A pre-lithiation negative electrode and its preparation method and battery

Abstract

The present application relates to a pre-lithiation negative electrode, a preparation method thereof, and a battery, and belongs to the field of battery technology. The pre-lithiation negative electrode includes a negative electrode active material layer and a pre-lithiation layer arranged on the surface thereof, the pre-lithiation layer is a metal lithium composite material layer, comprising a lithium-containing core and a control cocoon that wraps the lithium-containing core, and the control cocoon comprises one-dimensional nanocarbon materials and boron nitride that are interwoven with each other. Boron nitride and one-dimensional nanocarbon materials are interwoven with each other to form a structure of alternating boron nitride hard units and one-dimensional nanocarbon material soft units, which are distributed on the entire surface of the negative electrode, while playing a pre-lithiation role through the lithium-containing core, and enhancing the interfacial mechanical properties of the negative electrode. The pre-lithiation negative electrode provided by the present invention can balance the distribution of lithium ions and electrons, control the lithium replenishment rate, and quickly conduct heat during the lithium replenishment process, and has excellent safety performance and cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a pre-lithiation negative electrode, a preparation method thereof, and a battery. Background Art

[0002] Lithium-ion batteries (LIBs) are currently the most widely used secondary batteries due to their long cycle life, high energy density, and lack of memory effect. Currently, graphite, silicon-carbon materials, and silicon-oxygen materials are commonly used as negative electrodes in LIBs. However, during the initial charge and discharge process, SEI formation on the negative electrode surface consumes a significant amount of lithium, resulting in a low initial coulombic efficiency (CE). This significantly reduces the actual specific energy of LIBs, severely restricting their large-scale commercial application. Therefore, improving CE has become a hot topic of research.

[0003] At present, the commonly used lithium replenishing agents for negative electrode lithium replenishment include lithium film and lithium powder. Among them, CN 112952036 A discloses a pre-lithiation negative electrode sheet and its manufacturing process as well as a lithium-ion battery. The pre-lithiation negative electrode sheet includes a negative electrode current collector; a first negative electrode film layer provided on the surface of the negative electrode current collector; and a second negative electrode film layer, wherein the second negative electrode film layer is provided on the surface of the first negative electrode film layer. Among them, the first negative electrode film layer contains lithium powder, and the second negative electrode film layer does not contain lithium powder. The pre-lithiation negative electrode in this invention can achieve pre-lithiation, but the first negative electrode film layer containing lithium powder is in close contact with the current collector. After the lithium powder takes effect, it forms a cavity in the negative electrode, causing the electronic path to be disconnected, which is not conducive to the improvement of the negative electrode performance; and the lithium replenishment rate is uncontrollable and will generate heat rapidly.

[0004] CN116504973A discloses a lithium-carbon material with a cocoon structure. The cocoon structure comprises a cocoon body formed of a structural carbon material and one or more metallic lithium particles contained within the cocoon body. Each metallic lithium particle consists of a metallic lithium core and an organic conductive layer coating the core surface. This material, used for pre-lithiation of the negative electrode surface, can improve the utilization rate of the metallic lithium core. However, the cocoon body, made of structural carbon material with good conductivity, easily deposits metallic lithium on its surface, generating and growing lithium dendrites and causing short circuits. Furthermore, the lithium replenishment rate is uncontrollable, resulting in rapid heat generation.

[0005] In actual applications, when lithium replenishment products such as lithium membranes are used to replenish lithium in large quantities using a roll-to-roll production method, a large amount of heat will be generated and accumulated due to the uncontrollable lithium replenishment rate. If improperly controlled, fire may occur in serious cases.

[0006] Therefore, developing a new type of pre-lithiation negative electrode that can achieve controllable lithium replenishment rate while regulating the deposition of metallic lithium into the negative electrode bulk, inhibiting the generation and growth of lithium dendrites on the surface of the pre-lithiation negative electrode, and improving the cycle life of the pre-lithiation negative electrode, which can be adapted to both liquid and solid-state battery systems, is the key to realizing the commercial application of batteries. Summary of the Invention

[0007] In order to solve the technical problem that when carbon materials are simply used as cocoons, metallic lithium is easily deposited on the surface of the pre-lithiation negative electrode, resulting in the generation and growth of lithium dendrites, and to achieve the technical effect of effectively inhibiting the growth of lithium dendrites and improving the electrochemical performance of the pre-lithiation negative electrode, the present invention provides a novel pre-lithiation negative electrode, a preparation method thereof, and a battery.

[0008] In a first aspect, the present invention provides a pre-lithiation negative electrode, which includes a current collector, a negative electrode active material layer arranged on at least one surface of the current collector, and a pre-lithiation layer arranged on the surface of the negative electrode active material layer and away from the current collector, wherein the pre-lithiation layer is a metal lithium composite material layer; the metal lithium composite material layer contains a lithium-containing core and a regulated cocoon wrapping the lithium-containing core, the regulated cocoon includes mutually interwoven one-dimensional nanocarbon material and boron nitride, and the boron nitride includes at least one of micro-nano boron nitride particles, boron nitride nanofibers, boron nitride nanotubes and boron nitride nanosheets.

[0009] In the present invention, the metal-lithium composite material layer comprises a lithium-containing core and a control cocoon encapsulating the lithium-containing core. The lithium-containing core can achieve a pre-lithiation effect. The control cocoon is formed by the interweaving of boron nitride and a one-dimensional nanocarbon material, having a structure of alternating boron nitride hard units and one-dimensional nanocarbon material soft units. The control cocoons are interconnected and distributed across the surface of the active material layer, forming a continuous skeleton structure of the metal-lithium composite material layer. This stabilizes the pre-lithiation layer structure and enhances the interfacial mechanical properties of the negative electrode. Boron nitride, which conducts ions but not electrons, can weaken the conductivity of the one-dimensional nanocarbon material, balance the distribution of lithium ions and electrons on the negative electrode surface, regulate the inward transmission of lithium ions and the inward deposition of metallic lithium, and control the rate of lithium replenishment. Combined with the good thermal conductivity of boron nitride, the heat generated during the lithium replenishment process is facilitated by rapid conduction, significantly improving the cycle performance and safety of the pre-lithiation negative electrode.

[0010] The pre-lithiation negative electrode of the present invention is different from the pre-lithiation of lithium films, lithium powders and lithium-carbon materials in CN116504973A in the prior art. The existing materials have good electronic conductivity, and it is difficult to control the lithium replenishment rate when replenishing lithium through short circuit. The lithium replenishment process will generate a lot of heat, and the metallic lithium is deposited on the surface of the negative electrode during the cycle, which is prone to short circuit. However, the pre-lithiation negative electrode of the present invention retains a three-dimensional continuous skeleton structure in the pre-lithiation layer after the pre-lithiation is completed, which plays the role of an artificial SEI layer and can be adapted to both liquid and solid-state battery systems, with strong applicability. After the pre-lithiation is completed, the lithium-containing core is consumed and holes appear. Through the joint regulation of boron nitride and one-dimensional nanocarbon materials, the lithium from the positive electrode can be deposited in the holes. At this time, the pre-lithiation layer also plays the role of accommodating the lithium from the positive electrode, which can be adapted to positive electrodes with higher surface density, which is conducive to the preparation of high-energy-density batteries.

[0011] Optionally, the thickness of the pre-lithium layer is 1-20 microns, for example, 1 micron, 1.5 microns, 2 microns, 3 microns, 5 microns, 7 microns, 10 microns, 15 microns, 18 microns or 20 microns, including but not limited to the listed point values. The thickness of the pre-lithium layer can be adjusted according to actual needs. In combination with actual conditions, the graphite negative electrode has a higher initial efficiency and can be adapted to a thinner lithium replenishment layer. After lithium replenishment, it is equivalent to an artificial SEI layer, which inhibits dendrites and improves safety, preferably 2-5 microns; the silicon-carbon negative electrode has a lower initial efficiency and requires a thicker lithium replenishment layer. After lithium replenishment, the lithium replenishment layer can inhibit dendrites and improve cycle performance, preferably 2-10 microns.

[0012] Optionally, the distribution form of the pre-lithium layer includes at least one of the following: entire surface, stripes or intermittent.

[0013] Optionally, the lithium-containing core includes metallic lithium and / or a lithium alloy, and the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, carbon, magnesium, indium, gallium, aluminum or zinc.

[0014] Optionally, the content of metallic lithium in the lithium alloy is greater than 50%, preferably 60-95%.

[0015] Optionally, the average particle size of the lithium-containing core is 1-100 μm, preferably 5-50 μm.

[0016] Optionally, the one-dimensional nanocarbon material includes at least one of nanocarbon fibers, single-walled carbon nanotubes, or multi-walled carbon nanotubes (including double-walled carbon nanotubes).

[0017] Optionally, the outer diameter of the one-dimensional nanocarbon material is ≤300 nm, preferably 1-20 nm, and more preferably 1-10 nm.

[0018] Optionally, the length of the one-dimensional nanocarbon material is 0.5 μm to 500 μm, preferably 1-100 μm, and more preferably 5-50 μm.

[0019] Optionally, the diameters of the boron nitride nanotubes and the boron nitride nanofibers are independently 1-500 nm, preferably 5-200 nm, and more preferably 10-100 nm.

[0020] Optionally, the lengths of the boron nitride nanotubes and the boron nitride nanofibers are independently 1-50 μm, preferably 5-20 μm.

[0021] Optionally, the aspect ratio of the boron nitride nanotubes and the boron nitride nanofibers is independently 5-50,000, preferably 100-3,000, and more preferably 500-2,000.

[0022] In the present invention, the term "independently" means that the parameters of the boron nitride nanotubes and boron nitride nanofibers do not affect each other and can be selected independently. For example, if the diameter of the boron nitride nanotubes is 500 nm, the diameter of the boron nitride nanofibers can be 500 nm, 200 nm, or 100 nm.

[0023] Optionally, the boron nitride nanosheets have a sheet diameter of 0.05-10 μm, preferably 0.5-5 μm.

[0024] Optionally, the number of layers of the boron nitride nanosheets is 1-10.

[0025] Optionally, the average particle size of the boron nitride particles is 100 nm-10 μm, preferably 500 nm-5 μm.

[0026] Optionally, the mass ratio of the one-dimensional nanocarbon material to boron nitride is 1:(0.1-100). The mass ratio can control the lithium replenishment rate while quickly conducting the heat generated during the lithium replenishment process, further improving safety, and is preferably 1:(0.5-50).

[0027] Optionally, the mass ratio of the cocoon to the lithium-containing core is 1:(0.1-100), which can accurately control the lithium replenishment rate, and is preferably 1:(0.5-50).

[0028] Optionally, the thickness of the metal lithium composite material layer is 1-100 microns, preferably 5-50 microns.

[0029] Optionally, the thickness of the cocoon body is regulated to be 0.1-5 μm, preferably 0.5-3 μm.

[0030] Optionally, the ratio between the average particle size of the lithium-containing core and the thickness of the cocoon is (1-20):1, preferably (5-10):1.

[0031] Optionally, the current collector of the negative electrode includes at least one of double-glazed copper foil, single-glazed copper foil, textured copper foil, porous copper foil, carbon-coated copper foil, polymer fiber conductive cloth, carbon cloth, carbon nanotube paper, nickel foil or stainless steel foil.

[0032] In a second aspect, the present invention further provides a method for preparing the pre-lithiation negative electrode described in the first aspect, the method comprising the following steps:

[0033] (1) mixing a one-dimensional nanocarbon material, boron nitride, a lithium-containing core, and an organic solvent to obtain a mixture;

[0034] (2) drying the mixture in step (1) by high-speed winding or spray drying to obtain a metal lithium composite material;

[0035] (3) forming the metal lithium composite material in step (2) by a wet or dry process to prepare a pre-lithium layer, and compounding it onto the surface of the negative electrode active material layer to obtain the negative electrode;

[0036] Alternatively, the metal lithium composite material is dispersed on the surface of the negative electrode active material layer, and then rolled to obtain the pre-lithiated negative electrode;

[0037] Wherein, the organic solvent in step (1) is inert to the lithium-containing core.

[0038] Optionally, the organic solvent in step (1) includes at least one of liquid alkanes having 5 to 20 carbon atoms, liquid cycloalkanes having 5 to 20 carbon atoms, benzene, toluene, xylene, solvent oil D20, solvent oil D40, solvent oil D60, solvent oil D80, silicone oil, light paraffin, N-methylpyrrolidone or N,N-dimethylformamide.

[0039] Optionally, in step (1), the one-dimensional nanocarbon material and the organic solvent are first mixed, and then boron nitride is added, mixed for a second time, and then the lithium-containing core is added and mixed; or, in step (1), the boron nitride and the organic solvent are first mixed, and then the one-dimensional nanocarbon material is added, mixed for a second time, and then the lithium-containing core is added and mixed.

[0040] Optionally, the mixing in step (1) adopts at least one of high-speed dispersion, high-pressure homogenization or high-pressure turbulence.

[0041] Optionally, the pressure of the high-pressure homogenization and high-pressure turbulence is independently 500-2000 bar, preferably 600-1500 bar.

[0042] Optionally, the rotation speed of the high-speed winding in step (2) is above 3000 rpm, preferably 5000-15000 rpm.

[0043] Optionally, the high-speed winding time is 5-90 min, preferably 10-60 min.

[0044] Optionally, the inlet air temperature of the spray drying in step (2) is 180-240°C, for example, it can be 180°C, 185°C, 190°C, 200°C, 210°C, 220°C, 230°C or 240°C, including but not limited to the above-mentioned values, preferably 200-220°C.

[0045] Optionally, the outlet air temperature of the spray drying is 80-120°C, for example, 80°C, 85°C, 90°C, 100°C, 110°C or 120°C, including but not limited to the above-mentioned values, preferably 100-110°C.

[0046] Optionally, the atomization pressure of spray drying is 0.1~0.5 MPa, for example, it can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa or 0.5 MPa, including but not limited to the above-mentioned values, preferably 0.2~0.4 MPa.

[0047] Optionally, the dry process in step (3) may be direct roll forming, a binder fiberization method, or an electrostatic spraying method; the wet process in step (3) may be a coating method, a screen printing method, or a spraying method. As long as the method can prepare the lithium metal composite material into a pre-lithium layer, it falls within the scope of protection of the present invention.

[0048] In a third aspect, the present invention further provides a battery comprising the pre-lithiation negative electrode as described in the first aspect.

[0049] The beneficial effects of the present invention are:

[0050] 1. The pre-lithiation layer of the present invention, compared to the lithium powder and cocoon-structured lithium-carbon materials used in the prior art, features structural stability and strong interfacial mechanical properties through the introduction of boron nitride and the interaction between boron nitride and one-dimensional nanocarbon materials, thus improving cycling performance.

[0051] 2. The pre-lithiated anode provided by the present invention utilizes the properties of boron nitride that it conducts ions rather than electrons to weaken the conductivity of the one-dimensional nanocarbon material, balance the distribution of lithium ions and electrons, and regulate the deposition of metallic lithium within the bulk phase, preventing metallic lithium from depositing on the anode surface. This facilitates the formation of a stable solid electrolyte membrane. The pre-lithiated anode exhibits both long cycle life and high rate performance.

[0052] 3. The pre-lithiation anode provided by the present invention achieves control over the lithium replenishment rate through the selection of boron nitride. Furthermore, boron nitride has excellent thermal conductivity, which facilitates the conduction of heat generated during the lithium replenishment process, thus resolving safety issues caused by heat accumulation.

[0053] 4. The pre-lithiation anode provided by the present invention converts the lithium-containing core into pores after pre-lithiation. Lithium from the positive electrode can be deposited in the pores through the regulation of the cocoon. In this case, the pre-lithiation layer also serves to accommodate lithium from the positive electrode, which can be adapted to a positive electrode with a higher surface density. After pre-lithiation, the pre-lithiation layer has a continuous three-dimensional porous skeleton, which acts as an artificial SEI layer, inhibiting dendrites and improving safety and cycle performance.

[0054] 5. The pre-lithiation anode provided by the present invention, through the rational design of the cocoon structure in the raw material lithium metal composite material, can simultaneously control the uniform distribution of lithium ions and electrons, facilitating the uniform and dense deposition of metallic lithium. By rationally designing parameters such as the ratio of the one-dimensional nanocarbon material and boron nitride, the pre-lithiation rate is controllable and heat conduction is rapid. The pre-lithiation anode has excellent cycling performance and safety performance, meeting the requirements of high-energy-density lithium batteries.

[0055] 6. The preparation method provided in this application has a simple process, a short flow, and is easy to industrialize and produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a partial cross-sectional SEM image of the pre-lithiation layer of the pre-lithiation negative electrode after the pre-lithiation is completed in Example 2;

[0057] Figure 2 This is a partial cross-sectional SEM image of the charged state of the pre-lithiation negative electrode after pre-lithiation is completed in Example 2. DETAILED DESCRIPTION

[0058] The technical solutions of the present invention will be described clearly and completely below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0059] Example 1

[0060] This embodiment provides a pre-lithiation negative electrode, which includes graphite and a pre-lithiation layer. The pre-lithiation layer includes a metal lithium composite material. The metal lithium composite material includes metal lithium powder with an average particle size of 5 μm and a regulated cocoon arranged on the surface of the metal lithium powder. The regulated cocoon includes interwoven double-walled carbon nanotubes and boron nitride particles.

[0061] The outer diameter of the double-walled carbon nanotubes is 4 nm and the length is 10 μm; the average particle size of the boron nitride particles is 1 μm; the mass ratio of the double-walled carbon nanotubes to boron nitride is 1:0.1; the mass ratio of the regulated cocoon to the metallic lithium powder is 1:0.1; the thickness of the regulated cocoon is 1 μm, and the ratio between the average particle size of the metallic lithium powder and the thickness of the regulated cocoon is 50:1.

[0062] The preparation method of the pre-lithiation negative electrode in this embodiment includes the following steps:

[0063] (1) 1 g of double-walled carbon nanotubes, 0.1 g of boron nitride particles, and n-hexane were mixed and dispersed at a high speed of 10,000 rpm for 60 min to obtain a mixture;

[0064] (2) adding 0.11 g of metallic lithium powder to the mixture of step (1), dispersing at high speed at a speed of 8000 rpm for 10 min, filtering, and vacuum drying at 80° C. to obtain a metallic lithium composite material;

[0065] (3) The metal lithium composite material in step (2) is formed by mechanical roller pressing at a pressure of 20 kg to form a pre-lithiation layer with a thickness of 5 microns. The pre-lithiation layer is then mechanically composited onto the surface of a graphite negative electrode with a graphite thickness of 100 microns to obtain a pre-lithiation negative electrode.

[0066] Example 2

[0067] This embodiment provides a pre-lithiation negative electrode, which includes silicon carbon (purchased from BYD, model BSO-2) and a pre-lithiation layer, and the pre-lithiation layer is a metal lithium composite material. The metal lithium composite material includes metal lithium powder with an average particle size of 20 microns and a regulated cocoon arranged on its surface, and the regulated cocoon includes interwoven single-walled carbon nanotubes and boron nitride nanotubes.

[0068] The outer diameter of the single-walled carbon nanotube is 2nm and the length is 50μm; the mass ratio of the single-walled carbon nanotube to the boron nitride nanotube is 1:100; the mass ratio of the regulated cocoon to the metallic lithium powder is 1:0.5; the thickness of the regulated cocoon is 5μm, and the ratio between the average particle size of the metallic lithium powder and the thickness of the regulated cocoon is 6:1.

[0069] The preparation method of the pre-lithiation negative electrode in this embodiment includes the following steps:

[0070] (1) 0.18 g of single-walled carbon nanotubes, 18 g of boron nitride nanotubes (outer diameter 500 nm, length 5 μm), 9.09 g of metallic lithium powder, and p-xylene were mixed and homogenized using a high-pressure homogenizer at a pressure of 1000 bar for 60 min to obtain a mixture;

[0071] (2) spray drying the mixture of step (1) at an inlet temperature of 220° C., an outlet temperature of 80° C., and an atomization pressure of 0.5 MPa to obtain a metal lithium composite material;

[0072] (3) The metal lithium composite material in step (2) is formed by mechanical rolling at a pressure of 20 kg to obtain a pre-lithiation layer with a thickness of 10 μm. The pre-lithiation layer is then mechanically composited to the surface of the silicon-carbon negative electrode to a thickness of 100 μm to obtain a pre-lithiation negative electrode.

[0073] Take the pre-lithiated negative electrode and NCM811 positive electrode in Example 2 to assemble a button-type full cell. After the pre-lithiation is completed, select a button-type full cell for dissection and take the negative electrode test cross-section SEM image. The local SEM image is as follows: Figure 1As shown in the figure, it can be clearly seen that after the pre-lithiation is completed, the metallic lithium powder is consumed, and many holes are formed in the pre-lithiation layer. The cocoons in the pre-lithiation layer are regulated to interweave and connect with each other to form a three-dimensional porous skeleton, which can be used as an artificial SEI layer.

[0074] The button-type full battery after pre-lithiation is subjected to cycle testing, the battery is disassembled in the charged state, and the cross-sectional SEM of the negative electrode is tested. The local SEM image is as follows Figure 2 As shown in the figure, it can be clearly seen that metallic lithium is deposited in the pores formed after pre-lithiation, which plays the role of accommodating the lithium from the positive electrode.

[0075] Example 3

[0076] Compared with Example 2, the only difference is that the mass of boron nitride is replaced by 0.09 g, the mass ratio of single-walled carbon nanotubes to boron nitride nanotubes is 1:0.5, and the other conditions remain unchanged.

[0077] Example 4

[0078] Compared with Example 2, the only difference is that the mass of boron nitride is replaced by 9 g, the mass ratio of single-walled carbon nanotubes to boron nitride nanotubes is 1:50, and the other conditions remain unchanged.

[0079] Example 5

[0080] Compared with Example 2, the only difference is that the mass of the metallic lithium powder is replaced with 18.2 g, the mass ratio of the cocoon body to the metallic lithium powder is adjusted to 1:0.1, and the other conditions remain unchanged.

[0081] Example 6

[0082] Compared with Example 2, the only difference is that the mass of the cocoon is replaced with 0.091 g, the mass ratio of the cocoon to the metallic lithium powder is 1:100, and the other conditions remain unchanged.

[0083] Example 7

[0084] Compared with Example 2, the only difference is that the boron nitride nanotubes are replaced with boron nitride particles (average particle size 50 nm).

[0085] Example 8

[0086] Compared with Example 2, the only difference is that the boron nitride nanotubes are replaced with boron nitride nanosheets (with a thickness of about 50 nm and a sheet diameter of about 2 microns).

[0087] Example 9

[0088] Compared with Example 2, the only difference is that the boron nitride nanotubes are replaced by boron nitride nanotubes and boron nitride nanosheets, the mass ratio of the boron nitride nanotubes to the boron nitride nanosheets is 1:1, and the other conditions remain unchanged.

[0089] Example 10

[0090] Compared with Example 2, the only difference is that the single-walled carbon nanotubes are replaced by single-walled carbon nanotubes and nanofibers (diameter 300 nm, length 5 microns), the mass ratio of the two is 1:1, and the other conditions remain unchanged.

[0091] Comparative Example 1

[0092] Compared with Example 2, the only difference is that the pre-lithiation layer of the pre-lithiation negative electrode includes metallic lithium powder and a cocoon disposed on its surface, the cocoon includes single-walled carbon nanotubes, and does not include boron nitride nanotubes. Other conditions remain unchanged.

[0093] Comparative Example 2

[0094] Compared with Example 2, the only difference is that the pre-lithiation layer of the pre-lithiation negative electrode includes metallic lithium powder and a cocoon disposed on its surface, the cocoon includes boron nitride nanotubes, and does not include single-walled carbon nanotubes. Other conditions remain unchanged.

[0095] Comparative Example 3

[0096] Compared with Example 2, the only difference is that the pre-lithiation layer of the pre-lithiation negative electrode includes metallic lithium powder, and other conditions remain unchanged.

[0097] Comparative Example 4

[0098] Compared with Example 2, the only difference is that the pre-lithiation layer of the pre-lithiation negative electrode includes a mechanical mixture of metallic lithium powder, boron nitride nanotubes and single-walled carbon nanotubes, and does not form the cocoon structure of the present invention.

[0099] Comparative Example 5

[0100] Compared with Example 2, the only difference is that the boron nitride nanotubes in the pre-lithiation layer of the pre-lithiation negative electrode are replaced with graphene sheets of conductive material.

[0101] Comparative Example 6

[0102] Compared with Example 2, the pre-lithium layer in this comparative example is a metallic lithium strip, and the other conditions are the same as those in Example 2.

[0103] Performance testing:

[0104] The negative electrodes from Examples 1-10 and Comparative Examples 1-6 were assembled with NCM811 positive electrodes to test cycling performance. The capacity retention after 900 cycles at 1.5C / 3C is shown in Table 1. Furthermore, the pre-lithiation negative electrode was prepared in a dry room with a dew point of -60°C and a temperature of 20°C. During the preparation process, the negative electrode surface temperature was monitored with an infrared thermometer. The temperature change data is detailed in Table 1. Temperature difference = pre-lithiation negative electrode surface temperature - negative electrode surface temperature before pre-lithiation.

[0105] Table 1

[0106]

[0107] From Table 1 we can see that:

[0108] (1) Comparing Example 2 with Examples 3-4, it can be seen that the capacity retention rate of the pre-lithiated negative electrode in Example 3-4 is higher than that in Example 2. This is because the mass ratio of single-walled carbon nanotubes to boron nitride nanotubes in Example 4 is within the preferred range of the present invention, the structural stability of the pre-lithiated layer is better than that in Example 2, and the effect of regulating the inward deposition of lithium from the positive electrode is better than that in Example 2;

[0109] (2) Comparing Example 2 with Examples 5-6, it can be seen that the capacity retention rate of the pre-lithiated negative electrode in Example 2 is slightly higher than that in Examples 5-6. This is because the mass of the cocoon and the metallic lithium powder is appropriately regulated in Example 2. Within the preferred range of the present invention, the regulation and accommodation effect of the lithium from the positive electrode during pre-lithiation is better than that in Examples 5-6.

[0110] (3) Comparing Example 2 with Examples 7-9, it can be seen that the capacity retention rate of the pre-lithiation negative electrode in Example 2 is higher than that in Examples 7-8. This is because the boron nitride particles in Example 7 are in point contact with the single-walled carbon nanotubes in the control cocoon, and the effect of weakening the conductivity of the single-walled carbon nanotubes is point weakening. In Example 8, the boron nitride nanosheets are in surface contact with the single-walled carbon nanotubes in the control cocoon, and the effect of weakening the conductivity of the single-walled carbon nanotubes is surface weakening. The structure and the conductivity weakening effect of the single-walled carbon nanotubes are not as good as those of the boron nitride nanosheets in Example 2. Although boron nitride nanotubes are linear, their positions in the cocoon are controlled to be different, which can simultaneously achieve the effects of line contact (parallel contact with the single-walled carbon nanotubes) and point contact (vertical contact with the single-walled carbon nanotubes); the capacity retention rate of the pre-lithiation negative electrode in Example 9 is higher than that in Example 2. This is because the boron nitride nanosheets and boron nitride nanotubes in Example 9 have different shapes, which can form point, line and surface contact effects with the single-walled carbon nanotubes. The multiple contact effects cooperate with each other to jointly weaken the conductivity of the single-walled carbon nanotubes, which has a better effect;

[0111] (4) By comparing Example 2 with Comparative Examples 1-6, it can be seen that the capacity retention rate of the pre-lithiated negative electrode in Example 2 is higher than that in Comparative Examples 1-6. This is because the negative electrode structure and cocoon composition of Comparative Examples 1-6 are different from those of the pre-lithiated negative electrode in the present invention.

[0112] As can be seen from Table 1, the temperature difference change of the pre-lithiation negative electrode of the present invention is significantly smaller than that of Comparative Examples 1-6. Therefore, it can be seen that the pre-lithiation and pre-lithiation rate of the present invention is controllable, does not release heat rapidly, and can conduct heat in time, and the surface temperature of the negative electrode remains basically unchanged.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A pre-lithiation negative electrode, characterized in that The pre-lithiation negative electrode comprises a current collector, a negative electrode active material layer disposed on at least one surface of the current collector, and a pre-lithiation layer disposed on the surface of the negative electrode active material layer and away from the current collector, wherein the pre-lithiation layer is a metal lithium composite material layer; The metal lithium composite material layer comprises a lithium-containing core and a regulated cocoon that wraps the lithium-containing core. The regulated cocoon comprises one-dimensional nanocarbon materials and boron nitride that are interwoven with each other. The boron nitride comprises at least one of micro-nano boron nitride particles, boron nitride nanofibers, boron nitride nanotubes, and boron nitride nanosheets.

2. The negative electrode according to claim 1, characterized in that The thickness of the pre-lithium layer is 1-20 microns; The distribution form of the pre-lithium layer includes at least one of the following: entire surface, stripes or intermittent.

3. The negative electrode according to claim 1, characterized in that The average particle size of the lithium-containing core is 1-100 μm, and the lithium-containing core includes metallic lithium and / or a lithium alloy, and the alloying elements in the lithium alloy include at least one of tin, gold, barium, bismuth, calcium, germanium, platinum, lead, antimony, silver, boron, carbon, magnesium, indium, gallium, aluminum or zinc; wherein the content of metallic lithium in the lithium alloy is greater than 50%.

4. The negative electrode according to claim 1, characterized in that The one-dimensional nanocarbon material satisfies at least one of the following conditions: The one-dimensional nanocarbon material comprises at least one of nanocarbon fibers, single-walled carbon nanotubes or multi-walled carbon nanotubes; The outer diameter of the one-dimensional nanocarbon material is ≤300nm; The length of the one-dimensional nanocarbon material is 0.5 μm-500 μm.

5. The negative electrode according to any one of claims 1 to 4, characterized in that The micro-nano boron nitride particles, boron nitride nanofibers, boron nitride nanotubes and boron nitride nanosheets meet at least one of the following conditions: The diameters of the boron nitride nanotubes and the boron nitride nanofibers are independently 1-500 nm; The lengths of the boron nitride nanotubes and the boron nitride nanofibers are independently 1-50 μm; The aspect ratios of the boron nitride nanotubes and the boron nitride nanofibers are independently 5-50000; The boron nitride nanosheets have a sheet diameter of 0.05-10 μm; The number of layers of the boron nitride nanosheets is 1-10; The average particle size of the boron nitride particles is 100 nm-10 μm.

6. The negative electrode according to claim 1, characterized in that The mass ratio of the one-dimensional nanocarbon material to the boron nitride is 1:(0.1-100); the mass ratio of the regulating cocoon to the lithium-containing core is 1:(0.1-100).

7. The negative electrode according to claim 1, characterized in that The current collector includes at least one of double-glazed copper foil, single-glazed copper foil, textured copper foil, porous copper foil, carbon-coated copper foil, polymer fiber conductive cloth, carbon cloth, carbon nanotube paper, nickel foil and stainless steel foil.

8. The negative electrode according to any one of claims 1 to 7, characterized in that The negative electrode active material layer includes at least one of graphite, silicon carbon, silicon oxygen, tin-based materials and lithium titanate.

9. A method for preparing the negative electrode according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: (1) mixing a one-dimensional nanocarbon material, boron nitride, a lithium-containing core, and an organic solvent to obtain a mixture; (2) drying the mixture in step (1) by high-speed winding or spray drying to obtain a metal lithium composite material; (3) forming the metal lithium composite material in step (2) by a wet or dry process to prepare a pre-lithium layer, and compounding it onto the surface of the negative electrode active material layer to obtain the negative electrode; Alternatively, the metal lithium composite material is dispersed on the surface of the negative electrode active material layer, and then rolled to obtain the pre-lithiated negative electrode; Wherein, the organic solvent in step (1) is inert to the lithium-containing core.

10. A battery, characterized in that: The battery comprises the negative electrode according to any one of claims 1 to 8.

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