Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a negative electrode sheet and a positive electrode sheet. The negative electrode sheet comprises a negative electrode film layer, which comprises artificial graphite having a graphitization degree of greater than 93%. The positive electrode sheet comprises a positive electrode film layer, which comprises a positive electrode active material having a single-crystal-particle morphology. On the basis of the total number of moles of nickel, cobalt and manganese in the chemical formula of the positive electrode active material being 1, the number of moles of nickel in the chemical formula of the positive electrode active material is a, a being 0.6 to 1. The areal density of the negative electrode film layer is σ1, and the areal density of the positive electrode film layer is σ2, where σ1 / σ2 is 0.35 to 0.75. The secondary battery has a low expansion force, good cycling performance and high energy density.

Description

Secondary batteries and electrical appliances

[0001] Cross-referencing

[0002] This application claims priority to Chinese Patent Application No. 202410676285.4, filed on May 29, 2024, entitled “Secondary Battery and Electrical Device”, which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and more particularly to a secondary battery and an electrical device. Background Technology

[0004] In recent years, as the application scope of secondary batteries has become increasingly wide, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0005] With the significant advancements in rechargeable batteries, higher demands have been placed on their cycle performance and energy density. Therefore, finding a rechargeable battery that simultaneously possesses good cycle performance and high energy density is one of the key areas of focus for those skilled in the art.

[0006] Summary of the Invention

[0007] This application is made in view of the above-mentioned problems, and one of its objectives is to provide a secondary battery that has low expansion force, good cycle performance and high energy density.

[0008] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode and a positive electrode.

[0009] The negative electrode sheet includes a negative electrode film layer, the negative electrode film layer contains a negative electrode active material, and the negative electrode active material includes artificial graphite with a graphitization degree >93%.

[0010] The positive electrode sheet includes a positive electrode film layer, which includes a positive electrode active material with a morphology of single crystal particles; taking the total molar number of nickel, cobalt and manganese elements in the chemical formula of the positive electrode active material as 1, the molar number of nickel in the chemical formula of the positive electrode active material is a, where a is 0.6 to 1;

[0011] The areal density of the negative electrode film is σ1, the areal density of the positive electrode film is σ2, and σ1 / σ2 is 0.35 to 0.75.

[0012] In the aforementioned secondary battery, the positive electrode film layer uses a single-crystal high-nickel positive electrode active material, which has a high charge-discharge specific capacity and can effectively improve the battery's energy density. Furthermore, the high-nickel positive electrode active material undergoes lattice contraction at high SOC (State of Charge) levels, which can partially offset the expansion force generated by the negative electrode active material, improving the battery's cycle performance. The negative electrode uses artificial graphite with a graphitization degree >93%, which has a very high charge-discharge specific capacity. Combined with the high-nickel positive electrode active material, this significantly improves the battery's energy density. By combining the single-crystal high-nickel positive electrode active material and the highly graphitized artificial graphite at an appropriate positive and negative electrode film layer density ratio, this secondary battery exhibits low expansion force, good cycle performance, and high energy density.

[0013] In any embodiment, 0.85 ≤ a ≤ 0.95. Thus, the positive electrode active material of this single crystal particle has a higher charge-discharge specific capacity, which can further improve the energy density of the battery and further improve the cycle performance of the battery.

[0014] In any implementation, 0.9 ≤ a ≤ 0.95. This allows for further improvement in battery energy density and cycle performance.

[0015] In any embodiment, based on the total mass of the positive electrode active material, the mass fraction of the single crystal particles is ≥80%; optionally, the mass fraction of the single crystal particles is 100%. This allows the positive electrode to have a high charge / discharge specific capacity, resulting in a battery with a high energy density.

[0016] In any embodiment, the volume average particle size Dv50 of the positive electrode active material of the single crystal particles is 1 μm to 5 μm. This effectively improves the cycle life of the battery.

[0017] In any embodiment, the positive electrode film layer further contains the positive electrode active material with a polycrystalline particle morphology, wherein the volume average particle size Dv50 of the polycrystalline positive electrode active material is 5 μm to 15 μm. Thus, by combining the single-crystal positive electrode active material with the polycrystalline positive electrode active material, the compaction density of the positive electrode film layer can be increased, thereby further improving the energy density of the battery.

[0018] In any embodiment, based on the total mass of the positive electrode active material, the mass fraction of the positive electrode active material in the polycrystalline particles is ≤80%. This allows the secondary battery to simultaneously possess high energy density and good cycle performance.

[0019] In any embodiment, the areal density σ2 of the positive electrode film layer is greater than 13 mg / cm². 2In this way, the relatively high areal density of the positive electrode film layer can endow the positive electrode sheet with a relatively large tap density, thereby improving the energy density of the battery.

[0020] In any implementation, the negative electrode active material further includes a silicon-based material; based on the total mass of the negative electrode active material, the mass fraction of the silicon-based material is 1% to 15%. In this way, while improving the energy density of the battery, it is possible to avoid excessive expansion of the negative electrode and thus affect the cycle performance, enabling the battery to have both good cycle performance and higher energy density.

[0021] In any implementation, the silicon-based material includes silicon oxide material, and the general formula of the silicon oxide material is SiO y , where 0.5 < y < 1.5. In this way, the volume expansion of the silicon oxide material is relatively small, which is beneficial to improving the cycle performance of the battery.

[0022] In any implementation, the silicon-based material includes prelithiated silicon oxide particles, and the prelithiated silicon oxide particles include single-crystalline silicon with a diameter of 0.5 nm to 50 nm; based on the volume of the prelithiated silicon oxide particles, the volume ratio of the single-crystalline silicon in the prelithiated silicon oxide particles is 20% to 40%. In this way, it is possible to improve the first Coulombic efficiency of the negative electrode, reduce the lithium loss in the early stage of battery charge and discharge, and improve the battery capacity.

[0023] In any implementation, the secondary battery further includes an electrolyte, and the ratio of the mass of the electrolyte to the capacity of the secondary battery is 1.5 g / Ah to 1.9 g / Ah. In this way, by using a relatively small amount of electrolyte in the secondary battery, the energy density of the secondary battery can be further improved.

[0024] In any implementation, the secondary battery is a stacked battery. In this way, the secondary battery is less likely to have the problem of electrode sheet fracture, and can operate normally under a greater expansion force condition compared to a wound-structured secondary battery, and the cycle performance of the battery is better.

[0025] The second aspect of the present application provides an electrical device, which includes the secondary battery of the first aspect of the present application.

[0026] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0028] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0029] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0030] Figure 3 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0031] Explanation of reference numerals in the attached drawings: 5. Battery cell; 51. Casing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0032] Hereinafter, embodiments of the secondary battery and power-consuming device of this application are described in detail with appropriate reference to the accompanying drawings. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0034] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] 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 or implementation 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. The term "implementation" as used herein has a similar understanding.

[0037] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0039] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0040] Currently, due to the significant advancements in rechargeable batteries, higher demands are being placed on their cycle performance and energy density. Therefore, the search for rechargeable batteries with both superior cycle performance and high energy density has become a key focus for those skilled in the art.

[0041] In some embodiments, the first aspect of this application provides a secondary battery, the secondary battery comprising a negative electrode and a positive electrode; the negative electrode includes a negative electrode film layer containing a negative electrode active material, the negative electrode active material comprising artificial graphite with a graphitization degree >93%; the positive electrode includes a positive electrode film layer containing a positive electrode active material with a morphology of single-crystal particles; taking the total molar number of nickel, cobalt and manganese elements in the chemical formula of the positive electrode active material as 1, the molar number of nickel in the chemical formula of the positive electrode active material is a, a is 0.6 to 1; the areal density of the negative electrode film layer is σ1, the areal density of the positive electrode film layer is σ2, and σ1 / σ2 is 0.35 to 0.75.

[0042] In the rechargeable battery described above, the positive electrode film layer uses a high-nickel positive electrode active material with single-crystal particles, which has a high charge / discharge specific capacity and can effectively improve the energy density of the battery. Furthermore, the high-nickel positive electrode active material undergoes lattice contraction in the high SOC range, which can partially offset the expansion force generated by the negative electrode active material. This prevents the electrolyte from being squeezed out of the electrode sheet or the electrode liquid from being obstructed in the electrode sheet under conditions of large negative electrode expansion force, thereby mitigating the accelerated capacity decay caused by negative electrode expansion and improving the battery's cycle performance. Moreover, the negative electrode uses high-graphitization artificial graphite with a graphitization degree >93%, which has a very high charge / discharge specific capacity. Combined with the high-nickel positive electrode active material, this significantly improves the battery's energy density. By combining the high-nickel positive electrode active material with single-crystal particles and the high-graphitization artificial graphite at an appropriate positive and negative electrode film layer density ratio, this rechargeable battery not only has low expansion force and good cycle performance but also high energy density.

[0043] It should be noted that the degree of graphitization is an indicator of the extent to which carbon atoms in graphite form a close-packed hexagonal graphite crystal structure. The closer the lattice size of graphite is to the lattice constant of ideal graphite, the higher its degree of graphitization. The degree of graphitization can be determined by X-ray diffraction, that is, first measuring the interlayer spacing d002 of the (002) crystal planes of graphite, and then substituting it into the Mering-Maire formula (Franklin's formula) to calculate the degree of graphitization. The degree of graphitization can reflect the structural order and electrical conductivity of graphite materials.

[0044] It is understandable that the ratio σ1 / σ2 of the areal density σ1 of the negative electrode film to the areal density σ2 of the positive electrode film can be 0.35, 0.45, 0.6, 0.65, 0.7, 0.75, or any value within the range formed by any two of the above values.

[0045] In some embodiments, the molar number of Ni in the chemical formula of the aforementioned positive electrode active material is 0.85 ≤ a ≤ 0.95. Thus, using single-crystal positive electrode active material with a higher Ni content in the positive electrode film results in a higher charge / discharge specific capacity, further improving the battery's energy density. Furthermore, it exhibits relatively greater lattice contraction at high SOC, better offsetting the negative electrode expansion force and further improving the battery's cycle performance.

[0046] In some embodiments, the molar number of Ni in the chemical formula of the aforementioned positive electrode active material is 0.9 ≤ a ≤ 0.95. Using 9-series single-crystal particles can further improve the energy density of the battery, and compared to other positive electrode active materials (such as lithium iron phosphate, ternary materials with lower Ni content, etc.), 9-series single crystals exhibit significant lattice shrinkage, reaching up to 5% in the high SOC range, which can further improve the cycle performance of the battery.

[0047] In some embodiments, the mass fraction of single-crystal particles is ≥80% based on the total mass of the positive electrode active material; alternatively, the mass fraction of single-crystal particles is 100%. This enables the positive electrode to have a high charge / discharge specific capacity, resulting in a high energy density for the battery.

[0048] In some embodiments, the volume average particle size (Dv50) of the single-crystal positive electrode active material is 1 μm to 5 μm. Single-crystal positive electrode active materials with a volume average particle size (Dv50) between 1 μm and 5 μm have a more stable structure and can avoid particle breakage under greater negative electrode expansion forces, effectively improving the cycle life of the battery. It can be understood that the single-crystal positive electrode active material is a material composed of a single crystal. The volume average particle size (Dv50) of the single-crystal positive electrode active material can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, or any value within the range of any two of the above values.

[0049] In some embodiments, the positive electrode film layer also contains positive electrode active material with a polycrystalline particle morphology. In other words, the positive electrode film layer contains both single-crystal positive electrode active material and polycrystalline positive electrode active material. By mixing single-crystal and polycrystalline positive electrode active materials in the positive electrode film layer, the positive electrode compaction density can be increased, thereby further improving the energy density of the battery.

[0050] In some of these embodiments, the volume-average particle size Dv50 of the polycrystalline particle-based positive electrode active material is 5 μm to 15 μm. The polycrystalline particle-based positive electrode active material is a secondary particle composed of multiple single-crystal particles, and its particle size is larger than that of the single-crystal particles. It can be understood that the volume-average particle size Dv50 of the polycrystalline particle-based positive electrode active material can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, and any value within the range formed by any two of the above values.

[0051] In some of these embodiments, based on the total mass of the positive electrode active material in the positive electrode film layer, the mass fraction of the polycrystalline particle-based positive electrode active material ≤ 80%. Although mixing a certain amount of the polycrystalline particle-based positive electrode active material in the positive electrode film layer can increase the compaction density of the positive electrode, and the polycrystalline particle-based positive electrode active material also has a relatively high charge-discharge specific capacity, the polycrystalline particle-based positive electrode active material is prone to cracks under the action of the large negative expansion force, which will have a certain impact on the cycle performance of the battery. Therefore, considering comprehensively, the mass fraction of the polycrystalline particle-based positive electrode active material should be controlled within 80%. It can be understood that the mass fraction of the polycrystalline particle-based positive electrode active material can be 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and any value within the range formed by any two of the above values. Further, the mass fraction of the polycrystalline particle-based positive electrode active material ≤ 20%.

[0052] In some of these embodiments, the areal density of the positive electrode film layer > 13 mg / cm 2 . The areal density of the positive electrode film layer in the positive electrode tab > 13 mg / cm 2 , making the positive electrode tab have a relatively large compaction density and can improve the energy density of the battery.

[0053] In some of these embodiments, the artificial graphite of the negative electrode active material includes large-particle graphite and small-particle graphite, where the volume-average particle size Dv50 of the large-particle graphite is d1, 18 μm ≤ d1 ≤ 24 μm; the volume-average particle size Dv50 of the small-particle graphite is d2, 0.4d1 < d2 < 0.9d1. By combining the large-particle graphite and the small-particle graphite, the compaction density of the negative electrode tab can be increased, thereby improving the energy density of the battery.

[0054] Understandably, the volume average particle size Dv50 d1 of the large particle graphite can be 18μm, 18.2μm, 18.5μm, 18.8μm, 19μm, 19.2μm, 19.5μm, 19.8μm, 20μm, 20.2μm, 20.5μm, 20.8μm, 21μm, 21.2μm, 21.5μm, 21.8μm, 22μm, 22.2μm, 22.5μm, 22.8μm, 23μm, 23.2μm, 23.5μm, 23.8μm, 24μm, and any value within the range formed by any two of the above values; the volume average particle size Dv50 d2 of the small particle graphite can be 0.4d1, 0.45d1, 0.5d1, 0.55d1, 0.6d1, 0.65d1, 0.7d1, 0.75d1, 0.8d1, 0.85d1, 0.9d1, and any value within the range formed by any two of the above values.

[0055] In some embodiments, based on the total mass of the artificial graphite, the mass fraction of the large particle graphite is e1, 0% < e1 ≤ 40%, and the mass fraction of the small particle graphite is e2, 40% ≤ e2 < 100%. The large particle graphite and the small particle graphite are combined according to the above mass ratio, which is beneficial to improving the compaction density of the negative electrode sheet and the energy density of the battery.

[0056] It can be understood that the mass fraction e1 of the large particle graphite can be 1%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, and any value within the range formed by any two of the above values; the mass fraction e2 of the small particle graphite can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, and any value within the range formed by any two of the above values.

[0057] In some embodiments, the negative electrode active material in the negative electrode film layer further includes a silicon-based material; and based on the total mass of the negative electrode active material, the mass fraction of the silicon-based material is 1% - 15%. The silicon-based material has a higher charge-discharge specific capacity compared to the graphite material. By incorporating a certain amount of the silicon-based material in the negative electrode film layer, the energy density of the battery can be further improved. However, the silicon-based material has a large volume expansion during charge and discharge. Controlling the mass ratio of the silicon-based material in the negative electrode active material within the range of 1% - 15% can, while improving the energy density of the battery, avoid excessive negative electrode expansion and affect the cycle performance.

[0058] It can be understood that the mass ratio of the silicon-based material in the negative electrode active material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, and any value within the range formed by any two of the above values.

[0059] In some of these embodiments, the volume average particle size Dv50 of the silicon-based material in the negative electrode film layer is d3, and 0.15d1 ≤ d3 ≤ 0.5d1. Using a silicon-based material with a smaller particle size than that of large-particle graphite can further increase the compaction density of the negative electrode sheet and improve the energy density of the battery; moreover, the small-particle-size silicon-based material is more conducive to the diffusion of lithium ions in the negative electrode film layer, which is beneficial to improving the kinetics of the battery.

[0060] It can be understood that the volume average particle size Dv50 of the silicon-based material in the negative electrode film layer can be 0.15d1, 0.18d1, 0.20d1, 0.22d1, 0.25d1, 0.28d1, 0.30d1, 0.32d1, 0.35d1, 0.38d1, 0.40d1, 0.42d1, 0.45d1, 0.48d1, 0.5d1, and any value within the range formed by any two of the above values.

[0061] In some of these embodiments, the silicon-based material includes silicon oxide material, and the general formula of the silicon oxide material is SiO y , where 0.5 < y < 1.5. Compared with using elemental silicon as the silicon-based material, using the silicon oxide material with the above general formula has a smaller volume expansion during charge and discharge, can reduce the expansion force of the battery, and thus is beneficial to improving the cycle performance of the battery. Further, the volume average particle size Dv50 of the silicon oxide material is 2 μm to 8 μm, the volume average particle size Dv10 is 0.5 μm to 3 μm, and the specific surface area is 1 m 2 / g to 1.5 m 2 / g.

[0062] It should be noted that since no obvious lithium intercalation reaction occurs in the overhang region of the negative electrode sheet in the early stage of the use of the secondary battery, the negative electrode film layer in this region is close to the initial powder state. After disassembling the secondary battery, nuclear magnetic resonance or XRD can be used to observe whether the negative electrode film layer in the overhang region contains silicon oxide material, so as to determine whether the silicon-based material in the negative electrode film layer includes silicon oxide material. Here, the overhang region of the negative electrode sheet refers to the part where the length and width directions of the negative electrode sheet exceed the positive electrode sheet.

[0063] In some embodiments, the silicon-based material includes pre-lithiated silicon-oxygen particles, which contain monocrystalline silicon. The diameter of the monocrystalline silicon is 0.5 nm to 50 nm; based on the volume of the pre-lithiated silicon-oxygen particles, the volume percentage of monocrystalline silicon in the pre-lithiated silicon-oxygen particles is 20% to 40%. By using pre-lithiated silicon-oxygen materials, the initial coulombic efficiency of the negative electrode can be improved, lithium loss in the early stages of battery charging and discharging can be reduced, and high battery capacity can be guaranteed. Ensuring that the diameter of the monocrystalline silicon in the pre-lithiated silicon-oxygen particles is within the range of 0.5 nm to 50 nm, and the volume percentage of monocrystalline silicon is 20% to 40%, can improve the cycle stability and kinetics of the negative electrode active material, reduce the volume expansion of the negative electrode active material, and accelerate the diffusion rate of Li ions, thereby increasing the negative electrode capacity. It should be noted that the diameter of the monocrystalline silicon in the pre-lithiated silicon-oxygen particles refers to the cluster size of the monocrystalline silicon, that is, the maximum diameter of the monocrystalline silicon cluster. This maximum diameter can be obtained by observing the distribution and size of silicon in the cross-sectional CP dispersion mode, and further measured by software.

[0064] In some embodiments, the pre-lithiated silicon oxide particles satisfy the following general formula: nSi·mLi₂SiO₃; where n and m are both positive numbers, 0.8 <n / m<1.2。

[0065] In some embodiments, the secondary battery also includes an electrolyte, with the mass ratio of the electrolyte to the capacity of the secondary battery being 1.5 g / Ah to 1.9 g / Ah. This results in a lower electrolyte content in the secondary battery, which, combined with higher electrode compaction density, highly graphitized graphite, and high-nickel cathode active materials, can further improve the energy density of the secondary battery. It is understood that the ratio of electrolyte to secondary battery capacity can be 1.5 g / Ah, 1.52 g / Ah, 1.55 g / Ah, 1.58 g / Ah, 1.6 g / Ah, 1.62 g / Ah, 1.65 g / Ah, 1.68 g / Ah, 1.7 g / Ah, 1.72 g / Ah, 1.75 g / Ah, 1.78 g / Ah, 1.8 g / Ah, 1.82 g / Ah, 1.85 g / Ah, 1.88 g / Ah, 1.9 g / Ah, or any value within the range of any two of the above values. The ratio of electrolyte to secondary battery capacity (g / Ah) = electrolyte content (g) / secondary battery capacity (Ah).

[0066] In some embodiments, the secondary battery is a stacked battery. Under conditions of high expansion at the negative electrode, the electrode is highly susceptible to breakage due to expansion and stretching. In wound secondary batteries, stress concentration is more likely to occur at the corners of the electrode, easily leading to cracking. However, in stacked secondary batteries, since neither the positive nor negative electrode has corners, the main force direction on the electrode is along its large surface area, making breakage less likely. Therefore, stacked secondary batteries can operate normally under greater expansion forces compared to wound secondary batteries.

[0067] In some embodiments, the second aspect of this application also provides an electrical device that includes the secondary battery of the first aspect of this application.

[0068] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0069] In one embodiment of this application, a secondary battery is provided.

[0070] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0071] Positive electrode sheet

[0072] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer contains a positive electrode active material.

[0073] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0074] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0075] In some embodiments, the positive electrode active material includes positive electrode active material with a single crystal particle morphology and a chemical formula of Li x (Ni a Co b Mn c ) 1- d M d O 2-y A y ; wherein, 0.2 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 1, 0 < b ≤ 0.2, 0 < c ≤ 0.4, 0 ≤ d < 1, 0 ≤ y < 2, M includes at least one of Al, Mg, Fe, Cu, V, Ti, Zr, W, Sb, Dy, and Te, and A includes at least one of P, S, and halogen.

[0076] It can be understood that during the charge and discharge process of the battery, the insertion and extraction and consumption of lithium (Li) will occur, and the content of Li in the positive electrode plate of the battery is different when the battery is discharged to different states. In the listing of positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. When the positive electrode material is applied to the positive electrode plate in the battery system, after charge and discharge cycles, the content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but it is not limited thereto. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before being fed into the positive electrode slurry. It can be understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to a modification method acceptable for the positive electrode material, and non-limiting examples include coating modification.

[0077] In the listing of positive electrode materials in this application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but it is not limited thereto.

[0078] The positive electrode active material accounts for 80% to 100% of the weight of the positive electrode film, based on the total weight of the positive electrode film.

[0079] In some embodiments, the positive electrode film layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. The binder constitutes 0% to 20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0080] In some embodiments, the positive electrode film may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent comprises 0% to 20% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0081] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry has a solid content of 40 wt% to 80 wt% and a viscosity at room temperature adjusted to 5000 mPa·s to 25000 mPa·s. The positive electrode slurry is then coated onto the surface of a positive current collector, dried, and cold-pressed using a cold rolling mill to form the positive electrode sheet. The compacted density of the positive electrode sheet can be 3.3 g / cm³. 3 ~3.7g / cm 3 .

[0082] The formula for calculating the compaction density is:

[0083] Compacted density = Double-sided coating surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0084] The mass M of the positive electrode active material per unit area of ​​the positive electrode film can be obtained by weighing using a standard balance.

[0085] The thickness T of the positive electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film mentioned in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for assembling the battery after cold pressing and compaction.

[0086] Negative electrode sheet

[0087] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0088] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0089] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0090] In some embodiments, the negative electrode active material comprises artificial graphite with a graphitization degree >93%. Additionally, silicon-based materials may also be included. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. In some specific examples, the silicon-based material employs silicon oxide materials or pre-lithiated silicon oxide particles.

[0091] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may include one or more 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).

[0092] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0094] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s.

[0095] electrolytes

[0096] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0097] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0098] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0099] In some embodiments, the solvent may include one or more of the following: fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0100] 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.

[0101] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0102] Separating membrane

[0103] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0104] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0105] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0106] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0107] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0108] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0109] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0110] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0111] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0112] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0113] In some embodiments, the battery cells 5 can be assembled into a battery module, and the number of battery cells 5 contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0114] In the battery module, multiple battery cells 5 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be secured with fasteners.

[0115] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0116] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0117] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0118] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0119] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0120] Figure 3 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0121] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0122] The following are some examples.

[0123] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0124] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0125] I. Examples and Comparative Examples

[0126] Example 1:

[0127] 1) Preparation of positive electrode sheet

[0128] The positive electrode active material Li of single crystal particles 1.02 (Ni 0.75 Co 0.12Mn 0.13 ) 0.98 O2, conductive carbon black Super P, single-walled carbon nanotubes, and PVDF binder are mixed uniformly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:1.5:0.5:1 to obtain a positive electrode slurry. The positive electrode slurry is coated onto a positive electrode current collector aluminum foil, and then subjected to drying, cold pressing, slitting, and cutting processes to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 3.3 g / cm³. 3 The areal density of the positive electrode film is 20 mg / cm³. 2 The volume average particle size Dv50 of the single-crystal positive electrode active material is 2.5 μm.

[0129] 2) Preparation of negative electrode sheet

[0130] Artificial graphite, conductive carbon black, and polyacrylic acid binder, which are the negative electrode active materials, are mixed evenly in an appropriate amount of deionized water at a mass ratio of 96:2:2 to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil for the negative electrode current collector, and the negative electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0131] The areal density of the negative electrode film is 12 mg / cm³. 2 The degree of graphitization of the artificial graphite is 94%. The artificial graphite includes large-particle graphite and small-particle graphite. The volume average particle size Dv50 of the large-particle graphite is 21 μm, and the volume average particle size Dv50 of the small-particle graphite is 15 μm. The mass fraction of the graphite is 50% for large-particle graphite and 50% for small-particle graphite.

[0132] 3) Electrolyte preparation

[0133] EC, DMC and EMC were mixed in a volume ratio of 3:5:2 to obtain an organic solvent. The fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0134] 4) Separating membrane

[0135] A PE membrane with a thickness of 12μm was used as the separator.

[0136] 5) Secondary battery preparation

[0137] The positive electrode, separator, and negative electrode are stacked in sequence to obtain an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained. The ratio of the electrolyte mass to the battery capacity is 1.7 g / Ah.

[0138] Example 2:

[0139] This embodiment is basically the same as Embodiment 1, except that the chemical formula of the positive electrode active material of the single crystal particles is Li. 1.02 (Ni 0.85 Co 0.07 Mn 0.08 ) 0.98 O2, the areal density of the negative electrode film is 13 mg / cm³ 2 .

[0140] Example 3:

[0141] This embodiment is basically the same as Embodiment 1, except that the chemical formula of the positive electrode active material of the single crystal particles is Li. 1.02 (Ni 0.90 Co 0.07 Mn 0.03 ) 0.98 O2, the areal density of the negative electrode film is 14 mg / cm³ 2 .

[0142] Example 4:

[0143] This embodiment is basically the same as Embodiment 1, except that the chemical formula of the positive electrode active material of the single crystal particles is Li. 1.02 (Ni 0.95 Co 0.04 Mn 0.01 ) 0.98 O2, the areal density of the negative electrode film is 15 mg / cm³ 2 .

[0144] Example 5:

[0145] This embodiment is basically the same as Embodiment 3, except that the volume average particle size Dv50 of the single-crystal positive electrode active material is 1 μm.

[0146] Example 6:

[0147] This embodiment is basically the same as Embodiment 3, except that: the volume average particle size Dv50 of the single-crystal positive electrode active material is 5 μm; correspondingly, the compaction density of the positive electrode sheet is 3.5 g / cm³. 3 .

[0148] Example 7:

[0149] This comparative example is basically the same as Example 1, except that the compaction density of the positive electrode sheet is 2.8 g / cm³. 3 .

[0150] Example 8:

[0151] This embodiment is basically the same as Embodiment 3, except that: the positive electrode film layer also includes polycrystalline positive electrode active material; based on the total mass of the positive electrode active material, the mass fraction of polycrystalline positive electrode active material is 20%, and the mass fraction of single-crystal positive electrode active material is 80%; the volume average particle size Dv50 of the polycrystalline positive electrode active material is 10 μm; and the compaction density of the positive electrode sheet is 3.6 g / cm³. 3 .

[0152] Example 9:

[0153] This embodiment is basically the same as Embodiment 3, except that: the positive electrode film layer also includes polycrystalline positive electrode active material; based on the total mass of the positive electrode active material, the mass fraction of polycrystalline positive electrode active material is 50%, and the mass fraction of single-crystal positive electrode active material is 50%; the volume average particle size Dv50 of the polycrystalline positive electrode active material is 10 μm; and the compaction density of the positive electrode sheet is 3.5 g / cm³. 3 .

[0154] Example 10:

[0155] This embodiment is basically the same as Embodiment 3, except that: the positive electrode film layer also includes polycrystalline positive electrode active material; based on the total mass of the positive electrode active material, the mass fraction of polycrystalline positive electrode active material is 80%, and the mass fraction of single-crystal positive electrode active material is 20%; the volume average particle size Dv50 of the polycrystalline positive electrode active material is 10 μm; and the compaction density of the positive electrode sheet is 3.4 g / cm³. 3 .

[0156] Example 11:

[0157] This embodiment is basically the same as Embodiment 8, except that: the volume average particle size Dv50 of the polycrystalline positive electrode active material is 5 μm; and the compaction density of the positive electrode sheet is 3.6 g / cm³. 3 .

[0158] Example 12:

[0159] This embodiment is basically the same as Embodiment 8, except that: the volume average particle size Dv50 of the polycrystalline positive electrode active material is 15 μm; and the compaction density of the positive electrode sheet is 3.6 g / cm³. 3 .

[0160] Example 13:

[0161] This embodiment is basically the same as Embodiment 3, except that the negative electrode active material also includes a silicon-oxygen material, the chemical formula of which is SiO2. y, 0.5 < y < 1.5; The volume average particle size Dv50 of the silicon oxide material is 7.7 μm, the volume average particle size Dv10 is 4.2 μm, and the specific surface area is 2.04 m 2 ; Based on the total mass of the negative electrode active material, the mass fraction of the silicon-based material is 1%. Accordingly, the negative electrode areal density is 13 mg / cm 2 .

[0162] Example 14:

[0163] This example is basically the same as Example 13, except that: Based on the total mass of the negative electrode active material, the mass fraction of the silicon-based material is 10%. Accordingly, the negative electrode areal density is 9 mg / cm 2 .

[0164] Example 15:

[0165] This example is basically the same as Example 13, except that: Based on the total mass of the negative electrode active material, the mass fraction of the silicon-based material is 15%. Accordingly, the negative electrode areal density is 7 mg / cm 2 .

[0166] Example 16:

[0167] This example is basically the same as Example 14, except that: The silicon-based material is pre-lithiated silicon oxide particles, and the chemical formula of the pre-lithiated silicon oxide is nSi·mLi2SiO3, where n and m are both positive numbers, and 0.8 < n / m < 1.2; The diameter of the single crystal silicon in the pre-lithiated silicon oxide particles is 5 nm; The volume proportion of the single crystal silicon in the pre-lithiated silicon oxide particles is 20%; Accordingly, the negative electrode areal density is 7 mg / cm 2 .

[0168] Example 17:

[0169] This example is basically the same as Example 14, except that: The silicon oxide material is pre-lithiated silicon oxide particles, and the diameter of the single crystal silicon in the pre-lithiated silicon oxide particles is 25 nm; The volume proportion of the single crystal silicon in the pre-lithiated silicon oxide particles is 30%; Accordingly, the negative electrode areal density is 7 mg / cm 2 .

[0170] Example 18:

[0171] This example is basically the same as Example 14, except that: The silicon oxide material is pre-lithiated silicon oxide particles, and the diameter of the single crystal silicon in the pre-lithiated silicon oxide particles is 50 nm; The volume proportion of the single crystal silicon in the pre-lithiated silicon oxide particles is 40%; Accordingly, the negative electrode areal density is 7 mg / cm 2 .

[0172] Comparative Example 1:

[0173] This comparative example is basically the same as Example 3, except that the chemical formula of the positive electrode active material is Li. 1.02 (Ni 0.50 Co 0.25 Mn 0.25 ) 0.98 O2; where a = 0.5.

[0174] Comparative Example 2:

[0175] This comparative example is basically the same as Example 1, except that an equal amount of natural graphite is used instead of the artificial graphite in Example 1 as the negative electrode active material.

[0176] Comparative Example 3:

[0177] This comparative example is basically the same as Example 1, except that the degree of graphitization of the negative electrode active material, artificial graphite, is 88%.

[0178] II. Testing Methods

[0179] 1) Calculation of surface density and compacted density

[0180] Take the positive / negative double-sided electrode sheets from the disassembled battery cell, first centrifuge to remove the electrolyte, then dry at 120℃ for 2 hours; use a punching machine to cut a piece with an area of ​​S mm. 2 The electrode was removed, and then weighed, with the weight recorded as W1 g. After weighing, it was soaked in a water / ethanol solution to remove the membranes on both sides of the current collector. After drying, the current collector was weighed and recorded as W2 g.

[0181] One-sided lateral density = (W1-W2) / 2S, unit is g / mm 2 .

[0182] Compacted density = surface density / (extruded electrode thickness - current collector thickness).

[0183] 2) Volume average particle size Dv50 and Dv10 tests

[0184] Particle size was measured using a laser particle size analyzer.

[0185] Preprocessing:

[0186] 1. Disassemble a 0% SOC battery cell, take an appropriate amount of negative electrode sheet, scrape off the surface powder, soak it in dimethyl carbonate (DMC) for 24 hours, and then place the powder in an oven to dry at 60°C for 4 hours; place the dried negative electrode sheet in a tube furnace and calcine at 550°C for 6 hours under argon protection to obtain a graphite sample with the binder removed.

[0187] 2. Take a clean beaker, add an appropriate amount of the treated sample, add dispersant, and sonicate at 120W / 5min to ensure that the sample is completely dispersed in the dispersant.

[0188] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light (shading degree: 8-12%).

[0189] Wherein, Dv50 indicates that the diameter of 50% of the total volume particles in the particle size distribution is smaller than this value; Dv10 indicates that the diameter of 10% of the total volume particles in the particle size distribution is smaller than this value.

[0190] 3) Testing of the type and content of silicon-based materials in the negative electrode active material

[0191] 1. Determine silicon type using a combination of SEM and EDS:

[0192] Scanning electron microscopy (SEM) analysis of the cross-sectional morphology of ion polishing particles, by adjusting the equipment to backscatter mode, reveals the morphology and size of silicon particles. EDS analysis can then determine whether the silicon particles are silicon-carbon or silicon-oxygen.

[0193] 2. The silicon content in the electrode was determined using the ashing method:

[0194] The sample is burned in oxygen, converting carbon, sulfur, and other substances into CO2, SO2, etc., which are then converted into corresponding signals by a detector in an absorption cell. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the CO2 and SO2 concentrations. The values ​​from the entire analysis process are then accumulated. After analysis, this accumulated value is divided by the weight value in the computer, multiplied by a correction factor, and the blank is subtracted to obtain the percentage content of carbon, sulfur, and other substances in the sample. The residue after combustion is weighed, then thoroughly soaked in saturated sodium hydroxide. The diluted solution is used for ICP testing to determine the silicon content, and the actual weight percentage is calculated based on the type of silicon.

[0195] 4) Measurement of the diameter and volume fraction of monocrystalline silicon

[0196] 1.a. Sample preparation: Mix the sample preparation adhesive (PVDF is dispersed in NMP beforehand, PVDF content is about 8%) with the pre-physicochemically treated silica particles evenly (particle weight is about 5 times that of adhesive), then apply it to copper foil (6 micrometers), and dry at 60℃ for 30 minutes for later use; b. Cut the sample into 6mm*6mm pieces with scissors and attach them to the CP (argon ion polishing) sample stage, with the sample protruding within 1mm of the sample stage; c. Cutting: Voltage 7.5KV (efficiency and mass balance point), time 30 minutes (time can be adjusted appropriately according to the material and sample thickness).

[0197] 2. Parameter settings: Set the scanning electron microscope parameters as follows: Mode: BSD, Voltage: 20KV, Aperture: 60μm, Working distance: 6mm, High current selected, Noise reduction mode N=50.

[0198] 3. Testing Procedure: The test is conducted using a scanning electron microscope. Focusing is performed in In-lens mode on the interior of medium or large particles. Then, switch to BSD mode and take a picture at around 5K (ideally with the entire particle in the field of view). Use software to read the diameter of the monocrystalline silicon particles and calculate the volume ratio of the monocrystalline silicon.

[0199] 5) Specific surface area test

[0200] 1. Pretreatment: Take an appropriate amount of sample in a special sample tube, heat and degas for 2 hours, and weigh the total weight after cooling to room temperature. Subtract the mass of the sample tube to obtain the sample mass.

[0201] 2. Testing: The sample tube is placed in the workstation and the amount of gas adsorbed on the solid surface under liquid nitrogen insulation conditions (-196℃) is measured. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample is obtained, and the specific surface area of ​​the solid sample per unit mass is calculated.

[0202] Adsorbed gas: nitrogen; Adsorption pressure points: 0.05MPa / 0.10MPa / 0.15MPa / 0.20MPa / 0.25MPa / 0.30MPa; Test atmosphere: high-purity liquid nitrogen atmosphere.

[0203] 6) 45℃ 800-cycle SOH test method & 1500-cycle large-area surface pressure test method

[0204] Take a fresh battery cell, with three steel clamps, install a KEPRE pressure sensor to monitor the expansion force, and set the preload force to 3000N;

[0205] The loop process is as follows:

[0206] Charge at a constant current rate of 1.2C to 3.76V; charge at a constant current rate of 0.87C to 4.08V; charge at a constant current rate of 0.33C to 4.2V, then charge at a constant voltage to 0.05C; let stand for 10 minutes; discharge at a constant voltage rate of 1C to 2.8V; let stand for 10 minutes.

[0207] Repeat the above steps until the cell has completed 800 cycles. Then, read the state of equilibrium (SOH) retention rate of the cell at the point of 800 cycles. When the cell has completed 1500 cycles, calculate the surface pressure of the large surface area.

[0208] Surface pressure of the largest surface = Expansion force / Area of ​​the surface with maximum force. For example: If the measured expansion force is 100mm (height) * 150mm (width) of the surface with maximum force, and the area of ​​the surface with maximum force is 80mm (height) * 135mm (width), then the surface pressure of the expansion force = 2400kgf * 10 / (80 * 135)mm. 2 =2.22MPa.

[0209] 7) Energy density calculation

[0210] The battery cell casing measures 33mm in thickness, 220mm in width, and 102.5mm in height.

[0211] Cell volumetric energy density = initial cell capacity * plateau voltage / cell volume; unit is Wh / L.

[0212] 8) Battery capacity testing methods

[0213] Take a battery cell and find its design capacity C1; discharge it at a constant current rate of 0.33C1 to 2.8V; let it rest for 10 minutes; charge it at a constant current rate of 0.33C1 to the battery design voltage (4.25V is used in this case); charge it at a constant voltage of 4.25V to 0.05C1; let it rest for 10 minutes; discharge it at a constant current rate of 0.33C1 to 2.8V. The resulting capacity is the cell capacity C0.

[0214] The parameters and performance data of the secondary batteries in the above embodiments and comparative examples are shown in Tables 1, 2, 3 and 4.

[0215] Table 1

[0216] Table 2

[0217] Table 3

[0218] Table 4

[0219] From the data in the table above, we can see that:

[0220] The secondary batteries of the various embodiments of this application not only have low expansion force and good cycle performance, but also high energy density, and have excellent overall performance.

[0221] Comparing Examples 1-4, it can be seen that as the Ni content in the positive electrode active material increases, the discharge specific capacity of the positive electrode active material increases accordingly. Therefore, selecting a positive electrode active material with a higher Ni content (e.g., a is 0.9-0.95) can significantly improve the energy density of the battery.

[0222] Comparing Examples 3 and 5-7, it is evident that as the particle size of the single-crystal positive electrode active material decreases, the compaction capability of the positive electrode active material decreases. Consequently, under the same compaction density, the cycle performance of the battery will decline. Within the compaction capability range of the positive electrode active material, reducing the compaction density of the positive electrode sheet, while beneficial for improving battery cycle performance, will affect the battery's energy density. Therefore, a suitable compaction density can be matched according to the particle size of the single-crystal material to obtain better overall performance.

[0223] Comparing Examples 3 and 8-10, it can be seen that mixing a certain amount of single-crystal particles and polycrystalline particles into the positive electrode active material can increase the compaction density of the positive electrode sheet, thereby improving the energy density of the battery, without significantly deteriorating the cycle performance and expansion force of the battery.

[0224] Comparing Examples 3 and 13-15, it can be seen that incorporating a certain amount of silicon-based material into the negative electrode active material can effectively improve the energy density of the battery. However, the amount of silicon-based material added needs to be controlled within a certain range to mitigate the deterioration of battery cycle performance caused by the addition of silicon-based material. Controlling the content of silicon-based material in the negative electrode active material within the range of 1% to 15% can effectively improve the energy density of the battery and give the battery better cycle performance.

[0225] Comparing Examples 14 and 16-18, it can be seen that using specific pre-physicochemical silicon-oxygen particles can further improve the energy density of the battery and optimize the cycle performance of the battery to a certain extent.

[0226] Comparing Example 3 and Comparative Example 1, it can be seen that when the Ni content in the positive electrode active material is too low, the lattice contraction of the positive electrode active material is small during charging, resulting in a large expansion force of the battery. The positive electrode sheet is very sensitive to the expansion force of the battery during charging, which leads to a significant deterioration in the cycle performance of the battery and a significant reduction in the energy density of the battery.

[0227] A comparison of Example 1 and Comparative Example 2 shows that when an equal amount of natural graphite is used instead of artificial graphite as the negative electrode active material, the expansion force after battery cycling increases significantly, and the battery's cycle performance deteriorates significantly. A comparison of Example 1 and Comparative Example 3 shows that when the graphitization degree of the artificial graphite drops below 93%, the expansion force after battery cycling also increases significantly, the battery's cycle performance deteriorates significantly, and the energy density decreases.

[0228] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0229] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, comprising a negative electrode tab and a positive electrode tab; the negative electrode tab comprises a negative electrode film layer, the negative electrode film layer containing a negative electrode active material, the negative electrode active material comprising artificial graphite with a graphitization degree > 93%; the positive electrode tab comprises a positive electrode film layer, the positive electrode film layer containing a positive electrode active material with a morphology of single crystal particles; in a chemical formula of the positive electrode active material, the number of moles of nickel element is a, and a is 0.6-1, based on the total number of moles of nickel element, cobalt element and manganese element in the chemical formula of the positive electrode active material; the surface density of the negative electrode film layer is σ1, the surface density of the positive electrode film layer is σ2, and σ1 / σ2 is 0.35-0.

75.

2. The secondary battery according to claim 1, wherein 0.9≤a≤0.95。 3. The secondary battery according to claim 1 or 2, wherein The mass fraction of the single crystal particles is ≥80%, based on the total mass of the positive electrode active material.

4. The secondary battery according to any one of claims 1 to 3, wherein The mass fraction of the single crystal particles is 100%, based on the total mass of the positive electrode active material.

5. The secondary battery according to any one of claims 1 to 4, wherein The volume average particle size Dv50 of the single crystal particles is 1-5 μm.

6. The secondary battery according to any one of claims 1 to 5, wherein The positive electrode active material further comprises a positive electrode active material with a morphology of polycrystal particles, the volume average particle size Dv50 of the polycrystal particles being 5-15 μm.

7. The secondary battery according to claim 6, wherein The mass fraction of the polycrystal particles is ≤80%, based on the total mass of the positive electrode active material.

8. The secondary battery according to any one of claims 1 to 7, wherein The face density σ2 of the positive electrode film layer is > 13 mg / cm 2 .

9. The secondary battery according to any one of claims 1 to 8, wherein The negative electrode active material further comprises a silicon-based material, the mass fraction of the silicon-based material being 1-15%, based on the total mass of the negative electrode active material.

10. The secondary battery according to claim 9, wherein The silicon-based material includes a silicon-oxygen material having a general formula of SiO y where 0.5 < y < 1.

5.

11. The secondary battery according to claim 9 or 10, wherein The silicon-based material comprises pre-lithiated silicon-oxygen particles, the pre-lithiated silicon-oxygen particles containing single crystal silicon.

12. The secondary battery according to claim 11, wherein The diameter of the single crystal silicon is 0.5-50 nm.

13. The secondary battery according to claim 11 or 12, wherein The volume fraction of the single crystal silicon in the pre-lithiated silicon-oxygen particles is 20-40%, based on the volume of the pre-lithiated silicon-oxygen particles.

14. The secondary battery according to any one of claims 1 to 13, wherein The secondary battery further comprises an electrolyte, the ratio of the mass of the electrolyte to the capacity of the secondary battery being 1.5-1.9 g / Ah.

15. The secondary battery according to any one of claims 1 to 14, wherein The secondary battery is a stacked battery.

16. An electrical device, comprising: The secondary battery comprises any one of the secondary batteries in claims 1-15.

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