Negative plate, preparation method thereof and lithium ion secondary battery

Abstract

The invention provides a negative plate, a preparation method thereof and a lithium ion secondary battery, and belongs to the technical field of new energy storage materials. The negative plate comprises a negative current collector and an active material layer located on the negative current collector, the active substance layer comprises an active substance, a conductive agent, a binder and an additive; the additive comprises at least one of a phosphorus-carbon composite material, a carbon nanotube and polyacrylic acid. When the negative plate disclosed by the invention is used for recycling a battery, deposition of dissolution of transition metal ions on the surface of the negative plate can be resisted, and the safety and the cycling stability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy storage materials, and in particular to a negative electrode sheet and a preparation method thereof, and a lithium ion secondary battery. Background Art

[0002] As lithium ion secondary batteries have become widely used, they have been widely used in devices such as portable electronic devices, battery packs or energy storage devices for hybrid vehicles and electric vehicles.

[0003] In lithium-ion secondary batteries, the positive electrode materials usually contain transition metal ions (such as cobalt, nickel, manganese, etc.), which are important for achieving high energy density of the battery. During use, such as high-temperature storage or cycling, the transition metal ions in the positive electrode materials will dissolve, enter the electrolyte, further migrate to the negative terminal of the battery, and deposit on the surface of the negative electrode sheet. This migration and deposition process causes the battery to have performance degradation after multiple charging cycles.

[0004] Therefore, how to reduce the deposition of transition metal ions on the negative electrode sheet has become an urgent problem to be solved. Summary of the invention

[0005] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides a negative electrode sheet and a preparation method thereof, and a lithium-ion secondary battery.

[0006] According to an embodiment of one aspect of the present invention, a negative electrode sheet is provided, comprising: a negative electrode current collector, and an active material layer located on the negative electrode current collector; the active material layer comprises: an active material, a conductive agent, a binder and an additive; wherein the additive comprises at least one of a phosphorus-carbon composite material, carbon nanotubes and polyacrylic acid.

[0007] In some exemplary embodiments, the phosphorus-carbon composite material includes phosphorus and a carbon material, and the phosphorus is connected to the carbon material through a chemical bond.

[0008] In some exemplary embodiments, the mass content of phosphorus in the phosphorus-carbon composite material is 30-70%.

[0009] In some exemplary embodiments, the mass of the additive accounts for 1-20% of the total mass of the negative electrode sheet.

[0010] In some exemplary embodiments, the conductive agent includes conductive carbon. Preferably, the conductive agent includes at least one of carbon black, carbon nanotubes, graphene, carbon fibers, and porous carbon.

[0011] In some exemplary embodiments, the mass ratio of the active material, the conductive agent, and the binder is 8:1:1.

[0012] In some exemplary embodiments, the active material includes at least one of a carbon-based material and a silicon-based material; the carbon-based material includes at least one of graphite, hard carbon, and soft carbon; the silicon-based material includes at least one of nano-silicon, micro-silicon, a silicon-carbon composite material, and silicon oxide.

[0013] In some exemplary embodiments, the carbon material includes at least one of graphite, hard carbon, soft carbon, and carbon black; and the phosphorus includes at least one of red phosphorus, black phosphorus, white phosphorus, blue phosphorus, and purple phosphorus.

[0014] According to another embodiment of the present invention, a method for preparing the above-mentioned negative electrode sheet is provided, comprising: adding active material, additive, binder, and conductive agent into a solvent respectively, stirring and coating them on a negative electrode collector, and performing drying to obtain a negative electrode sheet.

[0015] In some exemplary embodiments, the drying temperature is 55-65° C., the treatment time is 9-11 hours, and the solvent includes at least one of water or N-methylpyrrolidone.

[0016] According to another aspect of the embodiments of the present invention, there is provided a lithium-ion secondary battery, comprising the negative electrode sheet as described above.

[0017] According to an embodiment of the present invention, by adding at least one additive of a phosphorus-carbon composite material, carbon nanotubes, and polyacrylic acid to the active material layer of the negative electrode sheet, the deposition of transition metal ions (such as manganese, cobalt, nickel, etc.) on the negative electrode sheet can be reduced during the battery cycle. The additive can reduce the migration freedom of the transition metal ions by interacting with the transition metal ions, reduce or prevent the deposition and enrichment of the transition metal ions on the surface of the negative electrode sheet, thereby improving the specific capacity of the battery and extending the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0019] Figure 1 A schematic diagram showing the mechanism of the continuous adsorption and engulfment process of transition metal ions by the phosphorus-carbon composite material according to an embodiment of the present invention;

[0020] Figure 2 The negative electrode of Example 1 of the present invention and Comparative Example 1 contains 20 mM Mn 2+ Cyclic specific capacity and coulombic efficiency diagram in electrolyte;

[0021] Figure 3 A high-resolution transmission electron microscopy image of the phosphorus-carbon particles of the negative electrode of Example 1 of the present invention after battery cycling is shown;

[0022] Figure 4 A high-resolution transmission electron microscopy image of graphite particles of the negative electrode of Comparative Example 1 of the present invention after battery cycling is shown;

[0023] Figure 5 The negative electrode of Example 2 of the present invention and Comparative Example 2 contains 20 mM Mn 2+ Graph of cyclic specific capacity and coulombic efficiency in electrolyte. DETAILED DESCRIPTION

[0024] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0025] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0026] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0027] In the related art, the positive electrode materials used in lithium-ion battery systems include LiCoO 2 、LiMn 2 O 4 、Li(Ni x Co y Mn 1-x-y ) 2 The cathode materials in the research and development stage also include lithium-rich manganese-based materials and high-voltage spinel materials LiNi 0.5 Mn 1.5 O 2It can be seen that the above-mentioned positive electrode materials all contain transition metal ion elements, especially manganese. During the battery recycling process, the dissolution and deposition of transition metal ions is a difficult problem commonly faced by these positive electrodes. Among them, the problem of transition metal ion dissolution and deposition can be understood as: transition metal ions dissolve from the positive electrode material and migrate through the electrolyte to the negative electrode surface for deposition. Due to the dissolution and deposition of transition metal ions, the performance of the lithium-ion secondary battery system decays rapidly in actual use (including storage and cycling processes), especially during high-temperature storage or cycling. The dissolution problem is particularly serious.

[0028] Specifically, taking a battery system containing a Mn positive electrode as an example, Mn ions dissolve from the positive electrode and migrate and deposit on the surface of the negative electrode of a traditional lithium-ion secondary battery, resulting in serious decomposition of the electrolyte and blocking of lithium-ion transmission channels. The dissolution and deposition of Mn ions will lead to a series of phenomena such as increased internal resistance of the battery, gas production, capacity attenuation, decreased rate performance, and shortened cycle life, exacerbating the failure of lithium-ion batteries.

[0029] In order to overcome the negative impact of transition metal ion crosstalk (i.e., the dissolution and deposition process of transition metal ions) on lithium-ion batteries, relevant technologies attempt to solve the above-mentioned crosstalk problem by adding some reagents to the electrolyte, designing the positive electrode coating or designing the battery separator coating. However, the above-mentioned methods are relatively complicated, and reducing the process of transition metal ion dissolution also affects the performance of lithium-ion batteries such as energy density.

[0030] In the process of realizing the concept of the present invention, it is found that by adding additives to the active material layer of the negative electrode sheet, the additives can interact with transition metal ions, thereby reducing the deposition and enrichment of transition metal ions on the surface of the negative electrode sheet.

[0031] Specifically, according to an embodiment of one aspect of the present invention, a negative electrode sheet is provided, comprising: a negative electrode current collector, and an active material layer located on the negative electrode current collector; the active material layer comprises: an active material, a conductive agent, a binder and an additive; wherein the additive comprises at least one of a phosphorus-carbon composite material, carbon nanotubes and polyacrylic acid.

[0032] According to an embodiment of the present invention, by adding additives to the active material layer, the additives can interact with transition metal ions, thereby reducing the deposition and enrichment of transition metal ions on the surface of the negative electrode sheet, reducing the damage of the negative electrode sheet to the crosstalk of the transition metal ions, and thereby improving the cycle stability and service life of the battery.

[0033] The following will be described in detail based on the different interactions between several additives and transition metal ions.

[0034] In some exemplary embodiments, the additive is a phosphorus-carbon composite material, in which the carbon can provide excellent conductivity and mechanical strength, help promote electron transport, and reduce internal resistance. Phosphorus can fix transition metal ions on the surface and inside of the phosphorus-carbon composite material through continuous adsorption and engulfment of transition metal ions. Figure 1 The schematic diagram of the mechanism of the continuous adsorption and engulfment process of transition metal ions (such as manganese ions) by the phosphorus-carbon composite material of the embodiment of the present invention is shown. Figure 1 As shown, it can be seen that part of the transition metal ions are adsorbed on the surface of the phosphorus particles, and the other part is further engulfed into the bulk phase of the phosphorus particles, which helps to reduce the deposition on the surface of the negative electrode sheet and reduce the negative impact on the cycle of the negative electrode sheet. At the same time, the phosphorus-carbon composite material can react with the electrolyte to a certain extent, participate in the formation of the solid electrolyte (SEI) film during the battery cycle, further form protection for the negative electrode sheet, reduce the side reaction between the active material and the electrolyte, and extend the service life and cycle stability of the lithium-ion battery.

[0035] In some exemplary embodiments, the additive is polyacrylic acid, which is a good binder and can maintain good contact between active material particles, help increase the adhesion between the active material and the negative electrode current collector, help maintain the integrity of the negative electrode sheet structure, and can reduce the shedding of active materials during long-term battery cycles, thereby improving the cycle life and safety of the battery.

[0036] In some exemplary embodiments, the additive is carbon nanotubes, which help form a three-dimensional conductive network, help improve the overall conductivity of the active material layer, and thus promote electron transport, reduce internal resistance, and improve the charge and discharge efficiency and power density of the battery.

[0037] In some exemplary embodiments, a combination of the above materials may also be included, which helps to adapt to different battery application scenarios by adjusting the content of the above additives.

[0038] In some exemplary embodiments, the negative electrode current collector may be, for example, copper, copper alloy or stainless steel, preferably copper, because copper has good stability and is not easy to form a passivation layer during battery charging and discharging, so it can be widely used in lithium-ion batteries.

[0039] In some exemplary embodiments, the phosphorus-carbon composite material includes phosphorus and a carbon material, and the phosphorus is connected to the carbon material through a chemical bond.

[0040] It is understandable that although phosphorus can provide adsorption and phagocytosis of transition metal ions, phosphorus will undergo a relatively obvious volume change during the phagocytosis process and the charging and discharging process. By combining phosphorus and carbon materials to form a phosphorus-carbon composite material, the carbon material can effectively buffer the volume expansion caused by phosphorus, help maintain the stability of the negative electrode structure, reduce the loss of active substances, and improve the battery cycle life; at the same time, the carbon material can provide higher conductivity, which helps to improve the conductivity of the phosphorus-carbon composite material.

[0041] In some exemplary embodiments, the mass content of phosphorus in the phosphorus-carbon composite material is 30-70%, for example, 30%, 40%, 50%, 60% or 70%. If the phosphorus content is too high, the volume expansion during the charge and discharge process may be aggravated, resulting in poor cycle performance of the negative electrode sheet; if the phosphorus content is too low, it is difficult to provide adsorption and phagocytosis of transition metal ions, and the improvement of the crosstalk effect of transition metal ions is limited. Adjusting the phosphorus content within the above range provides sufficient adsorption and phagocytosis of transition metal ions while maintaining the stability of the negative electrode sheet, further improving the cycle performance and service life of the lithium-ion battery.

[0042] In some exemplary embodiments, the mass of the additive accounts for 1-20% of the total mass of the negative electrode sheet, for example, 1%, 5%, 10%, 15% or 20%. In the process of conducting experiments related to the present invention, it is found that by adjusting the mass percentage of the additive, different positive electrode materials can be matched, thereby improving the crosstalk of the adapted transition metal ions in different positive electrode materials.

[0043] In some exemplary embodiments, the conductive agent includes conductive carbon, preferably, the conductive agent includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, and porous carbon, wherein the carbon black may be, for example, Ketjen black. Thus, the addition of the conductive agent helps to construct an electronic conduction network, reduce the internal resistance of the negative electrode sheet, improve the charge and discharge efficiency, and thus improve the performance of the battery.

[0044] Preferably, the mass ratio of the active material, the conductive agent, and the binder is 8:1:1. Such a setting helps to regulate each material to a better mass value, so that the battery has better performance.

[0045] More preferably, the mass ratio of the active material, the conductive agent, the binder and the phosphorus-carbon composite material is 8:1:1:0.5.

[0046] In some exemplary embodiments, the active material includes at least one of a carbon-based material and a silicon-based material; the carbon-based material has good stability and provides a lower potential platform or a higher specific capacity in a lithium-ion battery. Specifically, the carbon-based material includes at least one of graphite, hard carbon, and soft carbon, wherein graphite provides a lower and flat potential platform during lithium removal and lithium insertion, which can improve battery safety. Hard carbon can have a higher specific capacity and performs better under low temperature conditions. Soft carbon has certain adjustable properties and has a higher electronic conductivity, which is conducive to fast charging and discharging processes. Silicon-based materials have less volume expansion or are easy to process. Specifically, the silicon-based material includes at least one of nano-silicon, micron silicon, silicon-carbon composite materials, and silicon oxide, wherein nano-silicon has a high theoretical specific capacity (about 4200mAh / g), and the nano size helps to alleviate the volume expansion problem of silicon during charging and discharging, and reduce the risk of electrode rupture. Micron silicon has better processing performance, can provide electrode forming characteristics, and has a lower cost than nano-silicon. Silicon oxide has a smaller volume expansion rate, which is conducive to improving the cycle performance of the electrode. Silicon-carbon composites can fully utilize the high specific capacity of silicon while taking into account the excellent conductivity and volume stability of carbon.

[0047] In some illustrative embodiments, the carbon material includes at least one of graphite, hard carbon, soft carbon, and carbon black. Graphite helps to provide a stable structure, alleviates the volume expansion of phosphorus during charging and discharging, and is beneficial to improving the efficiency of electronic conduction. The structure of hard carbon is disordered and can provide more active sites for the dispersion and fixation of phosphorus. Carbon black, for example, can be acetylene black or Ketjen black, has a high specific surface area and conductivity, can form an efficient electron transport network, and helps to enhance the conductivity of the negative electrode active material layer. Phosphorus includes at least one of red phosphorus, black phosphorus, white phosphorus, blue phosphorus, and purple phosphorus. Red phosphorus and black phosphorus are preferred. Red phosphorus has high safety and stability and has a high theoretical specific capacity. Black phosphorus has a layered structure, which is conducive to the insertion and extraction of lithium ions and shows excellent electrochemical properties.

[0048] According to another embodiment of the present invention, a method for preparing the above-mentioned negative electrode sheet is provided, comprising: adding active material, additive, binder, and conductive agent into a solvent respectively, stirring and coating them on a negative electrode collector, and performing drying to obtain a negative electrode sheet.

[0049] According to the embodiments of the present invention, the preparation process of the present invention is relatively simple, and by adding an additional additive to the negative electrode component, a negative electrode with reduced transition metal ion crosstalk can be obtained. The method of the present invention can improve the resistance of the negative electrode to transition metal ion crosstalk without reducing the energy density, and has good application prospects.

[0050] It should be noted that the types and qualities of the negative electrode current collector, active material, additive, binder, conductive agent and other materials of the present invention are consistent with those described above and will not be described in detail here.

[0051] It can be understood that the present invention rationally designs the negative electrode components, introduces additional additives, and produces a negative electrode that can resist transition metal ion crosstalk through a simple manufacturing method. Compared with the methods of diaphragm coating, electrolyte modification, and positive electrode modification in the related art, the present invention can simplify the production steps, have better economic benefits, and does not reduce the energy density, and can improve the negative electrode's resistance to transition metal ion crosstalk.

[0052] In some exemplary embodiments, the drying temperature is 55-65°C, for example, 55°C, 60°C or 65°C, preferably 60°C, and the treatment time is 9-11 hours, for example, 9h, 10h or 11h, preferably 10h; the solvent includes at least one of water or N-methylpyrrolidone. It can be understood that the preparation process of the negative electrode sheet of the present invention can be adapted to both aqueous solvents and organic solvents, and has good application prospects.

[0053] According to another aspect of the embodiments of the present invention, there is provided a lithium-ion secondary battery, comprising the negative electrode sheet as described above.

[0054] According to an embodiment of the present invention, the active material can provide the energy density of the negative electrode material, thereby improving the specific capacity of the negative electrode and increasing the energy density of the battery. The introduction of additives helps to form interactions with transition metal ions, especially phosphorus-carbon composite materials can reduce the occurrence of transition metal ion crosstalk through continuous adsorption and phagocytosis, thereby improving the cycle stability and service life of the battery. The introduction of conductive agents helps to reduce the internal resistance of the negative electrode and improve the rate performance of the battery. The coordinated use of the above materials helps to improve the various performances of lithium-ion secondary batteries.

[0055] The present invention is further described below by embodiments and related test experiments and results thereof. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments may also be implemented without these specific details. And, in the absence of conflict, the details in the following embodiments may be combined into other feasible embodiments at will.

[0056] It should be noted that the following specific examples are only for illustration, and the protection scope of the present invention is not limited thereto. The chemicals and raw materials used in the following examples are all commercially available or homemade by recognized processing methods.

[0057] Embodiment 1:

[0058] Preparation of phosphorus carbon particles:

[0059] Red phosphorus, graphite and carbon nanotubes were ball-milled at a mass ratio of 7:2:1 in a star-shaped ball mill at 600 rpm for 10 hours to prepare phosphorus-carbon particles.

[0060] Artificial graphite powder AML350 powder, Ketjen black conductive agent, polyvinylidene fluoride (PVDF) binder and phosphorus carbon particles were mixed and slurried evenly in N-methylpyrrolidone in a mass ratio of 8:1:1:0.5, coated on copper foil with a scraper, and dried in a vacuum oven at 60°C for 10 hours to obtain a whole negative electrode sheet.

[0061] After cutting the entire negative electrode sheet, it is assembled into a full battery with a ternary composite positive electrode (NCM523) of nickel cobalt manganese oxide purchased from a certain company (the capacity ratio of the negative electrode to the positive electrode is 1~1.1). The full battery electrolyte uses 1M lithium hexafluorophosphate (LiPF 6 ) and ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, and 10% volume of fluoroethylene carbonate is added to the total electrolyte, and then 20 mM / L of manganese and bis(trifluoromethylsulfonyl)imide (TFSI) is added to form a compound Mn(TFSI) 2 Salt, using Mn(TFSI) 2 The salt simulated the transition metal manganese ions overflowing from the positive electrode material and was used after stirring for 6 hours. The diaphragm used was a commercial PP diaphragm purchased from a certain company. The assembled full battery was subjected to a long cycle test.

[0062] Comparative Example 1:

[0063] The assembly process of this comparative example 1 is substantially the same as that of the embodiment 1, except that no phosphorus carbon particles are added in this comparative example 1.

[0064] The full batteries assembled in Example 1 and Comparative Example 1 were tested. Figure 2 The negative electrode of Example 1 of the present invention and Comparative Example 1 contains 20 mM Mn 2+ The cycle specific capacity and coulombic efficiency diagram in the electrolyte. The battery in Example 1 is marked as Gr / PIINCM523, the corresponding color is purple, and the coulombic efficiency corresponds to the hollow circle with purple outline. The battery in Comparative Example 1 is marked as GrIINCM523, the corresponding color is red, and the coulombic efficiency corresponds to the hollow circle with red outline. Figure 2 As shown, it can be seen that the coulombic efficiencies of the two are basically the same, but in terms of specific capacity, the specific capacity of Example 1 remains the same even after 50 cycles, and has good cycle performance; while the specific capacity of Comparative Example 1 continues to decay during the cycle, indicating that the cycle stability and life of the battery assembled therefrom are relatively poor.

[0065] In order to verify the mechanism of action of the additive, the negative electrodes of the full batteries of Example 1 and Comparative Example 1 were removed after recycling and subjected to high-resolution testing. Figure 3 The high-resolution transmission microscopy image of the phosphorus-carbon particles of the negative electrode of Example 1 of the present invention after battery cycling is shown. Figure 3 As shown in the figure, after the cycle, the manganese ions are evenly distributed in the bulk phase of the phosphorus-carbon particles, indicating that part of the manganese ions are swallowed by phosphorus into the bulk phase of the phosphorus particles (phosphorus particles in the phosphorus-carbon particles), and the remaining part is adsorbed by the phosphorus particles, thereby reducing the crosstalk of the positive electrode manganese ions, alleviating the negative impact on the graphite negative electrode, and improving the cycle stability and service life of the lithium-ion battery. Figure 4 The graphite particles of the negative electrode of Comparative Example 1 of the present invention after battery cycling are shown in a high-resolution transmission electron microscope image. Figure 4 As shown, it means that manganese ions will deposit on the surface of graphite particles instead of entering the bulk phase of graphite particles. Manganese ions deposited on the surface will catalyze the decomposition of the electrolyte, causing a series of side reactions and deterioration of battery performance.

[0066] Further related calculations are performed, specifically, the energy change of the red phosphorus system in which manganese ions are adsorbed and swallowed in the presence of electron injection is calculated, such as Figure 1 As shown, the energy of the system is constantly decreasing, indicating that the transition metal ions tend to be stably adsorbed and fixed on the surface of the phosphorus particles, and the process of being further swallowed up into the bulk phase of the phosphorus particles is thermodynamically stable.

[0067] Embodiment 2:

[0068] The additive used in this Example 2 is the phosphorus carbon particles prepared in Example 1.

[0069] Commercial silicon-carbon powder (Si content is 48%), Ketjen black conductive agent, polyacrylate lithium (PAA-Li) binder and phosphorus carbon particles are mixed and slurried evenly in water in a mass ratio of 8:1:1:0.5, coated on copper foil with a scraper, and dried in a vacuum oven at 60°C for 10 hours to obtain a whole negative electrode sheet.

[0070] After cutting the entire negative electrode sheet, it is assembled into a full battery with a ternary composite positive electrode (NCM523) of nickel cobalt manganese oxide purchased from a certain company (the capacity ratio of the negative electrode to the positive electrode is 1~1.1). The full battery electrolyte uses 1M lithium hexafluorophosphate (LiPF 6 ) and ethylene carbonate and diethyl carbonate in a volume ratio of 1:1, and 10% volume of fluoroethylene carbonate is added to the total electrolyte, and then 20 mM / L of manganese and bis(trifluoromethylsulfonyl)imide (TFSI) is added to form a compound Mn(TFSI) 2 Salt, using Mn(TFSI) 2The salt simulated the transition metal manganese ions overflowing from the positive electrode material and was used after stirring for 6 hours. The diaphragm used was a commercial PP diaphragm purchased from a certain company. The assembled full battery was subjected to a long cycle test.

[0071] Comparative Example 2:

[0072] The assembly process of this comparative example 2 is substantially the same as that of Example 2, except that no phosphorus carbon particles are added in this comparative example 2.

[0073] The full batteries assembled in Example 2 and Comparative Example 2 were tested. Figure 5 The negative electrode of Example 2 of the present invention and Comparative Example 2 contains 20 mM Mn 2+ The cycle specific capacity and coulombic efficiency diagram in the electrolyte. The battery in Example 2 is marked as Si / PIINCM523, the corresponding color is blue, and the coulombic efficiency corresponds to the hollow circle with a blue outline. The battery in Comparative Example 2 is marked as SiIINCM523, the corresponding color is red, and the coulombic efficiency corresponds to the hollow circle with a red outline. Figure 5 As shown, it can be seen that the coulombic efficiencies of the two are basically the same, but in terms of specific capacity, the specific capacity of Example 2 remains the same even after 50 cycles, and has good cycle performance; while the specific capacity of Comparative Example 2 continues to decay during the cycle, indicating that the cycle stability and life of the battery assembled therefrom are relatively poor.

[0074] The cycle performance test results of Example 1~Example 2 and Comparative Example 1~Comparative Example 2 are shown in Table 1 below.

[0075] Table 1 Cyclic performance test results of Examples 1 to 2 and Comparative Examples 1 to 2

[0076]

[0077] As can be seen from Table 1, the full battery system of Example 1 and Example 2 containing additive negative electrode has good tolerance to transition metal ions in the electrolyte, the first cycle coulombic efficiency and first cycle specific capacity remain normal, and the reversible capacity is still high after 50 cycles, without much impact. 2+ The crosstalk has a great influence and the specific capacity has a large attenuation.

[0078] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific 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, comprising: A negative electrode current collector and an active material layer located on the negative electrode current collector; The active material layer includes: active material, conductive agent, binder and additives; Wherein, the additive includes at least one of phosphorus-carbon composite materials, carbon nanotubes, and polyacrylic acid.

2. The negative electrode sheet according to claim 1, wherein: The phosphorus-carbon composite material comprises phosphorus and a carbon material, and the phosphorus is connected to the carbon material via a chemical bond.

3. The negative electrode sheet according to claim 1 or 2, wherein: The mass content of phosphorus in the phosphorus-carbon composite material is 30-70%.

4. The negative electrode sheet according to claim 1 or 2, wherein: The mass of the additive accounts for 1-20% of the total mass of the negative electrode sheet; The conductive agent includes conductive carbon. Preferably, the conductive agent includes at least one of carbon black, carbon nanotubes, graphene, carbon fiber, and porous carbon.

5. The negative electrode sheet according to claim 1, wherein: The mass ratio of the active material, the conductive agent and the binder is 8:1:

1.

6. The negative electrode sheet according to claim 1 or 2, wherein: The active material includes at least one of a carbon-based material and a silicon-based material; The carbon-based material includes at least one of graphite, hard carbon and soft carbon; The silicon-based material includes at least one of nano-silicon, micro-silicon, silicon-carbon composite material, and silicon monoxide.

7. The negative electrode sheet according to claim 2, wherein: The carbon material includes at least one of graphite, hard carbon, soft carbon and carbon black; The phosphorus includes at least one of red phosphorus, black phosphorus, white phosphorus, blue phosphorus, and purple phosphorus.

8. A method for preparing the negative electrode sheet according to any one of claims 1 to 7, comprising: The active material, additive, binder and conductive agent are respectively added into a solvent, stirred and coated on the negative electrode current collector, and dried to obtain the negative electrode sheet.

9. The preparation method according to claim 8, wherein: The drying temperature is 55-65°C and the treatment time is 9-11 hours; The solvent includes at least one of water and N-methylpyrrolidone.

10. A lithium ion secondary battery comprising the negative electrode sheet according to any one of claims 1 to 7.

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