Hard carbon material, secondary battery, and electronic device

Abstract

The application 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 has a sheet structure, the length of the sheet structure is L, and the width of the sheet structure is D1, wherein L satisfies 2 mu m <= L <= 16 mu m, and D1 satisfies 0.1 mu m <= D1 <= 3 mu m. By regulating the length and width parameters of the sheet structure of the hard carbon material within the above range, the hard carbon material can have good contact between particles, better processing performance, higher specific capacity, further improved compaction density of the battery pole piece, reduced pole piece resistance, improved rate performance and cycle performance of the secondary battery while improving the energy density of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and particularly relates to a hard carbon material, a secondary battery and an electronic device. BACKGROUND

[0002] With the rapid development of electric vehicles and mobile electronic devices in recent years, people have higher and higher requirements for the energy density, safety, cycle performance and the like of secondary batteries (for example, lithium ion batteries). The design of new secondary batteries with comprehensive performance improvement is the key to meeting the growing demand. Improving the composition and structure of electrode active materials in secondary batteries through design is one of the effective methods to improve the rapid charge-discharge performance and cycle performance of batteries, and is also the key to obtaining high-safety and high-energy-density batteries.

[0003] The negative active material accounts for 5%-15% of the cost of the battery and is one of the four main materials in the battery system. Graphite, as the most commonly used negative material of lithium ion batteries, has the advantages of stable charge-discharge platform, high efficiency and the like, but the current capacity development has reached the limit. Therefore, it is urgent to develop an improved negative electrode to further solve the problems faced by the current graphite negative electrode. Hard carbon material has attracted great attention due to its high theoretical capacity, low volume expansion and fast charge-discharge characteristics. However, the intrinsic hard skeleton and high porosity characteristics of hard carbon particles result in the problems of low compaction density and poor particle contact, and the capacity, cycle performance and rate performance of the secondary battery are not good. SUMMARY

[0004] The present application aims 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 related art, at least to some extent.

[0005] According to a first aspect of the present application, the present application provides a hard carbon material, the hard carbon material is in a sheet structure, the length of the sheet structure is L, the width of the sheet structure is D1, wherein L satisfies: 2 pm≤L≤16 pm; D1 satisfies: 0.1 pm≤D1≤3 pm. The length and width of the sheet hard carbon material provided by the present application will affect the stacking state between particles, and then affect the mass transfer process of the electrochemical reaction. When the length of the sheet hard carbon material is within the above range, the sheet hard carbon material is used alone or in combination with a negative electrode active material such as a graphite material, and can be in contact with multiple particles at the same time, thereby enhancing the electronic conductivity and ionic conductivity between particles, thereby accelerating the kinetic process of the battery and improving the rate performance. When the width of the sheet hard carbon material is within the above range, the processing performance of the material can be improved, so that the electrode sheet has good bonding performance, thereby improving the cycle stability of the secondary battery. That is, by adjusting the length, width and other parameters of the sheet hard carbon material of the present application within the above range, the hard carbon materials can have good contact and better processing performance, the compaction density of the battery electrode sheet can be improved, the electrode sheet resistance can be reduced, and the energy density of the secondary battery can be improved while the rate performance and cycle performance of the secondary battery are improved.

[0006] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0007] (1) the length L of the sheet structure satisfies: 2 pm≤L≤15 pm;

[0008] (2) the width D1 of the sheet structure satisfies: 0.5 pm≤D1≤1.9 pm;

[0009] (3) the height H1 of the sheet structure satisfies: 0.02 pm≤H1≤2.5 pm; or 0.05 pm≤H1≤1.9 pm;

[0010] (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;

[0011] (5) the ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12.

[0012] In some embodiments of the present application, the length L of the sheet structure satisfies: 2 pm≤L≤15 pm. When the length of the sheet hard carbon material provided by the present application is within the above range, the sheet hard carbon material can be further in contact with multiple particles at the same time when used alone or in combination with a negative electrode active material such as a graphite material, thereby further enhancing the electronic conductivity and ionic conductivity between particles, thereby further accelerating the kinetic process of the battery and further improving the rate performance.

[0013] In some embodiments of the present application, the width D1 of the sheet structure satisfies: 0.5 pm≤D1≤1.9 pm. When the width of the sheet-shaped hard carbon material provided by the present application is within the above range, the processing performance of the material can be further improved, so that the electrode sheet has good bonding performance, thereby further improving the cycle stability of the secondary battery.

[0014] In some embodiments of the present application, the height H1 of the sheet structure satisfies: 0.05 pm≤H1≤2.5 pm. Preferably, the height H1 of the sheet structure satisfies: 0.05 pm≤H1≤1.9 pm. When the height of the sheet-shaped hard carbon material provided by the present application is within the above range, the particles can be given a certain toughness, so that the material can have a certain degree of bending, and when the material is used alone or in combination with a negative electrode active material such as a graphite material, multiple surfaces of the particles can be contacted at the same time, thereby effectively reducing the interface impedance and improving the rate performance of the secondary battery.

[0015] In some embodiments of the present application, the ratio of the length L of the sheet structure to the height H1 of the sheet structure satisfies: 2.5≤L / H1≤750; preferably, the ratio of the length L of the sheet structure to the height H1 of the sheet structure satisfies: 2.5≤L / H1≤200. When the ratio of the length L to the height H1 of the sheet-shaped hard carbon material provided by the present application is within the above range, the rate performance of the secondary battery can be further improved.

[0016] In some embodiments of the present application, the ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12. When the ratio of the width D1 to the height H1 of the sheet-shaped hard carbon material provided by the present application is within the above range, the cycle performance and rate performance of the secondary battery can be further improved.

[0017] In some embodiments of the present application, the length L of the sheet structure is composed of three parts: the left arc length L1, the square region length L2, and the right arc length L3, and the relationship between L1, L2, and L3 satisfies: 2 pm≤L1+L2+L3≤16 pm, 0.01 pm≤L1≤1.5 pm, and 10≤L2 / L1≤80. The morphology of the arc surfaces of the hard carbon material is affected by the synthesis conditions, and different structures of the arc surfaces will affect the stacking state between the sheet structures. The existence of the arc surface structure can relieve the internal stress formed during the particle stacking process, avoid particle breakage, and at the same time, the stacking of multiple arc surfaces can easily form a small amount of pores to store electrolyte, improve the wettability of the active material to the electrolyte, and by adjusting the left arc length, square region length, and right arc length of the sheet structure of the hard carbon material within the above range, the hard carbon materials can have good contact, the compaction density of the battery electrode sheet can be improved, and thereby the energy density of the secondary battery can be improved.

[0018] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0019] (6) 2 pm≤L1+L2+L3≤15 pm;

[0020] (7) 0.05 pm≤L1≤1 pm;

[0021] (8) 11≤L2 / L1≤38.

[0022] In some embodiments of the present application, the hard carbon material satisfies: 2 pm≤L1+L2+L3≤15 pm.

[0023] In some embodiments of the present application, the hard carbon material satisfies: 0.05 pm≤L1≤1 pm.

[0024] In some embodiments of the present application, the hard carbon material satisfies: 11≤L2 / L1≤38.

[0025] By regulating the left side arc length, square region length and right side arc length of the flaky structure of the hard carbon material in the above range, the contact between the hard carbon materials can be further improved, and the compaction density of the battery pole piece and the energy density of the secondary battery can be improved.

[0026] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0027] (9) 0.8 pm≤L2≤15 pm; or, 1.9 pm≤L2≤13 pm;

[0028] (10) 0.05 pm≤L3≤1.5 pm; or, 0.05 pm≤L3≤1 pm.

[0029] In some embodiments of the present application, the square region length L2 of the hard carbon material satisfies: 1.9 pm≤L2≤13 pm. Or, 1.9 pm≤L2≤13 pm. By controlling the length L2 of the material in the range, the material can be in contact with multiple particles at the same time when used alone or in combination with a negative electrode active material such as a graphite material, thereby enhancing the electronic conductivity and ionic conductivity between the particles, thereby accelerating the kinetic process of the battery and improving the rate performance.

[0030] In some embodiments of the present application, the right side arc length L3 of the sheet structure satisfies: 0.05 μm≤L3≤1 μm; or, 0.05 μm≤L3≤1 μm. The presence of the arc structure can relieve the internal stress formed during the particle accumulation process, avoid particle breakage, and at the same time, the accumulation of multiple arcs can form a small amount of pores, store electrolyte, and improve the wettability of the active material to the electrolyte.

[0031] In some embodiments of the present application, the closed pore volume of the sheet structure is 0.01-0.4 cm 3 / g. In some embodiments of the present application, the closed pore volume of the sheet structure is 0.05-0.28 cm 3 / g. The increase of the closed pore content in the hard carbon material helps to store more active metal ions, thereby improving the active metal ion storage capacity. However, too many closed pores will reduce the density of the particles, and there is a risk of the closed pores becoming larger, which is not conducive to energy storage. By adjusting the closed pore volume of the hard carbon material within the above range, the hard carbon material can obtain higher capacity, and at the same time, the active material has a lower energy storage platform, thereby improving the energy density of the secondary battery.

[0032] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0033] (11) the sheet structure surface further has a carbon coating layer;

[0034] (12) the sheet structure surface further has a carbon coating layer, and the thickness of the carbon coating layer ranges from 20 to 100 nm;

[0035] (13) the sheet structure contains a first element, and the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn;

[0036] (14) the sheet structure contains a first element, and the first element 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%;

[0037] (15) the specific surface area of the sheet material ranges from 2 to 28 m 2 / g;

[0038] (16) the ID / IG value of the sheet material is 1.0 to 1.3.

[0039] In some embodiments of the present application, the surface of the flaky structure in the hard carbon material further has a carbon coating layer. Coating the surface of the hard carbon with a carbon layer helps to reduce defects on the surface of the flaky structure, while reducing the exposure of the pore structure of the flaky structure, thereby improving the first coulombic efficiency of the negative active material, so that the negative active material has a high reversible capacity, thereby improving the energy density and cycle stability of the secondary battery.

[0040] In some embodiments of the present application, the surface of the flaky structure in the hard carbon material further has a carbon coating layer, and the thickness of the carbon coating layer is in the range of 20-100 nm. Coating the surface of the hard carbon material with a carbon layer and controlling the thickness of the carbon coating layer in the above range helps to further reduce defects on the surface of the flaky structure, while further reducing the exposure of the pore structure of the flaky structure, thereby further improving the first coulombic efficiency of the negative active material, so that the negative active material has a high reversible capacity, thereby improving the energy density and cycle stability of the secondary battery.

[0041] In some embodiments of the present application, the flaky structure in the hard carbon material contains a first element, and the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. By introducing the first element into the flaky structure of the hard carbon material, the storage capacity of the active metal ion in the hard carbon material can be improved.

[0042] In some embodiments of the present application, the flaky structure in the hard carbon material contains a first element, and the first element 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 in the range of 0.01%-0.9%. By adjusting the content of the first element in the hard carbon material in the above range, the storage capacity of the active metal ion in the hard carbon material can be further improved, and the specific capacity of the battery anode can be improved when the hard carbon material of the present application is applied to a secondary battery, thereby improving the energy density of the secondary battery.

[0043] In some embodiments of the present application, the specific surface area of the flaky material in the hard carbon material is in the range of 2-28 m 2 / g. If the specific surface area of the hard carbon material is too large, the active metal ion will be adsorbed on the surface of the material, which will consume more electrolyte to form a stable SEI layer, resulting in a decrease in the first coulombic efficiency of the material. By adjusting the specific surface area of the hard carbon material in the above range, the present application can avoid excessive consumption of electrolyte, while ensuring the formation of a stable SEI, so that the hard carbon material has a higher reversible capacity and a higher first coulombic efficiency, thereby improving the energy density and cycle stability of the secondary battery.

[0044] In some embodiments of the present application, in the hard carbon material, the ID / IG value of the sheet structure is 1.0-1.3. 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 by the present application within the above range, the hard carbon material has a suitable defect degree, which can further promote ion adsorption and reduce irreversible capacity loss caused by high defect degree, thereby facilitating the improvement of the gram capacity of the hard carbon material.

[0045] According to a second aspect of the present application, the present application also provides a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises the hard carbon material according to any one of the first aspect of the present application. The negative electrode sheet comprising the above-mentioned hard carbon material has high capacity, good interface adhesion and high compaction density, and when it is applied to a secondary battery, the energy density of the secondary battery can be improved while the cycle performance and rate performance of the secondary battery are improved.

[0046] In some embodiments of the present application, the negative electrode active material comprises the hard carbon material according to any one of the first aspect of the present application and a graphite material. Generally, graphite has a higher compaction density, but the gram capacity of graphite is low and the rate performance is poor. The hard carbon material has a higher gram capacity, but the compaction density is relatively low. By compounding the hard carbon material with the graphite material, a negative electrode material with high capacity and high compaction is obtained, and a negative electrode active material layer with high capacity and high compaction density is obtained. However, ordinary granular hard carbon is not conducive to the compounding between the hard carbon material and the graphite and other negative electrode active materials. The sheet-shaped hard carbon material provided by the present application increases the contact between the hard carbon particles and the contact between the hard carbon and graphite particles, which is conducive to reducing the resistance of the electrode sheet and further improving the rate performance of the negative electrode active material.

[0047] In some embodiments of the present application, the negative electrode active material comprises the hard carbon material according to any one of the first aspect of the present application and a graphite material, and the mass percentage content of the hard carbon material is 0.1%-99.9% based on the total mass of the negative electrode active material. By adjusting the relative proportion of the sheet-shaped hard carbon and the graphite in the compounded electrode sheet and by adjusting the mass percentage content of the hard carbon material in the negative electrode active material layer within the range of the present 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.

[0048] In some embodiments of the present application, the compaction density of the negative electrode active material layer is 1.0-1.9 g / cm 3By regulating the compaction density of the negative active material layer to be within the above range, the content of the negative active material per unit area can be increased, thereby increasing the energy density of the secondary battery.

[0049] According to a third aspect of the present application, the present application provides a secondary battery comprising the negative electrode sheet according to any one of the embodiments of the second aspect of the present application. The secondary battery comprising the negative electrode sheet has high energy density and good cycle performance.

[0050] According to a fourth aspect of the present application, the present application provides an electronic device comprising the secondary battery according to any one of the embodiments of the third aspect of the present application. The electronic device comprising the secondary battery has a longer service life. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0052] Figure 1 A structural schematic diagram of a hard carbon material according to an embodiment of the present application;

[0053] Figure 2 A charge-discharge curve of the negative active material of Comparative Example 1-1 in the potential range of 0V to 2.5V of Li / Li+;

[0054] Figure 3 A charge-discharge curve of the negative active material of Example 1-2 in the potential range of 0V to 2.5V of Li / Li+;

[0055] Figure 4 A charge-discharge curve of the negative active material of Example 2-3 in the potential range of 0V to 2.5V of Li / Li+. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0057] It should be noted that in the specific embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

[0058] Graphite is the most commonly used anode material for lithium ion batteries, which has the advantages of stable charge-discharge platform, high efficiency, etc. However, the current capacity development has reached the limit. Therefore, it is urgent to develop an improved anode to further solve the problems faced by the current graphite anode. Hard carbon material has attracted great attention due to its high theoretical capacity, low volume expansion and fast charge-discharge characteristics. However, the intrinsic hard skeleton and high porosity of hard carbon particles result in low compaction density, poor particle contact, and other problems, and the capacity and cycle performance of the secondary battery are not good. Based on this, the inventors start from the anode active material itself and find through a large number of studies that by preparing hard carbon materials with special morphology, by pure use or compounding with commercial graphite, the problems of low capacity of anode sheet, poor adhesion, poor conductivity, etc. can be solved, thereby improving the compaction density of the battery sheet, and improving the energy density of the secondary battery while improving the rate performance and cycle performance of the secondary battery.

[0059] According to a first aspect of the present application, the present application provides a hard carbon material, the hard carbon material is in a sheet structure, the length of the sheet structure is L, the width of the sheet structure is D1, and the height of the sheet structure is H1, wherein L satisfies: 2 μm≤L≤16 μm; D1 satisfies: 0.1 μm≤D1≤3 μm. Specifically, the length L of the sheet structure can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or a range composed of any two of the above. Specifically, the width D1 of the sheet structure can be 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, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or a range composed of any two of the above.

[0060] Specifically, the hard carbon material provided in the present application has a sheet structure, which means that in the SEM electron microscope image of the provided hard carbon material, it can be clearly observed that the hard carbon material has at least one particle with a sheet structure, and the sheet structure particles can be stacked with each other. The length and width of the sheet-shaped hard carbon material provided in the present application will affect the stacking state between the particles, and further affect the mass transfer process of the electrochemical reaction. When the length of the sheet-shaped hard carbon material is within the above range, the sheet-shaped hard carbon material is used alone or in combination with a negative active material such as a graphite material, and can be in contact with multiple particles at the same time, thereby enhancing the electronic conductivity and ionic conductivity between the particles, thereby accelerating the kinetic process of the battery and improving the rate performance. When the width of the sheet-shaped hard carbon material is within the above range, the processing performance of the material can be improved, so that the electrode sheet has good bonding performance, thereby improving the cycle stability of the secondary battery. That is, by adjusting the length and width of the sheet-shaped hard carbon material in the present application within the above range, the hard carbon material has good contact and better processing performance, which can improve the compaction density of the battery electrode sheet, reduce the electrode resistance, and further improve the energy density of the secondary battery while improving the rate performance and cycle performance of the secondary battery.

[0061] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0062] (1) the length L of the sheet structure satisfies: 2 pm≤L≤15 pm;

[0063] (2) the width D1 of the sheet structure satisfies: 0.5 pm≤D1≤1.9 pm;

[0064] (3) the height H1 of the sheet structure satisfies: 0.02 pm≤H1≤2.5 pm; or, 0.05 pm≤H1≤1.9 pm;

[0065] (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;

[0066] (5) the ratio of the width D1 of the sheet structure to the height H1 of the sheet structure satisfies: 1≤D1 / H1≤12.

[0067] In some embodiments of the present application, the length L of the sheet structure satisfies: 2 pm≤L≤15 pm. When the length of the sheet-shaped hard carbon material provided in the present application is within the above range, the sheet-shaped hard carbon material can be further in contact with multiple particles at the same time when used alone or in combination with a negative active material such as a graphite material, thereby further enhancing the electronic conductivity and ionic conductivity between the particles, thereby further accelerating the kinetic process of the battery and further improving the rate performance.

[0068] In some embodiments of the present application, the width D1 of the flaky structure satisfies: 0.5 pm≤D1≤1.9 pm. When the width of the flaky hard carbon material provided by the present application is within the above range, the processing performance of the material can be further improved, so that the pole piece has good bonding performance, thereby further improving the cycle stability of the secondary battery.

[0069] In some embodiments of the present application, the height H1 of the flaky structure satisfies: 0.05 pm≤H1≤2.5 pm. Specifically, the height H1 of the flaky structure can be 0.05 pm, 0.06 pm, 0.07 pm, 0.08 pm, 0.09 pm, 0.1 pm, 0.15 pm, 0.2 pm, 0.25 pm, 0.3 pm, 0.35 pm, 0.4 pm, 0.45 pm, 0.5 pm, 0.55 pm, 0.6 pm, 0.65 pm, 0.7 pm, 0.75 pm, 0.8 pm, 0.85 pm, 0.9 pm, 1.0 pm, 1.1 pm, 1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm, 1.6 pm, 1.7 pm, 1.8 pm, 1.9 pm, 2 pm, 2.1 pm, 2.2 pm, 2.3 pm, 2.4 pm, 2.5 pm, or a range consisting of any two of the above. Preferably, the height H1 of the flaky structure satisfies: 0.05 pm≤H1≤1.9 pm. When the height of the flaky hard carbon material provided by the present application is within the above range, the particles can be given a certain toughness, so that the material can have a certain degree of bending. When the material is used alone or in combination with a negative electrode active material such as a graphite material, multiple surfaces of the particles can be contacted at the same time, thereby effectively reducing the interface impedance and improving the rate performance of the secondary battery.

[0070] In some embodiments of the present application, the ratio of the length L of the flaky structure to the height H1 of the flaky structure satisfies: 2.5≤L / H1≤750. Specifically, the ratio of the length L of the flaky structure to the height H1 of the flaky 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. Preferably, the ratio of the length L of the flaky structure to the height H1 of the flaky structure satisfies: 2.5≤L / H1≤200. When the ratio of the length L to the height H1 of the flaky hard carbon material provided by the present application is within the above range, the rate performance of the secondary battery can be further improved.

[0071] In some embodiments of the present application, the ratio of the width D1 of the flaky structure to the height H1 of the flaky structure satisfies: 1≤D1 / H1≤12. Specifically, the ratio of the width D1 of the flaky structure to the height H1 of the flaky 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 between any two of the above values. When the ratio of the width D1 to the height H1 of the flaky hard carbon material provided by the present application is within the above range, the cycle performance and rate performance of the secondary battery can be further improved.

[0072] In some embodiments of the present application, the length L of the sheet structure is composed of the left arc length L1, the square region length L2, and the right arc length L3, and the relationship L1+L2+L3 between the left arc length L1, the square region length L2, and the right arc length L3 of the sheet structure satisfies: 2 μm≤L1+L2+L3≤16 μm, 0.01 μm≤L1≤1.5 μm, and 10≤L2 / L1≤80. Specifically, the relationship L1+L2+L3 between the left arc length L1, the square region length L2, and the right arc length L3 of the sheet structure can be: 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or a range composed of any two of the above values. Specifically, the left arc length L1 of the sheet structure can be: 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 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 composed of any two of the above values. Specifically, the ratio L2 / L1 of the square region length L2 to the left arc length L1 of the sheet structure 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, 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 composed of any two of the above values. The morphology of the arc surfaces on both sides of the hard carbon material is affected by the synthesis conditions, and different structures of the arc surfaces will affect the stacking state between the sheet structures. The existence of the arc surface structure can relieve the internal stress formed during the particle stacking process and avoid particle breakage. At the same time, the stacking of multiple arc surfaces is easy to form a small amount of pores, which can store electrolyte and improve the wettability of active material to electrolyte. By adjusting the left arc length, the square region length, and the right arc length of the sheet structure of the hard carbon material within the above range, the hard carbon materials can have good contact, the compaction density of the battery pole piece can be improved, and the energy density of the secondary battery can be improved.

[0073] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0074] (6) 2 pm≤L1+L2+L3≤15 pm;

[0075] (7) 0.05 pm≤L1≤1 pm;

[0076] (8) 11≤L2 / L1≤38.

[0077] In some embodiments of the present application, the hard carbon material satisfies: 2 pm≤L1+L2+L3≤15 pm.

[0078] In some embodiments of the present application, the hard carbon material satisfies: 0.05 pm≤L1≤1 pm.

[0079] In some embodiments of the present application, the hard carbon material satisfies: 11≤L2 / L1≤38.

[0080] By regulating the left side arc length, square region length and right side arc length of the flaky structure of the hard carbon material of the present application within the above ranges, the hard carbon materials can be further facilitated to have good contact, and the compaction density of the battery pole piece and the energy density of the secondary battery can be improved.

[0081] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0082] (9) 0.8 pm≤L2≤15 pm; or, 1.9 pm≤L2≤13 pm;

[0083] (10) 0.05 pm≤L3≤1.5 pm; or, 0.05 pm≤L3≤1 pm.

[0084] In some embodiments of the present application, the square region length L2 of the sheet structure satisfies: 0.8 μm≤L2≤15 μm. Specifically, the square region length L2 of the sheet 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 between any two of the above values. Preferably, the square region length L2 of the sheet structure satisfies: 1.9 μm≤L2≤13 μm. Controlling the length L2 of the material within the range, the material can contact multiple particles at the same time when used alone or in combination with negative active materials such as graphite, enhancing the electronic conductivity and ionic conductivity between particles, thereby accelerating the kinetic process of the battery and improving the rate performance.

[0085] In some embodiments of the present application, the right side arc length L3 of the sheet structure satisfies: 0.05 μm≤L3≤1.5 μm. Specifically, the right side arc length L3 of the sheet 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 between any two of the above values. Preferably, the right side arc length L3 of the sheet structure satisfies: 0.05 μm≤L3≤1 μm. The presence of the arc structure can relieve the internal stress formed during the particle accumulation process, avoid particle breakage, and at the same time, the accumulation of multiple arcs can easily form a small amount of pores to store electrolyte, thereby improving the wettability of the active material to the electrolyte.

[0086] In some embodiments of the present application, the closed pore volume of the sheet structure is 0.01-0.4 cm3 / g. Specifically, the closed pore volume of the sheet structure can be 0.01 cm3 / g, 0.02 cm3 / g, 0.03 cm3 / g, 0.04 cm3 / g, 0.05 cm3 / g, 0.06 cm3 / g, 0.07 cm3 / g, 0.08 cm3 / g, 0.09 cm3 / g, 0.1 cm3 / g, 0.12 cm3 / g, 0.14 cm3 / g, 0.16 cm3 / g, 0.18 cm3 / g, 0.2 cm3 / g, 0.22 cm3 / g, 0.24 cm3 / g, 0.26 cm3 / g, 0.28 cm3 / g, 0.3 cm3 / g, 0.32 cm3 / g, 0.34 cm3 / g, 0.36 cm3 / g, 0.38 cm3 / g or a range between any two of the above values. 3 3 3 3 3 3 3 3 3 3 3 3 ​​​​​​​​​​​ / g, 0.15 cm 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 composed of any two of the above. Preferably, the closed pore volume of the sheet structure is 0.05-0.28 cm 3 / g. An increase in the closed pore content in the hard carbon material helps to store more active metal ions, thereby enabling the active metal ion storage capacity to be improved, but too many closed pores will reduce the density of the particles, and there is a risk that the closed pores will become larger, which is not conducive to energy storage. By regulating the closed pore volume in the hard carbon material to be within the above range, the hard carbon material can obtain a higher capacity, and the active material has a lower energy storage platform, thereby enabling the energy density of the secondary battery to be improved.

[0087] In some embodiments of the present application, the hard carbon material satisfies at least one of the following conditions:

[0088] (11) the sheet structure surface also has a carbon coating layer;

[0089] (12) the sheet structure surface also has a carbon coating layer, and the thickness of the carbon coating layer is in the range of 20-100 nm;

[0090] (13) the sheet structure contains a first element, and the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn;

[0091] (14) the sheet structure contains a first element, and the first element 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%-0.9%;

[0092] (15) the specific surface area of the sheet material is in the range of 2-28 m 2 / g;

[0093] (16) the ID / IG value of the sheet material is 1.0-1.3.

[0094] In some embodiments of the present application, the surface of the flaky structure in the hard carbon material further has a carbon coating layer. Coating the surface of the hard carbon with a carbon layer helps to reduce the defects on the surface of the flake, while reducing the exposure of the pore structure of the flake, improving the first coulombic efficiency of the negative active material, so that the negative active material has a high reversible capacity, thereby improving the energy density and cycle stability of the secondary battery.

[0095] In some embodiments of the present application, the surface of the flaky structure in the hard carbon material further has a carbon coating layer, and the thickness of the carbon coating layer 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 a range composed of any 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 the defects on the surface of the flake, while further reducing the exposure of the pore structure of the flake, further improving the first coulombic efficiency of the negative active material, so that the negative active material has a high reversible capacity, thereby improving the energy density and cycle stability of the secondary battery.

[0096] In some embodiments of the present application, the flaky structure in the hard carbon material contains a first element, and the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. By introducing the first element into the flaky structure of the hard carbon material, the storage capacity of the active metal ion in the hard carbon material can be improved.

[0097] In some embodiments of the present application, in the hard carbon material, the first element contained in the sheet structure includes any one of Li, Na, K, Rb, Mg, Ca, Zn, and the content of the first element 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 between any two of the above values. By regulating the content of the first element in the hard carbon material within the above range, the present application can further induce the storage of active metal ions in the hard carbon material, further improve the storage capacity of active metal ions, and help to improve the specific capacity of the battery anode and further improve the energy density of the secondary battery when the hard carbon material of the present application is applied to a secondary battery.

[0098] In some embodiments of the present application, in the hard carbon material, the specific surface area of the sheet material is 2 to 28 m 2 / g. Specifically, the specific surface area of the sheet material can be 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g, 19 m 2 / g, 20 m 2 / g, 21 m 2 / g, 22 m 2 / g, 23 m 2 / g, 24 m 2 / g, 25 m 2 / g, 26 m2 / g, 27m 2 / g, 28m 2 / g, or a range between any two of the above values. If the specific surface area of the hard carbon material is too large, the active metal ions will be adsorbed on the surface of the material, which will consume more electrolyte to form a stable SEI layer, resulting in a decrease in the initial coulombic efficiency of the material. By adjusting the specific surface area of the hard carbon material within the above range, the present application can avoid excessive consumption of electrolyte, while ensuring the formation of a stable SEI layer, so that the hard carbon material has a higher reversible capacity and a higher initial coulombic efficiency, thereby improving the energy density and cycle stability of the secondary battery.

[0099] In some embodiments of the present application, in the hard carbon material, the ID / IG value of the sheet structure is 1.0-1.3. Specifically, the ID / IG value of the sheet 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 between 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 adjusting the ID / IG value of the hard carbon material within the above range, the hard carbon material has a suitable defect degree, which can further promote ion adsorption and combination, while reducing the irreversible capacity loss caused by high defect degree, thereby improving the gram capacity of the hard carbon material.

[0100] According to a second aspect of the present application, the present application also provides a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising the hard carbon material of any one of the first aspect of the present application. The negative electrode sheet comprising the above hard carbon material has high capacity, good interface adhesion, and high compaction density, and when applied to a secondary battery, it can improve the energy density of the secondary battery while improving the cycle performance and rate performance of the secondary battery.

[0101] In some embodiments of the present application, the negative active material comprises the hard carbon material and the graphite material according to any one of the first aspect of the present application. Generally, graphite has a higher compaction density, but the graphite has a low specific capacity and poor rate performance. The hard carbon material has a high specific capacity, but the compaction density is relatively low. The present application obtains a negative electrode material with high capacity and high compaction by compounding the hard carbon material with the graphite material, and obtains a negative active material layer with high capacity and high compaction density. The ordinary granular hard carbon is not conducive to the compounding between the hard carbon material and the graphite and other negative active materials. The sheet-shaped hard carbon material provided by the present application increases the contact between the hard carbon particles and between the hard carbon and graphite particles, which is conducive to reducing the electrode resistance and further improving the rate performance of the negative active material.

[0102] In some embodiments of the present application, the negative active material comprises the hard carbon material and the graphite material according to any one of the first aspect of the present application, and the mass percentage of the hard carbon material is 0.1% to 99.9% based on the total mass of the negative active material. Specifically, 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 composed of any two of the above values. The present application regulates the relative proportion of the sheet-shaped hard carbon and the graphite in the compounded electrode sheet, and by regulating the mass percentage of the hard carbon material in the negative active material layer within the range of the present application, the compaction density of the negative active material layer can be optimized, thereby improving the energy density, rate performance and cycle retention rate of the secondary battery.

[0103] In some embodiments of the present application, the compaction density of the negative active material layer is 1.0-1.9 g / cm 3 . Specifically, the compaction density of the negative active material layer can be 1.0 g / cm 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 , 1.5 g / cm 3 , 1.55 g / cm3 1.6 g / cm3 3 1.65 g / cm3 3 1.7 g / cm3 3 1.75 g / cm3 3 1.8 g / cm3 3 1.85 g / cm3 3 1.90 g / cm3 3 or a range between any two of the above values. By adjusting the compaction density of the negative active material layer to be within the above range, the content of the negative active material per unit area can be increased, thereby increasing the energy density of the secondary battery.

[0104] According to a third aspect of the present application, the present application provides a secondary battery comprising the negative electrode tab according to any one of the embodiments of the second aspect of the present application. The secondary battery comprising the negative electrode tab has high energy density and good cycle performance.

[0105] The secondary battery of the present application further comprises a positive electrode tab. The present application does not have any particular limitation on the positive electrode tab as long as it can achieve the purpose of the present application. For example, the positive electrode tab comprises a positive electrode current collector and a positive active material layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector can comprise a metal foil or a composite current collector, etc. For example, the metal foil is an aluminum foil. In some embodiments, the secondary battery is a lithium ion battery, and the positive active material can include a lithium transition metal oxide, which can include but is not limited to at least one of lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganese iron phosphate, or lithium titanate, etc.

[0106] The present application does not have any particular limitation on the thickness of the positive electrode current collector and the positive active material layer as long as it can achieve the purpose of the present application. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm.

[0107] The secondary battery of the present application further comprises an electrolyte. In one embodiment, the electrolyte comprises a lithium salt and a non-aqueous solvent. The present application does not have any particular limitation on the concentration of the lithium salt in the electrolyte as long as it can achieve the purpose of the present application.

[0108] The secondary battery of the present application further includes a separator for separating the positive electrode sheet and the negative electrode sheet, preventing internal short circuit of the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. The separator of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separator mainly including polytetrafluoroethylene, polyester film (for example, polyethylene terephthalate (PET) film), cellulose film, polyimide film (PI), polyamide film (PA), spandex or aramid film, and the like.

[0109] The secondary battery of the present application further includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art in the secondary battery, and the present application does not limit the above-mentioned other components. The packaging bag of the present application is not particularly limited, and can be a packaging bag known in the art as long as the object of the present application can be achieved. For example, an aluminum plastic film packaging bag can be used.

[0110] The secondary battery of the present application is not particularly limited, and can include any device in which an electrochemical reaction occurs. In one embodiment of the present application, the secondary battery can include, but is not limited to, a lithium ion battery, a sodium ion battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.

[0111] According to a fourth aspect of the present application, the present application provides an electronic device including the secondary battery according to any one of the embodiments of the third aspect of the present application. The electronic device including the above-mentioned secondary battery has a longer service life.

[0112] The electronic device of the present application is not particularly limited, and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, and the like.

[0113] Embodiments

[0114] Hereinafter, embodiments and comparative examples are presented to more specifically explain the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0115] The test methods used in the following examples and comparative examples are as follows:

[0116] 1. Scanning Electron Microscope (SEM) Test

[0117] A scanning electron microscope (instrument model ZEISS SEM) was used to observe the microstructure of the prepared hard carbon material and take SEM photos. The length (L), width (D1), thickness / height (H1), and left arc length (L1), square area length (L2), and right arc length (L3) of each structure in the microstructure of the hard carbon material were measured using the measurement function of the scanning electron microscope. The specific test steps were as follows: the measurement function of the scanning electron microscope was used to measure the parameters of a single flaky particle, and the relevant parameters of ten flaky particles were recorded. The length (L), width (D1), thickness / height (H1), and left arc length (L1), square area length (L2), and right arc length (L3) of the final particle were the average values of the ten particles. For cross-section testing, an ion polisher (instrument model IB-09010CP) was used to cut a flat cross-section, and then SEM photos were taken. The principle of ion polishing was as follows: under vacuum conditions, the ion source ionized argon, which was accelerated and focused, and then high-speed argon ions impacted the atoms or molecules on the surface of the sample to achieve ion polishing. The height of the hard carbon material was measured by testing the cross-section of the hard carbon particle.

[0118] 2. Transmission Electron Microscope (TEM) Test

[0119] A projection electron microscope (FEI Tecnai F20) was used to observe the carbon coating layer of the hard carbon material and take TEM photos, and the thickness of the carbon coating layer of the hard carbon material was measured.

[0120] 3. Metal Element Analysis Test

[0121] A microwave digestion instrument (model CEM-Mars5) was used to digest the sample, and an ICP-OES instrument (instrument model PE7000DV) was used to quantitatively test the element content. After the sample was acid-digested into a solution, the liquid sample entered the atomization chamber, and under the action of the carrier gas, it formed an aerosol that entered the plasma through the central injection pipe and was fully evaporated, dissociated, atomized, ionized, and excited. Characteristic spectral lines of elements were emitted, and the wavelength of the spectral line was used for qualitative analysis, and the spectral line intensity was proportional to the concentration for quantitative analysis.

[0122] 4. Small Angle X-ray Scattering Test

[0123] A small angle X-ray scattering structure analyzer (instrument model Nano-inXider) was used to test the scattering vector change of the sample in the scattering intensity range of 0.01 nm-1 to 0.7 nm-1, and the closed pore volume in the hard carbon material particle was analyzed by fitting.

[0124] 5. Specific surface area, pore volume test

[0125] The hard carbon material powder was vacuum degassed at 100°C for 12h in a sample tube. The adsorption amount of nitrogen by the hard carbon material at different pressures was tested by an ASAP2460-physical adsorption analyzer, and the adsorption and desorption isotherms were drawn. The pore shape was determined according to the shape of the hysteresis loop, the micropore pore size distribution curve was fitted using the DFT model, and the specific surface area of the hard carbon material was calculated.

[0126] 6. Raman test

[0127] The Raman spectrum of the hard carbon material was tested by a Raman spectrometer. A range of 200μm×500μm was selected for testing, and more than 200 points were tested at equal intervals in the range, with the test range of each point being between 1000cm -1 and 2000cm -1 ; the peak appearing between 1320cm -1 and 1370cm -1 was the D peak, the peak appearing between 1570cm -1 and 1620cm -1 was the G peak, the intensity ratio of ID / IG of each point was counted, and then the average value of multiple points was calculated as the final intensity ratio of ID / IG.

[0128] 7. Compaction density test of negative electrode active material layer:

[0129] A lithium ion battery completely discharged was disassembled to obtain a negative electrode sheet, which was cleaned, dried, weighed using an electronic balance, and the weight was recorded as W1. The thickness T1 of the negative electrode sheet was measured using a micrometer. The negative electrode active material layer was washed off using a solvent DMC, dried, and the weight of the negative electrode current collector was measured and recorded as W2. The thickness T2 of the negative electrode current collector was measured using a micrometer. The weight W0 and thickness T0 of the negative electrode active material layer arranged on one side of the negative electrode current collector were calculated by the following formula, and the compaction density of the negative electrode active material layer was calculated. W0=W1-W2, T0=T1-T2, and the compaction density=W0 / (T0×S).

[0130] 8. Total lithium storage capacity and first efficiency test of negative electrode active material:

[0131] The first reversible gram capacity of the negative active material at 0V to 2.5V can be obtained by the following test method: taking a single-sided coated negative electrode sheet, cutting it into a 14mm diameter disc and using it as the working electrode, then using a lithium sheet as the counter electrode, using a porous polyethylene film (provided by Celgard) as the separator, injecting the electrolyte to assemble a button cell; first, the button cell is discharged to 0V at 0.05C / 0.01C / 0.005C three-stage small current, and the first discharge capacity of the button cell is recorded; then, the button cell is charged to 2.5V at 0.1C constant current, and the first charge capacity of the button cell is recorded. The first efficiency = the first charge capacity / the first discharge capacity x 100%; the first reversible gram capacity of the negative active material at 0V to 2.5V, i.e. the total lithium storage gram capacity = the first charge capacity / the mass of the negative active material, unit: mAh / g.

[0132] The above electrolyte includes a base solvent and a lithium salt, the base solvent is obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 1:1, and the lithium salt is LiPF6, the lithium salt concentration is 1 mol / L.

[0133] The total lithium storage gram capacity and the first efficiency of the comparative example are tested by the same method as the total lithium storage gram capacity and the first efficiency of the above hard carbon material.

[0134] 9. Energy density (ED) test method

[0135] In an environment of 25°C, the lithium ion battery is charged to a voltage of 4.48V or 3.95V at 0.2C constant current, and then constant voltage charging; discharged to a voltage of 2V at 0.2C constant current, which is recorded as one cycle, and the discharge capacity C and discharge energy E of the first cycle are recorded; and the length, width and height of the battery at 50% state of charge are tested to obtain the volume Vm of the battery, and the energy density ED = E / Vm; the lithium ion battery is cycled for 500 cycles by the above charging and discharging process, the discharge capacity C1 of the 500th cycle is tested, and the cycle capacity retention rate = C1 / C.

[0136] 10. Test method of rate performance

[0137] The lithium ion battery is subjected to rate charging at a constant temperature, first, the full-discharged lithium ion battery is charged to 4.48V at 1C constant current, and then charged to 0.05C constant voltage, and then discharged to 3.0V at 1C constant current to obtain the discharge capacity, which is recorded as capacity A; then, the lithium ion battery is charged to 4.48V at 5C constant current, and then charged to 0.05C constant voltage, and then discharged to 3.0V at 1C constant current to obtain the discharge capacity, which is recorded as capacity B, and the 5C / 1C rate performance is B / A.

[0138] Example 1-1

[0139] <Preparation of negative active material>

[0140] Stearic acid flake dispersion: 100 g of polyoxyethylene polypropylene ether was weighed into 10 L of water, and the dispersion was stirred at 80 °C for 2 h until the polyoxyethylene polypropylene ether was completely dispersed, then 75 g of stearic acid melt was added, and stirring was continued for 3 h until the solution formed a microemulsion, the obtained microemulsion was allowed to stand at room temperature for 24 h to obtain a stearic acid flake dispersion for standby use; 50 g of resorcinol and 66 g of formaldehyde were slowly stirred at room temperature to dissolve in 1000 mL of water, then 1000 mL of stearic acid flake dispersion was added, followed by the addition of 1.5 g of propylamine, after stirring for 30 min, 5 mL of 1.5 mol / L ammonia water solution was added, and the temperature was raised to 85 °C, and stirring was continued for 4 h; the obtained powder product was used as a precursor after centrifugation, suction filtration, water washing and drying; resin curing: the powder product was placed in a programmed temperature oven under an inert atmosphere, and the temperature program was controlled as 90 °C / 1 h + 110 °C / 1 h + 130 °C / 1 h + 150 °C / 1 h to ensure that the resin was fully cured; precursor mixing: 100 g of the cured powder product and 10 g of NaOH were uniformly mixed by a mixer; carbonization: the uniformly mixed precursor was placed in a rotary furnace, and the temperature was raised to the first calcination temperature T1 = 900 °C at a rate of 5 °C / min, and carbonization was carried out for 2 h, then the temperature was lowered and the carbonized material was obtained after cooling; acid washing and water washing: then the collected powder was washed with 1 M hydrochloric acid for 12 h, the filter residue was obtained after suction filtration, and then washed with deionized water for 12 h, suction filtered, and the filter residue was dried; surface coating layer formation: then the dried powder was transferred into a nitrogen atmosphere protection furnace, and the temperature was raised to the vapor deposition temperature T3 = 900 °C at a rate of 5 °C / min, then the gas atmosphere was changed to a mixture of reducing gas methane and argon, the vapor deposition time t3 = 2 h, after the vapor deposition was completed, the above mixture gas was disconnected, and replaced with nitrogen, and the hard carbon material, i.e. the negative electrode active material, was obtained after cooling to room temperature. Based on the mass of the mixture gas, the mass percentage of reducing gas methane is 10%.

[0141] <Preparation of negative electrode sheet>

[0142] The hard carbon material prepared above was mixed with the binder styrene-butadiene rubber and the thickening agent sodium carboxymethyl cellulose according to a mass ratio of 97:1.5:1.5, then deionized water was added as a solvent, and a negative electrode slurry with a solid content of 40 wt% was prepared and uniformly stirred. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and the copper foil was dried at 85 °C for 4 h to obtain a negative electrode sheet with a single-sided coated negative electrode active material layer with a coating thickness of 50 μm. After cold pressing, sheet cutting and slitting, the negative electrode sheet was dried under vacuum at 120 °C for 12 h.

[0143] <Preparation of positive electrode sheet>

[0144] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black (Super P), and the binder PVDF were mixed in a mass ratio of 97:1.4:1.6, N-methyl pyrrolidone (NMP) was added as a solvent, and stirring was performed until uniformity was achieved, thereby preparing a positive electrode slurry having a solid content of 72 wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil having a thickness of 13 μm, and drying was performed at 85°C, thereby obtaining a positive electrode active material-coated positive electrode sheet having a positive electrode active material layer thickness of 80 μm. After cold pressing, sheet cutting, and slitting, drying was performed at 85°C under vacuum for 4 h, thereby obtaining a positive electrode sheet.

[0145] <Preparation of electrolyte>

[0146] 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, 1,3-propane sultone, fluoroethylene carbonate, and succinonitrile were then added, and after dissolution and thorough stirring, lithium salt LiPF6 was added, and uniform mixing was performed, thereby obtaining an electrolyte having a lithium salt mass percentage of 12.5% and a 1,3-propane sultone, fluoroethylene carbonate, and succinonitrile mass percentage of 2% based on the mass of the electrolyte.

[0147] <Preparation of separator>

[0148] A polyethylene film having a thickness of 7 μm was used as the separator.

[0149] <Preparation of lithium ion battery>

[0150] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were sequentially stacked with the separator between the positive electrode sheet and the negative electrode sheet, thereby obtaining an electrode assembly. After welding of the tabs, the electrode assembly was placed in an aluminum-plastic film packaging bag, and was dried in a vacuum oven at 80°C for 12 h to remove water, and the electrolyte prepared above was injected, and the lithium ion battery was obtained after vacuum packaging, standing, formation, degassing, and shaping.

[0151] Example 1-2

[0152] Based on Example 1-1, the amount of added stearic acid tablet dispersion was adjusted to 500 mL, and the remaining steps and parameters of Example 1-2 were the same as those of Example 1-1.

[0153] Example 1-3

[0154] Based on Example 1-1, the amount of added stearic acid tablet dispersion was adjusted to 1500 mL, and the remaining steps and parameters of Example 1-3 were the same as those of Example 1-1.

[0155] Example 1-4

[0156] Based on Example 1-1, the amount of stearic acid tablet dispersion added was adjusted to 2000 mL, and the remaining step parameters of Example 1-4 were the same as those of Example 1-1.

[0157] Example 1-5

[0158] 100 g of polyvinylidene chloride (PVDC) powder and 10 g of LiOH were weighed and uniformly mixed by a mixer. The uniformly mixed precursors were placed in a rotary furnace, and heated to a first calcination temperature T1 = 900 °C at a heating rate of 5 °C / min, carbonized for 2 h, and then cooled to obtain a carbonized material. The collected powder was then washed with 1 M hydrochloric acid for 12 h, and the filter residue was washed with deionized water for 12 h, and then dried by filtration. The dried powder was then transferred to a nitrogen atmosphere protection furnace, and heated to a vapor deposition temperature T3 = 900 °C at a heating rate of 5 °C / min. Subsequently, the gas atmosphere was changed to a mixture of reducing gas methane and argon, and the vapor deposition time t3 = 2 h. After the vapor deposition was completed, the above mixture was disconnected, and replaced with nitrogen. When the temperature was cooled to room temperature, a hard carbon material, i.e., a negative electrode active material, was obtained. Based on the mass of the mixture, the mass percentage of reducing gas methane was 10%.

[0159] Example 1-6

[0160] Based on Example 1-5, the precursors were replaced with 100 g of polyvinylidene chloride powder and 10 g of NaOH, and the remaining parameters of Example 1-6 were the same as those of Example 1-5.

[0161] Example 1-7

[0162] Based on Example 1-5, the precursors were replaced with 100 g of polyvinylidene chloride powder and 10 g of KOH, and the remaining parameters of Example 1-7 were the same as those of Example 1-5.

[0163] Example 1-8

[0164] Based on Example 1-5, the precursors were replaced with 100 g of polyvinylidene chloride powder and 10 g of RbOH, and the remaining parameters of Example 1-8 were the same as those of Example 1-5.

[0165] Example 1-9

[0166] Based on Example 1-2, the amount of stearic acid melt added during the preparation of the stearic acid tablet dispersion was adjusted to 1 g, and the remaining steps and parameters of Example 1-9 were the same as those of Example 1-2.

[0167] Example 1-10

[0168] Based on Example 1-2, the amount of stearic acid melt added was adjusted to 15 g during the stearic acid flake dispersion preparation, and the remaining steps and parameters were the same as Example 1-2.

[0169] Example 1-11

[0170] Based on Example 1-2, the amount of resorcinol was adjusted to 25 g, the amount of formaldehyde was adjusted to 33 g, and the amount of aqueous ammonia solution added was adjusted to 10 mL during the resin prepolymerization process, and the remaining steps and parameters were the same as Example 1-2.

[0171] Example 1-12

[0172] Based on Example 1-2, the amount of resorcinol was adjusted to 75 g, the amount of formaldehyde was adjusted to 99 g, and the amount of aqueous ammonia solution added was adjusted to 2 mL during the resin prepolymerization process, and the remaining steps and parameters were the same as Example 1-2.

[0173] Example 1-13

[0174] Based on Example 1-2, the amount of NaOH was adjusted to 2 g during the precursor mixing process, and the remaining steps and parameters were the same as Example 1-2.

[0175] Example 1-14

[0176] Based on Example 1-2, the amount of NaOH was adjusted to 20 g during the precursor mixing process, and the remaining steps and parameters were the same as Example 1-2.

[0177] Comparative Example 1-1

[0178] Coconut shells were used instead of the polyvinylidene chloride powder used in Example 1-5. 100 g of mixed coconut shells and 10 g of NaOH were placed in a retort furnace with an inner container for direct carbonization, and the remaining subsequent steps were the same as Example 1-5.

[0179] Comparative Example 1-2

[0180] Commercially purchased artificial graphite was heated to 700°C in a retort furnace under 10% C2H2 gas for 2 h, and then the gas was switched to N2 gas. After natural cooling, the final graphite material was obtained.

[0181] Comparative Example 1-3

[0182] Based on Example 1-2, the steps of adding stearic acid flake dispersion, propylamine, and aqueous ammonia were removed, i.e., 50 g of resorcinol and 66 g of formaldehyde were weighed, and they were slowly stirred to dissolve in 1000 mL of water at room temperature. The temperature was raised to 85°C, and stirring was performed for 4 h. The remaining subsequent steps were the same as Example 1-2.

[0183] Comparative Example 1-4

[0184] Based on Example 1-2, stearic acid was replaced by stearic acid solution, i.e. 50 g of resorcinol, 66 g of formaldehyde were weighed, and dissolved in 1000 mL of water at room temperature under slow stirring, then 1000 mL of stearic acid was added (stearic acid was directly added to water and stirred to disperse, then added), followed by 1.5 g of propylamine, after stirring for 30 min, 5 mL of 1.5 mol / L ammonia solution was added, and the temperature was raised to 85°C, and stirred for 4 h; the rest of the subsequent steps were the same as Example 1-2.

[0185] Example 2-1

[0186] <Preparation of negative active material>

[0187] Commercially available artificial graphite was heated to 700°C in a rotary furnace under 10% C2H2 gas for 2 h, then the gas was switched to N2 gas, and the final graphite material was obtained after natural cooling.

[0188] <Preparation of negative electrode sheet>

[0189] The hard carbon material prepared in Example 1-2 was mixed with the graphite material prepared in Example 2-1 above at a mass ratio of 10:90 to prepare a negative active material, then the prepared negative active material was mixed with a binder, styrene-butadiene rubber, a thickening agent, sodium carboxymethyl cellulose, at a mass ratio of 97:1.5:1.5, then deionized water was added as a solvent, and a negative electrode slurry with a solid content of 40 wt% was prepared and stirred uniformly. The negative electrode slurry was uniformly coated on one surface of a negative current collector copper foil with a thickness of 6 μm, and the copper foil was dried at 85°C for 4 h to obtain a negative electrode sheet with a single-sided coated negative active material layer with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the negative electrode sheet was dried at 120°C under vacuum for 12 h.

[0190] The remaining steps of <Preparation of positive electrode sheet>, <Preparation of electrolyte>, <Preparation of separator>, and <Preparation of lithium ion battery> were the same as Example 1-1.

[0191] Example 2-2 to Example 2-5

[0192] Except for adjusting the preparation parameters according to Table A, the remaining parameters of Example 2-2 to Example 2-5 were the same as Example 2-1.

[0193] Comparative Example 2-1 to Comparative Example 2-5

[0194] 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.

[0195] Table a

[0196] Group Hard carbon mass ratio Graphite mass ratio Example 2-1 10％ 90％ Example 2-2 30％ 70％ Example 2-3 50％ 50％ Example 2-4 70％ 30％ Example 2-5 90％ 10％ Comparative Example 2-1 10％ 90％ Comparative Example 2-2 30％ 70％ Comparative Example 2-3 50％ 50％ Comparative Example 2-4 70％ 30％ Comparative Example 2-5 90％ 10％

[0197] Example of effect 1

[0198] 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:

[0199] Table 1

[0200]

[0201]

[0202] like Figure 1 As shown in Table 1, the hard carbon material provided in this application is in sheet form. Table 1 shows that the sheet-like hard carbon material with a specific morphology provided in this application exhibits a higher lithium storage capacity from 0V to 2.5V as the negative electrode active material. Furthermore, the negative electrode active material provided in this application has 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 specific capacity, initial efficiency, and other performance characteristics of the material.

[0203] 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.

[0204] Figure 3The charge-discharge curve of the negative electrode active material prepared in Example 1-2 is shown with lithium metal as the counter electrode in the potential range of 0V to 2.5V of Li / Li+; from Figure 3 It can be seen that the specific capacity of Example 1-2 is 483mAh / g in the potential range of 0V to 0.2V of Li / Li+; the specific capacity of the negative electrode active material of Example 1-2 is 720mAh / g in the potential range of 0V to 2.5V of Li / Li+, which indicates that the negative electrode active material of Example 1-2 has high specific capacity, and the negative electrode active material of Example 1-2 has a stable low potential platform, which shows higher energy density when applied to a full battery.

[0205] Effect Example 2

[0206] The compaction density of the negative electrode active material layer and the related performance of the lithium ion battery corresponding to the above-mentioned Example 1-2, Example 1-7, and Example 2-1 to Example 2-5 and Comparative Example 2-1 to Comparative Example 2-5 are further tested by the above-mentioned test method, and the results are shown in Table 2:

[0207] Table 2

[0208]

[0209]

[0210] Table 2 shows the compaction density of the negative electrode active material layer and the lithium ion battery data of Example 1-2, Example 1-7, Example 2-1 to Example 2-5, and Comparative Example 2-1 to Comparative Example 2-5. From Table 2, it can be seen that the compaction density of the negative electrode active material is obviously affected by the composition of the active material. Generally, graphite has a high compaction density, but the specific capacity of graphite is low and the rate performance is poor. Hard carbon material has a high specific capacity, but the compaction density is relatively low. The present application further compounding the hard carbon material with specific morphology and the graphite material, a negative electrode material with high capacity and high compaction is obtained. However, from the data in Table 2, it can also be further seen that the ordinary granular hard carbon and graphite are not conducive to compounding, and the flaky hard carbon material and graphite material provided by the present application are compounded, which increases the contact between hard carbon particles and between hard carbon and graphite particles, which is beneficial to reduce the electrode resistance and further improve the rate performance of the negative electrode active material. From Example 2-1 to Example 2-5, it can be seen that by adjusting the relative proportion of flaky hard carbon and graphite in the compounded electrode sheet, the compaction density of the negative electrode active material layer can be further optimized, thereby improving the energy density, rate performance and cycle retention rate of the secondary battery and other performances.

[0211] At the same time, Figure 4The charge-discharge curve of the negative electrode active material prepared in Example 2-3 is shown with lithium metal as the counter electrode in the potential range of 0V to 2.5V of Li / Li+; from Figure 4 It can be seen that there is a clear step in the potential range of 0-0.2V, but it is different from the charge-discharge curve of traditional graphite and hard carbon, which proves that the capacity of graphite and hard carbon can be effectively exerted, and there is good interface conduction between the particles. The specific capacity of Example 2-3 is 386mAh / g in the potential range of 0V to 0.2V of Li / Li+; the specific capacity of the negative electrode active material of Example 2-3 is 552mAh / g in the potential range of 0V to 2.5V of Li / Li+, which shows that the negative electrode active material of Example 2-3 has high specific capacity, wherein the negative electrode active material of Example 2-3 has a stable low potential platform, in addition, the negative electrode active material of Example 2-3 has high compaction density due to the compounding of graphite and hard carbon, so that the negative electrode active material of Example 2-3 applied to the full battery shows higher energy density, rate performance and cycle retention rate.

[0212] It can be understood that the present application is described through some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to the features and embodiments without departing from the spirit and scope of the present application. In addition, the features and embodiments can be modified to adapt to specific conditions and materials under the guidance of the present application without departing from the scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of the present application.

Claims

1. A hard carbon material, characterized in that, The hard carbon material has a flaky structure, the length of the flaky structure is L, and the width of the flaky structure is D1, wherein L satisfies 2 μm≤L≤16 μm; and D1 satisfies 0.1 μm≤D1≤3 μm.

2. The hard carbon material of claim 1, wherein, The hard carbon material satisfies at least one of the following conditions: (1) the length L of the flaky structure satisfies 2 μm≤L≤15 μm; (2) the width D1 of the flaky structure satisfies 0.5 μm≤D1≤1.9 μm; (3) the height H1 of the flaky 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 flaky structure to the height H1 of the flaky structure satisfies 2.5≤L / H1≤750; or 2.5≤L / H1≤200; (5) the ratio of the width D1 of the flaky structure to the height H1 of the flaky structure satisfies 1≤D1 / H1≤12.

3. The hard carbon material of any one of claims 1-2, wherein, The length L of the flaky structure is composed of a left arc length L1, a square length L2, and a right arc length L3, and L1, L2, and L3 satisfy the following relationships: 2 μm≤L1+L2+L3≤16 μm, 0.01 μm≤L1≤1.5 μm, and 10≤L2 / L1≤80.

4. The hard carbon material of claim 3, wherein, The hard carbon material satisfies at least one of the following conditions: (6) 2 μm≤L1+L2+L3≤15 μm; (7) 0.05 μm≤L1≤1 μm; (8) 11≤L2 / L1≤38.

5. The hard carbon material of claim 3, wherein, The hard carbon material satisfies at least one of the following conditions: (9) 0.8 μm≤L2≤15 μm; or 1.9 μm≤L2≤13 μm; (10) 0.05 μm≤L3≤1.5 μm; or 0.05 μm≤L3≤1 μm.

6. The hard carbon material of claim 1, wherein, The closed cell volume of the sheet structure is 0.01 to 0.4 cm 3 / g; or, the closed cell volume of the sheet structure is 0.05 to 0.28 cm 3 / g.

7. The hard carbon material of claim 1, wherein, The hard carbon material satisfies at least one of the following conditions: (11) the surface of the flaky structure further has a carbon coating layer; (12) the surface of the flaky structure further has a carbon coating layer, and the thickness of the carbon coating layer ranges from 20 nm to 100 nm; (13) the flaky structure contains a first element, and the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; (14) the flaky structure contains a first element, and the first element 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%; (15) the specific surface area of the flaky structure ranges from 2 to 28 m 2 / g; (16) the ID / IG value of the flaky structure is 1.0 to 1.

3.

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

9. The secondary battery according to claim 8, characterized by The compaction density of the negative active material layer ranges from 1.0 to 1.9 g / cm 3 .

10. An electronic device, comprising: The electronic device includes the secondary battery of claim 9.

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