Secondary battery cell, electric device, graphite material, and preparation method therefor

Abstract

A secondary battery cell, an electric device, a graphite material, and a preparation method therefor. The secondary battery cell comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material. The negative electrode active material comprises a graphite material having a pore structure. The pore structure comprises a mesoporous structure having a pore diameter of 2 nm to 50 nm, and the proportion of the mesoporous structure in the pore structure is greater than or equal to 50%.

Description

Secondary battery cells, electrical devices, graphite materials and their preparation methods

[0001] Cross-references to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202510126464.5, filed on January 27, 2025, entitled “Secondary Battery Cell, Electrical Device, Graphite Material and Preparation Method Thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of solid-state battery technology, and in particular to a secondary battery cell, an electrical device, a graphite material, and a method for preparing the same. Background Technology

[0004] In recent years, with the increasingly wide application of rechargeable batteries, 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 power tools, electric bicycles, electric motorcycles, electric cars, aerospace, and many other fields. With the application and promotion of rechargeable batteries, people have increasingly higher requirements for their capacity, rate performance, and cycle performance.

[0005] Therefore, how to achieve high capacity, excellent rate performance, and cycle performance in rechargeable batteries has become an urgent technical problem to be solved. Summary of the Invention

[0006] This disclosure is made in view of the above-mentioned issues, and its purpose is to provide a secondary battery cell, an electrical device, a graphite material and a method for preparing the same, wherein the secondary battery cell can achieve high capacity, excellent rate performance and cycle performance.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a secondary battery cell, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including a graphite material with a porous structure, the porous structure including a mesoporous structure with a pore size of 2nm to 50nm, and the mesoporous structure accounting for more than or equal to 50% of the porous structure.

[0008] The porous structure provides more lithium-ion transport channels and shortens the lithium-ion diffusion path, which is beneficial to improving the cycle performance and rate performance of the rechargeable battery cell. Simultaneously, the appropriate proportion of mesoporous structure ensures that the adsorption-desorption capacity generated by adsorption-desorption is within a suitable range, thus contributing to an increase in the plateau capacity of the rechargeable battery cell. Therefore, the rechargeable battery cell of this disclosure can achieve a balance between high capacity, excellent rate performance, and cycle performance.

[0009] In some embodiments, the proportion of mesoporous structures in the pore structure is 60% to 80%. By controlling the proportion of mesoporous structures within the above range, it is further beneficial to achieve high capacity, excellent rate performance, and cycle performance in the secondary battery.

[0010] In some embodiments, the pore structure includes macropores with a pore size greater than 50 nm. In some embodiments, the macropore structure accounts for 10% to 25% of the pore structure. By controlling the proportion of macropores to be relatively small, it is beneficial to enable the secondary battery cell to achieve high capacity, excellent rate performance, and cycle performance.

[0011] In some embodiments, the pore structure also includes microporous structures with a pore size of less than 2 nm. In some embodiments, the proportion of microporous structures in the pore structure is 10% to 15%. The relatively small proportion of microporous structures and the large proportion of mesoporous structures in graphite materials are beneficial for further improving the rate performance, cycle performance, and capacity of secondary batteries.

[0012] In some embodiments, the pore structure includes a through-hole structure. Through-hole structures can further increase ion transport channels and shorten the lithium-ion insertion path, which is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery cell.

[0013] In some embodiments, the Dv10 of the graphite material satisfies: 1 μm ≤ Dv10 ≤ 10 μm; in some embodiments, the Dv50 of the graphite material satisfies: 1 μm ≤ Dv50 ≤ 20 μm; in some embodiments, the Dv90 of the graphite material satisfies: 20 μm ≤ Dv90 ≤ 40 μm; in some embodiments, the volumetric particle size distribution (Dv90 - Dv10) / Dv50 of the graphite material is 1 to 3. In this disclosure, setting the graphite material to have a suitable particle size distribution is more conducive to improving the cycle performance and rate performance of the secondary battery cell.

[0014] In some embodiments, the specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g.

[0015] In some embodiments, the oil absorption value of the graphite material is 50 mL / 100g to 70 mL / 100g.

[0016] In some embodiments, the graphitization degree of the graphite material is 90% to 96%. A graphitization degree within this range allows the anode material to have suitable compaction density and capacity, which is beneficial for maximizing the volumetric energy density of the composite anode.

[0017] In some implementations, the OI value of the graphite material is 1 to 6, which is beneficial to improving the rate performance and cycle performance of the secondary battery cell.

[0018] In some embodiments, the negative electrode film layer further includes a solid electrolyte material; in some embodiments, the solid electrolyte material includes one or more of sulfide solid electrolyte materials, oxide electrolyte materials, halide electrolyte materials, and polymer electrolyte materials.

[0019] In some embodiments, the mass ratio of graphite material to solid electrolyte material in the negative electrode film is (6:4) to (9:1). This allows for a balance between the rate performance, cycle performance, and capacity of the secondary battery.

[0020] In some embodiments, the solid electrolyte material includes Li d MX d+3 The material includes 1≤d≤6, M including one or more of Al, Ga, In, Y, Zr, Nb, Sc, Ti, Mn, and La, and X including one or more of halogens, S, O, and P.

[0021] In some embodiments, the volumetric particle size distribution Dv50 of the solid electrolyte material is 0.5 μm to 3 μm.

[0022] In some embodiments, the secondary battery cell further includes a positive electrode and an electrolyte membrane; the electrolyte membrane is located between the positive electrode and the negative electrode.

[0023] In some embodiments, the aforementioned secondary battery cell is a solid-state secondary battery.

[0024] A second aspect of this disclosure provides an electrical device including a secondary battery cell as described in the first aspect.

[0025] This disclosure provides a graphite material comprising a pore structure, including mesoporous structures with pore sizes ranging from 2 nm to 50 nm, wherein the mesoporous structure accounts for more than or equal to 50% of the pore structure. This provides more channels for lithium-ion transport and shortens the solid-phase diffusion path for lithium-ion insertion; simultaneously, the adsorption / desorption capacity generated by adsorption / desorption is within a suitable range.

[0026] In some embodiments, the mesoporous structure accounts for 60% to 80% of the pore structure. This further facilitates the secondary battery to achieve high capacity, excellent rate performance, and cycle performance.

[0027] In some embodiments, the pore structure includes macropores with a pore size greater than 50 nm. In some embodiments, the macropore structure accounts for 10% to 25% of the pore structure. This is beneficial for enabling secondary battery cells to achieve high capacity, excellent rate performance, and cycle performance.

[0028] In some embodiments, the pore structure also includes microporous structures with a pore size of less than 2 nm. In some embodiments, the proportion of microporous structures in the pore structure is 10% to 15%. This is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery.

[0029] In some embodiments, the pore structure includes a through-hole structure. This is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery cell.

[0030] In some embodiments, the Dv10 of the graphite material satisfies: 1μm≤Dv10≤10μm; in some embodiments, the Dv50 of the graphite material satisfies: 1μm≤Dv50≤20μm; in some embodiments, the Dv90 of the graphite material satisfies: 20μm≤Dv90≤40μm; in some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1 to 3.

[0031] In some embodiments, the specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g.

[0032] In some embodiments, the oil absorption value of the graphite material is 50 mL / 100g to 70 mL / 100g.

[0033] In some embodiments, the graphitization degree of the graphite material is 90% to 96%.

[0034] In some implementations, the OI value of the graphite material is 1 to 6.

[0035] The fourth aspect of this disclosure provides a method for preparing the graphite material of the third aspect, comprising the following steps: S1, mixing a graphite precursor and a structure directing agent at a mass ratio of 1:(2-6), and sintering at 700℃-1500℃ for 1h-5h to obtain a sintered product; S2, acid washing the sintered product to obtain a graphite material, the graphite material comprising a pore structure, the pore structure comprising mesoporous structures with a pore size of 2nm-50nm, and the proportion of mesoporous structures in the pore structure being greater than or equal to 50%.

[0036] In this disclosure, by adjusting parameters such as the mass ratio of graphite precursor and structure directing agent, sintering time, and sintering temperature, porous graphite materials can be prepared, which is beneficial to improving the cycle performance and rate performance of secondary battery cells. Further adjusting the proportion of mesoporous structure in the porous structure allows the specific surface area and defect content of the graphite material to be within a suitable range, thereby ensuring that the adsorption-desorption capacity generated by adsorption-desorption is within a suitable range, which in turn is beneficial to improving the plateau capacity of secondary battery cells.

[0037] In some embodiments, the structure directing agent includes one or more of MgO, SiO2, CaCO3, and ZnCl2.

[0038] In some implementations, the graphite precursor includes natural graphite and / or synthetic graphite.

[0039] In some embodiments, the volumetric particle size distribution Dv50 of the graphite precursor is 2 μm to 50 μm. This is beneficial for forming graphite with a porous structure.

[0040] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite precursor is 2 to 6. This is beneficial for forming a graphite material with a suitable volumetric particle size distribution.

[0041] In some embodiments, the specific surface area of ​​the graphite precursor is 0.8 m². 2 / g~4m 2 / g. Therefore, graphite has a relatively dense surface structure, which is beneficial for controlling the pore structure formed subsequently. Attached Figure Description

[0042] Figure 1 is a schematic diagram of the structure of a graphite material according to an embodiment of the present disclosure.

[0043] Figure 2 is a schematic diagram of a battery cell according to one embodiment of the present disclosure.

[0044] Figure 3 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 2.

[0045] Figure 4 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0046] Figure 5 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0047] Figure 6 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 5.

[0048] Figure 7 is a schematic diagram of an electrical device in which a secondary battery cell is used as a power source according to an embodiment of the present disclosure.

[0049] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery cell, its preparation method, battery device, and power-consuming device of this disclosure. However, 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 unnecessarily lengthy descriptions 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 disclosure and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps of this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a 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 it is mentioned that the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0056] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0057] In traditional liquid-state battery systems, graphite anode materials are mature commercial products with low cost and stable chemical properties. Therefore, applying them to solid-state battery systems could expedite the practical application of all-solid-state batteries. Unlike traditional liquid-state battery systems where lithium ions are stored through contact between the electrolyte and the active material, solid-state batteries typically use a mixture of graphite and electrolyte materials as the anode material. This mixture creates a solid-solid interface between the graphite and electrolyte materials, resulting in high interfacial impedance and limited ion transport paths. Consequently, graphite composite anodes in solid-state batteries exhibit lower rate performance, cycle performance, and capacity.

[0058] In related technologies, the main approach to address the low rate performance, cycle performance, and capacity of graphite composite anodes is to improve the solid-solid contact between graphite and electrolyte materials. For example, adding a eutectic electrolyte with high ionic conductivity to the anode slurry can construct lithium-ion transport channels to improve its rate performance, cycle performance, and capacity. However, the method of adding a eutectic electrolyte with high ionic conductivity is costly and the process is complex, which is not conducive to industrial application.

[0059] Based on this, this disclosure proposes a secondary battery cell, a battery device, a graphite material, and a method for preparing the same. The secondary battery cell of this disclosure has improved rate performance, cycle performance, and capacity. The following provides a more detailed description of this disclosure and its optional embodiments.

[0060] Secondary battery cell

[0061] The first aspect of this disclosure provides a secondary battery cell, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including a graphite material with a porous structure, the porous structure including a mesoporous structure with a pore size of 2nm to 50nm, and the mesoporous structure accounting for more than or equal to 50% of the porous structure.

[0062] In this disclosure, the negative electrode active material includes graphite material with a porous structure. On the one hand, the porous structure provides more channels for lithium-ion transport and shortens the solid-phase diffusion path for lithium-ion insertion, which is beneficial to improving the cycle performance and rate performance of the secondary battery cell. On the other hand, the porous structure includes mesoporous structures with pore sizes of 2 nm to 50 nm, and the proportion of mesoporous structures in the porous structure is greater than or equal to 50%, which keeps the specific surface area and defect content of the graphite material within a suitable range, thereby keeping the adsorption-desorption capacity generated by adsorption-desorption within a suitable range, which is beneficial to improving the plateau capacity of the secondary battery cell. Therefore, the secondary battery cell in this disclosure can achieve a balance between high capacity, excellent rate performance, and cycle performance.

[0063] In this disclosure, "pore structure" refers to the void channels inside graphite materials.

[0064] Graphite is a layered crystal formed by the stacking of graphite sheets under the influence of van der Waals forces. Graphite includes a basal plane and an edge plane. The edge plane is the edge of the graphite sheet, and the basal plane is the plane containing the graphite sheet. Carbon atoms in the graphite sheet are bonded by strong covalent bonds, forming a firmly bonded atomic layer. Because stable covalent bonds are formed between carbon atoms in the basal plane, lithium ions are difficult to insert and extract to achieve charge storage. However, carbon atoms at the edge plane usually have higher reactivity and a larger specific surface area, serving as active sites for lithium ions. Therefore, lithium ions are more easily inserted and extracted at the edge plane. In this disclosure, "pore structure" refers to a pore structure that penetrates the graphite basal plane. By creating pores in the graphite material basal plane, lithium ion transport pathways can be increased, which is beneficial to improving the rate performance and cycle performance of secondary battery cells. In addition, the basal plane of graphite materials containing "pore structure" can also perform ion energy storage when in contact with solid electrolyte materials, which is beneficial to further improving the capacity of secondary battery cells.

[0065] For example, the proportion of mesoporous structures in the pore structure is 50%, 60%, 65%, 70%, 75%, 80%, 90%, 100%, or any value within a range of two such values.

[0066] In some embodiments, the proportion of mesoporous structures in the pore structure is 60% to 80%, optionally 70% to 80%. Mesoporous structures facilitate the rapid transport of lithium ions, reduce the resistance to active ion transport, and improve the rate performance of secondary batteries. By controlling the proportion of mesoporous structures within the above range, it is further beneficial to achieve a balance between high capacity, excellent rate performance, and cycle performance in secondary batteries.

[0067] In this disclosure, mesoporous structures with pore sizes in the range of 2 nm to 50 nm can be obtained by testing using instruments or methods known in the art. Specifically, the gas adsorption method is used for testing, specifically referring to the standard test of GB / T19587-2017, and the results are calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0068] In some embodiments, the pore structure also includes macropores with a pore size greater than 50 nm, and the proportion of macropores in the pore structure is 10% to 25%, optionally 15% to 20%. Macropores in graphite materials, on the one hand, lead to complex and lengthy conduction paths for active ions in the graphite-based anode, increasing ion transport resistance and negatively impacting the rate performance of the secondary battery. On the other hand, the presence of macropores weakens the structural strength of the graphite material and increases adsorption-desorption, which is detrimental to the cycle performance and plateau capacity improvement of the secondary battery. Therefore, controlling the proportion of macropores to be relatively small in this disclosure is beneficial for enabling the secondary battery cell to achieve high capacity, excellent rate performance, and cycle performance. Exemplarily, the proportion of macropores in the pore structure is 10%, 15%, 20%, 25%, or a value within a range of any two values.

[0069] In this disclosure, the macroporous structure can be obtained by testing using instruments or methods known in the art. Specifically, for example, the sample to be tested can be surface-cleaned, then placed in an instrument, pressurized and pumped, and the osmotic pressure after equilibrium is measured. Since the permeation rate of pore structures with different pore sizes is different, macroporous structures are easily permeated and have a lower equilibrium osmotic pressure; the measured osmotic pressure reflects the pore size distribution of the sample, thus revealing the proportion of macroporous structures.

[0070] In some embodiments, the pore structure further includes microporous structures with a pore size of less than 2 nm, and the proportion of microporous structures in the pore structure is 10% to 15%, optionally 8% to 12%. The small pore size of the microporous structures is not conducive to the transport of active ions. Therefore, in this disclosure, the proportion of microporous structures is controlled within the above range, resulting in a smaller proportion of microporous structures and a larger proportion of mesoporous structures in the graphite material, which is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery. Exemplarily, the proportion of microporous structures in the pore structure is 10%, 11%, 12%, 13%, 14%, 15%, or a value within a range consisting of any two values.

[0071] In some embodiments, the pore structure includes a through-hole structure that penetrates the graphite substrate. This through-hole structure further increases ion transport channels and shortens the lithium-ion insertion path, which is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery cell.

[0072] In this disclosure, "through-hole structure" refers to a single particle with two holes on its surface. These two holes form a connected channel through the internal channels of the particle. Therefore, the through-hole structure has the characteristic of allowing liquids, gases or other substances to enter from one end of the particle and exit from the other end.

[0073] Figure 1 shows a schematic diagram of the structure of a graphite material according to an embodiment of the present disclosure. It can be seen that the graphite material has a through-hole structure.

[0074] In this disclosure, the "through-hole structure" can be tested by combining BET with SEM / HRTEM. Specifically, BET is used to test the distribution of the pore structure, and SEM / HRTEM is used to directly observe the void structure on the surface and inside of the material to determine whether the material has through-hole channels, i.e., through-hole structure.

[0075] In some embodiments, the volumetric particle size distribution Dv50 of the graphite material is 1 μm to 20 μm, optionally 10 μm to 15 μm. Exemplarily, the volumetric particle size distribution Dv50 of the graphite material is a value between 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13.2 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any two of these values. The volumetric particle size distribution Dv10 of the graphite material is 1 μm to 10 μm, optionally 5 μm to 10 μm. Exemplarily, the volumetric particle size distribution Dv10 of the graphite material is a value between 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 7.5 μm, 8 μm, 9 μm, 10 μm, or any two of these values. The volumetric particle size distribution Dv90 of the graphite material is 20 μm to 40 μm. Exemplarily, the volumetric particle size distribution Dv90 of the graphite material is a value between 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any two of these values. The volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1 to 3, optionally 1.5 to 2. In this disclosure, setting the graphite material to have a suitable particle size distribution is more beneficial to improving the cycle performance and rate performance of the secondary battery cell. Exemplarily, (Dv90-Dv10) / Dv50 is a value between 1, 1.2, 1.5, 1.6, 1.7, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, or any two of these values.

[0076] In this disclosure, the volumetric particle sizes Dv10, Dv50, and Dv90 have their common meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0077] In some embodiments, the specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g, optionally, 85m 2 / g~280m 2 / g. A specific surface area of ​​graphite material within the above range is beneficial for increasing the effective contact area between the graphite material and the solid electrolyte material. This increases the active ion transport pathway, which is beneficial for further improving the rate performance and cycle performance of the secondary battery. For example, the specific surface area of ​​the graphite material is 50m². 2 / g、85m 2 / g, 100m 2 / g, 150m 2 / g、200m 2 / g、250m 2 / g、280m 2 / g、300m 2 / g, 350m 2 / g、400m 2 / g、450m 2 / g、500m 2 / g or any value within a range formed by two numerical values.

[0078] In this disclosure, specific surface area has a meaning known in the art, and it can be obtained by testing using instruments or methods known in the art. Specifically, the specific surface area of ​​the sample to be tested is determined by the gas adsorption method, specifically according to the standard test GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0079] In some embodiments, the oil absorption value of the graphite material is 50 mL / 100g to 70 mL / 100g, optionally 55 mL / 100g to 65 mL / 100g. An oil absorption value within this range gives the graphite material excellent dispersibility, which is beneficial for improving the electrochemical performance of the secondary battery. Exemplarily, the oil absorption value of the graphite material is 50 mL / 100g, 55 mL / 100g, 60 mL / 100g, 65 mL / 100g, 70 mL / 100g, or a value within a range of any two of these values.

[0080] In this disclosure, the oil absorption value, or DBP value, has a well-known meaning in the art, and the unit is cm. 3 / 100g can be determined using instruments and methods known in the art. For example, under specified test conditions, the volume (cm³) of di-n-butyl phthalate (DBP) absorbed by 100g of graphite. 3 )number.

[0081] In some embodiments, the graphitization degree of the graphite material is 90% to 96%, optionally 91% to 93%. A graphitization degree within this range allows the anode material to have suitable compaction density and capacity, which is beneficial for achieving the volumetric energy density of the composite anode. Exemplarily, the graphitization degree of the graphite material is 90%, 91%, 91.4%, 92%, 93%, 94%, 95%, 96%, or a value within a range of any two of these values.

[0082] Graphitization degree 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 graphitization degree. In this disclosure, the graphitization degree can be measured using an X-ray diffractometer (e.g., a Bruker D8 Discover), and specific testing methods can be found in JIS K 0131-1996, JB / T 4220-2011, and GB / T 24533-2019. Specifically, XRD testing is performed on the graphite material, first measuring d... 002 The size is then determined according to the formula G = (0.344 - d). 002 The degree of graphitization is calculated by d / (0.344-0.3354)×100%, where d 002 The interlayer spacing in graphite crystal structure is expressed in nanometers (nm). In X-ray diffraction analysis, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range is 20°-80°, and the scanning rate can be 4° / min.

[0083] In some embodiments, the OI value of the graphite material is 1 to 6, optionally 2 to 4. An OI value within this range reflects high isotropy of the graphite material, which is beneficial for improving its ion-conducting ability, thereby improving the rate performance and cycle performance of the secondary battery cell. Exemplarily, the OI value of the graphite material is 1, 2, 3, 4, 5, 6, or any value within a range of two such values.

[0084] In this disclosure, the term "OI value" has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray powder diffractometer (X'pert PRO), and the test can be performed in accordance with JIS K 0131-1996 and JB / T 4220-2011. Specifically, XRD testing is performed on graphite materials to obtain the X-ray diffraction pattern of graphite, and the OI value is determined according to the formula: OI = I 004 / I 110 Calculate the OI value of graphite. Where I... 004 I is the integrated area of ​​the diffraction peak of the carbon 004 crystal plane in graphite. 110 This represents the integrated area of ​​the diffraction peak on the 110 crystal plane of crystalline carbon in graphite. In the X-ray diffraction analysis test disclosed herein, a copper target can be used as the anode target, CuKα rays can be used as the radiation source, the ray wavelength scanning 2θ angle range is 20° to 80°, and the scanning rate is 4° / min.

[0085] In some embodiments, the negative electrode film layer further includes a solid electrolyte material, which may be one or more of sulfide solid electrolyte materials, oxide solid electrolyte materials, halide electrolyte materials, and polymer electrolyte materials. Sulfide solid electrolyte materials, oxide solid electrolyte materials, halide electrolyte materials, and polymer solid electrolyte materials have high ionic conductivity, which can improve the diffusion rate of active ions at the interface between the graphite material and the solid electrolyte, thus helping to reduce polarization and improve the rate performance and cycle performance of the secondary battery.

[0086] For example, sulfide solid electrolytes include at least one of binary compounds such as Li6PS5Cl, Li2S-GeS2, Li2S-P2S5, and Li2S-SiS2, and a ternary compound such as Li2S-MeS2-P2S5 (Me = Si, Ge, Sn, Al, etc.). Oxide solid electrolytes include lithium lanthanum zirconium oxide series oxides or tin oxide solid electrolytes. Halide solid electrolytes include chloride solid electrolytes; optionally, chloride solid electrolytes include Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.6 In 0.6 Zr 0.4 Cl6, Li1.5 ZrOCl 3.5 Li3InO 0.2 Cl 5.6 LiNbOCl4, Li 1.5 AlOCl 2.5 、Li3In 0.5 Y 0.5 One or more of Cl6. Polymer solid electrolytes include one or more of PEO (polyethylene oxide), PAN (polyacrylonitrile), and PMMA (polymethyl methacrylate).

[0087] In some embodiments, the solid electrolyte material includes Li d MX d+3 The material includes 1≤d≤6, M including one or more of Al, Ga, In, Y, Zr, Nb, Sc, Ti, Mn, and La, and X including one or more of halogens, S, O, and P.

[0088] In some embodiments, the mass ratio of graphite material to solid electrolyte material in the negative electrode film is (6:4) to (9:1), optionally (7:3) to (8:2). This allows for a balance between the rate performance, cycle performance, and capacity of the secondary battery. Exemplarily, the mass ratio of graphite material to solid electrolyte material is 6:4, 7:3, 8:2, 9:1, or any value within a range of two such ratios.

[0089] In some embodiments, the volumetric particle size distribution Dv50 of the solid electrolyte material is 0.5 μm to 3 μm, optionally 0.7 μm to 1 μm. A volumetric particle size distribution Dv50 within this range allows the electrolyte material to effectively fill the voids between the graphite materials in the negative electrode active material layer, thereby improving the contact between the graphite materials and the solid electrolyte material, which in turn helps to improve the rate performance of the secondary battery. Exemplarily, the volumetric particle size distribution Dv50 of the solid electrolyte material is 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a value within a range consisting of any two of these values.

[0090] In some embodiments, the negative electrode film layer further includes an adhesive, which may include nitrile rubber, styrene-butadiene rubber, or silicone rubber.

[0091] In some embodiments, the binder accounts for 1 wt% to 5 wt% of the mass of the negative electrode film. This allows for improved stability of the negative electrode sheet without affecting the energy density of the secondary battery, thus balancing the cycle performance and energy density of the individual secondary battery cells. For example, the mass percentage of the binder in the negative electrode film is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any value within a range of two such values.

[0092] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, vapor-grown carbon fiber (VGCF), acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. This allows for the formation of a more stable conductive network, thereby improving the conductivity of the composite negative electrode and further enhancing the electrical performance of the secondary battery cell.

[0093] In some embodiments, the conductive agent has a mass percentage of 0 wt% to 2 wt% in the negative electrode film. This is beneficial for further improving the rate performance and conductivity of the secondary battery. For example, the binder has a mass percentage in the negative electrode film of 0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2 wt%, or any value within a range of two such values.

[0094] In some embodiments, the secondary battery cell further includes a positive electrode and an electrolyte membrane; the electrolyte membrane is located between the positive and negative electrode. The electrolyte membrane can be any of a solid electrolyte membrane, a gel electrolyte membrane, or a semi-solid electrolyte membrane.

[0095] Typically, a single rechargeable battery cell includes a positive electrode, a negative electrode, and an electrolyte membrane. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte membrane, positioned between the positive and negative electrodes, serves to conduct ions and prevent short circuits between the positive and negative electrodes.

[0096] Negative electrode sheet

[0097] 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, wherein the negative electrode film layer is the negative electrode film layer in the above embodiment.

[0098] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0099] 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 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.).

[0100] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, solid electrolyte material, conductive agent, binder nitrile rubber and any other components, in a non-aqueous solvent (e.g. xylene) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0101] Positive electrode sheet

[0102] 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. The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art and is not particularly limited.

[0103] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0104] 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.).

[0105] In some embodiments, when the battery cell 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 disclosure 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 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 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.

[0106] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this disclosure, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0107] In the examples of positive electrode active materials disclosed herein, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0108] In some embodiments, the positive electrode film layer also includes a solid electrolyte material.

[0109] In some embodiments, the solid electrolyte material includes one or more of sulfide solid electrolyte materials, oxide electrolyte materials, halide electrolyte materials, and polymer electrolyte materials. Exemplarily, the sulfide solid electrolyte includes at least one of binary compounds such as Li6PS5Cl, Li2S-GeS2, Li2S-P2S5, and Li2S-SiS2, and a ternary compound such as Li2S-MeS2-P2S5 (Me = Si, Ge, Sn, Al, etc.). The oxide solid electrolyte includes lithium lanthanum zirconium oxide series oxides or tin oxide solid electrolytes. The halide solid electrolyte includes chloride solid electrolytes; optionally, the chloride solid electrolyte includes Li... 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.6 In 0.6 Zr 0.4 Cl6, Li 1.5 ZrOCl 3.5 Li3InO 0.2 Cl 5.6 LiNbOCl4, Li 1.5 AlOCl 2.5 、Li3In 0.5 Y 0.5 One or more of Cl6. Polymer solid electrolytes include one or more of PEO (polyethylene oxide), PAN (polyacrylonitrile), and PMMA (polymethyl methacrylate).

[0110] In some embodiments, the solid electrolyte material includes Li d MX d+3 The material includes 1≤d≤6, M including one or more of Al, Ga, In, Y, Zr, Nb, Sc, Ti, Mn, and La, and X including one or more of halogens, S, O, and P.

[0111] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0112] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one of vapor-grown carbon fiber (VGCF), superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] In some embodiments, the positive electrode sheet can be prepared by uniformly mixing the components used to prepare the positive electrode sheet, such as the positive electrode active material, solid electrolyte material, and conductive agent, to obtain a composite positive electrode powder. A binder, nitrile rubber, is added to the composite positive electrode powder, and the mixture is rolled to obtain a positive electrode sheet with a certain thickness.

[0114] Electrolyte membrane

[0115] In some embodiments, the secondary battery cell includes a gel electrolyte membrane, a semi-solid electrolyte membrane, or a solid electrolyte membrane. The solid electrolyte membrane can be obtained by mixing one or more of the following: a binary compound such as Li6PS5Cl, Li2S-GeS2, Li2S-P2S5, or Li2S-SiS2; a ternary compound such as Li2S-MeS2-P2S5 (Me = Si, Ge, Sn, Al, etc.); and a binder such as PTFE, polyvinylidene fluoride, ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin, and then rolling them out.

[0116] In some implementations, the positive electrode, negative electrode, and electrolyte membrane can be fabricated into an electrode assembly using a winding or stacking process.

[0117] In some embodiments, the secondary battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0118] In some embodiments, the outer packaging of the secondary battery cell can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery cell can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0119] This disclosure does not impose any particular limitation on the shape of the secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square-structured secondary battery cell 5 as an example.

[0120] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may 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 the secondary battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0121] In some implementations, the secondary battery cells can be assembled into a battery module. The number of secondary battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0122] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple secondary battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0123] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0124] 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.

[0125] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0126] Electrical appliances

[0127] A second aspect of this disclosure provides an electrical device that includes a secondary battery cell provided in the first aspect of this disclosure.

[0128] Secondary battery cells and the battery modules they are assembled into can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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.

[0129] As an electrical device, you can choose from individual secondary battery cells, battery modules, or battery packs according to your usage requirements.

[0130] Figure 7 shows an example of an electrical device. This 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 device, a battery pack or battery module can be used.

[0131] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0132] Graphite materials

[0133] The third aspect of this disclosure provides a graphite material, including a pore structure, wherein the pore structure includes a mesoporous structure with a pore size of 2 nm to 50 nm, and the mesoporous structure accounts for more than or equal to 50% of the pore structure.

[0134] In this disclosure, the graphite material possesses a porous structure. On one hand, this porous structure provides more channels for lithium-ion transport and shortens the solid-phase diffusion path for lithium-ion insertion, which is beneficial for improving the cycle performance and rate performance of the secondary battery. On the other hand, the porous structure includes mesoporous structures with pore sizes ranging from 2 nm to 50 nm, and the proportion of mesoporous structures in the porous structure is greater than or equal to 50%. This ensures that the specific surface area and defect content of the graphite material are within a suitable range, thereby ensuring that the adsorption-desorption capacity generated by adsorption-desorption is within a suitable range, which is beneficial for improving the plateau capacity of the secondary battery cell. Therefore, the secondary battery cell in this disclosure can achieve a balance between high capacity, excellent rate performance, and cycle performance.

[0135] In some embodiments, the proportion of mesoporous structures in the pore structure is 60% to 80%, optionally 70% to 80%. Mesoporous structures facilitate the rapid transport of lithium ions, reduce the resistance to active ion transport, and improve the rate performance of secondary batteries. By controlling the proportion of mesoporous structures within the above range, it is further beneficial to achieve a balance between high capacity, excellent rate performance, and cycle performance in secondary batteries.

[0136] In some embodiments, the pore structure also includes macropores with a pore size greater than 50 nm, and the proportion of macropores in the pore structure is 10% to 25%, optionally 15% to 20%. This is beneficial for enabling secondary battery cells to achieve high capacity, excellent rate performance, and cycle performance.

[0137] In some embodiments, the pore structure also includes microporous structures with a pore size of less than 2 nm, and the proportion of micropores in the pore structure is 10% to 15%. Optionally, it is 8% to 12%. This results in a smaller proportion of microporous structures and a larger proportion of mesoporous structures in the graphite material, which is beneficial to further improve the rate performance, cycle performance and capacity of the secondary battery.

[0138] In some embodiments, the pore structure includes a through-hole structure that penetrates the graphite substrate. This through-hole structure further increases ion transport channels and shortens the lithium-ion insertion path, which is beneficial for further improving the rate performance, cycle performance, and capacity of the secondary battery cell.

[0139] In some embodiments, the Dv10 of the graphite material is 1 μm to 10 μm, and / or, the Dv50 of the graphite material is 1 μm to 20 μm, and / or, the Dv90 of the graphite material is 20 μm to 40 μm, and / or, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1 to 3. In this disclosure, setting the graphite material to have a suitable particle size distribution is more conducive to improving the cycle performance and rate performance of the secondary battery cells.

[0140] In some embodiments, the specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g. The specific surface area of ​​graphite materials is within this range, which is beneficial to increasing the effective contact area between graphite and solid electrolyte materials, increasing ion transport pathways, and further improving the rate performance and cycle performance of secondary batteries.

[0141] In some embodiments, the oil absorption value of the graphite material is 50 mL / 100g to 70 mL / 100g. This results in excellent dispersibility of the graphite material, which is beneficial for improving the electrochemical performance of the secondary battery.

[0142] In some embodiments, the graphitization degree of the graphite material is 90% to 96%. This results in the anode material having suitable compaction density and capacity, which is beneficial for maximizing the volumetric energy density of the composite anode.

[0143] In some embodiments, the OI value of the graphite material is between 1 and 6. An OI value within this range indicates that the graphite material has high isotropy, which is beneficial for improving its ion-conducting ability, thereby improving the rate performance and cycle performance of the secondary battery cell.

[0144] Preparation methods of graphite materials

[0145] The fourth aspect of this disclosure provides a method for preparing a graphite material, comprising the following steps: S1, mixing a graphite precursor and a structure directing agent at a mass ratio of 1:(2-6), and sintering at 700℃-1500℃ for 1h-5h to obtain a sintered product; S2, acid washing the sintered product to obtain a graphite material, the graphite material comprising a pore structure, the pore structure comprising a mesoporous structure with a pore size of 2nm-50nm, and the mesoporous structure accounting for more than or equal to 50% of the pore structure.

[0146] In this disclosure, by adjusting parameters such as the mass ratio of graphite precursor and structure-directing agent, sintering time, and sintering temperature, a porous graphite material can be prepared. This porous structure includes mesoporous structures with pore sizes ranging from 2 nm to 50 nm, and the proportion of mesoporous structures in the porous structure is greater than or equal to 50%. As a negative electrode material for secondary battery cells, this graphite material's porous structure provides more channels for lithium-ion transport and shortens the solid-phase diffusion path for lithium-ion insertion, which is beneficial for improving the cycle performance and rate performance of the secondary battery cell. Furthermore, the mesoporous structure and its proportion within the aforementioned range ensure that the specific surface area and defect content of the graphite material are within a suitable range, thereby ensuring that the adsorption-desorption capacity generated by adsorption-desorption is within a suitable range, which is beneficial for improving the plateau capacity of the secondary battery cell. Therefore, the secondary battery cell of this disclosure can achieve a balance between high capacity, excellent rate performance, and cycle performance.

[0147] In some embodiments, the mass ratio of graphite precursor to structure directing agent is 1:(2-5). In some embodiments, the sintering temperature is 700℃ to 1200℃. In some embodiments, the sintering time is 1h to 3h.

[0148] For example, the mass ratio of graphite precursor to structure-directing agent is 1:2, 1:3, 1:4, 1:5, 1:6, or any value within a range of two such values. The sintering temperature is 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or any value within a range of two such values. The sintering time is 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any value within a range of two such values.

[0149] In some embodiments, in step S1, the structure directing agent includes one or more of MgO, SiO2, CaCO3, and ZnCl2; optionally, the structure directing agent includes MgO.

[0150] In some embodiments, in step S1, the graphite precursor includes natural graphite and / or synthetic graphite.

[0151] In some embodiments, the volumetric particle size distribution Dv50 of the graphite precursor is 2 μm to 50 μm, optionally 7 μm to 14 μm. This facilitates the formation of graphite with a porous structure. Exemplarily, the volumetric particle size distribution Dv50 of the graphite precursor is a value between 2 μm, 6 μm, 7 μm, 10 μm, 14 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, or any two of these values.

[0152] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite precursor is 2 to 6, and optionally, (Dv90-Dv10) / Dv50 is 2.5 to 4.5. This facilitates the formation of a graphite material with a suitable volumetric particle size distribution. Exemplarily, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite precursor is a value between 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or any two of these values.

[0153] In some embodiments, the specific surface area of ​​the graphite precursor is 0.8 m². 2 / g~4m 2 / g, optionally, is 0.9m 2 / g~2m 2 / g. Therefore, graphite possesses a relatively dense surface structure, which is beneficial for controlling the pore structure formed subsequently. For example, the specific surface area of ​​the graphite precursor is 0.8m². 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g or any value within a range of two values. In one specific embodiment, the specific surface area of ​​the graphite precursor is 1m². 2 / g.

[0154] In some embodiments, in step S2, one or more of HCl, HF, HBr, HNO3, and H2SO4 can be used for acid washing; optionally, 1 mol of HCl or 1 mol of HF can be used for acid washing.

[0155] In some embodiments, when MgO is used as the structure directing agent in step S1, HCl can be used for acid washing in step S2; when SiO2 is used as the structure directing agent in step S1, HF can be used for acid washing in step S2; when CaCO3 is used as the structure directing agent in step S1, HCl can be used for acid washing in step S2; when ZnCl2 is used as the structure directing agent in step S1, HCl can be used for acid washing in step S2.

[0156] Example

[0157] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0158] Example 1

[0159] (1) Preparation of graphite materials

[0160] Step S1: The graphite precursor (Dv50 is 25 μm, (Dv90-Dv10) / Dv50 is 3.5, and specific surface area is 1 m²) is prepared. 2 After being mixed evenly in a ball mill jar with the structure-directing agent (MgO) powder at a mass ratio of 1:3, the mixture was transferred to a tube furnace and sintered at 1000°C for 2 hours to obtain the sintered product.

[0161] Step S2: Then, the sintered product is acid-washed with 1M dilute HCl to obtain graphite material.

[0162] Characterization of graphite material properties

[0163] (a) Aperture distribution test

[0164] Test method: By testing the distribution of pore structure using BET, it can be determined that the graphite material has a pore structure inside. According to the BET test results, in the graphite material of Example 1, the proportion of mesoporous structures with pore size of 2nm to 50nm is 75%, the proportion of macroporous structures with pore size greater than 50nm is 15%, and the proportion of microporous structures with pore size less than 2nm is 10%.

[0165] (b) Volumetric particle size distribution test

[0166] The volumetric particle size distribution of the graphite material in Example 1 was tested using a laser particle size analyzer in accordance with GB / T 19077-2016. The test results showed that the Dv10 of the graphite material in Example 1 was 7.5 μm, the Dv50 was 13.2 μm, the Dv90 was 29.5 μm, and the ratio of (Dv90-Dv10) / Dv50 was 1.7.

[0167] (c) Other performance tests

[0168] Reference standard procedure: GB / T 19587-2017 The specific surface area of ​​the graphite material in Example 1 was tested using the BET method and found to be 85 m². 2 / g. Reference standard procedures: JIS K 0131-1996, JB / T 4220-2011. The graphitization degree of the graphite material was tested to be 91.4%, and the OI value of the graphite material was 3.58. The volume (cm³) of dibutyl phthalate (DBP) absorbed by 100g of the graphite material in Example 1 was tested. 3 The oil absorption value is 60mL / 100g.

[0169] (2) Preparation of negative electrode sheet

[0170] The graphite material prepared above, the sulfide solid electrolyte Li6PS5Cl (Dv50 of 0.7 μm), and the binder nitrile rubber were uniformly mixed at a weight ratio of 80:18:2 and dissolved in xylene to obtain a negative electrode slurry. The negative electrode slurry was coated on the surface of a 6 μm thick copper foil current collector, dried, and cold-pressed to obtain a negative electrode sheet.

[0171] (3) Assembly of button cells

[0172] In an argon-filled glove box, firstly, 100 mg of sulfide electrolyte Li6PS5Cl was placed into a solid mold with a diameter of 10 mm and cold-pressed for 1 min under a pressure of 1 t to obtain a solid electrolyte membrane. Then, the negative electrode was placed on one side of the solid electrolyte membrane and cold-pressed for 3 min under a pressure of 4 t to compact it. Next, a lithium sheet with a copper current collector was placed on the other side of the solid electrolyte membrane and cold-pressed for 5 min under a pressure of 4 t to prepare a coin cell. In this cell, the lithium sheet in the counter electrode faces the solid electrolyte membrane, the thickness of the lithium sheet is 50 μm, and the thickness of the copper current collector is 6 μm.

[0173] Button cell battery performance test:

[0174] (1) Capacity test

[0175] At 25°C, the coin cell prepared above was charged to 2V at a constant current rate of 0.1C; after standing for 30 minutes, the coin cell was discharged to 0.01V at a constant current rate of 0.1C, and the first discharge capacity was recorded. The nominal capacity at 1C was 372mAh / g. The results are recorded in Table 2 below.

[0176] (2) Ratio Performance Test

[0177] At 25°C, the coin cell prepared above was charged to 2V at a constant current rate of 0.1C; after standing for 30 minutes, the coin cell was discharged to 0.01V at a constant current rate of 2C. The discharge capacity at this time was recorded, which is the discharge capacity at 2C. The nominal capacity at 1C is 372mAh / g. The results are recorded in Table 2 below.

[0178] (3) Cyclic performance test

[0179] At 25°C, the coin cell prepared above was charged to 2V at a constant current rate of 0.1C; after standing for 30 minutes, the coin cell was discharged to 0.01V at a constant current rate of 0.1C, and the discharge capacity C0 was recorded. The above process was repeated 3000 times to obtain the discharge capacity Cn after 3000 cycles. The capacity retention rate after 3000 cycles was (Cn / C0)*100%. The nominal capacity at 1C was 372mAh / g. The results are recorded in Table 2 below.

[0180] Comparative Example 1

[0181] The coin cell was prepared using the same method as in Example 1, except that the graphite precursor described above was used as the graphite material in the negative electrode sheet, and the graphite precursor did not have a mesoporous structure.

[0182] Comparative Example 2

[0183] The secondary coin cell was prepared using the same method as in Example 1, except that the parameters in step S1 were adjusted so that the proportion of the mesoporous structure in the graphite material used in the negative electrode was 40%.

[0184] Table 1 below shows the relevant parameters of the graphite materials in Example 1 and Comparative Examples 1 and 2. Table 2 below shows the relevant parameters of the coin cells in Example 1 and Comparative Examples 1 and 2.

[0185] Table 1

[0186] In Table 1, " / " indicates that the item does not exist.

[0187] Table 2

[0188] In Table 2, " / " indicates that the item does not exist.

[0189] As can be seen from Tables 1 and 2, compared with Comparative Example 1 (using graphite material without mesoporous structure in the negative electrode sheet) and Comparative Example 2 (using graphite material with mesoporous structure accounting for less than 50%), Example 1, by using graphite material with mesoporous structure accounting for more than or equal to 50% as the negative electrode material, can achieve a balance between the rate performance, cycle performance and capacity of the secondary battery.

[0190] Examples 2 to 11

[0191] The coin cells were prepared using the same method as in Example 1, except that the preparation process of the graphite material was adjusted according to Table 3 below, and the graphite materials prepared in Examples 2 to 11 were characterized using the same test methods as in Example 1. The results are shown in Table 3.

[0192] The coin cells prepared in Examples 2 to 11 were tested for capacity, rate performance and cycle performance using the same test method as in Example 1. The results are shown in Table 4.

[0193] Table 3 below shows the relevant parameters of the graphite materials in Examples 2 to 11, and Table 4 below shows the relevant parameters of the coin cells in Examples 2 to 11. In addition, for ease of comparison, the relevant parameters in Example 1 are also shown here.

[0194] Table 3

[0195] Table 4

[0196] As can be seen from Tables 3 and 4, by using graphite materials with a mesoporous structure of 50% or more as negative electrode materials, the rate performance, cycle performance and capacity of secondary batteries can be balanced.

[0197] Example 12

[0198] The coin cell was prepared using the same method as in Example 1, except that no solid electrolyte material was added during the preparation of the negative electrode. Specifically, the prepared graphite material and the binder nitrile rubber were uniformly mixed at a weight ratio of 98:2 and dissolved in xylene to obtain a negative electrode slurry. The negative electrode slurry was coated onto the surface of a 6 μm thick copper foil current collector, dried, and cold-pressed to obtain the negative electrode sheet.

[0199] Comparative Example 3

[0200] The coin cell was prepared using the same method as in Example 12, except that the parameters in step S1 were adjusted so that the proportion of the mesoporous structure in the graphite material used in the negative electrode sheet of Comparative Example 3 was 40%.

[0201] The coin cells prepared in Example 12 and Comparative Example 3 were tested for capacity, rate performance and cycle performance using the same test methods as in Example 1. The results are shown in Table 6.

[0202] Table 5 below shows the relevant parameters of the graphite materials in Example 12 and Comparative Example 3, and Table 6 below shows the relevant parameters of the coin cells in Example 12 and Comparative Example 3. Additionally, for ease of comparison, the relevant parameters from Example 1 are also shown here.

[0203] Table 5

[0204] Table 6

[0205] As can be seen from Tables 5 and 6, in the preparation of the negative electrode without adding solid electrolyte material, compared with Comparative Example 3 (the proportion of mesoporous structure in graphite material is less than 50%), Example 12, by making the proportion of mesoporous structure in graphite material within the scope of this disclosure, can make the prepared secondary battery have relatively better rate performance and capacity, but has a greater impact on cycle performance.

[0206] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. 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, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A secondary battery cell, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a graphite material having a porous structure, the porous structure comprising a mesoporous structure with a pore size of 2 nm to 50 nm, and the mesoporous structure accounting for more than or equal to 50% of the porous structure.

2. The secondary battery cell according to claim 1, wherein, The mesoporous structure accounts for 60% to 80% of the total pore structure.

3. The secondary battery cell according to claim 1 or 2, wherein, The pore structure includes macropores with a pore size greater than 50 nm; optionally, the macropores account for 10% to 25% of the total pore structure.

4. The secondary battery cell according to any one of claims 1 to 3, wherein, The pore structure also includes microporous structures with a pore size of less than 2 nm; optionally, the proportion of the microporous structure in the pore structure is 10% to 15%.

5. The secondary battery cell according to any one of claims 1 to 4, wherein, The hole structure includes a through-hole structure.

6. The secondary battery cell according to any one of claims 1 to 5, wherein, The graphite material includes one or more of the following characteristics: (1) 1μm≤Dv10≤10μm; (2) 1μm≤Dv50≤20μm; (3) 20μm≤Dv90≤40μm; (4) The volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1 to 3; (5) The specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g; (6) The oil absorption value of the graphite material is 50mL / 100g to 70mL / 100g; (7) The graphitization degree of the graphite material is 90% to 96%; (8) The OI value of the graphite material is 1 to 6.

7. The secondary battery cell according to any one of claims 1 to 6, wherein, The negative electrode film layer also includes a solid electrolyte material; Optionally, the solid electrolyte material includes one or more of the following: sulfide solid electrolyte material, oxide electrolyte material, halide electrolyte material, and polymer electrolyte material.

8. The secondary battery cell according to claim 7, wherein, The mass ratio of the graphite material to the solid electrolyte material in the negative electrode film is (6:4) to (9:1).

9. The secondary battery cell according to claim 7 or 8, wherein, The solid electrolyte material includes Li d MX d+3 The material includes 1≤d≤6, M including one or more of Al, Ga, In, Y, Zr, Nb, Sc, Ti, Mn, and La, and X including one or more of halogens, S, O, and P.

10. The secondary battery cell according to any one of claims 7 to 9, wherein, The volumetric particle size distribution Dv50 of the solid electrolyte material is 0.5 μm to 3 μm.

11. The secondary battery cell according to any one of claims 1 to 10, wherein, The secondary battery cell also includes a positive electrode and an electrolyte membrane; The electrolyte membrane is located between the positive electrode and the negative electrode.

12. The secondary battery cell according to any one of claims 1 to 11, wherein, The secondary battery cell is a solid-state secondary battery.

13. An electrical device comprising a secondary battery cell according to any one of claims 1 to 12.

14. A graphite material comprising a pore structure, the pore structure comprising a mesoporous structure with a pore size of 2 nm to 50 nm, and the mesoporous structure accounting for more than or equal to 50% of the pore structure.

15. The graphite material according to claim 14, wherein, The mesoporous structure accounts for 60% to 80% of the total pore structure; and / or, The pore structure includes macropores with a pore size greater than 50 nm, and optionally, the macropores account for 10% to 25% of the total pore structure; and / or, The pore structure includes microporous structures with a pore size of less than 2 nm. Optionally, the proportion of the microporous structure in the pore structure is 10% to 15%.

16. The graphite material according to claim 14 or 15, wherein, The hole structure includes a through-hole structure.

17. The graphite material according to any one of claims 14 to 16, wherein, The graphite material includes one or more of the following characteristics: (1) 1μm≤Dv10≤10μm; (2) 1μm≤Dv50≤20μm; (3) 20μm≤Dv90≤40μm; (4) The volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite material is 1 to 3; (5) The specific surface area of ​​the graphite material is 50 m². 2 / g~500m 2 / g; (6) The oil absorption value of the graphite material is 50mL / 100g to 70mL / 100g; (7) The graphitization degree of the graphite material is 90% to 96%; (8) The OI value of the graphite material is 1 to 6.

18. A method for preparing a graphite material, the method comprising the following steps: S1, the graphite precursor and the structure directing agent are mixed at a mass ratio of 1:(2~6) and sintered at 700℃~1500℃ for 1h~5h to obtain the sintered product; S2, the sintered product is acid-washed to obtain a graphite material, the graphite material having a porous structure, the porous structure including mesoporous structures with a pore size of 2nm to 50nm, and the proportion of the mesoporous structures in the porous structure being greater than or equal to 50%.

19. The preparation method according to claim 18, wherein, The structure-directing agent includes one or more of MgO, SiO2, CaCO3, and ZnCl2.

20. The preparation method according to claim 18 or 19, wherein, The graphite precursor includes one or more of the following features: (1) The graphite precursors include natural graphite and / or artificial graphite; (2) The volumetric particle size distribution Dv50 of the graphite precursor is 2μm to 50μm; (3) The volumetric particle size distribution (Dv90-Dv10) / Dv50 of the graphite precursor is 2 to 6; (4) The specific surface area of ​​the graphite precursor is 0.8 m². 2 / g~4m 2 / g.

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