Negative plate and preparation method thereof, battery and electric equipment

Abstract

The invention discloses a negative plate and a preparation method thereof, a battery and electric equipment. The negative plate comprises a negative current collector, a negative active material layer and an oxygen-enriched layer. The negative electrode active material layer is arranged on at least one side surface of the negative electrode current collector. And the oxygen-enriched layer is arranged on one side, far away from the negative current collector, of the negative active material layer. Wherein the oxygen-enriched layer comprises at least one of lithium oxide, sodium oxide, sodium carbonate, lithium hydroxide and sodium hydroxide. According to the negative plate disclosed by the invention, the problem of iron dissolution of an LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system caused by water can be solved, and meanwhile, the impedance influence caused by relatively high content of a negative electrode film-forming additive can be reduced. In addition, the preparation cost of the oxygen-enriched layer is low, and the cost of the negative plate is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode sheet and a preparation method thereof, a battery and an electrical device. Background Art

[0002] Lithium iron phosphate (LFP) materials have high safety and low cost, so LFP materials are often used in batteries. However, after optimizing the overall cell space utilization, the blade battery reduces the impact of the intrinsic gram capacity of the LFP material on the Pack energy density. For the LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system, the cycle dive caused by dissolved Fe is an urgent problem to be solved. The mainstream understanding of the Fe dissolution phenomenon in the LFP / LFMP system is that water in the electrolyte hydrolyzes with the electrolyte salt to form HF hydrofluoric acid, which in turn destroys the SEI (Solid Electrolyte Interphase) membrane.

[0003] In the related art, the main method to inhibit the dissolution of Fe in the LFP / LFMP system is to increase the content of negative electrode film-forming additives in the electrolyte, repair the damaged SEI film through the film-forming additives, and then hinder the electron deposition of Fe ions at the negative electrode. However, increasing the content of negative electrode film-forming additives will increase the DC impedance of the battery cell and increase the cost of the battery. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the first purpose of the present invention is to provide a negative electrode sheet that is conducive to solving the problem of iron dissolution in the LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system caused by moisture, and at the same time can reduce the impedance effect caused by a high content of negative electrode film-forming additives. In addition, it is conducive to reducing the cost of the negative electrode sheet.

[0005] The second object of the present invention is to provide a method for preparing a negative electrode sheet.

[0006] The third object of the present invention is to provide a battery.

[0007] A fourth object of the present invention is to provide an electrical device.

[0008] According to the first aspect of the present invention, the negative electrode sheet of the embodiment includes: a negative electrode collector; a negative electrode active material layer, the negative electrode active material layer is arranged on at least one side of the surface of the negative electrode collector; an oxygen-rich layer, the oxygen-rich layer is arranged on the side of the negative electrode active material layer away from the negative electrode collector, wherein the oxygen-rich layer includes at least one of lithium oxide, sodium oxide, sodium carbonate, lithium hydroxide and sodium hydroxide.

[0009] According to the negative electrode sheet of the embodiment of the present invention, an oxygen-rich layer is provided on the side of the negative electrode active material layer away from the negative electrode current collector. During the formation process of the oxygen-rich layer after the battery is injected, moisture in the system can be absorbed. The oxygen-rich layer can provide an oxygen-modified SEI film during the formation process to form an SEI containing a Li-rich and O-rich phase. The impedance of this type of SEI will be lower than that of a normal SEI without O2 modification, so it is beneficial to reduce the DCIR (direct current resistance) of the battery. At the same time, the oxygen-rich layer can isolate the moisture in the negative electrode active material layer and the surrounding environment, further avoiding the occurrence of Fe dissolution in the LFP system, thereby reducing the phenomenon of battery cycle diving. Therefore, it is beneficial to solve the problem of iron dissolution in the LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system caused by moisture, and at the same time reduce the impedance effect caused by the high content of negative electrode film-forming additives. In addition, the preparation cost of the oxygen-rich layer is low, which is beneficial to reduce the cost of the negative electrode sheet.

[0010] According to some embodiments of the present invention, the thickness of the oxygen-rich layer is 1.4 um to 14.2 um.

[0011] According to some embodiments of the present invention, the oxygen-rich layer is formed by a water-absorbing oxygen-supplementing agent, and the water-absorbing oxygen-supplementing agent includes at least one of lithium peroxide, sodium peroxide and sodium percarbonate.

[0012] According to some embodiments of the present invention, the content of the water absorbing oxygen replenishing agent satisfies the following formula by mass: , X is the influence coefficient of the added water-absorbing oxygen replenisher on the low-temperature impedance of the battery, 0.01≤X≤15; the DCIR is the DC resistance value of the battery at 0°C, in Ω; the Q is the third discharge capacity of the battery at 25°C, in Ah.

[0013] According to some embodiments of the present invention, the ratio of the content of the water-absorbing oxygen replenisher to 100 g of the positive electrode active material is 0.1 to 4 by mass.

[0014] According to some embodiments of the present invention, the negative electrode active material layer includes a negative electrode active material, a binder and a conductive agent, the negative electrode active material includes at least one of natural graphite and artificial graphite; and / or, the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyurethane and polytetrafluoroethylene; and / or, The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene and conductive graphite.

[0015] According to some embodiments of the present invention, the double-sided surface density of the negative electrode sheet is 100 g / m 2 ~300g / m 2 .

[0016] According to some embodiments of the present invention, the compaction density of the negative electrode sheet is 1.2 g / cm 3 ~1.8g / cm 3 .

[0017] A method for preparing a negative electrode sheet according to an embodiment of the second aspect of the present invention comprises the following steps: coating the negative electrode active material layer slurry on the negative electrode current collector and drying to form a negative electrode active material layer; A water-absorbing oxygen replenishing agent is coated on the surface of the negative electrode active material layer to obtain a negative electrode sheet.

[0018] According to some embodiments of the present invention, coating the water absorbing oxygen supplementing agent specifically includes: spraying the dry material of the water absorbing oxygen supplementing agent; or transferring the dry material of the water absorbing oxygen supplementing agent by a transfer membrane.

[0019] The battery according to the third aspect of the present invention comprises: a positive electrode sheet; an electrolyte; a separator; and a negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet according to the first aspect of the present invention or the negative electrode sheet prepared by the preparation method according to the second aspect of the present invention.

[0020] An electrical device according to an embodiment of a fourth aspect of the present invention includes: a battery according to an embodiment of the third aspect of the present invention.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0022] The negative electrode sheet according to an embodiment of the present invention is described below.

[0023] The negative electrode sheet according to the embodiment of the present invention includes a negative electrode current collector, a negative electrode active material layer and an oxygen-rich layer.

[0024] Specifically, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the oxygen-rich layer is disposed on a side of the negative electrode active material layer away from the negative electrode current collector.

[0025] A negative electrode active material layer and an oxygen-rich layer are sequentially arranged on at least one side of the negative electrode current collector in a direction away from the negative electrode current collector. During the formation process of the oxygen-rich layer after the battery is injected, the water in the system can be absorbed. The oxygen-rich layer can provide an oxygen-modified SEI film during the formation process to form an SEI film containing a Li-rich and O-rich phase. The impedance of this type of SEI film is lower than that of a normal SEI film without O2 modification, so it is beneficial to reduce the DCIR (direct current resistance) of the battery. At the same time, the oxygen-rich layer can isolate the water in the negative electrode active material layer and the surrounding environment, further avoiding the occurrence of Fe dissolution in the LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system, thereby reducing the phenomenon of battery cycle diving. As a result, it is beneficial to solve the problem of iron dissolution in the LFP / LFMP system caused by water, and at the same time reduce the impedance effect caused by the higher content of negative electrode film-forming additives. In addition, the preparation cost of the oxygen-rich layer is low, which is beneficial to reduce the cost of the negative electrode sheet.

[0026] Among them, the oxygen-rich layer includes at least one of lithium oxide, sodium oxide, sodium carbonate, lithium hydroxide and sodium hydroxide. Lithium oxide (Li2O) and sodium oxide (Na2O) are sensitive to water and easily react with water to form lithium hydroxide. Sodium carbonate (Na2CO3) can exist stably. Lithium hydroxide (LiOH) and sodium hydroxide (NaOH) are conducive to the formation of SEI film on the surface of the negative electrode active material layer, protecting the material of the negative electrode active material layer, protecting the negative electrode active material layer from further electrolyte decomposition, reducing the occurrence of side reactions, improving the cycle stability of the battery, and extending the life of the battery. At the same time, the direct contact between the electrolyte and the negative electrode active material layer is reduced by the SEI film, thereby reducing the continuous electrolyte decomposition, which is conducive to improving the energy density and safety of the battery.

[0027] According to the negative electrode sheet of the embodiment of the present invention, an oxygen-rich layer is provided on the side of the negative electrode active material layer away from the negative electrode current collector. During the formation process of the oxygen-rich layer after the battery is injected, moisture in the system can be absorbed. The oxygen-rich layer can provide an oxygen-modified SEI film during the formation process to form an SEI containing a Li-rich and O-rich phase. The impedance of this type of SEI will be lower than that of a normal SEI without O2 modification, so it is beneficial to reduce the DCIR (direct current resistance) of the battery. At the same time, the oxygen-rich layer can isolate the moisture in the negative electrode active material layer and the surrounding environment, further avoiding the occurrence of Fe dissolution in the LFP system, thereby reducing the phenomenon of battery cycle diving. Therefore, it is beneficial to solve the problem of iron dissolution in the LFP / LFMP (lithium iron phosphate / lithium iron manganese phosphate) system caused by moisture, and at the same time reduce the impedance effect caused by the high content of negative electrode film-forming additives. In addition, the preparation cost of the oxygen-rich layer is low, which is beneficial to reduce the cost of the negative electrode sheet.

[0028] According to some embodiments of the present invention, the thickness of the oxygen-rich layer is 1.4um to 14.2um. The thickness of the oxygen-rich layer is relatively reasonable, which is conducive to giving full play to the role of the oxygen-rich layer while avoiding waste caused by excessive use of the oxygen-rich layer, and is conducive to controlling the cost of the negative electrode sheet and the thickness of the negative electrode sheet, thereby increasing the applicability of the negative electrode sheet.

[0029] According to some embodiments of the present invention, the oxygen-rich layer is formed by a water-absorbing oxygen-supplementing agent. Water in the battery will hydrolyze with the lithium salt in the electrolyte to form HF (hydrofluoric acid), and HF will attack the materials of the SEI film and the positive electrode sheet, thereby causing the Fe element in the positive electrode sheet to dissolve and form Fe impurities in the negative electrode sheet. The water-absorbing oxygen-supplementing agent can react with the water in the system, consume the water in the system, and effectively reduce the formation of Fe impurities in the negative electrode. After the battery is filled with liquid, the water-absorbing oxygen-supplementing agent itself will react with the water in the system, thereby eliminating the water that is difficult to bake in some systems. Due to the removal of water, the HF content in the electrolyte is reduced, and the destructiveness to the SEI film is reduced. At the same time, during the formation process, this type of water-absorbing oxygen-supplementing agent can be activated by current and high temperature, thereby releasing oxygen. The formation process is the process of forming the SEI film of the battery. When oxygen is introduced during the formation of SEI, the SEI film will be improved, so that the content of Li-rich and O-rich phases in the SEI film will increase, and the Li-rich and O-rich phases will reduce the system impedance.

[0030] The water-absorbing oxygen replenisher includes at least one of lithium peroxide, sodium peroxide and sodium percarbonate. Lithium peroxide (Li2O2), sodium peroxide (Na2O2), sodium percarbonate (Na2CO4) and lithium oxide (Li2O) each have different chemical behaviors and products when reacting with water.

[0031] Lithium peroxide reacts with water to produce lithium hydroxide (LiOH) and oxygen (O2):

[0032] Sodium peroxide reacts with water to produce sodium hydroxide (NaOH) and oxygen (O2):

[0033] Sodium percarbonate (Na2CO4) contains sodium carbonate (Na2CO3) and hydrogen peroxide (H2O2). When reacting with water, the hydrogen peroxide part decomposes:

[0034] The sodium carbonate part does not react directly with water, but will hydrolyze to form sodium bicarbonate (NaHCO3):

[0035] Therefore, using at least one of lithium peroxide, sodium peroxide and sodium percarbonate as a water-absorbing oxygen supplement is beneficial to the formation of an oxygen-rich layer, reducing the formation of Fe impurities in the negative electrode, and at the same time generating oxygen to improve the SEI film, thereby increasing the content of Li-rich and O-rich phases in the SEI film, thereby reducing the impedance of the system.

[0036] Further, by mass, the content of the water absorbing oxygen replenisher satisfies the following formula: , X is the influence coefficient of the added water-absorbing oxygen replenisher on the low-temperature impedance of the battery, 0.01≤X≤15; DCIR is the DC resistance value of the battery at 0°C, in Ω; Q is the third discharge capacity of the battery at 25°C, in Ah.

[0037] Therefore, through the limitation of the above formula, the mass content and impedance optimization of the water-absorbing oxygen replenisher are balanced, which is beneficial to optimize the performance of the battery and control the cost of the battery. The product of DCIR and Q is a relatively comparable value to avoid the problem of DCIR incomparability caused by cells of different capacities.

[0038] At 25°C, charge and discharge three times at 0.33C, with a voltage range of 2.0V to 3.8V. The third discharge capacity is calibrated as the battery capacity Q. After the capacity is calibrated, charge to 0.5Q at 0.33C at 25°C, let it stand for 4 hours in a 0°C environment and record the end-of-stand voltage V1. Discharge at 1.5C for 30s and record the end-of-discharge voltage V2. , the unit is Ω, where The unit is .

[0039] According to some embodiments of the present invention, the ratio of the content of the water-absorbing oxygen-supplementing agent to 100g of the positive electrode active material is 0.1 to 4 by mass. Therefore, the content of the water-absorbing oxygen-supplementing agent is relatively reasonable, which can fully consume the water in the battery, prevent the Fe element in the positive electrode active material of the battery from dissolving and forming Fe impurities in the negative electrode, optimize the electrochemical performance of the battery, and extend the life of the battery.

[0040] According to some embodiments of the present invention, the negative electrode active material layer includes a negative electrode active material, a binder and a conductive agent. The negative electrode active material refers to a material that can reversibly embed and de-embed ions during the charge and discharge process. The binder is used to maintain the structural integrity of the negative electrode active material layer and ensure good contact between the negative electrode active material and the negative electrode current collector. The conductive agent is conducive to improving the electronic conductivity of the negative electrode active material. The negative electrode active material includes at least one of natural graphite and artificial graphite. Both natural graphite and artificial graphite have high theoretical capacity and low cost. Using at least one of natural graphite and artificial graphite as the negative electrode active material is conducive to realizing the function of storing and releasing charge of the negative electrode sheet, and at the same time, the cost is low, which is conducive to reducing the cost of the negative electrode sheet.

[0041] The binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyurethane and polytetrafluoroethylene. The above binders have strong binding ability and low cost. Using at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyurethane and polytetrafluoroethylene as a binder not only helps to enhance the mechanical strength of the negative electrode sheet, but also promotes the contact between the electrolyte and the negative electrode active material to a certain extent, thereby improving the electrochemical performance of the negative electrode sheet.

[0042] The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene and conductive graphite. Conductive carbon black, carbon nanotubes, graphene and conductive graphite all have good electronic conductivity, which can ensure effective electron transport of the negative electrode active material. At least one of conductive carbon black, carbon nanotubes, graphene and conductive graphite is used as a conductive agent, which is easy to disperse in the negative electrode active material to form a uniform conductive network, and is compatible with the negative electrode active material and other battery components, and does not affect the overall performance of the battery.

[0043] According to some specific embodiments of the present invention, the double-sided surface density of the negative electrode sheet is 100 g / m 2 ~300g / m 2 . Surface density refers to the mass per unit area of ​​the negative electrode sheet. Surface density directly affects the energy density and overall performance of the battery. The double-sided surface density of the above-mentioned negative electrode sheet is relatively reasonable, which is conducive to reducing the risk of cracks or other mechanical damage to the negative electrode sheet during winding or lamination, while increasing the energy density of the negative electrode sheet.

[0044] According to some other specific embodiments of the present invention, the compaction density of the negative electrode sheet is 1.2 g / cm 3 ~1.8g / cm 3 The compaction density refers to the density of the negative electrode sheet under pressure. The compaction density is an indicator to measure the compactness of the negative electrode active material in the negative electrode sheet. The compaction density of the above negative electrode sheet is relatively reasonable, which is conducive to improving the energy density of the battery, that is, more negative electrode active materials can be accommodated in the same volume. At the same time, the diffusion rate of ions in the negative electrode sheet is relatively reasonable, which is conducive to improving the cycle performance and rate performance of the battery.

[0045] The method for preparing a negative electrode sheet according to the second embodiment of the present invention comprises the following steps: coating the negative electrode active material layer slurry on the negative electrode current collector and drying to form a negative electrode active material layer; A water-absorbing oxygen replenisher is coated on the surface of the negative electrode active material layer to obtain a negative electrode sheet.

[0046] According to the method for preparing the negative electrode sheet of the embodiment of the present invention, the preparation method is relatively simple, which is conducive to improving the preparation efficiency of the negative electrode sheet, thereby helping to reduce the cost of the negative electrode sheet and improve the market competitiveness of the negative electrode sheet.

[0047] According to some embodiments of the present invention, coating the water-absorbing oxygen-supplementing agent specifically includes: spraying the dry material of the water-absorbing oxygen-supplementing agent or transferring the dry material of the water-absorbing oxygen-supplementing agent by transfer film. Among them, spraying the dry material of the water-absorbing oxygen-supplementing agent is to spray the dry material of the water-absorbing oxygen-supplementing agent onto the surface of the negative electrode active material layer in the form of mist dispersion, and the spraying uniformity is high and the spraying speed is fast, which is conducive to improving the coating efficiency of the water-absorbing oxygen-supplementing agent. Transferring the dry material of the water-absorbing oxygen-supplementing agent by transfer film is dry transfer, which has flexibility and is conducive to ensuring that the water-absorbing oxygen-supplementing agent has no gaps on the surface of the negative electrode active material, which is conducive to ensuring the coating reliability of the water-absorbing oxygen-supplementing agent.

[0048] The battery according to the third aspect of the present invention comprises: a positive electrode; an electrolyte; a separator; and a negative electrode, wherein the negative electrode is the negative electrode according to the first aspect of the present invention or the negative electrode prepared by the preparation method according to the second aspect of the present invention.

[0049] According to the battery of the embodiment of the present invention, the positive electrode sheet, the electrolyte, the separator and the negative electrode sheet are matched to make the composed battery have high stability and stable electrochemical performance.

[0050] The positive electrode sheet includes a positive electrode conductive substrate and a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, a binder, a conductive agent and a solvent.

[0051] The binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and a cellulose-based polymer.

[0052] The conductive agent includes at least one of conductive carbon black (SP), carbon nanotube (CNT), graphene, and conductive graphite.

[0053] The positive electrode conductive substrate comprises at least one of a foam metal mesh and a metal film material, and the metal film material comprises an aluminum foil having a conductive layer.

[0054] The solvent includes at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), water and alcohols. Preferably, the solvent is N-methylpyrrolidone (NMP).

[0055] The positive electrode active material is not limited and can be any positive electrode active material of the existing power battery system and a combination thereof. In the present invention, the LFP / LFMP system is preferred.

[0056] The double-sided density of the positive electrode is 300g / m 2 ~500g / m 2 , preferably the compacted density is 2.10 g / cm 3 ~3.6g / cm 3 .

[0057] The separator in the battery is located between the positive electrode and the negative electrode, and is used for insulation and liquid retention between the positive and negative electrodes of the battery. There is no special limitation on the separator, and you can choose any type of separator used in batteries, such as PP (polypropylene) and PE (polyethylene). No specific limitation is made here. The electrolyte used in the battery is not limited, and various types of electrolytes used in batteries can be selected. The electrolyte injection coefficient is generally 2.0g / Ah to 4.5g / Ah; There is no restriction on the battery form, and the present invention patent preferably tests soft-pack batteries with air bags.

[0058] An electrical device according to an embodiment of a fourth aspect of the present invention includes: a battery according to an embodiment of the third aspect of the present invention.

[0059] According to the electric device of the embodiment of the present invention, by using the above-mentioned battery, the functional stability of the electric device is higher, the operating stability of the electric device is good, which is beneficial to improving the user experience and thus beneficial to improving the market competitiveness of the electric device.

[0060] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. In addition, if not explicitly stated, all reagents used in the following embodiments are commercially available, or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0061] Example (1) Preparation of positive electrode LFP was selected as the positive electrode active material, CNT and SP were used as conductive agents, and PVDF was used as a binder. The positive electrode active material: CNT: SP: PVDF: NMP = 100:12:0.3:2.5:55 was prepared into a slurry in a mass percentage, and the slurry was evenly coated on a 15um thick conductive Al foil, and then baked and die-cut to obtain a positive electrode sheet.

[0062] (2) Preparation of negative electrode Natural graphite is selected as the negative electrode active material, and its initial gram capacity is 355mAh / g. According to the mass percentage, graphite, conductive agent (conductive carbon black), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber and water are charged and discharged in the ratio of 100:0.5:1.5:3:130, mixed and stirred to obtain a uniform slurry, and the slurry is evenly coated on a conductive copper foil with a thickness of 8μm. After drying, the water-absorbing oxygen supplement (lithium peroxide) is evenly distributed on the electrode sheet before rolling, and then rolling is performed, and then the negative electrode sheet is obtained by slitting and die-cutting.

[0063] 3. Battery assembly The positive electrode sheet, negative electrode sheet and polypropylene separator are stacked in a Z-shaped stacking manner, assembled into a soft-pack battery by hot pressing, and vacuum-filled according to a filling coefficient of 3.5g / Ah. After sealing, aging, high-temperature formation, aging, and capacity separation are performed to produce a square soft-pack battery with a length of 80mm and a width of 60mm.

[0064] Performance Testing (1) Capacity: At 25°C, fully charge the battery to 3.8V at 0.33C constant current and constant voltage. After leaving it alone, discharge it to 2.0V at 0.33C constant current. Repeat this three times. The third discharge capacity is recorded as Q in Ah.

[0065] (2) Normal temperature DCIR test: At 25°C, charge and discharge three times at 0.33C, with a voltage range of 2.0-3.8V. The third discharge capacity is calibrated as the battery capacity Q. After the capacity is calibrated, charge to 0.5Q at 0.33C at 25°C, let it stand for 20 minutes and record the end-of-stand voltage V1. Discharge at 1.5C for 30 seconds and record the end-of-discharge voltage V2. , in mΩ, where The unit is .

[0066] (3) 0℃ DCIR test: At 25℃, charge and discharge three times at 0.33C, with a voltage range of 2.0-3.8V. The third discharge capacity is calibrated as the battery capacity Q. After the capacity is calibrated, charge to 0.5Q at 0.33C at 25℃, leave it at rest in a 0℃ environment for 4h and record the end-of-rest voltage V1. Discharge at 1.5C for 30s and record the end-of-discharge voltage V2. , in mΩ, where The unit is .

[0067] (4) 0℃ 0.33C / 25℃ 0.33C discharge retention rate: Charge three times at 0.33C at 25℃, with the last charge being C-25℃-0.33C. The voltage range is 2.0-3.8V. The battery is left for 30min during the charge and discharge process. After the battery is left at 0℃ for 4h, it is charged and discharged three times at 0.33C, with the last charge being C-0℃-0.33C. The voltage range is 2.0-3.8V. The battery is left for 30min during the charge and discharge process. C-0℃-0.33C / C-25℃-0.33C is the capacity retention rate.

[0068] (5) 45℃ temperature cycle: At 25℃, charge and discharge three times at 0.33C, with a voltage range of 2.0-3.8V, and calibrate the third discharge capacity as the battery capacity Q; after calibrating the capacity, charge to 3.8V at 1C constant current and constant voltage at 45℃, with a cut-off current of 0.05C, then let it stand for 30min, and discharge to 2.0V at 1C constant current, then let it stand for 30min; repeat the above steps 1000 times.

[0069] (6) ICP (inductively coupled plasma spectrometry) test of iron element in the negative electrode: After cycling at 45°C, the battery is disassembled to remove the negative electrode, and the negative electrode is immersed in DMC solvent. After the lithium salt is dissolved, the negative electrode is subjected to ICP to detect the iron element in ppm.

[0070] (7) Test of the thickness of the O-rich layer on the surface of the negative electrode sheet after disassembly: After the battery is normalized and the capacity is removed from the production line, the battery is discharged at 0.33C to 2.0V and then disassembled. The cross-section of the disassembled negative electrode sheet is subjected to SEM-EDS (scanning electron microscope-energy dispersive X-ray spectrometer) test to measure the thickness of the O-rich layer.

[0071] Table 1 Parameters of comparative examples and embodiments

[0072] By comparing Examples 1-10 and Comparative Example 1, it can be seen that after adding a certain amount of water-absorbing oxygen-supplementing agent, the Fe content will decrease rapidly after 1000 cycles at 45°C, so the addition of water-absorbing oxygen-supplementing agent will significantly reduce the occurrence of Fe impurities formed in the negative electrode sheet. At the same time, it can be found that there is an upper limit to the Fe content when adding excessive water-absorbing oxygen-supplementing agent, mainly because there is an upper limit to the water content in the system, which in turn makes the improvement of Fe dissolution limited.

[0073] Comparing Examples 1-10 and Comparative Example 1, the water-absorbing oxygen-supplementing agent releases O2 during high-temperature formation while absorbing water from the system. The introduction of O2 during the formation will modify the SEI film to form a SEI containing a Li-rich and O-rich phase. The impedance of this type of SEI will be lower than that of the normal SEI without O2 modification. Therefore, after adding a certain amount of water-absorbing oxygen-supplementing agent, the system at room temperature will decrease, its 0℃ The decrease is more obvious, so its 0℃ 0.33C / 25℃ 0.33C discharge retention rate is also better, and the corresponding X is in the range of 0.01-15.

[0074] By comparing Examples 6-8 and Example 10, it can be seen that although the content of water-absorbing oxygen replenisher in Example 10 is increased, the Fe content decreases rapidly after 1000 cycles at 45°C, while the Fe content decreases rapidly after 1000 cycles at room temperature and 0°C. On the contrary, it will increase, and the battery's 0℃0.33C / 25℃0.33C discharge retention rate will decrease, mainly because its X>15, which shows that the influence of the added water-absorbing oxygen replenisher on the impedance of the rich Li and rich O is smaller than the impedance influence of the water-absorbing oxygen replenisher itself. The main reason is that the conductivity of the water-absorbing oxygen replenisher is lower than that of the negative electrode. Therefore, when the amount added is too much, it will hinder the ionic conductivity and electronic conductivity in the electrode. Therefore, it is necessary to define X to control the impedance increase caused by the water-absorbing oxygen replenisher. Therefore, the room temperature and 0℃ in Example 10 On the contrary, it will increase and its 0℃ 0.33C / 25℃ 0.33C discharge retention rate will decrease.

[0075] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0076] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A negative electrode sheet, characterized in that: include: Anode current collector; A negative electrode active material layer, the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector; an oxygen-rich layer, the oxygen-rich layer being disposed on a side of the negative electrode active material layer away from the negative electrode current collector, Wherein, the oxygen-rich layer includes at least one of lithium oxide, sodium oxide, sodium carbonate, lithium hydroxide and sodium hydroxide.

2. The negative electrode sheet according to claim 1, characterized in that: The thickness of the oxygen-rich layer is 1.4 um to 14.2 um.

3. The negative electrode sheet according to claim 1, characterized in that: The oxygen-rich layer is formed by a water-absorbing oxygen-supplementing agent, and the water-absorbing oxygen-supplementing agent includes at least one of lithium peroxide, sodium peroxide and sodium percarbonate.

4. The negative electrode sheet according to claim 3, characterized in that: The content of the water absorbing oxygen replenisher satisfies the following formula by mass: , X is the influence coefficient of the added water-absorbing oxygen replenisher on the low-temperature impedance of the battery, 0.01≤X≤15; the DCIR is the DC resistance value of the battery at 0°C, in Ω; and Q is the third discharge capacity of the battery at 25°C, in Ah.

5. The negative electrode sheet according to claim 3, characterized in that: The ratio of the content of the water-absorbing oxygen replenisher to 100g of the positive electrode active material is 0.1 to 4 by mass.

6. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material layer includes a negative electrode active material, a binder and a conductive agent, The negative electrode active material includes at least one of natural graphite and artificial graphite; and / or, The binder comprises at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyurethane and polytetrafluoroethylene; and / or, The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene and conductive graphite.

7. The negative electrode sheet according to claim 1, characterized in that: The double-sided surface density of the negative electrode sheet is 100 g / m 2 ~300g / m 2 .

8. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the negative electrode sheet is 1.2 g / cm 3 ~1.8g / cm 3 .

9. A method for preparing a negative electrode sheet according to any one of claims 1 to 8, characterized in that: The steps include: coating the negative electrode active material layer slurry on the negative electrode current collector and drying to form a negative electrode active material layer; A water-absorbing oxygen replenishing agent is coated on the surface of the negative electrode active material layer to obtain a negative electrode sheet.

10. The preparation method according to claim 9, characterized in that: The coating of the water absorbing oxygen supplementing agent specifically comprises: spraying the dry material of the water absorbing oxygen supplementing agent; or, The transfer membrane transfers the dry material of the water absorbing oxygen supplement agent.

11. A battery, characterized in that: include: Positive electrode; Electrolyte; Diaphragm; A negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet according to any one of claims 1 to 8, or the negative electrode sheet prepared by the preparation method according to claim 9 or 10.

12. An electrical equipment, characterized in that: include: The battery according to claim 11.

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