Negative active material, secondary battery comprising the same, 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 containing the negative electrode active material and an electronic device. The negative electrode active material is in a granular form, and comprises secondary particles formed by a first phase material and a second phase material. There are pores in the interior of the secondary particles, and the area percentage of the pores in a single secondary particle is 0.5% to 35%. The negative electrode active material provided by the application has high capacity and high tap density. When the active material provided by the application is applied to a secondary battery, the energy density and cycle stability of the secondary battery can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a negative electrode active material, a secondary battery containing the negative electrode active material, and an electronic device. Background Technology

[0002] Lithium-ion rechargeable batteries have become a key research focus in the new energy field due to their high energy density, stable charge-discharge platform, low self-discharge rate, and long cycle life. The negative electrode active material in lithium-ion batteries is a crucial factor affecting battery performance; it is one of the four main materials in the battery system, accounting for 5%-15% of the battery cost. Currently, commercially available negative electrode materials are mainly graphite, including natural and artificial graphite. However, graphite has a high degree of crystallinity, poor compatibility with electrolytes, and a low diffusion rate of lithium ions between layers, resulting in poor electrical performance at high rates, making it difficult to meet the increasingly demanding requirements of electrochemical devices.

[0003] Hard carbon materials have attracted considerable attention due to their high theoretical capacity, low volume expansion, and rapid charge / discharge capabilities. In 1991, Sony Corporation of Japan first developed a lithium-ion battery using polyfurfuryl alcohol pyrolysis carbon as the negative electrode material. In hard carbon materials, lithium ions can be inserted and extracted from various angles, exhibiting excellent rate performance and cycle characteristics. However, the low compaction density and initial coulombic efficiency of hard carbon itself limit its application in lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode active material, a secondary battery containing the negative electrode active material, and an electronic device.

[0005] According to a first aspect of this application, this application provides a negative electrode active material, the negative electrode active material being granular, the negative electrode active material comprising secondary particles formed by a first phase material and a second phase material; the secondary particles are formed by the second phase material coating the surface of the first phase material, and / or by the aggregation of the first phase material and the second phase material; pores exist inside the secondary particles, the pores being distributed between the first phase and the second phase of the secondary particles, the pores accounting for 0.5% to 35% of the area of ​​a single secondary particle.

[0006] The negative electrode active material provided in this application is granular, and is a secondary particle formed by a first phase material and a second phase material. By controlling the special arrangement of the first and second phases in the negative electrode active material, this application enables good contact between the first and second phases, ensuring electron transfer, thereby reducing electrode resistance, increasing the compaction density of the active material, and ultimately improving the energy density and cycle performance of the secondary battery. Simultaneously, this application has discovered that reserving pores between the first and second phase materials can alleviate the volume expansion of the first phase material during cycling, improving the cycle stability of the negative electrode active material. Furthermore, the inventors of this application have found that the percentage of the area occupied by pores between the first and second phase materials in the cross-section of a single secondary particle in the negative electrode active material further affects the stability of the negative electrode active material. Controlling the percentage of the pore area within the aforementioned range can avoid electrolyte loss while providing space for the expansion of the first phase material during cycling, further alleviating the volume expansion of the first phase material during cycling, thereby further improving the cycle stability of the negative electrode active material. If the area percentage of pores in a single secondary particle exceeds the above range, for example, if it is lower than the above range, the reserved pores will not be sufficient to meet the particle expansion. The cyclic expansion of the first phase particles will easily lead to the breakage of the secondary particles, and the cycle stability of the secondary battery will decrease. If it is higher than the above range, it will lead to an increase in the exposed active area, a decrease in the first efficiency, a lower cell energy density, an increase in the amount of electrolyte consumed during the cycle, and affect the cycle performance of the secondary battery.

[0007] In some embodiments of this application, the area percentage of the pores in a single secondary particle is 18% to 30%. This application has found that when the area percentage of the pores is further controlled within the above range, electrolyte loss can be avoided while providing space for graphite to expand during cycling, further mitigating the volume expansion of the first-phase material during cycling, thereby further improving the cycle stability of the negative electrode active material. If the area percentage of the pores in a single secondary particle exceeds the above range (e.g., below the above range), the reserved pores will be insufficient to meet particle expansion, and the cyclic expansion of the first-phase particles will easily lead to the breakage of the secondary particles, reducing the cycle stability of the secondary battery. If it exceeds the above range, it will lead to an increase in the exposed active area, a decrease in initial efficiency, a lower cell energy density, and an increase in the amount of electrolyte consumed during cycling, affecting the cycle performance of the secondary battery.

[0008] In some embodiments of this application, the cross-section of the second phase material contains circular holes, the diameter of which is D1, and D1 satisfies: 45nm ≤ D1 ≤ 550nm. In the negative electrode active material provided by this application, the second phase material contains circular holes. The inventors of this application have discovered that the presence of circular holes in the second phase material can further alleviate the volume expansion of the second phase material during cycling, thereby improving the cycle stability of the negative electrode active material. Furthermore, the inventors have discovered that the diameter of the circular holes in the second phase material affects the cycle stability of the negative electrode active material. When the circular holes in the second phase material are too large, the compaction density of the secondary particles becomes too low; conversely, if the circular holes are too small, it is not conducive to alleviating the volume expansion of the second phase material during cycling. Controlling the diameter of the circular holes in the second phase material within the aforementioned range can further improve the cycle stability of the negative electrode active material, thereby enhancing the cycle stability of the secondary battery.

[0009] In some embodiments of this application, the cross-section of the second phase material has circular holes, and the diameter D1 of the circular holes satisfies: 55nm ≤ D1 ≤ 480nm. Controlling the diameter of the circular holes in the second phase material within the above range can further improve the cycle stability of the negative electrode active material, thereby enhancing the cycle stability of the secondary battery.

[0010] In some embodiments of this application, the second phase material contains a first element; the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. The heterogeneous elements (non-carbon elements) in the negative electrode active material can affect its performance. The negative electrode active material provided in this application, by introducing metal ions in situ, can induce the storage of active metal ions within the negative electrode active material, further enhancing its storage capacity and resulting in higher specific capacity and reversible capacity, thereby further improving its energy density and capacity retention.

[0011] In some embodiments of this application, the content of the first element relative to the total mass of the negative electrode active material is 0.01% to 1.2%. By controlling the content of the first element in the second phase material within the above range, it is possible to further induce the storage of active metal ions in the negative electrode active material, further improve the storage capacity of active metal ions, and apply the negative electrode active material of this application to a secondary battery to further improve the specific capacity of the battery negative electrode, thereby further improving the energy density of the secondary battery.

[0012] In some embodiments of this application, the content of the first element relative to the total mass of the negative electrode active material is 0.02% to 0.95%. By controlling the content of the first element in the second phase material within the above range, it is more conducive to inducing the storage of active metal ions in the negative electrode active material, and further improving the storage capacity of active metal ions.

[0013] In some embodiments of this application, the negative electrode active material satisfies at least one of the following conditions (1) to (4):

[0014] (1) The secondary particles have a coating layer on their surface, and the thickness of the coating layer on the secondary particles is in the range of 10 to 110 nm; preferably, the thickness of the coating layer on the secondary particles is in the range of 25 to 100 nm.

[0015] (2) The particle size Dv50 range of the first phase material is 1μm≤Dv50≤10μm; preferably, the particle size Dv50 range of the first phase material is 2μm≤Dv50≤5μm.

[0016] (3) The ID / IG value of the secondary particles ranges from 0.4 to 1.2;

[0017] (4) The compaction density of the negative electrode active material is in the range of 1.2 to 1.8 g / cc.

[0018] In the negative electrode active material provided in this application, the surface of the secondary particles further has a coating layer, and the thickness of the coating layer is 10-110 nm. Preferably, the thickness of the coating layer on the surface of the secondary particles ranges from 25-100 nm. By setting a coating layer on the surface of the secondary particles and controlling the thickness of the coating layer within the above range, it helps to reduce surface defects of the negative electrode active material and reduce the exposure of pore structures in the negative electrode active material. This can improve the initial coulombic efficiency of the negative electrode active material, enabling it to have high reversible capacity, thereby improving the energy density and cycle stability of the secondary battery.

[0019] In the negative electrode active material provided in this application, the particle size Dv50 of the first phase material ranges from 1 μm to 10 μm. Preferably, the particle size Dv50 of the first phase material ranges from 2 μm to 5 μm. By controlling the particle size Dv50 of the first phase material particles in the secondary particles within the aforementioned range, the distribution between the first and second phase materials can be made more uniform, the aggregate structure formed can be more compact, and the compaction density of the negative electrode active material and the corresponding negative electrode sheet can be further improved, thereby improving the energy density of the secondary battery. Here, Dv50 refers to the particle size that, in the volumetric particle size distribution of the material, reaches 50% of the cumulative volume.

[0020] In the negative electrode active material provided in this application, the ID / IG value of the secondary particles ranges from 0.4 to 1.2. By adjusting the range of the ID / IG value of the secondary particles within the above range, the negative electrode active material can have a suitable degree of defect, which can better promote the adsorption and binding of ions, while reducing the irreversible capacity loss caused by high defect degree, thereby helping to improve the specific capacity of the negative electrode active material.

[0021] In the negative electrode active material provided in this application, the compaction density of the negative electrode active material is 1.2 to 1.8 g / cc. By adjusting the compaction density of the negative electrode active material within the above range, the content of the negative electrode active material per unit area can be increased, thereby increasing the energy density of the secondary battery.

[0022] According to a second aspect of this application, this application also provides a method for preparing a negative electrode active material, the method comprising: mixing solid particles corresponding to a first phase material, a precursor corresponding to a second phase material, and a pore-forming agent containing metal elements; sequentially subjecting the mixed system to spray drying, carbonization, sieving, and washing treatments; and then forming a coating layer on the surface of the negative electrode active material by vapor deposition to obtain the negative electrode active material.

[0023] In some embodiments of this application, the method for preparing the negative electrode active material further includes:

[0024] (1) Mix the solid particles corresponding to the first phase material, the precursor corresponding to the second phase material, and the pore-forming agent containing metal elements to obtain a mixed system;

[0025] (2) The mixture is spray-dried using a spray drying device in an environment filled with inert gas;

[0026] (3) The spray-dried mixed precursor is carbonized in an inert atmosphere;

[0027] (4) Take the carbonized solid and crush and screen it, then acid wash and water wash it;

[0028] (5) Perform vapor deposition under special atmospheric conditions to form a coating layer on the surface of the negative electrode active material to obtain the negative electrode active material.

[0029] After mixing the first-phase solid particles and the second-phase material precursor with a pore-forming agent containing metal elements, spray drying is performed to achieve uniform mixing and simultaneous drying and granulation, forming secondary particles. The first-phase material has a stable structure and is not affected by sintering and activators, serving as a framework to support the secondary particles. The second-phase material can uniformly encapsulate the first-phase material and simultaneously form pores between the two phases, further mitigating the volume expansion of the first-phase material during cycling, thereby further improving the cycle stability of the negative electrode active material. The interaction between the activator and the second-phase material can also form more active sites, increasing the reversible capacity of the negative electrode active material. The negative electrode active material prepared using the method provided in the second aspect of this application has a stable low-potential plateau, high specific capacity, and high reversible capacity. Using it as the negative electrode sheet of a secondary battery can improve the energy density and cycle performance of the secondary battery.

[0030] In some embodiments of this application, the special atmosphere is a mixture of a reducing gas and argon; preferably, the reducing gas includes at least one of acetylene or methane; preferably, the volume percentage of the reducing gas is 5% to 20% based on the volume of the mixture.

[0031] In some embodiments of this application, the solid particles corresponding to the first phase material include any one of natural graphite and artificial graphite. Selecting the above materials as the first phase material ensures structural stability, is unaffected by sintering and activators, can serve as a framework to support secondary particles, and helps improve the compaction density of the material.

[0032] In some embodiments of this application, the particle size Dv50 of the solid particles corresponding to the first phase material is in the range of 2μm ≤ Dv50 ≤ 5μm. In the preparation method provided in this application, the particle size of the solid particles corresponding to the first phase material affects the percentage of pore area in the cross-section of a single particle in the secondary particles of the finally prepared negative electrode active material. By controlling the particle size of the solid particles corresponding to the first phase material within the above range, the percentage of pore area in the cross-section of a single particle in the secondary particles of the negative electrode active material can be further controlled within a suitable range, thereby further improving the cycle stability of the negative electrode active material.

[0033] In some embodiments of this application, the precursor corresponding to the second phase material includes at least one selected from phenolic resin, resorcinol-formaldehyde resin, epoxy resin, cellulose, or lignin. Using at least one of these materials as the second phase material allows the second phase material to uniformly coat the first phase material, while simultaneously forming pores between the two phases. This further mitigates the volume expansion of the first phase material during cycling, thereby further improving the cycle stability of the negative electrode active material and enhancing the cycle performance of the secondary battery.

[0034] In some embodiments of this application, the pore-forming agent containing alkali metal elements includes at least one selected from LiOH, NaOH, KOH, RbOH, Mg(OH)2, Ca(OH)2, Zn(OH)2, K2CO3, Na2CO3, sodium carboxymethyl cellulose, and sodium lignosulfonate. Selecting at least one of the above materials as an activator allows the activator to interact with the second-phase material, forming more active sites and improving the reversible capacity of the negative electrode active material.

[0035] In some embodiments of this application, the spray drying temperature is T1, which ranges from 130°C to 230°C. Adjusting the spray drying temperature within this range ensures good curing of the second-phase material, and further allows for control of the diameter of internal pores and circular holes, thereby improving the pyrolysis residual carbon rate and structural strength of the carbonized material.

[0036] In some embodiments of this application, the carbonization temperature is T2, and T2 ranges from 600℃ to 1000℃. In some embodiments of this application, the carbonization time is t1, and t1 ranges from 1h to 4h. The carbonization temperature and carbonization time in the preparation method of this application further affect the content of the first element in the secondary particles. By adjusting the carbonization temperature within the above-mentioned range of this application, the content of the first element can be kept within a more suitable range, thereby further improving the cycle stability, energy density, capacity retention, and other properties of the negative electrode active material.

[0037] In some embodiments of this application, the vapor deposition temperature is T3, which ranges from 700℃ to 1200℃. In some embodiments of this application, the vapor deposition time is t2, which ranges from 0.5h to 20h. By optimizing the vapor deposition conditions, the material interface can be improved, the coating thickness can be controlled, electrolyte degradation can be reduced, and irreversible capacity generation can be avoided, thereby improving both the energy density and cycle performance of the secondary battery.

[0038] According to a third aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer comprises the negative active material provided in the first aspect of this application or a negative active material prepared according to the preparation method provided in the second aspect of this application. The secondary battery provided in the third aspect of this application has high energy density and good cycle performance.

[0039] In some embodiments of this application, the provided secondary battery uses lithium metal as the counter electrode for the negative electrode. The charging curve of the capacity-voltage differential curve obtained by testing within the range of 0 to 2.5V vs Li+ / Li has at least four characteristic peaks. Preferably, the characteristic peaks include F1, F2, F3, and F4, wherein F1 is located between 0.06 and 0.08V in the capacity-voltage differential curve, F2 is located between 0.09 and 0.12V, F3 is located between 0.13 and 0.15V, and F4 is located between 0.21 and 0.25V. Preferably, the peak intensity corresponding to F1 is C1, the peak intensity corresponding to F2 is C2, and the peak intensity corresponding to F3 is C3. The relationship between C1 and C2, C3 satisfies: 0.1 ≤ C1 / C2 ≤ 1.0, 1 ≤ C2 / C3 ≤ 20. Among the aforementioned characteristic peaks, the positions of the peaks near 0.1V and 0.14V are similar to those of the graphite anode, mainly due to the extraction of lithium ions between graphite layers. The broad peaks near 0.06–0.08V represent the storage of lithium ions in the second phase material. By controlling the values ​​of C1 / C2 and C2 / C3 in the anode active material within the aforementioned range, the amount of lithium ions extracted in the low plateau region can be increased, thereby increasing the specific capacity of the anode material and ultimately improving the energy density of the secondary battery.

[0040] In some embodiments of this application, in the provided secondary battery, the negative electrode uses lithium metal as the counter electrode. In the capacity-voltage differential curve obtained by testing within the range of 0 to 2.5V vs Li+ / Li, the discharge curve exhibits at least three characteristic peaks. Preferably, the characteristic peaks include E1, E2, and E3, wherein E1 is located between 0.05 and 0.07V in the capacity-voltage differential curve, E2 is located between 0.08 and 0.11V, and E3 is located between 0.16 and 0.20V. Preferably, the peak intensity corresponding to E1 is D1, and the peak intensity corresponding to E2 is D2, with the relationship between D1 and D2 satisfying 1.3 ≤ D1 / D2 ≤ 3.0. The change in the peak intensity of D1 / D2 represents the change in the lithium-ion storage capacity in the second phase. By controlling the value of D1 / D2 in the negative electrode active material within the above range, the amount of lithium-ion insertion in the low plateau region can be increased, thereby increasing the specific capacity of the negative electrode material and thus improving the energy density of the secondary battery.

[0041] According to a fourth aspect of this application, an electronic device is provided, the electronic device comprising the secondary battery described in the third aspect of this application. The electronic device provided in the fourth aspect of this application has high energy density and good cycle performance, thereby providing a long service life. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0043] Figure 1 These are scanning electron microscope images of the negative electrode active materials in Examples 1-5;

[0044] Figure 2 These are cross-sectional electron microscope images of the negative electrode active materials in Examples 1-5;

[0045] Figure 3 The charge-discharge curves of the negative electrode active material of Comparative Example 1 in the Li / Li+ potential range from 0V to 2.5V are shown.

[0046] Figure 4 The capacitance-voltage differential curves of the negative electrode active material of Comparative Example 2 in the Li / Li+ potential range from 0V to 2.5V are shown.

[0047] Figure 5 The charge-discharge curves of the negative electrode active materials of Examples 1-9 in the Li / Li+ potential range from 0V to 2.5V are shown.

[0048] Figure 6 The capacitance-voltage differential curves of the negative electrode active materials of Examples 1-9 in the Li / Li+ potential range from 0V to 2.5V are shown. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0050] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0051] Hard carbon materials have attracted considerable attention due to their high theoretical capacity, low volume expansion, and rapid charge-discharge capabilities. Lithium ions can be inserted and extracted from hard carbon materials from various angles, resulting in excellent rate performance and cycle characteristics. However, the low compaction density and initial coulombic efficiency of hard carbon itself limit its application in lithium-ion batteries. Based on this, the inventors of this application, starting from the negative electrode active material itself, have discovered through extensive research that by optimizing the preparation process of hard carbon materials and simultaneously combining graphite with hard carbon materials, high-capacity, high initial efficiency, and high-compact composite materials can be prepared. This can solve the problems of low specific capacity and poor cycle stability of negative electrode sheets, thereby improving the energy density and cycle performance of secondary batteries.

[0052] According to a first aspect of this application, this application provides a negative electrode active material, the negative electrode active material being granular, the negative electrode active material comprising secondary particles formed by a first phase material and a second phase material; the secondary particles are formed by the second phase material coating the surface of the first phase material, and / or by the aggregation of the first phase material and the second phase material; pores exist inside the secondary particles, the pores being distributed between the first phase and the second phase of the secondary particles, the pores accounting for 0.5% to 35% of the area of ​​a single secondary particle.

[0053] Specifically, in the provided negative electrode active material, the area percentage of the pores in a single secondary particle can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range of any two of the above values. Preferably, the area percentage of the pores in a single secondary particle can be between 18% and 30%.

[0054] The negative electrode active material provided in this application is granular, and is a secondary particle formed by a first phase material and a second phase material. By controlling the special arrangement of the first and second phases in the negative electrode active material, this application enables good contact between the first and second phases, ensuring electron transfer, thereby reducing electrode resistance, increasing the compaction density of the active material, and ultimately improving the energy density and cycle performance of the secondary battery. Simultaneously, this application has discovered that reserving pores between the first and second phase materials can alleviate the volume expansion of the first phase material during cycling, improving the cycle stability of the negative electrode active material. Furthermore, the inventors of this application have found that the percentage of the area occupied by pores between the first and second phase materials in the cross-section of a single secondary particle in the negative electrode active material further affects the stability of the negative electrode active material. Controlling the percentage of the pore area within the aforementioned range can avoid electrolyte loss while providing space for the expansion of the first phase material during cycling, further alleviating the volume expansion of the first phase material during cycling, thereby further improving the cycle stability of the negative electrode active material. If the area percentage of pores in a single secondary particle exceeds the above range, for example, if it is lower than the above range, the reserved pores will not be sufficient to meet the particle expansion. The cyclic expansion of the first phase particles will easily lead to the breakage of the secondary particles, and the cycle stability of the secondary battery will decrease. If it is higher than the above range, it will lead to an increase in the exposed active area, a decrease in the first efficiency, a lower cell energy density, an increase in the amount of electrolyte consumed during the cycle, and affect the cycle performance of the secondary battery.

[0055] In some embodiments of this application, the cross-section of the second phase material has a circular hole, the diameter of which is D1, and D1 satisfies: 45nm ≤ D1 ≤ 550nm. Specifically, the diameter D1 of the circular hole can be 45nm, 46nm, 47nm, 48nm, 49nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, or 280nm. The wavelengths m, 290nm, 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, 400nm, 410nm, 420nm, 430nm, 440nm, 450nm, 460nm, 470nm, 480nm, 490nm, 500nm, 510nm, 520nm, 530nm, 540nm, and 550nm, or any range of two of the above values, are given. Preferably, the diameter D1 of the circular hole satisfies: 55nm ≤ D1 ≤ 480nm. In the negative electrode active material provided in this application, there are circular pores in the second phase material. The inventors of this application have found that the presence of circular pores in the second phase material can further alleviate the volume expansion of the second phase material during cycling and improve the cycle stability of the negative electrode active material. Furthermore, the inventors of this application have found that the diameter of the circular pores in the second phase material affects the cycle stability of the negative electrode active material. When the circular pores in the second phase material are too large, the compaction density of the secondary particles will be too low, while if the circular pores are too small, it will not be conducive to alleviating the volume expansion of the second phase material during cycling. By controlling the diameter of the circular pores in the second phase material within the above-mentioned range, the cycle stability of the negative electrode active material can be further improved, thereby enhancing the cycle stability of the secondary battery.

[0056] In some embodiments of this application, the second phase material contains a first element; the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn. The heterogeneous elements (non-carbon elements) in the negative electrode active material can affect its performance. The negative electrode active material provided in this application, by introducing metal ions in situ, can induce the storage of active metal ions within the negative electrode active material, further enhancing its storage capacity and resulting in higher specific capacity and reversible capacity, thereby further improving its energy density and capacity retention.

[0057] In some embodiments of this application, the content of the first element relative to the total mass of the negative electrode active material is 0.01% to 1.2%. Specifically, the content percentage of the first 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%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.23%, 0.34%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.78%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, or a range consisting of any two of the above values. Preferably, the content of the first element relative to the total mass of the negative electrode active material can be 0.02% to 0.95%. By controlling the content of the first element in the second phase material within the above range, active metal ions can be further induced to be stored in the negative electrode active material, thereby further improving the storage capacity of active metal ions. Applying the negative electrode active material of this application to a secondary battery can further improve the specific capacity of the battery negative electrode, and thus further improve the energy density of the secondary battery.

[0058] In some embodiments of this application, the negative electrode active material satisfies at least one of the following conditions (1) to (4):

[0059] (1) The secondary particles have a coating layer on their surface, and the thickness of the coating layer on the secondary particles is in the range of 10 to 110 nm; preferably, the thickness of the coating layer on the secondary particles is in the range of 25 to 100 nm.

[0060] (2) The particle size Dv50 range of the first phase material is 1μm≤Dv50≤10μm; preferably, the particle size Dv50 range of the first phase material is 2μm≤Dv50≤5μm.

[0061] (3) The ID / IG value of the secondary particles ranges from 0.4 to 1.2;

[0062] (4) The compaction density of the negative electrode active material is in the range of 1.2 to 1.8 g / cc.

[0063] In some embodiments of this application, the surface of the secondary particles has a coating layer, the thickness of which ranges from 10 to 110 nm. Specifically, the thickness of the coating layer can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, or any combination of two of the above values. Preferably, the thickness of the coating layer on the secondary particles ranges from 25 to 100 nm. By providing a coating layer on the surface of the secondary particles and controlling the thickness of the coating layer within the above range, it helps to reduce surface defects in the negative electrode active material and reduce the exposure of pore structures in the negative electrode active material, thereby improving the initial coulombic efficiency of the negative electrode active material, resulting in high reversible capacity, and thus improving the energy density and cycle stability of the secondary battery.

[0064] In some embodiments of this application, the particle size Dv50 of the first phase material in the provided negative electrode active material ranges from 1 μm ≤ Dv50 ≤ 10 μm. Specifically, the particle size Dv50 of the first phase material can be 1 μm, 1.5 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, ... The particle size distribution is 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, or any two of the above values. Preferably, the particle size Dv50 of the first phase material is in the range of 2 μm ≤ Dv50 ≤ 5 μm. By controlling the particle size Dv50 of the first phase material in the secondary particles within the range described above in this application, the distribution between the first phase material and the second phase material can be made more uniform, the aggregate structure formed can be more compact, and the compaction density of the negative electrode active material and the corresponding negative electrode sheet can be further improved, thereby improving the energy density of the secondary battery. Dv50 refers to the particle size that reaches 50% of the volumetric accumulation in the particle size distribution of a material, measured from the smallest particle size.

[0065] In some embodiments of this application, the ID / IG value of the secondary particles ranges from 0.4 to 1.2. Specifically, the ID / IG value of the secondary particles 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. By controlling the ID / IG value of the secondary particles within the above range, the negative electrode active material can have a suitable degree of defect, which can better promote the adsorption and binding of ions, while reducing irreversible capacity loss caused by high defect levels, thereby helping to improve the specific capacity of the negative electrode active material.

[0066] In some embodiments of this application, the compaction density of the negative electrode active material ranges from 1.2 to 1.8 g / cc. Specifically, the compaction density of the negative electrode active material can be 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.7 g / cc, 1.8 g / cc, or a range consisting of any two of the above values. By controlling the compaction density of the negative electrode active material 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.

[0067] According to a second aspect of this application, this application also provides a method for preparing a negative electrode active material, the method comprising: mixing solid particles corresponding to a first phase material, a precursor corresponding to a second phase material, and a pore-forming agent containing metal elements; sequentially subjecting the mixed system to spray drying, carbonization, sieving, and washing treatments; and then forming a coating layer on the surface of the negative electrode active material by vapor deposition to obtain the negative electrode active material.

[0068] In some embodiments of this application, the method for preparing the negative electrode active material further includes:

[0069] (1) The solid particles corresponding to the first phase material (precursor 1), the precursor corresponding to the second phase material (precursor 2), and the pore-forming agent containing metal elements are mixed to obtain a mixed system.

[0070] (2) The mixture is spray-dried using a spray drying device in an environment filled with inert gas;

[0071] (3) The spray-dried mixed precursor is carbonized in an inert atmosphere;

[0072] (4) Take the carbonized solid and crush and screen it, then acid wash and water wash it;

[0073] (5) Perform vapor deposition under special atmospheric conditions to form a coating layer on the surface of the negative electrode active material to obtain the negative electrode active material.

[0074] After mixing the first-phase solid particles and the second-phase material precursor with a pore-forming agent containing metal elements, spray drying is performed to achieve uniform mixing and simultaneous drying and granulation, forming secondary particles. The first-phase material has a stable structure and is not affected by sintering and activators, serving as a framework to support the secondary particles. The second-phase material can uniformly coat the first-phase material and simultaneously form pores between the two phases, further mitigating the volume expansion of the first-phase material during cycling, thereby further improving the cycle stability of the negative electrode active material. The interaction between the activator and the second-phase material can also form more active sites, increasing the reversible capacity of the negative electrode active material. Controlling the carbonization conditions of the particles can regulate the reaction degree between the activator and the second-phase material, controlling the internal porosity and the content of the first element, resulting in better lithium storage performance. Optimizing the vapor deposition conditions can improve the material interface, control the coating thickness, reduce electrolyte degradation, avoid irreversible capacity generation, and improve the energy density and cycle performance of the secondary battery. The negative electrode active material prepared by the method provided in the second aspect of this application has a stable low potential plateau, high specific capacity and high reversible capacity. When used as the negative electrode sheet of a secondary battery, it can improve the energy density of the secondary battery and improve its cycle performance.

[0075] In some embodiments of this application, the special atmosphere is a mixture of a reducing gas and argon; preferably, the reducing gas includes at least one of acetylene or methane; preferably, the volume percentage of the reducing gas is 5% to 20% based on the volume of the mixture. Specifically, based on the volume of the mixture, the volume percentage of the reducing gas can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of the above values.

[0076] In some embodiments of this application, the solid particles corresponding to the first phase material include any one of natural graphite and artificial graphite. Selecting the above materials as the first phase material ensures structural stability, is unaffected by sintering and activators, can serve as a framework to support secondary particles, and helps improve the compaction density of the material.

[0077] In some embodiments of this application, the particle size Dv50 of the solid particles corresponding to the first phase material ranges from 1 μm ≤ Dv50 ≤ 10 μm. Specifically, the particle size Dv50 of the solid particles corresponding to the first phase material can be 1 μm, 1.5 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, etc. The particle size distribution (Dv50) of the solid particles corresponding to the first phase material is 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, or a range consisting of any two of the above values. Preferably, the particle size Dv50 of the solid particles corresponding to the first phase material is in the range of 2 μm ≤ Dv50 ≤ 5 μm. In the preparation method provided in this application, the particle size of the solid particles corresponding to the first phase material affects the percentage of the cross-sectional pore area of ​​a single particle in the secondary particles of the final negative electrode active material. By controlling the particle size of the solid particles corresponding to the first phase material within the above range, the percentage of the cross-sectional pore area of ​​a single particle in the secondary particles of the negative electrode active material can be further controlled within a suitable range, thereby further improving the cycle stability of the negative electrode active material.

[0078] In some embodiments of this application, the precursor corresponding to the second phase material includes at least one selected from phenolic resin, resorcinol-formaldehyde resin, epoxy resin, cellulose, or lignin. Using at least one of these materials as the second phase material allows the second phase material to uniformly coat the first phase material, while simultaneously forming pores between the two phases. This further mitigates the volume expansion of the first phase material during cycling, thereby further improving the cycle stability of the negative electrode active material and enhancing the cycle performance of the secondary battery.

[0079] In some embodiments of this application, the pore-forming agent containing alkali metal elements includes at least one selected from LiOH, NaOH, KOH, RbOH, Mg(OH)2, Ca(OH)2, Zn(OH)2, K2CO3, Na2CO3, sodium carboxymethyl cellulose, and sodium lignosulfonate. Selecting at least one of the above materials as an activator allows the activator to interact with the second-phase material, forming more active sites and improving the reversible capacity of the negative electrode active material.

[0080] In some embodiments of this application, the spray drying temperature is T1, which ranges from 130℃ to 230℃. Specifically, the spray drying temperature T1 can be 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, or a range consisting of any two of the above values. Controlling the spray drying temperature within this range ensures good curing of the second-phase material, and further allows for control of the internal pores and diameter of circular pores, improving the pyrolysis residual carbon rate and structural strength of the carbonized material.

[0081] In some embodiments of this application, the carbonization temperature is T2, and the range of T2 is 600℃ to 1000℃. Specifically, the carbonization temperature T2 can be 600℃, 650℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 950℃, 1000℃, or a range consisting of any two of the above values.

[0082] In some embodiments of this application, the carbonization time is t1, and t1 ranges from 1h to 4h. Specifically, the carbonization time t1 can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h, 4.0h, or a range consisting of any two of the above values.

[0083] The carbonization temperature and carbonization time in the preparation method of this application will further affect the content of the first element in the secondary particles. By adjusting the carbonization temperature within the range mentioned above in this application, the content of the first element can be kept within a more suitable range, thereby further improving the cycle stability, energy density, capacity retention and other properties of the negative electrode active material.

[0084] In some embodiments of this application, the vapor deposition temperature is T3, and T3 ranges from 700℃ to 1200℃. Specifically, the vapor deposition temperature T3 can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, or any combination of two of the above values. In some embodiments of this application, the vapor deposition time is t2, and t2 ranges from 0.5h to 20h. Specifically, the vapor deposition time t2 can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any combination of two of the above values. By optimizing vapor deposition conditions, the material interface can be improved, the coating thickness can be controlled, electrolyte degradation can be reduced, and irreversible capacity generation can be avoided, thereby improving the energy density and cycle performance of the secondary battery.

[0085] According to a third aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer comprises the negative active material provided in the first aspect of this application or a negative active material prepared according to the preparation method provided in the second aspect of this application. The secondary battery provided in the third aspect of this application has high energy density and good cycle performance.

[0086] In some embodiments of this application, the provided secondary battery uses lithium metal as the counter electrode for the negative electrode. The charging curve of the capacity-voltage differential curve obtained by testing within the range of 0 to 2.5V vs Li+ / Li has at least four characteristic peaks. Preferably, the characteristic peaks include F1, F2, F3, and F4, wherein F1 is located between 0.06 and 0.08V in the capacity-voltage differential curve, F2 is located between 0.09 and 0.12V, F3 is located between 0.13 and 0.15V, and F4 is located between 0.21 and 0.25V. Preferably, the peak intensity corresponding to F1 is C1, the peak intensity corresponding to F2 is C2, and the peak intensity corresponding to F3 is C3. The relationship between C1 and C2, C3 satisfies: 0.1 ≤ C1 / C2 ≤ 1.0, 1 ≤ C2 / C3 ≤ 20. Specifically, C1 / C2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or any range of two of the above values. Specifically, C2 / C3 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any range of two of the above values. Among the above characteristic peaks, the peaks near 0.1V and 0.14V are similar in position to those of the graphite anode, mainly due to the extraction of lithium ions between graphite layers. The broad peaks near 0.06–0.08V represent the storage of lithium ions in the second-phase material. By controlling the values ​​of C1 / C2 and C2 / C3 in the anode active material within the above ranges, the extraction amount of lithium ions in the low plateau region can be increased, thereby increasing the specific capacity of the anode material and ultimately improving the energy density of the secondary battery.

[0087] In some embodiments of this application, in the provided secondary battery, the negative electrode uses lithium metal as the counter electrode, and the discharge curve of the capacity-voltage differential curve obtained by testing in the range of 0 to 2.5V vs Li+ / Li has at least three characteristic peaks; preferably, the characteristic peaks include E1, E2, and E3, wherein E1 is located between 0.05 and 0.07V in the capacity-voltage differential curve, E2 is located between 0.05 and 0.07V in the capacity-voltage differential curve, and E3 is located between 0.16 and 0.20V; preferably, the peak intensity corresponding to E1 is D1, the peak intensity corresponding to E2 is D2, and the relationship between D1 and D2 satisfies 1.3 ≤ D1 / D2 ≤ 3.0. Specifically, D1 / D2 can be 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 any range of two of the above values. The peak intensity variation of D1 / D2 represents the variation in lithium-ion storage capacity in the second phase. By controlling the D1 / D2 value in the negative electrode active material within the above range, the amount of lithium-ion insertion in the low plateau region can be increased, thereby increasing the specific capacity of the negative electrode material and ultimately improving the energy density of the secondary battery.

[0088] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with conductive metal, etc.

[0089] The negative electrode active material layer of this application may further include a conductive agent and a binder. This application does not impose any particular limitations on the aforementioned conductive agent and binder, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, carbon materials, metals, or conductive polymers. The binder may include, but is not limited to, at least one of polyacrylol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0090] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil is aluminum foil. In some embodiments, the secondary battery is a lithium-ion battery, and the positive active material may include lithium transition metal oxide, which may include, but is not limited to, at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese iron phosphate, or lithium titanate.

[0091] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm.

[0092] The secondary battery of this application also includes an electrolyte. In one embodiment, the electrolyte includes a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved.

[0093] The secondary battery of this application also includes a separator for separating the positive electrode and the negative electrode, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes.

[0094] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0095] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0096] According to a fourth aspect of this application, an electronic device is provided, the electronic device comprising the secondary battery described in the third aspect of this application. The secondary battery provided in the third aspect of this application has high energy density and good cycle performance, thereby enabling the electronic device provided in the fourth aspect of this application to have a long service life.

[0097] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0098] Example

[0099] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0100] The test methods and equipment used in the embodiments and comparative examples of this application are as follows:

[0101] 1. Scanning Electron Microscopy (SEM) Testing

[0102] The prepared negative electrode active material particles were observed using a scanning electron microscope (ZEISSSEM) and SEM images were taken. The porosity and circular pores of the particles were measured using the measurement function of the scanning electron microscope.

[0103] For cross-section testing, an ion polisher (instrument model IB-09010CP) was used to cut out a flat cross-section, which was then photographed by SEM. The principle of ion polishing is that under vacuum conditions, the ion source ionizes argon gas. After acceleration and focusing, the high-speed argon ions knock out the atoms or molecules on the sample surface, thus achieving ion polishing.

[0104] The calculation / statistical method for the percentage of pore area in a single particle of negative electrode active material is as follows: using the measurement function of scanning electron microscope, the cross-sectional area S1 of a single particle is measured and calculated, and the pore area S2 in the cross-section of a single particle is measured and calculated. The percentage of pore area in a single particle is S2 / S1×100%.

[0105] For negative electrode active material particles, the diameter of the circular pores in the particles is calculated / statistically as follows: the diameter of the circular pores in the particles is measured and calculated using the measurement function of a scanning electron microscope.

[0106] 2. Transmission electron microscopy (TEM) testing

[0107] The carbon coating layer of the prepared negative electrode active material was observed using a transmission electron microscope (FEI Tecnai F20), and TEM images were taken to measure the thickness of the carbon coating layer of the negative electrode active material.

[0108] 3. Particle size test

[0109] The particle size distribution of the prepared negative electrode active material was tested using a Malvern particle size analyzer (Master Sizer 2000). In the volume-based particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the volume accumulation was defined as Dv50, and the particle size reaching 99% of the volume accumulation was defined as Dv99.

[0110] 4. Metal element analysis and testing

[0111] The samples were digested using a microwave digester (model CEM-Mars5), and the elemental content in the prepared negative electrode active material was quantitatively determined using an ICP-OES instrument (model PE7000DV). After the samples were digested into a solution by acid, the liquid samples entered the atomization chamber, where they formed an aerosol under the action of a carrier gas. The aerosol then entered the plasma through the central jet tube and was fully evaporated, dissociated, atomized, ionized, and excited, emitting characteristic spectral lines of the elements. Qualitative analysis was performed based on the wavelength of the spectral lines, and quantitative analysis was performed based on the proportionality between the spectral line intensity and the concentration.

[0112] 5. Raman test

[0113] The Raman spectra of the prepared negative electrode active material were measured using a Raman spectroscopy instrument. During the test, a range of 200 μm × 500 μm was selected, and more than 200 points were measured at equal intervals within this range, with each point measured over 1000 cm⁻¹. -1 Up to 2000cm -1 Between; at 1320cm -1 Up to 1370cm -1 The peak that appears between these two points is designated as peak D, 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.

[0114] 6. Powder compaction density test of negative electrode active material:

[0115] Referring to standard GB / T 24533-2009, the test was conducted using a Sansi Zongheng UTM7305 electronic pressure testing machine. A certain mass of negative electrode active material powder was weighed and added to a special compaction mold. The mold was hollow in the middle with a metal disc on the top and bottom. The powder was placed between the metal discs, and a metal cylinder was placed on top. The mold was placed on a compaction density instrument, and the required test tonnage was set to 5 tons. The thickness of the powder under the corresponding pressure could be read on the equipment. The compaction density of the negative electrode active material was calculated using the density formula.

[0116] 7. Total lithium storage capacity and initial efficiency test of the negative electrode active material:

[0117] The initial reversible specific capacity of the negative electrode active material from 0V to 2.5V can be obtained by the following test method: A single-sided coated negative electrode sheet is cut into a 14mm diameter disc and used as the working electrode. A lithium sheet is then used as the counter electrode, and a polyethylene membrane with a porosity of 35% is used as the separator. After injecting electrolyte, a button cell is assembled. The electrolyte includes a base solvent and a lithium salt. The base solvent is a 1:1 mass mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The lithium salt is LiPF6, and the lithium salt concentration is specified. The concentration is 1 mol / L. The button cell was first discharged to 0V with three stages of small current (0.05C / 0.01C / 0.005C) and the first discharge capacity was recorded. Then, it was charged to 2.5V with a constant current of 0.1C and the first charge capacity was recorded. The first efficiency = first charge capacity / first discharge capacity × 100%. The first reversible specific capacity of the negative electrode active material from 0V to 2.5V, i.e., the total lithium storage specific capacity (total reversible capacity), is equal to the first charge capacity / the mass of the negative electrode active material, in mAh / g.

[0118] 8. Capacity-voltage differential curve testing of negative electrode active materials

[0119] Similar to the initial reversible specific capacity test method for negative electrode active materials from 0V to 2.5V, the corresponding software is used to convert the capacity-voltage curve into a capacity-voltage differential curve, i.e., the dQ / dV curve.

[0120] 9. Energy Density (ED) Test

[0121] 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 .

[0122] Example 1-1

[0123] <Preparation of Negative Electrode Active Materials>

[0124] 80g of natural graphite (precursor 1) was weighed and dispersed in 1L of water, wherein the particle size Dv50 of the natural graphite was 2μm. Then, 40g of lignin (precursor 2) and 5g of pore-forming agent NaOH were added, and the dispersion was stirred at room temperature for 3h until the sample was completely dispersed. Then, the temperature was increased to 60℃ at a heating rate of 5℃ / min, and the reaction was carried out for 6h. After cooling, a pre-reacted dispersion was obtained. The prepared dispersion was dried by spray drying, and the inlet air temperature was controlled at T1 = 200℃. After spraying, the powder product was collected. The powder product was used as a mixed precursor and placed in a rotary kiln with an inner liner. The temperature was increased to the temperature of the first calcination T at a heating rate of 5℃ / min. The carbonization temperature was 700℃, the carbonization time was t1 = 2h, the temperature was lowered, and the carbonized material was obtained after cooling. The collected powder was then washed with 1M hydrochloric acid for 12h, filtered, and the filter residue was washed with deionized water for 12h. The filter residue was then dried. The dried powder was then transferred to a nitrogen atmosphere protection furnace and heated to the vapor deposition temperature T3 = 800℃ at a heating rate of 5℃ / min. The gas atmosphere was then changed to a mixture of reducing gases acetylene and argon (based on the mass of the mixture, the mass percentage of reducing gas acetylene was 20%). The vapor deposition time was t2 = 4h. After the vapor deposition was completed, the above mixture was disconnected and replaced with nitrogen. After cooling to room temperature, the hard carbon material, i.e., the negative electrode active material, was obtained.

[0125] <Preparation of Negative Electrode Sheets>

[0126] The aforementioned negative electrode active material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 97:1.5:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 40 wt%, and the mixture was stirred until homogeneous. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 76.6 mm × 875 mm.

[0127] <Preparation of the positive electrode>

[0128] Lithium cobalt oxide (CCO) as the positive electrode active material, conductive carbon black (Super P) as the conductive agent, and PVDF as the binder were mixed at a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous, resulting in a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil used as a positive electrode current collector, and dried at 85 °C to obtain a single-sided coated positive electrode sheet with a positive electrode active material layer thickness of 80 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85 °C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0129] <Preparation of Electrolyte>

[0130] In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1. Then, 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were added, dissolved, and stirred thoroughly. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. The concentration of lithium salt was 1 mol / L. Based on the mass of the base solvent, the mass percentages of 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were all 2%.

[0131] <Preparation of the diaphragm>

[0132] A polyethylene film with a thickness of 7μm was used as the diaphragm.

[0133] <Preparation of Lithium-ion Batteries>

[0134] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, degassing, and shaping processes.

[0135] Examples 1-2 to 1-24

[0136] Except for adjusting the preparation parameters according to Table a, the remaining parameters of Examples 1-2 to 1-24 are the same as those of Example 1-1.

[0137] Table a

[0138]

[0139]

[0140] Examples 1-25

[0141] Based on Examples 1-5, the step of adding pore-forming agent NaOH was removed to prepare the negative electrode active material. The remaining steps and parameters were the same as in Examples 1-5. The relevant parameters and properties of the prepared negative electrode active materials were compared.

[0142] Examples 1-26

[0143] Based on Examples 1-5, the step of adding natural graphite was removed to prepare the negative electrode active material. The remaining steps and parameters were the same as in Examples 1-5. The relevant parameters and properties of the prepared negative electrode active materials were compared.

[0144] Comparative Example 1

[0145] Coconut shells were used to replace the mixed precursors used in the <Preparation of Negative Electrode Active Material> in Example 1-1. That is, coconut shells were used as the precursors, and the precursors were placed directly in a rotary kiln with an inner liner. The temperature was increased to the temperature of the first calcination, T2 = 700°C, at a heating rate of 5°C / min. The carbonization time was t1 = 2h. After cooling, the carbonized material was obtained. The remaining subsequent steps were the same as in Example 1.

[0146] Comparative Example 2

[0147] Commercially purchased artificial graphite was heated to 700°C in a rotary kiln under 10% C2H2 gas and maintained for 2 hours. Then the gas was switched to N2 gas and the material was allowed to cool naturally to obtain the final graphite material.

[0148] Comparative Example 3

[0149] Based on Examples 1-5, the step of adding lignin was removed to prepare the negative electrode active material. The remaining steps and parameters were the same as in Examples 1-5. The relevant parameters and properties of the prepared negative electrode active materials were compared.

[0150] The relevant parameters and properties of the active materials prepared in the above embodiments and comparative examples were tested using the above testing methods. The results are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] The results presented in Table 1 demonstrate that the negative electrode active material provided in this application possesses high energy density while exhibiting significantly improved cycle performance. Meanwhile, Figure 1 Scanning electron microscope (SEM) images of the negative electrode active materials of Examples 1-5 of this application are shown, in conjunction with... Figure 1As can be seen, the negative electrode active material provided in this application is granular, and the granules are secondary granules, formed by the aggregation of primary granules. Figure 2 Cross-sectional electron microscope images of the negative electrode active materials of Examples 1-5 of this application are shown, in conjunction with Figure 2 It can be seen that the secondary particles in the negative electrode active material provided in this application include a first phase material and a second phase material. The secondary particles are formed by the second phase material coating the surface of the first phase material, and / or by the aggregation of the first phase material and the second phase material, and according to... Figure 2 The cross-sectional electron microscope images shown reveal pores within the secondary particles of the negative electrode active material provided in this application, distributed between the first and second phases of the secondary particles. Furthermore, the embodiments and comparative data presented in Table 1 further demonstrate that by controlling the area percentage of pores within a single secondary particle within the range described in this application, the energy density of the negative electrode active material can be significantly improved, while simultaneously enhancing cycle performance.

[0155] at the same time, Figure 3 The charge-discharge curves of a battery assembled using a negative electrode sheet prepared from the negative electrode active material obtained in Comparative Example 1 as the working electrode and a lithium metal sheet as the counter electrode are shown in the Li / Li+ potential range from 0V to 2.5V. Figure 3 It can be seen that the specific capacity of the negative electrode active material of Comparative Example 1 is 233 mAh / g in the Li / Li+ potential range of 0V to 0.2V; and the specific capacity of the negative electrode active material of Comparative Example 1 is 454 mAh / g in the Li / Li+ potential range of 0V to 2.5V.

[0156] Figure 4 The capacity-voltage differential curves of a battery assembled using a negative electrode sheet prepared with the negative electrode active material obtained in Comparative Example 2 as the working electrode and a lithium metal sheet as the counter electrode are shown in the Li / Li+ potential range from 0V to 2.5V. The capacity-voltage differential curves show three distinct characteristic peaks in the charging curve. The intensities of the characteristic peaks near 0.1V and 0.14V are denoted as C2 and C3, respectively, with a peak intensity ratio of C2 / C3 = 20.8. Simultaneously, the capacity-voltage differential curves also show three distinct characteristic peaks in the discharging curve. The intensities of the characteristic peaks near 0.06V and 0.09V are denoted as D1 and D2, respectively, with a peak intensity ratio of D1 / D2 = 1.3.

[0157] Figure 5 The charge-discharge curves of a battery assembled using a negative electrode sheet prepared from the negative electrode active material obtained in Examples 1-9 as the working electrode and a lithium metal sheet as the counter electrode are shown in the Li / Li+ potential range from 0V to 2.5V. Figure 5It can be seen that the specific capacity of the negative electrode active materials in Examples 1-9 is 323 mAh / g in the Li / Li+ potential range of 0V to 0.2V; and the specific capacity of the negative electrode active materials in Examples 1-9 is 408 mAh / g in the Li / Li+ potential range of 0V to 2.5V.

[0158] Figure 6 The capacity-voltage differential curves of a battery assembled using a negative electrode sheet prepared from the negative electrode active material obtained in Examples 1-9 as the working electrode and a lithium metal sheet as the counter electrode are shown in the Li / Li+ potential range from 0V to 2.5V. From the capacity-voltage differential curves, it can be seen that the charging curve has four distinct characteristic peaks. Among them, there is a broad peak near 0.06–0.08V, denoted as C1. The intensities of the characteristic peaks near 0.1V and 0.14V are denoted as C2 and C3, respectively, with peak intensity ratios satisfying C1 / C2 = 0.19 and C2 / C3 = 1.7. Simultaneously, the capacity-voltage differential curves also show that the discharging curve has three distinct characteristic peaks. The intensities of the characteristic peaks near 0.06V and 0.09V are denoted as D1 and D2, respectively, with a peak intensity ratio D1 / D2 = 2.0.

[0159] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention are protected by the present invention.

Claims

1. A negative electrode active material, characterized in that, The negative electrode active material is in the form of particles, and the negative electrode active material includes secondary particles formed by a first phase material and a second phase material; the secondary particles have pores inside, and the area percentage of the pores in a single secondary particle is 0.5% to 35%.

2. The negative electrode active material according to claim 1, characterized in that, The area percentage of the pores in a single secondary particle is 18% to 30%.

3. The negative electrode active material according to claim 1, characterized in that, The cross-section of the second phase material has a circular hole with a diameter of D1, and D1 satisfies: 45nm≤D1≤550 nm.

4. The negative electrode active material according to claim 3, characterized in that, D1 satisfies: 55nm≤D1≤480nm.

5. The negative electrode active material according to claim 1, characterized in that, The second phase material contains a first element; the first element includes any one of Li, Na, K, Rb, Mg, Ca, and Zn; the content of the first element relative to the total mass of the negative electrode active material is 0.005% to 1.2%.

6. The negative electrode active material according to claim 5, characterized in that, The content of the first element relative to the total mass of the negative electrode active material is 0.02% to 0.95%.

7. The negative electrode active material according to claim 1, characterized in that, The negative electrode active material satisfies at least one of the following conditions (1) to (4): (1) The secondary particles have a coating layer on their surface, and the thickness of the coating layer on the surface of the secondary particles is in the range of 10~110 nm; (2) The particle size Dv50 of the first phase material is in the range of 1 μm ≤ Dv50 ≤ 10 μm; (3) The ID / IG value of the secondary particles ranges from 0.4 to 1.2; (4) The compaction density of the negative electrode active material is in the range of 1.2~1.8 g / cc.

8. The negative electrode active material according to claim 7, characterized in that, The secondary particles have a coating layer on their surface, and the thickness of the coating layer on the secondary particle surface ranges from 25 to 100 nm.

9. The negative electrode active material according to claim 7, characterized in that, The particle size Dv50 of the first phase material is in the range of 2μm≤Dv50≤5μm.

10. A method for preparing a negative electrode active material, characterized in that, include: The solid particles corresponding to the first phase material, the precursor corresponding to the second phase material, and the pore-forming agent containing alkali metal elements are mixed. The resulting mixture is then subjected to spray drying, carbonization, sieving, and washing. Finally, a coating layer is formed on the surface of the negative electrode active material by vapor deposition to obtain the negative electrode active material.

11. The preparation method according to claim 10, characterized in that, The solid particles corresponding to the first phase material include any one of natural graphite and artificial graphite; and / or, The precursor corresponding to the second phase material includes at least one of phenolic resin, resorcinol-formaldehyde resin, epoxy resin, cellulose, or lignin; and / or, The pore-forming agent containing alkali metal elements includes at least one selected from LiOH, NaOH, KOH, RbOH, Mg(OH)2, Ca(OH)2, Zn(OH)2, K2CO3, Na2CO3, sodium carboxymethyl cellulose, and sodium lignin sulfonate; and / or, The spray drying temperature is T1, and T1 ranges from 130℃ to 230℃; and / or, The carbonization temperature is T2, and T2 ranges from 600℃ to 1000℃; and / or, The carbonization time is t1, and t1 ranges from 1 hour to 4 hours; and / or, The vapor deposition temperature is T3, which ranges from 700℃ to 1200℃; and / or, The vapor deposition time is t2, which ranges from 0.5h to 20h.

12. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes the negative active material according to any one of claims 1-9 or the negative active material prepared by the preparation method according to any one of claims 10-11.

13. The secondary battery according to claim 12, characterized in that, The negative electrode uses lithium metal as the counter electrode, operating at 0 to 2.5V vs Li + In the capacity-voltage differential curves obtained from the / Li test, the charging curve has at least four characteristic peaks: F1, F2, F3, and F4. Specifically, F1 is located between 0.06 and 0.08 V in the capacity-voltage differential curve, F2 is located between 0.09 and 0.12 V in the capacity-voltage differential curve, F3 is located between 0.13 and 0.15 V in the capacity-voltage differential curve, and F4 is located between 0.21 and 0.25 V in the capacity-voltage differential curve. The peak intensity corresponding to F1 is C1, the peak intensity corresponding to F2 is C2, and the peak intensity corresponding to F3 is C3. The relationship between C1 and C2 and C3 satisfies: 0.1≤C1 / C2≤1.0, 1≤C2 / C3≤20.

14. The secondary battery according to claim 12, characterized in that, The negative electrode uses lithium metal as the counter electrode, operating at 0 to 2.5V vs Li + In the capacity-voltage differential curve obtained by testing within the / Li range, the discharge curve has at least three characteristic peaks: E1, E2, and E3. Specifically, E1 is located between 0.05 and 0.07 V in the capacity-voltage differential curve, E2 is located between 0.08 and 0.11 V in the capacity-voltage differential curve, and E3 is located between 0.16 and 0.20 V. The peak intensity corresponding to E1 is D1, and the peak intensity corresponding to E2 is D2. The relationship between D1 and D2 satisfies: 1.3 ≤ D1 / D2 ≤ 3.

0.

15. An electronic device, characterized in that, The electronic device includes a secondary battery as described in any one of claims 12-14.

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