Composite negative electrode, preparation method thereof and lithium ion battery

Abstract

The invention provides a composite negative electrode, a preparation method thereof and a lithium ion battery, and belongs to the technical field of new energy storage materials. The preparation method of the composite negative electrode comprises the following steps: preparing a phosphorus negative electrode as an initial pole piece, wherein the phosphorus negative electrode contains a phosphorus-carbon composite material as an active substance; and compounding a lithium metal layer on the initial pole piece to obtain the lithium metal-phosphorus composite negative electrode. The lithium metal layer is compounded with the phosphorus negative electrode, so that reversible capacity loss caused by interface side reaction when the phosphorus-carbon material is used as the negative electrode can be made up, the first coulombic efficiency is higher than the practical standard, and relatively high cycling stability is achieved.

Description

Technical Field

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

[0002] With the popularization of lithium-ion battery applications, how to further develop high-energy-density lithium secondary batteries is one of the technical challenges in the current battery field, especially in the power battery market.

[0003] The graphite anode currently in the mainstream market has the advantages of fast lithium ion diffusion and stable cycle performance, but its theoretical intrinsic lithium storage capacity is only 372 mAh / g, which greatly limits the further improvement of battery energy density. Emerging high-gram-capacity anodes mainly include silicon anodes (theoretical capacity 4200 mAh / g) and phosphorus anodes (theoretical capacity 2600 mAh / g). These two types of "alloy-type" anode materials can still maintain a gram capacity of more than 1000 mAh / g after being composited with carbon materials, which is nearly three times that of graphite anodes. Therefore, based on the difference in the amount of lithium stored in the anode, silicon-carbon and phosphorus-carbon are usually selected as anode materials in current new high-energy-density battery systems. In particular, phosphorus-carbon materials have the characteristics of high lithium ion diffusion coefficient and fast charging without lithium precipitation, making them the preferred choice.

[0004] During the use of phosphorus-carbon negative electrodes, it was found that due to the existence of interfacial side reactions, the phosphorus-carbon negative electrode underwent a dramatic volume expansion during the lithium insertion process, and the electrode potential of phosphorus was low, which made it easy for spontaneous side reactions to occur with the electrolyte. Although the carbon material could buffer part of the volume expansion, it was difficult to inhibit the direct contact between phosphorus and the electrolyte, which resulted in a more serious loss of reversible capacity and caused the first coulombic efficiency to be lower than the practical standard. 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 composite negative electrode and a preparation method thereof, and a lithium-ion battery.

[0006] According to an embodiment of one aspect of the present invention, a method for preparing a composite negative electrode is provided, comprising: preparing a phosphorus negative electrode as an initial electrode sheet, the phosphorus negative electrode comprising a phosphorus-carbon composite material as an active material; and compounding a lithium metal layer on the initial electrode sheet to obtain a lithium metal-phosphorus composite negative electrode.

[0007] In some embodiments, compounding the lithium metal layer on the initial electrode includes: introducing the lithium metal layer by rolling; or, introducing the lithium metal layer by melting; or, introducing the lithium metal layer by electrodeposition.

[0008] In some embodiments, introducing a lithium metal layer by rolling includes: superimposing a lithium metal foil on the surface of an initial pole piece, and achieving the composite of the initial pole piece and the lithium metal layer by mechanical rolling; or, introducing a lithium metal layer by melting includes: heating the lithium metal to melt it in an inert atmosphere, and applying the molten lithium metal to the surface of the initial pole piece; or, introducing a lithium metal layer by electrodeposition includes: depositing a lithium metal layer on the surface of the initial pole piece by electrochemical deposition.

[0009] In some embodiments, the phosphorus in the phosphorus-carbon composite material includes at least one of red phosphorus, black phosphorus, and white phosphorus; and the carbon in the phosphorus-carbon composite material includes at least one of a carbon material having a layered structure and a carbon material having a porous structure.

[0010] In some embodiments, the phosphorus-carbon composite material is prepared by the following method, which includes: mixing phosphorus and carbon material in a mass ratio of 1:1 to obtain a mixed powder; and heating the mixed powder under an inert atmosphere to obtain the phosphorus-carbon composite material.

[0011] In some embodiments, the composite negative electrode includes a lithiated phosphorus negative electrode layer formed by reacting metallic lithium with a phosphorus-carbon composite material.

[0012] In some embodiments, the capacity of the phosphorus-carbon material layer is AmAh, the first coulombic efficiency is ICE, and the capacity of the lithium metal is BmAh, and the three satisfy: B≥A(1-ICE); or, the lithium capacity embedded in the phosphorus negative electrode is 0.5~2.0mAh / cm 2 .

[0013] According to another embodiment of the present invention, a composite negative electrode prepared by the above-mentioned preparation method is provided.

[0014] In some embodiments, the overall areal capacity of the composite negative electrode is >3 mAh / cm 2 .

[0015] According to another embodiment of the present invention, there is provided a lithium-ion battery including a negative electrode, wherein the negative electrode is the composite negative electrode described above.

[0016] According to the method for preparing a composite negative electrode of an embodiment of the present invention, a lithium metal layer is composited on a phosphorus negative electrode. The lithium metal layer can provide additional lithium ion storage sites and serve as a conductive bridge for lithium ions to accelerate lithium ion transmission and alleviate the low conductivity problem of phosphorus. Moreover, lithium metal, as an efficient electronic conductor, helps to reduce the contact resistance between phosphorus and carbon particles. The presence of the lithium metal layer inhibits interfacial side reactions, reduces the chance of direct contact between phosphorus and the electrolyte, reduces charge transfer impedance, and takes into account the volume expansion of the phosphorus negative electrode caused by buffering lithium ion insertion and removal. Furthermore, the introduction of the lithium metal layer helps to improve the reversible capacity of the composite negative electrode, ensures that the first coulombic efficiency is higher than the practical standard, and broadens the application range of the phosphorus negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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:

[0018] Figure 1 A flow chart showing a method for preparing a composite negative electrode according to an embodiment of the present invention is shown;

[0019] Figure 2 A schematic cross-sectional view of an initial electrode sheet and a composite negative electrode according to an embodiment of the present invention is shown;

[0020] Figure 3 shows the charge / discharge curves of the first two cycles of the half-cell of Example 1 of the present invention;

[0021] Figure 4 Shown are the charge / discharge curves of the first cycle of the full battery of Example 1 of the present invention and Comparative Example 1;

[0022] Figure 5 The capacity retention diagram of the full batteries of Example 1 of the present invention and Comparative Example 1 after 100 cycles is shown. DETAILED DESCRIPTION

[0023] Hereinafter, 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 the concept of the present invention.

[0024] 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.

[0025] When expressions such as “at least one of A, B, and C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly 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 systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.). When expressions such as “at least one of A, B, or C, etc.” are used, they should generally be interpreted in accordance with the meaning commonly 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 systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.).

[0026] As a typical alloy-type negative electrode material, the phosphorus-carbon negative electrode suffers from severe reversible capacity loss due to interfacial side reactions, which is mainly manifested in the first coulombic efficiency being lower than the practical standard.

[0027] During the implementation of the present invention, the inventors discovered that to ensure stable cycling of the phosphorus-carbon anode in the battery system, they attempted to supplement the anode with lithium to compensate for lithium loss caused by interfacial side reactions. Commonly used lithium supplements, such as lithium powder or lithium-rich compounds, typically only compensate for less than 10% of lithium ion loss, significantly lowering the initial Coulombic efficiency loss achieved by the phosphorus-carbon anode.

[0028] In order to solve the above problems, a lithium metal layer is composited on the phosphorus negative electrode, and the phosphorus negative electrode is used to provide the main reversible capacity contribution. A lithium metal layer is introduced to provide additional supplementary capacity. By compositeing the lithium metal layer with the phosphorus negative electrode, the overall energy density of the composite negative electrode is improved, thereby improving the battery's first coulombic efficiency.

[0029] Specifically, according to an embodiment of one aspect of the present invention, a method for preparing a composite negative electrode is provided. Figure 1 The flowchart of the method for preparing the composite negative electrode according to the embodiment of the present invention is shown. Figure 2 The cross-sectional diagram of the initial electrode and the composite negative electrode of the embodiment of the present invention is shown as follows: Figure 1~Figure 2 As shown, it includes operations S101~S102.

[0030] In operation S101 , a phosphorus negative electrode is prepared as an initial electrode sheet, wherein the phosphorus negative electrode includes a phosphorus-carbon composite material as an active material.

[0031] In operation S102 , a lithium metal layer is composited on the initial electrode to obtain a lithium metal-phosphorus composite negative electrode.

[0032] According to an embodiment of the present invention, since the initial lithium removal and lithium insertion efficiency of the phosphorus negative electrode is low during battery application, directly using the phosphorus negative electrode to assemble a full battery will produce a relatively large amount of irreversible lithium loss, which in turn leads to a low initial coulombic efficiency. The present invention can pre-lithiate the phosphorus negative electrode by introducing a lithium metal layer to compensate for the irreversible lithium loss, thereby further improving the initial coulombic efficiency when the full battery is assembled.

[0033] Furthermore, during the cycle of assembled full batteries, the phosphorus negative electrode undergoes significant volume changes during charge / discharge, which triggers the continuous generation of new interfaces and side reactions, leading to rapid decay of the battery's reversible capacity and shortening its cycle life. The present invention introduces a lithium metal layer as a supplemental capacity layer, allowing the lithium metal to preferentially release lithium ions from the composite negative electrode, avoiding deep de-lithiation / insertion of the phosphorus negative electrode, reducing volume expansion and interface changes, and further extending the cycle life of the full battery.

[0034] In some embodiments, the composite negative electrode includes a lithiated phosphorus negative electrode layer formed by reacting metallic lithium with a phosphorus-carbon composite material. The lithiated phosphorus negative electrode layer formed is as follows: Figure 2 As shown, phosphorus has a high theoretical specific capacity and a moderate lithiation potential, and can undergo an alloying reaction with lithium. When metallic lithium comes into contact with a phosphorus-carbon composite material, lithium atoms will be embedded in the structure of the phosphorus-carbon composite material to a certain extent, reacting with the phosphorus therein to form compounds such as lithiated phosphorus, forming chemical bonds between the phosphorus atoms and the lithium atoms, thus achieving a combination of the two. This combination of the two further compensates for the irreversible lithium loss and subsequently further improves the initial coulombic efficiency.

[0035] In some embodiments, the phosphorus negative electrode serves as the initial electrode, providing the main capacity contribution, and the introduced lithium metal layer serves as a supplementary capacity to improve the overall energy density of the composite negative electrode. At the same time, the initial phosphorus negative electrode can be pre-lithiated to improve the first coulombic efficiency of the battery.

[0036] Furthermore, the active material on the phosphorus negative electrode is a phosphorus-carbon composite material with a gram capacity of 800~1200mAh / g. A lithium metal layer is introduced with a gram capacity of 3860mAh / g. After the two are combined, the overall gram capacity of the resulting composite negative electrode is between the phosphorus-carbon composite material and lithium metal, thereby expanding the capacity range of the phosphorus negative electrode.

[0037] In some embodiments, the composite lithium metal layer on the initial electrode includes introducing the lithium metal layer by rolling, or introducing the lithium metal layer by melting, or introducing the lithium metal layer by electrodeposition. It can be understood that rolling and heating during the rolling process helps to put the metallic lithium into a molten state, and rolling promotes full contact between the lithium and the phosphorus-carbon composite material. Similarly, melting is conducive to promoting full contact between the two, achieving mutual infiltration between the two, and improving the bonding force between the lithium metal layer and the phosphorus negative electrode. The electrodeposition method uses electrochemical action to uniformly deposit lithium on the surface or pores of the phosphorus negative electrode, forming a nanoscale bonding interface, which helps to reduce the interface resistance and improve the bonding force between the two. Introducing the lithium metal layer in the above manner suppresses the volume expansion of the phosphorus negative electrode during the process of delithiation / lithiation, thereby extending the cycle life.

[0038] In some embodiments, introducing the lithium metal layer by rolling includes: superimposing a lithium metal foil on the surface of the initial electrode, and achieving the composite of the initial electrode and the lithium metal layer by mechanical rolling.

[0039] In some embodiments, introducing the lithium metal layer by melting includes: heating the lithium metal to melt the lithium metal under an inert atmosphere, and applying the molten lithium metal to the surface of the initial electrode.

[0040] In some embodiments, introducing the lithium metal layer by electrodeposition includes: depositing the lithium metal layer on the surface of the initial electrode by electrochemical deposition.

[0041] It should be noted that the above-mentioned rolling process is relatively simple and does not require additional equipment. It can be integrated into the existing electrode sheet rolling process, and the composite between the lithium foil and the phosphorus negative electrode can be achieved by adjusting the rolling temperature. The above-mentioned melting method is suitable for electrodes with complex structures or porous structures, such as carbon foam as a negative electrode loaded with phosphorus as a matrix, to achieve uniform dispersion of lithium supplement materials. Compared with the above two methods, the above-mentioned electrodeposition method is more precise and controllable, and can achieve uniform coverage of the lithium metal layer on the surface of the phosphorus negative electrode, avoiding the risk of dendrites caused by local lithium excess.

[0042] In some embodiments, the phosphorus in the phosphorus-carbon composite material includes at least one of red phosphorus, black phosphorus, and white phosphorus. The performance of red phosphorus is relatively stable and environmentally friendly; black phosphorus has a layered structure similar to graphite, has good conductivity and high theoretical capacity; white phosphorus has high activity, but due to its certain toxicity, it can be mixed with other phosphorus as needed, and is not particularly limited here. The carbon in the phosphorus-carbon composite material includes at least one of a carbon material with a layered structure and a carbon material with a porous structure. The carbon carrier with a layered structure, such as graphene, can provide a large surface area and excellent conductivity, which is conducive to the penetration of electrolyte and the rapid diffusion of lithium ions, thereby improving the charge and discharge efficiency and cycle life of the battery. The carbon material with a porous structure, such as activated carbon, has a high specific surface area and a rich pore structure, which is conducive to the full embedding of lithium atoms and promotes the interaction between lithium atoms and phosphorus.

[0043] In some embodiments, the phosphorus-carbon composite material is prepared by the following method, which includes: mixing phosphorus and carbon material in a mass ratio of 1:1 to obtain a mixed powder; and heating the mixed powder under an inert atmosphere to obtain the phosphorus-carbon composite material.

[0044] In some embodiments, the inert gas may be, for example, argon or nitrogen.

[0045] In some embodiments, the heating method can be first heating to 550~650℃, for example, 550℃, 600℃ or 650℃, and keeping warm for 2h; then cooling to 280~300℃, for example, 280℃, 285℃, 290℃, 295℃ or 300℃, and keeping warm for 12h, and then naturally cooling to room temperature.

[0046] In the phosphorus anode, the phosphorus and carbon content is 50% by weight, respectively. This helps optimize the conductivity and capacity of the phosphorus anode. This carbon content helps enhance the overall conductivity of the phosphorus anode, improving the battery's operating efficiency and power density. This phosphorus content helps maximize the energy density of the phosphorus anode while maintaining good conductivity, thereby increasing the battery's total capacity.

[0047] In some embodiments, the capacity of the phosphorus anode is AmAh, the initial Coulombic efficiency is ICE, and the capacity of the lithium metal is BmAh. The following conditions are satisfied: B ≥ A(1-ICE). It should be noted that when B = A × (1-ICE), the amount of lithium metal can meet the initial Coulombic efficiency loss of the phosphorus anode, achieving pre-lithiation of the phosphorus anode. Further increasing the amount of lithium metal on this basis can supplement lithium storage in the phosphorus anode.

[0048] In some embodiments, the lithium capacity embedded in the phosphorus negative electrode is 0.5 to 2.0 mAh / cm 2When the amount of embedded material is too small, it is difficult to achieve the effect of improving the capacity of the phosphorus negative electrode; when the amount of embedded material is too large, the capacity of the phosphorus negative electrode is covered.

[0049] Alternatively, the lithium embedded in the phosphorus negative electrode may have a capacity of, for example, 0.5 mAh / cm 2 、1mAh / cm 2 、1.5mAh / cm 2 , or 2mAh / cm 2 etc., or a range consisting of any two of the above values.

[0050] Preferably, the lithium capacity embedded in the phosphorus negative electrode is 1 mAh / cm 2 During the experiments related to the present invention, it was found that increasing the amount of lithium embedded in a certain range is helpful to improve the cycle life of the full battery. 2 , which can not only balance the capacity of phosphorus and lithium, but also effectively improve the battery cycle life.

[0051] According to another embodiment of the present invention, there is provided a composite negative electrode prepared by the above-mentioned preparation method.

[0052] According to the embodiment of the present invention, as mentioned above, by compounding a lithium metal layer on the phosphorus negative electrode, the capacity of the phosphorus negative electrode can be increased, the first coulombic efficiency can be improved, and the application range of the phosphorus negative electrode can be broadened.

[0053] In some embodiments, the overall areal capacity of the composite negative electrode is >3 mAh / cm 2 , where the surface capacity contribution of phosphorus negative electrode is > 2 mAh / cm 2 , the remaining capacity is provided by lithium metal.

[0054] According to another embodiment of the present invention, there is provided a lithium-ion battery including a negative electrode, wherein the negative electrode is the composite negative electrode.

[0055] According to an embodiment of the present invention, by introducing a lithium metal layer on the surface of the phosphorus negative electrode, the energy density and cycle stability of the composite negative electrode in full battery applications are improved, which has wide application in the subsequent construction of high energy density and high power density battery systems.

[0056] According to embodiments of the present invention, the initial coulombic efficiency of lithium-ion batteries is improved by pre-lithiation and lithium replenishment of the phosphorus negative electrode. Excess lithium metal can also be used as a supplemental capacity to increase the overall energy density of the composite negative electrode. This invention devises a strategy for pre-lithiation and lithium replenishment of the phosphorus negative electrode. By introducing a lithium metal layer on the phosphorus negative electrode surface, the energy density and cycling stability of the composite negative electrode in full-battery applications are improved.

[0057] The present invention proposes a lithium-ion battery with the aforementioned composite anode, whose main component is a phosphorus anode. By introducing lithium metal onto the phosphorus anode substrate and pre-lithiating / replenishing the phosphorus anode, the coulombic efficiency of the phosphorus anode and the overall cycling stability of the battery can be improved. The composite anode proposed in the present invention has wide applications in constructing high-energy-density and high-power-density battery systems.

[0058] The present invention will be further described below by way of examples, drawings, and related test experiments and results thereof. In the detailed description that follows, 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 apparent that one or more embodiments may be implemented without these specific details. Moreover, the details in the following embodiments may be arbitrarily combined into other feasible embodiments, unless conflicting.

[0059] It should be noted that the following specific examples are for illustration only and the scope of protection of the present invention is not limited thereto. The chemicals and raw materials used in the following examples were either commercially available or prepared in-house using recognized processing methods.

[0060] Example 1:

[0061] Preparation of phosphorus-carbon composite materials:

[0062] Red phosphorus and activated carbon powders were mixed uniformly in a 1:1 mass ratio and then transferred to a sealed, high-temperature, high-pressure reactor. The air inside the reactor was evacuated and replaced with argon, and the gas was evacuated again to reduce the internal pressure to less than 0.1 MPa. The reactor was heated to 600°C and maintained at this temperature for 2 hours. The temperature was then rapidly cooled to 285°C and maintained for 12 hours. The heat was then turned off and the mixture was allowed to cool naturally to room temperature. The reactor was opened in an argon glove box and the product, the phosphorus-carbon composite material powder, was collected.

[0063] Preparation of phosphorus negative electrode:

[0064] The prepared phosphorus-carbon composite powder was mixed with a conductive agent (Ketjen Black) and a binder (polyvinylidene fluoride) in a mass ratio of 90:5:5 and dispersed in N-methylpyrrolidone solvent to form a slurry. The mixed slurry was coated on a copper current collector and dried in a vacuum oven at 80°C for 10 hours to obtain an initial phosphorus negative electrode sheet. The electrode sheet was then cut into 12 mm diameter discs for later use (denoted as PC negative electrodes).

[0065] The prepared PC negative electrode was assembled into a CR2032 standard button cell (denoted as Li||PC) using lithium metal foil (300 μm thick, 14 mm diameter disc) as the counter electrode. 2The battery was subjected to two cycles of charge / discharge tests at a current density of 0.01-2.00 V. Figure 3 The charge / discharge curves of the first two cycles of the half-cell of Example 1 of the present invention are shown in FIG. Figure 3 As shown, the first discharge capacity of the PC negative electrode is 3.2 mAh / cm 2 , the first Coulombic efficiency was 76%.

[0066] The process of inserting lithium into the PC negative electrode and compounding the lithium metal layer:

[0067] The Li||PC half-cell that has completed two cycles of charge / discharge is discharged for the third time (lithium insertion reaction at the PC negative electrode) at 0.5 mA / cm 2 Discharged at a current density of 1 hour, 0.5 mAh / cm was embedded into the PC negative electrode. 2 The charge / discharge test was stopped, the button cell was disassembled in an argon glove box, and the pre-lithiation / lithiation-supplemented PC negative electrode was taken out for standby use (referred to as Li-PC negative electrode).

[0068] Assemble the Li-PC anode into a full battery:

[0069] The surface capacity is 3.0 mAh / cm 2 The lithium cobalt oxide (LCO) positive electrode is matched with the above-mentioned Li-PC negative electrode to assemble a full battery (LCO||Li-PC). 2 The charge / discharge test (1.50-4.20 V) was carried out at a current density of 1.50-4.20 V (equivalent to 0.5C).

[0070] Comparative Example 1:

[0071] The surface capacity is 3.0 mAh / cm 2 The lithium cobalt oxide (LCO) positive electrode was matched with the PC negative electrode prepared above to assemble into a full battery (LCO||PC). 2 A charge / discharge test (1.50-4.20 V) was conducted at a current density of 1.50 V (equivalent to 0.5 C) (except for the negative electrode, everything else was substantially the same as in Example 1).

[0072] Application examples:

[0073] The charge / discharge curves and cycle capacity retention of the first cycle of LCO||Li-PC and LCO||PC full batteries were recorded respectively. Figure 4 Shown are the charge / discharge curves of the first cycle of the full battery of Example 1 of the present invention and Comparative Example 1; Figure 5 The capacity retention diagram of the full battery of Example 1 of the present invention and Comparative Example 1 after 100 cycles is shown. Figure 4As shown in the figure, after the pre-lithiation / lithiation-supplemented Li-PC negative electrode of Example 1 is assembled into a full battery, the initial Coulombic efficiency reaches 94%, which is much higher than the full battery assembled with the PC negative electrode of Comparative Example 1 (only 75%). This shows that the initial Coulombic efficiency of Example 1 has reached the practical standard and is conducive to industrial promotion. After 100 cycles, as shown in the figure, Figure 5 As shown in Figure 1, the capacity retention rate of the LCO||Li-PC full cell of Example 1 is still 95%, while the capacity retention rate of the LCO||PC full cell of Comparative Example 1 has declined to 75%. These results show that the Li-PC anode prepared by pre-lithiation / lithiation of the PC anode can effectively improve the initial coulombic efficiency and battery cycle life of the full cell.

[0074] Example 2 to Example 4:

[0075] According to the method in Example 1, multiple groups of the same PC negative electrode were taken and the 2 The discharge experiments were carried out at a current density of 2 hours, 3 hours, and 4 hours respectively, and the lithium capacity embedded in the PC negative electrode corresponded to 1.0 mAh / cm 2 、1.5mAh / cm 2 , 2.0mAh / cm 2 , stop the charge / discharge test, disassemble the button battery in an argon glove box, and take out the Li-PC negative electrodes with different lithium insertion amounts for use.

[0076] The same assembly method as in Example 1 was used, and the surface capacity was 3.0 mAh / cm 2 The lithium cobalt oxide (LCO) positive electrode was matched with the aforementioned Li-PC negative electrodes with different lithium insertion amounts to assemble a full battery. 2 The battery was charged and discharged at a current density of 1.50-4.20 V (equivalent to 0.5 C), and the first coulombic efficiency and the 100th charge capacity of the full battery were recorded, as shown in Table 1 below.

[0077] Table 1

[0078]

[0079] The results show that compared with Example 1 and Comparative Example 1, the first coulombic efficiency is greatly improved due to the insertion of lithium. By comparing Examples 1 to 4, it can be seen that increasing the amount of lithium insertion has little effect on the first coulombic efficiency, but increasing the amount of lithium insertion within a certain range helps to improve the cycle life of the full battery. By comparing Examples 1 to 4, it can be seen that when the amount of lithium insertion is 1.0 mAh / cm 2 When the cycle capacity is around 1.0 mAh / cm, the effect of maintaining the cycle capacity is relatively better, exceeding 1.0 mAh / cm 2In the future, excessive lithium insertion will mask the capacity of the phosphorus negative electrode to a certain extent.

[0080] 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 are only specific embodiments of the present invention and are 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 method for preparing a composite negative electrode, comprising: preparing a phosphorus negative electrode as an initial electrode, wherein the phosphorus negative electrode comprises a phosphorus-carbon composite material as an active material; A lithium metal layer is compounded on the initial electrode to obtain a lithium metal-phosphorus composite negative electrode.

2. The preparation method according to claim 1, wherein The composite lithium metal layer on the initial pole piece includes: Introducing the lithium metal layer by roller pressing; or, Introducing the lithium metal layer by melting; or, The lithium metal layer was introduced by electrodeposition.

3. The preparation method according to claim 2, wherein The method of introducing the lithium metal layer by rolling comprises: Superimposing a lithium metal foil on the surface of the initial pole piece, and achieving the composite of the initial pole piece and the lithium metal layer by mechanical rolling; or, The method of introducing the lithium metal layer by melting comprises: In an inert atmosphere, heating to melt lithium metal, and applying the molten lithium metal to the surface of the initial electrode; or, The method of introducing the lithium metal layer by electrodeposition comprises: A lithium metal layer is deposited on the surface of the initial electrode by electrochemical deposition.

4. The preparation method according to claim 1, wherein The phosphorus in the phosphorus-carbon composite material includes at least one of red phosphorus, black phosphorus, and white phosphorus; The carbon in the phosphorus-carbon composite material includes at least one of a carbon material with a layered structure and a carbon material with a porous structure.

5. The preparation method according to claim 3, wherein The phosphorus-carbon composite material is prepared by the following method, which comprises: mixing phosphorus and carbon materials in a mass ratio of 1:1 to obtain a mixed powder; The mixed powder is heated under an inert atmosphere to obtain the phosphorus-carbon composite material.

6. The preparation method according to claim 1, wherein The composite negative electrode includes a lithiated phosphorus negative electrode layer formed by the reaction of metallic lithium and the phosphorus-carbon composite material.

7. The preparation method according to claim 6, wherein The capacity of the phosphorus negative electrode is AmAh, the first coulombic efficiency is ICE, and the capacity of the lithium metal is BmAh. The three satisfy: B≥A(1-ICE); or, The lithium capacity embedded in the phosphorus negative electrode is 0.5~2.0mAh / cm 2 .

8. A composite negative electrode prepared by the preparation method according to any one of claims 1 to 7.

9. The composite negative electrode according to claim 8, wherein The overall surface capacity of the composite negative electrode is greater than 3 mAh / cm 2 . 10 . A lithium ion battery comprising a negative electrode, wherein the negative electrode is the composite negative electrode according to claim 8 or 9 .

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