Negative pole piece and preparation method thereof, battery monomer and power utilization device

Abstract

The invention relates to the technical field of secondary batteries, and provides a negative pole piece and a preparation method thereof, a battery monomer and an electric device. The negative electrode piece comprises a negative electrode current collector and a negative electrode active layer arranged on at least one surface of the negative electrode current collector, an interface layer is arranged on the surface of one side, far away from the negative electrode current collector, of the negative electrode active layer, and the material of the interface layer meets the following conditions: the theoretical reduction potential is 0-0.8 V; and the lithium ion conductivity is greater than or equal to 2 * 10 <-8 > S / cm. According to the interface layer provided by the invention, the theoretical reduction potential and the lithium ion conductivity of the adopted material are selected, so that the interface layer has a relatively wide electrochemical window and relatively high lithium ion conductivity, and a stable lithium ion and electron transmission path is favorably formed on the surface of the negative electrode active layer; the electrochemical performance such as the cycle performance of the battery is further improved, so that the battery shows relatively long cycle life.

Description

Technical Field

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

[0002] In recent years, the application scope of secondary batteries represented by lithium-ion batteries has become increasingly wide. Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their cycle performance and safety performance.

[0003] At present, in secondary batteries represented by lithium-ion batteries, the negative electrode sheet, as an important component of the secondary battery, has a great influence on the cycle performance and life of the secondary battery. Therefore, seeking a negative electrode sheet that can improve the cycle performance and life of the secondary battery is one of the key areas of focus for researchers.

[0004] The above statements are only used to provide background information related to the present application and do not necessarily constitute prior art. Summary of the invention

[0005] The purpose of the present application is to provide a negative electrode plate and a preparation method thereof, a battery cell and an electrical device, aiming to improve the cycle performance and life of a secondary battery.

[0006] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein an interface layer is disposed on a surface of the negative electrode active layer away from the negative electrode current collector, and a material of the interface layer meets the following conditions:

[0008] The theoretical reduction potential is 0-0.8V;

[0009] Lithium ion conductivity ≥2×10 -8 S / cm.

[0010] The interface layer of the embodiment of the present application has a wider electrochemical window and higher lithium ion conductivity by selecting the theoretical reduction potential and lithium ion conductivity of the material used, which is conducive to forming a stable lithium ion and electron transmission pathway on the surface of the negative electrode active layer, further improving the electrochemical properties of the battery including cycle performance, so that the battery exhibits a higher cycle life.

[0011] In some embodiments, the negative electrode plate further includes a mixed layer, which is located between the negative electrode active layer and the interface layer, and includes the material contained in the negative electrode active layer and the material of the interface layer. The presence of the mixed layer allows the material of the interface layer to fully coat the surface of the negative electrode active material, binder and other components contained in the negative electrode active layer, further improving the lithium ion transmission rate of the negative electrode active layer.

[0012] In some embodiments, the lithium ion conductivity G of the material of the interface layer satisfies: 2.4×10 -8 S / cm≤G≤1×10 - 4 The interface layer material is within the lithium ion conductivity range, so that the interface layer has excellent lithium ion transmission ability, which is beneficial to improving the cycle capacity retention rate of the battery.

[0013] In some embodiments, the material of the interface layer includes a lithium-containing compound. The interface layer material is conducive to building a stable lithium ion transmission channel, thereby improving the cycle performance of the battery.

[0014] In some embodiments, the material of the interface layer includes at least one of lithium zirconate, lithium phosphate, lithium silicate, lithium aluminate, and lithium borate. The interface layer material has a low theoretical reduction potential and high lithium ion conductivity, and can construct a stable interface layer on the surface of the negative electrode active layer for transmitting lithium ions and electrons.

[0015] In some embodiments, the material of the interface layer includes an amorphous material. The interface layer material is in an amorphous state, and the transmission of lithium ions between the grain boundaries of the amorphous interface is beneficial.

[0016] In some embodiments, the interface layer is coated on the surface of the negative electrode active layer in a continuous layered form. The interface layer is in a continuous layered form and can form a stable coating layer on the surface of the negative electrode active layer, thereby facilitating the improvement of the stability of the negative electrode active material contained in the negative electrode active layer during the cycle and reducing the occurrence of side reactions of the negative electrode active material.

[0017] In some embodiments, the theoretical oxidation potential of the material of the interface layer is 2 V to 4.5 V. The theoretical oxidation potential of the interface layer material is selected so that the interface layer material has a wide electrochemical window and can stably exist during the battery charging and discharging process, thereby forming a stable lithium ion and electron transmission path on the surface of the negative electrode active layer.

[0018] In some embodiments, the thickness of the interface layer is 0.5 nm to 5 nm.

[0019] In some embodiments, the thickness of the interface layer is 0.5 nm to 2.5 nm.

[0020] By controlling and selecting the thickness of the interface layer, the stability of the interface layer is improved, which is conducive to establishing a stable lithium ion transmission path.

[0021] In some embodiments, the compaction density of the negative electrode active layer is 1.45 to 1.65 g·cm -3 The optimization and control of the compaction density of the negative electrode active layer is conducive to the deposition of a stable interface layer on the negative electrode active surface.

[0022] In some embodiments, the negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, expanded graphite, artificial graphite, highly oriented graphite and three-dimensional graphite. The negative electrode active material has high conductivity and cycle performance and low cost, which is conducive to the negative electrode plate to maintain high cycle stability and electron transfer rate.

[0023] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising at least the following steps:

[0024] Preparing a negative electrode active layer on at least one surface of a negative electrode current collector to obtain an initial negative electrode sheet;

[0025] An interface layer is prepared by vapor deposition on the surface of the negative electrode active layer on the side away from the negative electrode current collector to obtain the negative electrode plate of the embodiment of the present application.

[0026] The preparation method provided in the embodiment of the present application can effectively obtain a negative electrode sheet having an interface layer disposed on the surface of the negative electrode active layer, thereby facilitating improving the electrochemical performance of the battery including cycle stability.

[0027] In some embodiments, the vapor deposition method includes at least one of an atomic layer deposition method and a chemical vapor deposition method. The vapor deposition method can effectively form an interface layer on the surface of the negative electrode active layer to improve the cycle stability of the negative electrode plate.

[0028] In some embodiments, the step of preparing the interface layer on the surface of the negative electrode active layer away from the negative electrode current collector by atomic layer deposition comprises:

[0029] Place the initial negative electrode in the reaction chamber and then perform the following pulse cycles:

[0030] injecting a first gaseous precursor into the reaction chamber;

[0031] Stop introducing the first gas phase precursor and inject the second gas phase into the reaction chamber;

[0032] Stop introducing the second gas phase, and inject the third gas phase precursor into the reaction chamber;

[0033] Stop introducing the third gaseous precursor, inject the second gaseous precursor into the reaction chamber, and stop introducing the second gaseous precursor after the injection of the second gaseous precursor is completed.

[0034] Among them, the first gas phase precursor includes a lithium source or an M source, the second gas phase includes water vapor, and the third gas phase precursor includes a lithium source or an M source. The first gas phase precursor is different from the third gas phase precursor, and the M source includes at least one of a metal source or a non-metal source.

[0035] The use of atomic layer deposition can enable each reaction raw material to achieve atomic-level reaction, thereby constructing a continuous and stable interface layer on the surface of the negative electrode active layer, which is more conducive to improving the structural stability of the negative electrode sheet, thereby making the battery have higher cycle stability.

[0036] In some embodiments, before the pulse cycle is performed, the reaction chamber is first evacuated and nitrogen is injected to adjust the pressure of the reaction chamber to 0.1 MPa to 0.2 MPa. Under this pressure condition, the reaction between the first gas phase precursor, the second gas phase and the third gas phase precursor is more conducive to deposition on the surface of the negative electrode active layer to form an interface layer.

[0037] In some embodiments, the single injection time of the first gas phase precursor is the same as the single injection time of the third gas phase precursor, the single injection time of the second gas phase is ≥ the single injection time of the first gas phase precursor; the single injection time of the first gas phase precursor is 10ms to 30ms, and the single injection time of the second gas phase is 10ms to 30ms. Under this condition, the raw materials including the first gas phase precursor, the second gas phase and the third gas phase precursor can react completely, so that the thickness of the film layer deposited in the pulse cycle is the same, and a uniform and continuous interface layer is further obtained.

[0038] In some embodiments, the number of pulse cycles is 5 to 50. Under the pulse cycle conditions, an interface layer with a suitable thickness can be formed on the surface of the negative electrode active layer.

[0039] In a third aspect, an embodiment of the present application provides a battery cell, which includes the negative electrode sheet in the above embodiment or the negative electrode sheet prepared by the method for preparing the negative electrode sheet in the above embodiment.

[0040] The negative electrode plate contained in the battery cell in the embodiment of the present application has a stable lithium ion and electron transmission pathway, thereby improving the cycle life of the battery cell.

[0041] In some embodiments, at least a portion of the surface of the negative electrode active layer is covered with a SEI film, the SEI film includes an inner SEI film covering at least a portion of the surface of the negative electrode active layer and an outer SEI film covering the inner SEI film, the inner SEI film includes a lithium-containing inorganic compound, the lithium-containing inorganic compound includes the material of the interface layer, and the outer SEI film includes a lithium-containing organic compound.

[0042] During the formation process, a SEI film is formed on the surface of the negative electrode plate. Since an interface layer is provided on the surface of the negative electrode active layer, the components of the SEI film can be optimized, which is beneficial to improving the structural stability of the SEI film during the battery cycle.

[0043] In a fourth aspect, an embodiment of the present application provides a battery, which includes the battery monomer in the above embodiment. The battery improves the electrochemical performance of the battery including the cycle performance by providing the battery monomer.

[0044] In a fifth aspect, an embodiment of the present application provides an electric device, which includes the battery in the above embodiment. By installing the battery in the electric device, the battery has a longer life and a lower replacement frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0046] Figure 1 This is a schematic diagram of a negative electrode plate structure in some embodiments of the present application;

[0047] Figure 2 It is another schematic diagram of the structure of the negative electrode sheet in some embodiments of the present application;

[0048] Figure 3 It is another schematic diagram of the structure of the negative electrode sheet in some embodiments of the present application;

[0049] Figure 4 It is a partial enlarged view of the negative electrode sheet in some embodiments of the present application;

[0050] Figure 5 It is another schematic diagram of the structure of the negative electrode sheet in some embodiments of the present application;

[0051] Figure 6 is a schematic diagram of the structure of a vehicle in some embodiments of the present application;

[0052] Figure 7 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0053] Figure 8 This is a schematic diagram of the structure of a battery cell according to some embodiments of the present application.

[0054] Among them, the reference numerals in the figure are:

[0055] 1000. Vehicles;

[0056] 100, battery, 200, controller, 300, motor;

[0057] 10. box body, 11. upper box body, 12. lower box body;

[0058] 20. Battery cell, 21. Housing, 22. Electrode assembly, 23. Cover plate;

[0059] 1. Negative electrode current collector, 2. Negative electrode active layer, 3. Interface layer, 4. Mixed layer. DETAILED DESCRIPTION

[0060] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0062] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0063] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0064] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0065] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0066] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0067] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0068] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0069] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0070] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0071] In the description of the embodiments of the present application, SEI (solid electrolyte interface) membrane refers to a solid electrolyte interface membrane having the characteristics of a solid electrolyte, that is, a membrane formed by a passivation layer covering the surface of the electrode material when the electrode material and the electrolyte react at the solid-liquid interface during the first charge and discharge process of a liquid lithium-ion battery.

[0072] In recent years, lithium-ion batteries have developed rapidly and their application fields have been continuously expanded. In particular, the development of new energy vehicles has further promoted the large-scale application of lithium-ion batteries. As one of the key materials of lithium-ion batteries, the negative electrode material has a great impact on the performance of the battery due to its lithium storage capacity, coulomb efficiency, and cycle stability. As the current mainstream commercial lithium secondary battery negative electrode material, graphite has the advantages of small volume effect (volume change <10%), good cycle performance, and low cost. However, when graphite is used as a negative electrode material for lithium-ion batteries, the gram capacity is insufficient, there are many side reactions, and the stability of the layered structure needs to be improved, resulting in a decrease in the cycle performance of lithium-ion batteries.

[0073] To solve this problem, existing lithium-ion batteries can play a buffering and protective role by coating the surface of natural graphite with lithium-containing solid electrolytes. At the same time, the lithium-containing solid electrolytes have lithium ion diffusion channels that can quickly transfer lithium ions to the natural graphite layer for storage, ensuring the normal embedding of lithium ions in natural graphite. For example, a solid electrolyte with a certain thickness is coated on the surface of graphite, such as Li 1+x Al x Ti 2-x (PO4)3(2≥x≥0) is a lithium ion conductor with the chemical formula Li 7-x La 3+x Zr2O 12 (0.5≥x≥0.1) garnet-type ion conductors, Li2S-P2S5, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , chemical formula is Li 3x La 2 / 3-xPerovskite-type lithium lanthanum titanate of TiO3 (0.5≥x≥0.1), etc.

[0074] However, the lithium-containing solid electrolytes used in current technologies have the following pain points: the inorganic nanoparticles of the oxide solid electrolyte are difficult to form a uniform coating on the graphite surface; the sulfide electrolyte cannot exist stably in the electrolyte system; the solid electrolyte is close to electronic insulation, and after it is coated on the surface of the graphite particles, an electronic insulation layer is formed between the negative electrode active material and the conductive agent, blocking the electron transmission between the graphite and the conductive agent, affecting the electron transmission within the electrode.

[0075] That is to say, the oxide solid electrolyte coated on the surface of the negative electrode active material cannot guarantee a stable lithium ion transmission pathway during the cycle process, and also affects the electron transmission inside the electrode to a certain extent, thereby affecting the cycle performance of the battery.

[0076] Based on the above background, the first aspect of the embodiment of the present application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, an interface layer is disposed on the surface of the negative electrode active layer on a side away from the negative electrode current collector, and the material of the interface layer meets the following conditions:

[0077] The theoretical reduction potential is 0-0.8V;

[0078] Lithium ion conductivity ≥2×10 -8 S / cm.

[0079] The schematic diagram of the negative electrode plate structure of the embodiment of the present application is as follows Figure 1-2 As shown. Figure 1 In the embodiment, a negative electrode active layer 2 is provided on one surface of a negative electrode current collector 1, and an interface layer 3 is provided on the surface of the negative electrode active layer 2. Figure 2 In the embodiment, negative electrode active layers 2 are disposed on two oppositely disposed surfaces of the negative electrode current collector 1 , and interface layers 3 are disposed on the surfaces of the two negative electrode active layers 2 .

[0080] The interface layer of the embodiment of the present application is selected by the theoretical reduction potential and lithium ion conductivity of the material used, specifically the theoretical reduction potential and lithium ion conductivity are controlled within the above range, so that the interface layer material does not undergo chemical reactions itself during the battery cycle, nor does it undergo chemical reactions with negative electrode active materials, current collectors and other materials, and maintains structural stability within a wider electrochemical window range, which is beneficial to improving the structural stability of the negative electrode sheet, and can also effectively reduce the occurrence of side reactions of the negative electrode active material, thereby giving the battery higher cycle stability. At the same time, the interface material also has a higher lithium ion conductivity, which is beneficial to improving the rate of lithium ion insertion and extraction of the negative electrode sheet, and a stable lithium ion transmission path can be formed on the surface of the negative electrode active layer under the condition that the interface layer remains stable. If the theoretical reduction potential of the interface layer material is higher than the above range, the interface material itself is prone to reduction reaction during the formation or charge and discharge process, which is not conducive to maintaining the structural stability of the interface layer, thereby affecting the lithium ion transmission stability and structural stability of the negative electrode sheet. If the lithium ion conductivity of the interface layer material is lower than the above range, it is not conducive to the insertion and extraction of lithium ions in the interface layer, thereby affecting the transmission rate of lithium ions.

[0081] In addition, in the embodiment of the present application, the interface layer is arranged on the surface of the negative electrode active layer to achieve simultaneous coating of the particles of materials contained in the negative electrode active layer, such as the negative electrode active material, the conductive agent, the binder and the like. It can be understood that at this time, there is direct contact between the interface layer material and the negative electrode active material particles and the conductive agent particles, and there is also direct and sufficient contact between the negative electrode active material and the conductive agent, thereby not affecting the electron transmission between the negative electrode active material and the conductive agent, and further not affecting the electron transmission inside the electrode.

[0082] Based on this, the embodiment of the present application constructs a stable lithium ion transmission path and an anode protection layer by setting a stable interface layer on the surface of the negative electrode active layer. Under the premise of not affecting the electron transmission inside the electrode, the lithium ion transmission capacity of the negative electrode active layer and the structural stability during the cycle are effectively improved, so that the battery has a higher cycle stability.

[0083] Exemplarily, the theoretical reduction potential of the material of the interface layer includes, but is not limited to, 0.22V, 0.25V, 0.29V, 0.69V, and 0.76V.

[0084] For example, the lithium ion conductivity of the material of the interface layer includes but is not limited to 2.4×10 -8 S / cm, 2.5×10 -8 S / cm, 5.6×10 -8 S / cm, 2×10 -6 S / cm.

[0085] In some embodiments, the negative electrode plate further includes a mixed layer, the mixed layer is located between the negative electrode active layer and the interface layer, and the mixed layer includes the material contained in the negative electrode active layer and the material of the interface layer. The material of the interface layer can be filled in the pores of the surface layer of the negative electrode active layer, so that the interface layer material can fully cover the material contained in the negative electrode active layer, such as the negative electrode active material, the binder, the conductive agent, etc., which is conducive to the full contact between the interface layer material and the negative electrode active material, the conductive agent, etc., and further improves the lithium ion transmission rate of the negative electrode active layer.

[0086] The schematic diagram of the negative electrode plate structure of the embodiment of the present application is as follows Figure 3 to Figure 5 As shown. Figure 3 In the embodiment, a negative electrode active layer 2 is provided on one surface of a negative electrode current collector 1, a mixed layer 4 is provided on the surface of the negative electrode active layer 2, and an interface layer 3 is provided on the surface of the mixed layer 4. The interface layer material contained in the interface layer 3 can enter / penetrate into the surface layer of the negative electrode active layer 2, and the mixed layer 4 is formed on the surface of the negative electrode active layer 2 on the side adjacent to the interface layer 3. Figure 4 yes Figure 3 From the enlarged partial view of the negative electrode sheet shown, it can be clearly seen that the mixed layer 4 contains both the interface layer material and the material contained in the negative electrode active layer.

[0087] exist Figure 5 In the embodiment, negative electrode current collectors 1 are provided with negative electrode active layers 2 on two surfaces facing each other, mixed layers 4 are provided on the surfaces of the two negative electrode active layers 2, and interface layers 3 are provided on the surfaces of the two mixed layers 4. The interface layer material contained in the interface layer 3 will enter the surface layer of the negative electrode active layer 2, and the mixed layer 4 is formed on the surface of the negative electrode active layer 2 on the side close to the interface layer 3.

[0088] In some embodiments, the lithium ion conductivity G of the material of the interface layer satisfies: 2.4×10 -8 S / cm≤G≤1×10 - 4 S / cm. For example, the lithium ion conductivity of the interface layer material can be 2.4×10 -8 S / cm, 1×10 -7 S / cm, 1×10 - 6 S / cm, 1×10 -5 S / cm, 1×10 -4 S / cm or within the range of any of the above values. The interface layer material is within the lithium ion conductivity range, so that the interface layer has excellent lithium ion transmission ability, which is conducive to the insertion and extraction of lithium ions, so that the battery has a higher cycle capacity retention rate.

[0089] In some embodiments, the material of the interface layer includes a lithium-containing compound. The interface layer material is conducive to constructing a stable lithium ion transmission channel on the surface of the negative electrode active layer, thereby further improving the lithium ion transmission rate and diffusion rate of the negative electrode plate, and giving the battery higher cycle performance.

[0090] In some embodiments, the material of the interface layer includes at least one of lithium zirconate, lithium phosphate, lithium silicate, lithium aluminate, and lithium borate. The interface layer material has a relatively low theoretical reduction potential, such as 0.25V for lithium zirconate, 0.69V for lithium phosphate, 0.76V for lithium silicate, 0.22V for lithium aluminate, and 0.29V for lithium borate, so that the material does not undergo chemical reactions itself during the battery cycle, nor does it undergo chemical reactions with negative electrode active materials, current collectors, and other materials, thereby achieving effective protection of negative electrode active materials, reducing the occurrence of side reactions of negative electrode active materials, and improving the structural stability of negative electrode sheets. At the same time, the interface layer material has a relatively high lithium ion conductivity, such as 2.4×10 -8 S / cm, the lithium ion conductivity of lithium phosphate is 5.6×10 -8 S / cm, the lithium ion conductivity of lithium silicate is 2.5×10 -8 S / cm, the lithium ion conductivity of lithium aluminate is 2.5×10 -8 S / cm, the lithium ion conductivity of lithium borate is 2×10 -6 S / cm, which can effectively improve the lithium ion transmission capacity of the negative electrode, so that the battery has higher cycle stability and higher capacity.

[0091] In some embodiments, the material of the interface layer includes an amorphous material. The interface material is disposed on the surface of the negative electrode active layer in an amorphous state. The amorphous state is also called non-crystalline. In contrast to the crystal, the amorphous state means that the atoms in the interface material are not arranged in a certain spatial order. The interface layer material is in an amorphous state, and the transmission of lithium ions is facilitated between the grain boundaries of the interface layer in the amorphous state.

[0092] In some embodiments, the interface layer is coated on the surface of the negative electrode active layer in a continuous layered form. The interface layer is in a continuous layered form and can form a stable coating layer on the surface of the negative electrode active layer, thereby effectively protecting the negative electrode active layer, reducing the occurrence of side reactions of the negative electrode active material, and further improving the structural stability of the negative electrode active material contained in the negative electrode active layer, so that the negative electrode sheet has a higher cycle stability.

[0093] In some embodiments, the theoretical oxidation potential of the material of the interface layer is 2V to 4.5V. The theoretical oxidation potential of the interface layer material is selected, specifically the theoretical oxidation potential of the interface layer material is controlled within the above range, so that the interface layer material has a wider electrochemical window, and can not chemically react with the negative electrode active material, the current collector and other materials during the charge and discharge process of the battery, thereby constructing a stable lithium ion transmission path on the surface of the negative electrode active layer. Exemplarily, the theoretical oxidation potential of the material of the interface layer includes but is not limited to 3.44V, 3.68V, 3.41V, 3.74V, and 4.21V.

[0094] In some embodiments, the thickness of the interface layer is 0.5 nm to 5 nm. In some examples, the thickness of the interface layer can be 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc., which are typical but non-limiting values.

[0095] In some embodiments, the thickness of the interface layer is 0.5 nm to 2.5 nm. In some examples, the thickness of the interface layer can be 0.5 nm, 0.8 nm, 1.0 nm, 1.5 nm, 2 nm, 2.5 nm, etc., which are typical but non-limiting values.

[0096] If the thickness of the interface layer is too low, it will not be able to effectively protect the negative electrode active layer, which is not conducive to improving the structural stability of the negative electrode active material; if the thickness of the interface layer is too high, it will significantly increase the transmission path of lithium ions, which is not conducive to improving the transmission rate of lithium ions. By further controlling the thickness of the interface layer, a stable protective layer can be formed on the negative electrode active surface, which is conducive to reducing the occurrence of side reactions of the negative electrode active material and improving the stability of the electrode sheet. At the same time, the interface layer within this thickness range allows the surface of the negative electrode active layer to have sufficient lithium salt, which is conducive to establishing a stable lithium ion transmission path on the surface of the negative electrode active layer, further improving the capacity cycle retention rate of the negative electrode sheet.

[0097] In some embodiments, the compaction density of the negative electrode active layer is 1.45 to 1.65 g·cm -3 For example, the compaction density of the negative electrode active layer may be 1.45 g·cm -3 , 1.5 g·cm -3 , 1.55 g·cm -3 , 1.6 g·cm -3 , 1.65g·cm -3 Typical but non-limiting values ​​are shown below. If the compaction density of the negative electrode active layer is too low, the negative electrode active material contained in the unit volume of the negative electrode active layer is less, and the negative electrode sheet specifically exhibits a lower capacity density; if the compaction density of the negative electrode active layer is too high, it is difficult to form a stable interface layer on the surface of the negative electrode active layer, which is not conducive to building a stable lithium ion transmission channel on the surface of the negative electrode active layer.

[0098] In some embodiments, the negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, expanded graphite, artificial graphite, highly oriented graphite and three-dimensional graphite. The negative electrode active material has high conductivity and cycle performance and low cost, which is conducive to the negative electrode plate to maintain high cycle stability and electron transfer rate.

[0099] In some embodiments, the negative electrode active layer contains a conductive agent, and the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0100] In some embodiments, the negative electrode active layer contains a binder, and the binder includes at least one of styrene-butadiene rubber, phenolic resin, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0101] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising at least the following steps:

[0102] Step S10, preparing a negative electrode active layer on at least one surface of the negative electrode current collector to obtain an initial negative electrode sheet;

[0103] Step S20: preparing an interface layer on the surface of the negative electrode active layer on the side away from the negative electrode current collector by a vapor deposition method to obtain the negative electrode plate of the embodiment of the present application.

[0104] The preparation method provided in the embodiment of the present application can effectively form an interface layer on the surface of the negative electrode active layer, thereby obtaining a negative electrode sheet with a stable lithium ion and electron transmission channel constructed on the surface, further improving the electrochemical performance of the battery including cycle stability.

[0105] In some embodiments, the steps of preparing the negative electrode active layer on at least one surface of the negative electrode current collector are as follows:

[0106] A negative electrode slurry containing a binder, a negative electrode active material, and a conductive agent is coated on a negative electrode current collector, and after drying and cold pressing, a negative electrode active layer is prepared on the negative electrode current collector to obtain an initial negative electrode sheet.

[0107] In some embodiments, the negative electrode slurry further includes a dispersant, wherein the mass ratio of the negative electrode active material, the conductive agent, the binder and the dispersant is 95-98:1-2:0.5-1:0.5-1.

[0108] In some embodiments, the compaction density of the initial negative electrode sheet is 1.45 to 1.65 g·cm -3 In the exemplary embodiment, the compaction density of the initial negative electrode sheet can be 1.45 g·cm -3, 1.5 g·cm -3 , 1.55 g·cm -3 , 1.6 g·cm -3 , 1.65g·cm -3 etc. are typical but not limiting values.

[0109] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. The metal foil may be a copper foil. The composite current collector may be a polymer material substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed on the surface of a polymer material substrate by copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.

[0110] In some embodiments, the conductive agent in the negative electrode slurry includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0111] In some embodiments, the binder in the negative electrode slurry includes at least one of styrene-butadiene rubber, phenolic resin, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0112] In some embodiments, the vapor deposition method includes at least one of an atomic layer deposition method and a chemical vapor deposition method. The vapor deposition method can effectively form an interface layer on the surface of the negative electrode active layer to improve the cycle stability of the negative electrode plate.

[0113] In some embodiments, the step of preparing the interface layer on the surface of the negative electrode active layer away from the negative electrode current collector by atomic layer deposition comprises:

[0114] Place the initial negative electrode in the reaction chamber and then perform the following pulse cycles:

[0115] injecting a first gaseous precursor into the reaction chamber;

[0116] Stop introducing the first gas phase precursor and inject the second gas phase into the reaction chamber;

[0117] Stop introducing the second gas phase, and inject the third gas phase precursor into the reaction chamber;

[0118] Stop introducing the third gaseous precursor, inject the second gaseous precursor into the reaction chamber, and stop introducing the second gaseous precursor after the injection of the second gaseous precursor is completed.

[0119] Among them, the first gas phase precursor includes a lithium source or an M source, the second gas phase includes water vapor, and the third gas phase precursor includes a lithium source or an M source. The first gas phase precursor is different from the third gas phase precursor, and the M source includes at least one of a metal source or a non-metal source.

[0120] The atomic layer deposition method can realize the reaction of each reaction raw material at the atomic level, thereby forming a stable and continuous interface layer on the surface of the negative electrode active layer, which is beneficial to protecting the negative electrode active material and reducing the occurrence of side reactions of the negative electrode active material.

[0121] Exemplarily, the formation process of lithium aluminate is as follows:

[0122] Al(CH3)3+C(CH3)3OLi+2H2O→LiAlO2+C(CH3)3OH+3CH4.

[0123] In some embodiments, the lithium source includes lithium tert-butoxide.

[0124] In some embodiments, the metal source includes at least one of a zirconium source and an aluminum source.

[0125] Exemplarily, the aluminum source includes at least one of trimethylaluminum, triethoxide aluminum, and triisopropoxide aluminum.

[0126] In some embodiments, the non-metal source includes at least one of a boron source, a phosphorus source, and a silicon source.

[0127] In some embodiments, the heating temperature of the lithium source is 150°C to 200°C, so that the lithium source is vaporized and then introduced into the reaction chamber in the form of a first gas phase precursor. Exemplary heating temperatures include but are not limited to 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.

[0128] In some embodiments, the heating temperature of the metal source or the non-metal source is 150°C to 200°C, so that the metal source or the non-metal source is vaporized and then introduced into the reaction chamber in the form of a third gas-phase precursor. Exemplary heating temperatures include but are not limited to 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C.

[0129] In some embodiments, before performing the pulse cycle, the reaction chamber is first evacuated and nitrogen is injected to adjust the pressure in the reaction chamber to 0.1 MPa to 0.2 MPa. Under this pressure condition, it is more conducive to the reaction between the first gas phase precursor, the second gas phase and the third gas phase precursor, and they are deposited on the surface of the negative electrode active layer to form an interface layer. Exemplarily, the pressure in the reaction chamber can be 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, 0.2 MPa and other typical but non-limiting values.

[0130] In some embodiments, the single injection time of the first gas phase precursor is the same as the single injection time of the third gas phase precursor, the single injection time of the second gas phase is ≥ the single injection time of the first gas phase precursor, the single injection time of the first gas phase precursor is 10ms to 30ms, and the single injection time of the second gas phase is 10ms to 30ms. Exemplarily, the single injection time of the first gas phase precursor can be a typical but non-limiting value such as 10ms, 12ms, 15ms, 18ms, 20ms, 25ms, 27ms, 30ms, etc. The single injection time of the second gas phase can be a typical but non-limiting value such as 10ms, 12ms, 15ms, 18ms, 20ms, 25ms, 27ms, 30ms, etc. Under this condition, the raw materials including the first gas phase precursor, the second gas phase and the third gas phase precursor can react completely, so that the thickness of the film layer deposited in the pulse cycle is the same, and a uniform and continuous interface layer is further obtained.

[0131] In some embodiments, the number of pulse cycles is 5 to 50 times. The thickness of the interface layer is controlled by different deposition cycles. Within the range of the number of pulse cycles, an appropriate thickness of the interface layer can be obtained. Exemplarily, the number of pulse cycles can be 5, 10, 15, 20, 25, 30, 35, 40, 50, etc., which are typical but non-limiting values.

[0132] In a third aspect, an embodiment of the present application provides a battery cell, which includes the negative electrode sheet in the above embodiment or the negative electrode sheet prepared by the method for preparing the negative electrode sheet in the above embodiment. The negative electrode sheet contained in the battery cell in the embodiment of the present application has a stable lithium ion and electron transmission path, thereby improving the cycle life of the battery cell.

[0133] In some embodiments, the electrode assembly and the electrolyte can be assembled to form a battery cell. The electrode assembly includes a negative electrode sheet, a separator, and a positive electrode sheet, wherein the negative electrode sheet is the negative electrode sheet of the embodiment of the present application.

[0134] For example, the negative electrode sheet, the separator and the positive electrode sheet can be wound or laminated to form an electrode assembly, which is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, shaped, etc. to obtain a battery cell. The shape of the battery cell is not particularly limited, and it can be cylindrical, square or any other shape.

[0135] It should be understood that the electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0136] In some embodiments, the method for preparing the positive electrode sheet comprises the following steps:

[0137] The positive electrode slurry containing a binder, a positive electrode active material and a conductive agent is coated on the positive electrode current collector, dried in an oven at a temperature of 80 to 110° C., and rolled to obtain a positive electrode sheet.

[0138] In some embodiments, the positive electrode active material may adopt the commonly used positive electrode active materials in this application. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, lithium transition metal oxides include but are not limited to at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, nickel-cobalt-manganese-aluminum quaternary materials, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, and lithium manganese oxide.

[0139] In some embodiments, the present application does not specifically limit the conductive agent in the positive electrode slurry, and can be selected according to needs. As an example, the conductive agent can include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0140] In some embodiments, the positive electrode current collector may be made of a metal foil or a porous metal plate having good electrical conductivity and mechanical properties, such as aluminum foil.

[0141] In some embodiments, at least part of the surface of the negative electrode active layer of the negative electrode plate in the battery cell is covered with a SEI film, the SEI film includes an inner SEI film covering at least part of the surface of the negative electrode active layer and an outer SEI film covering the inner SEI film, the inner SEI film includes a lithium-containing inorganic compound, the lithium-containing inorganic compound includes the material of the interface layer, and the outer SEI film includes a lithium-containing organic compound. Exemplarily, the lithium-containing inorganic compound includes at least one of lithium fluoride, lithium oxide, and lithium carbonate, and the lithium-containing organic compound includes alkyl lithium carbonate.

[0142] During the formation process, since the interface layer material has a wide electrochemical window, the interface layer material does not react itself during the formation process, nor does it participate in the reduction reaction. Therefore, the interface layer material still exists in the form of the original material during the formation process. The negative electrode active material, binder and other components contained in the negative electrode active layer undergo chemical reactions to gradually form organic lithium and inorganic lithium. At this time, the reaction products of the negative electrode active layer gradually merge and agglomerate with the interface layer material. Since the thickness of the interface layer is relatively thin and the products of the negative electrode active layer are relatively large, the products of the negative electrode active layer gradually wrap the interface layer material. Since the interface layer material is located inside the negative electrode active layer product, the interface layer material is located in the inner layer of the SEI film, thereby achieving changes and optimization of the inner layer of the SEI film. Since the SEI film contains the interface layer material, it is beneficial to improve the structural stability of the SEI film and the transmission capacity of lithium ions during the battery cycle, so that the battery cell has a higher cycle capacity retention rate.

[0143] At least part of the surface of the negative electrode active layer refers to: the surface of part of the negative electrode active layer, or the entire surface of the negative electrode active layer. During the formation process, it cannot be guaranteed that all surfaces of the negative electrode active materials contained in all negative electrode active layers have formed SEI films. Therefore, whether the surface of part of the negative electrode active layer meets the above conditions or the surface of the entire negative electrode active layer meets the above conditions, it is within the protection scope of this application.

[0144] There may be a clear boundary line between the inner SEI film and the outer SEI film, or there may be an unclear boundary line. Generally, the boundary line between the inner SEI film and the outer SEI film is not obvious.

[0145] In a fourth aspect, an embodiment of the present application provides a battery, which includes at least one battery cell in the above embodiment, generally including multiple battery cells, and the multiple battery cells are connected in series, in parallel or in mixed connection to increase the power supply capacity of the battery. In some cases, the battery also includes a box, and the battery cells are accommodated in the box.

[0146] Therefore, in the embodiment, the battery may include any one of a battery cell, a battery module, and a battery pack. The battery improves the electrochemical performance of the battery including the cycle performance by providing the battery cell.

[0147] Since the battery contains the battery cells of the embodiment of the present application, the battery has higher cycle stability, so that the cycle life of the battery is longer.

[0148] In some embodiments, when the battery of the embodiment of the present application is a battery module, the battery module contains a plurality of the above-mentioned battery cells, and the plurality of battery cells can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells can be fixed by fasteners.

[0149] In some embodiments, the battery module may further include a housing having a receiving space, and the plurality of battery cells are received in the receiving space.

[0150] In some embodiments, when the battery of the present application is a battery pack, the battery pack may contain a plurality of the above-mentioned battery cells, and the plurality of the battery cells may be assembled into the above-mentioned battery module. Therefore, the specific number of battery cells or battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0151] As in the embodiment, the battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, the upper box body is used to cover the lower box body and form a closed space for accommodating the battery modules. The plurality of battery modules may be arranged in the battery box in any manner.

[0152] In a fifth aspect, an embodiment of the present application provides an electric device, which includes the battery in the above embodiment. By installing the battery in the electric device, the battery has a longer life and a lower replacement frequency.

[0153] In the embodiment of the present application, the battery can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. Therefore, the electric device in the embodiment of the present application has a long standby or battery life and good safety performance.

[0154] The electrical device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc. The electrical device may select the above-mentioned battery cell, battery module or battery pack according to its use requirements.

[0155] In the exemplary embodiment, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0156] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0157] In some embodiments, Figure 6 The vehicle 1000 is taken as an example. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A lithium-ion battery 100 is arranged inside the vehicle 1000. The lithium-ion battery 100 may be arranged at the bottom, head or tail of the vehicle 1000. The lithium-ion battery 100 may be used to power the vehicle 1000. For example, the lithium-ion battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the lithium-ion battery 100 to power the motor 300, for example, for the starting, navigation and driving power requirements of the vehicle 1000.

[0158] In some embodiments, the lithium-ion battery 100 can be used not only as an operating power source for the vehicle 1000 , but also as a driving power source for the vehicle 1000 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000 .

[0159] Please refer to Figure 7 , Figure 7 An exploded view of a lithium-ion battery 100 provided for some embodiments of the present application. The lithium-ion battery 100 includes a case 10 and a lithium-ion battery cell 20, and the lithium-ion battery cell 20 is contained in the case 10. Among them, the case 10 is used to provide a storage space for the lithium-ion battery cell 20, and the case 10 can adopt a variety of structures. In some embodiments, the case 10 may include an upper case 11 and a lower case 12, and the upper case 11 and the lower case 12 cover each other, and the upper case 11 and the lower case 12 jointly define a closed space for accommodating the lithium-ion battery cell 20. Of course, the case 10 formed by the upper case 11 and the lower case 12 can be in a variety of shapes, such as a cylinder, a cuboid, etc. A plurality of battery cells 20 can be arranged in the battery box in any manner.

[0160] In the lithium-ion battery 100, there may be multiple lithium-ion battery cells 20, and the multiple lithium-ion battery cells 20 may be connected in series, in parallel, or in a mixed connection. The mixed connection means that the multiple lithium-ion battery cells 20 are both connected in series and in parallel. The multiple lithium-ion battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole body formed by the multiple lithium-ion battery cells 20 is accommodated in the box 10; of course, the lithium-ion battery 100 may also be a lithium-ion battery module formed by first connecting multiple lithium-ion battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple lithium-ion battery modules are connected in series, in parallel, or in a mixed connection to form a whole body, and then accommodated in the box 10.

[0161] In some embodiments, reference Figure 8 , the outer packaging of the battery cell 20 may include a shell 21 and a cover plate 23. Among them, the shell 21 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 21 has an opening connected to the accommodating cavity, and the cover plate 23 is used to cover the opening to close the accommodating cavity. The positive electrode sheet, the isolation membrane and the negative electrode sheet contained in the secondary battery of the embodiment of the present application can form an electrode assembly 22 through a winding process and / or a lamination process. The electrode assembly 22 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the electrode assembly 22. The number of electrode assemblies 22 contained in the battery cell 20 may be one or more, which can be adjusted according to actual needs.

[0162] Example

[0163] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0164] Example 1

[0165] This embodiment provides a negative electrode plate and a battery cell.

[0166] Preparation of negative electrode sheet:

[0167] The negative electrode active material natural graphite, conductive carbon black SP, binder SBR (styrene-butadiene rubber) and dispersant (sodium carboxymethyl cellulose) are dispersed and dissolved in deionized water in a mass ratio of 96:2:1:1, and mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the two opposite surfaces of the negative electrode collector copper foil, and after drying, cold pressing, slitting, and cutting (specifications are 5cm*5cm), an initial negative electrode sheet is obtained.

[0168] The initial negative electrode sheet is placed in the chamber of the atomic deposition equipment, the chamber is evacuated and then nitrogen is injected, and the pressure in the chamber is adjusted to 0.1-0.2MPa; the lithium source, aluminum source and deionized water are used as the reaction raw materials in a ratio of 1:1:2, the lithium source (lithium tert-butoxide) is heated to 180°C to vaporize the lithium source, and then the aluminum source (trimethylaluminum) and water are heated in the same way to vaporize them; then the following pulse cycle is performed:

[0169] Inject lithium source into the chamber with an injection time of 20ms;

[0170] Stop the lithium source and inject water vapor into the chamber for 20 ms;

[0171] Stop the water vapor and introduce the aluminum source into the chamber for 20 ms;

[0172] Stop the aluminum source and inject water vapor into the chamber for 20 ms. After the injection is completed, stop the water vapor.

[0173] Repeating this pulse cycle process will cause the lithium source, aluminum source, and water vapor to react, forming a lithium aluminate interface layer on the surface of the negative electrode active layer away from the current collector. The thickness of the interface layer is controlled to be 0.25nm. After the reaction is completed, the negative electrode plate is removed and the cavity is cleaned with nitrogen.

[0174] Preparation of positive electrode:

[0175] The positive electrode active material lithium iron phosphate, conductive carbon black SP and binder PVDF (polyvinylidene fluoride) are dispersed in the solvent NMP (N-methylpyrrolidone) and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil, and after drying, cold pressing, slitting and cutting, a positive electrode sheet is obtained, wherein the mass ratio of the positive electrode active material, the conductive carbon black and the binder PVDF is 96:2:2.

[0176] Arrange the prepared positive electrode sheet, negative electrode sheet and PP separator in the order of positive electrode-separator-negative electrode, so that the separator is placed in the middle of the positive and negative electrode sheets to isolate the positive and negative electrodes, and stack them layer by layer to form a laminated electrode assembly.

[0177] Preparation of electrolyte:

[0178] In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), lithium salt LiPF6 is added to a non-aqueous organic solvent at a certain concentration, the organic solvent is ethylene carbonate, dimethyl carbonate, and the content of cyclic carbonate (ethylene carbonate) is 30wt%. After the lithium salt is completely dissolved, add appropriate amounts of other additives. After stirring evenly, an electrolyte with a lithium salt concentration of 1.0mol / L is obtained.

[0179] Preparation of lithium-ion battery cells:

[0180] After welding the pole lugs, the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried electrode assembly. The assembly is allowed to stand, undergo formation, and perform capacity testing to complete the preparation of the lithium-ion battery cell.

[0181] Example 2

[0182] This embodiment provides a negative electrode plate and a battery cell. The same as the first embodiment, except that the thickness of the interface layer in the negative electrode plate is 0.5 nm.

[0183] Example 3

[0184] This embodiment provides a negative electrode plate and a battery cell. The same as the first embodiment, except that the thickness of the interface layer in the negative electrode plate is 2.5 nm.

[0185] Example 4

[0186] This embodiment provides a negative electrode plate and a battery cell. The same as the first embodiment, except that the thickness of the interface layer in the negative electrode plate is 5 nm.

[0187] Example 5

[0188] This embodiment provides a negative electrode plate and a battery cell. The same as the first embodiment, except that the thickness of the interface layer in the negative electrode plate is 10 nm.

[0189] Example 6

[0190] This embodiment provides a negative electrode plate and a battery cell. As in Embodiment 1, the thickness of the interface layer is 0.25 nm, except that the aluminum source in the preparation of the negative electrode plate is replaced with a zirconium source (tetrakis(dimethylamino)zirconium), and a lithium zirconate interface layer is formed on the surface of the negative electrode active layer.

[0191] Example 7

[0192] This embodiment provides a negative electrode plate and a battery cell. The same as embodiment 6, except that the thickness of the interface layer in the negative electrode plate is 0.5 nm.

[0193] Example 8

[0194] This embodiment provides a negative electrode plate and a battery cell. The same as the embodiment 6, except that the thickness of the interface layer in the negative electrode plate is 2.5 nm.

[0195] Example 9

[0196] This embodiment provides a negative electrode plate and a battery cell. The same as the embodiment 6, except that the thickness of the interface layer in the negative electrode plate is 5 nm.

[0197] Example 10

[0198] This embodiment provides a negative electrode plate and a battery cell. The same as the embodiment 6, except that the thickness of the interface layer in the negative electrode plate is 10 nm.

[0199] Comparative Example 1

[0200] This comparative example provides a negative electrode plate and a battery cell, which are the same as Example 1, except that no atomic layer deposition is performed on the surface of the initial negative electrode plate.

[0201] Comparative Example 2

[0202] This comparative example provides a negative electrode plate and a battery cell. The same as Example 1, except that the aluminum source in the preparation of the negative electrode plate is replaced by a niobium source, and a lithium niobate interface layer is formed on the surface of the negative electrode active layer.

[0203] Electrochemical performance test

[0204] Place the assembled battery cells on the electrochemical test channel and test the cycle retention rate according to the test process in Table 1 below:

[0205] Table 1 Test process

[0206]

[0207]

[0208] Measure the capacity after cycling and calculate the cycle retention rate.

[0209] The electrochemical properties of the interface layer materials used in the negative electrode sheets prepared in Examples 1 to 10 and Comparative Example 2 are listed in Table 2 below.

[0210] Table 2 Electrochemical properties of interface layer materials

[0211]

[0212] in:

[0213] The lithium ion conductivity is tested by AC impedance method. The specific test steps are as follows:

[0214] The blocking electrode was prepared by gold spraying on the test material with a diameter of 6 mm and a thickness of 1.3 mm using magnetron sputtering;

[0215] The test data was obtained by using an impedance analyzer, applying an AC voltage amplitude of 10mV, a frequency range of 13MHz-10Hz, and a temperature (253K, 263K, 273K, 283K, 293K, 298K) in a nitrogen environment.

[0216] The lithium ion conductivity is calculated according to formula (I):

[0217] σ=L / (R×S)(I).

[0218] In formula (I), σ is the ionic conductivity (unit: S / cm), R is the impedance (unit: Ω), L is the thickness (unit: cm), and S is the effective area of ​​the electrode (unit: cm 2 ).

[0219] The test results of the battery cells prepared in Examples 1 to 10 and Comparative Examples 1 to 2 are tabulated in Table 3 below.

[0220] According to Table 3, the battery cells provided with the interface layer all have higher lithium ion diffusion capacity and higher capacity cycle retention rate. In combination with Examples 1 to 5 and Examples 6 to 10, it can be found that as the thickness of the interface layer increases, its electrochemical properties including lithium ion diffusion capacity, first coulomb efficiency and capacity cycle retention rate all show a trend of first increasing and then decreasing. This may be because if the thickness of the interface layer is too thin, it is impossible to effectively protect the negative electrode active material and to build a stable lithium ion transmission path; if the thickness of the interface layer is too thick, the transmission path of lithium ions increases significantly, which is not conducive to improving the transmission rate of lithium ions, but instead causes the electrochemical performance of the battery cell to decrease.

[0221] Table 3 Electrical performance test results

[0222]

[0223] Among them, the cyclic voltammetry method is used to test the lithium ion diffusion coefficient. The specific test steps are:

[0224] The cyclic voltammetry curves of the battery cells at different scan rates (0.1, 0.3, 0.5, 0.8, 1.0 mV / s) were tested using an electrochemical workstation, with a voltage range of 0.01-2.0 V.

[0225] The current and the square root of the scan rate are calculated based on the cyclic voltammogram data, and then the relationship diagram between the two is obtained and the coefficients of the relationship equation between the current and the square root of the scan rate are fitted;

[0226] The coefficient obtained by fitting the current and the square root of the scan rate was substituted into the Randles-Sevcik equation for calculation, and finally the lithium ion diffusion coefficient of the anode was obtained.

[0227] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application 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 replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active layer arranged on at least one surface of the negative electrode current collector, an interface layer is arranged on the surface of the negative electrode active layer on a side away from the negative electrode current collector, and the material of the interface layer meets the following conditions: The theoretical reduction potential is 0-0.8V; Lithium ion conductivity ≥2×10 -8 S / cm.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode plate further includes a mixed layer, the mixed layer is located between the negative electrode active layer and the interface layer, and the mixed layer includes the material contained in the negative electrode active layer and the material of the interface layer.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The lithium ion conductivity G of the material of the interface layer satisfies: 2.4×10 -8 S / cm≤G≤1×10 -4 S / cm.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The material of the interface layer includes a lithium-containing compound.

5. The negative electrode sheet according to claim 4, characterized in that: The material of the interface layer includes at least one of lithium zirconate, lithium phosphate, lithium silicate, lithium aluminate, and lithium borate.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The material of the interface layer includes an amorphous material.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The interface layer is coated on the surface of the negative electrode active layer in a continuous layered form.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The theoretical oxidation potential of the material of the interface layer is 2V to 4.5V.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The thickness of the interface layer is 0.5 nm to 5 nm; optionally, the thickness of the interface layer is 0.5 nm to 2.5 nm.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The compaction density of the negative electrode active layer is 1.45 to 1.65 g·cm -3 .

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that: The negative electrode active layer contains a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, expanded graphite, artificial graphite, highly oriented graphite and three-dimensional graphite.

12. A method for preparing a negative electrode sheet, characterized in that: At least the following steps are included: preparing a negative electrode active layer on at least one surface of a negative electrode current collector to obtain an initial negative electrode sheet; An interface layer is prepared by vapor deposition on the surface of the negative electrode active layer on the side away from the negative electrode current collector to obtain the negative electrode sheet according to any one of claims 1 to 11.

13. The method for preparing a negative electrode sheet according to claim 12, characterized in that: The vapor deposition method includes at least one of an atomic layer deposition method and a chemical vapor deposition method.

14. The method for preparing a negative electrode sheet according to claim 13, characterized in that: The step of preparing an interface layer on the surface of the negative electrode active layer away from the negative electrode current collector by atomic layer deposition comprises: The initial negative electrode plate is placed in the reaction chamber, and then the following pulse cycles are performed in sequence: injecting a first gaseous precursor into the reaction chamber; Stop introducing the first gaseous precursor, and inject the second gaseous precursor into the reaction chamber; Stopping the introduction of the second gas phase and injecting a third gas phase precursor into the reaction chamber; Stop introducing the third gaseous precursor, inject the second gaseous phase into the reaction chamber, and stop introducing the second gaseous phase after the injection of the second gaseous phase is completed; Among them, the first gas phase precursor includes a lithium source or an M source, the second gas phase includes water vapor, the third gas phase precursor includes a lithium source or an M source, and the first gas phase precursor is different from the third gas phase precursor, wherein the M source includes at least one of a metal source or a non-metal source.

15. The method for preparing a negative electrode sheet according to claim 14, characterized in that: Before performing the pulse cycle, the reaction chamber is first evacuated and nitrogen is injected to adjust the pressure of the reaction chamber to 0.1 MPa to 0.2 MPa; and / or The single injection time of the first gas phase precursor is the same as the single injection time of the third gas phase precursor, and the single injection time of the second gas phase is ≥ the single injection time of the first gas phase precursor; The single injection time of the first gas phase precursor is 10ms to 30ms, and the single injection time of the second gas phase is 10ms to 30ms; and / or The number of pulse cycles is 5 to 50 times.

16. A battery cell, characterized in that: The battery cell comprises the negative electrode sheet according to any one of claims 1 to 11 or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to any one of claims 12 to 15.

17. The battery cell according to claim 16, characterized in that: At least part of the surface of the negative electrode active layer is covered with a SEI film, and the SEI film includes an inner SEI film covering at least part of the surface of the negative electrode active layer and an outer SEI film covering the inner SEI film, the inner SEI film includes a lithium-containing inorganic compound, and the lithium-containing inorganic compound includes the material of the interface layer; the outer SEI film includes a lithium-containing organic compound.

18. A battery, characterized in that: Comprising the battery cell according to claim 16 or 17.

19. An electrical device, characterized in that: Comprising the battery of claim 18.

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