negative electrode sheet, the positive electrode sheet and the solid electrolyte.

[0038] The electrolyte is composed of a solvent, a lithium salt (sodium salt), and an additive. Further preferably, if the battery is a lithium battery, the electrolyte includes a lithium salt; or if the battery is a sodium battery, the electrolyte includes a sodium salt.

[0039] The shell is aluminum-plastic film.

[0040] The negative electrode sheet of a battery without negative electrode active material, its preparation method, and the battery of the present invention have the following advantages over the prior art:

[0041] The present invention uses the synergistic effect of the negative electrode current collector and the nano-carbon fluoride and binder in the protective layer to ensure that the protective layer is intact and stable, thereby forming a complete and stable fluoride-rich lithium (sodium) SEI, thereby preventing lithium (sodium) from directly contacting other components of the battery to cause side reactions, improving the high-temperature performance of the battery, and suppressing high-temperature flatulence of the battery.

[0042] The protective layer can induce uniform deposition of lithium (sodium), inhibit the formation of dendrites and dead lithium (sodium), and effectively improve the coulombic efficiency and cycle performance of the battery;

[0043] Since the battery provided by the present invention does not use negative electrode active materials, compared with conventional lithium (sodium) ion batteries that use carbon materials or silicon materials as negative electrode active materials, the energy density of the battery can be greatly improved;

[0044] Since the battery provided by the present invention does not use active metals such as lithium and sodium, a drying room or inert gas protection is not required during the battery assembly process, which can reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 Schematic diagram of the cross-sectional structure of the battery of Example 1 of the present invention;

[0047] Figure 2 The cyclic charge and discharge curves of Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0048] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] Example 1

[0050] The battery of this embodiment includes a negative electrode sheet consisting of a negative electrode current collector 1 and a protective layer 2, a positive electrode sheet 3, a separator 4, a shell and an electrolyte. The preparation thereof includes the following steps:

[0051] (1) Preparation of negative electrode sheet

[0052] Nano-graphite fluoride CF 0.53 Weigh the materials (D50:120nm) and binder LA133 in a mass ratio of 95:5, add them to deionized water, and stir to mix thoroughly to prepare a slurry. The slurry is coated on the negative electrode current collector 1 (8μm thick copper foil) and dried to form a protective layer 2 with a thickness of 2μm. The negative electrode current collector 1 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0053] (2) Preparation of positive electrode sheet

[0054] The positive electrode active material 30 is lithium cobalt oxide, the positive electrode conductive agent is SP, the positive electrode binder is PVDF, and the positive electrode current collector is aluminum foil. The mass ratio of the positive electrode active material 30, positive electrode conductive agent, and positive electrode binder is 97:1.5:1.5. The positive electrode active material 30, positive electrode conductive agent, and positive electrode binder are made into a slurry, coated on the positive electrode current collector, and then dried, rolled, and die-cut to produce the positive electrode sheet 3.

[0055] (3) Battery preparation

[0056] A soft-pack laminate structure is adopted, wherein the negative electrode sheet, the separator 4, and the positive electrode sheet 3 are alternately stacked to form an electrode group, and then the tabs are welded and encapsulated with an aluminum-plastic film shell. An electrolyte is injected (the volume ratio of the components of the electrolyte solvent is EC:DMC:DEC=1:1:1, the electrolyte of the electrolyte is lithium hexafluorophosphate with a concentration of 1 mol / L, and the electrolyte additive is VC with a mass ratio of 1%), and the battery without negative electrode active material is obtained by formation charging.

[0057] Example 2

[0058] (1) Preparation of negative electrode sheet

[0059] Nano-fluorinated hard carbon CF 0.35Weigh the materials (D50:40nm) and binder LA133 in a mass ratio of 99:1, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to the negative electrode current collector 1 (8μm thick copper foil) and dry it to form a protective layer 2 with a thickness of 0.5μm. The negative electrode current collector 2 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0060] (2) Positive electrode and battery preparation

[0061] The positive electrode sheet 3 and the battery were prepared in the same manner as in Example 1.

[0062] Example 3

[0063] (1) Preparation of negative electrode sheet

[0064] Nano-fluorinated activated carbon (CF) (D50:400nm) and binder LA133 were weighed in a 90:10 mass ratio and added to deionized water. The mixture was stirred to prepare a slurry. The slurry was coated on the negative electrode current collector 1 (8μm thick copper foil) and dried to form a protective layer 2 with a thickness of 4μm. The negative electrode current collector 2 coated with the protective layer 2 was die-cut to form a negative electrode sheet.

[0065] (2) Positive electrode and battery preparation

[0066] The positive electrode sheet 3 and the battery were prepared in the same manner as in Example 1.

[0067] Example 4

[0068] (1) Preparation of negative electrode sheet

[0069] Nano-graphite fluoride CF 0.61 Weigh the materials (D50: 200nm) and binder LA133 and PAA in a mass ratio of 94:3:3, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to the negative electrode current collector 1 (20μm thick aluminum foil) and dry it to form a protective layer 2 with a thickness of 2μm. The negative electrode current collector 2 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0070] (2) Preparation of positive electrode sheet

[0071] The positive electrode active material 30 is sodium nickel iron manganese oxide (NaNi 0.33 Fe 0.33 Mn 0.33O2), SP is used as the positive electrode conductive agent, PVDF is used as the positive electrode binder, and aluminum foil is used as the positive electrode current collector. The mass ratio of positive electrode active material 30, positive electrode conductive agent, and positive electrode binder is 95:2:3. A slurry of positive electrode active material 30, positive electrode conductive agent, and positive electrode binder is coated on the positive electrode current collector. After drying, roll pressing, and die-cutting, a positive electrode sheet 3 is produced.

[0072] (3) Battery preparation

[0073] The battery was prepared by the same method as in Example 1, except that the electrolyte composition used was a solvent with a volume ratio of EC:DMC:DEC=1:1:1, the electrolyte was sodium hexafluorophosphate with a concentration of 1 mol / L, and the additive was FEC with a mass ratio of 2%.

[0074] Example 5

[0075] (1) Preparation of negative electrode sheet

[0076] The negative electrode sheet was prepared using the method of Example 4.

[0077] (2) Preparation of positive electrode sheet

[0078] The positive electrode sheet 3 is prepared by the method of Example 4, except that the positive electrode active material 30 is replaced with sodium vanadium phosphate.

[0079] (3) Battery preparation

[0080] The battery was prepared using the method of Example 4.

[0081] Example 6

[0082] (1) Preparation of negative electrode sheet

[0083] Nano-graphite fluoride CF 0.61 Weigh the materials (D50: 100nm) and binder LA133 and PAA in a mass ratio of 94:4:2, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to the negative electrode current collector 1 (8μm thick copper foil) and dry it to form a protective layer 2 with a thickness of 2μm. The negative electrode current collector 2 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0084] (2) Preparation of positive electrode sheet

[0085] The positive electrode sheet 3 was prepared in the same manner as in Example 1.

[0086] (3) Battery preparation

[0087] The soft-pack laminated structure is used to combine the negative electrode sheet, solid electrolyte (Li7La3Zr2O 12), the positive electrode sheets 3 are alternately stacked to form an electrode group, and then the tabs are welded, and the battery is encapsulated with an aluminum-plastic film shell. The electrolyte is injected (the volume ratio of the components of the electrolyte solvent is EC:DMC:DEC=1:1:1, the electrolyte is lithium hexafluorophosphate with a concentration of 1 mol / L, and the electrolyte additive is VC with a mass ratio of 1%), the injection amount is 20% of that in Example 1, and the battery is formed and charged to obtain the battery without negative electrode active material.

[0088] Example 7

[0089] (1) Preparation of negative electrode sheet

[0090] Nano-graphite fluoride CF 0.5 Weigh the materials (D50: 100nm) and binder LA133 and PAA in a mass ratio of 94:4:2, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to the negative electrode current collector 1 (8μm thick copper foil) and dry it to form a protective layer 2 with a thickness of 2μm. The negative electrode current collector 2 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0091] (2) Positive electrode and battery preparation

[0092] The positive electrode sheet 3 and the battery were prepared in the same manner as in Example 6.

[0093] Example 8

[0094] (1) Preparation of negative electrode sheet

[0095] Nano-graphite fluoride CF 0.9 Weigh the materials (D50: 120nm) and binder LA133 and PAA in a mass ratio of 94:4:2, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to the negative electrode current collector 1 (8μm thick copper foil) and dry it to form a protective layer 2 with a thickness of 2μm. The negative electrode current collector 2 coated with the protective layer 2 is die-cut to form a negative electrode sheet.

[0096] (2) Positive electrode and battery preparation

[0097] The positive electrode sheet 3 and the battery were prepared in the same manner as in Example 6.

[0098] Comparative Example 1

[0099] (1) Preparation of negative electrode sheet

[0100] The 8um thick copper foil without protective layer is die-cut to make the negative electrode sheet.

[0101] (2) Positive electrode and battery preparation

[0102] The positive electrode sheet and battery were prepared in the same manner as in Example 1.

[0103] Comparative Example 2

[0104] (1) Preparation of negative electrode sheet

[0105] The negative electrode sheet was prepared in the same manner as in Comparative Example 1.

[0106] (2) Positive electrode and battery preparation

[0107] The positive electrode sheet and battery were prepared in the same manner as in Example 6.

[0108] Comparative Example 3

[0109] (1) Preparation of negative electrode sheet

[0110] The negative electrode sheet was prepared in the same manner as in Comparative Example 1.

[0111] (2) Solid electrolyte modification

[0112] Nano-graphite fluoride CF 0.61 (D50 is 100nm) and the binder LA133 and PTFE are weighed in a ratio of 94:4:2, added to deionized water, stirred and mixed evenly to prepare a slurry, and the slurry was coated on the solid electrolyte (Li7La3Zr2O 12 ) and dry.

[0113] (3) Positive electrode and battery preparation

[0114] The positive electrode sheet and battery were prepared in the same manner as in Example 6.

[0115] Comparative Example 4

[0116] (1) Preparation of negative electrode sheet

[0117] Nano-graphite fluoride CF 0.61 (D50: 100nm) was added to deionized water and stirred to mix thoroughly to prepare a slurry. The slurry was coated on an 8µm thick copper foil current collector and dried to form a 2µm thick coating. The current collector coated with the coating was die-cut to form a negative electrode sheet.

[0118] (2) Positive electrode and battery preparation

[0119] The positive electrode sheet and battery were prepared in the same manner as in Example 6.

[0120] Comparative Example 5

[0121] (1) Preparation of negative electrode sheet

[0122] The negative electrode was prepared in the same manner as in Example 6, except that micronized graphite fluoride CF was used. 0.61 (D50 is 5um), the thickness of the protective layer is 12um.

[0123] (2) Positive electrode and battery preparation

[0124] The positive electrode sheet and battery were prepared in the same manner as in Example 6.

[0125] Comparative Example 6

[0126] (1) Preparation of negative electrode sheet

[0127] Nano-silicon, nano-graphite fluoride CF 0.9 Weigh the materials (D50:120nm), binder LA133, and conductive agent SP in a mass ratio of 70:105:5:10, add them to deionized water, and stir to mix thoroughly to prepare a slurry. Apply the slurry to an 8μm thick copper foil current collector and dry it to form a coating with a thickness of 2μm. Die-cut the coated current collector to produce the negative electrode sheet.

[0128] (2) Positive electrode and battery preparation

[0129] The positive electrode sheet and battery were prepared in the same manner as in Example 1.

[0130] Comparative Example 7

[0131] (1) Preparation of negative electrode sheet

[0132] The negative electrode active material is graphite, the conductive agent is SP, the binder is LA133, and the current collector is copper foil. The mass ratio of the negative electrode active material, conductive agent, and binder is 95:2:3. The negative electrode active material, conductive agent, and binder are made into a slurry, coated on the current collector, and then dried, rolled, and die-cut to form the negative electrode sheet.

[0133] (2) Positive electrode and battery preparation

[0134] The positive electrode sheet and battery were prepared in the same manner as in Example 1.

[0135] test

[0136] Charge and discharge method: The charging current of Examples 1 to 3 and Comparative Example 1 is 0.5C, the charging cut-off voltage is 4.2V, the discharging current is 0.5C, and the discharging cut-off voltage is 2.75V; the charging current of Examples 4 and 5 is 0.5C, the charging cut-off voltage is 4V, the discharging current is 0.5C, and the discharging cut-off voltage is 1.5V; the charging current of Examples 6 to 8 and Comparative Examples 2 to 5 is 0.1C, the charging cut-off voltage is 4.2V, the discharging current is 0.1C, and the discharging cut-off voltage is 2.75V.

[0137] (1) High temperature performance test

[0138] The batteries without negative electrode active material prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were subjected to a discharge and charge test at room temperature, then stored in a 55°C high temperature box for 30 days and discharged at 55°C. The battery discharge capacity and gas production volume were tested. The results are shown in Table 1.

[0139] Table 1-High temperature performance test data

[0140]

[0141] Since comparative examples 1 and 2 use metal foil without a protective layer as the negative electrode, the severe volume expansion of the negative electrode during charging makes it difficult to form a stable and complete SEI on its surface. At high temperatures, the electrolyte will react with the lithium in the SEI cracks, resulting in the consumption of active lithium, severe battery bloating, and a significant decrease in discharge capacity.

[0142] The difference between Comparative Example 3 and Example 6 is that the protective layer is coated on the solid electrolyte. Although there is a protective layer, the protective layer is not attached to the current collector, so no synergistic effect can be produced and the negative electrode cannot be effectively protected. At high temperatures, the electrolyte will react with the lithium in the SEI cracks, resulting in the consumption of active lithium, severe battery flatulence, and a significant decrease in discharge capacity.

[0143] The difference between Comparative Example 4 and Example 6 is that no binder is used in the protective layer, resulting in poor strength of the protective layer and poor adhesion to the current collector, so no synergistic effect can be produced. The severe volume expansion of the negative electrode during charging causes the protective layer to rupture. At high temperatures, the electrolyte will react with the lithium in the SEI cracks, resulting in the consumption of active lithium, severe battery flatulence, and a significant decrease in discharge capacity.

[0144] The difference between Comparative Example 5 and Example 6 is that micron-sized carbon fluoride is used. Micron-sized carbon fluoride will undergo a large volume expansion during the charging process, causing the protective layer to rupture. At high temperatures, the electrolyte will react with the lithium in the SEI cracks, resulting in the consumption of active lithium, battery swelling, and a significant decrease in discharge capacity.

[0145] Comparative Example 6 differs from Example 1 in that a large amount of nanosilicon and SP is added, resulting in a relatively low nano-carbon fluoride content in the coating (approximately 55%). This prevents the nano-carbon fluoride particles from maintaining continuous and close contact, leading to numerous defects in the protective layer. Furthermore, the nano-silicon undergoes significant volume expansion during charging, causing the silicon particles to rupture, which in turn fractures the protective layer and results in numerous defects and cracks in the resulting SEI. At high temperatures, the electrolyte reacts with the lithium in these SEI defects and cracks, consuming the active lithium, causing battery bloating and a significant decrease in discharge capacity.

[0146] In Examples 1 to 8, the negative electrode sheet of the battery without negative electrode active material described in the present invention is used. The nano-carbon fluoride and the binder in the negative electrode current collector and the protective layer can produce a synergistic effect, so that the protective layer can be intact and stable, thereby forming a complete and stable fluoride-rich lithium (sodium) SEI, thereby preventing lithium (sodium) from directly contacting the electrolyte to cause side reactions, inhibiting high-temperature flatulence of the battery, and greatly improving the high-temperature capacity retention rate of the battery.

[0147] Based on Comparative Example 2, the effects of Example 6 and Comparative Examples 3-5 on improving the high-temperature performance of the battery can be calculated (see Table 2). Example 6 improves the high-temperature storage capacity retention by as much as 60.7%, while the average improvement for Comparative Examples 3-5 is only approximately 13.9%, far lower than Example 6. Furthermore, the sum of the effects of Comparative Examples 3-5 is 41.6%, still far lower than Example 6. Example 6 inhibits gas production during high-temperature storage by as much as 5.6 mL, while the average inhibition for Comparative Examples 3-5 is only approximately 1.1 mL, far lower than Example 6. Furthermore, the sum of the effects of Comparative Examples 3-5 is 3.3 mL, still far lower than Example 6. This demonstrates that the technical effect of the present invention (Example 6) is superior to the sum of the effects of the three sub-schemes (Comparative Examples 3-5) derived from the present invention, demonstrating the synergistic effect of the various components of the negative electrode sheet for batteries without negative active material described herein.

[0148] Table 2 - Data Table

[0149]

[0150] (2) Cyclic performance test

[0151] The negative electrode active material-free batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were subjected to 50 cycles of charge and discharge testing. The results are shown in Tables 3 and Figure 1 shown.

[0152] Table 3 - Cyclic performance test data

[0153]

[0154] Since comparative examples 1 and 2 use metal foil without a protective layer as the negative electrode, dendrites and dead lithium (sodium) are easily formed during the charge and discharge process, and the active lithium (sodium) is quickly consumed, resulting in low coulombic efficiency of the battery and poor cycle performance. After 50 cycles, the capacity retention rate is less than 5%.

[0155] The carbon fluoride coatings of Comparative Examples 3 to 5 can induce uniform lithium deposition, inhibit the formation of dendrites and dead lithium, and significantly improve the initial efficiency and cycle capacity retention rate of the battery.

[0156] Examples 1 to 6 use the negative electrode sheet of the battery without negative electrode active material described in the present invention. The protective layer can induce uniform deposition of lithium (sodium), inhibit the formation of dendrites and dead lithium (sodium), and significantly improve the battery's initial efficiency and cycle capacity retention rate.

[0157] (3) Energy density test

[0158] The batteries of Example 1 and Comparative Example 7 were weighed and then discharged at a discharge current of 0.5C and a discharge cutoff voltage of 2.75V. The discharge energy of the batteries was measured and the battery energy density was calculated. The data are shown in Table 4.

[0159] Table 4 - Energy density data table

[0160]

[0161] A comparison reveals that the energy density of Example 1 is 28% higher than that of Comparative Example 7, indicating that the energy density of the negative electrode active material-free battery provided by the present invention is significantly higher than that of conventional lithium-ion batteries. Due to the relatively small capacity of the test battery and the high weight of structural components such as the housing and tabs, the energy density advantage of the negative electrode active material-free battery has not yet been fully realized. It has been calculated that if the battery capacity reaches 10Ah, the energy density of the negative electrode active material-free battery can be over 40% higher than that of conventional lithium-ion batteries.

[0162] In summary, the present invention can significantly improve the high-temperature performance of batteries without negative electrode active materials, inhibit battery high-temperature flatulence, and improve the coulombic efficiency and cycle performance of the battery.

[0163] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A negative electrode sheet for a battery without negative electrode active material, characterized in that: The invention comprises a negative electrode current collector (1) and a protective layer (2) attached to the negative electrode current collector, wherein the negative electrode current collector (1) is a metal foil, and the protective layer (2) comprises nano-carbon fluoride and a binder, wherein the mass ratio of the nano-carbon fluoride to the binder is (90-99): (10-1); the thickness of the protective layer (2) is 0.5-4 μm, and the chemical formula of the nano-carbon fluoride is CF x , wherein 0.35≤x≤1, and the nano-carbon fluoride particle size D50 is 40 to 400 nm.

2. The negative electrode sheet for a battery without negative electrode active material according to claim 1, wherein: The nano-fluorinated carbon is one or a combination of nano-fluorinated graphite, nano-fluorinated hard carbon, nano-fluorinated soft carbon, nano-fluorinated activated carbon, fluorinated carbon nanotubes, fluorinated graphene, and fluorinated carbon fiber.

3. The negative electrode sheet for a battery without negative electrode active material according to claim 1, wherein: The binder is one or a combination of PVDF, PTFE, SBR, CMC, PAA, and LA133.

4. The method for preparing a negative electrode sheet for a battery without negative electrode active material according to claim 1, wherein: The following steps are included: Weigh nano-carbon fluoride and binder in proportion, add them to the solvent respectively, stir and mix them evenly to prepare a slurry; The slurry is coated on the negative electrode current collector (1), and dried to form a protective layer (2); The negative electrode current collector (1) coated with the protective layer (2) is die-cut to form a negative electrode sheet.

5. A battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 1 to 4.

6. The battery according to claim 5, wherein: The invention also includes a positive electrode sheet (3) and a shell, wherein the negative electrode sheet and the positive electrode sheet (3) are arranged opposite to each other, and the shell encapsulates the negative electrode sheet and the positive electrode sheet (3). The positive electrode sheet (3) is coated with a positive electrode active material (30), and the protective layer (2) is coated on the area of ​​the negative electrode current collector (1) facing the positive electrode active material (30).

7. The battery according to claim 5, wherein: The battery is a lithium battery or a sodium battery.

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