Negative active material, secondary battery, and electronic device

Abstract

The application belongs to the technical field of electrochemistry, and particularly relates to a negative electrode active material, a secondary battery and an electronic device. The negative electrode active material is in a granular form, and the negative electrode active material comprises first particles and second particles, the sphericity of the first particles is greater than that of the second particles, the sphericity of the first particles is 0.6-1.0, and the particle size Dv50 of the first particles is less than that of the second particles. The negative electrode active material is applied to a secondary battery, so that the compaction density of a battery pole piece is improved, and the energy density of the secondary battery is improved while the cycle performance of the secondary battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a negative active material, a secondary battery and an electronic device. BACKGROUND

[0002] The negative active material plays a role of carrier of lithium ion and electron in the charging and discharging process of the battery, accounts for 5%-15% in the cost of the battery, and is one of four main materials in the battery system. With the development of society, the demand for secondary batteries with high energy density, long cycle life and low self-discharge rate is increasing. As the most commonly used negative material of lithium ion battery, the capacity development of graphite has reached the limit, and therefore it is urgent to develop a high-capacity negative material to meet the increasing performance requirements.

[0003] Among the many negative active materials to be developed, hard carbon material has attracted great attention due to its high theoretical capacity, low volume expansion and fast charge and discharge characteristics. However, the current hard carbon material still faces the problems of low specific capacity, low first coulomb efficiency and high charge and discharge potential. And the hard carbon material with single morphology also faces the problems of low tap density, poor electrode adhesion and the like, which affect the capacity and cycle performance of the battery cell. SUMMARY

[0004] The purpose of the present application is to provide a negative active material, a secondary battery and an electronic device to improve the energy density of the secondary battery. The specific technical solutions are as follows:

[0005] According to a first aspect of the present application, the present application provides a negative active material, which is in a granular form, and the negative active material comprises first particles and second particles, the sphericity of the first particles is greater than that of the second particles, the sphericity of the first particles is 0.6-1.0, and the particle size Dv50 of the first particles is less than that of the second particles.

[0006] The negative electrode active material provided by the present application is in a granular form and comprises first particles and second particles. The negative electrode active material with the above characteristics avoids the problem of poor adhesion caused by point contact between the negative electrode active materials when only the first particles are present. At the same time, in the negative electrode active material provided by the present application, the first particles are uniformly distributed between the second particles. The first particles with high sphericity and small particle size can slip during cold pressing of the electrode sheet, thereby relieving the cold pressing stress and avoiding hard contact between the particles, so as to avoid stress concentration. The problem of cold pressing breakage of large particles is effectively solved, the negative electrode material exposes more new surfaces after cold pressing is avoided, further electrolyte loss is avoided, and the energy density and cycle performance of the battery cell are improved. In addition, the compaction density of the negative electrode sheet comprising the negative electrode active material is also improved, the negative electrode binder can better wrap the first particles, the contact area between the section of the first particles and the irregular surface of the second particles is larger, and the transfer of lithium ions between the negative electrode active materials can be effectively promoted. At the same time, by adjusting the sphericity and particle size of the first particles and the second particles in the negative electrode active material, the first particles and the second particles can be combined well, so that the negative electrode active material has good contact between the particles. The application of the negative electrode active material of the present application to the secondary battery can improve the compaction density of the battery electrode sheet, and further improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0007] In some embodiments of the present application, the sphericity of the first particles is 0.7-1.0.

[0008] In some embodiments of the present application, the sphericity of the second particles is 0.1-0.6; or the sphericity of the second particles is 0.2-0.6.

[0009] In some embodiments of the present application, the ratio of the sphericity of the first particles to the sphericity of the second particles is 1.1-10.0; or the ratio of the sphericity of the first particles to the sphericity of the second particles is 1.1-5.5.

[0010] By regulating the sphericity parameter of the first particles and the second particles in the negative electrode active material within the above range, the negative electrode active material particles can slide during the cold pressing of the electrode sheet, relieve the cold pressing stress, avoid hard contact between the particles, thereby avoiding stress concentration, avoiding the exposure of more new surfaces of the negative electrode material after cold pressing and further electrolyte loss, in addition, the negative electrode particles have further good contact, which can effectively promote the transmission of lithium ions between the negative electrode active materials. If the sphericity parameter of the first particles exceeds the above range, such as being lower than the above range, it will cause stress concentration between the first particles and the second particles, and the cold pressing will easily cause the particles to be crushed, the first efficiency and the energy density will be reduced, and if it is higher than the above range, it will cause the contact area between the first particles and the second particles to be reduced, the bonding effect of the binder will be poor, the particles will fall off during the cycle process, and the cycle retention rate will be reduced. The negative electrode active material with the above characteristics applied to the secondary battery can further improve the compaction density of the battery electrode sheet, and further achieve the improvement of the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0011] In some embodiments of the present application, the particle size Dv50 of the first particles ranges from 1 μm to 10 μm; or the particle size Dv50 of the first particles ranges from 3 μm to 8 μm.

[0012] In some embodiments of the present application, the particle size of the second particles ranges from 1.5 μm to 20 μm; or the particle size Dv50 of the first particles ranges from 8 μm to 20 μm.

[0013] In some embodiments of the present application, the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.05 to 0.9; or the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.1 to 0.9.

[0014] In some embodiments of the present application, by regulating the particle size of the first particles and the second particles in the negative electrode active material within the above range, the negative electrode active material particles have further good contact, if the particle size parameter of the first particles exceeds the above range, such as being lower than the above range, it will cause the bonding effect of the binder to be poor, the contact between the small particles will be poor, and the transmission efficiency of lithium ions will be reduced, and if it is higher than the above range, it will cause the particle strength to decrease, the cold pressing will easily cause the particles to be crushed, new active surfaces are exposed, and the first efficiency and the cycle performance of the battery will be reduced. The negative electrode active material with the above characteristics applied to the secondary battery can further improve the compaction density of the battery electrode sheet, and further achieve the improvement of the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0015] In some embodiments of the present application, the first particles comprise a hard carbon material.

[0016] In some embodiments of the present application, the second particles comprise a hard carbon material.

[0017] In some embodiments of the present application, the first particles and the second particles further comprise a first element and a second element, the first element comprises any one of Li, Na, K, Rb, Mg, Ca, Zn; and the second element is N element.

[0018] By regulating the first element and the second element contained in the first particles and the second particles of the negative electrode active material, the first element can induce the storage of active metal ions in the negative electrode active material, further improving the storage capacity of active metal ions; the second element helps to expand the carbon layer spacing of the negative electrode active material, promotes the deintercalation of active metal ions inside the active material, and can make the negative electrode active material have high reversible capacity.

[0019] In some embodiments of the present application, the content of the first element relative to the total mass of the negative electrode active material is 0.01% to 1%.

[0020] In some embodiments of the present application, the content of the first element in the first particles is A1 based on the total mass of the first particles, the content of the first element in the second particles is A2 based on the total mass of the second particles, A2 / A1 satisfies the following relationship: 0.8≤A2 / A1≤1.2; and / or, the content of the first element in the first particles A1 ranges from 0.01% to 0.9%; and / or, the content of the first element in the second particles A2 ranges from 0.01% to 0.9%.

[0021] In some embodiments of the present application, the content of the second element relative to the total mass of the negative electrode active material is 0.01% to 3%.

[0022] In some embodiments of the present application, the content of the second element in the first particles is B1 based on the total mass of the first particles, the content of the second element in the second particles is B2, and B2 / B1 satisfies the following relationship: 0.8≤B2 / B1≤1.2; and / or, the content of the second element in the first particles B1 ranges from 0.06% to 2.8%; and / or, the content of the second element in the second particles B2 ranges from 0.05% to 3%.

[0023] In some embodiments of the present application, by regulating the content of the first element in the first particles and the second particles in the negative electrode active material within the above range, the storage of active metal ions in the negative electrode active material can be further induced, the storage capacity of active metal ions is further improved, the specific capacity of the battery negative electrode is improved when the negative electrode active material of the present application is applied to a secondary battery, and the energy density of the secondary battery can be further improved. In some embodiments of the present application, by regulating the content of the N element in the first particles and the second particles in the active material within the above range, the interlayer spacing of the carbon layer of the negative electrode active material can be further expanded, the deintercalation of active metal ions in the active material is further promoted, and the negative electrode active material can further have high reversible capacity.

[0024] In some embodiments of the present application, the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles is 0.75-1.0.

[0025] In some embodiments of the present application, the closed pore volume of the first particles is 0.05-0.4 cc / g; or, the closed pore volume of the first particles is 0.12-0.36 cc / g.

[0026] In some embodiments of the present application, the closed pore volume of the second particles is 0.06-0.4 cc / g; or, the closed pore volume of the second particles is 0.06-0.34 cc / g.

[0027] In some embodiments of the present application, by regulating the closed pore volume of the first particles and the second particles in the negative electrode active material within the above range, the storage capacity of active metal ions can be improved, and the active material has a lower energy storage platform, thereby improving the storage capacity of active metal ions. By regulating the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles in the active material within the above range, the capacity difference between the particles can be avoided, and the active metal ions are prevented from being precipitated in the form of atoms at full charge.

[0028] In some embodiments of the present application, the first particles and the second particles further have carbon coating layers on the surfaces, respectively; the thickness of the carbon coating layer is 20-200 nm.

[0029] In some embodiments of the present application, the mass ratio of the first particles to the second particles is 0.6-3.0.

[0030] In some embodiments of the present application, the ratio of the ID / IG value of the first particles to the ID / IG value of the second particles is 0.93-1.12; and / or, the ID / IG of the first particles is 1.0-1.3; and / or, the ID / IG of the second particles is 1.0-1.3.

[0031] In some embodiments of the present application, the strength of the first particles and the second particles is tested using a nanoindentation method, and the particle strength ratio of the first particles to the second particles ranges from 1.1 to 2.8; or, the strength of the first particles ranges from 0.1 to 6 Gpa; or, the strength of the second particles ranges from 0.1 to 6 Gpa.

[0032] In some embodiments of the present application, the first particles and the second particles have a carbon coating layer on the surface in the negative electrode active material provided by the present application, and by controlling the thickness of the carbon coating layer within the above range, the defects on the surface of the particles are reduced, the exposure of the pore structure of the particles is reduced, the first coulombic efficiency of the negative electrode active material is improved, the negative electrode active material has high reversible capacity, and the energy density and cycle stability of the secondary battery are improved.

[0033] In some embodiments of the present application, by adjusting the particle mass ratio of the first particles to the second particles in the negative electrode active material within the above range, good contact between the particles of the negative electrode active material can be achieved, and when the negative electrode active material of the present application is applied to a secondary battery, the compaction density of the battery electrode sheet can be improved, and the energy density and cycle performance of the secondary battery can be improved.

[0034] In some embodiments of the present application, I D ID is the peak area of the D peak in the Raman spectrum of the material, I G ID is the peak area of the D peak in the Raman spectrum of the material, I By controlling the ID / IG value of the first particles and the ID / IG value of the second particles in the negative electrode active material provided by the present application within the above range, it is shown that the negative electrode active material provided has a suitable defect degree, which can promote ion adsorption and combination, reduce irreversible capacity loss caused by high defect degree, and thus improve the specific capacity of the negative electrode active material.

[0035] In some embodiments of the present application, by adjusting the particle strength ratio of the first particles to the second particles in the negative electrode active material provided by the present application within the above range, the particle morphology of the negative electrode sheet can be maintained during cold pressing, and thus the first coulombic efficiency of the negative electrode active material can be improved, and the cycle performance of the secondary battery can be improved.

[0036] According to the 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 the negative electrode active material according to any one of the first aspect of the present application. The negative electrode sheet provided by the second aspect of the present application has high capacity, and when it is applied to a secondary battery, the energy density and cycle performance of the secondary battery can be improved.

[0037] In some embodiments of this application, the compaction density of the negative electrode active material layer ranges from 0.90 to 1.3 g / cc; or, the compaction density of the negative electrode active material layer ranges from 0.9 to 1.25 g / cc.

[0038] In some embodiments of this application, the negative electrode is used as the working electrode, and lithium metal is used as the counter electrode to assemble a half-cell. Charge-discharge tests are performed in the range of 0 to 2.5V vs Li+ / Li. Based on the charge-discharge curves obtained from these tests, the range of 0 to 0.20V (vs Li+ / Li) is considered optimal. + The total specific capacity of the negative electrode active material (C10 mAh / g) is denoted as C10 mAh / g, the specific capacity at 0 to 0.20V (vs Li+ / Li) is denoted as C11 mAh / g, and the specific capacity at 0.2 to 2.5V (vs Li+ / Li) is denoted as C12 mAh / g. The negative electrode active material satisfies 600≤C10≤850, 300≤C11≤590, and / or 0.4≤C12 / C11≤1.2.

[0039] In some embodiments of this application, the compaction density of the negative electrode active material layer ranges from 0.90 to 1.3 g / cc; preferably, the compaction density of the negative electrode active material layer ranges from 0.95 to 1.20 g / cc. By controlling 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 improving the energy density of the secondary battery.

[0040] In some embodiments of this application, the negative electrode is used as the working electrode, and lithium metal is used as the counter electrode to assemble a half-cell, with a voltage of 0 to 2.5V vs. Li + Charge and discharge were performed within the / Li range, and based on the charge and discharge curves obtained from the charge and discharge tests, the values ​​were within the range of 0 to 0.20V (vs Li). + The total specific capacity of Li is denoted as C10 mAh / g, and is measured at 0 to 0.20 V (vs Li). + The specific capacity of Li is denoted as C11 mAh / g; at 0.2 to 2.5 V (vs Li + The specific capacity of the negative electrode active material is denoted as C12 mAh / g, and the negative electrode active material satisfies 600≤C10≤850, 300≤C11≤590; and / or, 0.4≤C12 / C11≤1.2. By controlling the C10, C11, and C12 values ​​of the negative electrode active material within the above ranges, the negative electrode active material layer can possess a high total lithium storage capacity and a low average lithium delithiation potential. Using a negative electrode active material layer with the above characteristics as the negative electrode of a lithium-ion battery is beneficial for further improving the energy density of lithium-ion batteries.

[0041] According to a third aspect of the present application, the present application provides a secondary battery, which comprises a positive electrode sheet, an electrolyte and 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.

[0042] According to a fourth aspect of the present application, the present application provides an electronic device, which comprises 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

[0043] 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 as follows. 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.

[0044] Figure 1 The scanning electron microscope photos of the negative electrode active materials prepared for Examples 1-5; wherein, "1" represents the first particles, i.e. corresponding to Figure 1 the particles with smaller particle size and higher sphericity, and "2" represents the second particles, i.e. corresponding to the particles with larger particle size and higher sphericity;

[0045] Figure 2 The charge-discharge curves of the negative electrode active material of Comparative Example 1 in the potential range of 0V to 2.5V of Li / Li + ;

[0046] Figure 3 The charge-discharge curves of the negative electrode active materials of Examples 1-5 in the potential range of 0V to 2.5V of Li / Li + ;

[0047] Figure 4 The charge-discharge curves of the negative electrode active materials of Examples 2-4 in the potential range of 0V to 2.5V of Li / Li + ; DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some 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 belong to the scope of protection of the present application.

[0049] 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.

[0050] Among the many negative active materials to be developed, hard carbon materials have attracted great attention due to their high theoretical capacity, low volume expansion, and fast charge and discharge characteristics. However, the hard carbon material currently still faces problems such as low specific capacity, low first coulomb efficiency, and high charge and discharge potential. And the hard carbon material with single morphology also faces problems such as low tap density, poor electrode adhesion, and the like, which affect the capacity and cycle performance of the battery cell.

[0051] Based on this, the inventors of the present application have found, through a large amount of research, that by preparing a negative active material with high specific capacity and controlling the particle morphology of the negative active material, the problems of poor adhesion and poor conductivity of the negative electrode sheet can be solved, thereby improving the tap density of the battery electrode sheet and further improving the energy density of the secondary battery and improving the cycle performance of the secondary battery.

[0052] According to a first aspect of the present application, the present application provides a negative active material, the negative active material is in a granular shape, and the negative active material comprises first particles and second particles, the sphericity of the first particles is greater than the sphericity of the second particles, the sphericity of the first particles is 0.6-1.0, and the particle size Dv50 of the first particles is less than the particle size Dv50 of the second particles. Wherein, the particle size Dv50 of the first particles refers to the particle size reaching 50% of the volume accumulation from the small particle size in the particle size distribution on the volume basis of the first particles; and the particle size Dv50 of the second particles refers to the particle size reaching 50% of the volume accumulation from the small particle size in the particle size distribution on the volume basis of the second particles.

[0053] The negative electrode active material provided by the present application is in a granular form and comprises first particles and second particles. The negative electrode active material having the above characteristics avoids the problem of poor adhesion caused by point contact between the negative electrode active materials when only the first particles are present. At the same time, the first particles are uniformly distributed between the second particles in the negative electrode active material provided by the present application. The first particles having a high sphericity and a small particle size can slip during cold pressing of the electrode sheet, thereby relieving the cold pressing stress and avoiding hard contact between the particles and stress concentration. The problem of cold pressing breakage of large particles is effectively solved, the negative electrode material exposes more new surfaces after cold pressing is avoided, further electrolyte loss is avoided, and the energy density and cycle performance of the battery cell are improved. In addition, the compaction density of the negative electrode sheet comprising the negative electrode active material is also improved, the negative electrode binder can better wrap the first particles, the contact area between the section of the first particles and the irregular surface of the second particles is larger, and the transfer of lithium ions between the negative electrode active materials can be effectively promoted. At the same time, by adjusting the sphericity and particle size of the first particles and the second particles in the negative electrode active material, the first particles and the second particles are well combined, which can make the particles in the negative electrode active material have good contact. The application of the negative electrode active material of the present application to the secondary battery can improve the compaction density of the battery electrode sheet, and thus improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0054] In some embodiments of the present application, the sphericity of the first particles is 0.7-1.0.

[0055] In some embodiments of the present application, the sphericity of the second particles is 0.1-0.6; or the sphericity of the second particles is 0.2-0.6.

[0056] In some embodiments of the present application, the ratio of the sphericity of the first particles to the sphericity of the second particles is 1.1-10.0; or the ratio of the sphericity of the first particles to the sphericity of the second particles is 1.1-5.5.

[0057] In some embodiments of the present application, the sphericity of the first particles in the provided negative electrode active material is 0.6-1.0. Specifically, the sphericity of the first particles can be 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a range defined by any two of the above values. Preferably, the sphericity of the first particles can be 0.7-1.0. By adjusting the sphericity of the first particles in the negative electrode active material to be within the above range, the negative electrode active material particles can have further good contact with each other. If the sphericity of the first particles is outside the above range, for example, lower than the above range, stress concentration between the first particles and the second particles can occur, and the cold pressing can cause the particles to be crushed, resulting in a decrease in the initial efficiency and the energy density. If the sphericity of the first particles is higher than the above range, the contact area between the first particles and the second particles can decrease, and the adhesive effect of the binder can be poor, resulting in a decrease in the cycle retention rate. The use of the negative electrode active material with the above characteristics in a secondary battery can further improve the compaction density of the battery electrode sheet, and thus further improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0058] In some embodiments of the present application, the sphericity of the second particles in the provided negative electrode active material is 0.1-0.6. Specifically, the sphericity of the second particles can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.6, or a range defined by any two of the above values. Preferably, the sphericity of the second particles can be 0.2-0.6. By adjusting the sphericity of the second particles in the negative electrode active material to be within the above range, the particles of the negative electrode active material can have further good contact with each other. If the sphericity of the second particles is outside the above range, for example, lower than the above range, the particles can have obvious sharp ends, and the electrons and lithium ions can easily be attracted to the negative electrode, resulting in lithium precipitation and easy puncture of the separator, leading to failure of the battery cell. If the sphericity of the second particles is higher than the above range, the contact area between the first particles and the second particles can be reduced, and the adhesive effect of the binder can be poor, resulting in particle shedding during the cycle process and reduced cycle retention rate. The negative electrode active material with the above characteristics can be applied to a secondary battery, which can further improve the compaction density of the battery electrode sheet, and further improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0059] In some embodiments of the present application, the ratio of the sphericity of the first particles to the sphericity of the second particles in the provided negative electrode active material ranges from 1.1 to 10.0. Specifically, the ratio of the sphericity of the first particles to the sphericity of the second particles can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, or a range defined by any two of the above values. Preferably, the ratio of the sphericity of the first particles to the sphericity of the second particles can range from 1.1 to 5.5. By adjusting the ratio of the sphericity of the first particles to the sphericity of the second particles in the negative electrode active material within the above range, the negative electrode active material particles can have further good contact. If the ratio of the sphericity of the first particles to the sphericity of the second particles exceeds the above range, for example, is lower than the above range, stress is concentrated between the first particles and the second particles, and cold pressing can cause the particles to be crushed, resulting in reduced first efficiency and energy density. If the ratio of the sphericity of the first particles to the sphericity of the second particles is higher than the above range, the particles can be poorly bonded and in contact, and lithium ion diffusion can be hindered. The negative electrode active material with the above characteristics can be applied to a secondary battery, which can further improve the compaction density of the battery electrode sheet, and further improve the energy density of the secondary battery and the cycle performance of the secondary battery.

[0060] In some embodiments of the present application, the size of the particle diameter Dv50 of the first particles ranges from 1 μm to 10 μm; or the size of the particle diameter Dv50 of the first particles ranges from 3 μm to 8 μm.

[0061] In some embodiments of the present application, the size of the particle diameter Dv50 of the second particles ranges from 1.5 μm to 20 μm; or the size of the particle diameter Dv50 of the first particles ranges from 8 μm to 20 μm.

[0062] In some embodiments of the present application, the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.05 to 0.9; or the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.1 to 0.9.

[0063] In some embodiments of the present application, the particle size Dv50 of the first particles in the provided negative electrode active material ranges from 1 μm to 10 μm, wherein the particle size Dv50 of the first particles refers to the particle size at which 50% of the volume is accumulated from the small particle size in the particle size distribution on the volume basis of the first particles. Specifically, the particle size Dv50 of the first particles can be 1 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9.0 μm, 9.5 μm, 10.0 μm, or a range defined by any two of the above values. Preferably, the particle size Dv50 of the first particles ranges from 3 μm to 8 μm. In some embodiments of the present application, by adjusting the particle size Dv50 of the first particles in the negative electrode active material within the above range, the negative electrode active material particles can have further good contact. If the particle size of the first particles is outside the above range, for example, is lower than the above range, the adhesion of the binder is poor, the small particles have poor contact, and the transmission efficiency of lithium ions is reduced. If the particle size of the first particles is higher than the above range, the particle strength is reduced, the cold pressing easily causes the particles to be crushed, the new active surface is exposed, and the first efficiency and the cycle performance of the battery are reduced. The negative electrode active material with the above characteristics can be applied to a secondary battery, which can further improve the compaction density of the electrode sheet, and further improve the energy density of the secondary battery and the cycle performance of the secondary battery.

[0064] In some embodiments of the present application, the provided negative electrode active material has a second particle size Dv50 in the range of 1.5 pm≤Dv50≤20 pm, wherein the second particle size Dv50 of the second particle refers to the particle size at which 50% of the volume is accumulated from the small particle size in the particle size distribution on the volume basis of the second particle. Specifically, the second particle size Dv50 can be 1.5 pm, 2.0 pm, 2.5 pm, 3.0 pm, 3.5 pm, 4.0 pm, 4.5 pm, 5.0 pm, 5.5 pm, 6.0 pm, 6.5 pm, 7.0 pm, 7.5 pm, 8.0 pm, 8.5 pm, 9.0 pm, 9.5 pm, 10.0 pm, 10.5 pm, 11.0 pm, 11.5 pm, 12.0 pm, 12.5 pm, 13.0 pm, 13.5 pm, 14.0 pm, 14.5 pm, 15.0 pm, 15.5 pm, 16.0 pm, 16.5 pm, 17.0 pm, 17.5 pm, 18.0 pm, 18.5 pm, 19.5 pm, 20 pm, or a range defined by any two of the above values. Preferably, the first particle size Dv50 is in the range of 8 pm≤Dv50≤20 pm. In some embodiments of the present application, by adjusting the second particle size Dv50 of the negative electrode active material in the above range, the negative electrode active material particles can have further good contact. If the second particle size is outside the above range, for example, below the above range, the bonding effect of the binder will be poor, the small particles will have poor contact, and the transmission efficiency of lithium ions will be reduced. If the second particle size is above the above range, the particle strength will decrease, and the cold pressing will easily cause the particles to be crushed, exposing new active surfaces, and the first efficiency and cycle performance of the battery will decrease. The negative electrode active material with the above characteristics can be applied to a secondary battery, which can further improve the compaction density of the battery electrode sheet, and further improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0065] In some embodiments of the present application, the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles in the provided negative electrode active material ranges from 0.05 to 0.9. Specifically, the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles can be 0.005, 0.01, 0.02, 0.03, 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, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or a range defined by any two of the above values. Preferably, the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.1 to 0.9. In some embodiments of the present application, by adjusting the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles in the negative electrode active material within the above range, the negative electrode active material particles can have further good contact. If the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles is outside the above range, for example, lower than the above range, the adhesive bonding effect will be poor, the small particles will have poor contact, and the transmission efficiency of lithium ions will be reduced. If the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles is higher than the above range, the sharp tips of the second particles will easily cause stress concentration on the cross section of the first particles, and the cold pressing will easily cause the particles to be crushed, exposing new active surfaces, and the first efficiency and cycle performance of the battery will be reduced. The negative electrode active material with the above characteristics can be applied to a secondary battery, which can further improve the compaction density of the battery electrode sheet, and further improve the energy density of the secondary battery while improving the cycle performance of the secondary battery.

[0066] In some embodiments of the present application, the first particles comprise a hard carbon material.

[0067] In some embodiments of the present application, the second particles comprise a hard carbon material.

[0068] In some embodiments of the present application, the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; and the second element is N. The first element can induce active metal ions to be stored in the negative active material, further improving the storage capacity of active metal ions; and the second element can help expand the carbon layer spacing of the negative active material, promote the deintercalation of active metal ions inside the active material, and enable the negative active material to have a high reversible capacity.

[0069] In some embodiments of the present application, the content of the first element in the negative active material is 0.01% to 1% based on the total mass of the negative active material.

[0070] In some embodiments of the present application, the content of the first element in the first particle is A1 based on the total mass of the first particle, the content of the first element in the second particle is A2 based on the total mass of the second particle, A2 / A1 satisfies the following relationship: 0.8≤A2 / A1≤1.2; and / or, the content of the first element in the first particle A1 ranges from 0.01% to 0.9%; and / or, the content of the first element in the second particle A2 ranges from 0.01% to 0.9%.

[0071] In some embodiments of the present application, the content of the second element in the negative active material is 0.01% to 3% based on the total mass of the negative active material.

[0072] In some embodiments of the present application, the content of the second element in the first particle is B1 based on the total mass of the first particle, the content of the second element in the second particle is B2, and B2 / B1 satisfies the following relationship: 0.8≤B2 / B1≤1.2; and / or, the content of the second element in the first particle B1 ranges from 0.06% to 2.8%; and / or, the content of the second element in the second particle B2 ranges from 0.05% to 3%.

[0073] In some embodiments of the present application, the content of the first element in the provided negative electrode active material ranges from 0.01% to 1% based on the total mass of the negative electrode active material. Specifically, the content of the first element in the negative electrode active material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 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%, 1%, or a range between any two of the above values. In some embodiments of the present application, by adjusting the content of the first element in the negative electrode active material within the above range, the storage of active metal ions in the negative electrode active material can be further induced, and the storage capacity of active metal ions can be further improved. When the negative electrode active material of the present application is applied to a secondary battery, the specific capacity of the negative electrode of the battery can be improved, and thus the energy density of the secondary battery can be improved.

[0074] In some embodiments of the present application, the content of the first element in the first particle is A1 based on the total mass of the first particle, the content of the first element in the second particle is A2 based on the total mass of the second particle, and A2 / A1 satisfies the following relationship: 0.8≤A2 / A1≤1.2. Specifically, the ratio A2 / A1 of the content A2 of the first element in the second particle to the content A1 of the first element in the first particle can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.1, 1.2, or a range between any two of the above values. In some embodiments of the present application, by adjusting the ratio A2 / A1 of the content A2 of the first element in the second particle to the content A1 of the first element in the first particle within the above range, the difference between the particles can be reduced, the uniform storage of lithium ions in the entire negative electrode active material can be achieved, and thus the cycle stability of the secondary battery can be improved.

[0075] In some embodiments of the present application, the content A1 of the first element in the first particles in the provided negative electrode active material is in the range of 0.01% to 0.9%. Specifically, the content A1 of the first element in the first particles can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or a range formed by any two of the above values. In some embodiments of the present application, by regulating the content A1 of the first element in the first particles in the negative electrode active material within the above range, the active metal ions can be induced to store in the negative electrode active material, further improving the active metal ion storage capacity. When the negative electrode active material of the present application is applied to a secondary battery, the gram capacity of the battery negative electrode can be improved, and thus the energy density of the secondary battery can be improved.

[0076] In some embodiments of the present application, the content A2 of the first element in the second particles in the provided negative electrode active material is in the range of 0.01% to 0.9%. Specifically, the content A2 of the first element in the second particles can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or a range formed by any two of the above values. In some embodiments of the present application, by regulating the content A2 of the first element in the second particles in the negative electrode active material within the above range, the active metal ions can be induced to store in the negative electrode active material, further improving the active metal ion storage capacity. When the negative electrode active material of the present application is applied to a secondary battery, the gram capacity of the battery negative electrode can be improved, and thus the energy density of the secondary battery can be improved.

[0077] In some embodiments of the present application, the content of the second element in the provided negative electrode active material is 0.01% to 3% relative to the total mass of the negative electrode active material. Specifically, the content of the second element relative to the total mass of the negative electrode active material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 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%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or a range between any two of the above values. In some embodiments of the present application, by adjusting the content of the N element in the negative electrode active material within the above range, the interlayer spacing of the carbon layer of the negative electrode active material can be further expanded, the deintercalation of active metal ions in the active material can be further promoted, and the negative electrode active material can have a high reversible capacity.

[0078] In some embodiments of the present application, the content of the second element in the first particles is B1, the content of the second element in the second particles is B2, and the ratio B2 / B1 satisfies the following relationship: 0.8≤B2 / B1≤1.2. Specifically, the ratio B2 / B1 of the content B2 of the second element in the second particles to the content B1 of the second element in the first particles can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.1, 1.2, or a range between any two of the above values. In some embodiments of the present application, by adjusting the ratio B2 / B1 of the content B2 of the second element in the second particles to the content B1 of the second element in the first particles within the above range, the difference between the particles can be reduced, the lithium ions can be uniformly stored in the entire negative electrode active material, and the cycle stability of the secondary battery can be improved.

[0079] In some embodiments of the present application, the content B1 of the second element in the first particles in the provided negative electrode active material ranges from 0.06% to 2.8%. Specifically, the content B1 of the second element in the first particles can be 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, or a range between any two of the above values. In some embodiments of the present application, by regulating the content B1 of the second element in the first particles in the negative electrode active material within the above range, the carbon layer spacing of the negative electrode active material can be expanded, the deintercalation of active metal ions in the active material can be promoted, and the negative electrode active material can have a high reversible capacity while avoiding the increase in irreversible capacity caused by excessively high B1.

[0080] In some embodiments of the present application, the content B2 of the second element in the second particles in the provided negative electrode active material ranges from 0.05% to 3%. Specifically, the content B2 of the second element in the second particles can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or a range between any two of the above values. In some embodiments of the present application, by regulating the content B2 of the second element in the second particles in the negative electrode active material within the above range, the carbon layer spacing of the negative electrode active material can be expanded, the deintercalation of active metal ions in the active material can be promoted, and the negative electrode active material can have a high reversible capacity while avoiding the increase in irreversible capacity caused by excessively high B1.

[0081] In some embodiments of the present application, the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles is 0.75 to 1.0.

[0082] In some embodiments of the present application, the closed pore volume of the first particles ranges from 0.05 to 0.4 cc / g; or, the closed pore volume of the first particles ranges from 0.12 to 0.36 cc / g.

[0083] In some embodiments of the present application, the second particles have a closed pore volume ranging from 0.06 to 0.4 cc / g; or, the second particles have a closed pore volume ranging from 0.06 to 0.34 cc / g.

[0084] In some embodiments of the present application, the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles in the provided negative electrode active material ranges from 0.75 to 1.0. Specifically, the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles can be 0.75, 0.76, 0.77, 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a range defined by any two of the above values. In some embodiments of the present application, by regulating the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles within the above range, the active metal ion storage capacity can be improved, while the active material has a lower energy storage platform, thereby improving the energy density of the battery. By regulating the ratio of the closed pore volume of the first particles to the closed pore volume of the second particles within the above range, the capacity difference between the particles can be avoided, and the active metal ions in the form of atoms can be prevented from being precipitated at full charge.

[0085] In some embodiments of the present application, the closed pore volume of the first particles in the provided negative electrode active material ranges from 0.05 to 0.4 cc / g. Specifically, the closed pore volume of the first particles can be 0.05 cc / g, 0.06 cc / g, 0.07 cc / g, 0.08 cc / g, 0.09 cc / g, 0.1 cc / g, 0.11 cc / g, 0.12 cc / g, 0.13 cc / g, 0.14 cc / g, 0.15 cc / g, 0.16 cc / g, 0.17 cc / g, 0.18 cc / g, 0.19 cc / g, 0.20 cc / g, 0.21 cc / g, 0.22 cc / g, 0.23 cc / g, 0.24 cc / g, 0.25 cc / g, 0.26 cc / g, 0.27 cc / g, 0.28 cc / g, 0.29 cc / g, 0.30 cc / g, 0.31 cc / g, 0.32 cc / g, 0.33 cc / g, 0.34 cc / g, 0.35 cc / g, 0.36 cc / g, 0.37 cc / g, 0.38 cc / g, 0.39 cc / g, 0.4 cc / g, or a range defined by any two of the above values. Preferably, the closed pore volume of the first particles ranges from 0.12 to 0.36 cc / g. In some embodiments of the present application, the closed pore volume of the first particles is regulated within the above range, which can improve the active metal ion storage capacity, while making the active material have a lower energy storage platform, thereby improving the energy density of the battery; at the same time, it avoids the generation of invalid closed pores, and also ensures that the particles have a certain strength, avoiding the capacity reduction caused by the crushing and rupture of the particles during cold pressing.

[0086] In some embodiments of the present application, the closed pore volume of the second particles in the provided negative electrode active material ranges from 0.06 to 0.4 cc / g. Specifically, the closed pore volume of the second particles can be 0.06 cc / g, 0.07 cc / g, 0.08 cc / g, 0.09 cc / g, 0.1 cc / g, 0.11 cc / g, 0.12 cc / g, 0.13 cc / g, 0.14 cc / g, 0.15 cc / g, 0.16 cc / g, 0.17 cc / g, 0.18 cc / g, 0.19 cc / g, 0.20 cc / g, 0.21 cc / g, 0.22 cc / g, 0.23 cc / g, 0.24 cc / g, 0.25 cc / g, 0.26 cc / g, 0.27 cc / g, 0.28 cc / g, 0.29 cc / g, 0.30 cc / g, 0.31 cc / g, 0.32 cc / g, 0.33 cc / g, 0.34 cc / g, 0.35 cc / g, 0.36 cc / g, 0.37 cc / g, 0.38 cc / g, 0.39 cc / g, 0.4 cc / g, or a range defined by any two of the above values. Preferably, the closed pore volume of the second particles ranges from 0.06 to 0.34 cc / g. In some embodiments of the present application, the closed pore volume of the second particles is regulated within the above range, which can improve the active metal ion storage capacity, while making the active material have a lower energy storage platform, thereby improving the energy density of the battery; at the same time, it can avoid the generation of invalid closed pores, and also ensure that the particles have a certain strength, so as to avoid the capacity reduction caused by the crushing and rupture of the particles during cold pressing.

[0087] In some embodiments of the present application, the first particles and the second particles further have carbon coating layers on their surfaces, respectively; and the thickness of the carbon coating layer ranges from 20 to 200 nm.

[0088] In some embodiments of the present application, the mass ratio of the first particles to the second particles ranges from 0.6 to 3.0.

[0089] In some embodiments of the present application, the ratio of the ID / IG value of the first particles to the ID / IG value of the second particles ranges from 0.93 to 1.12; and / or, the ID / IG value of the first particles ranges from 1.0 to 1.3; and / or, the ID / IG value of the second particles ranges from 1.0 to 1.3.

[0090] (17) The strength of the first particles and the second particles is tested by using a nanoindentation method, and the ratio of the strength of the first particles to the strength of the second particles ranges from 1.1 to 2.8; or, the strength of the first particles ranges from 0.1 to 6 Gpa; or, the strength of the second particles ranges from 0.1 to 6 Gpa.

[0091] In some embodiments of the present application, the first particles and the second particles further have a carbon coating layer on the surface thereof. The thickness of the carbon coating layer is 20-200 nm. Specifically, the thickness of the carbon coating layer can be 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 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, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, or a range defined by any two of the above values. In some embodiments of the present application, the first particles and the second particles have a carbon coating layer on the surface thereof, and by controlling the thickness of the carbon coating layer within the above range, the defects on the surface of the particles are reduced, the exposure of the pore structure of the particles is reduced, the initial coulombic efficiency of the negative active material is improved, the negative active material has a high reversible capacity, and the energy density and the cycle stability of the secondary battery are improved.

[0092] In some embodiments of the present application, the mass ratio of the first particles to the second particles is 0.6-3.0. Specifically, the mass ratio of the first particles to the second particles can be 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, or a range defined by any two of the above values. In some embodiments of the present application, by controlling the mass ratio of the first particles to the second particles within the above range, the negative active material particles have good contact with each other, the negative active material of the present application can improve the compaction density of the battery pole piece when applied to a secondary battery, and the energy density of the secondary battery is improved while the cycle performance of the secondary battery is improved.

[0093] In some embodiments of the present application, the ratio of the ID / IG value of the first particles to the ID / IG value of the second particles in the provided negative electrode active material ranges from 0.93 to 1.12. Specifically, the ratio of the ID / IG value of the first particles to the ID / IG value of the second particles can be 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, or a range between any two of the aforementioned values. In some embodiments of the present application, the ID / IG value of the first particles ranges from 0.95 to 1.05. D I D is the peak area of the D peak in the Raman spectrum of the negative electrode active material, G I D is the peak area of the D peak in the Raman spectrum of the negative electrode active material, By controlling the ID / IG value of the first particles and the ID / IG value of the second particles in the provided negative electrode active material within the aforementioned ranges, the provided negative electrode active material has a suitable defect degree, which can promote ion adsorption and combination, while reducing the irreversible capacity loss caused by high defect degree, thereby facilitating the improvement of the gram capacity of the negative electrode active material.

[0094] In some embodiments of the present application, the ID / IG value of the first particles in the provided negative electrode active material ranges from 1.0 to 1.3. Specifically, the ID / IG value of the first particles can be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, or a range between any two of the aforementioned values. In some embodiments of the present application, by adjusting the ID / IG value of the first particles within the aforementioned range, the provided negative electrode active material has a suitable defect degree, which can promote ion adsorption and combination, while reducing the irreversible capacity loss caused by high defect degree, thereby facilitating the improvement of the gram capacity of the negative electrode active material.

[0095] In some embodiments of the present application, the ID / IG of the second particles in the provided negative electrode active material ranges from 1.1 to 1.3. Specifically, the ID / IG of the second particles can be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, or a range between any two of the above values. In some embodiments of the present application, by regulating the ID / IG of the second particles in the range above, the provided negative electrode active material has a suitable defect degree, which can promote ion adsorption and at the same time reduce the irreversible capacity loss caused by high defect degree, thereby facilitating the improvement of the specific capacity of the negative electrode active material.

[0096] In some embodiments of the present application, the particle strength ratio of the first particles to the second particles in the provided negative electrode active material ranges from 1.1 to 2.8, as tested by nanoindentation. Specifically, the particle strength ratio of the first particles to the second particles can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, or a range between any two of the above values. In some embodiments of the present application, by regulating the particle strength ratio of the first particles to the second particles in the provided negative electrode active material in the range above, the particle morphology of the negative electrode sheet can be maintained during cold pressing, thereby improving the initial coulombic efficiency of the negative electrode active material and the cycle performance of the secondary battery.

[0097] In some embodiments of the present application, the strength of the first particles in the provided negative electrode active material ranges from 0.1 to 6 Gpa, as tested by nanoindentation. In some embodiments of the present application, by regulating the strength of the first particles in the range above, as tested by nanoindentation, the particle morphology of the negative electrode sheet can be maintained during cold pressing, thereby improving the initial coulombic efficiency of the negative electrode active material and the cycle performance of the secondary battery.

[0098] In some embodiments of the present application, the strength of the second particle is in the range of 0.1-6 GPa, as tested by a nanoindentation method. In some embodiments of the present application, by regulating the strength of the second particle in the above range, as tested by a nanoindentation method, the morphology of the particles can be maintained during the cold-pressing process, and the crushing and breaking of the particles can be avoided, thereby improving the initial coulombic efficiency of the negative active material and the cycle performance of the secondary battery.

[0099] According to a second aspect of the present application, the present application further provides a negative electrode sheet, which comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer comprises the negative active material according to any one of the first aspect of the present application. The negative electrode sheet provided by the second aspect of the present application has high capacity, and when applied to a secondary battery, the energy density of the secondary battery can be improved while the cycle performance of the secondary battery is improved.

[0100] The negative current collector according to the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the negative current collector can comprise a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a polymer substrate coated with a conductive metal, etc.

[0101] The negative active material layer according to the present application can further comprise a conductive agent and a binder. The conductive agent and the binder according to the present application are not particularly limited as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, a carbon material, a metal, or a conductive polymer, etc. The binder can include, but is not limited to, at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na), etc.

[0102] In some embodiments of the present application, the compaction density of the negative active material layer is in the range of 0.90-1.3 g / cc; or the compaction density of the negative active material layer is in the range of 0.95-1.25 g / cc.

[0103] In some embodiments of the present application, the negative electrode sheet is assembled as a working electrode with lithium metal as a counter electrode to perform a charge-discharge test in the range of 0 to 2.5 V vs Li+ / Li. Based on the charge-discharge curve obtained from the charge-discharge test, the total capacity in the range of 0 to 0.20 V (vs Li+ / Li) is recorded as C10 mAh / g, the capacity in the range of 0 to 0.20 V (vs Li+ / Li) is recorded as C11 mAh / g, and the capacity in the range of 0.2 to 2.5 V (vs Li+ / Li) is recorded as C12 mAh / g. The negative electrode active material satisfies 600≤C10≤850, 300≤C11≤590; and / or, 0.4≤C12 / C11≤1.2.

[0104] In some embodiments of the present application, the compaction density of the negative electrode active material layer in the provided negative electrode sheet is in the range of 0.90-1.3 g / cc. Specifically, the compaction density of the negative electrode active material layer can be 0.90 g / cc, 0.91 g / cc, 0.92 g / cc, 0.93 g / cc, 0.94 g / cc, 0.95 g / cc, 0.96 g / cc, 0.97 g / cc, 0.98 g / cc, 0.99 g / cc, 1.0 g / cc, 1.11 g / cc, 1.12 g / cc, 1.13 g / cc, 1.14 g / cc, 1.15 g / cc, 1.16 g / cc, 1.17 g / cc, 1.18 g / cc, 1.19 g / cc, 1.20 g / cc, 1.21 g / cc, 1.22 g / cc, 1.23 g / cc, 1.24 g / cc, 1.25 g / cc, 1.26 g / cc, 1.27 g / cc, 1.28 g / cc, 1.29 g / cc, 1.3 g / cc, or a range defined by any two of the above values. Preferably, the compaction density of the negative electrode active material layer can be in the range of 0.9-1.25 g / cc. In some embodiments of the present application, by adjusting the compaction density of the negative electrode active material layer within the above range, the content of the negative electrode active material per unit area can be increased, thereby improving the energy density of the secondary battery.

[0105] In some embodiments of the present application, in the provided negative electrode sheet, the negative electrode sheet is assembled into a half-cell with lithium metal as a counter electrode, and charge-discharge tests are carried out in the range of 0-2.5 V vs Li+ / Li. Based on the charge-discharge curve obtained from the charge-discharge test, the total specific capacity at 0-0.20 V (vs Li+ / Li) is denoted as C10 mAh / g, the specific capacity at 0-0.20 V (vs Li+ / Li) is denoted as C11 mAh / g, and the specific capacity at 0.2-2.5 V (vs Li+ / Li) is denoted as C12 mAh / g. The negative electrode active material satisfies 600≤C10≤850, 300≤C11≤590; and / or, 0.4≤C12 / C11≤1.2. Specifically, C10 can be 600 mAh / g, 610 mAh / g, 620 mAh / g, 630 mAh / g, 640 mAh / g, 650 mAh / g, 660 mAh / g, 670 mAh / g, 680 mAh / g, 690 mAh / g, 700 mAh / g, 710 mAh / g, 720 mAh / g, 730 mAh / g, 740 mAh / g, 750 mAh / g, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, or a range consisting of any two of the above values. Specifically, C11 can be 300 mAh / g, 310 mAh / g, 320 mAh / g, 330 mAh / g, 340 mAh / g, 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, 390 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g, 490 mAh / g, 500 mAh / g, 510 mAh / g, 520 mAh / g, 530 mAh / g, 540 mAh / g, 550 mAh / g, 560 mAh / g, 570 mAh / g, 580 mAh / g, 590 mAh / g, or a range consisting of any two of the above values. Specifically, C12 / C11 can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or a range consisting of any two of the above values. Controlling C10, C11, and C12 of the negative electrode active material within the above ranges can make the negative electrode active material layer have high total specific capacity for lithium storage and low average potential for lithium extraction. Using the negative electrode active material layer with the above characteristics as the negative electrode of a lithium ion battery can further improve the energy density of the lithium ion battery.

[0106] 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.

[0107] The secondary battery of the present application further comprises a positive electrode tab. The positive electrode tab of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the positive electrode tab comprises a positive electrode current collector and a positive electrode 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 electrode active material can comprise a lithium transition metal oxide, which can comprise, 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.

[0108] The thickness of the positive electrode current collector and the positive electrode active material layer of the present application is not particularly limited as long as the purpose of the present 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.

[0109] 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 concentration of the lithium salt in the electrolyte of the present application is not particularly limited as long as the purpose of the present application can be achieved.

[0110] The secondary battery of the present application further comprises a separator for separating the positive electrode tab and the negative electrode tab, 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 purpose of the present application can be achieved, for example, the material of the separator can comprise, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separator mainly comprising polytetrafluoroethylene, polyester film (such as polyethylene terephthalate (PET) film), cellulose film, polyimide film (PI), polyamide film (PA), spandex or aramid film, etc.

[0111] The secondary battery of the present application further comprises a packaging bag for containing the positive electrode tab, the separator, the negative electrode tab, and the electrolyte, as well as other components in the secondary battery known in the art, which are not limited by the present application. 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 purpose of the present application can be achieved. For example, an aluminum plastic film packaging bag can be used.

[0112] The secondary battery of the present application is not particularly limited, and can include any device that undergoes an electrochemical reaction. 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, etc.

[0113] According to a fourth aspect of the present application, the present application provides an electronic device comprising the secondary battery of any one of the embodiments of the third aspect of the present application. The electronic device comprising the secondary battery described above has a longer service life.

[0114] 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 computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a 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, an electric tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, etc.

[0115] Embodiments

[0116] Hereinafter, embodiments and comparative examples are cited to more specifically describe 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 on a mass basis.

[0117] The test methods used in the following examples and comparative examples are as follows:

[0118] 1. Sphericity test of particles

[0119] Before the test, the particles in the negative electrode active material were sieved, and the particles in the negative electrode active material were sieved according to particle size, and further sphericity test of the corresponding particles was performed. In the sphericity test of the particles, a laser particle size analyzer (model BT-2900) was used to analyze the sphericity of the solid powder based on the analysis method of GB / T38887-2020. The solid powder was dispersed using electromagnetic vibration sampling and free-fall dispersion technology, and combined with high-speed CCD and multi-thread and edge recognition technology image processing software, the particle sphericity was output.

[0120] 2. Particle size test of particles

[0121] The particle size of the powder material is tested by a Malvern particle size tester: the powder material is dispersed in an ethanol dispersant, after ultrasonic treatment for 30 minutes, the sample is added into the Malvern particle size tester, and the Dv50 of the powder material is tested.

[0122] 3. Metal element analysis test

[0123] The sample is digested by a microwave digestion instrument (model CEM-Mars5), and the element content is quantitatively tested by an ICP-OES instrument (instrument model PE7000DV). After the sample is digested into a solution by acid, the liquid sample enters the atomization chamber, forms an aerosol under the action of the carrier gas, enters the plasma through the central injection pipe, and is fully evaporated, dissociated, atomized, ionized and excited, and emits characteristic spectral lines of elements. The wavelength of the spectral line is used for qualitative analysis, and the spectral line intensity is proportional to the concentration for quantitative analysis.

[0124] 4. Non-metal element analysis test

[0125] The ratio and content of C and N elements in the active material are tested by X-ray photoelectron spectroscopy (instrument model Thermo ESCALAB 250XI). Three different parts of the same material are selected, and the content of the above elements is tested and the mass percentage content is calculated.

[0126] 5. Scanning electron microscope (SEM) test of negative electrode active material

[0127] The scanning electron microscope (instrument model ZEISS SEM) is used to observe the negative electrode active material particles and take SEM photos. For cross-section test, an ion polishing instrument (instrument model IB-09010CP) is used to cut a flat cross-section, and then SEM is taken. The principle of ion polishing is that under vacuum conditions, the ion source ionizes argon, which is accelerated and focused, and the high-speed argon ions hit the atoms or molecules on the surface of the sample, achieving ion polishing.

[0128] 6. Small-angle X-ray scattering test

[0129] The small-angle X-ray scattering structure analyzer (instrument model Nano-inXider) is 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 negative electrode active material particles is analyzed by fitting.

[0130] 7. Raman test

[0131] The Raman spectra of the first particle material and the second particle material are tested by a Raman spectrometer. During testing, a range of 200 μm x 500 μm is selected, and more than 200 points are tested at equal intervals in the range, and the test range of each point is 1000 cm -1Up to 2000cm -1 Between; recorded at 1320cm -1 Up to 1370cm -1 The peak that appears between these points is the D peak, located at 1570 cm⁻¹. -1 Up to 1620cm -1 The peaks that appear between them are called G peaks, and the I values ​​at each point are statistically analyzed. D / I G The intensity ratio is then calculated, and the average value of multiple points is taken as the final I. D / I G The strength ratio.

[0132] 8. Particle strength test

[0133] The hardness and elastic modulus of individual particles of porous materials were tested using a nanoindenter (Hysitron TI 950), according to the JB / T 12721-2016 standard. Before testing, the powder was dispersed in epoxy resin and cured. The cured resin was then cut using ion polishing. A nanoindenter was used to apply pressure to individual particles, and the indentation depth on the particle surface was monitored to calculate the particle strength. Five particles from the same sample were tested in parallel, and the average value was taken.

[0134] 9. Compaction density test of the negative electrode active material layer:

[0135] 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).

[0136] 10. Total lithium storage capacity and initial efficiency test of the negative electrode active material:

[0137] The initial reversible specific capacity of the negative electrode active material from 0V to 2.5V can be obtained by the following test method: Take a single-sided coated negative electrode sheet, cut it into a circular piece with a diameter of 14mm and use it as the working electrode. Then, use a lithium sheet as the counter electrode, a porous polyethylene membrane (provided by Celgard) as the separator, inject electrolyte and assemble it to obtain a button cell. Discharge the button cell to 0V with a small current in three stages of 0.05C / 0.01C / 0.005C respectively, and record the initial discharge capacity of the button cell. Then charge it to 2.5V with a constant current of 0.1C and record the initial charge capacity of the button cell. First-time efficiency = First-time charge capacity / First-time discharge capacity × 100%; First-time reversible specific capacity of the negative electrode active material in the Li / Li+ potential range of 0V to 2.5V, i.e., total lithium storage specific capacity (total reversible capacity) C10 = First-time charge capacity / Mass of negative electrode active material, in mAh / g; Li / Li+ potential range of 0V to 0.2V... + The specific capacity within the potential range is denoted as C11; the negative electrode active material in Li / Li + Li / Li with a potential range of 0.2V to 2.5V + The specific capacity within the potential range is denoted as C12.

[0138] 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.

[0139] The total lithium storage capacity and initial efficiency tests in the comparative examples are conducted using the same methods as those used for the aforementioned negative electrode active materials.

[0140] 11. Energy Density (ED) Test

[0141] In an environment of 25℃, the lithium-ion battery was 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 was then discharged at a constant current of 0.2C to a voltage of 2V. This was recorded as one cycle, and the discharge capacity C and discharge energy E of the first cycle were recorded. The length, width, and height of the battery at 50% charge were measured to obtain the battery volume V. m Average discharge voltage U = E / C; Energy density ED = E / V m .

[0142] Example 1-1

[0143] <Preparation of Negative Electrode Active Materials>

[0144] (1) Pre-polymerization: 1386 g of phenol and 1024 g of urotropine were weighed and dispersed in 32 L of aqueous solution, and the mixture was placed in a 50 L glass reactor and stirred at room temperature for 2 h at a speed of 300 rpm. Then, the temperature was raised to a pre-polymerization temperature of 95 °C at a rate of 5 °C / min, and the reaction was carried out for 24 h. After cooling, a pre-polymerized resin solution was obtained;

[0145] (2) Spray drying + curing: the pre-polymerized resin solution prepared was dried by spray drying, with the inlet air temperature controlled at 200 °C, the outlet air temperature at 100 °C, and the feeding rate at 5 L / min. After spraying, the powder product was collected. The powder product was placed in a programmed temperature oven in an inert atmosphere, and the temperature program was controlled at 90 °C / 1 h + 110 °C / 1 h + 130 °C / 1 h + 150 °C / 1 h to ensure that the resin was fully cured, and a cured powder product was obtained;

[0146] (3) Carbonization: 1000 g of the cured powder product and 100 g of LiOH were uniformly mixed by a mixer, and the mixed precursors were placed in a rotary furnace with an inner container, and the temperature was raised to a first calcination temperature T1 = 900 °C at a rate of 5 °C / min, and carbonized for 2 h. After cooling, a carbonized material was obtained;

[0147] (4) Washing: the obtained carbonized powder material was washed with 1 M hydrochloric acid for 12 h, and the filter residue was washed with deionized water for 12 h after suction filtration. The filter residue was dried by suction filtration to obtain a dried powder;

[0148] (5) Carbon coating: the washed and dried powder was transferred to a nitrogen atmosphere protection furnace, and the temperature was raised to a 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 acetylene 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. After cooling to room temperature, a hard carbon material, i.e. a negative electrode active material, was obtained. The mass percentage of reducing gas acetylene in the mixture was 20%.

[0149] <Preparation of negative electrode sheet>

[0150] The prepared negative active material, a binder styrene-butadiene rubber, and a thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 97:1.5:1.5, and then 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 uniformly; the uniformly stirred 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 tab with a single-side coated negative active material layer with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the negative electrode tab was dried at 120°C under vacuum for 12 h to obtain a negative electrode tab with a size of 76.6 mm x 875 mm.

[0151] <Preparation of a positive electrode tab>

[0152] The positive active material lithium cobaltate, a conductive agent conductive carbon black (Super P), and a binder PVDF were mixed in a mass ratio of 97:1.4:1.6, N-methyl pyrrolidone (NMP) was added as a solvent, and the mixture was stirred uniformly to prepare a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 13 μm, and the aluminum foil was dried at 85°C to obtain a positive electrode tab with a single-side coated positive active material layer with a positive active material layer thickness of 80 μm. After cold pressing, cutting, and slitting, the positive electrode tab was dried at 85°C under vacuum for 4 h to obtain a positive electrode tab with a size of 74 mm x 867 mm.

[0153] <Preparation of an electrolyte>

[0154] In a dry argon atmosphere glove box, a base solvent ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1, and then 1,3-propane sultone, fluoroethylene carbonate, and succinonitrile were added, and after being dissolved and stirred thoroughly, a lithium salt LiPF6 was added, and the mixture was stirred uniformly to obtain an electrolyte, wherein the concentration of the lithium salt was 1 mol / L, and the mass percentage of 1,3-propane sultone, fluoroethylene carbonate, and succinonitrile was 2% based on the mass of the base solvent.

[0155] <Preparation of a separator>

[0156] A polyethylene film with a thickness of 7 μm was used as a separator.

[0157] <Preparation of a lithium ion battery>

[0158] The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. After welding the tab, the electrode assembly is placed in an aluminum plastic film packaging bag, dried in a vacuum oven at 80°C for 12h to remove water, injected with the electrolyte prepared above, and subjected to vacuum packaging, standing, formation, degassing, shaping, and other processes to obtain a lithium ion battery.

[0159] Examples 1-2 to 1-11 and Examples 2-1 to 2-8

[0160] The remaining preparation step parameters of Examples 1-2 to 1-11 and Examples 2-1 to 2-8 are the same as those of Example 1-1, except that the preparation parameters are adjusted according to Table A.

[0161] Comparative Example 1

[0162] Coconut shells are used to replace the precursors used in the preparation of the negative electrode active material in Example 1-1, i.e., in step (3) of Example 1-1, 1000g of coconut shells are directly weighed into a rotary furnace with an inner container, heated to a first calcination temperature T1 = 900°C at a heating rate of 5°C / min, carbonized for 2h, cooled, and then the carbonized material is obtained. The subsequent steps are continued, and the remaining subsequent steps are the same as those of Example 1-1.

[0163] Comparative Example 2

[0164] Pitch is used to replace the precursors used in the preparation of the negative electrode active material in Example 1-1, i.e., in step (3) of Example 1-1, 1000g of pitch is directly weighed into a rotary furnace with an inner container, heated to a first calcination temperature T1 = 900°C at a heating rate of 5°C / min, carbonized for 2h, cooled, and then the carbonized material is obtained. The subsequent steps are continued, and the remaining subsequent steps are the same as those of Example 1-1.

[0165] Table A

[0166]

[0167] Effect Example 1

[0168] The first particle sphericity, the first particle size, the second particle sphericity, the second particle size, the first element type, the mass percentage content of the first element in the first particle A1, the mass percentage content of the first element in the second particle A2, the second element type, the mass percentage content of the second element in the first particle B1, the mass percentage content of the second element in the second particle B2, A2 / A1, B2 / B1, the compactness of the negative electrode active material layer containing the above negative electrode active material, and the total reversible capacity (mAh / g), the energy density ED (Wh / L), the cycle retention rate (500 cycles) and other related performances of the negative electrode active material of each example were tested by the above test method, and the results are shown in Table 1:

[0169] Table 1

[0170]

[0171]

[0172] From the results presented in Table 1, it can be seen that the negative electrode active material provided by the present application has higher gram capacity and reversible capacity, and the lithium ion battery comprising the negative electrode active material of the present application has higher energy density and higher cycle retention rate, thereby indicating that the lithium ion battery provided by the present application has higher energy density and better cycle performance. In combination with the data presented in the above examples, it can be seen that the negative electrode active material provided by the present application has higher gram capacity and reversible capacity, and the lithium ion battery comprising the negative electrode active material of the present application has higher energy density and higher cycle retention rate, thereby indicating that the lithium ion battery provided by the present application has higher energy density and better cycle performance.

[0173] At the same time, the scanning electron microscope photograph of the negative electrode active material of Example 1-5 is shown in Figure 1 , according to Figure 1The results show that the negative active material is in a granular shape, and contains two kinds of particles, the smaller particles have a higher sphericity, and the larger particles have a lower sphericity. In the negative active material corresponding to Examples 1-5, the sphericity of the first particles is 0.9, the sphericity of the second particles is 0.5, the particle size Dv50 of the first particles is 5 μm, and the particle size Dv50 of the second particles is 12 μm, that is, the sphericity of the first particles is higher than that of the second particles, and the particle size of the first particles is smaller than that of the second particles. The negative active material with the above particle morphology can combine the first particles and the second particles well, and avoid the poor adhesion performance caused by the point contact between the negative active materials when only the first particles are present. At the same time, the first particles are uniformly distributed between the second particles in the negative active material provided by the application. The first particles with high sphericity and small particle size can slip during cold pressing of the electrode sheet, relieve the cold pressing stress, and avoid hard contact between the particles, thereby avoiding stress concentration. The problem of cold pressing breakage of large particles is effectively solved, the negative active material exposes more new surfaces after cold pressing, and the electrolyte loss is further avoided, thereby improving the energy density and cycle performance of the battery cell. In addition, the compaction density of the negative electrode sheet containing the above negative active material is also significantly improved, the negative electrode binder can better wrap the first particles, the contact area between the section of the first particles and the irregular surface of the second particles is larger, and the transmission of lithium ions between the negative active materials can be effectively promoted.

[0174] Figure 2 The battery was assembled by taking the negative electrode sheet prepared from Comparative Example 1 as the working electrode and taking a lithium metal sheet as the counter electrode. The charge-discharge curve in the potential range of 0V to 2.5V of Li / Li+was shown. From Figure 2 It can be seen that the specific capacity C11 of the negative active material of Comparative Example 1 in the potential range of 0V to 0.2V of Li / Li+is 233 mAh / g; the specific capacity C10 of the negative active material of Comparative Example 1 in the potential range of 0V to 2.5V of Li / Li+is 482 mAh / g, and the specific capacity C12 of the negative active material of Comparative Example 1 in the potential range of 0.2V to 2.5V of Li / Li+is 249 mAh / g.

[0175] Figure 3 The battery was assembled by taking the negative electrode sheet prepared from Comparative Example 1 as the working electrode and taking a lithium metal sheet as the counter electrode. The charge-discharge curve in the potential range of 0V to 2.5V of Li / Li+was shown. From Figure 3It can be seen that the specific capacity C11 of the negative electrode active material of Example 1-5 is 582 mAh / g in the potential range of Li / Li+of 0V to 0.2V; the specific capacity C10 of the negative electrode active material of Example 1-5 is 820 mAh / g in the potential range of Li / Li+of 0V to 2.5V, and the specific capacity C12 of the negative electrode active material of Example 1-5 is 238 mAh / g in the potential range of Li / Li+of 0.2V to 2.5V. Compared with Comparative Example 1, the negative electrode active material provided by the application has a significantly higher specific capacity, and the negative electrode active material of Example 1-5 has a stable low potential platform, and exhibits a higher energy density when applied to a full battery.

[0176] Effect Example 2

[0177] Based on the results presented in Table 1, the coating layer thickness, the mass ratio of the first particles to the second particles, the first particle closed pore volume cc / g, the second particle closed pore volume cc / g, the first particle ID / IG, the second particle ID / IG, the strength ratio of the first particles to the second particles, the first particle strength (Gpa) and other parameters of the negative electrode active material prepared by Example 2-1 to Example 2-8 were further tested by the above-mentioned test method, and the total reversible capacity (mAh / g), the energy density ED (Wh / L), the cycle retention rate (500 cycles) and other related performances of the negative electrode active material of each example (Example 2-1 to Example 2-8) were tested. In Table 2, each example (Example 2-1 to Example 2-8) is based on Example 1-2, the corresponding product parameters in Table 1 are basically the same as those of Example 1-2, only the corresponding product parameters in Table 2 are changed, the changes of the related performances of each example in Table 2 are compared, and the results are shown in Table 2:

[0178] Table 2

[0179]

[0180] According to the results presented in Table 2, it is further shown that the negative electrode active material provided by the application has higher specific capacity and reversible capacity, the lithium ion battery comprising the negative electrode active material of the application has higher energy density and higher cycle retention rate, and when the coating layer thickness, the mass ratio of the first particles to the second particles, the first particle closed pore volume cc / g, the second particle closed pore volume cc / g, the first particle ID / IG, the second particle ID / IG, the strength ratio of the first particles to the second particles, the first particle strength and other parameters of the negative electrode active material are further adjusted based on the product parameters in Table 1, the total reversible capacity (mAh / g), the energy density ED (Wh / L), the cycle retention rate (500 cycles) and other performances of the negative electrode active material can be further improved.

[0181] At the same time, Figure 4The battery was assembled with the negative electrode sheet prepared in Example 2-4 as the working electrode and a lithium metal sheet as the counter electrode, and the charge-discharge curve in the potential range of 0V to 2.5V of Li / Li+was shown from Figure 4 It can be seen that the specific capacity C11 of the negative electrode active material of Example 2-4 is 334mAh / g in the potential range of 0V to 0.2V of Li / Li+; the specific capacity C10 of the negative electrode active material of Example 2-4 is 641mAh / g in the potential range of 0V to 2.5V of Li / Li+, and the specific capacity C12 of the negative electrode active material of Example 2-4 is 307mAh / g in the potential range of 0.2V to 2.5V of Li / Li+. Compared with Comparative Example 1, the negative electrode active material provided by the present application has higher specific capacity, and the negative electrode active material of Example 2-4 has a stable low potential platform, and exhibits a certain energy density when applied to a full battery.

[0182] It can be understood that the present application is described by some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, these features and embodiments can be modified to adapt to specific conditions and materials 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 negative electrode active material, characterized by, The negative active material is in a granular form, and the negative active material comprises first particles and second particles, the sphericity of the first particles is greater than the sphericity of the second particles, the sphericity of the first particles is 0.6-1.0, and the particle size Dv50 of the first particles is less than the particle size Dv50 of the second particles; the first particles contain a first element and a second element, the second particles contain the first element and the second element, the first element comprises any one of Li, Na, K, Rb, Mg, Ca, and Zn, and the second element is N element.

2. The negative electrode active material according to claim 1, characterized by The negative active material satisfies at least one of conditions (1)-(5) as follows: (1) the sphericity of the first particles is 0.7-1.0; (2) the sphericity of the second particles is 0.1-0.6; or the sphericity of the second particles is 0.2-0.6; (3) the ratio of the sphericity of the first particles to the sphericity of the second particles ranges from 1.1 to 10.0; or the ratio of the sphericity of the first particles to the sphericity of the second particles ranges from 1.1 to 5.5; (4) the first particles further comprise a hard carbon material; (5) the second particles further comprise a hard carbon material.

3. The negative electrode active material according to claim 1, characterized by The negative active material satisfies at least one of conditions (6)-(8) as follows: (6) the particle size Dv50 of the first particles ranges from 1 μm to 10 μm; or the particle size Dv50 of the first particles ranges from 3 μm to 8 μm; (7) the particle size of the second particles ranges from 1.5 μm to 20 μm; or the particle size Dv50 of the first particles ranges from 8 μm to 20 μm; (8) the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.05 to 0.9; or the ratio of the particle size Dv50 of the first particles to the particle size Dv50 of the second particles ranges from 0.1 to 0.

9.

4. The negative electrode active material according to claim 1, characterized by The negative active material satisfies at least one of conditions (9)-(12) as follows: (9) the content of the first element in the total mass of the negative active material ranges from 0.01% to 1% relative to the total mass of the negative active material; (10) the content of the first element in the first particles is A1 based on the total mass of the first particles, the content of the first element in the second particles is A2 based on the total mass of the second particles, A2 / A1 satisfies the following relationship: 0.8≤A2 / A1≤1.2; and / or, the content A1 of the first element in the first particles ranges from 0.01% to 0.9%; and / or, the content A2 of the first element in the second particles ranges from 0.01% to 0.9%; (11) the content of the second element in the total mass of the negative active material ranges from 0.01% to 3% relative to the total mass of the negative active material; (12) the content of the second element in the first particle is B1, the content of the second element in the second particle is B2, and the ratio of B2 / B1 satisfies the following relationship: 0.8≤B2 / B1≤1.2, based on the total mass of the first particle; and / or, the content of the second element in the first particle B1 ranges from 0.06% to 2.8%; and / or, the content of the second element in the second particle B2 ranges from 0.05% to 3%.

5. The negative active material according to claim 1, wherein The negative electrode active material satisfies at least one of the following conditions (13) to (15): (13) the ratio of the closed pore volume of the first particle to the closed pore volume of the second particle ranges from 0.75 to 1.0; (14) the closed pore volume of the first particle ranges from 0.05 to 0.4 cc / g; or, the closed pore volume of the first particle ranges from 0.12 to 0.36 cc / g; (15) the closed pore volume of the second particle ranges from 0.06 to 0.4 cc / g; or, the closed pore volume of the second particle ranges from 0.06 to 0.34 cc / g.

6. The negative electrode active material according to claim 1, wherein The negative electrode active material satisfies at least one of the following conditions (16) to (19): (16) the first particle and the second particle further have a carbon coating layer on the surface, respectively; the thickness of the carbon coating layer ranges from 20 to 200 nm; (17) the ratio of the particle mass of the first particle to the particle mass of the second particle ranges from 0.6 to 3.0; (18) the ratio of the ID / IG value of the first particle to the ID / IG value of the second particle ranges from 0.93 to 1.12; and / or, the ID / IG of the first particle ranges from 1.0 to 1.3; and / or, the ID / IG of the second particle ranges from 1.0 to 1.3; (19) the strength of the first particle and the second particle is tested by using a nanoindentation method, and the ratio of the strength of the first particle to the strength of the second particle ranges from 1.1 to 2.8; or, the strength of the first particle ranges from 0.1 to 6.0 Gpa; or, the strength of the second particle ranges from 0.1 to 6.0 Gpa.

7. 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 arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized by The negative electrode sheet satisfies at least one of the following conditions (20) to (21): (20) the compaction density of the negative electrode active material layer ranges from 0.90 to 1.3 g / cc; or, the compaction density of the negative electrode active material layer ranges from 0.9 to 1.25 g / cc; (21) Assembling a half battery by taking the negative electrode sheet as a working electrode and taking lithium metal as a counter electrode, performing charge-discharge test in the range of 0 to 2.5 V vs Li + , and recording the total capacity in the range of 0 to 0.20 V vs Li + / Li as C10 mAh / g, the capacity in the range of 0.2 to 2.5 V vs Li + / Li as C11 mAh / g, and the capacity in the range of 0 to 0.20 V vs Li + / Li as C12 mAh / g, the negative electrode active material satisfies: 600≤C10≤850, 300≤C11≤590; and / or, 0.4≤C12 / C11≤1.

2.

9. An electronic device, comprising: The electronic device comprises the secondary battery according to any one of claims 7 or 8.

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