An expanded graphite and a preparation method thereof, an electrode sheet, a battery, a battery pack, and an electric device

Abstract

The application provides expanded graphite and a preparation method thereof, a pole piece, a battery, a battery pack and an electric device. The interlamellar spacing of the expanded graphite is 40 nm to 100 nm. The expanded graphite can consider electronic transmission, structural resilience and interface fitting in the pole piece, helps to improve the stable contact of the internal interface of the battery, thereby being beneficial to reducing the operation difficulty, and further improving the cycle performance and rate performance of the solid-state battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an expanded graphite and its preparation method, an electrode, a battery, a battery pack, and an electrical device. Background Technology

[0002] Compared to traditional liquid batteries, solid-state batteries have natural advantages in terms of safety, such as the absence of electrolyte leakage or combustion risks. At the same time, they have higher theoretical energy density, making them particularly suitable for applications with high requirements for safety and energy density.

[0003] However, unlike liquid batteries, the solid-solid interface inside solid-state batteries is unstable. During operation, additional high pressure is usually required to maintain good interface contact and ensure stable cycle and rate performance. But this high pressure places stringent requirements on the battery assembly process, packaging structure, and the mechanical strength of the electrode materials, which is not conducive to achieving lightweight and flexible battery design and reducing manufacturing costs.

[0004] Therefore, reducing the operational complexity of solid-state batteries and improving their cycle performance and rate performance have become important research directions to promote their practical application. Summary of the Invention

[0005] This application provides an expanded graphite, which, by controlling the interlayer spacing of the expanded graphite within a specific range, can effectively reduce the demand for high operating voltage when applied to electrodes while maintaining excellent cycle performance and rate performance.

[0006] This application also provides a method for preparing expanded graphite, used to prepare the above-mentioned expanded graphite.

[0007] This application also provides an electrode comprising the aforementioned expanded graphite, thereby enabling solid-state batteries using this electrode to effectively reduce their dependence on high voltage.

[0008] This application also provides a battery including the aforementioned electrode, which thus maintains excellent cycle performance and rate performance even under low-voltage operating conditions.

[0009] This application also provides a battery pack comprising at least two of the aforementioned batteries, thus the battery pack can maintain excellent cycle performance and rate performance even under low-voltage operating conditions.

[0010] This application also provides an electrical device, including the above-mentioned battery or battery pack, which has the advantage of low manufacturing cost.

[0011] This application provides an expanded graphite with a layer spacing of 40nm~100nm.

[0012] The expanded graphite as described above has a plate spacing of 50 nm to 85 nm; and / or, the plate thickness of the expanded graphite is 1 nm to 10 nm.

[0013] The expanded graphite as described above has an average diameter of 0.5 μm to 8 μm, preferably 0.5 μm to 5 μm; and / or, the expanded graphite includes sulfur, preferably, the sulfur content in the expanded graphite is 20 ppm to 800 ppm.

[0014] The expanded graphite described above has an Id / Ig value of 0.15 to 0.55, preferably 0.2 to 0.5, in Raman spectroscopy.

[0015] This application also provides a method for preparing expanded graphite according to any one of the above claims, comprising the following steps: subjecting a mixed system comprising expanded graphite precursor, oxidant and intercalating agent to an oxidative intercalation reaction to obtain an expanded graphite intermediate; subjecting the expanded graphite intermediate to compression treatment and expansion treatment in sequence to obtain the expanded graphite; wherein the pressure of the compression treatment is 10 MPa to 50 MPa.

[0016] In the preparation method described above, the temperature of the oxidation intercalation reaction is 30℃~75℃, and the time of the oxidation intercalation reaction is 30min~120min; and / or, the pressure of the compression treatment is 20MPa~40MPa; and / or, the temperature of the expansion treatment is 700℃~1000℃, and the time of the expansion treatment is 0.5min~2min.

[0017] In the preparation method described above, the expanded graphite precursor includes at least one of natural flake graphite and cryptocrystalline graphite; and / or, the oxidant includes at least one of potassium dichromate, sodium dichromate and hydrogen peroxide; and / or, the intercalating agent includes at least one of sulfuric acid, phosphoric acid and nitric acid; and / or, the mass ratio of the expanded graphite precursor, the oxidant and the intercalating agent is 1:(0.05~1):(0.5~10).

[0018] The preparation method described above further includes, before the expansion treatment: heating the compressed product to 800℃~1200℃ in a composite gas and holding it at that temperature for 0.5h~3h; wherein the composite gas includes an inert gas and a sulfur source gas in a volume ratio of (90~95):(5~10); preferably, the sulfur source gas includes at least one of hydrogen sulfide and sulfur hexafluoride.

[0019] This application also provides an electrode sheet comprising expanded graphite as described in any of the preceding claims, or expanded graphite obtained by any of the preceding claims preparation methods.

[0020] The electrode as described above is a positive electrode, which includes a positive current collector and a positive active layer disposed on at least a portion of the surface of the positive current collector; the positive active layer includes 0.1% to 5% of the expanded graphite by mass percentage.

[0021] The electrode as described above is a negative electrode, which includes a negative current collector and a negative active layer disposed on at least a portion of the surface of the negative current collector; the negative active layer includes 0.1% to 5% of the expanded graphite by mass percentage.

[0022] This application also provides a battery comprising the electrode sheet described in any of the above claims.

[0023] The battery described above has an operating pressure of less than or equal to 10 MPa.

[0024] This application also provides a battery pack comprising at least two of the aforementioned batteries.

[0025] This application also provides an electrical device, including the battery or battery pack described above.

[0026] The expanded graphite provided in this application, by controlling the interlayer spacing to 40nm~100nm, enables the expanded graphite in the electrode to simultaneously construct conductive pathways and adapt to interface contacts, thereby improving the interface contact stability inside the battery under low pressure conditions and thus improving the battery's excellent cycle performance and rate performance. Attached Figure Description

[0027] Figure 1 This is a SEM image of expanded graphite from Embodiment 1 of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Due to the inherent properties of materials, the solid-solid interface compatibility between solid electrolytes and active materials is poor. Although adding solid electrolytes to the electrodes can alleviate the interface problem between the electrodes and the solid electrolyte layer to some extent, it is still difficult to maintain long-term stability of the interface between the two types of materials during battery cycling. At present, the interface adhesion is mainly maintained by applying high voltage during battery operation, such as applying high restraint pressure to the battery using constant-gap stainless steel clamps, thereby ensuring good cycle performance and rate performance. However, this undoubtedly increases the requirements for packaging and structural design, and also increases manufacturing costs.

[0030] To reduce the dependence of solid-state batteries on high operating voltages, the inventors conducted an in-depth analysis of the electrode structure. Typically, to improve the electron transport capability of the electrode, an appropriate amount of conductive agent (such as carbon black) needs to be added and uniformly dispersed within the electrode. Current research on conductive agents mainly focuses on their conductivity, neglecting the potential role of their mechanical properties. The inventors thus conceived the idea of ​​actively maintaining interfacial stability by improving the mechanical properties of the conductive agent through structural design, thereby reducing the solid-state battery's reliance on external high voltages.

[0031] Following this line of thought, expanded graphite, with its compression-rebound properties, attracted the inventors' attention. They attempted to utilize its elastic deformation characteristics, making it adapt to interface deformation during battery operation like a spring, thereby maintaining good interfacial contact. However, the mechanical properties of existing forms of expanded graphite still have shortcomings. Therefore, it is necessary to conduct targeted structural design on expanded graphite to improve its dynamic interfacial adaptability during cycling, thereby reducing the battery's high-voltage requirements while achieving excellent cycle and rate performance.

[0032] Based on this, this application provides an expanded graphite with a layer spacing of 40nm~100nm.

[0033] Specifically, such as Figure 1 As shown, the expanded graphite framework of this application originates from the stacking of graphite crystal sheets, forming a three-dimensional layered network with compressible and resilient properties. Each graphite sheet is composed of multiple (greater than or equal to 3) stacked graphite sheets. The spacing between the graphite sheets differs from the spacing between individual graphene layers within each graphene sheet. The spacing between the expanded graphite sheets in this application refers to the distance between adjacent graphite sheets, primarily used to reflect the mechanical resilience and compressibility of the expanded graphite.

[0034] Specifically, when the interlayer spacing is greater than or equal to 40 nm, it indicates that the layered structure in the expanded graphite is highly expanded, with sufficient compression and rebound space. This is beneficial for actively compensating for the microscopic gaps between active material particles and solid electrolyte particles through structural deformation under low-pressure operating conditions, thereby maintaining the continuity of the electronic conductive network and sufficient contact between solid and solid interfaces. When the interlayer spacing is less than or equal to 100 nm, it indicates that the interlayer expansion is appropriate, and there is sufficient interaction force between the graphite layers. The expanded graphite can effectively rebound without becoming excessively loose after being compressed, thereby avoiding irreversible slippage or structural collapse caused by weak interlayer bonding force, and preventing problems such as decreased resilience and insufficient mechanical support.

[0035] The expanded graphite in this application does not merely exist as a traditional electronically conductive filler, but rather, through its layered unfolded structure, constructs a composite support network that combines electronic transport and mechanical buffering. When mixed with active materials, solid electrolytes, and optional binders, the expanded graphite sheets can undergo a certain degree of reversible compression under pressure, causing partial compression of the layered voids and forming surface, line, or multi-point overlapping contacts with surrounding particles. After the external pressure is released, the interlayer space retained within provides sufficient springback margin, thereby continuously compensating for interfacial gaps caused by particle rearrangement, volume changes, or localized stress release.

[0036] In summary, when the expanded graphite of this application is applied to the electrode, it can not only exhibit excellent conductivity, but also actively adapt to interface changes by utilizing reversible compression and rebound characteristics, thereby reducing dependence on external high voltage while improving the cycle performance and rate performance of the battery.

[0037] Furthermore, when the interlayer spacing of expanded graphite is 50nm~85nm, the reversible compression and rebound characteristics of expanded graphite can be further optimized, which is beneficial to further improve the interface stability of solid-state batteries.

[0038] In one specific implementation, the thickness of the expanded graphite sheets is 1 nm to 10 nm.

[0039] By controlling the thickness of the expanded graphite sheets within the aforementioned range, it is possible to ensure that the expanded graphite sheets have sufficient mechanical strength to maintain structural integrity, while also giving them appropriate flexibility. This allows them to undergo reversible bending or compression under low pressure conditions due to interfacial deformation, thereby continuously compensating for the interfacial gaps caused by changes in the volume of the active material, maintaining the continuity of the conductive network and stable contact between the solid and solid interfaces, and further improving the cycle performance and rate performance of solid-state batteries.

[0040] In one specific embodiment, the average diameter of the expanded graphite is 0.5 μm to 8 μm.

[0041] In detail, by controlling the average diameter of expanded graphite within the aforementioned range, it can achieve both good filling properties and structural support, avoiding uneven dispersion and poor interfacial adhesion caused by excessively large particle size, while overcoming the problem of insufficient support caused by excessively small particle size. This particle size range is conducive to the full spreading and overlapping of expanded graphite in the electrode, forming a low-resistance continuous electronic network, and maintaining adhesion to the active material and electrolyte interface after pressure release, thereby enhancing the structural adaptability and interfacial stability of the electrode, and further improving the rate performance, cycle life and overall reliability of solid-state batteries.

[0042] Furthermore, when the average diameter of expanded graphite is 0.5μm~5μm, the rate performance, cycle life and overall reliability of solid-state batteries are further improved.

[0043] In one specific implementation, expanded graphite includes sulfur.

[0044] It is understandable that expanded graphite contains sulfur, which can form sulfur-containing functional groups or sulfur-doped structures on the surface of expanded graphite, effectively improving the interfacial contact between expanded graphite and solid electrolyte, thereby improving the cycle performance and rate performance of solid-state batteries.

[0045] In one specific embodiment, the sulfur content in the expanded graphite is 20ppm to 800ppm.

[0046] Specifically, when the sulfur content is controlled within the aforementioned range, an appropriate amount of sulfur-containing functional groups or sulfur-doped structures are formed on the surface of expanded graphite. This effectively improves its chemical affinity and interfacial contact with solid electrolytes (especially sulfide solid electrolytes), while avoiding interfacial side reactions or structural degradation caused by excessive sulfur. Simultaneously, this sulfur content range synergistically complements the aforementioned interlayer spacing, enabling expanded graphite in solid-state batteries to possess excellent electronic conductivity, reversible compression resilience, and interfacial chemical stability. This further reduces interfacial impedance and maintains stable solid-solid interface contact under low-pressure operating conditions, thereby improving the cycle performance and rate performance of solid-state batteries.

[0047] In one specific implementation, the Id / Ig value of expanded graphite is 0.15 to 0.55.

[0048] The Id / Ig value represents the ordered crystalline structure of expanded graphite (G peak, 1580 cm⁻¹). -1 (nearby) and defect-disordered structure (D peak, 1350 cm) -1 The relative proportions of Id / Ig (nearby). By controlling Id / Ig within the above range, the intrinsic conductivity of expanded graphite can be maintained while suppressing the interfacial side reaction activity caused by excessive defects, thereby reducing its tendency for undesirable interfacial reactions with the solid electrolyte.

[0049] Specifically, solid electrolytes typically exhibit high reactivity. Traditional conductive agents (such as carbon black and carbon nanotubes) have poor surface crystallinity and abundant defect sites, making them prone to side reactions upon contact with solid electrolytes. This leads to the formation of a high-impedance interfacial phase, resulting in increased interfacial resistance and decreased cycle stability. By controlling the Id / Ig value of expanded graphite within the aforementioned range, on the one hand, it ensures that the expanded graphite has a sufficiently high degree of order in its microcrystals, which is beneficial for the rapid transport of electrons along the microcrystal plane and maintains excellent conductivity. On the other hand, it avoids the introduction of excessive active sites due to too many disordered defects, reducing side reactions between the expanded graphite surface and the solid electrolyte, thereby suppressing the deterioration of interfacial impedance.

[0050] Therefore, by controlling the Id / Ig value of expanded graphite within the above range, the interfacial chemical stability inside the electrode can be further improved, thereby further improving the cycle performance and rate performance of solid-state batteries.

[0051] Furthermore, when the Id / Ig value of expanded graphite is 0.2~0.5, the interfacial chemical stability inside the electrode is higher, and the cycle performance and rate performance of the solid-state battery are further improved.

[0052] When testing expanded graphite in batteries, it can be tested directly or the discharged battery can be disassembled, and the electrode sheets can be removed and separated. The separation method is as follows: place the electrode sheets in a hydrochloric acid solution with a concentration of 1 mol / L to 3 mol / L and sonicate for 0.2 h to 2 h; separate the resulting solution from the insoluble components by filtration or centrifugation. The insoluble components mainly include active materials and conductive agents; dry the insoluble components and grind them into particles, then add them to solvents such as ethanol, acetone, or xylene and sonicate to form a suspension, and then separate them by centrifugation to obtain expanded graphite.

[0053] The above parameters of expanded graphite were tested using the following methods:

[0054] 1. Spacing and thickness of the boards: such as Figure 1 As shown, the spacing between expanded graphite plates and the thickness of expanded graphite plates were analyzed by SEM. The average value was taken from 100 random locations for each of the plate spacing and thickness.

[0055] 2. Average diameter: SEM scan of expanded graphite was performed, and the maximum size of 10 expanded graphite particles in the stacking direction was randomly counted. The average diameter was obtained by averaging the values.

[0056] 3. Id / Ig value: Raman spectroscopy was performed on expanded graphite with an excitation wavelength of 532 nm. The peak heights and intensities of the D peak (approximately 1350 cm⁻¹) and the G peak (approximately 1580 cm⁻¹) were read. Finally, the ratio of the G peak intensity to the D peak intensity was calculated, which is the Ig / Id value.

[0057] 4. Sulfur content in expanded graphite: The sulfur content in expanded graphite was measured by inductively coupled plasma optical emission spectrometry (ICP) and recorded.

[0058] This application also provides a method for preparing the aforementioned expanded graphite, comprising the following steps: subjecting a mixed system including an expanded graphite precursor, an oxidant and an intercalating agent to an oxidative intercalation reaction to obtain an expanded graphite intermediate; subjecting the expanded graphite intermediate to a compression treatment and an expansion treatment in sequence to obtain expanded graphite; wherein the compression treatment pressure is 10 MPa to 50 MPa.

[0059] The above preparation method allows for precise control of the interlayer spacing of expanded graphite to a target range. Specifically, during the oxidation intercalation reaction, the oxidant introduces oxygen-containing functional groups into the graphite interlayers, while the intercalating agent inserts into the interlayers to expand the interlayer spacing, forming an expanded graphite intermediate with a loose structure and weakened interlayer bonding. Subsequently, the expanded graphite intermediate is compressed by applying physical pressure within the aforementioned range, forcing the over-expanded graphite layers to undergo controllable densification, shrinking the interlayer spacing to a suitable range, and restoring certain interlayer interactions. Finally, an expansion treatment is performed, causing the intercalating material to rapidly decompose and escape at high temperature, allowing the graphite layers to expand appropriately again, forming expanded graphite with reversible compression and resilience properties.

[0060] In one specific embodiment, the temperature of the oxidation intercalation reaction is 30℃~75℃, and the time of the oxidation intercalation reaction is 30min~120min.

[0061] In detail, by carrying out the oxidation intercalation reaction at the above temperature and time, the oxidant and intercalating agent can gradually enter the graphite interlayer under relatively mild conditions, forming a uniform and controllable interlayer activation structure. This is beneficial for subsequent rapid expansion and avoids excessive damage to the graphite skeleton caused by excessive temperature, thus achieving a better balance between sufficient intercalation and structural integrity.

[0062] Furthermore, when the compression treatment pressure is 20MPa~40MPa, the obtained expanded graphite has better mechanical properties in solid-state batteries, thereby further reducing the battery's dependence on external high voltage and improving the cycle performance and rate performance of solid-state batteries.

[0063] In one specific embodiment, the puffing temperature is 700℃~1000℃, and the puffing time is 0.5min~2min.

[0064] In detail, when the compressed product is heated at the above temperature and time, the interlayer residual components will rapidly decompose and release gas, which will promote the peeling of the layers. The air environment further helps to form a stable expanded morphology, so that the expanded graphite can obtain a larger interlayer spacing and a more moderate level of crystallization defects, which is conducive to better contact and adaptation with the active materials and solid electrolytes in solid-state batteries.

[0065] In one specific embodiment, the expanded graphite precursor includes at least one of natural flake graphite and cryptocrystalline graphite.

[0066] Based on their crystal morphology, graphite can be divided into flake graphite and cryptocrystalline graphite. Flake graphite is a natural phanerocrystalline graphite, resembling fish scales, belonging to the hexagonal crystal system, and exhibiting a layered structure. It possesses excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance, and is abundant and inexpensive. Cryptocrystalline graphite, on the other hand, is an aggregate of microcrystalline graphite with a crystal diameter of less than 1 micrometer. It appears as a black, earthy substance and is also known as earthy graphite, microcrystalline graphite, or amorphous graphite.

[0067] The aforementioned expanded graphite precursor can balance the wide availability of raw material sources and the adaptability of preparation processes. This is beneficial for producing expanded graphite with more uniform sheet expansion and better electrical conductivity, and also helps to further reduce production costs and improve process flexibility.

[0068] In one specific embodiment, the oxidant includes at least one of potassium dichromate, sodium dichromate, and hydrogen peroxide.

[0069] In detail, the aforementioned oxidant has moderate oxidizing power and controllable reaction, enabling uniform and appropriate interlayer oxidation of the expanded graphite precursor during the intercalation process. This avoids excessive oxidation leading to graphite skeleton collapse or increased structural disorder, while also preventing low intercalation efficiency caused by insufficient oxidation. This allows for more effective control of the expanded graphite's layer expansion and surface chemical state, thereby optimizing its compression resilience and interfacial compatibility.

[0070] In one specific embodiment, the intercalating agent includes at least one of sulfuric acid, phosphoric acid, and nitric acid.

[0071] In detail, the aforementioned intercalating agent can effectively insert into the interlayer of graphite, working synergistically with the oxidant to promote the controllable expansion of the layered structure, while avoiding the introduction of difficult-to-remove impurity ions or adverse effects on subsequent battery systems. While ensuring intercalation efficiency, it achieves more effective control over the interlayer spacing of expanded graphite plates and maintains the ordered structure of graphite microcrystals. This ensures that expanded graphite in solid-state batteries possesses excellent conductivity continuity, elastic adaptability, and interfacial chemical stability, further reducing the battery's dependence on external high voltage.

[0072] In one specific embodiment, the mass ratio of the expanded graphite precursor, oxidant, and intercalating agent is 1:(0.05~1):(0.5~10).

[0073] In detail, when the mass ratio of the three components is controlled within the above range, the oxidant can achieve uniform and moderate interlayer oxidation of the graphite precursor, while the intercalating agent synergistically enters the interlayer to fully expand the graphite layers, forming an expanded graphite intermediate with a loose structure but a complete skeleton. After subsequent compression and expansion treatments, this intermediate can yield expanded graphite with superior compression resilience, thereby further improving battery cycle performance and rate performance.

[0074] In one specific embodiment, before the expansion treatment, the process further includes: heating the compressed product to 800°C~1200°C in a composite gas and holding it at that temperature for 0.5h~3h; wherein the composite gas includes an inert gas and a sulfur source gas in a volume ratio of (90~95):(5~10); preferably, the sulfur source gas includes at least one of hydrogen sulfide and sulfur hexafluoride.

[0075] By performing surface modification on the compressed product in the composite gas as described above, an appropriate amount of sulfur can be introduced onto the surface of expanded graphite, thereby further improving the interfacial compatibility between expanded graphite and solid electrolyte.

[0076] Specifically, the active sulfur produced by the decomposition of sulfur source gas at high temperatures can chemically bond or physically adsorb with carbon atoms on the surface of expanded graphite, forming sulfur-containing functional groups or sulfur-doped structures. The introduced sulfur element can form a good chemical affinity with solid electrolytes, especially sulfide solid electrolytes, enhancing the bonding strength between the two phases, suppressing the formation of high-resistivity interface phases, thereby further reducing interface impedance, improving interface stability, and maintaining superior cycling performance and rate performance.

[0077] This application also provides an electrode sheet comprising the aforementioned expanded graphite or expanded graphite obtained by the aforementioned preparation method. This electrode sheet has advantages corresponding to the aforementioned expanded graphite, which will not be elaborated further here.

[0078] This application does not specifically limit the type of electrode; for example, it can be a positive electrode or a negative electrode. Specifically, the electrode in this application includes a current collector and an active layer formed of active material disposed on the surface of the current collector.

[0079] In the specific preparation of the electrode, for example, the expanded graphite of this application can be dispersed with active materials, conductive agents, solid electrolytes and binders in an appropriate amount of xylene solvent, and thoroughly stirred and mixed to form a uniform slurry; the slurry is uniformly coated on the current collector, and after drying, rolling and cutting, the electrode is obtained.

[0080] The positive electrode current collector can be at least one of aluminum foil or nickel foil; the negative electrode current collector can be at least one of copper foil, nickel foam, or copper foam; the positive electrode active material can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, or lithium-rich manganese-based materials; the negative electrode active material can be at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), or tin-based negative electrode materials (mainly including tin and tin alloys).

[0081] The positive electrode binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), hydrogenated nitrile butadiene rubber (HNBR), polytetrafluoroethylene (PTFE), and styrene-butadiene rubber; the negative electrode binder includes, but is not limited to, one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyolefins (such as polypropylene, polyethylene, etc.), hydrogenated nitrile butadiene rubber (HNBR), carboxymethyl cellulose (CMC), and sodium alginate.

[0082] The solid electrolyte can be selected from at least one of sulfide solid electrolytes, metal oxide solid electrolytes, and polymer solid electrolytes. Taking sulfide solid electrolytes as an example, they can be glass-based sulfide solid electrolytes (sulfide glasses), glass-ceramic-based sulfide solid electrolytes, or crystalline sulfide solid electrolytes. Sulfide glasses are amorphous and have a glass transition temperature (Tg). Furthermore, when the sulfide solid electrolyte has a crystalline phase, examples of crystalline phases include the Thio-LISICON type, the LGPS type, and the sulfide-germanium ore type. The sulfide solid electrolyte may contain, for example, Li, X (X being at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S. Additionally, the sulfide solid electrolyte may further contain at least one of O and a halogen element. Furthermore, the sulfide solid electrolyte may contain S as the main component of the anionic element. Sulfide solid electrolytes can be selected from, for example, Li₂S-P₂S₅, Li₂S-P₂S₅-LiI, Li₂S-P₂S₅-GeS₂, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-P₂S₅-LiBr, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (Where m and n are positive numbers; Z is any one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (Where x and y are positive numbers; M is any one of P, Si, Ge, B, Al, Ga, and In). There are no particular limitations on the composition of sulfide solid electrolytes; for example, xLi₂S·(100-x)P₂S₅ (70≤x≤80) and yLiI·zLiBr·(100-yz)(xLi₂S·(1-x)P₂S₅) (0.7≤x≤0.8, 0≤y≤30, 0≤z≤30) can be listed.

[0083] In one specific embodiment, the electrode is a positive electrode, which includes a positive current collector and a positive active layer disposed on at least a portion of the surface of the positive current collector; the positive active layer includes 0.1% to 5% expanded graphite by mass percentage.

[0084] Specifically, an appropriate amount of expanded graphite can construct a highly efficient and continuous electron transport network within the positive electrode active layer. Simultaneously, its reversible compression and rebound properties, characteristic of its layered structure, provide elastic buffering capacity, thereby adapting to the volume changes of the positive electrode active material during charge and discharge, maintaining tight adhesion at the solid-solid interface, and further improving the cycle performance and rate performance of the solid-state battery. Furthermore, based on mass percentage, the positive electrode active layer can also include 70%–75% positive electrode active material, 1%–2% binder, and 21%–28% solid electrolyte.

[0085] In one specific embodiment, the electrode is a negative electrode, which includes a negative current collector and a negative active layer disposed on at least a portion of the surface of the negative current collector; the negative active layer includes 0.1% to 5% expanded graphite by mass percentage.

[0086] Specifically, an appropriate amount of expanded graphite, with its reversible compression and rebound properties due to its layered structure, can better adapt to drastic volume fluctuations in the negative electrode active layer. Through its own structural deformation, it continuously compensates for interfacial gaps caused by particle displacement or volume changes, thereby maintaining the continuity of the conductive network and the contact stability of the solid-solid interface. The negative electrode can maintain stable electrochemical performance under complex operating conditions, thus further improving the cycle life and rate performance of solid-state batteries. Furthermore, according to mass percentage, the negative electrode active layer can also include 60%–65% negative electrode active material, 1%–2% binder, and 31%–38% solid electrolyte.

[0087] This application also provides a battery including the aforementioned electrode, which has advantages corresponding to the aforementioned expanded graphite, which will not be elaborated further here.

[0088] In the specific battery fabrication process, for example, it can be carried out in an environment with a dew point temperature below -50°C. The solid electrolyte and binder are dispersed in xylene to obtain a solid electrolyte slurry. The solid electrolyte slurry is then coated onto the surface of a metal substrate and dried to obtain a solid electrolyte layer. The electrolyte layer is then rolled and transferred onto a negative electrode, and the substrate is peeled off. The negative electrode, electrolyte layer, and positive electrode are stacked in that order to form a battery cell, which is then subjected to isostatic pressing at 500 MPa to obtain the battery. The selection range of solid electrolyte and binder in the solid electrolyte layer can be referenced from the selection range of solid electrolyte and binder in the aforementioned electrode.

[0089] In one specific implementation, the battery's operating pressure is less than or equal to 10 MPa.

[0090] Specifically, the battery operating pressure refers to the restraint pressure experienced during operation. Controlling the battery operating pressure within the aforementioned range allows for full utilization of the structural adaptability advantages of the expanded graphite in this application under low-pressure conditions. The expanded graphite in this application can actively compensate for the microscopic gaps between active material particles and solid electrolyte particles through the elastic deformation of its layered structure, maintaining the continuity of the electronic conductivity network and sufficient contact at the solid-solid interface. Therefore, by controlling the battery operating pressure within the aforementioned range, not only can the dependence of solid-state batteries on external high voltage be reduced, simplifying the packaging structure and assembly process, reducing battery weight, and lowering manufacturing costs, but also, through the synergistic effect of the expanded graphite in this application, excellent cycle performance and rate performance can be maintained, promoting the development of solid-state batteries towards lightweight, flexible, and low-cost designs.

[0091] This application also provides a battery pack comprising at least two of the aforementioned batteries, which has advantages corresponding to the expanded graphite described above, which will not be elaborated further here.

[0092] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0093] This application also provides an electrical device, including the aforementioned battery or battery pack, which has advantages corresponding to the aforementioned expanded graphite, and will not be elaborated further here.

[0094] The electrical equipment used in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars, car chassis), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without any particular limitation.

[0095] The expanded graphite, electrode, and battery provided in this application will be described in detail below through specific embodiments.

[0096] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0097] Example 1

[0098] The battery preparation method of this embodiment includes the following steps:

[0099] 1) Add expanded graphite precursor (natural flake graphite) to the intercalating agent (sulfuric acid), and then add the oxidizing agent (potassium dichromate) to obtain a mixed system. Heat to 50℃ and carry out an oxidation intercalation reaction for 80 min. After filtration, wash the precipitate with deionized water and dry to obtain expanded graphite intermediate. The mass ratio of expanded graphite precursor, oxidizing agent and intercalating agent is 1:0.5:1.2.

[0100] 2) The expanded graphite intermediate was placed in a powder compressor and subjected to a pressure of 30 MPa. Then, in a composite gas (argon and hydrogen sulfide in a volume ratio of 95:5), the compressed product was heated to 1100℃ and held for 2 hours to complete the surface modification. After that, it was placed in air, heated to 900℃ and held for 1 minute to obtain expanded graphite.

[0101] 3) The positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2), solid electrolyte (Li6PS5Cl), conductive agent (expanded graphite), and binder (styrene-butadiene rubber) are dispersed in a solvent (xylene) to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector (aluminum foil), and after drying, cold pressing, and slitting, a positive electrode sheet is obtained. The mass ratio of the positive electrode active material, solid electrolyte, and binder is 70:28:1, and the mass percentage of the conductive agent in the positive electrode active layer is 1%.

[0102] 4) The negative electrode active material (silicon-carbon material with a Si to C mass ratio of 46:54), solid electrolyte (Li6PS5Cl), conductive agent (carbon black), and binder (styrene-butadiene rubber) are dispersed in a solvent (xylene) at a mass ratio of 60:38:1:1 to obtain a negative electrode slurry; the negative electrode slurry is coated on both surfaces of the negative electrode current collector (copper foil), and after drying, cold pressing, and slitting, a negative electrode sheet is obtained; wherein, the mass ratio of negative electrode active material, solid electrolyte, and binder is 60:38:1, and the mass percentage content of conductive agent in the negative electrode active layer is 1%;

[0103] 5) Disperse the solid electrolyte (Li6PS5Cl) and binder (styrene-butadiene rubber) in a solvent (xylene) at a mass ratio of 97:3 to obtain a solid electrolyte slurry; coat the solid electrolyte slurry onto the surface of an aluminum foil substrate and dry it to obtain an electrolyte layer;

[0104] 6) Roll transfer the electrolyte layer onto the negative electrode sheet and peel off the aluminum foil substrate; stack the negative electrode sheet, electrolyte layer and positive electrode sheet in the order of negative electrode sheet, electrolyte layer and positive electrode sheet to form a cell, so that the capacity ratio of negative electrode sheet to positive electrode sheet is 1:1; then perform isostatic pressing at 500 MPa pressure to obtain the battery.

[0105] Examples 2 to 14 and Comparative Examples 3 to 5 differ from Example 1 in that the electrode type, compression pressure, intercalation oxidation reaction temperature, intercalation oxidation reaction time, expansion treatment temperature, selection of expanded graphite precursor, oxidant, and intercalating agent and their mass ratio, surface modification temperature and time, selection and volume ratio of inert gas and sulfur source gas, and mass percentage of expanded graphite material in the active layer are different. For details, please refer to Table 1.

[0106] In Examples 1-10, Example 13, and Comparative Examples 3 and 4, only the positive electrode sheet uses expanded graphite; in Examples 11-12 and Comparative Example 5, only the negative electrode sheet uses expanded graphite; in Example 14, both the positive and negative electrode sheets use expanded graphite. When only the positive or negative electrode sheet uses fibrous carbon material, the conductive agent for the other electrode sheet is carbon black.

[0107] Except for the differences shown in Table 1 and those described above, the remaining steps and conditions are the same as in Example 1.

[0108] Table 1

[0109]

[0110] Comparative Example 1

[0111] The preparation method of this comparative battery is basically the same as that of Example 1, except that carbon black is used as the conductive agent in step 2).

[0112] Comparative Example 2

[0113] The preparation method of this comparative battery is basically the same as that of Example 1, except that carbon fiber is used as the conductive agent in step 2).

[0114] Experimental Example 1

[0115] 1. The interlayer spacing, sulfur content, interlayer thickness, average diameter, and Id / Ig value of expanded graphite in all embodiments and comparative examples were tested, and the test results are shown in Table 2; among them,

[0116] The discharged battery was disassembled, and the electrode was removed. The electrode was placed in a 2 mol / L hydrochloric acid solution and sonicated for 1 hour. The resulting solution was separated from the insoluble components by filtration or centrifugation. The insoluble components were dried and ground into particles, then added to ethanol and sonicated to form a suspension. The expanded graphite was then obtained by centrifugation.

[0117] 1) Spacing and thickness of the boards: such as Figure 1 As shown, the spacing between expanded graphite plates and the thickness of expanded graphite plates were analyzed by SEM. The average value was taken from 100 random locations for each of the plate spacing and thickness.

[0118] 2) Average diameter: SEM scan of expanded graphite was performed, and the maximum size of 10 expanded graphite particles in the stacking direction was randomly counted. The average diameter was obtained by averaging the values.

[0119] 3) Id / Ig value: Raman spectroscopy (532 nm) was performed on expanded graphite, and the peak height intensity of the D peak (approximately 1350 cm⁻¹) and the G peak (approximately 1580 cm⁻¹) were read respectively. Finally, the ratio of the intensity of the G peak to the intensity of the D peak was calculated, which is the Ig / Id value.

[0120] 4) S element content: The S element content of expanded graphite was measured by inductively coupled plasma spectrometry (ICP) and recorded.

[0121] 2. Cyclic testing and rate testing were performed on the batteries of the examples and comparative examples, respectively. The test results are shown in Table 1; among them,

[0122] Cyclic test: Apply a preset restraint pressure (operating pressure) to the battery using a constant gap stainless steel clamp, charge it at a constant current of 0.5C to 4.2V at 25℃, maintain constant voltage charging until the current is less than or equal to 0.05C, let it stand for 10 minutes, and then discharge it at 0.5C to 2.5V; record the first discharge capacity as C1, repeat the cycle for 200 cycles, and record the capacity after 200 cycles as C200. The battery's capacity retention rate after 200 cycles is C200 / C1*100%.

[0123] Rate test: Apply a preset restraint pressure (operating pressure) to the battery using a constant gap stainless steel clamp, charge it to 4.2V at a constant current of 0.1C at 25℃, maintain constant voltage charging until the current is less than or equal to 0.05C, and then discharge it to 2.5V at 0.1C. Record the discharge capacity as C0. Subsequently, charge it to 4.2V at a constant current of 1C and record the 1C charging capacity as C1. The 1C rate capacity retention rate is C1 / C0*100%.

[0124] Table 2

[0125]

[0126] As can be seen from Tables 1 and 2, the expanded graphite of this application can effectively reduce the high voltage requirement during solid-state battery operation when applied to the electrode, while achieving excellent cycle performance and rate performance.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An expanded graphite, characterized in that, The interlayer spacing of the expanded graphite is 40nm~100nm.

2. The expanded graphite according to claim 1, characterized in that, The interlayer spacing of the expanded graphite is 50 nm to 85 nm; and / or, The thickness of the expanded graphite sheets is 1 nm to 10 nm.

3. The expanded graphite according to claim 1 or 2, characterized in that, The expanded graphite has an average diameter of 0.5 μm to 8 μm, preferably 0.5 μm to 5 μm; and / or, The expanded graphite includes sulfur, and preferably, the sulfur content in the expanded graphite is 20ppm to 800ppm.

4. The expanded graphite according to any one of claims 1-3, characterized in that, In Raman spectroscopy, the Id / Ig value of the expanded graphite is 0.15~0.55, preferably 0.2~0.

5.

5. A method for preparing expanded graphite according to any one of claims 1-4, characterized in that, Includes the following steps: An oxidative intercalation reaction is carried out on a mixed system comprising an expanded graphite precursor, an oxidant, and an intercalating agent to obtain an expanded graphite intermediate; the expanded graphite intermediate is then subjected to compression and expansion treatments in sequence to obtain the expanded graphite; wherein the compression treatment pressure is 10 MPa to 50 MPa.

6. The preparation method according to claim 5, characterized in that, The oxidation intercalation reaction is carried out at a temperature of 30℃ to 75℃ for a duration of 30 min to 120 min; and / or, The compression treatment pressure is 20MPa~40MPa; and / or, The puffing process is carried out at a temperature of 700℃ to 1000℃ for a duration of 0.5 min to 2 min.

7. The preparation method according to claim 5 or 6, characterized in that, The expanded graphite precursor includes at least one of natural flake graphite and cryptocrystalline graphite; and / or, The oxidant includes at least one of potassium dichromate, sodium dichromate, and hydrogen peroxide; and / or, The intercalating agent includes at least one of sulfuric acid, phosphoric acid, and nitric acid; and / or, The mass ratio of the expanded graphite precursor, the oxidant, and the intercalating agent is 1:(0.05~1):(0.5~10).

8. The preparation method according to any one of claims 5-7, characterized in that, The process before expansion further includes: heating the compressed product to 800℃~1200℃ in a composite gas and holding it at that temperature for 0.5h~3h; wherein the composite gas includes an inert gas and a sulfur source gas in a volume ratio of (90~95):(5~10); preferably, the sulfur source gas includes at least one of hydrogen sulfide and sulfur hexafluoride.

9. An electrode sheet, characterized in that, This includes expanded graphite as described in any one of claims 1-4, or expanded graphite obtained by the preparation method described in any one of claims 5-8.

10. The electrode sheet according to claim 9, characterized in that, The electrode is a positive electrode, which includes a positive current collector and a positive active layer disposed on at least a portion of the surface of the positive current collector; the positive active layer includes 0.1% to 5% of the expanded graphite by mass percentage.

11. The electrode sheet according to claim 9, characterized in that, The electrode is a negative electrode, which includes a negative current collector and a negative active layer disposed on at least a portion of the surface of the negative current collector; the negative active layer includes 0.1% to 5% of the expanded graphite by mass percentage.

12. A battery, characterized in that, Includes the electrode sheet as described in any one of claims 9-11.

13. The battery according to claim 12, characterized in that, The battery operates at a pressure of less than or equal to 10 MPa.

14. A battery pack, characterized in that, It includes at least two batteries as described in claim 12 or 13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 12 or 13, or the battery pack as described in claim 14.

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