Secondary battery and electric equipment

Abstract

The invention discloses a battery monomer, a secondary battery and electric equipment, and belongs to the technical field of secondary batteries. The graphite material with higher first effect and ID / IG value of 0.06-0.25 and the silicon-based material are matched to serve as the negative electrode active material, so that the negative electrode plate can still keep higher first effect on the basis of adding the silicon-based material, and further can be matched with the positive electrode active material lithium-containing phosphate with high first effect (generally, the first effect is not less than 94%); on the premise of fully exerting the characteristic of high first effect of the lithium-containing phosphate, the energy density of the whole battery monomer is improved, and the effect of considering the energy density and the first effect of the battery is achieved. Meanwhile, the lithium intercalation gram capacity of the silicon-based material is controlled to be 1000mAh / g to 2300mAh / g, so that the negative pole piece has relatively high energy density under the condition that the negative active material layer is relatively thin, and further the energy density and the rate capability can be considered.

Description

Technical Field

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

[0002] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their energy density has received increasing attention. Graphite is the most commonly used negative electrode active material in rechargeable batteries, but its theoretical specific capacity is only 372 mAh / g, leaving very limited room for energy density improvement. Silicon-based materials have a theoretical specific capacity as high as 4200 mAh / g, making them the most promising negative electrode active materials. However, silicon-based materials have a relatively low initial efficiency, and are generally not used in combination with high-efficiency positive electrode active materials such as lithium iron phosphate to improve battery energy density. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery and electrical device that overcomes the technical bias that silicon-based materials with low initial efficiency cannot be paired with positive electrode active materials with high initial efficiency to improve battery energy density.

[0004] In one aspect, this application provides a secondary battery, wherein the battery cell includes a positive electrode and a negative electrode;

[0005] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is attached to the positive current collector. The positive active material layer includes a positive active material, which includes a lithium phosphate.

[0006] The negative electrode sheet includes a negative current collector and a negative active material layer, wherein the negative active material layer is attached to the negative current collector; the negative active material layer includes a negative active material, which includes graphite material and silicon-based material, wherein the graphite material includes a first graphite, the first graphite having an ID / IG value of 0.06 to 0.25, and the silicon-based material having a lithium intercalation capacity of 1000 mAh / g to 2300 mAh / g.

[0007] In the technical solution of this application embodiment, graphite materials with an ID / IG value of 0.06 to 0.25 have high initial efficiency. By combining them with silicon-based materials as negative electrode active materials, the negative electrode sheet can maintain a high initial efficiency even with the addition of silicon-based materials. This allows for the combination with high-efficiency positive electrode active materials containing lithium phosphate (typically with an initial efficiency of not less than 94%). While fully utilizing the high initial efficiency of lithium phosphate, the energy density of the entire battery cell is improved, achieving a balance between battery energy density and initial efficiency. Simultaneously, by controlling the lithium intercalation capacity of the silicon-based material to be 1000 mAh / g to 2300 mAh / g, the negative electrode active material layer can be made relatively thin while still achieving a high energy density, thus balancing energy density and rate performance.

[0008] In some embodiments, the ID / IG value of the first graphite is 0.06 to 0.10.

[0009] In the above implementation process, graphite materials with an ID / IG value of 0.06 to 0.10 have higher initial efficiency. By combining them with silicon-based materials as negative electrode active materials, the negative electrode sheet can maintain a higher initial efficiency even with the addition of silicon-based materials.

[0010] In some embodiments, the first graphite accounts for not less than 50% of the mass of the graphite material.

[0011] In the above implementation process, the higher the proportion of the first graphite in the graphite material, the better it is to improve the first efficiency of the negative electrode sheet. By controlling the proportion of the first graphite in the graphite material to be no less than 50%, the negative electrode sheet can have a high first efficiency, which can then be matched with a positive electrode active material with a high first efficiency to improve the energy density of the entire battery cell.

[0012] In some embodiments, the first graphite accounts for not less than 70% of the mass of the graphite material.

[0013] In the above implementation process, by controlling the proportion of the first graphite in the graphite material to be no less than 70%, the negative electrode sheet has a higher initial efficiency, which can then be matched with a positive electrode active material with a higher initial efficiency to improve the energy density of the entire battery cell.

[0014] In some embodiments, the true density of the first graphite is 2.225 g / cm³. 3 ~2.245g / cm 3 ; and / or

[0015] The compacted density of the first graphite under a pressure of 1.5t is 1.5 g / cm³. 3 ~1.8g / cm 3 ; and / or

[0016] The first-efficiency of the first graphite is 94.6% to 96.2%.

[0017] In some embodiments, the lithium intercalation capacity of the negative electrode active material layer is 370 mAh / g to 700 mAh / g.

[0018] In the above implementation process, the lithium intercalation capacity of the negative electrode active material layer is generally positively correlated with the amount of silicon-based material used. A larger lithium intercalation capacity requires a larger amount of silicon-based material, which is more conducive to improving the overall energy density of the battery cell. Conversely, a smaller lithium intercalation capacity requires a smaller amount of silicon-based material, which is more conducive to the first-time efficiency of the battery cell. Controlling the lithium intercalation capacity of the negative electrode active material layer to 370 mAh / g to 700 mAh / g is beneficial for balancing the energy density and first-time efficiency of the battery cell. Simultaneously, due to the introduction of silicon, a good capacity can be maintained even with a relatively thin positive electrode active material layer, thus enabling capacity matching with the positive electrode sheet.

[0019] In some embodiments, the lithium intercalation capacity of the negative electrode active material layer is 400 mAh / g to 520 mAh / g.

[0020] In the above implementation process, controlling the lithium intercalation capacity of the negative electrode active material layer to be 400mAh / g to 520mAh / g can better balance the energy density and first efficiency of the battery cell.

[0021] In some embodiments, the mass percentage of silicon in the negative electrode active material is ≤15%.

[0022] In the above implementation process, the greater the amount of silicon-based material used, that is, the greater the mass proportion of silicon, the better it is for improving the energy density of the entire battery cell. Conversely, the smaller the amount of silicon-based material used, that is, the smaller the mass proportion of silicon, the better it is for the initial efficiency of the entire battery cell. Controlling the mass proportion of silicon in the negative electrode active material to 0 < ≤ 15% is beneficial for balancing the energy density and initial efficiency of the battery cell.

[0023] In some embodiments, in the negative electrode active material, the mass percentage of silicon element is ≤5%.

[0024] In the above implementation process, controlling the mass percentage of silicon element in the negative electrode active material to be ≤5% can better balance the energy density and initial efficiency of the battery cell.

[0025] In some embodiments, the thickness of the negative electrode active material layer does not exceed 0.170 μm.

[0026] In the above implementation process, by adding silicon-based materials as negative electrode active materials to the negative electrode active material layer, compared with negative electrode sheets without silicon-based materials, the negative electrode active material layer can be made thinner under the same energy density requirements. The thinner the negative electrode active material layer, the more favorable the ion transport rate, which in turn benefits the rate performance of the battery. By controlling the thickness of the negative electrode active material layer composed of a combination of first graphite and silicon-based materials to not exceed 0.170 μm, it is possible to achieve a balance between the battery's rate performance, energy density, and first-efficiency performance.

[0027] In some embodiments, the silicon-based material includes a silicon-carbon composite material, which includes porous carbon and silicon-containing particles distributed in the pore structure of the porous carbon.

[0028] In some embodiments, the negative electrode active material layer includes a first sublayer and a second sublayer, the first sublayer being disposed between the negative electrode current collector and the second sublayer, and the first graphite being disposed in the first sublayer and / or the second sublayer.

[0029] In some embodiments, the second sublayer comprises a first graphite, wherein the first graphite accounts for not less than 50% of the mass of the second sublayer; and / or

[0030] The first sublayer includes a second graphite, the second graphite having an ID / IG value greater than 0.25, and the second graphite accounting for no less than 50% of the mass of the first sublayer.

[0031] In the above implementation process, controlling the mass ratio of the first graphite in the second sublayer to be no less than 50% is beneficial for maintaining good initial efficiency of the silicon-based negative electrode sheet. Conversely, ensuring the second graphite accounts for no less than 50% of the mass ratio in the first sublayer is beneficial for the rate performance of the negative electrode sheet.

[0032] In some embodiments, the thickness ratio of the first sublayer to the second sublayer is (0.5–1.5):(0.5–1.5); and / or

[0033] The thickness of the first sublayer is 0.04 μm to 0.13 μm; and / or

[0034] The thickness of the second sublayer is 0.04 μm to 0.13 μm.

[0035] In the above implementation process, by controlling the thickness ratio of the first sublayer and the second sublayer to (0.5~1.5):(0.5~1.5), it is beneficial to control the proportion of the first graphite and the second graphite in the entire negative electrode active material layer to a more suitable range, which is beneficial to balance the first efficiency and rate performance of the battery.

[0036] In some embodiments, the ultimate compaction density of the graphite material in the first sublayer is >1.75 g / cm³. 3 ; and / or

[0037] The expansion rate of the graphite material in the second sublayer is <20%.

[0038] In the above implementation process, the ultimate compaction density of the graphite material in the first sublayer is controlled to be >1.75 g / cm³. 3 This is beneficial for increasing the compaction density of the negative electrode sheet. By controlling the expansion rate of the graphite material in the second sublayer to be less than 20%, it is beneficial for reducing the full-fill expansion of the negative electrode sheet.

[0039] In some embodiments, the silicon-based material has a Dv01 > 1 μm; and / or

[0040] The silicon-based material has a Dv50 of 4μm to 12μm; and / or

[0041] The specific surface area of ​​the silicon-based material is <5m². 2 / g; and / or

[0042] The silicon-based material has a first-efficiency of 90%–94% at 2.0V; and / or

[0043] The silicon-based material contains 45% to 60% carbon by mass.

[0044] In some embodiments, the compaction density of the positive electrode active material layer is 2.6 g / cm³. 3 ~3.0g / cm 3 .

[0045] In the above implementation process, the compaction density of the positive electrode active material layer is controlled to be 2.6 g / cm³. 3 ~3.0g / cm 3 In terms of energy density, it can better match the negative electrode sheet containing silicon-based materials, thus forming a battery with higher energy density.

[0046] In some embodiments, the first-efficiency of the lithium phosphate is not less than 94%; and / or

[0047] The compacted density of the lithium phosphate (3t) is 2.7 g / cm³. 3 ~3.1g / cm 3 .

[0048] In the above implementation process, lithium phosphate has a high initial efficiency. It is used as the positive active material of the positive electrode sheet and combined with the negative electrode sheet composed of the first graphite and silicon-based materials as the negative active materials to form a battery cell, so that the battery cell has a high initial efficiency and energy density.

[0049] In some embodiments, the lithium-containing phosphate includes LiMPO4, M includes Fe and non-Fe elements, and the non-Fe elements include one or both of a first doping element and a second doping element, wherein the first doping element is an iron site doping and the second doping element is a phosphorus site doping.

[0050] Optionally, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge;

[0051] Optionally, the first doping element includes at least two of Mn, Ti, V, Ni, Co, and Mg;

[0052] Optionally, the second doping element includes one or more elements selected from B, S, Si, and N;

[0053] Optionally, the lithium phosphate includes Li 1+x Fe 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and R includes one or more elements selected from B, S, Si, and N.

[0054] Optionally, the lithium phosphate includes Li a A e Fe 1-f B f P 1-g C g O 4-n D n ,

[0055] Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W;

[0056] The B includes one or more elements selected from Ti, V, Zr, Mn, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge;

[0057] The C includes one or more elements selected from B, S, Si, and N;

[0058] The D includes one or more elements selected from S, F, Cl, and Br;

[0059] The value of a is selected from the range of 0.9 to 1.1, the value of e is selected from the range of 0.001 to 0.1, the value of f is selected from the range of 0.001 to 0.5, the value of g is selected from the range of 0.001 to 0.1, the value of n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0060] Secondly, this application provides an electrical device that includes the secondary battery provided in the first aspect. Attached Figure Description

[0061] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0062] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0063] Figure 2 This is an exploded structural diagram of a secondary battery provided in some embodiments of this application;

[0064] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0065] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0066] Figure 5 This is a first structural schematic diagram of the negative electrode sheet provided in some embodiments of this application;

[0067] Figure 6 This is a schematic diagram of the second structure of the negative electrode sheet provided in some embodiments of this application;

[0068] Figure 7 This is a flowchart illustrating a method for preparing a negative electrode sheet according to some embodiments of this application.

[0069] The reference numerals in the detailed embodiments are as follows:

[0070] 1000 - Vehicle; 100 - Secondary battery; 200 - Motor; 300 - Controller; 10 - Housing; 11 - Accommodation space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Shell; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Negative electrode sheet; 2311 - Negative current collector; 2312 - Negative active material layer; 2312a - First sublayer; 2312b - Second sublayer; 24 - Current collector component; 25 - Insulation protection component. Detailed Implementation

[0071] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0072] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0073] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0074] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0075] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0076] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0077] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0078] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0079] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0080] Power batteries can be either lithium-ion or sodium-ion rechargeable batteries, which have wide applications in portable electronic devices, electric vehicles, and other fields. Graphite is the most commonly used negative electrode active material for rechargeable batteries, but its theoretical specific capacity is only 372 mAh / g, limiting its potential for energy density improvement. Silicon-based materials, with a theoretical specific capacity as high as 4200 mAh / g, are the most promising negative electrode active materials.

[0081] To improve the energy density of secondary batteries, silicon-based materials are usually added to the negative electrode as negative electrode active materials. However, the initial efficiency of silicon-based materials is relatively low, usually not exceeding 92%, while the initial efficiency of lithium phosphate is usually not less than 94%. When the two are used together, it is difficult to fully utilize the high initial efficiency of lithium phosphate. Therefore, they are not used together with positive electrode active materials with high initial efficiency, such as lithium phosphate, to improve the energy density of the battery.

[0082] Based on the above considerations, in order to overcome the technical bias that silicon-based materials with low initial efficiency cannot be paired with positive electrode active materials with high initial efficiency to improve battery energy density, this application proposes a battery cell, which includes a positive electrode and a negative electrode.

[0083] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is attached to the positive current collector. The positive active material layer includes a positive active material, which includes a lithium phosphate.

[0084] The negative electrode sheet includes a negative current collector and a negative active material layer, wherein the negative active material layer is attached to the negative current collector; the negative active material layer includes a negative active material, which includes graphite material and silicon-based material, wherein the graphite material includes a first graphite, the first graphite having an ID / IG value of 0.06 to 0.25, and the silicon-based material having a lithium intercalation capacity of 1000 mAh / g to 2300 mAh / g.

[0085] Silicon-based materials have relatively low initial efficiency. If used alone as a negative electrode active material or combined with ordinary graphite, it is difficult to match the high initial efficiency of lithium phosphate as a positive electrode active material. Using the two together makes it difficult to fully utilize the high initial efficiency of lithium phosphate. Therefore, it is necessary to introduce graphite materials with high initial efficiency. Graphite materials with an ID / IG value of 0.06 to 0.25 have fewer surface defects and do not consume active lithium, thus having a high initial efficiency. By combining graphite materials with a high initial efficiency (ID / IG value of 0.06 to 0.25) with silicon-based materials as negative electrode active materials, the negative electrode can maintain a high initial efficiency even with the addition of silicon-based materials. This allows for the combination with high-efficiency positive electrode active materials such as lithium phosphate (usually with an initial efficiency of not less than 94%). Under the premise of fully utilizing the high initial efficiency of lithium phosphate, the energy density of the entire battery cell can be improved, achieving a balance between battery energy density and initial efficiency. Meanwhile, by controlling the lithium intercalation capacity of silicon-based materials to be 1000mAh / g to 2300mAh / g, the negative electrode active material layer can be made thinner, so that the negative electrode sheet can have a high energy density, thus achieving a balance between energy density and rate performance.

[0086] The battery cell can be used, but is not limited to, in electrical equipment such as vehicles 1000, ships, or aircraft. The power system of such electrical equipment can be composed of a secondary battery 100 disclosed in this application.

[0087] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0088] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0089] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 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 secondary battery 100 is installed inside the vehicle 1000, and the secondary battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The secondary battery 100 can be used to power the vehicle 1000; for example, the secondary battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0090] In some embodiments of this application, the secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0091] In this application, the secondary battery 100 can refer to a single battery cell 20, or it can refer to a single physical module comprising multiple battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, battery module, etc. The secondary battery 100 may include a housing 10 for encapsulating multiple battery cells 20, and the housing 10 can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells 20.

[0092] Figure 2 This is an exploded structural diagram of a secondary battery 100 provided in some embodiments of this application. Please refer to... Figure 2The secondary battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0093] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0094] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2 As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0095] In the secondary battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed configuration to form a whole assembly, which is then housed in the housing 10. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0096] In some embodiments, the secondary battery 100 may further include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0097] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... Figure 3 and Figure 4The battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0098] The shape of the outer casing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the outer casing 21 can be a cuboid structure. Figure 3 and Figure 4 An example is shown where the housing 21 and electrode assembly 23 are square.

[0099] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0100] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0101] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used to electrically connect to the negative electrode plate 231 of the electrode assembly 23.

[0102] In some embodiments, such as Figure 4As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23.

[0103] The electrode assembly 23 includes a positive electrode plate, a negative electrode plate 231, and a separator. The electrode assembly 23 can be a wound electrode assembly or a stacked electrode assembly, and the embodiments of this application are not limited thereto.

[0104] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector. The positive current collector without the positive active material layer protrudes from the positive current collector with the positive active material layer. The positive current collector without the positive active material layer serves as the positive electrode tab.

[0105] 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.).

[0106] In some embodiments, when the secondary battery 100 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials 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 LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At 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.

[0107] In some embodiments, when the secondary battery 100 is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries. As examples, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds may be used. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0108] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x M02, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0109] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (Y04). n- The price state.

[0110] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0111] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) n+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (Y04). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) n+ The valence state; the halogen can be at least one of F, Cl and Br.

[0112] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0113] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6 where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0114] In some embodiments, the positive electrode active material 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.

[0115] In some embodiments, the positive electrode active material layer 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.

[0116] 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.

[0117] The negative electrode sheet 231 includes a negative electrode current collector 2311 and a negative electrode active material layer 2312. The negative electrode active material layer 2312 is coated on the surface of the negative electrode current collector 2311. The negative electrode current collector 2311 without the negative electrode active material layer 2312 is protruding from the negative electrode current collector 2311 with the negative electrode active material layer 2312 coated. The negative electrode current collector 2311 without the negative electrode active material layer 2312 is used as a negative electrode tab.

[0118] In some embodiments, the negative electrode current collector 2311 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the negative electrode active material layer 2312 includes a negative electrode active material, which may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0120] In some embodiments, the negative electrode active material layer 2312 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).

[0121] In some embodiments, the negative electrode active material layer 2312 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.

[0122] In some embodiments, the negative electrode active material layer 2312 may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, the negative electrode 231 can be prepared by dispersing the components used to prepare the negative electrode 231, such as 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 2311, and after drying, cold pressing and other processes, the negative electrode 231 can be obtained.

[0124] In some implementations, in order to ensure that a large current can pass through without melting, there are multiple positive electrode tabs stacked together, and multiple negative electrode tabs stacked together.

[0125] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0126] 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.

[0127] The electrolyte acts as a conductor of ions between the positive and negative electrode plates 231. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0128] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] This application provides a battery cell 20, which includes a positive electrode sheet and a negative electrode sheet 231. The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is attached to the positive current collector and includes a positive active material, which includes a lithium phosphate. Figure 5 This is a first structural schematic diagram of the negative electrode 231 provided in some embodiments of this application. Figure 6 Schematic diagram of the second structure of the negative electrode 231 provided in some embodiments of this application Figure 2 Please see Figure 5 and Figure 6 The negative electrode 231 includes a negative current collector 2311 and a negative active material layer 2312, the negative active material layer 2312 being attached to the negative current collector 2311; the negative active material layer 2312 includes a negative active material, the negative active material including graphite material and silicon-based material, the graphite material including first graphite, the first graphite having an ID / IG value of 0.06 to 0.25, and the silicon-based material having a lithium intercalation capacity of 1000 mAh / g to 2300 mAh / g.

[0133] The positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] Lithium-containing phosphates have high initial efficiency and can be lithium iron phosphate materials, specifically lithium iron phosphate, lithium manganese iron phosphate, etc.

[0135] The negative electrode current collector 2311 can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). Please continue reading. Figure 5 In one embodiment, a negative electrode active material layer 2312 is sequentially disposed on one surface of the negative electrode current collector 2311; please continue reading Figure 6 In another embodiment, a negative electrode active material layer 2312 is provided on both surfaces of the negative electrode current collector 2311.

[0136] Graphite is an allotrope composed of carbon atoms, and its crystal structure is layered. Each layer consists of parallel carbon atoms arranged in a hexagonal structure.

[0137] Silicon-based materials include, but are not limited to, elemental silicon and silicon oxides (e.g., SiO2). xThe silicon-based material is selected from one or more of the following: 0 < x ≤ 2, silicon-carbon compounds (e.g., coated structures, embedded structures), and silicon alloys. In some embodiments, the silicon-based material may also be doped with one or two elements selected from lithium and magnesium. This application does not impose any particular limitation on the method of doping lithium and magnesium into the silicon-based material; for example, electrochemical deposition can be used. Exemplarily, the preparation process of the silicon-carbon compound can be as follows: Step 1: Weigh 500g of porous carbon and place it in a reactor (rotary kiln or fluidized bed), heat it to 500°C under argon protection, and hold it at that temperature for 2 hours to allow the air adsorbed within the porous carbon to be fully desorbed. Step 2: Introduce a mixed gas of silane and argon (silane to argon volume ratio 1:4) into the rotary kiln at a flow rate of 4L / min, maintain a slight positive pressure of 200Pa, and rotate the rotary kiln at a rotation frequency of 20Hz to obtain silicon-carbon particles. Step 3: Heat the rotary kiln to 600℃, introduce a mixture of acetylene and argon gas at a flow rate of 3L / min, and rotate the kiln at a frequency of 20Hz to coat the silicon carbide particles. Finally, after natural cooling, pass the mixture through a 200-mesh sieve to obtain silicon carbide compounds.

[0138] The ID / IG value has a well-known meaning in the art and can be determined using instruments and methods known in the art, such as the JJF1544-2015 standard, using a Raman spectrometer, such as the inVia Qontor type Raman spectrometer. The D and G peaks represent the lattice defects of carbon atoms and the in-plane stretching vibrations of sp2 hybridization of carbon atoms, respectively. ID and IG are the intensities of the two peaks. The ID / IG value is used to characterize the degree of defect in carbon materials; a larger ratio indicates a higher degree of defect. Graphite materials with an ID / IG value of 0.06–0.25 have high first-efficiency. Generally, uncoated graphite or graphite with only partially co-coated carbon areas has an ID / IG value of 0.06–0.25.

[0139] The battery cell 20 uses graphite material with an ID / IG value of 0.06 to 0.25 and silicon-based material as the negative electrode active material. This allows the negative electrode sheet 231 to maintain a high initial efficiency even with the addition of silicon-based material. This, in turn, allows for the combination with a positive electrode active material that also has a high initial efficiency, thus improving the overall energy density of the battery cell 20 and achieving a balance between energy density and initial efficiency. Simultaneously, by controlling the lithium intercalation capacity of the silicon-based material to be between 1000 mAh / g and 2300 mAh / g, the negative electrode sheet can achieve a high energy density even with a relatively thin negative electrode active material layer, thereby balancing energy density and rate performance.

[0140] In the technical solution of this application embodiment, the ID / IG value of the first graphite is 0.06 to 0.10. Graphite materials with an ID / IG value of 0.06 to 0.10 have higher initial efficiency. By combining it with silicon-based materials as negative electrode active materials, the negative electrode 231 can maintain higher initial efficiency even with the addition of silicon-based materials.

[0141] For example, the ID / IG value of the first graphite can be 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24 or 0.25, etc., or it can be any value in the range of 0.06 to 0.25.

[0142] In the technical solution of this application embodiment, the mass proportion of the first graphite in the graphite material is not less than 50%. The larger the proportion of the first graphite in the graphite material, the more beneficial it is to improve the first-time efficiency of the negative electrode 231. By controlling the proportion of the first graphite in the graphite material to be not less than 50%, the negative electrode 231 has a higher first-time efficiency, which can then be combined with a positive electrode active material with a higher first-time efficiency to improve the energy density of the entire battery cell 20.

[0143] Optionally, the first graphite accounts for no less than 70% of the mass of the graphite material. By controlling the proportion of the first graphite in the graphite material to be no less than 70%, the negative electrode 231 has a higher initial efficiency, which can then be combined with a positive electrode active material with a higher initial efficiency to improve the energy density of the entire battery cell 20.

[0144] For example, the mass percentage of the first graphite in the graphite material can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc., or it can be any value within the range of not less than 50%.

[0145] In the technical solution of this application embodiment, the true density of the first graphite is 2.225 g / cm³. 3 ~2.245g / cm 3 .

[0146] True density refers to the actual mass of a unit volume of solid material in each negative electrode active material layer 2312 under an absolutely dense state, that is, the density after removing internal pores or voids between particles. It can be tested using methods known in the art. As an example, a mass M of the analyte is weighed and placed in a true density analyzer (AccuPyc II 1340 analyzer) at room temperature (15℃-25℃). The test system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and expansion chamber, and then calculating the gas volume in the sample chamber and expansion chamber respectively according to the ideal gas law, the difference between the two is obtained to obtain the gas volume displaced by the analyte under certain temperature and pressure conditions, which is the true volume V of the analyte. The true density of the analyte is the mass M of the analyte / the true volume V of the analyte, and the unit of true density is g / cm³. 3 .

[0147] For example, the true density of the first graphite may be 2.225 g / cm³. 3 2.226 g / cm 3 2.227 g / cm 3 2.228 g / cm 3 2.229 g / cm 3 2.230g / cm 3 2.231 g / cm 3 2.232 g / cm 3 2.233 g / cm 3 2.234 g / cm 3 2.235g / cm 3 2.236 g / cm 3 2.237 g / cm 3 2.238 g / cm 3 2.239 g / cm 3 2.240 g / cm 3 2.241 g / cm 3 2.242 g / cm 3 2.243 g / cm 3 2.244 g / cm 3 or 2.245 g / cm 3 , etc., can also be 2.225 g / cm³. 3 ~2.245g / cm 3 Any value within the range.

[0148] Typically, the true density of uncoated graphite or graphite with only partial carbon coating is 2.225 g / cm³. 3 ~2.245g / cm 3 .

[0149] In the technical solution of this application embodiment, the compaction density of the first graphite under a pressure of 1.5t is 1.5g / cm³. 3 ~1.8g / cm 3 .

[0150] Compacted density refers to the mass per unit volume of a powder under specified conditions. It characterizes the compactness and porosity of powder particles. The compacted density of first graphite can be determined using instruments and methods known in the art, such as referring to GB / T24533-2009 standard, using an electronic pressure testing machine, such as the UTM7305 electronic pressure testing machine. Accurately weigh approximately 1g of sample and add it to a container with a base area of ​​1.327cm². 2 In the mold, a pressure of 14700N is applied to the sample using a pressurizing device and held at this pressure for 30 seconds before the pressure is released. The height of the sample is then measured, and the compacted density of the material can be obtained using the formula ρ = m / (1.327 × h). In this formula, ρ represents the compacted density of the material, m represents the mass of the sample, and h represents the height of the sample after the 14700N pressure is applied and held for 30 seconds before the pressure is released.

[0151] For example, the compaction density of the first graphite under a pressure of 1.5t can be 1.5 g / cm³. 3 1.56g / cm 3 1.565g / cm 3 1.57g / cm 3 1.575g / cm 3 1.58g / cm 3 1.585g / cm 3 1.59g / cm 3 1.595g / cm 3 1.60g / cm 3 1.605 g / cm 3 1.61 g / cm 3 1.615g / cm 3 1.62g / cm 3 1.625g / cm 3 1.63g / cm 3 1.635g / cm 3 1.638 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.7g / cm 31.71g / cm 3 1.72g / cm 3 1.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 Or 1.8g / cm 3 It can also be 1.5 g / cm³. 3 ~1.8g / cm 3 Any value within the range.

[0152] Typically, the compaction density of uncoated graphite or graphite with only partial carbon coating meets the requirement of 1.5 g / cm³. 3 ~1.8g / cm 3 .

[0153] In the technical solution of this application embodiment, the first efficiency of the first graphite is 94.6% to 96.2%.

[0154] First-cycle efficiency (CEE) refers to the ratio of discharge capacity to charge capacity during the first charge and discharge cycle of a battery. It represents the maximum value of this ratio over the battery's lifetime. The testing process is as follows: Under normal temperature and pressure, the battery is discharged at a constant current rate of 0.1C to 0.005V, then discharged at a constant current rate of 0.04C to 0.005V. After resting for 5 minutes, the discharge capacity is recorded as Q1, which is the first-cycle lithium insertion capacity. Next, the battery is charged at a constant current rate of 0.1C to 2.0V, and then rested for 5 minutes. The charging capacity is recorded as Q2, which is the first-cycle lithium removal capacity. The CEE is calculated using the formula: CEE = Q2 / Q1 * 100%. For testing the CEE of first-strut graphite, first-strut graphite can be used as the active material to prepare an electrode sheet, which is then assembled into a half-cell (i.e., this electrode sheet serves as the positive electrode, and the lithium metal sheet serves as the negative electrode). The above-described CEE testing process is then applied.

[0155] For example, the first effect of the first graphite can be 94.6%, 94.7%, 94.8%, 94.9%, 95%, 95.1%, 95.2%, 95.3%, 95.4%, 95.5%, 95.6%, 95.7%, 95.8%, 95.9%, 96%, 96.1%, or 96.2%, etc., or it can be any value in the range of 94.6% to 96.2%.

[0156] Typically, graphite without carbon coating or with only partial carbon coating achieves a first-efficiency of 94.6% to 96.2%.

[0157] In the technical solution of this application embodiment, the lithium intercalation capacity of the negative electrode active material layer 2312 is 370mAh / g to 700mAh / g.

[0158] For example, the lithium intercalation capacity of the negative electrode active material layer 2312 can be 370mAh / g, 380mAh / g, 390mAh / g, 400mAh / g, 420mAh / g, 440mAh / g, 460mAh / g, 480mAh / g, 500mAh / g, 520mAh / g, 540mAh / g, 560mAh / g, 580mAh / g, 600mAh / g, 620mAh / g, 640mAh / g, 660mAh / g, 680mAh / g, or 700mAh / g, etc., or it can be any value in the range of 370mAh / g to 700mAh / g.

[0159] Lithium intercalation capacity refers to the maximum capacity that lithium ions can intercalate into the negative electrode active material layer 2312 during the charging process of a lithium-ion battery. The testing process is as follows: the negative electrode sheet is punched into small 14nm wafers and assembled with lithium metal sheets and a separator to form a coin cell. At 25℃ and normal pressure, the battery is discharged at a constant current rate of 0.1C to 0.005V, then discharged at a constant current rate of 0.04C to 0.005V. After standing for 5 minutes, the discharge capacity C0 is recorded; C0 is the lithium intercalation capacity.

[0160] The lithium intercalation capacity of the negative electrode active material layer 2312 is generally positively correlated with the amount of silicon-based material used. A larger lithium intercalation capacity of the negative electrode active material layer 2312 allows for a larger amount of silicon-based material, which is more beneficial for improving the energy density of the entire battery cell 20. Conversely, a smaller lithium intercalation capacity of the negative electrode active material layer 2312 allows for a smaller amount of silicon-based material, which is more beneficial for the first-time efficiency of the entire battery cell 20. Controlling the lithium intercalation capacity of the negative electrode active material layer 2312 to 350 mAh / g to 500 mAh / g is beneficial for balancing the energy density and first-time efficiency of the battery cell 20.

[0161] Optionally, the lithium intercalation capacity of the negative electrode active material layer 2312 is 400 mAh / g to 520 mAh / g. Controlling the lithium intercalation capacity of the negative electrode active material layer to 400 mAh / g to 520 mAh / g can better balance the energy density and initial efficiency of the battery cell.

[0162] For example, the lithium intercalation capacity of the negative electrode active material layer 2312 can be 400mAh / g, 410mAh / g, 412mAh / g, 414mAh / g, 416mAh / g, 418mAh / g, 420mAh / g, 422mAh / g, 424mAh / g, 426mAh / g, 428mAh / g, 430mAh / g, 432mAh / g, 434mAh / g, 436mAh / g, 438mAh / g, 440mAh / g, 450mAh / g, 460mAh / g, 470mAh / g, 480mAh / g, 490mAh / g, 500mAh / g, 510mAh / g, or 520mAh / g, etc., or it can be any value in the range of 400mAh / g to 520mAh / g.

[0163] In the technical solution of this application embodiment, the mass percentage of silicon in the negative electrode active material is ≤15% (0 < silicon content). A higher amount of silicon-based material, i.e., a higher mass percentage of silicon, is more beneficial for improving the energy density of the entire battery cell 20. Conversely, a lower amount of silicon-based material, i.e., a lower mass percentage of silicon, is more beneficial for the initial efficiency of the entire battery cell 20. Controlling the mass percentage of silicon in the negative electrode active material to ≤15% is beneficial for balancing the energy density and initial efficiency of the battery cell 20.

[0164] Optionally, in the negative electrode active material, the mass percentage of silicon (0 < 5%) can be ≤ 5%. Controlling the mass percentage of silicon (0 < 5%) in the negative electrode active material can better balance the energy density and initial efficiency of the battery cell.

[0165] For example, in the negative electrode active material, the mass percentage of silicon element can be 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or so, or any value within the range not exceeding 15%.

[0166] In the technical solution of this application embodiment, the thickness of the negative electrode active material layer 2312 does not exceed 0.170 μm. By adding a silicon-based material as the negative electrode active material to the negative electrode active material layer 2312, compared to a negative electrode sheet 231 without silicon-based material, the negative electrode active material layer 2312 can be made thinner under the same energy density requirements. A thinner negative electrode active material layer 2312 is more conducive to ion transport rate, thereby improving the rate performance of the battery. By controlling the thickness of the negative electrode active material layer 2312, which is composed of a combination of first graphite and silicon-based materials as the negative electrode active material, to not exceed 0.170 μm, a balance can be achieved in terms of battery rate performance, energy density, and initial efficiency.

[0167] For example, the thickness of the negative electrode active material layer 2312 can be 0.1μm, 0.11μm, 0.12μm, 0.13μm, 0.14μm, 0.15μm, 0.16μm or 0.17μm, etc., or it can be any value within the range of no more than 0.170μm.

[0168] In the technical solution of this application embodiment, the negative electrode active material layer 2312 includes a first sublayer 2312a and a second sublayer 2312b. The first sublayer 2312a is disposed between the negative electrode current collector 2311 and the second sublayer 2312b, and the first graphite is disposed in the first sublayer 2312a and / or the second sublayer 2312b.

[0169] The first sublayer 2312a and the second sublayer 2312b together constitute the negative electrode active material layer 2312. The first sublayer 2312a is the layer that is in contact with the negative electrode current collector 2311, and the second sublayer 2312b is the layer that is in contact with the surface of the first sublayer 2312a that is away from the negative electrode current collector 2311.

[0170] The first graphite being disposed in the first sublayer 2312a and / or the second sublayer 2312b means that: only the first sublayer 2312a contains the first graphite, or only the second sublayer 2312b contains the first graphite, or both the first sublayer 2312a and the second sublayer 2312b contain the first graphite.

[0171] In the technical solution of this application embodiment, the second sub-layer 2312b includes a first graphite, and the mass proportion of the first graphite in the second sub-layer 2312b is not less than 50%. By controlling the mass proportion of the first graphite in the second sub-layer 2312b to be not less than 50%, it is beneficial for the silicon-based negative electrode 231 to maintain a good initial efficiency.

[0172] For example, the mass percentage of the first graphite in the second sublayer 2312b can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc., or it can be any value within the range of not less than 50%.

[0173] In the technical solution of this application embodiment, the first sub-layer 2312a includes a second graphite, the second graphite having an ID / IG value greater than 0.25, and the second graphite accounting for not less than 50% of the mass of the first sub-layer 2312a. Having the second graphite accounting for not less than 50% of the mass of the first sub-layer 2312a is beneficial to the rate performance of the negative electrode 231. Typically, graphite with good carbon coating or graphite with complete carbon coating has an ID / IG value greater than 0.25.

[0174] For example, the mass percentage of the second graphite in the first sublayer 2312a can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, etc., or it can be any value within the range of not less than 50%.

[0175] In the technical solution of this application embodiment, the thickness ratio of the first sublayer 2312a to the second sublayer 2312b is (0.5~1.5):(0.5~1.5). Further, the thickness of the first sublayer is 0.04μm~0.13μm; the thickness of the second sublayer is 0.04μm~0.13μm. The thickness of the first sublayer 2312a and the second sublayer 2312b can be obtained by cross-sectional electrolytic scanning of the negative electrode sheet 231. By controlling the thickness ratio of the first sublayer 2312a to the second sublayer 2312b to (0.5~1.5):(0.5~1.5), it is beneficial to control the proportion of the first graphite and the second graphite in the entire negative electrode active material layer 2312 to a more suitable range, thereby balancing the initial efficiency and rate performance of the battery.

[0176] For example, the thickness ratio of the first sublayer 2312a and the second sublayer 2312b can be 0.5:1, 0.5:1.5, 1:0.5, 1:1, 1:1.5, 1.5:0.5 or 1.5:1, etc., or it can be any value in the range of (0.5 to 1.5): (0.5 to 1.5).

[0177] In the technical solution of this application embodiment, the ultimate compaction density of the graphite material in the first sublayer 2312a is >1.75 g / cm³. 3 .

[0178] Ultimate compaction density refers to the maximum compaction density that a material can withstand in its layer, reflecting its compressive strength to some extent. The test method for ultimate compaction density is as follows: First, a small compaction density is achieved by roller pressing, specifying the position and angle of the crease. Then, a fixed pressure is applied for flat pressing. The creases on the electrode are then observed. Finally, when the compaction density reaches a certain value, the electrode breaks or develops light-transmitting holes. The highest compaction density at which no breakage or light-transmitting holes occur is the ultimate compaction density.

[0179] By controlling the ultimate compaction density of the graphite material in the first sublayer 2312a to be >1.75 g / cm³ 3 This is beneficial for increasing the compaction density of the negative electrode sheet 231.

[0180] For example, the ultimate compaction density of the graphite material in the first sublayer 2312a can be 1.76 g / cm³. 3 1.77g / cm 3 1.78g / cm3 1.79g / cm 3 1.8g / cm 3 1.81 g / cm 3 1.82g / cm 3 1.83g / cm 3 1.84 g / cm 3 1.85g / cm 3 1.86 g / cm 3 1.87 g / cm 3 1.88g / cm 3 1.89 g / cm 3 Or 1.9g / cm 3 etc., it can also be >1.75g / cm 3 Any value within the range.

[0181] In the technical solution of this application embodiment, the expansion rate of the graphite material in the second sublayer 2312b is <20%.

[0182] The expansion rate test can be performed as follows: graphite material is used as the active material to prepare an electrode sheet, and the thickness of the electrode sheet is measured using a micrometer. The micrometer needs to be calibrated and zeroed before the test. The thickness of the electrode sheet after cold pressing is D1, and the thickness of the anode electrode sheet under full charge is D2. The expansion rate is calculated as (D2-D1) / D1*100%.

[0183] By controlling the expansion rate of the graphite material in the second sublayer 2312b to be less than 20%, it is beneficial to reduce the full-charge expansion of the negative electrode 231.

[0184] For example, the expansion rate of the graphite material in the second sublayer 2312b can be 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, or 20%, etc., or it can be any value in the range of <20%.

[0185] In the technical solution of this application embodiment, the Dv01 of the silicon-based material is greater than 1 μm; the Dv50 of the silicon-based material is 4 μm to 12 μm; and the specific surface area of ​​the silicon-based material is less than 5 m². 2 / g; the lithium intercalation capacity of the silicon-based material is 1000mAh / g to 2300mAh / g; the first-efficiency of the silicon-based material at 2.0V is 90% to 94%; the carbon content in the silicon-based material is 45% to 60% by mass.

[0186] Dv01 and Dv50 represent the particle sizes corresponding to 1% and 50% of the cumulative volumetric particle size distribution. The cumulative volumetric particle size distribution, also known as the differential particle size distribution, is a curve plotted with particle size on the x-axis and the differential distribution of particle size at different dimensions on the y-axis. It accurately reflects the particle size distribution characteristics of the material. A laser particle size analyzer can be used to determine the volumetric particle size distribution of the material and plot the interval particle size distribution curve. When measuring the particle size of the negative electrode active material in the active material layer of the electrode sheet, the negative electrode active material layer 2312 can be removed, immersed in the solvent NMP, and the binder in the negative electrode active material layer 2312 can be washed out to obtain the powder material of the negative electrode active material layer 2312. After drying the powder material, a Mastersizer3000 laser particle size analyzer is used to detect the cumulative volumetric particle size distribution. The peaks in the cumulative volumetric particle size distribution can be used to determine the Dv01 and Dv50 of the silicon-based material.

[0187] The specific surface area of ​​a material is a well-known concept in the art and can be measured using instruments and methods known in the art. For example, referring to GB / T 19587-2017 standard for determining the specific surface area of ​​solid substances by gas adsorption BET method, the nitrogen adsorption specific surface area analysis test method is used, and the result is calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0188] The first-efficiency test of silicon-based materials can be performed by preparing silicon-based materials as active materials into electrodes and assembling them into half-cells (i.e., the electrodes are used as positive electrodes and lithium metal sheets are used as negative electrodes), and then the first-efficiency test process described above can be used for testing.

[0189] The elemental content has a well-known meaning in the art and can be tested using methods known in the art. The carbon content in silicon-based materials can be tested according to GB / T 20123-2006 / ISO 15350:2000, and the testing instrument can be an HCS-140 infrared carbon-sulfur analyzer.

[0190] In the technical solution of this application embodiment, the compaction density of the positive electrode active material layer is 2.6 g / cm³. 3 ~3.0g / cm 3 By controlling the compaction density of the positive electrode active material layer to 2.6 g / cm³, 3 ~3.0g / cm 3 In terms of energy density, it can better match the negative electrode sheet containing silicon-based materials, thus forming a battery with higher energy density.

[0191] For example, the compaction density of the positive electrode active material layer can be 2.6 g / cm³. 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 2.85g / cm 3 2.9g / cm 3 2.95g / cm 3 Or 3.0g / cm 3 It can also be 2.6 g / cm³. 3 ~3.0g / cm 3 Any value within the range.

[0192] In the technical solution of this application embodiment, the first-efficiency of the lithium phosphate is not less than 94%. The first-efficiency test of the lithium phosphate can be carried out by preparing the lithium phosphate as an active material into an electrode, assembling it into a half cell (i.e., the electrode is used as the positive electrode and the lithium metal sheet is used as the negative electrode), and then testing is carried out using the above-mentioned first-efficiency test process.

[0193] In the technical solution of this application embodiment, the compacted density of the 3t lithium phosphate is 2.7g / cm³. 3 ~3.1g / cm 3 .

[0194] For example, the compacted density of 3 tons of lithium phosphate can be 2.7 g / cm³. 3 2.75g / cm 3 2.8g / cm 3 2.85g / cm 3 2.9g / cm 3 2.95g / cm 3 3.0g / cm 3 3.05g / cm 3 Or 3.1g / cm 3 It can also be 2.7 g / cm³. 3 ~3.1g / cm 3 Any value within the range.

[0195] In the technical solution of this application embodiment, the lithium phosphate includes LiMPO4, and M includes Fe and non-Fe elements.

[0196] It should be noted that the above LiMPO4 is not a specific molecular structure formula, but a general expression of lithium iron phosphate.

[0197] In some embodiments of this application, the non-Fe element includes one or both of a first doping element and a second doping element, wherein the first doping element is an iron site doping element and the second doping element is a phosphorus site doping element.

[0198] In some embodiments of this application, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0199] In some embodiments of this application, the first doping element includes at least two of Mn, Ti, V, Ni, Co, and Mg.

[0200] In some embodiments of this application, the second doping element includes one or more elements selected from B, S, Si, and N.

[0201] In some embodiments of this application, the lithium phosphate includes Li 1+x Fe 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0202] In some embodiments of the technical solutions of this application, the compound Li 1+x Fe 1-y A y P 1-z R z The method for preparing O4 may include the following steps:

[0203] (1) Dissolve and stir the iron source, the iron site doped element A source and acid in a solvent to generate a suspension of iron salt doped with element A. Filter the suspension and dry the filter cake to obtain iron salt doped with element A.

[0204] (2) The lithium source, phosphorus source, element R source, solvent and iron salt doped with element A obtained in step (1) are added to the reaction vessel, ground and mixed to obtain a slurry;

[0205] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0206] (4) The particles obtained in step (3) are sintered to obtain the positive electrode active material.

[0207] In any embodiment, the iron source may be an iron-containing substance known in the art that can be used to prepare lithium iron phosphate, such as one or a combination of elemental iron, ferrous oxide, ferric phosphate, ferric oxalate, and ferric carbonate.

[0208] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0209] In some embodiments of this application, the lithium phosphate includes Li a A e Fe 1-f B f P 1-g C g O 4-n D n The positive electrode active material is electrically neutral. Specifically, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Mn, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; e is selected from the range of 0.001 to 0.1; f is selected from the range of 0.001 to 0.5; g is selected from the range of 0.001 to 0.1; n is selected from the range of 0.001 to 0.1.

[0210] It should be noted that Li a A e Fe 1-f B f P 1-g C g O 4-n D n The compound is actually a specific LiMPO4 material. Its preparation method can be found in the Li... 1+x Fe 1-y A y P 1-z R z O4 is not specified here.

[0211] The following uses Li 0.994 Mo 0.001 Mn 0.65Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 The preparation process is further explained as follows: 1. Preparation of doped material: 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), resulting in a doped suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain the median particle size Dv. 50 The doped particles are approximately 100 nm in size. 2. Preparation of Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 1 mol of the above-mentioned doped particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0212] In some embodiments of this application, the lithium phosphate also has a carbon-containing coating layer.

[0213] The conductivity of lithium phosphates is improved by introducing a carbon-containing coating. In this case, the structure of the lithium phosphate is actually a core-shell structure with a LiMPO4 core and a coating layer on the surface of the core.

[0214] In the enumeration of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, that is, the state before feeding. When the positive electrode material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0215] Furthermore, due to differences in material preparation processes and conditions, the molar content of oxygen is usually not strictly the same as the coefficient of oxygen in the chemical formula, and fluctuations may occur. For example, in Li... 1+x Fe 1-y A y P 1-z R z The molar content of O in O4 is not strictly 4.

[0216] It should be noted that the above list of positive electrode active materials is merely an illustrative example to illustrate the feasibility of this solution and is not intended to limit the solution. The implementation of this solution only requires the positive electrode active material to meet the corresponding first-efficiency requirement. In other embodiments, those skilled in the art can select specific substances of the positive electrode active material according to actual needs, such as the materials listed above and their modified forms, where modification includes doping or coating, or select other materials that meet the first-efficiency requirement of this application.

[0217] For example, lithium phosphates can be LiFePO4 or LiMn. 0.1 Fe 0.9 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.9 Fe 0.1 In LiMPO4, M includes both Fe and non-Fe elements. The non-Fe elements include one or both of a first dopant and a second dopant. The first dopant is an iron-site dopant, and the second dopant is a phosphorus-site dopant. The first dopant includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge. The second dopant includes one or more of B, S, Si, and N.

[0218] Having introduced the materials and structure of the negative electrode 231, the preparation method of the negative electrode 231 will be described in detail below.

[0219] The preparation method of the negative electrode 231 includes the following steps: preparing a slurry by combining a first graphite and a silicon-based material and optionally adding other negative electrode active materials, coating the slurry onto the negative electrode current collector 2311 to prepare a negative electrode active material layer 2312, wherein the ID / IG value of the first graphite is 0.06 to 0.25.

[0220] This method combines graphite materials with high initial efficiency (ID / IG value of 0.06 to 0.25) with silicon-based materials as negative electrode active materials, enabling the negative electrode 231 to maintain high initial efficiency even with the addition of silicon-based materials. This allows it to be combined with positive electrode active materials with high initial efficiency to improve the energy density of the entire battery cell 20, achieving a balance between battery energy density and initial efficiency.

[0221] Figure 7 For flowcharts illustrating the preparation method of the negative electrode 231 provided in some embodiments of this application, please refer to [link / reference]. Figure 7 This application provides a method for preparing a negative electrode sheet 231, the method comprising:

[0222] S110, Preparation of the first slurry: The first graphite, silicon-based material, binder and conductive agent are dispersed in a solvent to form the first slurry.

[0223] The binder can be one or more of styrene-butadiene rubber, waterborne acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polyvinyl butyral. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, graphene, or acetylene black. The solvent can be one or more of dimethyl glutarate and N-methylpyrrolidone. Leveling agents, dispersants, etc., may also be added to the first slurry.

[0224] S120, Preparation of the second slurry: The second graphite, silicon-based material, binder and conductive agent are dispersed in a solvent to form the second slurry.

[0225] The binder, conductive agent, and solvent can be the same as those in the first positive electrode active slurry. The binder in the first positive electrode active slurry can be the same as or different from the binder in the second positive electrode active material; the conductive agent in the first positive electrode active slurry can be the same as or different from the conductive agent in the second positive electrode active material; and the solvent in the first positive electrode active slurry can be the same as or different from the solvent in the second positive electrode active material. Furthermore, leveling agents, dispersants, etc., can also be added to the second positive electrode active slurry; this application does not impose any limitations on this.

[0226] S130, Preparation of the first sublayer 2312a: The first slurry is coated on the surface of the negative electrode current collector 2311 and then dried to form the first sublayer 2312a. During coating, the slurry can be applied to one or both surfaces of the negative electrode current collector 2311 as needed.

[0227] The coating method can be, for example, scraping, roller coating, or slot coating; this application does not limit the method. It should be noted that steps S120 and S130 can be interchanged or performed simultaneously; this application does not limit the method.

[0228] S140, Preparation of the second sublayer 2312b: The second slurry is coated onto the surface of the first sublayer 2312a and then dried to form the second sublayer 2312b. During coating, the second sublayer 2312b can be formed on the surface of the first sublayer 2312a, depending on the condition of the first sublayer 2312a.

[0229] S150, roll-press the second sub-layer 2312b to obtain the negative electrode sheet 231.

[0230] After the negative electrode 231 is prepared, the first separator, the positive electrode, the second separator and the negative electrode 231 are stacked in sequence, wound to form a wound flat structure, and then hot-pressed to obtain the wound electrode assembly 23; or, after the negative electrode 231 is prepared, the positive electrode, the separator, the negative electrode 231 and the separator are stacked in sequence to form the stacked electrode assembly 23.

[0231] The electrode assembly 23 can be used to prepare a battery cell 20, which can be used to prepare a secondary battery 100 and provide electrical energy to electrical devices.

[0232] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0233] Examples and Comparative Examples

[0234] Preparation of the positive electrode sheet

[0235] Lithium iron phosphate, carbon black, and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1:2.5 and stirred to obtain a coating slurry. The slurry was then uniformly coated onto the positive current collector, dried, rolled, and then die-cut to obtain the positive electrode sheet.

[0236] Preparation of the negative electrode sheet

[0237] Preparation of the first sublayer: The negative electrode active material, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare the first slurry; the first slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried to obtain the first sublayer;

[0238] Preparation of the second sublayer: The negative electrode active material, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare the second slurry; the second slurry is uniformly coated on the first sublayer once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0239] It should be noted that if a first sublayer is not present in a certain embodiment or comparative example, the second sublayer is directly prepared on the negative electrode current collector 2311. If a second sublayer is not present in a certain embodiment or comparative example, the preparation of the second sublayer is not performed.

[0240] Preparation of Electrolyte

[0241] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a mass ratio of 3 / 7. 1 mol / L LiPF6 lithium salt is added and dispersed evenly. Then, 2 wt% fluoroethylene carbonate is dissolved in the above organic solvent and stirred evenly to obtain the electrolyte.

[0242]

Isolation Film

[0243] Polypropylene film is used as the separator.

[0244] [Preparation of Lithium-ion Batteries]

[0245] The positive electrode, separator, and negative electrode 231 are stacked in sequence, with the separator positioned between the positive and negative electrode 231 to provide isolation. The resulting battery cell is then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain a lithium-ion battery product with a volume of 0.411L.

[0246] The main parameter controls for each embodiment and comparative example are shown in the table below:

[0247]

[0248]

[0249] It should be noted that the lithium intercalation capacity of the silicon-based materials used in each embodiment and comparative example is 1540 mAh / g.

[0250] The lithium-ion batteries provided in each embodiment and comparative example were tested, including:

[0251] First-time efficiency and volumetric energy density tests: The battery was placed in a negative pressure environment at 45℃ for 20 minutes and then charged at a rate of 0.05C to 20% SOC (the theoretical cell capacity C can be calculated based on the cathode size after winding) to obtain the formation capacity C0. The battery was then left to stand at 45℃ for 48 hours before being transferred to room temperature and pressure and charged at a rate of 0.2C to 3.65V. It was then charged at a constant voltage of 3.65V to 0.05C to obtain the charging capacity C1. Finally, it was discharged at a rate of 0.1C to 2V at room temperature and pressure to obtain the discharge capacity C2, and the discharge energy E (Wh) was also obtained. The first-time efficiency is obtained using the formula: First-time efficiency = C2 ÷ (C0 + C1) * 100%. The volumetric energy density is obtained using the formula: Cell volumetric energy density = E ÷ 0.411L.

[0252] Rate performance test (fast charging performance): After placing the battery in a 25℃ environment for 30 minutes, discharge it to 2.0V using a 0.33C rate, let it rest for 5 minutes, and then charge it to 3.8V using a 2C rate. Calculate the charging capacity retention rate at the 2C rate as C3. The rate performance result is calculated as C3 / (C0+C1)*100%.

[0253] 1000-cycle capacity retention: At 45℃, the battery is charged at a constant current rate of 0.5C to 4.5V, then charged at a constant voltage rate to a current of 0.05C, and then discharged at a constant current rate of 0.5C to 3.0V. This charging / discharging process is repeated, and the capacity retention rate of the battery after 1000 cycles is calculated.

[0254] The test results are shown in the table below:

[0255]

[0256]

[0257] As can be seen from the table above, the battery provided in this application embodiment has a high initial efficiency, as well as a high volumetric energy density, good rate performance, and high capacity retention.

[0258] A comparison of the data from Examples 1 to 3 shows that as the ID / IG ratio of the first graphite gradually increases, the initial efficiency of the battery gradually deteriorates, while the rate performance of the battery gradually improves. By controlling the ID / IG value of the first graphite in the range of 0.06 to 0.25, the initial efficiency of the battery is above 92%, and the rate performance (2C charging capacity retention rate) is above 93%.

[0259] By comparing the data from Examples 1 and 4 to 6, it can be seen that as the mass ratio of the first graphite in the negative electrode active material layer gradually increases, the initial efficiency of the battery gradually improves, while the rate performance of the battery gradually deteriorates. By controlling the mass ratio of the first graphite in the negative electrode active material layer to be no less than 50%, the initial efficiency of the battery is above 93%, and the rate performance (2C charging capacity retention rate) is above 93%.

[0260] A comparison of the data from Examples 1 and 7 to 9 shows that as the mass percentage of silicon-based material in the negative electrode active material layer gradually decreases, the initial efficiency of the battery gradually improves, the volumetric energy density of the battery gradually decreases, and the cycle capacity retention rate of the battery gradually improves. By controlling the mass percentage of silicon-based material in the negative electrode active material layer to not exceed 30%, the initial efficiency of the battery is above 92.8%, the volumetric energy density is above 440Wh / L, and the cycle capacity retention rate after 1000 cycles is above 91.3%.

[0261] By comparing the data from Examples 1 and 10 to 11, it can be seen that as the thickness of the negative electrode active material layer gradually increases, the volumetric energy density of the battery gradually increases, and the rate performance of the battery gradually deteriorates. By controlling the thickness of the negative electrode active material layer to not exceed 0.17 μm, the rate performance (2C charging capacity retention rate) of the battery is above 93.5%.

[0262] A comparison of the data from Examples 5 and 12-13 shows that the layered arrangement enables the battery to have better initial efficiency. In particular, placing the second graphite on the side closer to the negative electrode current collector enables the battery to have better rate performance.

[0263] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode and a negative electrode; The positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is attached to the positive current collector. The positive active material layer includes a positive active material, which includes a lithium phosphate. The negative electrode sheet includes a negative current collector and a negative active material layer, wherein the negative active material layer is attached to the negative current collector; the negative active material layer includes a negative active material, which includes graphite material and silicon-based material, wherein the graphite material includes a first graphite, the first graphite having an ID / IG value of 0.06 to 0.25, and the silicon-based material having a lithium intercalation capacity of 1000 mAh / g to 2300 mAh / g.

2. The secondary battery according to claim 1, characterized in that, The ID / IG value of the first graphite is 0.06 to 0.

10.

3. The secondary battery according to any one of claims 1 to 2, characterized in that, The first graphite comprises at least 50% of the total mass of the graphite material.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The first graphite comprises at least 70% of the total mass of the graphite material.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The true density of the first graphite is 2.225 g / cm³. 3 ~2.245g / cm 3 ; and / or The compacted density of the first graphite under a pressure of 1.5t is 1.5 g / cm³. 3 ~1.8g / cm 3 ; and / or The first-efficiency of the first graphite is 94.6% to 96.2%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The lithium intercalation capacity of the negative electrode active material layer is 370mAh / g to 700mAh / g.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The lithium intercalation capacity of the negative electrode active material layer is 400mAh / g to 520mAh / g.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, In the negative electrode active material, the mass percentage of silicon element is ≤15%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, In the negative electrode active material, the mass percentage of silicon element is ≤5%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The thickness of the negative electrode active material layer does not exceed 0.170 μm.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The silicon-based material includes a silicon-carbon composite material, which comprises porous carbon and silicon-containing particles distributed in the pore structure of the porous carbon.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The negative electrode active material layer includes a first sublayer and a second sublayer, wherein the first sublayer is disposed between the negative electrode current collector and the second sublayer, and the first graphite is disposed in the first sublayer and / or the second sublayer.

13. The secondary battery according to claim 12, characterized in that, The second sublayer comprises a first graphite, wherein the first graphite constitutes not less than 50% of the mass of the second sublayer; and / or The first sublayer includes a second graphite, the second graphite having an ID / IG value greater than 0.25, and the second graphite accounting for no less than 50% of the mass of the first sublayer.

14. The secondary battery according to any one of claims 12 to 13, characterized in that, The thickness ratio of the first sublayer to the second sublayer is (0.5–1.5):(0.5–1.5); and / or The thickness of the first sublayer is 0.04 μm to 0.13 μm; and / or The thickness of the second sublayer is 0.04 μm to 0.13 μm.

15. The secondary battery according to any one of claims 12 to 14, characterized in that, The ultimate compaction density of the graphite material in the first sublayer is >1.75 g / cm³. 3 ; and / or The expansion rate of the graphite material in the second sublayer is <20%.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The silicon-based material has a Dv01 > 1 μm; and / or The silicon-based material has a Dv50 of 4μm to 12μm; and / or The specific surface area of ​​the silicon-based material is <5m². 2 / g; and / or The silicon-based material has a first-efficiency of 90%–94% at 2.0V; and / or The silicon-based material contains 45% to 60% carbon by mass.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The compaction density of the positive electrode active material layer is 2.6 g / cm³. 3 ~3.0g / cm 3 .

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The first-efficiency of the lithium-containing phosphate is not less than 94%; and / or The compacted density of the lithium phosphate (3t) is 2.7 g / cm³. 3 ~3.1g / cm 3 .

19. The secondary battery according to any one of claims 1 to 18, characterized in that, The lithium-containing phosphate includes LiMPO4, M includes Fe and non-Fe elements, and the non-Fe elements include one or both of a first doping element and a second doping element, wherein the first doping element is an iron site doping and the second doping element is a phosphorus site doping.

20. The secondary battery according to claim 19, characterized in that, The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or The second doping element includes one or more elements selected from B, S, Si, and N.

21. The secondary battery according to claim 19, characterized in that, The lithium-containing phosphate includes Li 1+x Fe 1-y A y P 1- z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

22. The secondary battery according to claim 19, characterized in that, The lithium-containing phosphate includes Li a A e Fe 1- f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; e is selected from the range of 0.001 to 0.1; f is selected from the range of 0.001 to 0.5; g is selected from the range of 0.001 to 0.1; and n is selected from the range of 0.001 to 0.

1.

23. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in any one of claims 1 to 22.

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