CN117855384B

CN117855384B - Negative electrode, preparation method thereof, secondary battery, electric equipment and energy storage system

Info

Publication number: CN117855384B
Application number: CN202410211911.2A
Authority: CN
Inventors: 禹智昊; 王冰冰; 路雪慧; 吴晓东
Original assignee: Honor Device Co Ltd; Tianmu Lake Institute of Advanced Energy Storage Technologies Co Ltd
Current assignee: Honor Device Co Ltd; Tianmu Lake Institute of Advanced Energy Storage Technologies Co Ltd
Priority date: 2024-02-27
Filing date: 2024-02-27
Publication date: 2024-07-09
Anticipated expiration: 2044-02-27
Also published as: CN117855384A

Abstract

The application provides a negative electrode, a preparation method thereof, a secondary battery, electric equipment and an energy storage system. The electrode comprises a negative electrode material layer and a solid electrolyte interface film, wherein the solid electrolyte interface film is at least arranged on the surface of the negative electrode material layer; wherein the solid electrolyte interface film comprises an organic phase and a plurality of inorganic crystal regions dispersed in the organic phase, and the maximum cross-sectional dimension a of each inorganic crystal region is less than or equal to 10nm. The solid electrolyte interface film on the surface of the negative electrode has higher structural stability, is not easy to crack in the charge-discharge cycle process, is beneficial to reducing electrolyte loss, and can improve the long cycle performance of the battery.

Description

Negative electrode, preparation method thereof, secondary battery, electric equipment and energy storage system

Technical Field

The application relates to the technical field of batteries, in particular to a negative electrode, a preparation method of the negative electrode, a secondary battery, electric equipment and an energy storage system.

Background

In the formation process of the lithium secondary battery, a solid electrolyte interface (solid electrolyte interface, SEI) film is generated on the surface of the negative electrode, and the SEI film generated in the formation process is generally of a multi-layer structure, loose in structure and poor in stability. In the related art, it is reported that an artificial SEI film is directly formed on the surface of a negative electrode by a liquid phase chemical method. However, the existing artificial SEI film mainly comprises organic components, a small amount of inorganic phases exist, the crystal area size of the inorganic phases is larger (generally tens of nanometers or more), stress concentration exists in the SEI film, local stress between inorganic crystal areas is larger, and the SEI film is easy to break along the crystal area in the process of charge-discharge cycle of a battery, so that the negative electrode surface is directly exposed in electrolyte to cause side reaction, continuous consumption of the electrolyte and reduction of battery capacity are caused, and the application of a lithium secondary battery is seriously affected.

Disclosure of Invention

In view of the above, the embodiment of the application provides a negative electrode, a preparation method thereof, a secondary battery, electric equipment and an energy storage system. The solid electrolyte interface film on the surface of the negative electrode has higher structural stability, is not easy to crack in the charge-discharge cycle process, is beneficial to reducing electrolyte loss, and can improve the long cycle performance of the battery.

The first aspect of the embodiment of the application provides a negative electrode, which comprises a negative electrode material layer and a solid electrolyte interface film, wherein the solid electrolyte interface film is at least arranged on the surface of the negative electrode material layer; wherein the solid electrolyte interface film comprises an organic phase and a plurality of inorganic crystal regions dispersed in the organic phase, and the maximum cross-sectional dimension a of each inorganic crystal region is less than or equal to 10nm.

In the solid electrolyte interface film, the organic phase can provide better toughness, the inorganic crystal region can provide higher strength, so that when the anode material layer deforms in the battery charging and discharging cycle process, the organic phase region deforms along with the expansion of the anode material layer, the size of the inorganic crystal region is small, the stress between the inorganic crystal regions is weak, the risk of cracking of the solid electrolyte interface film along the boundary of the crystal region can be reduced, and the inorganic crystal region can provide a transmission channel of active ions. Therefore, the solid electrolyte interface film has higher strength, better toughness and stable structure, is not easy to crack in the charge-discharge cycle process, can effectively improve the capacity of the battery in the long cycle process, and is beneficial to popularization and application of the lithium secondary battery.

In some embodiments of the application, the solid electrolyte interfacial film comprises a material of the organic phase and a material of the inorganic crystalline region within any volume of 2a _maxnm×2a_maxnm×2a_max nm; wherein a _max=Max{a_n},{a_n is a set of maximum cross-sectional dimensions of a plurality of the inorganic crystalline regions in the solid electrolyte interface film, n >1. Thus, the solid electrolyte interface film has high uniformity, can optimize the performance of the solid electrolyte interface film, and can improve the stability of the solid electrolyte interface film and optimize the ion conductivity.

In some embodiments of the application, the inorganic crystalline region has a maximum cross-sectional dimension of 1nm to 3nm. Thus, more organic-inorganic interfaces can be constructed in the solid electrolyte interface film, which is more beneficial to the exertion of the synergistic effect of the organic phase and the inorganic crystal area; meanwhile, the structural stability of the solid electrolyte interface film can be improved, so that the solid electrolyte interface film can be more suitable for the volume change of the anode material layer in the charge-discharge cycle process.

In some embodiments of the application, the solid electrolyte interfacial film comprises a material of the organic phase and a material of the inorganic crystalline region within any 2nm x 2nm area. Thus, the solid electrolyte interface film has a higher uniformity, which can exhibit superior structural stability and strength during charge and discharge cycles.

In some embodiments of the application, the material of the organic phase comprises at least one of R ₁-O-Li、R₂R₃-C=N^-Li⁺、R₄-NH^-Li⁺ and R ₄-NH₂ or a polymer thereof; wherein R ₁、R₄ is independently selected from C2-C8 alkenyl, R ₂、R₃ is independently selected from at least one of C2-C8 alkenyl and/or hydrogen atom, and R ₂、R₃ is not hydrogen at the same time; the polymerization degree of the polymer is more than or equal to 50. Thus, the solid electrolyte interface film is easy to prepare and has better toughness; meanwhile, the materials of the organic phase are matched with a battery system, so that side reactions are not caused.

In some embodiments of the application, the material of the inorganic crystalline region comprises at least one of LiF, li ₂ O, and Li ₃ N. The material has higher ion conductivity, and the formed crystal area has higher strength.

In some embodiments of the present application, the solid electrolyte interfacial film has a total volume of the inorganic crystalline region of 20% to 80%, and a total volume of the organic phase of 20% to 80%. Thus, the solid electrolyte interface film has sufficient substances to provide strength support and active ion channels, and appropriate substances to provide toughness, and the solid electrolyte interface film has better comprehensive performance.

In some embodiments of the application, the spacing between two adjacent inorganic crystal regions is less than or equal to 20nm. Thus, the SEI film with higher strength and stronger toughness can be obtained, and the stress concentration is less likely to occur in the SEI film, so that the SEI film has better stability in the long-cycle process.

In some embodiments of the application, chemical bonds are formed between at least a portion of the material of the inorganic crystalline region and the material of the organic phase. The chemical bonding can promote the interfacial binding force between the material of the inorganic crystal region and the material of the organic phase, thereby being beneficial to guaranteeing the structural stability of the solid electrolyte interfacial film.

In some embodiments of the present application, the solid electrolyte interface film has no holes penetrating in the thickness direction thereof; or the solid electrolyte interface film has holes penetrating along the thickness direction, and the pore diameter of the holes is less than or equal to 1nm. Thus, the condition that the electrolyte is contacted with and reacts with the negative electrode active material in the negative electrode material through the holes can be avoided as much as possible, and irreversible loss of the electrolyte and the active material in the formation process can be avoided.

In some embodiments of the present application, the number of holes penetrating in the thickness direction of the solid electrolyte interface film is 10 or less within any 10nm×10nm volume of the solid electrolyte interface film. Thus, high density of the solid electrolyte interface film can be ensured.

In some embodiments of the present application, the negative electrode material layer is a lithium metal layer, and the solid electrolyte interface film is disposed on one side surface of the negative electrode material layer and on a side surface of the negative electrode material layer; or the negative electrode material layer comprises a granular negative electrode active material, and the solid electrolyte interface film is coated on the surface of the negative electrode active material.

In some embodiments of the application, the negative electrode further comprises a current collector; the current collector is arranged on one side surface of the negative electrode material layer, which is away from the solid electrolyte interface film.

In some embodiments of the application, the solid electrolyte interfacial film has a thickness of 20nm to 300nm. Thus, firstly, the active ion transmission is facilitated, and secondly, the preparation is easy.

In some embodiments of the application, the Young's modulus of the solid electrolyte interface film is greater than or equal to 4.1GPa.

The second aspect of the embodiment of the present application provides a method for preparing a negative electrode, which can be used for preparing the negative electrode provided in the first aspect of the embodiment of the present application, including:

Setting liquid raw materials for forming the organic phase and the inorganic crystal area on the surface of a cathode material layer precursor to form the cathode material layer and the solid electrolyte interface film, so as to obtain the cathode; wherein the anode material layer precursor contains a simple substance of lithium.

The preparation method is simple to operate, high in flexibility, high in process reliability and high in production efficiency, and is suitable for large-scale industrial production. In addition, the preparation method is to generate a solid electrolyte interface film on the surface of the negative electrode material layer in situ, and the solid electrolyte interface film is matched with the surface morphology of the negative electrode material layer. When the anode material layer includes a granular anode active material, the liquid raw material may permeate the anode material layer, so that the formed solid electrolyte interface film may be coated on the surface of the granular anode active material.

In some embodiments of the application, the liquid feedstock comprises a first feedstock and a second feedstock;

The first raw material comprises an organic matter containing an oxidation group and a carbon-carbon double bond, wherein the organic matter comprises at least one of R ₁-O-O-R₁'、R₂R₃-C=N-R₃'、R₄ -N=O and R ₅-NO₂, R ₁、R₁ 'is independently selected from alkenyl groups of C2-C8 and/or hydrogen atoms, and R ₁、R₁' is not hydrogen at the same time; r ₂、R₃、R₃ 'is independently selected from at least one of C2-C8 alkenyl and/or hydrogen atom, and R ₂、R₃、R₃' is not hydrogen at the same time; r ₄、R₅ is independently selected from C2-C8 alkenyl;

The second raw material comprises a substance containing active elements, wherein the active elements comprise at least one of fluorine element, nitrogen element and oxygen element; the active element-containing substance includes at least one of a fluorine element source, an oxygen element source, and a nitrogen element source; the fluorine element source comprises at least one of fluorinated alkane, fluorinated alkene, fluorinated carbonate, fluorinated ether and fluorine-containing inorganic substance; the oxygen element source comprises at least one of a carbonate, an ether, and an oxygen-containing additive; the nitrogen element source includes at least one of an imide salt, a metal nitride, and a nitrate. The first raw material and the second raw material can be decomposed in a competition way under the action of a lithium simple substance, and an oxidation group in the first raw material is reduced to form an organic phase; the second raw material is decomposed to form inorganic phases with lithium ions formed by a lithium simple substance or lithium ions from other sources in the system, and the inorganic phases are crystallized to form an inorganic crystal area. The competition decomposition of the first raw material and the second raw material avoids the condition that the inorganic reaction is faster than the organic reaction in the related art, so that the solid electrolyte interface film has a multi-layer structure, and a special single-layer structure with mixed and distributed organic phase and inorganic crystal areas can be formed.

In some embodiments of the application, the molar ratio of the carbon-carbon double bond to the oxidizing group in the first feedstock is 1: (0.33-3). Thus, it is advantageous to control the polymerization degree of the polymer in the organic phase within a proper range, thereby optimizing the performance of the solid electrolyte interface film.

In some embodiments of the application, the molar ratio of the oxidizing groups to the active elements is (0.2-5): 1. thus, the uniformity of the solid electrolyte interface film is improved, and the area ratio of the organic phase to the inorganic crystal area in the final solid electrolyte interface film can be controlled within a proper range.

In some embodiments of the application, the second feedstock is a lithium-containing solution in which at least one of the fluorine element source, the oxygen element source, and the nitrogen element source is dissolved. As such, lithium ions in the lithium-containing solvent may provide a source of lithium for the material of the inorganic crystalline region.

In some embodiments of the application, the liquid feedstock further comprises a free radical initiator. The radical initiator may initiate polymerization between monomers having carbon-carbon unsaturation in the organic phase.

In some embodiments of the present application, the method further comprises performing a heat treatment after disposing the liquid raw material on the surface of the anode material layer precursor; the temperature of the heating treatment is 70-110 ℃. Therefore, the monomer with carbon-carbon double bond in the organic phase can be subjected to polymerization reaction, so that the toughness and mechanical strength of the organic phase are improved, and the structural stability of the SEI film is further improved.

A third aspect of the embodiment of the present application provides a secondary battery, including a positive electrode, a negative electrode provided by the embodiment of the present application, and an electrolyte between the positive electrode and the negative electrode. With the negative electrode provided by the embodiment of the application, the secondary battery can realize excellent long-cycle performance, such as higher cycle capacity retention rate.

A fourth aspect of the embodiment of the present application provides an electric device, including a secondary battery provided by the embodiment of the present application. The secondary battery provided by the embodiment of the application is adopted, so that the electric equipment has a good market prospect.

A fifth aspect of the embodiment of the present application provides an energy storage system, including the secondary battery provided by the embodiment of the present application. Due to the adoption of the secondary battery provided by the embodiment of the application, the energy storage system can realize excellent long-cycle performance.

Drawings

Fig. 1 is a schematic view of a cross-section of a negative electrode according to an embodiment of the present application;

Fig. 2 is a schematic view of a partial region in a negative electrode according to another embodiment of the present application;

FIG. 3 is a transmission electron microscope (Transmission Electron Microscope, TEM) photograph of a solid electrolyte interface film of the negative electrode surface provided in example 1 of the present application;

FIG. 4 is a TEM photograph of the solid electrolyte interface film produced in comparative example 1.

Detailed Description

Lithium secondary batteries are widely used because of their high energy density and long service life. For lithium secondary batteries using a liquid electrolyte, an SEI film is generated on the surface of the negative electrode of the battery, particularly for a high-activity negative electrode active material (e.g., lithium metal), which reacts with an electrolyte and rapidly generates an SEI film on the surface of the negative electrode during formation of the battery, at this time, not only irreversible loss of active lithium and electrolyte is caused, but also the SEI film generated by electrochemical reaction is often in a loose and porous unstable structure due to the influence of uneven current distribution and decomposition of organic components (e.g., decomposition of an ester solvent) in the electrolyte due to an excessively fast reaction rate. At this time, when the volume of the negative electrode active material changes (expands), the loose and unstable structure is easily broken, so that the negative electrode active material is directly exposed in the electrolyte, and the exposed negative electrode active material reacts with the electrolyte to generate a new SEI film, which causes continuous consumption of the electrolyte and consumption of more irreversible active materials, and in the long-cycle process, the thickness of the SEI film is continuously increased, the capacity is reduced, and the performance of the lithium secondary battery is seriously affected. In order to solve the above problems, the industry has attempted to construct an artificial SEI film on the surface of a negative electrode, but the conventional artificial SEI film mainly comprises an organic phase, and even if an inorganic phase is inserted, the size of a crystal region formed by the inorganic phase is large, and when the negative electrode expands, the stress between the crystal regions is large, and the SEI film is liable to break along the inter-crystal region, so that the improvement effect is limited.

To solve the above-mentioned technical problems, referring to fig. 1, an embodiment of the present application provides a negative electrode 1, which includes a negative electrode material layer 10 and a solid electrolyte interface (solid electrolyte interface, SEI) film 20, wherein the SEI film 20 is at least disposed on a surface of the negative electrode material layer 10; the SEI film 20 includes an organic phase 21 and a plurality of inorganic crystal regions 22 dispersed in the organic phase 21, and a maximum cross-sectional dimension a of each inorganic crystal region 22 is 10nm or less. Wherein, one black dot in the SEI film 20 in fig. 1 represents one inorganic crystalline region 22, and a gray region represents the organic phase 21. It should be noted that, fig. 1 is only an exemplary drawing, and the thickness of the negative electrode material layer 10 and the thickness of the SEI film 20 in fig. 1, the arrangement, size and concentration of the inorganic crystal regions 22 and the size of the organic phase 21 are all exemplary, and do not limit the embodiments of the present application. The side of the anode material layer 10 may also have an SEI film 20.

In the above SEI film 20, the organic phase 21 may provide superior toughness, the inorganic crystalline region 22 may provide higher strength, so that when the anode material layer 10 is deformed during charge and discharge cycles of the battery, the organic phase 21 region deforms along with expansion of the anode material layer 10, and the inorganic crystalline region 22 has a small size, there is almost no stress concentration point between the inorganic crystalline regions 22, or weak stress concentration hardly causes cracking of the SEI film 20 along the boundaries of the crystalline regions, and the inorganic crystalline regions 22 may provide a transmission channel of active ions. Therefore, the SEI film 20 has high strength, excellent toughness and stable structure, is not easy to crack in the charge-discharge cycle process, can effectively improve the capacity of the battery in the long cycle process, and is beneficial to popularization and application of the lithium secondary battery.

In an embodiment of the present application, the maximum cross-sectional dimension of the inorganic crystalline region 22 may be determined using a transmission electron microscope (Transmission Electron Microscope, TEM). Specifically, the SEI film 20 is pretreated, for example, an ion thinning technique is adopted to process the SEI film 20 to obtain a sample to be tested, and the cross-sectional dimension of the inorganic crystal region 22 is observed under TEM. Under TEM, the inorganic crystalline region 22 sees a clear lattice morphology (e.g., the striped texture in fig. 3), while the organic phase 21 has no apparent or lattice morphology (e.g., the black circled regions in fig. 3). Specifically, the maximum cross-sectional dimension a of the inorganic crystalline region 22 may be, but is not limited to, 0.5nm, 0.8nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc. If the maximum cross-sectional dimension of the inorganic crystal regions 22 is too large (> 10 nm), a large stress exists between the inorganic crystal regions 22, and the SEI film 20 is easily broken along stress points between the crystal regions during charge and discharge cycles, so that the performance of the battery is affected.

In the embodiment of the present application, the organic phase 21 may be amorphous or have a certain regularity. The application is not limited in this regard. In the embodiment of the present application, the single inorganic crystal region 22 may be a single crystal or an aggregate of a plurality of crystal grains, which is not limited in the embodiment of the present application and has no significant effect on the properties of the SEI film 20.

In some embodiments of the present application, the volume of any 2a _maxnm×2a_maxnm×2a_max of the SEI film 20 includes the material of the organic phase 21 and the material of the inorganic crystalline region 22; where a _max=Max{a_n},{a_n is a set of maximum cross-sectional dimensions a, n >1, of the plurality of inorganic crystalline regions 22 in the solid electrolyte interface film 20, it being understood that n is a positive integer. Thus, the SEI film 20 within the volume of any one of the above 2a _maxnm×2a_maxnm×2a_max has both a material providing toughness and a material providing strength, and can provide a transmission channel of lithium ions, and the SEI film 20 has a high uniformity degree, so that the ionic conductivity of the SEI film 20 can be optimized while improving the structural stability thereof. The SEI film 20 according to the embodiment of the present application must satisfy a _max.ltoreq.10 nm, so that in some embodiments, the SEI film 20 includes the material of the organic phase 21 and the material of the inorganic crystal region 22 within any volume of 20 nm. In some embodiments, the material of the organic phase 21 and the material of the inorganic crystal region 22 are included in any 2a _maxnm×2a_maxnm×2a_max nm volume of the SEI film 20. Further, the volume of any 20nm ×20×20nm ×20nm of the SEI film 20 includes the material of the organic phase 21 and the material of the inorganic crystal region 22. Specifically, three-dimensional imaging can be performed using time-of-flight secondary ion mass spectrometry (Time of Flight Secondary Ion Mass Spectrometry, TOF-SIMS) to measure the material of the organic phase 21 and the composition of the inorganic crystalline region 22 in any of the above-identified regions.

In the embodiment of the present application, the inorganic crystalline region 22 is dispersed in the organic phase 21. In other words, any two adjacent inorganic crystalline regions 22 are filled with the organic phase 21. In some embodiments of the present application, the inorganic crystalline region 22 has a maximum cross-sectional dimension of 1nm to 3nm. Thus, more organic-inorganic interfaces can be constructed in the SEI film 20, which is more beneficial to the exertion of the synergistic effect of the organic phase 21 and the inorganic crystal region 22; meanwhile, the risk that stress concentration points are formed between the inorganic crystal regions 22 or at the edges of the inorganic crystal regions 22 can be reduced, so that the risk that cracks are generated in the inorganic crystal regions 22 or even the cracks occur is smaller, the structural stability of the SEI film 20 is better, and the SEI film 20 can be more suitable for the volume change of the cathode material layer 10 in the charge-discharge cycle process. Specifically, the maximum cross-sectional dimension of the inorganic crystalline region 22 may be, but is not limited to, 1nm, 1.2nm, 1.5nm, 1.8nm, 2nmn, 2.2nm, 2.5nm, 2.8nm, 3nm.

In some embodiments of the present application, the spacing between two adjacent inorganic crystalline regions 22 is less than or equal to 20nm. That is, the maximum cross-sectional dimension of each organic phase 21 region is 20nm or less. Thus, the SEI film 20 with higher strength and stronger toughness can be obtained, and the stress concentration is less likely to occur in the SEI film 20, so that the SEI film 20 has better stability in a long-cycle process. Specifically, the maximum cross-sectional dimension of each organic phase 21 region may be, but is not limited to, 2nm, 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm.

In some embodiments of the present application, the SEI film 20 includes a material of the organic phase 21 and a material of the inorganic crystal region 22 within any 2nm×2nm area. Thus, the SEI film 20 has higher uniformity, and can exhibit superior structural stability and strength during charge and discharge cycles, thereby facilitating the capacity retention rate of the battery during long cycles. TEM testing of the surface of the SEI film 20 or the cross section exposed after the thinning treatment thereof makes it possible to observe both the material of the organic phase 21 and the material of the inorganic crystal region 22 in an area of 2nm on the surface or any cross section thereof.

In some embodiments of the present application, the SEI film 20 has a total volume ratio of 20% to 80% of the inorganic crystalline region 22 and a total volume ratio of 20% to 80% of the organic phase 21. Thus, the SEI film 20 has both sufficient amount of material to provide strength support and active ion channels and appropriate amount of material to provide toughness, and the SEI film 20 has superior overall performance. When the other parameters are the same, the higher the total volume ratio of the inorganic crystal region 22 in the SEI film 20, the better the strength of the SEI film 20, and the better the ion conductivity; conversely, the better the toughness of the SEI film 20; those skilled in the art can select according to the actual application (for example, the expansion ratio of the anode active material 11). Specifically, the total volume ratio of the inorganic crystalline region 22 may be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%. In embodiments of the present application, TOF-SIMS may be used to test the above parameters. In some embodiments, the total volume of the inorganic crystalline region 22 is 20% -80% within any 10nm×10nm volume of the SEI film 20. Thus, the uniformity of the SEI film 20 is better. Specifically, three-dimensional imaging can be performed using TOF-SIMS, and the mass ratio of the material of the organic phase 21 and the mass ratio of the components of the inorganic crystalline region 22 are measured in any of the above-described regions defined by frames.

In the embodiment of the present application, the structure of the SEI film 20 may be regarded as that the adjacent inorganic crystal regions 22 are filled with the organic phase 21, so that the higher the filling degree, the tighter the bonding between the material of the inorganic crystal region 22 and the material of the organic phase 21, and the stronger the bonding force, the higher the densification degree of the SEI film 20. In some embodiments of the present application, the SEI film 20 has no holes penetrating in the thickness direction of the SEI film 20. Therefore, the electrolyte can be prevented from contacting and reacting with the anode active material in the anode material layer 10 through the through-holes, and thus irreversible loss of the electrolyte and active ions (e.g., lithium ions) during formation can be prevented. In the embodiment of the present application, the cross section of the SEI film 20 is observed by TEM, and no through holes extending in the thickness direction of the SEI film 20 are observed under TEM. Wherein, the cross section of SEI film means: a section obtained by cutting off the SEI film in any plane parallel to the SEI film thickness direction.

In other embodiments, the SEI film 20 may have a small number of holes penetrating in the thickness direction of the SEI film 20, but the hole diameters of the holes penetrating in the thickness direction of the SEI film 20 are less than or equal to 1nm, as observed under TEM. The SEI film 20 has a certain thickness and the electrolyte has a certain viscosity, so that the electrolyte is difficult to penetrate the holes of the above-mentioned pore diameter to contact with the negative electrode material layer 10 in a short time; the consumption of electrolyte during long cycles is substantially negligible, even if permeable. In order to ensure that the SEI film 20 has high density, the risk of the electrolyte contacting and reacting with the negative electrode material layer 10 is strictly controlled, and in some embodiments, the number of holes penetrating through the SEI film 20 in the thickness direction is less than or equal to 10 within any 10nm×10nm volume of the SEI film 20. Specifically, the number of the aforementioned holes penetrating in the thickness direction of the SEI film 20 may be 2 or less, 3 or less, 5 or less, or 8 or less within any 10nm volume of the SEI film 20.

In some embodiments of the application, chemical bonds are formed between at least a portion of the material of inorganic crystalline region 22 and the material of organic phase 21. The chemical bonding can promote the interfacial bonding force between the material of the inorganic crystal region 22 and the material of the organic phase 21, thereby facilitating the guarantee of the structural stability of the SEI film 20.

When the density of the SEI film 20 is high, the surface of the negative electrode does not regenerate a new SEI film 20 in the formation process when the negative electrode is assembled into a battery. Therefore, the loss of active lithium ions and electrolyte can be reduced, and the first coulombic efficiency of the battery can be improved.

In some embodiments of the present application, the SEI film 20 has a thickness of 20nm to 300nm. The thickness of the SEI film 20 is controlled within the above range, which facilitates the transmission of active lithium ions, thereby facilitating the exertion of battery performance; secondly, the preparation is easy, and the higher uniformity is easy to realize. Specifically, the thickness of the SEI film 20 may be, but is not limited to, 20nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm. In the embodiment of the application, a scanning electron microscope can be used for testing the thickness of the SEI film.

In some embodiments of the present application, the Young's modulus of SEI film 20 is greater than or equal to 4.1GPa. For example, 4.5GPa to 5GPa, etc. In the embodiment of the application, an atomic force microscope (Atomic Force Microscope, AFM) can be used for testing the Young's modulus of the SEI film. Specifically, a tapping (Tapping) mode of an AFM is adopted, so that a needle point penetrates into an SEI film, a load F=K _c×d,K_c is calculated according to a Hooke law to be a cantilever beam mechanical constant, d is the needle point deformation, a load-indentation curve of the test point is obtained, then the curve is fitted by an Oliver-Pharr method to obtain the Young modulus of the test point, 3 test points are selected for each SEI film sample to be tested, and an average value is calculated to obtain the Young modulus of the SEI film.

In some embodiments of the present application, the SEI film 20 is grown in situ on the surface of the anode material layer 10.

In some embodiments of the present application, the material of inorganic crystalline region 22 includes, but is not limited to, at least one of LiF, li ₂ O, and Li ₃ N. The inorganic material has better ionic conductivity and higher mechanical strength of a crystal structure, and the inorganic crystal region 22 formed by the material can provide better active lithium ion transmission channels, so that the SEI film 20 has higher ionic conductivity and mechanical property, and is beneficial to improving the multiplying power performance of the battery and realizing quick charge performance and the like while taking the long cycle capacity retention rate of the battery into consideration. In the embodiment of the present application, when the SEI film 20 contains a plurality of the above inorganic materials at the same time, different inorganic materials may belong to different inorganic crystal regions 22, or may exist in the same inorganic crystal region 22. For example, when the material of inorganic crystalline region 22 includes both LiF and Li ₂ O, some of the material of inorganic crystalline region 22 is LiF and other of the material of inorganic crystalline region 22 is Li ₂ O; it is also possible that a single inorganic crystalline region 22 has both LiF and Li ₂ O therein; alternatively, both conditions may exist.

In some embodiments of the application, the material of organic phase 21 includes, but is not limited to, at least one of R ₁-O-Li、R₂R₃-C=N^-Li⁺ and R ₄-NH^-Li⁺、R₄-NH₂ or a polymer thereof; wherein R ₁、R₄ is selected from C2-C8 alkenyl groups, R ₂、R₃ is selected from at least one of C2-C8 alkenyl groups and hydrogen atoms, and R ₂、R₃ is not hydrogen at the same time. Thus, the SEI film 20 is easy to prepare and has superior toughness; meanwhile, the materials of the organic phase are matched with a battery system, so that side reactions are not caused. Specifically, R ₁、R₂、R₃、R₄ may be a linear alkenyl group or a branched alkenyl group. The alkenyl group may further contain a substituent in the examples of the present application selected from the group consisting of vinyl, 1-propenyl and 2-propenyl 、CH₂=CH-CH₂-CH₂-、CH₂-CH₂-CH=CH-、CH₂-CH=CH-CH₂-、CH₂=CH-CH=CH-、CH₃-CH₂-CH₂-CH=CH-、CH₂=CH-CH₂-CH₂-CH₂-、CH₃-CH=CH-CH₂-CH₂-、CH₃-CH₂-CH=CH-CH₂-、CH₂=CH-CH=CH-CH₂-、CH₂=CH-CH₂-CH=CH-、CH₂=CH-CH=CH-CH₂-CH₂-、CH₃-CH=CH-CH=CH-CH₂-、CH₂=CH-CH₂-CH₂-CH₂-CH₂-、CH₃-CH=CH-CH₂-CH₂-CH₂-、CH₃-CH₂-CH=CH-CH₂-CH₂-、CH₃-CH₂-CH₂-CH=CH-CH₂-、CH₃-CH=CH-CH₂-CH₂-CH₂-CH₂-、CH₂=CH-CH=CH-CH₂-CH₂-CH₂-、CH_3-CH=CH-CH=CH-CH₂-CH₂-、CH₃-CH₂-CH=CH-CH₂-CH₂-CH₂-、CH₃-CH₂-CH₂-CH=CH-CH₂-CH₂-、CH₃-CH₂-CH₂-CH₂-CH=CH-CH₂-、(CH₃)₃C-CH=CH-CH₂-、CH₂=CH-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-、CH₃-CH=CH-CH₂-CH₂-CH₂-CH₂-CH₂-、CH₃-CH₂-CH=CH-CH₂-CH₂-CH₂-CH₂-、CH₃-CH₂-CH₂-CH=CH-CH₂-CH₂-CH₂-、CH₃-CH₂-CH₂-CH₂-CH=CH-CH₂-CH₂-、CH₃-CH₂-CH₂-CH₂-CH₂-CH=CH-CH₂-、CH₃-CH₂-CH₂-CH=CH₂-CH=CH-CH₂-、CH₂=CH-CH₂-CH₂-CH=CH-CH₂-CH₂-、CH₂=CH-CH₂-CH=CH-CH₂-CH₂-CH₂-、CH₃-CH=CH-CH₂-CH₂-CH=CH-CH₂-、(CH₃)₃C-CH=CH-CH₂-CH₂-., but the present application is not limited thereto, and those skilled in the art can select the alkenyl group according to the actual circumstances.

Specifically, R ₁ -O-Li may be, but is not limited to, CH₂=CH-O-Li、CH₂=CH-CH₂-O-Li、CH₂-CH₂-CH=CH-CH=CH-CH₂-CH₂-O-Li、(CH₃)₃-C-CH=CH-CH₂-O-Li、 or the like. R ₂R₃-C=N^-Li⁺ may be, but is not limited to, CH ₂=CH-CH=N^-Li⁺、CH₂=CH-CH₂-CH=N^-Li⁺,、Etc. R ₄-NH^-Li⁺ may be, but is not limited to CH₂=CH-NH^-Li⁺、CH₂=CH-CH₂-NH^-Li⁺、CH₂-CH₂-CH=CH-CH=CH-CH₂-CH₂-NH^-Li⁺、(CH₃)₃-C-CH=CH-CH₂-NH^-Li⁺ or the like. R ₄-NH₂ may be, but is not limited to CH₂=CH-NH₂、CH₂=CH-CH₂-NH₂、CH₂-CH₂-CH=CH-CH=CH-CH₂-CH₂-NH₂、(CH₃)₃-C-CH=CH-CH₂-NH₂ or the like.

In some embodiments, the material of organic phase 21 comprises a polymer of at least one of R₁-O-Li、R₂R₃-C=N^-Li⁺、R₄-NH^-Li⁺、R₄-NH₂、R₅-NH^-Li⁺、R₅-NH₂; it is understood that the polymer may be a polymer obtained by addition polymerization between one or more of the above-mentioned organic monomers. Specifically, the material of the organic phase 21 may comprise polymers of the different monomers mentioned above, and/or copolymers of at least one of the monomers mentioned above. For example, the material of the organic phase 21 may include a mixture of a polymer of R ₁ -O-Li and a polymer of R ₄-NH^-Li⁺, and/or a copolymer of R ₁ -O-Li and R ₄-NH^-Li⁺. In some embodiments, the material of the organic phase 21 is a polymer of at least one monomer described above. When the material of the organic phase 21 includes the above polymer, or all the materials are polymers, toughness of the organic phase 21 can be further improved, and certain strength and mechanical stability are given to the organic phase 21, so that mechanical properties (for example, toughness, young's modulus, etc.) of the SEI film 20 are better improved, thereby optimizing structural stability of the SEI film 20 in a long cycle process, and further reducing risk of cracking of the SEI film 20.

In some embodiments, the polymers have a degree of polymerization of 50 or greater. The degree of polymerization is defined as the average of the number of repeating units contained in the polymer macromolecular chain or the number of individual structural units contained in the polymer macromolecular chain. Specifically, taking CH ₂=CH-CH₂ -O-Li as an example, the above polymer may be，n≥50。

In some embodiments of the application, the anode 1 is a metallic lithium anode, i.e. the anode material layer 10 is a lithium metal layer. The lithium metal layer is used as the anode material layer 10, so that the generation of the SEI film 20 is easier, the reactivity of a lithium simple substance is high, the volume change rate in the charge-discharge cycle process is large, and the SEI film 20 provided by the embodiment of the application has more obvious improvement on the electrochemical performance with the anode. At this time, in some embodiments, the SEI film 20 is disposed on one side surface of the anode material layer 10 and on the side surface of the anode material layer 10. As will be appreciated, in the negative electrode used in the secondary battery, a current collector (not shown in fig. 1) is generally further included. Specifically, the SEI film 20 covers the surface of the lithium metal layer facing away from the current collector and the side surfaces of the lithium metal layer, and the side surfaces of the lithium metal layer are connected to the opposite side surfaces thereof. In the embodiment of the application, the lithium metal can be lithium simple substance metal or lithium alloy. Wherein the lithium alloy includes, but is not limited to, one or more of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy, lithium bismuth alloy. The lithium metal layer may be dense or may have a three-dimensional network structure.

In the embodiment of the present application, the current collector may be any negative electrode current collector known in the art to be suitable for a lithium secondary battery, for example, copper foil, or the like.

In some embodiments of the present application, the anode material layer 10 includes a particulate anode active material 11. At this time, the SEI film is not only provided on one side surface and side surfaces of the anode material layer 10, but in some embodiments, the SEI film 20 coats the surface of the granular anode active material 11, as shown in fig. 2. At this time, a current collector is disposed at a side surface of the negative electrode material layer 10 facing away from the SEI film 20. The sides of the anode material layer 10 are connected to opposite side surfaces of the anode material layer 10. In the present embodiment, the particulate form is a concept of a layered structure such as a lithium foil, and the nano-tubular and sheet-shaped negative electrode active material 11 is also regarded as the particulate negative electrode active material 11. Fig. 2 is an exemplary drawing, and the particle size of the anode active material 11, the thickness of the SEI film 20, the size and concentration of the inorganic crystalline region 22, and the size of the organic phase 21 in fig. 2 are all exemplary and do not constitute any limitation to the embodiments of the present application.

In the embodiment of the present application, the above-mentioned anode active material 11 may be any anode active material known in the art to be suitable for a lithium secondary battery, for example, elemental silicon, silicon carbon composite, siOx, graphite, or the like; of course, the lithium element may be in the form of particles. In some embodiments, when the anode active material 11 is a material that does not contain lithium, such as elemental silicon, a silicon-carbon composite, siOx, or the like, the surface of the anode material layer 10 facing away from the current collector further has a lithium metal layer, and lithium metal in the lithium metal layer may function as a lithium supplementing agent. At this time, in some embodiments of the present application, the anode active material 11 layer further includes a conductive agent and a binder. The conductive agent and binder may be those well known to those skilled in the art as being suitable for the negative electrode of the lithium secondary battery.

Correspondingly, the embodiment of the application provides a preparation method of the negative electrode, which can be used for preparing the negative electrode 1 provided by the embodiment of the application, and comprises the following steps:

S01, setting liquid raw materials for forming an organic phase and an inorganic crystal area on the surface of a cathode material layer precursor to form a cathode material layer and a solid electrolyte interface film, so as to obtain the cathode in the embodiment of the application; wherein the anode material layer precursor contains a simple substance of lithium. In some embodiments, at least one side surface of the anode material layer precursor is covered with a simple substance of lithium. In some embodiments, the negative electrode material layer precursor is a lithium metal layer.

The preparation method is simple to operate, high in flexibility, high in process reliability and high in production efficiency, and is suitable for large-scale industrial production. In addition, the SEI film is generated on the surface of the anode material layer in situ, is matched with the surface morphology of the anode material layer, can be firmly covered on the surface of the anode material layer, is not easy to separate, and can be coated on the surface of the granular anode active material when the anode material layer comprises the granular anode active material.

In some embodiments of the application, in step S01, the liquid feedstock includes a first feedstock and a second feedstock. The first feedstock comprises an organic compound comprising an oxidized group and a carbon-carbon double bond, the organic compound comprising at least one of R ₁-O-O-R₁'、R₂R₃-C=N-R₃'、R₄ -n=o and R ₅-NO₂, wherein R ₁、R₁' is independently selected from at least one of a C2-C8 alkenyl group and a hydrogen atom, And R ₁、R₁' is not simultaneously hydrogen; R ₂、R₃、R₃ 'is independently selected from at least one of C2-C8 alkenyl and hydrogen atom, and R ₂、R₃、R₃' is not hydrogen at the same time; r ₄、R₅ is independently selected from C2-C8 alkenyl. The selection range of the C2-C8 alkenyl group can be referred to the relevant description, and is not repeated here. Wherein, R ₁ and R ₁' can be the same or different. R ₂、R₃、R₃' may be the same or different. In particular, R ₁-O-O-R₁' may be, but is not limited to, a dipropenyl peroxide; R ₂R₃-C=N-R₃' may be, but is not limited to, butenone imine; r ₄ -n=o may be, but is not limited to, 2-nitrosopropene; r ₅-NO₂ may be, but is not limited to, 2-nitropropene. In the embodiment of the application, the first raw material is in a liquid state. The oxygen-containing group is a peroxy bond, -c=n-, -n=o, -NO ₂.

The second raw material comprises a substance containing an active element, wherein the active element comprises at least one of fluorine element, nitrogen element and oxygen element; the active element-containing substance includes at least one of a fluorine element source, an oxygen element source, and a nitrogen element source; the fluorine element source comprises at least one of fluorinated alkane, fluorinated alkene, fluorinated carbonate, fluorinated ether and fluorine-containing inorganic substance; the oxygen source includes at least one of a carbonate, an ether, and an oxygen-containing additive (e.g., vitamin C); the nitrogen source includes at least one of an imide salt (e.g., liTFSI), a metal nitride (e.g., mg ₃N₂), and a nitrate (e.g., liNO ₃).

In some embodiments of the present application, when the active element-containing substance is an inorganic substance or a solid organic substance, the second raw material further includes a solvent. The solvent includes, but is not limited to, a good solvent such as dimethyl sulfoxide (DMSO). In some embodiments, the second raw material is a lithium-containing solution in which at least one of a fluorine element source, an oxygen element source, and a nitrogen element source is dissolved. As such, lithium ions in the lithium-containing solvent may provide a source of lithium for the material of the inorganic crystalline region.

The lithium simple substance has a certain reducibility, and after the liquid raw material is arranged on the surface of the anode material layer precursor, the first raw material and the second raw material are subjected to competitive decomposition under the action of the lithium simple substance, and the oxidation groups in the first raw material are reduced to form an organic phase; the second raw material is decomposed to form inorganic phases with lithium ions formed by a lithium simple substance or lithium ions from other sources in the system, and the inorganic phases are crystallized to form an inorganic crystal area. For example, R ₁-O-O-R₁ 'is reduced to R ₁ -O-Li and R ₁'-O-Li;R₂R₃-C=N-R₃' is reduced to lithium imine, R ₄ -n=o and R ₅-NO₂ is reduced to lithium imine, etc., or a complex of lithium imine, etc. It will be appreciated that the material of the organic phase which is formed by the competing decomposition at this time is a small molecule which does not undergo an addition reaction. The fluorine element source is decomposed and generates LiF with lithium ions; the oxygen element source is decomposed and generates Li ₂ O with lithium ions; the nitrogen source decomposes and reacts with lithium ions to form Li ₃ N. More importantly, the competition decomposition of the first raw material and the second raw material avoids the condition that the SEI film is of a multi-layer structure due to the fact that the inorganic reaction is faster than the organic reaction in the related art, so that a special single-layer structure in which an organic phase and an inorganic crystal area are mixed and distributed can be formed; and there is stronger chemical attraction (for example, coulomb force effect) between the first raw material and the second raw material, the competition and attraction exist simultaneously, so that the generated inorganic crystal region and the organic phase are tightly combined, and the size of the inorganic crystal region can be controlled in a smaller range, so as to form a uniform and compact SEI film.

It will be appreciated that for the reaction between the first and second starting materials and the elemental lithium described above, the elemental lithium is generally in excess. For lithium metal anodes, the lithium element is in excess; for the negative electrode which is additionally added with the lithium simple substance and uses other negative electrode active materials (such as silicon materials), the lithium simple substance is needed to be used for supplementing lithium from the practical production, so the lithium simple substance is also excessive; therefore, the content of the lithium simple substance in the anode material layer is not limited, and the lithium simple substance can be selected by a person skilled in the art according to actual production requirements. In some embodiments of the application, the molar ratio of carbon-carbon double bonds to oxidized groups in the first feedstock is 1: (0.33-3). In this way, it is advantageous to control the polymerization degree of the polymer in the organic phase within a proper range, thereby optimizing the performance of the SEI film. Specifically, the molar ratio of carbon-carbon double bonds to oxidizing groups in the first feedstock may be, but is not limited to, 1:0.33, 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2.0, 1:2.2, 1:2.5, 1:2.8, 1:3.0. In some embodiments, the molar ratio of carbon-carbon double bonds to oxidized groups in the first feedstock is 1:1.

In some embodiments of the application, the molar ratio of oxidizing groups to active elements in the liquid feedstock is (0.2-5): 1. thus, the uniformity of the SEI film is improved, and the area ratio of the organic phase and the inorganic crystal region in the final SEI film can be controlled within a proper range, for example, the total volume ratio of the inorganic crystal region in the SEI film can be 20% -80%. In particular, the molar ratio of oxidizing groups to active elements may be, but is not limited to 0.2:1、0.5:1、0.8:1、1:1、1.2:1、1.5:1、1.8:1、2:1、2.2:1、2.5:1、2.8:1、3:1、3.2:1、3.5:1、3.8:1、4:1、4.2:1、4.5:1、4.8:1、5:1.

In some embodiments of the application, the molar ratio of carbon-carbon double bonds to oxidized groups in the first feedstock is 1: (0.33-3), and the molar ratio of the oxidizing groups to the active elements in the liquid raw material is (0.2-5): 1. by adjusting the above parameters within the above ranges, the mass ratio and the respective sizes of the inorganic crystal region and the organic phase can be adjusted.

In some embodiments of the present application, in step S01, disposing a liquid raw material on a surface of the anode material layer precursor includes: the liquid raw material is coated on the surface of the anode material layer, or the anode material layer is immersed in the liquid raw material. In some embodiments, the negative electrode preform is passed through a liquid bath containing a liquid feedstock; the negative electrode preform comprises a current collector and a negative electrode material layer precursor arranged on the surface of the current collector. In some embodiments, the method further includes washing and drying after disposing the liquid raw material on the surface of the anode material layer precursor to remove the excessive substances in the first raw material and/or the second raw material (which do not participate in the generation of the SEI film).

In some embodiments of the application, the liquid feedstock further comprises a free radical initiator. The free radical initiator may initiate addition polymerization between monomers in the formed organic phase. The above-mentioned radical initiator may be selected from the initiators commonly used for radical polymerization, for example, medium-temperature radical initiators such as azobisisobutyronitrile (abbreviated as AIBN), azobisisoheptonitrile, dibenzoyl peroxide and the like. Specifically, the first raw material and the second raw material may be separately stored, and the first raw material and the second raw material are mixed to obtain a liquid raw material before being used for preparing the SEI film; in order to avoid causing unnecessary side reactions, a radical initiator may be added to the system again when the first raw material and the second raw material are mixed, or the radical initiator may be added to the second raw material. At this time, in order to polymerize the monomer in the organic phase generated in step S01, in some embodiments of the present application, step S02 is further included: the surface of the anode material layer precursor is provided with a liquid raw material and then subjected to a heat treatment. Thus, the toughness and mechanical strength of the organic phase in the SEI film can be improved, thereby further improving the structural stability of the SEI film. In an embodiment of the present application, the temperature of the heating treatment in step S02 may be determined according to the decomposition temperature of the radical initiator, for example, 70 ℃ to 110 ℃. In some embodiments of the present application, the heating time period is 1h to 5h. Specifically, when the heating time length is controlled within the above range, the heating time length is further adjusted, so that the mechanical properties of the SEI film can be further adjusted. In actual production, the above-mentioned heating process may be combined with the foregoing drying process, that is, the cleaned negative electrode with the SEI film is subjected to drying treatment at 70-110 ℃.

It will be appreciated that the battery to be formed also needs to be heated in the formation process of the battery. When an SEI film in which the organic phase is a polymer is to be obtained, it is also possible to add a radical initiator to the electrolyte without adding the radical initiator to the liquid raw material, and to polymerize the monomer of the organic phase in the SEI film by heating at the time of the subsequent battery formation process.

The embodiment of the application also provides a secondary battery, which comprises a positive electrode, a negative electrode provided by the embodiment of the application and an electrolyte positioned between the positive electrode and the negative electrode. With the negative electrode provided by the embodiment of the application, the secondary battery can realize excellent long-cycle performance, such as higher cycle capacity retention rate.

In some embodiments of the present application, in the secondary battery, the material of the organic phase in the SEI film of the negative electrode surface is a polymer.

In some embodiments of the application, the negative electrode material layer is a lithium metal layer.

In other embodiments of the present application, the negative electrode material layer further includes a negative electrode active material other than lithium metal, for example, a silicon-based negative electrode material, or the like. At this time, the negative electrode material layer further includes a binder and a conductive agent. In the embodiment of the present application, the above-mentioned binder and conductive agent may be a binder and conductive agent well known in the art to be suitable for a negative electrode of a lithium secondary battery.

In some embodiments of the application, the electrolyte is a liquid electrolyte comprising a solvent, an electrolyte salt, and optionally an additive. The solvent of the electrolyte may be any solvent known in the art, including but not limited to at least one of an ester solvent and an ether solvent. Among them, the ester solvents include, but are not limited to, carbonate solvents. The carbonate-based solvent includes, but is not limited to, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), etc.

The above lithium salt may be an electrolyte salt commonly used by those skilled in the art, including but not limited to at least one of lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium sulfate (Li ₂SO₄), lithium difluorooxalato borate (abbreviated as lipob), lithium dioxaato borate (abbreviated as LiBOB), lithium bis (trifluoromethanesulfonic acid) imide (abbreviated as LiTFSI), lithium hexafluoroarsenate (LiAsF ₆), lithium trifluoromethanesulfonate (abbreviated as LiTFA or LiOTF), and lithium perchlorate (LiClO ₄).

In some embodiments of the present application, the positive electrode may be a positive electrode suitable for a lithium secondary battery and adapted to the negative electrode. In general, the positive electrode includes a positive electrode current collector (e.g., aluminum foil) and a positive electrode material layer including a positive electrode active material. For example, when the negative electrode material layer is a lithium metal layer, the above positive electrode active material includes, but is not limited to, one or more of elemental sulfur and sulfur-containing compounds including, but not limited to, one or more of Li₂S、Mo₆S₈、CuS、MnS、FeS₂、CoS₂、NiS₂、Fe_0.5Co_0.5S₂ and vulcanized polyacrylonitrile. When the anode active material is a silicon-based anode active material, or a carbon-based anode active material, the above-mentioned cathode active material includes, but is not limited to, at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, nickel cobalt aluminum ternary (NCA) and nickel cobalt manganese ternary (NMC), lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium manganese silicate, lithium vanadium phosphate, and the like.

In some embodiments of the present application, the positive electrode material layer further includes a binder and a conductive agent. The above-mentioned binder and conductive agent may be a binder and conductive agent known in the art to be suitable for the positive electrode of a lithium secondary battery.

The embodiment of the application also provides electric equipment, which comprises the secondary battery provided by the embodiment of the application. The secondary battery provided by the embodiment of the application is adopted, so that the electric equipment has a good market prospect.

In some embodiments of the present application, the powered device includes, but is not limited to, a 3C-type electronic product, such as a cell phone, a notebook computer, a tablet computer, a drone, a wearable electronic device, and the like. The powered device may also include a powered vehicle, such as a new energy automobile, an electric bicycle, and the like.

The embodiment of the application also provides an energy storage system which comprises the secondary battery provided by the embodiment of the application. Due to the adoption of the secondary battery provided by the embodiment of the application, the energy storage system can realize excellent long-cycle performance.

In some embodiments of the present application, the energy storage system includes an energy storage device and a power converter, the energy storage device includes a receiving cavity and the secondary battery received in the receiving cavity, and the power converter is configured to perform power conversion processing on voltage and/or current, and input the changed voltage and/or current to the energy storage device, so that the energy storage device can meet the electricity requirement of the electric equipment.

The technical scheme of the application is described in detail in a plurality of embodiments.

Example 1

Using a commercially available lithium metal negative electrode (lithium metal on copper foil current collector), a blend solution of dipropenyl peroxide and fluoroether was used in a molar ratio of 1:1 soaking the lithium metal cathode, cleaning the cathode by adopting DMC solvent, and treating for 1 hour in an oven at 80 ℃ to obtain the cathode.

Example 2

A commercially available lithium-carbon composite negative electrode (metal lithium on copper foil current collector) was used, and a blend solution of butenoimine and fluoroether was used in a molar ratio of 2:1 soaking the lithium metal cathode, cleaning the cathode by adopting DMC solvent, and carrying out oven treatment at 80 ℃ for 2 hours to obtain the cathode.

To highlight the beneficial effects of the embodiments of the present application, the following comparative examples are set forth.

Comparative example 1

The same commercial lithium metal negative electrode as in example 1 was used as the negative electrode.

Performance testing

(1) Specifically, a positive electrode material (specifically lithium cobaltate), a conductive agent (specifically super P) and a binder (specifically polyvinylidene fluoride, PVDF) are mixed in a mass ratio of 90:5:5, and the obtained mixture is added to a dispersant (specifically N-methyl-2-pyrrolidone, NMP) to obtain a positive electrode slurry. And coating the positive electrode slurry on a positive electrode current collector (specifically an aluminum foil), drying and rolling to obtain a positive electrode plate.

The positive electrode tab was assembled with the negative electrodes of the above examples and comparative examples to form a test battery having a capacity of 1.5 Ah.

(2) Each of the test batteries obtained by the above assembly was subjected to a charge-discharge cycle test in a 25 ℃ incubator, specifically, charged to 3.95V at a constant current and constant voltage of 1C, and subjected to a constant voltage cut-off current of 0.05C, and then discharged to 2V at a constant current of 1C, and the number of cycles was counted when the retention rate of the recording capacity was attenuated to 80%, and the results are summarized in table 1.

(3) First effect test: and (3) charging the lithium ion battery to a charge cutoff voltage at 25 ℃ at a multiplying power of 0.2C, then reducing the constant voltage charge to 0.025C, and discharging to a discharge cutoff voltage at a multiplying power of 0.2C, thereby obtaining a first-cycle charge capacity and a first-cycle discharge capacity. First-turn coulombic efficiency = first-turn discharge capacity/first-turn charge capacity, and the results are summarized in table 1.

(4) The battery after the first charge and discharge was disassembled, and the morphology of the SEI film on the surface of each negative electrode was observed under TEM, and the results are summarized in table 2. Further, SEI film TEM photographs of example 1 and comparative example 1 are shown in fig. 3 and 4, respectively; as can be seen, the SEI film of example 1 is a composite structure of an organic phase and an inorganic crystalline region that are uniform and dense; the SEI film of comparative example 2 is remarkably loose in structure. Wherein, any material comprising the organic phase and the inorganic crystal region in the volume of 2a _maxnm×2a_maxnm×2a_max nm is regarded as uniform.

Three-dimensional imaging was performed using time-of-flight secondary ion mass spectrometry, and the total volume ratio of inorganic crystal regions within any 10nm×10nm volume of the SEI film of each example negative electrode was tested, and the results are summarized in table 1.

The young's modulus of the SEI film of each example negative electrode was measured using an atomic force microscope. Specifically, a tapping (Tapping) mode of an AFM is adopted to obtain a load-indentation curve of the test point, then an Oliver-Pharr method is utilized to fit the curve to obtain Young modulus of the test point, 3 test points are selected for each SEI film sample to test, an average value is calculated, and the results are summarized in Table 1.

TABLE 1

TABLE 2

As can be seen from the data of tables 1 and 2, the negative electrode prepared according to the embodiment of the present application can effectively prolong the cycle life of the lithium secondary battery, that is, can effectively delay the capacity fade. In addition, compared with comparative example 1, the first coulombic efficiency of the battery is also significantly improved because the negative electrode provided by the embodiment of the present application does not need to generate an SEI film through electrochemical reaction in the formation process. In addition, the applicant carries out verification experiments by replacing butenoimine in the embodiment 2 with 2-nitrosopropene and 2-nitropropene respectively, and also prepares an SEI film with uniformly and densely arranged inorganic crystal regions and organic phases, wherein the maximum cross section dimension a of the inorganic crystal regions is smaller than 10nm.

In the embodiments of the present application, the range values indicated by "a-b" include the end values a and b, and for example, the range indicated by "1nm to 10nm" includes the end values of 1nm and 10nm.

While the foregoing is directed to exemplary embodiments of the present application, it will be appreciated by those skilled in the art that various modifications and adaptations can be made thereto without departing from the principles of the present application, and such modifications and adaptations are intended to be comprehended within the scope of the present application.

Claims

1. A method for producing a negative electrode, comprising:

Setting liquid raw materials for forming organic phases and inorganic crystal areas on the surface of a cathode material layer precursor to form a cathode material layer and a solid electrolyte interface film, so as to obtain a cathode; wherein the anode material layer precursor contains a simple substance of lithium;

The liquid raw materials comprise a first raw material and a second raw material; the first raw material comprises an organic matter containing an oxidation group and a carbon-carbon double bond, and the second raw material comprises a substance containing an active element;

The molar ratio of the oxidizing group to the active element is (0.2-5): 1, a step of;

The organic matter comprises at least one of R ₁-O-O-R₁'、R₂R₃-C=N-R₃'、R₄ -N=O and R ₅-NO₂, wherein R ₁、R₁ 'is independently selected from alkenyl groups of C2-C8 and/or hydrogen atoms, and R ₁、R₁' is not hydrogen at the same time; r ₂、R₃、R₃ 'is independently selected from C2-C8 alkenyl and/or hydrogen atoms, and R ₂、R₃、R₃' is not hydrogen at the same time; r ₄、R₅ is independently selected from C2-C8 alkenyl;

The active element comprises at least one of fluorine element, nitrogen element and oxygen element; the active element-containing substance includes at least one of a fluorine element source, an oxygen element source, and a nitrogen element source; the fluorine element source comprises at least one of fluorinated alkane, fluorinated alkene, fluorinated carbonate, fluorinated ether and fluorine-containing inorganic substance; the oxygen element source comprises at least one of carbonate, ether and vitamin C; the nitrogen element source includes at least one of an imide salt, a metal nitride, and a nitrate.

2. The method according to claim 1, wherein a molar ratio of the carbon-carbon double bond to the oxidizing group in the first raw material is 1: (0.33-3).

3. The production method according to claim 1, wherein the second raw material is a lithium-containing solution in which at least one of the fluorine element source, the oxygen element source, and the nitrogen element source is dissolved.

4. The method of claim 1, wherein the liquid feedstock further comprises a free radical initiator.

5. The production method according to any one of claims 1 to 4, further comprising performing a heat treatment after disposing the liquid raw material on a surface of the anode material layer precursor; the temperature of the heating treatment is 70-110 ℃.

6. The anode produced by the production method according to any one of claims 1 to 5, comprising the anode material layer and the solid electrolyte interface film provided at least on a surface of the anode material layer; wherein the solid electrolyte interface film comprises the organic phase and a plurality of inorganic crystal regions dispersed in the organic phase, and the maximum cross-sectional dimension a of each inorganic crystal region is less than or equal to 10nm.

7. The anode according to claim 6, wherein a volume of any 2a _max nm×2a_max nm×2a_max nm of the solid electrolyte interface film includes a material of the organic phase and a material of the inorganic crystal region;

Wherein a _max=Max{a_n},{a_n is a set of maximum cross-sectional dimensions of a plurality of the inorganic crystalline regions in the solid electrolyte interface film, n >1.

8. The anode according to claim 6, wherein the maximum cross-sectional dimension a of the inorganic crystalline region is 1nm to 3nm.

9. The anode according to claim 8, wherein the solid electrolyte interface film includes a material of the organic phase and a material of the inorganic crystal region in any 2nm x 2nm area.

10. The anode according to claim 6, wherein the material of the organic phase comprises at least one of R₁-O-Li、R₁'-O-Li、R₂R₃-C=N^-Li⁺、R₄-NH^-Li⁺、R₄-NH₂、R₅-NH^-Li⁺ and R ₅-NH₂ or a polymer thereof; wherein R ₁、R₁'、R₄、R₅ is independently selected from C2-C8 alkenyl, R ₂、R₃ is independently selected from C2-C8 alkenyl and/or hydrogen atom, and R ₂、R₃ is not hydrogen at the same time; the polymerization degree of the polymer is more than or equal to 50.

11. The anode of claim 6, wherein the material of the inorganic crystalline region comprises at least one of LiF, li ₂ O, and Li ₃ N.

12. The negative electrode according to claim 6, wherein the total volume of the inorganic crystal region in the solid electrolyte interface film is 20% to 80%, and the total volume of the organic phase is 20% to 80%.

13. The negative electrode according to claim 6, wherein a distance between two adjacent inorganic crystal regions is 20nm or less.

14. The anode according to claim 6, wherein a chemical bond is formed between at least a portion of the material of the inorganic crystalline region and the material of the organic phase.

15. The anode according to claim 6, wherein the solid electrolyte interface film has no holes penetrating in a thickness direction thereof; or the solid electrolyte interface film has holes penetrating along the thickness direction, and the pore diameter of the holes penetrating along the thickness direction is less than or equal to 1nm.

16. The negative electrode according to claim 15, wherein the solid electrolyte interface film has holes penetrating in a thickness direction thereof, and the number of the holes penetrating in the thickness direction thereof is 10 or less in any volume of 10nm x 10nm of the solid electrolyte interface film.

17. The anode according to claim 6, wherein the anode material layer is a lithium metal layer, and the solid electrolyte interface film is provided on one side surface of the anode material layer and on a side surface of the anode material layer; or the negative electrode material layer comprises a granular negative electrode active material, and the solid electrolyte interface film is coated on the surface of the negative electrode active material.

18. The anode according to claim 17, wherein the anode further comprises a current collector; the current collector is arranged on one side surface of the negative electrode material layer, which is away from the solid electrolyte interface film.

19. The anode according to claim 6, wherein the solid electrolyte interface film has a thickness of 20nm to 300nm.

20. The anode according to any one of claims 6 to 19, wherein the young's modulus of the solid electrolyte interface film is equal to or greater than 4.1GPa.

21. A secondary battery comprising a positive electrode and a negative electrode according to any one of claims 6 to 20, and an electrolyte between the positive electrode and the negative electrode.

22. A powered device comprising the secondary battery of claim 21.

23. An energy storage system comprising the secondary battery of claim 21.