Hard carbon material, secondary battery and electronic device

Abstract

The invention belongs to the technical field of electrochemistry, and particularly relates to a hard carbon material, a secondary battery and an electronic device. The hard carbon material is of a sheet-shaped structure, the length of the sheet-shaped structure is L, the width of the sheet-shaped structure is D1, and L is larger than or equal to 2 micrometers and smaller than or equal to 16 micrometers; d1 satisfies 0.1 [mu] m < = D1 < = 3 [mu] m. According to the invention, the length and width parameters of the sheet structure of the hard carbon material are regulated to be within the range, so that particles of the hard carbon material have good contact, better processing performance and higher gram volume, the compaction density of the battery pole piece is further improved, the resistance of the pole piece is reduced, and the service life of the battery pole piece is prolonged. The rate capability and the cycle performance of the secondary battery are improved while the energy density of the secondary battery is improved.

Description

[0001] This application is a divisional application of the parent patent number 202411854039.X, entitled "A Hard Carbon Material, a Secondary Battery and an Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a hard carbon material, a secondary battery, and an electronic device. Background Technology

[0003] With the rapid development of electric vehicles and mobile electronic devices in recent years, people have increasingly higher demands for the energy density, safety, and cycle performance of secondary batteries (such as lithium-ion batteries). The design of new secondary batteries with comprehensively improved performance is key to meeting these growing needs. Improving the composition and structure of the electrode active materials in secondary batteries through design is one of the effective methods to enhance the battery's fast charge / discharge performance and cycle performance, and is also crucial for obtaining high-safety, high-energy-density batteries.

[0004] Negative electrode active materials account for 5%-15% of battery costs and are one of the four main materials in the battery system. Graphite, as the most commonly used negative electrode material for lithium-ion batteries, has advantages such as stable charge-discharge platform and high efficiency; however, its capacity development has reached its limit. Therefore, there is an urgent need to develop an improved negative electrode to further solve the current problems faced by graphite negative electrodes. Hard carbon materials have attracted great attention due to their high theoretical capacity, low volume expansion, and fast charge-discharge characteristics. However, the inherent hard framework and high porosity of hard carbon particles lead to problems such as low compaction density and poor interparticle contact, resulting in poor capacity, cycle performance, and rate performance of secondary batteries. Summary of the Invention

[0005] The purpose of this application is to provide a hard carbon material, a secondary battery, and an electronic device in an attempt to solve at least one problem existing in the relevant field to some extent.

[0006] According to a first aspect of this application, a hard carbon material is provided, the hard carbon material having a sheet-like structure, the length of the sheet-like structure being L, and the width of the sheet-like structure being D1, wherein L satisfies: 2μm≤L≤16μm; and D1 satisfies: 0.1 μm≤D1≤3 μm. The length and width of the sheet-like hard carbon material provided by this application will affect the stacking state between particles, and thus affect the mass transfer process of the electrochemical reaction. When the length of the sheet-like hard carbon material is within the above-mentioned range, when the sheet-like hard carbon material is used alone or in combination with negative electrode active materials such as graphite, it can contact multiple particles simultaneously, enhancing the electronic and ionic conductivity between particles, thereby accelerating the kinetic process of the battery and improving the rate performance. When the width of the sheet-like hard carbon material is within the above-mentioned range, it can improve the processing performance of the material, giving the electrode good adhesion performance, thereby improving the cycle stability of the secondary battery. That is, by adjusting the length, width and other parameters of the sheet-like hard carbon material of this application within the above range, the hard carbon materials can have good contact and better processing performance, which can improve the compaction density of the battery electrode, reduce the electrode resistance, and thus improve the energy density of the secondary battery while improving the rate performance and cycle performance of the secondary battery.

[0007] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (1) The length L of the sheet-like structure satisfies: 2μm≤L≤15μm; (2) The width D1 of the sheet-like structure satisfies: 0.5 μm ≤ D1 ≤ 1.9 μm; (3) The height H1 of the sheet-like structure satisfies: 0.02 μm ≤ H1 ≤ 2.5 μm; or, 0.05 μm ≤ H1 ≤ 1.9 μm; (4) The ratio of the length L of the sheet structure to the height H1 of the sheet structure satisfies: 2.5≤L / H1≤750; or, 2.5≤L / H1≤200; (5) The ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12.

[0008] In some embodiments of this application, the length L of the sheet-like structure satisfies: 2μm≤L≤15μm. When the length of the sheet-like hard carbon material provided in this application is within the above range, when the sheet-like hard carbon material is used alone or in combination with negative electrode active materials such as graphite, it can further contact multiple particles simultaneously, further enhancing the electronic and ionic conductivity between particles, thereby accelerating the battery's kinetic process and further improving rate performance.

[0009] In some embodiments of this application, the width D1 of the sheet-like structure satisfies: 0.5 μm ≤ D1 ≤ 1.9 μm. When the width of the sheet-like hard carbon material provided in this application is within the above range, the processing performance of the material can be further improved, resulting in good adhesion performance of the electrode sheet, thereby further improving the cycle stability of the secondary battery.

[0010] In some embodiments of this application, the height H1 of the sheet-like structure satisfies: 0.05 μm ≤ H1 ≤ 2.5 μm. Preferably, the height H1 of the sheet-like structure satisfies: 0.05 μm ≤ H1 ≤ 1.9 μm. When the height of the sheet-like hard carbon material provided in this application is within the above range, it can impart a certain degree of toughness to the particles, allowing the material to bend to a certain extent. When the material is used alone or in combination with negative electrode active materials such as graphite, it can simultaneously contact multiple surfaces of the particles, thereby effectively reducing interfacial impedance and improving the rate performance of the secondary battery.

[0011] In some embodiments of this application, the ratio of the length L of the sheet-like structure to the height H1 of the sheet-like structure satisfies: 2.5 ≤ L / H1 ≤ 750; preferably, the ratio of the length L of the sheet-like structure to the height H1 of the sheet-like structure satisfies 2.5 ≤ L / H1 ≤ 200. When the ratio of the length L to the height H1 of the sheet-like hard carbon material provided in this application is within the above range, the rate performance of the secondary battery can be further improved.

[0012] In some embodiments of this application, the ratio of the width D1 of the sheet-like structure to the height H1 of the sheet-like structure satisfies: 1 ≤ D1 / H1 ≤ 12. When the ratio of the width D1 to the height H1 of the sheet-like hard carbon material provided in this application is within the above range, the cycle performance and rate performance of the secondary battery can be further improved.

[0013] In some embodiments of this application, the length L of the sheet-like structure is composed of three parts: the length L1 of the left arc surface, the length L2 of the square region, and the length L3 of the right arc surface. The relationship between L1, L2, and L3 satisfies: 2μm≤L1+L2+L3≤16 μm, 0.01 μm≤L1≤1.5 μm, and 10≤L2 / L1≤80. The morphology of the arc surfaces on both sides of the hard carbon material is affected by the synthesis conditions. Different arc surface structures will affect the stacking state between the sheet-like structures. The presence of the arc surface structure can alleviate the internal stress formed during particle stacking and prevent particle breakage. At the same time, the stacking of multiple arc surfaces easily forms a small number of pores, which can store electrolyte and improve the wettability of the active material to the electrolyte. By controlling the length of the left arc surface, the length of the square region, and the length of the right arc surface of the sheet-like structure of the hard carbon material in this application within the above range, good contact between the hard carbon materials can be achieved, which can improve the compaction density of the battery electrode and thus improve the energy density of the secondary battery.

[0014] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (6) 2μm≤L1+L2+L3≤15μm; (7) 0.05μm≤L1≤1μm; (8) 11≤L2 / L1≤38.

[0015] In some embodiments of this application, the hard carbon material satisfies: 2μm≤L1+L2+L3≤15μm.

[0016] In some embodiments of this application, the hard carbon material satisfies the following condition: 0.05 μm ≤ L1 ≤ 1 μm.

[0017] In some embodiments of this application, the hard carbon material satisfies: 11≤L2 / L1≤38.

[0018] By adjusting the length of the left arc surface, the length of the square region, and the length of the right arc surface of the hard carbon material sheet structure in this application within the above-mentioned range, it is possible to further promote good contact between the hard carbon materials, thereby improving the compaction density of the battery electrode and the energy density of the secondary battery.

[0019] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (9) 0.8 μm≤L2≤15μm; or, 1.9 μm≤L2≤13μm; (10) 0.05 μm≤L3≤1.5μm; or 0.05 μm≤L3≤1μm.

[0020] In some embodiments of this application, the length L2 of the square region of the hard carbon material satisfies: 1.9 μm ≤ L2 ≤ 13 μm. Alternatively, 1.9 μm ≤ L2 ≤ 13 μm. By controlling the length L2 of the material within this range, when the material is used alone or in combination with negative electrode active materials such as graphite, it can simultaneously contact multiple particles, enhancing the electronic and ionic conductivity between particles, thereby accelerating the battery's kinetic process and improving rate performance.

[0021] In some embodiments of this application, the length L3 of the right arc surface of the sheet-like structure satisfies: 0.05 μm ≤ L3 ≤ 1 μm; or, 0.05 μm ≤ L3 ≤ 1 μm. The presence of the arc surface structure can alleviate the internal stress formed during particle accumulation, prevent particle breakage, and at the same time, the accumulation of multiple arc surfaces easily forms a small number of pores, which can store electrolyte and improve the wettability of the active material to the electrolyte.

[0022] In some embodiments of this application, the closed-cell volume of the sheet-like structure is 0.01~0.4 cm³. 3 / g. In some embodiments of this application, the closed-cell volume of the sheet-like structure is 0.05~0.28 cm³. 3 / g. Increasing the closed-pore content in hard carbon materials helps to store more active metal ions, thereby improving the active metal ion storage capacity. However, excessive closed pores will reduce the particle density and there is a risk that the closed pores will become larger, which is not conducive to energy storage. This application achieves higher capacity for hard carbon materials by controlling the closed-pore volume within the above-mentioned range, while also giving the active material a lower energy storage platform, thereby improving the energy density of secondary batteries.

[0023] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (11) The surface of the sheet-like structure also has a carbon coating layer; (12) The surface of the sheet-like structure also has a carbon coating layer, the thickness of which is 20~100 nm; (13) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; (14) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; the content of the first element relative to the total mass of the hard carbon material is 0.01% to 0.9%; (15) The specific surface area of ​​the sheet material ranges from 2 to 28 m². 2 / g; (16) The ID / IG value of the sheet material is 1.0~1.3.

[0024] In some embodiments of this application, the hard carbon material further includes a carbon coating layer on the surface of the sheet-like structure. Coating the hard carbon surface with a carbon layer helps reduce surface defects and minimizes the exposure of pore structures, thereby improving the initial coulombic efficiency of the negative electrode active material. This results in a high reversible capacity for the negative electrode active material, ultimately enhancing the energy density and cycle stability of the secondary battery.

[0025] In some embodiments of this application, the hard carbon material further includes a carbon coating layer on the surface of the sheet-like structure, the thickness of which ranges from 20 to 100 nm. Coating the surface of the hard carbon material with a carbon layer and controlling the thickness of the carbon coating layer within the aforementioned range helps to further reduce surface defects and expose pore structures, thereby improving the initial coulombic efficiency of the negative electrode active material. This results in a high reversible capacity for the negative electrode active material, ultimately enhancing the energy density and cycle stability of the secondary battery.

[0026] In some embodiments of this application, the sheet-like structure of the hard carbon material contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. By introducing the first element into the sheet-like structure of the hard carbon material, active metal ions can be induced to be stored in the hard carbon material, thereby increasing the storage capacity of active metal ions.

[0027] In some embodiments of this application, the sheet-like structure in the hard carbon material contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn, and the content of the first element relative to the total mass of the hard carbon material is 0.01% to 0.9%. By controlling the content of the first element in the hard carbon material within the above range, this application can further induce the storage of active metal ions in the hard carbon material, further improving the active metal ion storage capacity. Applying the hard carbon material of this application to secondary batteries can help improve the specific capacity of the battery negative electrode, thereby improving the energy density of the secondary battery.

[0028] In some embodiments of this application, the specific surface area of ​​the sheet-like material in the hard carbon material ranges from 2 to 28 m². 2 / g. An excessively large specific surface area of ​​hard carbon materials leads to the adsorption of active metal ions on the material surface, consuming more electrolyte to form a stable SEI layer, resulting in a decrease in the material's initial coulombic efficiency. This application, by controlling the specific surface area of ​​the hard carbon material within the aforementioned range, avoids excessive electrolyte consumption while ensuring stable SEI formation, thereby enabling the hard carbon material to have higher reversible capacity and higher initial coulombic efficiency, ultimately improving the energy density and cycle stability of the secondary battery.

[0029] In some embodiments of this application, the ID / IG value of the sheet-like structure in the hard carbon material is 1.0 to 1.3. ID is the peak area of ​​the D peak in the Raman spectrum of the hard carbon material, and IG is the peak area of ​​the G peak in the Raman spectrum of the hard carbon material. By adjusting the ID / IG value of the hard carbon material provided in this application within the above range, the hard carbon material has a suitable degree of defect, which can further promote ion adsorption and binding, while reducing irreversible capacity loss caused by high defect degree, thereby helping to improve the specific capacity of the hard carbon material.

[0030] According to a second aspect of this application, a negative electrode sheet is also provided. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material, which includes the hard carbon material described in any of the first aspects of this application. The negative electrode sheet containing the aforementioned hard carbon material has high capacity, good interfacial adhesion, and high compaction density. When applied to a secondary battery, it can improve the energy density of the secondary battery while also improving its cycle performance and rate performance.

[0031] In some embodiments of this application, the negative electrode active material includes the hard carbon material and graphite material described in any of the first aspects of this application. Graphite typically has a high compaction density, but its specific capacity is low, resulting in poor rate performance. Hard carbon material has a high specific capacity, but its compaction density is relatively low. This application, by compounding the hard carbon material with graphite material, obtains a negative electrode material with both high capacity and high compaction density, and a negative electrode active material layer with both high capacity and high compaction density. However, ordinary granular hard carbon is not conducive to the compounding of hard carbon material with negative electrode active materials such as graphite. The sheet-like hard carbon material provided in this application increases the contact between hard carbon particles and between hard carbon and graphite particles, which helps to reduce electrode resistance and further improves the rate performance of the negative electrode active material.

[0032] In some embodiments of this application, the negative electrode active material includes the hard carbon material and graphite material described in any of the first aspects of this application, and the mass percentage of the hard carbon material is from 0.1% to 99.9% based on the total mass of the negative electrode active material. This application regulates the relative ratio of sheet-like hard carbon and graphite in the composite electrode sheet. By regulating the mass percentage of hard carbon material in the negative electrode active material layer within the range of this application, the compaction density of the negative electrode active material layer can be optimized, thereby improving the energy density, rate performance, and cycle retention rate of the secondary battery.

[0033] In some embodiments of this application, the compaction density of the negative electrode active material layer ranges from 1.0 to 1.9 g / cm³. 3By adjusting the compaction density of the negative electrode active material layer within the aforementioned range, the content of negative electrode active material per unit area can be increased, thereby improving the energy density of the secondary battery.

[0034] According to a third aspect of this application, a secondary battery is provided, which includes the negative electrode sheet provided in any embodiment of the second aspect of this application. The secondary battery including the aforementioned negative electrode sheet has high energy density and good cycle performance.

[0035] According to a fourth aspect of this application, an electronic device is provided that includes a secondary battery provided in any embodiment of the third aspect of this application. The electronic device including the aforementioned secondary battery has a long service life. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0037] Figure 1 This is a structural schematic diagram of a hard carbon material provided in an embodiment of this application; Figure 2 The charge-discharge curves of the negative electrode active material of Comparative Example 1-1 in the Li / Li+ potential range from 0V to 2.5V are shown. Figure 3 The charge-discharge curves of the negative electrode active materials of Examples 1-2 in the Li / Li+ potential range from 0V to 2.5V are shown. Figure 4 The charge-discharge curves of the negative electrode active materials of Examples 2-3 are shown in the Li / Li+ potential range from 0V to 2.5V. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0039] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0040] Graphite, as the most commonly used anode material for lithium-ion batteries, boasts advantages such as a stable charge-discharge platform and high efficiency; however, its capacity development has reached its limit. Therefore, there is an urgent need to develop an improved anode material to further address the current problems faced by graphite anodes. Hard carbon materials have attracted considerable attention due to their high theoretical capacity, low volume expansion, and rapid charge-discharge capabilities. However, the inherently hard skeleton and high porosity of hard carbon particles lead to problems such as low compaction density and poor interparticle contact, resulting in suboptimal capacity, cycle performance, and rate performance of secondary batteries. Based on this, the inventors, starting from the anode active material itself, discovered through extensive research that by preparing hard carbon materials with special morphologies, and using them purely or in combination with commercial graphite, they can solve problems such as low specific capacity, poor adhesion, and poor conductivity of the anode sheet. This can improve the compaction density of the battery electrode, thereby increasing the energy density of the secondary battery while simultaneously improving its rate performance and cycle performance.

[0041] According to a first aspect of this application, a hard carbon material is provided, the hard carbon material having a sheet-like structure, the length of the sheet-like structure being L, the width of the sheet-like structure being D1, and the height of the sheet-like structure being H1, wherein L satisfies: 2μm≤L≤16μm; and D1 satisfies: 0.1 μm≤D1≤3 μm. Specifically, the length L of the sheet-like structure can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, or a range consisting of any two of the above values. Specifically, the width D1 of the sheet-like structure can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3μm, or a range consisting of any two of the above values.

[0042] Specifically, the hard carbon material provided in this application has a sheet-like structure, meaning that in the SEM image of the provided hard carbon material, it can be clearly observed that the hard carbon material has at least one sheet-like particle, and the sheet-like particles can be stacked on top of each other. The length and width of the sheet-like hard carbon material provided in this application will affect the stacking state between particles, and thus affect the mass transfer process of the electrochemical reaction. When the length of the sheet-like hard carbon material is within the above-mentioned range, when the sheet-like hard carbon material is used alone or in combination with negative electrode active materials such as graphite, it can contact multiple particles simultaneously, enhancing the electronic and ionic conductivity between particles, thereby accelerating the kinetic process of the battery and improving the rate performance. When the width of the sheet-like hard carbon material is within the above-mentioned range, it can improve the processing performance of the material, giving the electrode good adhesion performance, thereby improving the cycle stability of the secondary battery. That is, by adjusting the length, width and other parameters of the sheet-like hard carbon material of this application within the above range, the hard carbon materials can have good contact and better processing performance, which can improve the compaction density of the battery electrode, reduce the electrode resistance, and thus improve the energy density of the secondary battery while improving the rate performance and cycle performance of the secondary battery.

[0043] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (1) The length L of the sheet-like structure satisfies: 2μm≤L≤15μm; (2) The width D1 of the sheet-like structure satisfies: 0.5 μm ≤ D1 ≤ 1.9 μm; (3) The height H1 of the sheet-like structure satisfies: 0.02 μm ≤ H1 ≤ 2.5 μm; or, 0.05 μm ≤ H1 ≤ 1.9 μm; (4) The ratio of the length L of the sheet structure to the height H1 of the sheet structure satisfies: 2.5≤L / H1≤750; or, 2.5≤L / H1≤200; (5) The ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12.

[0044] In some embodiments of this application, the length L of the sheet-like structure satisfies: 2μm≤L≤15μm. When the length of the sheet-like hard carbon material provided in this application is within the above range, when the sheet-like hard carbon material is used alone or in combination with negative electrode active materials such as graphite, it can further contact multiple particles simultaneously, further enhancing the electronic and ionic conductivity between particles, thereby accelerating the battery's kinetic process and further improving rate performance.

[0045] In some embodiments of this application, the width D1 of the sheet-like structure satisfies: 0.5 μm ≤ D1 ≤ 1.9 μm. When the width of the sheet-like hard carbon material provided in this application is within the above range, the processing performance of the material can be further improved, resulting in good adhesion performance of the electrode sheet, thereby further improving the cycle stability of the secondary battery.

[0046] In some embodiments of this application, the height H1 of the sheet structure satisfies: 0.05 μm ≤ H1 ≤ 2.5 μm. Specifically, the height H1 of the sheet-like structure can be 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2 The height of the sheet-like structure is 2.05 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or any two of the above values. Preferably, the height H1 of the sheet-like structure satisfies: 0.05 μm ≤ H1 ≤ 1.9 μm. When the height of the sheet-like hard carbon material provided in this application is within the above range, it can impart a certain degree of toughness to the particles, allowing the material to bend to a certain extent. When the material is used alone or in combination with negative electrode active materials such as graphite, it can simultaneously contact multiple surfaces of the particles, thereby effectively reducing interfacial impedance and improving the rate performance of the secondary battery.

[0047] In some embodiments of this application, the ratio of the length L of the sheet-like structure to the height H1 of the sheet-like structure satisfies: 2.5 ≤ L / H1 ≤ 750. Specifically, the ratio of the length L of the sheet-like structure to the height H1 of the sheet-like structure can be: 2.5, 3, 3.3, 4.0, 4.2, 4.5, 5.0, 5.5, 6.0, 7.0, 8.0, 9.0, 10.0, 10.3, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 160, 170, 180, 187, 187.5, 190, 200, 210, 220, 225, 230, 240, 250, 260, 300, 400, 500, 600, 700, 750, or a range consisting of any two of the above values. Preferably, the ratio of the length L of the sheet-like structure to the height H1 of the sheet-like structure satisfies 2.5 ≤ L / H1 ≤ 200. When the ratio of the length L to the height H1 of the sheet-like hard carbon material provided in this application is within the above range, the rate performance of the secondary battery can be further improved.

[0048] In some embodiments of this application, the ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1 ≤ D1 / H1 ≤ 12. Specifically, the ratio of the width D1 of the sheet structure to the height H1 of the sheet structure can be: 1, 1.07, 1.13, 1.15, 1.18, 1.2, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 11.25, 11.35, 11.45, 11.65, 11.67, 12, or a range consisting of any two of the above values. When the ratio of the width D1 to the height H1 of the sheet-like hard carbon material provided in this application is within the above range, the cycle performance and rate performance of the secondary battery can be further improved.

[0049] In some embodiments of this application, the length L of the sheet-like structure is composed of three parts: the length L1 of the left arc surface, the length L2 of the square area, and the length L3 of the right arc surface. The relationship L1+L2+L3 between the length L1 of the left arc surface, the length L2 of the square area, and the length L3 of the right arc surface of the sheet-like structure satisfies: 2μm≤L1+L2+L3≤16μm, 0.01μm≤L1≤1.5μm, and 10≤L2 / L1≤80. Specifically, the relationship L1+L2+L3 between the length L1 of the left arc surface, the length L2 of the square area, and the length L3 of the right arc surface of the sheet-like structure can be: 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, or a range consisting of any two of the above values. Specifically, the length L1 of the left arc surface of the sheet-like structure can be 0.01μm, 0.02μm, 0.03μm, 0.04μm, 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, or a range consisting of any two of the above values. Specifically, the ratio L2 / L1 of the square region length L2 of the sheet-like structure to the left arc surface length L1 can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or 41. 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, or a range consisting of any two of the above values. The morphology of the two curved surfaces of the hard carbon material is affected by the synthesis conditions. Different curved surfaces will affect the stacking state between the sheet-like structures. The presence of the curved surface structure can alleviate the internal stress formed during the particle stacking process and prevent particle breakage. At the same time, the stacking of multiple curved surfaces can easily form a small number of pores, which can store electrolyte and improve the wettability of active materials to electrolyte. By controlling the length of the left curved surface, the length of the square area, and the length of the right curved surface of the sheet-like structure of the hard carbon material in this application within the above range, good contact between the hard carbon materials can be achieved, which can improve the compaction density of the battery electrode and thus improve the energy density of the secondary battery.

[0050] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (6) 2μm≤L1+L2+L3≤15μm; (7) 0.05μm≤L1≤1μm; (8) 11≤L2 / L1≤38.

[0051] In some embodiments of this application, the hard carbon material satisfies: 2μm≤L1+L2+L3≤15μm.

[0052] In some embodiments of this application, the hard carbon material satisfies the following condition: 0.05 μm ≤ L1 ≤ 1 μm.

[0053] In some embodiments of this application, the hard carbon material satisfies: 11≤L2 / L1≤38.

[0054] By adjusting the length of the left arc surface, the length of the square region, and the length of the right arc surface of the hard carbon material sheet structure in this application within the above-mentioned range, it is possible to further promote good contact between the hard carbon materials, thereby improving the compaction density of the battery electrode and the energy density of the secondary battery.

[0055] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (9) 0.8 μm≤L2≤15μm; or, 1.9 μm≤L2≤13μm; (10) 0.05 μm≤L3≤1.5μm; or 0.05 μm≤L3≤1μm.

[0056] In some embodiments of this application, the length L2 of the square region of the sheet-like structure satisfies: 0.8 μm ≤ L2 ≤ 15 μm. Specifically, the length L2 of the square region of the sheet-like structure can be: 0.8, 0.9, 1.0, 1.5, 1.9, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.5, 6.0, 6.5, 6.6, 7.0, 7.5, 7.6, 8.0, 8.5, 9.0, 10.0, 10.4, 10.5, 11, 11.5, 12.0, 12.5, 13.0, 14.0, 15.0, or a range of any two of the above values. Preferably, the length L2 of the square region of the sheet-like structure satisfies: 1.9 μm ≤ L2 ≤ 13 μm. By controlling the length L2 of the material within the specified range, when the material is used alone or in combination with negative electrode active materials such as graphite, it can simultaneously contact multiple particles, enhancing the electronic and ionic conductivity between particles, thereby accelerating the battery's kinetic process and improving rate performance.

[0057] In some embodiments of this application, the length L3 of the right arc surface of the sheet-like structure satisfies: 0.05 μm ≤ L3 ≤ 1.5 μm. Specifically, the length L3 of the right arc surface of the sheet-like structure can be 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or a range consisting of any two of the above values. Preferably, the length L3 of the right arc surface of the sheet-like structure satisfies: 0.05 μm ≤ L3 ≤ 1 μm. The presence of the arc surface structure can alleviate the internal stress formed during particle accumulation, prevent particle breakage, and at the same time, the accumulation of multiple arc surfaces easily forms a small number of pores, which can store electrolyte and improve the wettability of the active material to the electrolyte.

[0058] In some embodiments of this application, the closed-cell volume of the sheet-like structure is 0.01~0.4 cm³. 3 / g. Specifically, the closed-cell volume of the sheet-like structure can be 0.01 cm³. 3 / g, 0.02 cm 3 / g, 0.03 cm 3 / g, 0.04 cm 3 / g, 0.05 cm 3 / g, 0.06 cm 3 / g, 0.07 cm 3 / g, 0.08 cm 3 / g, 0.09 cm 3 / g, 0.1 cm 3 / g, 0.12 cm 3 / g, 0.15cm 3 / g, 0.2 cm 3 / g, 0.21 cm 3 / g, 0.24 cm 3 / g, 0.25 cm 3 / g, 0.28 cm 3 / g, 0.3 cm 3 / g, 0.35 cm 3 / g, 0.4 cm 3 / g or a range consisting of any two of the above values. Preferably, the closed-cell volume of the sheet-like structure is 0.05~0.28 cm³. 3 / g. Increasing the closed-pore content in hard carbon materials helps to store more active metal ions, thereby improving the active metal ion storage capacity. However, excessive closed pores will reduce the particle density and there is a risk that the closed pores will become larger, which is not conducive to energy storage. This application achieves higher capacity for hard carbon materials by controlling the closed-pore volume within the above-mentioned range, while also giving the active material a lower energy storage platform, thereby improving the energy density of secondary batteries.

[0059] In some embodiments of this application, the hard carbon material satisfies at least one of the following conditions: (11) The surface of the sheet-like structure also has a carbon coating layer; (12) The surface of the sheet-like structure also has a carbon coating layer, the thickness of which is 20~100 nm; (13) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; (14) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; the content of the first element relative to the total mass of the hard carbon material is 0.01% to 0.9%; (15) The specific surface area of ​​the sheet material ranges from 2 to 28 m². 2 / g; (16) The ID / IG value of the sheet material is 1.0~1.3.

[0060] In some embodiments of this application, the hard carbon material further includes a carbon coating layer on the surface of the sheet-like structure. Coating the hard carbon surface with a carbon layer helps reduce surface defects and minimizes the exposure of pore structures, thereby improving the initial coulombic efficiency of the negative electrode active material. This results in a high reversible capacity for the negative electrode active material, ultimately enhancing the energy density and cycle stability of the secondary battery.

[0061] In some embodiments of this application, the hard carbon material further includes a carbon coating layer on the surface of the sheet-like structure, the thickness of which ranges from 20 to 100 nm. Specifically, the thickness of the carbon coating layer can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any combination of two of the above values. Coating the surface of the hard carbon material with a carbon layer and controlling the thickness of the carbon coating layer within the above range helps to further reduce surface defects and further reduce the exposure of pore structures, further improving the initial coulombic efficiency of the negative electrode active material, resulting in high reversible capacity of the negative electrode active material, thereby improving the energy density and cycle stability of the secondary battery.

[0062] In some embodiments of this application, the sheet-like structure of the hard carbon material contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. By introducing the first element into the sheet-like structure of the hard carbon material, active metal ions can be induced to be stored in the hard carbon material, thereby increasing the storage capacity of active metal ions.

[0063] In some embodiments of this application, the hard carbon material contains a first element in its sheet-like structure. The first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn, and its content relative to the total mass of the hard carbon material is 0.01% to 0.9%. Specifically, the content of the first element relative to the total mass of the hard carbon material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.23%, 0.34%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.78%, 0.8%, 0.85%, 0.9%, or a range consisting of any two of the above values. This application, by controlling the content of the first element in the hard carbon material within the aforementioned range, can further induce the storage of active metal ions in the hard carbon material, thereby further improving the storage capacity of active metal ions. Applying the hard carbon material of this application to a secondary battery can help improve the specific capacity of the battery negative electrode, thereby improving the energy density of the secondary battery.

[0064] In some embodiments of this application, the specific surface area of ​​the sheet-like material in the hard carbon material ranges from 2 to 28 m². 2 / g. Specifically, the specific surface area of ​​the sheet-like material can be 2m². 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2 / g、26m 2 / g、27m 2 / g、28m 2 / g or any two of the above values. An excessively large specific surface area of ​​hard carbon materials will cause active metal ions to adsorb onto the material surface, consuming more electrolyte to form a stable SEI layer, leading to a decrease in the material's initial coulombic efficiency. This application, by controlling the specific surface area of ​​the hard carbon material within the above range, avoids excessive electrolyte consumption while ensuring stable SEI formation, resulting in higher reversible capacity and higher initial coulombic efficiency for the hard carbon material, thereby improving the energy density and cycle stability of the secondary battery.

[0065] In some embodiments of this application, the ID / IG value of the sheet-like structure in the hard carbon material is 1.0 to 1.3. Specifically, the ID / IG value of the sheet-like structure can be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.13, 1.15, 1.16, 1.2, 1.23, 1.25, 1.27, 1.3, or a range of any two of the above values. ID is the peak area of ​​the D peak in the Raman spectrum of the hard carbon material, and IG is the peak area of ​​the G peak in the Raman spectrum of the hard carbon material. By controlling the ID / IG value of the hard carbon material provided in this application within the above range, the hard carbon material has a suitable degree of defect, which can further promote ion adsorption and binding, while reducing irreversible capacity loss caused by high defect degree, thereby helping to improve the specific capacity of the hard carbon material.

[0066] According to a second aspect of this application, a negative electrode sheet is also provided. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material, which includes the hard carbon material described in any of the first aspects of this application. The negative electrode sheet containing the aforementioned hard carbon material has high capacity, good interfacial adhesion, and high compaction density. When applied to a secondary battery, it can improve the energy density of the secondary battery while also improving its cycle performance and rate performance.

[0067] In some embodiments of this application, the negative electrode active material includes the hard carbon material and graphite material described in any of the first aspects of this application. Graphite typically has a high compaction density, but its specific capacity is low, resulting in poor rate performance. Hard carbon material has a high specific capacity, but its compaction density is relatively low. This application, by compounding the hard carbon material with graphite material, obtains a negative electrode material with both high capacity and high compaction density, and a negative electrode active material layer with both high capacity and high compaction density. However, ordinary granular hard carbon is not conducive to the compounding of hard carbon material with negative electrode active materials such as graphite. The sheet-like hard carbon material provided in this application increases the contact between hard carbon particles and between hard carbon and graphite particles, which helps to reduce electrode resistance and further improves the rate performance of the negative electrode active material.

[0068] In some embodiments of this application, the negative electrode active material includes the hard carbon material and graphite material described in any of the first aspects of this application, and the mass percentage of the hard carbon material is from 0.1% to 99.9% based on the total mass of the negative electrode active material. Specifically, based on the total mass of the negative electrode active material, the mass percentage of the hard carbon material can be 0.1%, 0.5%, 1.0%, 5.0%, 10.0%, 15.0%, 20.0%, 25.0%, 30.0%, 35.0%, 40.0%, 45.0%, 50.0%, 55.0%, 60.0%, 65.0%, 70.0%, 75.0%, 80.0%, 85.0%, 90.0%, 95.0%, 99.9%, or a range consisting of any two of the above values. This application regulates the relative proportion of sheet-like hard carbon and graphite in the composite electrode. By controlling the mass percentage of hard carbon material in the negative electrode active material layer within the scope of this application, the compaction density of the negative electrode active material layer can be optimized, thereby improving the energy density, rate performance and cycle retention of the secondary battery.

[0069] In some embodiments of this application, the compaction density of the negative electrode active material layer ranges from 1.0 to 1.9 g / cm³. 3 Specifically, the compaction density of the negative electrode active material layer can be 1.0 g / cm³. 3 1.05 g / cm 3 1.1 g / cm 3 1.15 g / cm 3 1.2 g / cm 3 1.25 g / cm 3 1.3 g / cm 3 1.35 g / cm 3 1.4 g / cm 3 1.45 g / cm 3 1.5g / cm 3 1.55 g / cm 3 1.6 g / cm 3 1.65 g / cm 3 1.7 g / cm 3 1.75 g / cm 3 1.8 g / cm 3 1.85 g / cm 3 1.90 g / cm 3 Or it can be a range consisting of any two of the above values. By adjusting the compaction density of the negative electrode active material layer within the above range, the content of negative electrode active material per unit area can be increased, thereby increasing the energy density of the secondary battery.

[0070] According to a third aspect of this application, a secondary battery is provided, which includes the negative electrode sheet provided in any embodiment of the second aspect of this application. The secondary battery including the aforementioned negative electrode sheet has high energy density and good cycle performance.

[0071] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil is aluminum foil. In some embodiments, the secondary battery is a lithium-ion battery, and the positive active material may include lithium transition metal oxide, which may include, but is not limited to, at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese iron phosphate, or lithium titanate.

[0072] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm.

[0073] The secondary battery of this application also includes an electrolyte. In one embodiment, the electrolyte includes a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved.

[0074] The secondary battery of this application also includes a separator for separating the positive electrode and the negative electrode, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes.

[0075] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0076] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0077] According to a fourth aspect of this application, an electronic device is provided that includes a secondary battery provided in any embodiment of the third aspect of this application. The electronic device including the aforementioned secondary battery has a long service life.

[0078] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0079] Example The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0080] The test methods used in the following examples and comparative examples are as follows: 1. Scanning Electron Microscopy (SEM) Testing The microstructure of the prepared hard carbon material was observed using a scanning electron microscope (SEM) (model ZEISSSEM), and SEM images were taken. The measurement function of the SEM was used to measure the length (L), width (D1), thickness / height (H1), left arc length (L1), square area length (L2), and right arc length (L3) of each structure in the microstructure of the hard carbon material. The specific test steps were as follows: the measurement function of the SEM was used to measure the various parameters of a single plate-like particle, and the relevant parameters of ten plate-like particles were recorded. Finally, the length (L), width (D1), thickness / height (H1), left arc length (L1), square area length (L2), and right arc length (L3) of the ten particles were taken as the average value. For cross-section testing, an ion polisher (instrument model IB-09010CP) was used to cut out a flat cross-section, which was then photographed by SEM. The principle of ion polishing is that under vacuum conditions, the ion source ionizes argon gas. After acceleration and focusing, the high-speed argon ions knock out atoms or molecules on the sample surface, thus achieving ion polishing. The height of the hard carbon material was measured by testing the cross-section of hard carbon particles.

[0081] 2. Transmission electron microscopy (TEM) testing The carbon coating layer of hard carbon materials was observed using a transmission electron microscope (FEI Tecnai F20), and TEM images were taken to measure the thickness of the carbon coating layer.

[0082] 3. Metal element analysis and testing The samples were digested using a microwave digester (model CEM-Mars5), and the elemental content was quantitatively determined using an ICP-OES instrument (model PE7000DV). After the samples were digested into solutions by acid, the liquid samples entered the nebulization chamber, where they formed aerosols under the action of a carrier gas. These aerosols were then injected into the plasma through the central jet tube and fully evaporated, dissociated, atomized, ionized, and excited, emitting characteristic spectral lines of the elements. Qualitative analysis was performed based on the wavelength of the spectral lines, and quantitative analysis was performed based on the proportionality between the spectral line intensity and the concentration.

[0083] 4. Small-angle X-ray scattering test The scattering vector variation of the sample in the range of scattering intensity from 0.01 nm-1 to 0.7 nm-1 was tested using a small-angle X-ray scattering structure analyzer (Nano-inXider instrument) and the closed-pore volume in the hard carbon material particles was fitted and analyzed.

[0084] 5. Specific surface area and pore volume test Hard carbon material powder was placed in a sample tube and degassed under vacuum at 100℃ for 12 hours. The adsorption capacity of the hard carbon material for nitrogen under different pressures was measured using an ASAP2460 physical adsorption analyzer, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the shape of the hysteresis loop, and the pore size distribution curve of the micropores was fitted using a DFT model. The specific surface area of ​​the hard carbon material was then calculated.

[0085] 6. Raman test Raman spectra of hard carbon materials were measured using a Raman spectrometer. A 200 μm × 500 μm area was selected for testing, and more than 200 points were measured at equal intervals within this area, with each point measured over 1000 cm⁻¹. -1 Up to 2000cm -1 Between; recorded at 1320cm -1 Up to 1370cm -1 The peak that appears between these two points is the D peak, located at 1570 cm⁻¹. -1 Up to 1620cm -1 The peaks that appear between the points are called G peaks. The intensity ratio of ID / IG at each point is calculated, and then the average value of multiple points is used as the final intensity ratio of ID / IG.

[0086] 7. Compaction density test of the negative electrode active material layer: Take a fully discharged lithium-ion battery, disassemble the negative electrode sheet, clean and dry it. Weigh the negative electrode sheet with an area of ​​S using an electronic balance, and record the weight as W1. Measure the thickness T1 of the negative electrode sheet using a micrometer. Wash away the negative electrode active material layer with the solvent DMC, dry it, and measure the weight of the negative electrode current collector, recording it as W2. Measure the thickness T2 of the negative electrode current collector using a micrometer. Calculate the weight W0 and thickness T0 of the negative electrode active material layer on the side of the negative electrode current collector, as well as the compaction density of the negative electrode active material layer, using the following formula: W0 = W1 - W2, T0 = T1 - T2, then compaction density = W0 / (T0 × S).

[0087] 8. Total lithium storage capacity and initial efficiency test of the negative electrode active material: The initial reversible specific capacity of the negative electrode active material from 0V to 2.5V can be obtained by the following test method: A single-sided coated negative electrode sheet is cut into a 14mm diameter disc and used as the working electrode. A lithium sheet is then used as the counter electrode, and a porous polyethylene membrane (provided by Celgard) is used as the separator. After injecting electrolyte, a button cell is assembled. The button cell is first discharged to 0V using three stages of small currents: 0.05C, 0.01C, and 0.005C, and the initial discharge capacity is recorded. Then, it is charged to 2.5V using a constant current of 0.1C, and the initial charge capacity is recorded. Initial efficiency = (initial charge capacity / initial discharge capacity) × 100%. The initial reversible specific capacity of the negative electrode active material from 0V to 2.5V, i.e., the total lithium storage capacity, is calculated as: (initial charge capacity / mass of the negative electrode active material), in mAh / g.

[0088] The electrolyte consists of a base solvent and a lithium salt. The base solvent is obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a mass ratio of 1:1. The lithium salt is LiPF6 with a concentration of 1 mol / L.

[0089] The comparative tests for total lithium storage capacity and initial efficiency were conducted using the same methods as those for the aforementioned hard carbon materials.

[0090] 9. Energy Density (ED) Test In an environment of 25℃, the lithium-ion battery is charged at a constant current of 0.2C to a voltage of 4.48V or 3.95V, and then charged at a constant voltage; it is then discharged at a constant current of 0.2C to a voltage of 2V. This is recorded as one cycle, and the discharge capacity C and discharge energy E of the first cycle are recorded. The length, width and height of the battery at 50% charge are measured to obtain the battery volume Vm, and the energy density ED = E / Vm is calculated. The lithium-ion battery is subjected to the above charge and discharge process for 500 cycles, and the discharge capacity C1 after 500 cycles is measured. The cycle capacity retention rate = C1 / C is calculated.

[0091] 10. Test methods for rate performance To perform rate charging of a lithium-ion battery at a constant temperature, first charge the fully discharged lithium-ion battery at a constant current of 1C to 4.48V, then charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 1C to 3.0V. The resulting discharge capacity is recorded as capacity A. Next, charge the battery at a constant current of 5C to 4.48V, then charge it at a constant voltage to 0.05C, and then discharge it at a constant current of 1C to 3.0V. The resulting discharge capacity is recorded as capacity B. The ratio of B to A represents the 5C / 1C rate performance.

[0092] Example 1-1 <Preparation of Negative Electrode Active Materials> Stearic acid tablet dispersion: Weigh 100g of polyoxyethylene polypropylene ether and disperse it in 10L of water. Stir the dispersion at 80℃ for 2 hours until the polyoxyethylene polypropylene ether is completely dispersed. Then add 75g of stearic acid melt and continue stirring for 3 hours until a microemulsion is formed. Let the resulting microemulsion stand at room temperature for 24 hours to obtain the stearic acid tablet dispersion for later use. Weigh 50g of resorcinol and 66g of formaldehyde and slowly stir them at room temperature to dissolve them in 1000mL of water. Then add 1000mL of the stearic acid tablet dispersion, followed by 1.5g of propylamine. After stirring for 30 minutes, add 5mL of the solution. A 1.5 mol / L ammonia solution was heated to 85°C and stirred for 4 hours. The resulting powder product was centrifuged, filtered, washed with water, and dried to serve as a precursor. Resin curing: The powder product was placed in a programmable temperature-controlled oven under an inert atmosphere, with the temperature program controlled as 90°C / 1h + 110°C / 1h + 130°C / 1h + 150°C / 1h to ensure complete resin curing. Precursor mixing: 100g of the cured powder product and 10g of... NaOH is used to uniformly mix two precursors using a mixer. Carbonization: The mixed precursors are placed in a rotary kiln and heated to the primary calcination temperature T1 = 900℃ at a heating rate of 5℃ / min for 2 hours. After cooling, the carbonized material is obtained. Acid washing and water washing: The collected powder is then washed with 1M hydrochloric acid for 12 hours, filtered, and the filter residue is washed with deionized water for 12 hours. The filter residue is then dried. Surface coating formation: The dried powder is then transferred to a nitrogen atmosphere furnace and heated to the vapor deposition temperature T3 = 900℃ at a heating rate of 5℃ / min. The gas atmosphere is then replaced with a mixture of reducing gases methane and argon. The vapor deposition time is t3 = 2 hours. After vapor deposition, the mixed gas is disconnected and replaced with nitrogen. The mixture is cooled to room temperature to obtain the hard carbon material, i.e., the negative electrode active material. Based on the mass of the mixed gas, the mass percentage of reducing gas methane is 10%.

[0093] <Preparation of Negative Electrode Sheets> The hard carbon material prepared above was mixed with styrene-butadiene rubber (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener at a mass ratio of 97:1.5:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 40 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0094] <Preparation of the positive electrode> Lithium cobalt oxide (CCO), conductive carbon black (Super P), and PVDF (PVDF) binder were mixed in a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous, yielding a CCO slurry with a solid content of 72 wt%. The CCO slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil used as a CCO current collector. The foil was then dried at 85°C to obtain a single-sided coated CCO electrode sheet with an 80 μm thick CCO active material layer. After cold pressing, cutting, and slitting, the electrode sheet was dried under vacuum at 85°C for 4 hours to obtain the final CCO electrode sheet.

[0095] <Preparation of Electrolyte> In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1. Then, 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were added, dissolved, and stirred thoroughly. After this process, lithium salt LiPF6 was added, and the mixture was stirred until homogeneous to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt was 12.5%, and the mass percentages of 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were all 2%.

[0096] <Preparation of the diaphragm> A polyethylene film with a thickness of 7μm was used as the diaphragm.

[0097] <Preparation of Lithium-ion Batteries> The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, degassing, and shaping processes.

[0098] Examples 1-2 Based on Example 1-1, the amount of stearic acid tablet dispersion added was adjusted to 500 mL. The remaining steps and parameters of Example 1-2 were the same as those of Example 1-1.

[0099] Examples 1-3 Based on Example 1-1, the amount of stearic acid tablet dispersion added was adjusted to 1500 mL. The remaining steps and parameters of Example 1-3 were the same as those of Example 1-1.

[0100] Examples 1-4 Based on Example 1-1, the amount of stearic acid tablet dispersion added was adjusted to 2000 mL. The remaining steps and parameters of Examples 1-4 were the same as those of Example 1-1.

[0101] Examples 1-5 Weigh 100g of polyvinylidene chloride (PVDC) powder and 10g of LiOH, and mix the two precursors uniformly using a mixer. Place the mixed precursors in a rotary kiln and heat to the primary calcination temperature T1=900℃ at a heating rate of 5℃ / min, carbonize for 2h, cool down, and obtain the carbonized material. Then, wash the collected powder with 1M hydrochloric acid for 12h, filter, and wash the filter residue with deionized water for 12h, filter and dry the filter residue. Then, transfer the dried powder to a nitrogen atmosphere protected furnace and heat to the vapor deposition temperature T3=900℃ at a heating rate of 5℃ / min. Then, change the gas atmosphere to a mixture of reducing gases methane and argon, and vapor deposition time t3=2h. After vapor deposition, disconnect the above mixed gas and replace it with nitrogen. After cooling to room temperature, hard carbon material, i.e., negative electrode active material, is obtained. Based on the mass of the mixed gas, the mass percentage of reducing gas methane is 10%.

[0102] Examples 1-6 Based on Examples 1-5, the precursors were replaced with 100g of polyvinylidene chloride powder and 10g of NaOH. The remaining parameters of Examples 1-6 were the same as those of Examples 1-5.

[0103] Examples 1-7 Based on Examples 1-5, the precursors were replaced with 100g of polyvinylidene chloride powder and 10g of KOH. The remaining parameters of Examples 1-7 were the same as those of Examples 1-5.

[0104] Examples 1-8 Based on Examples 1-5, the precursors were replaced with 100g of polyvinylidene chloride powder and 10g of RbOH. The remaining parameters of Examples 1-8 were the same as those of Examples 1-5.

[0105] Examples 1-9 Based on Examples 1-2, the amount of stearic acid melt added was adjusted to 1g during the preparation of stearic acid sheet dispersion. The remaining steps and parameters of Examples 1-9 were the same as those of Examples 1-2.

[0106] Examples 1-10 Based on Examples 1-2, the amount of stearic acid melt added was adjusted to 15g during the preparation of stearic acid sheet dispersion. The remaining steps and parameters of Examples 1-10 were the same as those of Examples 1-2.

[0107] Examples 1-11 Based on Examples 1-2, during the resin prepolymerization process, the amount of resorcinol was adjusted to 25g, the amount of formaldehyde was adjusted to 33g, and the amount of ammonia solution added was adjusted to 10mL. The remaining steps and parameters of Examples 1-11 were the same as those of Examples 1-2.

[0108] Examples 1-12 Based on Examples 1-2, during the resin prepolymerization process, the amount of resorcinol was adjusted to 75g, the amount of formaldehyde was adjusted to 99g, and the amount of ammonia solution added was adjusted to 2mL. The remaining steps and parameters of Examples 1-11 were the same as those of Examples 1-2.

[0109] Examples 1-13 Based on Examples 1-2, the amount of NaOH was adjusted to 2g during the precursor mixing process. The remaining steps and parameters of Examples 1-13 were the same as those of Examples 1-2.

[0110] Examples 1-14 Based on Examples 1-2, the amount of NaOH was adjusted to 20g during the precursor mixing process. The remaining steps and parameters of Examples 1-14 were the same as those of Examples 1-2.

[0111] Comparative Example 1-1 Coconut shells were used instead of the polyvinylidene chloride powder used in Examples 1-5. 100g of the mixed coconut shells and 10g of NaOH were placed in a rotary kiln with an inner liner for direct carbonization. The remaining subsequent steps were the same as in Examples 1-5.

[0112] Comparative Examples 1-2 Commercially purchased artificial graphite was heated to 700°C in a rotary kiln under 10% C2H2 gas and maintained for 2 hours. Then the gas was switched to N2 gas and the material was allowed to cool naturally to obtain the final graphite material.

[0113] Comparative Examples 1-3 Based on Examples 1-2, the steps of adding stearic acid tablet dispersion, propylamine, and ammonia were omitted. Instead, 50 g of resorcinol and 66 g of formaldehyde were directly weighed, and the mixture was slowly stirred at room temperature to dissolve in 1000 mL of water. The temperature was then raised to 85°C and stirred for 4 hours. The remaining subsequent steps were the same as in Examples 1-2.

[0114] Comparative Examples 1-4 Based on Examples 1-2, the stearic acid tablet dispersion was replaced with stearic acid. Specifically, 50 g of resorcinol and 66 g of formaldehyde were weighed and slowly stirred at room temperature to dissolve them in 1000 mL of water. Then, 1000 mL of stearic acid was added (stearic acid was directly added to the water and stirred to disperse before adding). Subsequently, 1.5 g of propylamine was added, and after stirring for 30 min, 5 mL of 1.5 mol / L ammonia solution was added. The temperature was raised to 85 °C and stirred for 4 h. The remaining subsequent steps were the same as in Examples 1-2.

[0115] Example 2-1 <Preparation of Negative Electrode Active Materials> Commercially purchased artificial graphite was heated to 700°C in a rotary kiln under 10% C2H2 gas and maintained for 2 hours. Then the gas was switched to N2 gas and the material was allowed to cool naturally to obtain the final graphite material.

[0116] <Preparation of Negative Electrode Sheets> The hard carbon material obtained in Examples 1-2 was mixed with the graphite material prepared in Example 2-1 at a mass ratio of 10:90 to prepare a negative electrode active material. Then, the prepared negative electrode active material was mixed with a binder (styrene-butadiene rubber) and a thickener (sodium carboxymethyl cellulose) at a mass ratio of 97:1.5:1.5. Deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 40 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0117] The remaining steps for <preparation of positive electrode>, <preparation of electrolyte>, <preparation of separator>, and <preparation of lithium-ion battery> are the same as in Example 1-1.

[0118] Examples 2-2 to 2-5 Except for adjusting the preparation parameters according to Table a, the other parameters of Examples 2-2 to 2-5 are the same as those of Example 2-1.

[0119] Comparative Examples 2-1 to 2-5 Based on Example 2-1, the difference from Example 2-1 is that the hard carbon material used is the hard carbon material prepared in Comparative Example 1-1, and the ratio between the hard carbon material and graphite is adjusted according to Table a. All other aspects are the same as in Example 2-1.

[0120] Table a

[0121] Example 1 Using the above testing methods, the relevant parameters and properties of the materials prepared in Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-4 were further tested, and the results are shown in Table 1: Table 1

[0122] like Figure 1 As shown in Table 1, the hard carbon material provided in this application is in sheet form. The results indicate that using the sheet-like hard carbon material with a specific morphology provided in this application as the negative electrode active material results in a higher lithium storage capacity from 0V to 2.5V. Furthermore, the negative electrode active material provided in this application exhibits higher specific capacity and reversible capacity. The morphology of the hard carbon material provided in this application is mainly affected by the sample synthesis conditions, primarily the template agent (stearic acid sheet dispersion) and the activator (NaOH, LiOH, KOH, RbOH). When the template agent is less, the prepared hard carbon material is longer; when the template agent is more abundant, the prepared hard carbon material becomes shorter and thinner. When the type of activator changes, the higher the activity of the activator, the smaller the overall particle size of the prepared material. This application adjusts the relevant parameters of the hard carbon material by adjusting the corresponding process parameters, resulting in a significant improvement in the material's specific capacity, initial efficiency, and other performance characteristics.

[0123] at the same time, Figure 2 The negative electrode active material of Comparative Example 1-1 is shown, with lithium metal as the counter electrode, in the Li / Li ratio range from 0V to 2.5V. + The charge-discharge curves within the potential range. From Figure 2 It can be seen that the specific capacity of the negative electrode active material of Comparative Example 1-1 is 233 mAh / g in the Li / Li+ potential range of 0V to 0.2V; and the specific capacity of the negative electrode active material of Comparative Example 1-1 is 482 mAh / g in the Li / Li+ potential range of 0V to 2.5V.

[0124] Figure 3 The charge-discharge curves of the negative electrode active materials prepared in Examples 1-2, using lithium metal as the counter electrode, are shown in the Li / Li+ potential range from 0V to 2.5V; from Figure 3 It can be seen that within the Li / Li+ potential range of 0V to 0.2V, the specific capacity of Examples 1-2 is 483 mAh / g; within the Li / Li+ potential range of 0V to 2.5V, the specific capacity of the negative electrode active materials of Examples 1-2 is 720 mAh / g, indicating that the negative electrode active materials of Examples 1-2 have high specific capacity. Among them, the negative electrode active materials of Examples 1-2 have a stable low potential plateau, and exhibit higher energy density when applied to full cells.

[0125] Example 2 Using the above testing methods, the compaction density of the negative electrode active material layer and the relevant performance of the lithium-ion battery corresponding to Examples 1-2, 1-7, 2-1 to 2-5, and Comparative Examples 2-1 to 2-5 were further tested, and the results are shown in Table 2. Table 2

[0126] Table 2 shows the compaction density of the negative electrode active material layers and lithium-ion battery data for Examples 1-2, 1-7, 2-1 to 2-5, and Comparative Examples 2-1 to 2-5. As can be seen from Table 2, the compaction density of the negative electrode active material is significantly affected by the composition of the active material. Generally, graphite has a high compaction density, but its specific capacity is low, resulting in poor rate performance. Hard carbon materials have a high specific capacity, but their compaction density is relatively low. This application further combines hard carbon materials with graphite materials to obtain a negative electrode material that combines high capacity and high compaction. However, the data in Table 2 also shows that using ordinary granular hard carbon and graphite is not conducive to the combination. Using the sheet-like hard carbon material and graphite materials provided in this application to combine them increases the contact between hard carbon particles and between hard carbon and graphite particles, which helps to reduce electrode resistance and further improve the rate performance of the negative electrode active material. As can be seen from Examples 2-1 to 2-5, adjusting the relative proportion of sheet hard carbon and graphite in the composite electrode can further optimize the compaction density of the negative electrode active material layer, thereby improving the energy density, rate performance and cycle retention of the secondary battery.

[0127] at the same time, Figure 4 The charge-discharge curves of the negative electrode active materials prepared in Examples 2-3, using lithium metal as the counter electrode, are shown in the Li / Li+ potential range from 0V to 2.5V; from Figure 4 It can be seen that there is a clear step in the potential range of 0~0.2V, but it differs from the charge-discharge curves of traditional graphite and hard carbon, proving that the capacity of both graphite and hard carbon can be effectively utilized, and there is good interfacial conduction between particles. In the Li / Li+ potential range of 0V to 0.2V, the specific capacity of Examples 2-3 is 386mAh / g; in the Li / Li+ potential range of 0V to 2.5V, the specific capacity of the negative electrode active materials of Examples 2-3 is 552 mAh / g, indicating that the negative electrode active materials of Examples 2-3 have high specific capacity. Among them, the negative electrode active materials of Examples 2-3 have a stable low potential plateau. In addition, due to the combination of graphite and hard carbon, the negative electrode active materials of Examples 2-3 also have high compaction density, which makes the negative electrode active materials of Examples 2-3 exhibit higher energy density, rate performance and cycle retention when applied to full batteries.

[0128] It is understood that this application has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this application. Furthermore, based on the teachings of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this application.

Claims

1. A hard carbon material, characterized in that, The hard carbon material has a sheet-like structure with a length of L and a width of D1, wherein L satisfies: 2μm≤L≤16μm; and D1 satisfies: 0.1 μm≤D1≤3 μm. The hard carbon material satisfies at least one of the following conditions: (1) The surface of the sheet-like structure also has a carbon coating layer; (2) The surface of the sheet-like structure also has a carbon coating layer, the thickness of which is 20~100 nm; (3) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; (4) The sheet-like structure contains a first element, which includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; the content of the first element relative to the total mass of the hard carbon material is 0.01% to 0.9%; (5) The specific surface area of ​​the sheet-like structure ranges from 2 to 28 m². 2 / g; (6) The ID / IG value of the sheet structure is 1.0~1.

3.

2. The hard carbon material according to claim 1, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) The length L of the sheet-like structure satisfies: 2μm≤L≤15μm; (2) The width D1 of the sheet-like structure satisfies: 0.5 μm ≤ D1 ≤ 1.9 μm; (3) The height H1 of the sheet-like structure satisfies: 0.02 μm ≤ H1 ≤ 2.5 μm; or, 0.05 μm ≤ H1 ≤ 1.9 μm; (4) The ratio of the length L of the sheet structure to the height H1 of the sheet structure satisfies: 2.5≤L / H1≤750; or 2.5≤L / H1≤200.

3. The hard carbon material according to any one of claims 1-2, characterized in that, The ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12.

4. The hard carbon material according to any one of claims 1-2, characterized in that, The length L of the sheet-like structure is composed of three parts: the length L1 of the left arc surface, the length L2 of the square area, and the length L3 of the right arc surface. L1, L2, and L3 satisfy the following relationships: 2μm≤L1+L2+L3≤16μm, 0.01 μm≤L1≤1.5 μm, and 10≤L2 / L1≤80.

5. The hard carbon material according to claim 4, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) 2μm≤L1+L2+L3≤15μm; (2) 0.05μm≤L1≤1μm; (3) 11≤L2 / L1≤38.

6. The hard carbon material according to claim 4, characterized in that, The hard carbon material satisfies at least one of the following conditions: (1) 0.8 μm≤L2≤15μm; or, 1.9 μm≤L2≤13μm; (2) 0.05 μm≤L3≤1.5μm; or 0.05 μm≤L3≤1μm.

7. The hard carbon material according to any one of claims 1-2, characterized in that, The closed-cell volume of the sheet-like structure is 0.01~0.4 cm³. 3 / g; or, the closed-cell volume of the sheet-like structure is 0.05~0.28 cm³. 3 / g.

8. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer located on at least one surface of the negative current collector, the negative active material layer including a negative active material, the negative active material including the hard carbon material according to any one of claims 1-7; or, The negative electrode active material includes the hard carbon material and graphite material as described in any one of claims 1-7; and / or, based on the total mass of the negative electrode active material, the mass percentage of the hard carbon material is from 0.1% to 99.9%.

9. The secondary battery according to claim 8, characterized in that, The compaction density of the negative electrode active material layer is in the range of 1.0 g / cm³. 3 ~1.9 g / cm 3 .

10. An electronic device, characterized in that, The electronic device includes the secondary battery as described in claim 9.

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