Battery cell and method for producing the same, battery, electric device

Abstract

A battery monomer, a preparation method thereof, a battery, and a power utilization device. The battery monomer comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode film layer, the negative electrode film layer comprises a negative electrode active material and a coating layer coated on at least a part of a surface of the negative electrode active material; the coating layer comprises a polymer containing a fluorine element, and the polymer comprises at least one of a polyethylene oxide and a modified polyethylene oxide. The technical scheme of the application can improve the first circle coulomb efficiency and the cycle performance of the battery, while taking into account the rate capability and stability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery cell and its preparation method, a battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide range of applications, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. While batteries have achieved tremendous development, higher requirements have also been placed on their performance in various aspects.

[0003] During the first charge and discharge cycle of a battery, the electrolyte and the negative electrode film react at the solid-liquid interface to form a stable solid electrolyte interface (SEI). However, the formation of the SEI layer can affect battery performance. For example, in lithium-ion batteries, the formation of the SEI layer consumes some lithium ions, thus affecting the battery's initial coulombic efficiency, cycle performance, rate performance, and stability.

[0004] Therefore, how to improve the first-cycle coulombic efficiency and cycle performance of lithium-ion batteries while taking into account rate performance and stability is an urgent problem to be solved. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell and its preparation method, battery, and power device, so as to improve the first-cycle coulombic efficiency and cycle performance of the battery while taking into account the rate performance and stability.

[0006] In a first aspect, a battery cell is provided, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material and a coating layer covering at least a portion of the surface of the negative electrode active material; the coating layer comprises a fluorine-containing polymer, the polymer comprising at least one of polyethylene oxide and modified polyethylene oxide.

[0007] The polymer in the coating layer has oxygen atoms in its ether bonds that can form good coordination with lithium ions, which enhances lithium-ion migration and thus improves the battery's lithium conductivity and rate performance. For batteries, appropriate polymers can be selected based on specific needs to meet different performance requirements and application scenarios. Furthermore, the introduction of fluorine not only increases the water resistance of the coating layer and reduces its shedding during slurry preparation, thereby enhancing the stability of the coating layer and the battery, but also improves lithium-ion conductivity, thus enhancing the battery's first-cycle coulombic efficiency and cycle performance.

[0008] In some embodiments, the glass transition temperature Tg of the polymer satisfies: Tg≤70℃.

[0009] By setting the range of Tg, the mobility of chain segments can be further improved, lithium-ion conduction can be promoted, and the DC internal resistance and rate performance can be reduced.

[0010] In some embodiments, the molecular weight (MW) of the polymer satisfies: 5000≤MW≤1000000; optionally, 800000≤MW≤1000000.

[0011] When the polymer's molecular weight (MW) is within this range, it effectively reduces the high solubility caused by excessively low molecular weight and also reduces the high viscosity and uneven coating caused by excessively high molecular weight, thus contributing to the effectiveness and stability of the coating layer. Furthermore, when the polymer molecular weight is 800,000 ≤ MW ≤ 1,000,000, the polymer has a more suitable molecular weight for the coating layer, which is beneficial for further improving the coating effect.

[0012] In some embodiments, the mass ratio ω1 of fluorine element to the negative electrode film layer satisfies: 1% ≤ ω1 ≤ 10%.

[0013] When the mass ratio ω1 is within this range, it is beneficial to reduce the decrease in the stability of the coating layer and the performance of the battery due to ω1 being too low. On the other hand, it is also beneficial to reduce the impact on the specific capacity of the negative electrode active material due to ω1 being too high, thereby reducing the transport performance of the active material.

[0014] In some embodiments, the mass ratio ω2 of the coating layer to the negative electrode film layer satisfies: 1% ≤ ω2 ≤ 2%.

[0015] Within this range, a mass ratio ω2 that is too low will result in incomplete or insufficient coating coverage, failing to effectively protect the negative electrode material and leading to a decline in battery performance. Conversely, a mass ratio that is too high may result in an excessively thick coating, increasing the battery's internal resistance and affecting lithium-ion transport efficiency, also reducing battery performance. Therefore, when the mass ratio of the coating layer to the negative electrode film is 1% ≤ ω ≤ 2%, a more suitable mass ratio can improve the coating effect of the negative electrode sheet and battery performance.

[0016] In some embodiments, the thickness d of the coating layer satisfies: 4.7nm ≤ d ≤ 9.5nm.

[0017] Within this thickness range, the coating layer effectively protects the electrode and reduces the reaction between the electrode and the electrolyte. This lowers the probability of hindering lithium-ion transport, which is beneficial to battery capacity and first-cycle coulombic efficiency. Therefore, when the coating layer thickness is 4.7 nm ≤ d ≤ 9.5 nm, a more suitable thickness can improve battery capacity and first-cycle coulombic efficiency.

[0018] In a second aspect, a method for preparing a battery cell is provided, comprising: providing a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte to prepare the battery cell; wherein the negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material and a coating layer covering the surface of the negative electrode active material; the coating layer includes a fluorine-containing polymer, the polymer including at least one of polyethylene oxide and modified polyethylene oxide; the negative electrode sheet, the positive electrode sheet, and the separator are subjected to a winding process or a stacking process to obtain an electrode assembly; and the electrolyte is immersed in the electrode assembly to prepare the battery cell.

[0019] The negative electrode sheet prepared by this method can enable batteries containing the negative electrode sheet to have better first-cycle coulombic efficiency and cycle performance, and can also improve rate performance and stability.

[0020] In some embodiments, the glass transition temperature Tg of the polymer satisfies: Tg≤70℃.

[0021] In practical applications of batteries, the appropriate glass transition temperature can be selected according to specific needs.

[0022] In some embodiments, when the negative electrode active material is at least one of graphite and hard carbon, providing the negative electrode sheet includes: preparing the polymer-coated negative electrode active material; fluorinating the polymer-coated negative electrode active material to obtain fluorinated polymer-coated negative electrode active material; and preparing the negative electrode sheet using the fluorinated polymer-coated negative electrode active material.

[0023] The coating layer formed on the surface of the negative electrode material provides a physical barrier for fluorination, effectively controlling the uniformity and depth of the fluorination reaction. This helps to form a uniform and stable coating layer, enhancing the cycle stability of the battery while reducing costs. The coating layer reduces direct contact between the electrolyte and the negative electrode, minimizing side reactions and thus improving battery performance. Therefore, coating before fluorination contributes to the uniformity of the coating layer, improves interfacial stability, enhances electrochemical performance, and provides mechanical protection for the negative electrode.

[0024] In some embodiments, when the negative electrode active material is at least one of graphite, silicon-based material, and hard carbon, providing the negative electrode sheet includes: fluorinating the polymer to obtain a fluorinated polymer; using the fluorinated polymer to prepare a fluorinated polymer-coated negative electrode active material; and using the fluorinated polymer-coated negative electrode active material to prepare the negative electrode sheet.

[0025] Fluorination enhances the chemical resistance and surface stability of the anode material, reducing side reactions. Subsequent coating steps strengthen the coating layer and reduce wear on the fluorinated layer. This structure optimizes lithium-ion transport, improving battery charge / discharge efficiency and stability. Therefore, fluorination followed by coating focuses on enhancing chemical stability, reducing lithium deposition, improving interfacial compatibility, and enhancing thermal stability.

[0026] In some embodiments, where the negative electrode active material is at least one of graphite and hard carbon, the fluorination includes at least one of gas-phase fluorination and plasma fluorination.

[0027] Among these options, gas-phase fluorination is suitable for low-cost and simple processes, while plasma fluorination is suitable for processing complex-shaped samples and offers advantages such as environmental friendliness and uniformity. Therefore, the fluorination treatment method can be selected based on the application requirements and cost-effectiveness considerations of the battery.

[0028] In some embodiments, when the negative electrode active material is silicon-based, the fluorination includes plasma fluorination.

[0029] The plasma fluorination method described above is suitable for processing silicon-based materials and features environmental friendliness and uniformity.

[0030] In some embodiments, the time t for gas-phase fluorination satisfies: 30s≤t≤10h; optionally, 5h≤t≤10h.

[0031] Setting the vapor-phase fluorination time within this range helps form a uniform and stable coating layer on the surface of the negative electrode material, thereby enhancing the cycle stability of the battery. Furthermore, it can reduce the impact on lithium-ion transport efficiency and increase battery internal resistance caused by an excessively thick coating layer, thus maintaining the battery's charge-discharge efficiency and stability. Moreover, when the vapor-phase fluorination time is 5h ≤ t ≤ 10h, the coating layer has a more suitable vapor-phase fluorination time t, resulting in a uniform and dense protective layer, which can further improve battery performance.

[0032] Thirdly, a battery is provided, comprising a battery cell according to the first aspect and any possible implementation thereof, and / or a battery cell obtained by a preparation method according to the second aspect and any possible implementation thereof.

[0033] Fourthly, an electrical device is provided, including the battery described in the third aspect. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the material of the negative electrode film layer according to one embodiment of this application;

[0036] Figure 2 This is a SEM image of the negative electrode film layer according to an embodiment of this application;

[0037] Figure 3 This is an EDS surface scan of fluorine in the negative electrode film layer according to an embodiment of this application.

[0038] Figure 4 This is a TEM image of the negative electrode film layer according to an embodiment of this application;

[0039] Figure 5 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0040] Figure 6 This is a schematic diagram of the structure of a battery cell according to another embodiment of this application;

[0041] Figure 7 This is a flowchart illustrating the preparation process of the negative electrode sheet according to one embodiment of this application;

[0042] Figure 8 This is a flowchart illustrating the preparation of the negative electrode sheet according to another embodiment of this application.

[0043] Figure 9 This is a schematic diagram of a battery according to one embodiment of this application;

[0044] Figure 10 This is a schematic diagram of the structure of a battery according to one embodiment of this application;

[0045] Figure 11 This is a schematic diagram of the structure of an electrical device according to one embodiment of this application. Detailed Implementation

[0046] The following detailed description of the battery cell, its preparation method, battery, and power-consuming device of this application, with appropriate reference to the accompanying drawings, may omit unnecessary details. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Battery performance is closely linked to its interface stability, including the interface between the electrode plates and the electrolyte. During the first charge and discharge cycle, the electrolyte and the negative electrode active material react at the solid-liquid interface to form a stable solid electrolyte interface (SEI) film. For example, in lithium-ion batteries, this process inevitably consumes some lithium ions, and this consumption is irreversible. If the consumption of lithium ions exceeds a reasonable range, the overall performance of the battery will be significantly affected. Therefore, reducing irreversible lithium ion loss is crucial for improving the battery's initial coulombic efficiency and long-term cycle stability.

[0052] To address these issues, one approach is to supplement active lithium, such as by adding lithium-replenishing materials or constructing lithium-replenishing structures within the battery. However, these materials generally have high activity, placing stringent requirements on battery processing conditions and limiting their industrialization potential. Another approach is to reduce active lithium consumption, such as by pre-constructing an "artificial" SEI film on the negative electrode surface, optimizing binders, or using specific electrolytes. However, these methods significantly impact rate performance, are complex, and are not highly efficient at reducing lithium-ion consumption. Furthermore, the process of preparing the "artificial" SEI film using related technologies is unstable. For example, in the preparation of an "artificial" SEI using polyethylene oxide (PEO), the poor water resistance of PEO makes it prone to coating layer detachment during slurry preparation, thus affecting the film's stability. Therefore, finding a more efficient and direct way to reduce active lithium-ion consumption, thereby improving the battery's first-cycle coulombic efficiency and cycle performance while simultaneously ensuring rate performance and stability, is a pressing issue that needs to be addressed.

[0053] In view of the above, this application provides a battery cell and a method for preparing the same, a battery, and an electrical device. The battery cell includes: a negative electrode sheet, the negative electrode sheet including a negative electrode film layer, the negative electrode film layer including a negative electrode active material and a coating layer covering at least a portion of the surface of the negative electrode active material; the coating layer includes a polymer containing fluorine, the polymer including at least one of polyethylene oxide and modified polyethylene oxide.

[0054] The ether bonds in the polymer can form good coordination with lithium ions, which enhances the migration ability of lithium ions in the polymer chain, thereby improving the lithium conductivity of the battery. On the other hand, the introduction of fluorine into the polymer can not only increase the water resistance of the coating layer and reduce its shedding during the slurry preparation process, thus enhancing the stability of the coating layer and the battery, but also improve the lithium ion conduction efficiency and the first-cycle coulombic efficiency and cycle performance of the battery.

[0055] [Battery cell]

[0056] This application provides a single battery cell. Typically, a single battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily reduces short circuits between the positive and negative electrodes while allowing ions to pass through.

[0057] Next, the negative electrode, positive electrode, electrolyte, and separator of this application will be described with appropriate reference to the accompanying drawings.

[0058] [Negative electrode plate]

[0059] The negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0060] Figure 1 This is a schematic diagram of the material of the negative electrode film layer 122 according to an embodiment of this application. Figure 1 As shown, the negative electrode film 122 includes a negative electrode active material 1221 and a coating layer 1222. The coating layer 1222 coats at least a portion of the surface of the negative electrode active material 1221 and includes a polymer containing fluorine.

[0061] It should be noted that the coating here can be a complete coating of the negative electrode active material 1221 or a partial coating of the negative electrode active material 1221.

[0062] The 1222 coating layer plays a crucial role in lithium-ion batteries, reducing irreversible lithium-ion loss by minimizing side reactions between the electrolyte and the negative electrode during charging and discharging. This reduction in loss not only improves the battery's initial discharge capacity but also contributes to enhancing its overall cycle stability.

[0063] In some embodiments, the coating layer comprises a fluorine-containing polymer, the polymer comprising at least one of polyethylene oxide and modified polyethylene oxide.

[0064] Specifically, polyethylene oxide (PEO) is a linear polyether obtained by polymerization of ethylene oxide monomers. It possesses excellent lithium conductivity, including a highly ordered molecular structure and good crystallinity. However, it is a water-soluble polymer, forming a high-viscosity solution in aqueous solution, which is detrimental to the use of the coating layer 1222. By introducing fluorine into PEO, its water resistance is improved, reducing the shedding of the coating layer 1222 during slurry preparation. Furthermore, the resulting lithium fluoride binds to lithium ions, enhancing the stability of the interfacial layer and reducing its breakage during charge and discharge. This modification not only improves the mechanical strength of the interface but also enhances the long-term cycle stability of the battery. The introduction of fluorine results in better chemical stability of the interfacial film under high voltage and high temperature conditions, further improving the overall performance of the battery.

[0065] Modified polyethylene oxide (PEO) involves introducing additional functional groups or structures into PEO to improve its ionic conductivity, expand its electrochemical window, and enhance its mechanical properties, thereby improving or endowing the material with new properties. For example, modified PEO can be obtained by copolymerizing PEO with ester polymers. The introduced ester bonds can coordinate with lithium ions, which is beneficial for enhancing lithium ion transport and thus improving conductivity.

[0066] Within the ether bonds of the aforementioned polymers, the oxygen atoms can form effective coordination with lithium ions. This coordination is not a simple physical adsorption but a relatively stable chemical interaction, allowing lithium ions to move more rapidly within the polymer chain. In battery applications, suitable polymers can be selected based on different usage requirements.

[0067] Introducing fluorine into polymers can further improve battery performance. Specifically, fluorine can replace hydrogen with fluorine, forming lithium fluoride with lithium ions. This not only improves lithium-ion conductivity but also reduces the battery's DC internal resistance, thereby enhancing rate performance. Furthermore, lithium fluoride exhibits excellent stability, reducing lithium-ion consumption during SEI film formation, thus improving the battery's initial coulombic efficiency and cycle stability.

[0068] In the embodiments of this application, the glass transition temperature Tg of the polymer satisfies: Tg≤70℃.

[0069] The glass transition temperature (Tg) refers to the specific temperature at which an amorphous polymer material transitions from a glassy state to a rubbery state. Setting Tg ≤ 70℃ is beneficial for maintaining high mobility of polymer chains. This high mobility is crucial for lithium-ion transport because it allows lithium ions to migrate more freely between polymer chains, reducing ion transport impedance within the battery. Therefore, this Tg can further promote lithium-ion transport rate and rate performance.

[0070] In some embodiments, the negative electrode active material 1221 may be graphite, including at least one of artificial graphite and natural graphite.

[0071] In some embodiments, the negative electrode active material 1221 may be hard carbon.

[0072] In some embodiments, the negative electrode active material 1221 may be a silicon-based material, which may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. These negative electrode active materials may be used alone or in combination of two or more.

[0073] like Figure 2 The image shown is a scanning electron microscope (SEM) image of the negative electrode film 122 according to an embodiment of this application. See also... Figure 2 The surface of the negative electrode film 122 is covered with particulate matter.

[0074] like Figure 3 The image shown is an energy dispersive X-ray spectrometer (EDS) scan of fluorine in the negative electrode film layer 122 according to an embodiment of this application. See also... Figure 3 The particulate matter described above was verified by EDS to be fluorine, which means that fluorine has been successfully introduced into the polymer matrix.

[0075] It should be noted that during battery cycling, an SEI film will form on the surface of the negative electrode 122. The coating layer 1222 is relatively close to this SEI film, so the coating layer 1222 can act as an "artificial" SEI film, forming a double SEI film with the SEI film formed by the battery, thereby inducing the formation of a more stable SEI film.

[0076] The SEI film is a passivation layer formed on the surface of the active material during the first charge and discharge process of a lithium-ion battery, resulting from the reaction between the active material and the electrolyte at the solid-liquid interface. The coating layer 1222, referred to as an "artificial" SEI film, means that it can function as an SEI film, but it is not a true SEI film.

[0077] During the charging process of a single battery cell, lithium ions are released from the positive electrode active material, move and embed into the negative electrode; while during the discharging process, lithium ions are released from the negative electrode, move and embed into the positive electrode active material.

[0078] In addition, it should be understood that the “lithium intercalation” or “intercalation” process described in this application refers to the process in which lithium ions are intercalated into the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the “deintercalation” or “deintercalation” process described in this application refers to the process in which lithium ions are deintercalated into the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0079] In some embodiments, the molecular weight (MW) of the polymer satisfies: 5000 ≤ MW ≤ 1000000. For example, MW is 5000, 10000, 50000, 100000, 500000, 800000, 1000000, or any value within the above range. The molecular weight (MW) of the polymer used in the embodiments of this application affects the battery performance. With a molecular weight within this range, a lower molecular weight will not cause excessive dissolution of the polymer in the electrolyte, thereby weakening its coating effect on the surface of the negative electrode material and affecting the cycle stability and overall performance of the battery. On the other hand, an excessively high molecular weight will not increase the solution viscosity, thereby affecting the coating process of the negative electrode sheet, leading to uneven coating and affecting the consistency and performance of the battery.

[0080] Optionally, 800,000 ≤ MW ≤ 1,000,000. For example, MW is 800,000, 850,000, 900,000, 950,000, 1,000,000, or any value within the above range. In this way, the polymer has a more suitable molecular weight for the coating layer 1222, which is beneficial to further improve the performance of the battery cell.

[0081] In some embodiments, the mass ratio ω1 of fluorine in the negative electrode film layer satisfies: 1% ≤ ω1 ≤ 10%. For example, ω1 can be 1%, 2%, 5%, 7%, 8%, 9%, 10%, or any value within the above range. For the negative electrode film layer, when ω1 < 1%, the fluoride content in the coating layer may be insufficient to form a stable coating layer. This reduces the interfacial stability of the battery, thereby affecting the cycle life and overall performance of the battery. When ω1 > 10%, excessive fluoride content may negatively affect the specific capacity of the negative electrode active material. This may affect the electronic and ion transport characteristics of the active material, reducing its transport performance, and thus affecting the charge / discharge efficiency and rate performance of the battery. Therefore, when ω1 is in the range of 1% ≤ ω1 ≤ 10%, the fluoride content is sufficient to form a stable coating layer without damaging the specific capacity and transport characteristics of the active material.

[0082] In the embodiments of this application, the mass ratio ω of the coating layer 1222 to the negative electrode film 122 satisfies: 1% ≤ ω2 ≤ 2%. For example, ω2 is 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or any value within the above range. With this mass ratio, a low mass ratio of the coating layer 1222 to the negative electrode film 122 will not prevent the coating layer 1222 from effectively covering the entire negative electrode surface, leading to side reactions between the electrolyte and the negative electrode material, thus affecting the cycle stability and safety of the battery. Furthermore, an excessively thin coating layer 1222 may not effectively reduce irreversible lithium-ion consumption, thereby affecting the battery's first-cycle coulombic efficiency. Conversely, an excessively high mass ratio of the coating layer 1222 to the negative electrode film 122 will not result in an excessively thick coating layer 1222, increasing the battery's internal resistance, affecting lithium-ion transport efficiency, and thus reducing the battery's charge-discharge performance.

[0083] When designing the 1222 coating layer for lithium-ion batteries, an appropriate mass ratio is a key factor affecting battery performance. A reasonable mass ratio helps balance the protection of the negative electrode material, reduce electrolyte side reactions, and maintain the internal stability of the battery. This design is beneficial to the battery's electrochemical performance, thereby improving the initial coulombic efficiency and extending the battery's cycle life, and contributing to the battery's long-term stability.

[0084] In some embodiments, the thickness d of the coating layer 1222 satisfies: 4.7 nm ≤ d ≤ 9.5 nm. For example, d can be 4.7 nm, 5.5 nm, 6 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, or any value within the above range. The thickness of the coating layer 1222 corresponds to the mass ratio ω of the coating layer to the negative electrode film layer; that is, the higher the mass ratio ω of the negative electrode film layer, the thicker the coating layer 1222.

[0085] like Figure 4 The image shown is a transmission electron microscope (TEM) image of the negative electrode film 122 according to an embodiment of this application. See also... Figure 4 It can be observed that the coating layer 1222 coats the surface of the negative electrode active material, and the thickness of this coating layer is 4.7 nm. Within this range, it is beneficial to improve the first-cycle coulombic efficiency and long cycle life of the battery. Specifically, when the thickness d of the coating layer 1222 is ≥ 4.7 nm, it can reduce the side reactions between the electrolyte and the electrode caused by the coating layer being too thin and unable to effectively protect the electrode, thus increasing the battery's internal resistance and affecting the battery's cycle stability. On the other hand, when the thickness d of the coating layer 1222 is ≤ 9.5 nm, it is beneficial to reduce the obstruction of lithium-ion transport caused by the coating layer 1222 being too thick, thereby reducing the increase in the battery's internal resistance and affecting the battery's charge / discharge efficiency and rate performance.

[0086] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0087] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0088] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0089] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0091] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0092] [Positive electrode plate]

[0093] The positive electrode may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0094] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0095] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the positive electrode active material can be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following: lithium-containing transition metal oxides, lithium phosphates with an olivine structure, or materials with a spinel structure. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0097] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0098] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0100] [Electrolytes]

[0101] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0102] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0103] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0104] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0105] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0106] [Isolation membrane]

[0107] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0108] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0109] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0110] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0111] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0112] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0113] Figure 6 This is a schematic diagram of the structure of a battery cell according to another embodiment of this application. Figure 6As shown, the outer packaging of the battery cell 100 includes a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The battery cell 100 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to specific practical needs.

[0114] In some embodiments, the battery cells 100 can also be assembled into a battery module. The number of battery cells 100 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0115] [Preparation methods for battery cells]

[0116] This application provides a method for preparing a battery cell, comprising: providing a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte to prepare a battery cell; wherein the negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material and a coating layer covering at least a portion of the surface of the negative electrode active material; the coating layer includes a fluorine-containing polymer, the polymer including at least one of polyethylene oxide and modified polyethylene oxide; the negative electrode sheet, the positive electrode sheet, and the separator are subjected to a winding process or a stacking process to obtain an electrode assembly; and the electrolyte is immersed in the electrode assembly to prepare a battery cell.

[0117] In the above scheme, the battery cell prepared by this method can enable the battery including the negative electrode to have good first-cycle coulombic efficiency and cycle performance, while also taking into account rate performance and stability.

[0118] In some embodiments, the glass transition temperature (Tg) of the polymer satisfies: Tg ≤ 70℃. A suitable glass transition temperature can be selected based on the actual application scenario and specific requirements of the battery.

[0119] Figure 7 This is a flowchart illustrating the preparation process of the negative electrode sheet according to one embodiment of this application.

[0120] In some embodiments, when the negative electrode active material 1221 is at least one of graphite and hard carbon, providing a negative electrode sheet includes:

[0121] S101, Preparation of polymer-coated negative electrode active material;

[0122] S102, Fluoride the polymer-coated negative electrode active material to obtain a fluorinated polymer-coated negative electrode active material.

[0123] S103 utilizes a fluorinated polymer-coated negative electrode active material to prepare a negative electrode sheet.

[0124] Specifically, by first forming a coating layer 1222 on the surface of the negative electrode material, a physical barrier can be provided for the fluorination process, helping to control the uniformity and depth of the fluorination reaction. This method helps to form a more uniform and stable coating layer 1222, improving the cycle stability and safety of the battery, and at a lower cost. Furthermore, the coating layer 1222 can reduce the direct contact between the electrolyte and the negative electrode material, thereby suppressing side reactions and reducing negative effects on the electrolyte.

[0125] In this embodiment, the fluorination treatment includes gas-phase fluorination. Gas-phase fluorination is a method for forming a fluorinated layer on a material surface through a fluorination reaction in a gaseous environment. It typically involves exposing the material to a fluorinated gas, forming the fluorinated layer directly on the material surface using high temperature or chemical reagents. The advantages of gas-phase fluorination include: lower cost, typically no need for catalyst post-treatment, and simple process; better modification effect: it can form a nanoscale fluorinated layer on the polymer surface, improving the material's barrier properties, surface adhesion, and other properties; and strong stability: the modification effect after gas-phase fluorination is stable and applicable to a variety of materials, such as carbon nanotubes, graphite, metal oxides, and separation membranes.

[0126] In some embodiments, fluorination treatment also includes plasma treatment. By applying high voltage or using energy sources such as radio frequency or microwaves, the gas is ionized to generate plasma. The surface of the material to be treated is then exposed to the plasma. Active particles interact with the material surface, altering its properties and forming a fluoride coating. The advantages of plasma treatment include: high efficiency: plasma fluorination technology is highly efficient and can rapidly change the surface properties of materials; environmental friendliness: this technology produces almost no harmful byproduct gases, reducing environmental pollution and protecting the safety of operators; surface uniformity: plasma fluorination can provide uniform surface modification and is suitable for samples with large areas or complex shapes; wide applicability: plasma fluorination technology can be applied to various materials, such as metals, ceramics, and polymers, and can improve the surface chemical composition, morphology, wettability, optical properties, and electrical properties of materials.

[0127] Among the fluorination methods for the coating layer 1222, gas-phase fluorination and plasma fluorination each have their advantages, and the choice depends on the specific application requirements and cost-effectiveness. For example, gas-phase fluorination is suitable for cost-sensitive and simple processes, while plasma fluorination is more advantageous in processing complex-shaped samples due to its environmental friendliness and uniformity.

[0128] Figure 8 This is a flowchart illustrating the preparation process of the negative electrode sheet according to another embodiment of this application.

[0129] In some embodiments, when the negative electrode active material 1221 is at least one of graphite, silicon-based material, and hard carbon, providing a negative electrode sheet includes:

[0130] S201, Fluoride the polymer to obtain a fluorinated polymer;

[0131] S202, using fluorinated polymers, prepare fluorinated polymer-coated negative electrode active materials;

[0132] S203 utilizes a fluorinated polymer-coated negative electrode active material to prepare a negative electrode sheet.

[0133] Specifically, fluorination treatment enhances the surface stability and chemical resistance of the negative electrode material, reducing side reactions with the electrolyte. Subsequent coating steps further stabilize the coating layer 1222, helping to reduce wear or damage to the fluorinated layer during battery operation. The formation of the fluorinated layer helps improve the electronic and ionic conductivity of the negative electrode material, promoting lithium-ion insertion and extraction, thereby increasing battery utilization.

[0134] In this embodiment, when the negative electrode active material 1221 is at least one of graphite and hard carbon, the fluorination treatment includes at least one of gas-phase fluorination and plasma treatment; when the negative electrode active material 1221 is silicon-based, the fluorination treatment includes plasma fluorination. The specific processing method is the same as in the above embodiments, and for simplicity, it will not be repeated here.

[0135] In practical battery applications, the coating and fluorination strategies can be selected based on specific application requirements. The choice between these strategies depends on factors such as the characteristics of the anode material, the required battery performance, and manufacturing costs. For example, for high-capacity and high-voltage anode materials, coating before fluorination may be preferred to promote the uniformity and stability of the coating layer. Conversely, for cost-sensitive applications, fluorination before coating may be considered to simplify the process.

[0136] In some embodiments, the time t for gas-phase fluorination satisfies: 30s ≤ t ≤ 10h. For example, t can be 30s, 1min, 5min, 10min, 30min, 1h, 2h, 5h, 10h, or any value within the above range.

[0137] In the coating layer 1222 of a lithium-ion battery, fluorination treatment can improve the water resistance of the polymer in the negative electrode material and reduce its shedding during the slurry preparation process, thereby enhancing the stability of the coating layer 1222, which is beneficial to the battery performance. The fluorination treatment in this embodiment involves introducing fluorine elements onto the surface of the negative electrode material to form a fluorine-containing coating layer 1222. This coating layer 1222 can reduce side reactions between the electrolyte and the negative electrode material, reduce irreversible lithium-ion consumption, and thus improve the battery's first-cycle coulombic efficiency and cycle stability.

[0138] The duration of the vapor-phase fluorination treatment directly affects battery performance. A vapor-phase fluorination time t ≥ 30 s facilitates the formation of a uniform and stable protective layer on the surface of the negative electrode material by the coating layer 1222, thereby improving the battery's cycle stability. A vapor-phase fluorination time t ≤ 10 h prevents the protective layer from being too thick, which could affect lithium-ion transport efficiency, increase battery internal resistance, and thus reduce charge-discharge performance. Conversely, a vapor-phase fluorination time t ≤ 10 h also prevents excessively long fluorination times from causing fluoride to reach saturation on the surface of the negative electrode active material 1221, thus avoiding negatively impacting the fluorination effect.

[0139] Optionally, 5h ≤ t ≤ 10h. For example, t can be 5h, 6h, 7h, 8h, 9h, 10h, or any value within the above range. In this way, for the negative electrode material, the coating layer 1222 has a more suitable gas-phase fluorination time, which is beneficial for forming a more uniform and dense protective layer, thereby further improving battery performance.

[0140] This application also provides a battery and an electrical device. The battery and electrical device of this application will now be described with appropriate reference to the accompanying drawings.

[0141] [Battery]

[0142] This application provides a battery, including the battery cell described in the above embodiments.

[0143] Figure 9 This is a schematic diagram of a battery according to one embodiment of this application. Figure 10 This is a schematic diagram of the battery structure according to one embodiment of this application. (Refer to...) Figure 9 and Figure 10 The battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box 401 and a lower box 402, the upper box 401 covering the lower box 402 to form a closed space for accommodating the battery cells 100. The plurality of battery cells 100 may be arranged in any manner within the battery box.

[0144] The technical solution of this application can be applied to various batteries, such as lithium-ion batteries, lithium metal batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, magnesium batteries, calcium batteries, zinc batteries, aluminum batteries, etc., and this application does not limit it. It should be noted that, for the sake of convenience, this application uses lithium-ion batteries as an example for illustration.

[0145] [Electrical appliances]

[0146] This application also provides an electrical device that includes the battery described in the foregoing embodiments. The electrical device includes at least one of the battery cell 100 or battery 400 provided in this application. The battery cell 100 or battery 400 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0147] For example, Figure 11 This is a schematic diagram of the structure of an electrical device according to one embodiment of this application. Figure 11 As shown, the electrical device is vehicle 1, which can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A motor 500, a controller 600, and a battery 400 can be installed inside vehicle 1. The controller 600 controls the battery 400 to supply power to the motor 500. For example, the battery 400 can be installed at the bottom, front, or rear of vehicle 1. The battery 400 can be used to power vehicle 1; for example, it can serve as the operating power source for vehicle 1's electrical system, such as meeting the power requirements for starting, navigation, and operation. In another embodiment of this application, the battery 400 can not only serve as the operating power source for vehicle 1 but also as the driving power source, replacing or partially replacing gasoline or natural gas to provide driving power to vehicle 1.

[0148] As the electrical device, either battery cell 100 or battery 400 can be selected according to its usage requirements.

[0149] The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery for this electrical device, a 100-cell battery or a 400-cell battery can be used.

[0150] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell (100) as their power source.

[0151] [Example]

[0152] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0153] [Example 1]

[0154] Preparation of battery cells:

[0155] (1) Preparation of negative electrode sheet:

[0156] (1.1) Preparation of the negative electrode film:

[0157] Coating: A 3 wt% aqueous solution of polyethylene oxide was prepared, followed by the addition of graphite at a ratio of 15 g / 100 ml. The solution was first stirred at 600 rpm at room temperature for 1 h to obtain a composite solution. Then, air bubbles in the suspension were removed by ultrasonication, followed by spray granulation to obtain sodium carboxymethyl cellulose (CMC)-Li coated carbon material. The polyethylene oxide had a molecular weight (MW) of 5000, a Tg of 57℃, a mass ratio (ω2) of 1% between the coating layer and the negative electrode film, and a coating layer thickness (d) of 4.7 nm.

[0158] Fluorination: The obtained coating material is placed in a fluorination apparatus, and the ratio of fluorine gas to helium gas is set to 10:90. Fluorination is carried out for 10 minutes to obtain the fluorinated coated carbon material (F-PEO@Gr). The fluorination time t is 10 minutes.

[0159] (1.2) Preparation of the negative electrode sheet: 96.8% fluorine-containing polyethylene oxide-coated graphite (F-PEO@Gr), 1.5% styrene-butadiene rubber (SBR) as binder, 1% carboxymethyl cellulose (CMC) as thickener, and 0.7% carbon black (Super P) as conductive agent were mixed evenly by mass. Deionized water was then added as a solvent, and the viscosity was controlled to be 13000-15000. The resulting slurry was then uniformly coated onto copper foil as the negative electrode, with an active material loading of 1.5-1.7 mg / cm³. -2 .

[0160] (2) Preparation of the positive electrode sheet:

[0161] Electrode 1: A nickel-cobalt-manganese lithium oxide battery (NCM811), polyvinylidene fluoride (PVDF) binder, and conductive carbon are mixed uniformly at a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) is added as a solvent and dispersant. The resulting slurry is then uniformly coated onto aluminum foil as the positive electrode, with an active material loading of 4.5 mg / cm³. -2 .

[0162] Electrode 2: Lithium sheet.

[0163] (3) Separator membrane: Ordinary polypropylene membrane is used.

[0164] (4) Preparation of electrolyte: The electrolyte is a solution of ethylene carbonate (EC) / 1,3-dioxolane (DOL) / ethyl methyl carbonate (EMC) (volume ratio of 1:1:1) in which 1.0 mol / L lithium hexafluorophosphate and 1.0% lithium nitrate are dissolved.

[0165] (5) Preparation of lithium-ion battery: The above positive electrode sheet, separator and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in the shell, the electrolyte prepared above is added, and after encapsulation, standing, formation and aging processes, a battery cell is obtained.

[0166] (6) Assembly: CR2025 coin cells were assembled and tested in an argon-filled glove box (water and oxygen levels were both below 0.1 ppm). NCM811 was used for the positive electrode to assemble the full cell, and lithium foil was used as the half cell.

[0167] In Example 1, the negative electrode film layer of the battery cell is a coating layer made of polyoxyethylene fluoride that first coats the negative electrode active material and then fluorinates it. The negative electrode active material is made of graphite.

[0168] [Examples 2-4]

[0169] The difference between Examples 2-4 and Example 1 is that the molecular weight (MW) of the polyethylene oxide is different.

[0170] [Examples 5-7]

[0171] The difference between Examples 5-7 and Example 4 is that the mass ratio ω2 of the coating layer to the negative electrode film layer is different, and the corresponding coating layer thickness d is also different.

[0172] [Examples 8-11]

[0173] The difference between Examples 8-11 and Example 4 is that the fluorination time t is different.

[0174] [Example 12]

[0175] The difference between Example 12 and Example 4 is that the polymer in the coating layer is modified polyethylene oxide, which has high ionic conductivity.

[0176] [Example 13]

[0177] The difference between Example 13 and Example 12 is that the molecular weight (MW) of the modified polyethylene oxide is different.

[0178] [Example 14]

[0179] The difference between Example 14 and Example 12 is that the mass ratio ω2 of the coating layer to the negative electrode film layer is different, and the corresponding coating layer thickness d is also different.

[0180] [Example 15]

[0181] The difference between Example 15 and Example 12 is that the fluorination time t is different.

[0182] [Comparative Example 1]

[0183] The difference between Comparative Example 1 and Example 1 is that the negative electrode film does not include a coating layer.

[0184] [Comparative Example 2]

[0185] The difference between Comparative Example 2 and Example 4 is that the coating layer in the negative electrode film layer was not fluorinated.

[0186] [Comparative Example 3]

[0187] The difference between Comparative Example 3 and Example 4 is that the polymer in the negative electrode film layer is modified polyethylene oxide, and the coating layer is not fluorinated.

[0188] Table 1 shows the specific parameters of the negative electrode sheet during the preparation of the battery cell, and Table 2 shows the relevant test results of the battery cell.

[0189] Table 1. Specific parameters of Examples 1-15 and Comparative Examples 1-3

[0190] negative electrode film polymer Tg MW ω2 d t Example 1 F-PEO@Gr Polyethylene oxide 57℃ 5000 1.0％ 4.7nm 10min Example 2 F-PEO@Gr Polyethylene oxide 57℃ 10000 1.0％ 4.7nm 10min Example 3 F-PEO@Gr Polyethylene oxide 57℃ 500000 1.0％ 4.7nm 10min Example 4 F-PEO@Gr Polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 10min Example 5 F-PEO@Gr Polyethylene oxide 57℃ 1000000 0.05％ 0.23nm 10min Example 6 F-PEO@Gr Polyethylene oxide 57℃ 1000000 2％ 9.5nm 10min Example 7 F-PEO@Gr Polyethylene oxide 57℃ 1000000 5％ 24nm 10min Example 8 F-PEO@Gr Polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 30s Example 9 F-PEO@Gr Polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 1min Example 10 F-PEO@Gr Polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 5h Example 11 F-PEO@Gr Polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 10h Example 12 F-PEO@Gr Modified polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 10min Example 13 F-PEO@Gr Modified polyethylene oxide 57℃ 500000 1.0％ 4.7nm 10min Example 14 F-PEO@Gr Modified polyethylene oxide 57℃ 1000000 2.0％ 9.5nm 10min Example 15 F-PEO@Gr Modified polyethylene oxide 57℃ 1000000 1.0％ 4.7nm 5h Comparative Example 1 Gr / / / / / / Comparative Example 2 PEO@Gr Polyethylene oxide 60℃ 1000000 1.0％ 4.7nm / Comparative Example 3 PEO@Gr Modified polyethylene oxide 61℃ 1000000 1.0％ 4.7nm /

[0191] In Table 1, “MW” refers to the molecular weight of the polymer, “Tg” refers to the glass transition temperature of the polymer, “ω” refers to the mass ratio of the coating layer to the negative electrode film, “d” refers to the coating layer thickness, and “t” refers to the fluorination time.

[0192] [Physical Characterization of Negative Electrode Film Materials]

[0193] (1) Surface morphology characterization

[0194] Surface morphology was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the coating thickness was measured by TEM.

[0195] Energy-dispersive X-ray spectroscopy (EDS) was used to measure the EDS surface scan of fluorine in the negative electrode film.

[0196] (2) Molecular weight measurement

[0197] Molecular weight determination was performed using gel permeation chromatography (GPC). The GPC molecular weight determination method involved dissolving the polymer in N-methylpyrrolidone (NMP) at a concentration of 5 mg / mL and allowing it to stand overnight to allow the molecular chains to fully expand. Then, the prepared polymer solution was injected into the GPC column using a syringe. The instrument then automatically performed the test and processed the results.

[0198] [Lithium-ion Battery Performance Characterization]

[0199] (1) Measurement of the first-cycle coulomb efficiency

[0200] The battery was tested using the Blue Electric testing system for charge and discharge.

[0201] Under conditions of 45℃, the battery charge / discharge voltage range was maintained at 2.8-4.25V, and the battery was cycled at a current density of 1C. The charge / discharge capacity of the battery was recorded at the third cycle, and the capacity ratio of discharge to charge was calculated. The test results are shown in Table 2. It should be noted that the first cycle of the battery is the formation stage, and the third cycle is more stable than the second cycle. Therefore, the third cycle was selected as the first cycle in the practical sense of this application.

[0202] (2) Power performance test

[0203] The power performance of a secondary battery is characterized by its direct current resistance (DCR). Generally, the lower the DCR, the better the battery's power performance.

[0204] The DCR test method can refer to the method in GB / T 31467 "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs".

[0205] For example, at 25°C, charge the lithium-ion battery to 4.25V with a constant current of 0.33C and let it stand for 1 minute; then charge it to 4.25V with a constant current of 0.1C and let it stand for 30 minutes; discharge it to 2.8V with a constant current of 0.33C and record the discharge capacity A0 at this point in Ah. Then charge it to 0.5A0Ah with a constant current of 0.33C and adjust the SOC to 50%.

[0206] After placing the battery at -20℃ for 2 hours, it was discharged at a constant current of 4C for 10 seconds, and ΔU was recorded. 放电 ΔI 放电 Then, it was charged with a constant current of 0.01C for 4000s, adjusted to 50% SOC, and then left to rest at -20℃ for 2 hours. Afterward, it was charged with a constant current of 0.1C for 10s, and ΔU was recorded. 充电 ΔI 充电 The discharge and charge DCR data of lithium-ion batteries can be calculated using the following formula.

[0207] R 放电 =ΔU 放电 / ΔI 放电

[0208] R 充电 =ΔU 充电 / ΔI 充电

[0209] Wherein, ΔU 放电 ΔI represents the voltage change within 10 seconds of the start of discharge. 放电 ΔU represents the current value within 10 seconds of the start of discharge. 充电 ΔI represents the voltage change within 10 seconds of the start of charging. 充电 This indicates the change in current within 10 seconds of the start of charging.

[0210] (3) Capacity retention test

[0211] The LAND CT2001A battery tester was used to conduct charge-discharge tests on the battery. Specifically, the constant current cycle performance of the battery was studied using the constant current charge-discharge method. The full-cell voltage window was 2.75V-4.3V, and the charge-discharge rate was set to 1C. The half-cell voltage window was 0.01V-1.50V, and the current density was 0.2A / g. The cycle life of the full-cell and half-cell was tested, and the battery capacity retention rate after 500 cycles was recorded. The test results are shown in Table 2.

[0212] Table 2 Test results of Examples 1-15 and Comparative Examples 1-3

[0213] First-lap coulomb efficiency (%) DCR(mΩ) Capacity retention rate (%) Example 1 88.8 261.1 79.5 Example 2 88.9 260.8 79.7 Example 3 89.3 255.4 80.2 Example 4 90.1 244.3 82.5 Example 5 88.9 262.3 79.7 Example 6 90.3 251.2 82.6 Example 7 90.4 270.2 82.5 Example 8 89.1 259.3 80.6 Example 9 89.3 257.2 81.1 Example 10 90.1 244.2 82.4 Example 11 90.2 244.1 82.6 Example 12 90.0 244.3 82.5 Example 13 89.4 256.2 81.4 Example 14 90.0 259.5 81.5 Example 15 90.2 243.9 82.6 Comparative Example 1 88.8 261.3 79.3 Comparative Example 2 88.7 261.2 79.3 Comparative Example 3 88.8 260.4 79.4

[0214] In this application, capacity retention rate is used to characterize the cycle performance of a battery. The higher the capacity retention rate, the higher the capacity is retained after the battery has cycled to a specific number of times, which means that the battery has better cycle performance.

[0215] As can be seen from Examples 1-15 and Comparative Example 1, coating the surface of the negative electrode active material with a polymer can, within a certain range, improve the first-cycle coulombic efficiency and cycle performance of the battery, and reduce the DCR.

[0216] As can be seen from Examples 1-11 and Comparative Example 2, coating the surface of the negative electrode active material with fluorine-containing polyethylene oxide can, within a certain range, further improve the first-cycle coulombic efficiency and cycle performance of the battery, and reduce DCR.

[0217] As can be seen from Examples 12-15 and Comparative Example 3, coating the surface of the negative electrode active material with fluorine-containing modified polyethylene oxide can, within a certain range, further improve the first-cycle coulombic efficiency and cycle performance of the battery, and reduce DCR.

[0218] As shown in Table 2, based on Examples 1-4 and 12-13, it can be seen that within a certain range, increasing the molecular weight (MW) of the polymer in the coating layer can improve the first-cycle coulombic efficiency and cycle performance of the battery, and reduce the DCR.

[0219] According to Examples 4 and 5-7, and Examples 12 and 14, by changing the mass ratio ω of the coating layer to the negative electrode film layer to ensure that the mass ratio satisfies 1% ≤ ω ≤ 2%, the initial coulombic efficiency and cycle performance of the battery can be balanced, while reducing the DCR. When ω < 1% or ω > 2%, for example, when ω is 0.05% or 5%, the initial coulombic efficiency and cycle performance of the battery decrease, and the DCR increases.

[0220] Based on Examples 4 and 8-11, and Examples 12 and 15, it is evident that, within a certain range, extending the fluorination time t can improve the initial coulombic efficiency and cycle performance of the battery, while reducing DCR. Within this range, further adjusting the fluorination time can help improve the initial coulombic efficiency and cycle performance of the battery while reducing DCR.

[0221] As can be seen from Examples 4 and 12, in polymers of polyethylene oxide and modified polyethylene oxide, the first-cycle coulombic efficiency is higher when polyethylene oxide is used as the coating layer.

[0222] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: A negative electrode sheet, the negative electrode sheet including a negative electrode film layer, the negative electrode film layer including a negative electrode active material and a coating layer covering at least a portion of the surface of the negative electrode active material; The coating layer comprises a fluorine-containing polymer, which includes at least one of polyethylene oxide and modified polyethylene oxide.

2. The battery cell according to claim 1, characterized in that, The glass transition temperature Tg of the polymer satisfies: Tg≤70℃.

3. The battery cell according to claim 1 or 2, characterized in that, The molecular weight (MW) of the polymer satisfies: 5000≤MW≤1000000; optionally, 800000≤MW≤1000000.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The mass ratio ω1 of fluorine in the negative electrode film layer satisfies: 1% ≤ ω1 ≤ 10%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The mass ratio ω2 of the coating layer to the negative electrode film layer satisfies: 1% ≤ ω2 ≤ 2%.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The thickness d of the coating layer satisfies: 4.7nm≤d≤9.5nm.

7. A method for preparing a single battery cell, characterized in that, include: We provide negative electrode plates, positive electrode plates, separators, and electrolytes; The negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material and a coating layer covering at least a portion of the surface of the negative electrode active material; the coating layer includes a fluorine-containing polymer, the polymer including at least one of polyethylene oxide and modified polyethylene oxide; The negative electrode, the positive electrode, and the separator are subjected to a winding process or a stacking process to obtain an electrode assembly; The electrolyte is immersed in the electrode assembly to prepare the battery cell.

8. The preparation method according to claim 7, characterized in that, The glass transition temperature Tg of the polymer satisfies: Tg≤70℃.

9. The preparation method according to claim 7 or 8, characterized in that, When the negative electrode active material is at least one of graphite and hard carbon, the provision of the negative electrode sheet includes: Prepare the polymer-coated negative electrode active material; The polymer-coated negative electrode active material is fluorinated to obtain the fluorinated polymer-coated negative electrode active material. The negative electrode sheet is prepared using the fluorinated polymer-coated negative electrode active material.

10. The preparation method according to claim 7 or 8, characterized in that, When the negative electrode active material is at least one of graphite, silicon-based, and hard carbon, the negative electrode sheet provided includes: The polymer is fluorinated to obtain the fluorinated polymer; Using the fluorinated polymer, a fluorinated polymer-coated negative electrode active material is prepared; The negative electrode sheet is prepared using the fluorinated polymer-coated negative electrode active material.

11. The preparation method according to claim 9 or 10, characterized in that, When the negative electrode active material is at least one of graphite and hard carbon, the fluorination includes at least one of gas-phase fluorination and plasma fluorination.

12. The preparation method according to claim 10, characterized in that, When the negative electrode active material is silicon-based, the fluorination includes plasma fluorination.

13. The preparation method according to claim 11, characterized in that, The time t for gas-phase fluorination satisfies: 30s≤t≤10h; optionally, 5h≤t≤10h.

14. A battery, characterized in that, include: The battery cell according to any one of claims 1-6, and / or the battery cell obtained by the preparation method according to any one of claims 7-13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 14.

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