Negative electrode active material, secondary battery and electronic device

Abstract

The present application provides a negative electrode active material, a secondary battery, and an electronic device. The negative electrode active material of the present application includes composite particles, which include a first region and a second region, wherein the first region has a disordered carbon structure and the second region has an ordered carbon structure and / or a metal oxide structure. The negative electrode active material of the present application has a high gram capacity and active ion diffusion coefficient, thereby enabling a secondary battery containing the negative electrode active material to have a high energy density and excellent cycle performance, rate performance, and fast charging capability.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a negative electrode active material, a secondary battery, and an electronic device. Background Art

[0002] Secondary batteries have advantages such as high operating voltage, wide application temperature range, and low self-discharge rate, and are widely used in mobile electronic devices, household appliances, electric vehicles and other fields. With the continuous development of products using them, various fields have also put forward higher requirements for the capacity, energy density, charge and discharge rate, and cycle stability of secondary batteries. At present, the negative electrode material of commercial secondary batteries is still mainly graphite. Graphite negative electrodes have advantages such as high conductivity and high stability, but their theoretical specific capacity is low. The current specific capacity of graphite negative electrodes is close to its theoretical maximum value of 372mAh / g. In addition, the expansion of graphite negative electrodes is more serious under fast charging system, resulting in a reduction in the life and reliability of secondary batteries.

[0003] Compared to graphite, hard carbon materials possess higher reversible specific capacities, typically ranging from 500 mAh / g to 700 mAh / g, and even exceeding 1000 mAh / g, demonstrating excellent rate charge and discharge performance. However, due to the high electrode potentials at which hard carbon materials are applied, they suffer from potential hysteresis (i.e., the lithium insertion potential is lower than the lithium deintercalation potential) and a high irreversible capacity in the first cycle, hindering their commercialization as anodes. Therefore, further research is needed to develop hard carbon materials with superior electrochemical properties and expand their applications. Summary of the Invention

[0004] In view of the above-mentioned problems existing in the prior art, the present application provides a negative electrode active material and a secondary battery comprising the negative electrode active material, so as to increase the gram capacity of the negative electrode active material and the active ion diffusion coefficient inside it, thereby increasing the energy density of the secondary battery and enhancing its cycle performance, rate performance and fast charging capability.

[0005] The first aspect of the present application provides a negative electrode active material, which includes composite particles, the composite particles include a first region and a second region, wherein the first region has a disordered carbon structure, the second region has an ordered carbon structure and / or a metal oxide structure, and the surface of the composite particles includes the first region. The inventors of the present application have found that for the first region with a disordered carbon structure, such as a hard carbon material region, since it is disordered amorphous graphite itself, the internal structure is arranged in a relatively disordered manner, and there are many pore structures at the same time, resulting in its true density and compaction density being not high. The present application introduces a first region with a disordered carbon structure and a second region with an ordered structure into the composite particles, which can not only maintain the capacity level of the negative electrode active material, but also effectively improve the compaction density of the negative electrode active material, thereby improving the energy density of the secondary battery. In addition, the second region with an ordered structure can also effectively reduce the free path of active ions, improve the internal diffusion kinetics of the negative electrode active material, reduce the internal polarization of the negative electrode active material, and improve the fast charging performance, rate performance and cycle performance of the secondary battery.

[0006] According to some embodiments of the present application, the first region includes a first active material, which includes hard carbon and / or soft carbon. Compared to soft carbon, hard carbon, after heat treatment at 1000°C or higher, has a larger d002 interplanar spacing and micropore content, thereby providing more active ion deintercalation sites.

[0007] According to some embodiments of the present application, the second region includes a second active material, and the second active material includes at least one of graphite, graphene, carbon nanotubes, lithium oxide, or transition metal oxide.

[0008] According to some embodiments of the present application, the average particle size of graphite is 10nm to 1000nm, the average sheet diameter of graphene is 10nm to 2000nm, the average diameter of carbon nanotubes is 10nm to 2000nm, the average particle size of lithium oxide is 10nm to 1000nm, and the average particle size of transition metal oxide is 10nm to 1000nm; preferably, the average particle size of graphite is 20nm to 300nm, the average sheet diameter of graphene is 20nm to 500nm, the average length diameter of carbon nanotubes is 20nm to 500nm, the average particle size of lithium oxide is 20nm to 300nm, and the average particle size of transition metal oxide is 20nm to 300nm. Active ions are more easily diffused in the second active material. In order to improve the active ion diffusion capacity in the negative electrode, a larger contact area is required between the first region and the second region. When the average particle size, average flake size or average diameter of the above-mentioned second active material is within this range, a larger contact area can be provided between the first region and the second region, thereby improving the diffusion capacity of active ions and further enhancing the rate performance, fast charging performance and cycle performance of the secondary battery.

[0009] According to some embodiments of the present application, the second region is randomly distributed or layered within the composite particle. When the second region is randomly distributed or layered within the composite particle, it can effectively reduce the free path of active ions, increase the solid-phase transfer rate of active ions, and further enhance the rate performance, fast charging performance, and cycle performance of the secondary battery.

[0010] According to some embodiments of the present application, the composite particles are primary particles. In some embodiments, the particle size of the composite particles satisfies 3 μm ≤ Dv50 ≤ 12 μm. When the particle size of the composite particles is within the above range, the kinetic performance of the secondary battery can be further improved, as well as the rate capability, fast charging performance, and cycling performance of the secondary battery.

[0011] According to some embodiments of the present application, the X-ray photoelectron spectrum of the negative electrode active material has a characteristic peak in the range of 283 eV to 288 eV, and the characteristic peak corresponds to the disordered carbon structure in the first region of the composite particles.

[0012] According to some embodiments of the present application, the ID / IG of the negative electrode active material is 0.6 to 1.3, wherein ID represents the shift at 1300 cm during Raman spectroscopy testing. -1 to 1400cm -1 The peak intensity within the range, IG indicates that the Raman spectrum is shifted at 1550cm -1 to 1650cm -1 Peak intensity within the range.

[0013] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in the 2θ range of 18° to 30°, corresponding to the disordered carbon structure in the first region of the composite particles. In some embodiments, the half-value width of the characteristic peak is 4° to 12°.

[0014] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in the range of 2θ of 26° to 27°, and the characteristic peak corresponds to graphite or carbon nanotubes (CNTs) in the second region.

[0015] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 2θ is 18° to 19°, 35° to 36°, or 43° to 44°, and the characteristic peak corresponds to lithium titanate in the second region.

[0016] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 2θ is 30° to 31°, 35° to 36°, 42.5° to 43.5°, 56.5° to 57.5° or 62° to 63°, and the characteristic peak corresponds to ferrosoferric oxide in the second region.

[0017] According to some embodiments of the present application, the specific surface area of ​​the negative electrode active material is 1 m 2 / g to 50m 2 When the specific surface area of ​​the negative electrode active material is within the above range, the rate performance, fast charging performance and cycle performance of the secondary battery can be further improved.

[0018] A second aspect of the present application provides a secondary battery, comprising a negative electrode, the negative electrode comprising a negative electrode active material layer and a current collector, the negative electrode active material layer comprising the negative electrode active material of the first aspect.

[0019] According to some embodiments of the present application, the porosity of the negative electrode active material layer is 10% to 50%. When the porosity of the negative electrode active material layer is within this range, the rate performance, fast charging performance and cycle performance of the secondary battery can be further improved. If the porosity is too large, the contact points between the negative electrode active material particles will be reduced, and the internal resistance of the secondary battery will increase; if the porosity is too small, it will lead to poor electrolyte wettability, the active ion transmission path will become longer, and the active ions will be hindered from shuttling between the positive and negative electrodes, making it impossible for the negative electrode sheet that is not in contact with the electrolyte to participate in the electrochemical reaction inside the secondary battery. At the same time, the interface resistance of the secondary battery will increase, affecting the rate performance, discharge capacity and service life of the secondary battery.

[0020] According to some embodiments of the present application, the bonding force between the negative electrode active material layer and the current collector is 3N / m to 30N / m. When the bonding force between the negative electrode active material layer and the current collector is within this range, the rate performance, fast charging performance and cycle performance of the secondary battery can be further improved. When the bonding force between the negative electrode active material layer and the current collector is too low, demolding and burrs are very likely to occur in the rolling or slitting process, leading to safety hazards of the secondary battery. When the bonding force between the negative electrode active material layer and the current collector is too high, the bonding strength between the active material and the current collector is too large, and the proportion of the binder is too high, which can easily lead to high internal resistance of the secondary battery, serious kinetic loss, and accelerated attenuation of long cycle performance.

[0021] A third aspect of the present application provides an electronic device comprising the secondary battery according to the second aspect.

[0022] The present application provides a first region and a second region in the composite particles, wherein the first region has a disordered carbon structure and the second region has an ordered carbon structure and / or a metal oxide structure, thereby maintaining the capacity level of the negative electrode active material and increasing the compaction density of the negative electrode active material layer and the energy density of the secondary battery. The second region with an ordered structure can also enhance the internal diffusion dynamics of the negative electrode active material, enabling the secondary battery to have a high active ion diffusion coefficient in the later stages of charge and discharge, thereby enhancing the fast charging capability, rate performance, and cycle performance of the secondary battery. In addition, the preparation method involved in the present application is simple, easy to operate and control, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a TEM image of the negative electrode active material of Example 4 of the present application.

[0024] Figure 2 This is a SEM image of the negative electrode active material of Example 4 of the present application.

[0025] Figure 3 This is a carbon fine spectrum of the X-ray electron spectrum of the negative electrode active material of Example 4 of the present application.

[0026] Figure 4 This is the Raman spectrum of the negative electrode active material of Example 4 of the present application.

[0027] Figure 5 This is the XRD spectrum of the negative electrode active material of Example 4 of the present application.

[0028] Figure 6 Schematic diagram of the internal arrangement of negative electrode active materials according to some embodiments of the present application. DETAILED DESCRIPTION

[0029] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0030] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0031] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0032] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0033] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0034] 1. Negative electrode active materials

[0035] The negative electrode active material provided by the present application includes composite particles, and the composite particles include a first region and a second region, wherein the first region has a disordered carbon structure, the second region has an ordered carbon structure and / or a metal oxide structure, and the surface of the composite particles includes the first region. The inventors of the present application have found that for the first region with a disordered carbon structure, such as the hard carbon material region, since it is disordered amorphous graphite itself, the internal structure is arranged in a relatively disordered manner, and there are more pore structures at the same time, resulting in its own true density and compaction density being not high. The present application can maintain the capacity level of the negative electrode active material by introducing the first region with a disordered carbon structure and the second region with an ordered structure into the composite particles, and the tightly arranged second region can effectively improve the compaction density of the negative electrode active material, thereby improving the energy density of the secondary battery. In addition, the second region with an ordered structure can also effectively reduce the free path of the active ions, increase the solid phase transfer speed of the active ions, thereby improving the internal diffusion kinetics of the negative electrode active material, reducing the internal polarization of the negative electrode active material, and improving the fast charging capability, rate performance and cycle performance of the secondary battery. In some embodiments, the surfaces of the composite particles are all first regions with a disordered carbon structure.

[0036] In this application, "disordered carbon structure" refers to a carbon structure with a very low degree of graphitization, close to an amorphous state (or without a fixed shape and periodic structural regularity). "Ordered carbon structure" refers to a carbon structure with a high degree of graphitization or a fixed shape and periodic structural regularity.

[0037] The “first region” in the present application may refer to a region having a disordered carbon structure on the surface of the composite particle.

[0038] According to some embodiments of the present application, the first region includes a first active material, which includes hard carbon and / or soft carbon. Compared to soft carbon, hard carbon, after heat treatment at 1000°C or higher, has a larger d002 interplanar spacing and micropore content, providing more active ion deintercalation sites. In some embodiments, the first active material includes hard carbon.

[0039] According to some embodiments of the present application, the second region includes a second active material, and the second active material includes at least one of graphite, graphene, carbon nanotubes, lithium oxide, or transition metal oxide. In some embodiments, the lithium oxide includes at least one of lithium transition metal composite oxides.

[0040] In this application, "transition metal" includes at least one of chromium, manganese, iron, cobalt, nickel, copper, zinc, or titanium. In some embodiments, the lithium oxide includes lithium titanate. In some embodiments, the transition metal oxide includes at least one of ferrosoferric oxide, manganese-manganese-manganic oxide, manganese dioxide, or cobalt-cobalt oxide.

[0041] According to some embodiments of the present application, the size of the second active material is 10 nm to 2000 nm, for example, 10 nm to 1000 nm. In this application, the size of the second active material has different meanings for different types of materials. For example, if the second active material is a graphene material, the size corresponds to the average sheet diameter of the graphene material; if the second active material is a carbon nanotube material, the size corresponds to the average length of the carbon nanotube material; if the second region is a graphite material, lithium oxide, or transition metal oxide, the size corresponds to the average particle size. That is, according to some embodiments of the present application, the average particle size of graphite is 10nm to 1000nm, the average sheet size of graphene is 10nm to 2000nm, the average length diameter of carbon nanotubes is 10nm to 2000nm, the average particle size of lithium oxide is 10nm to 1000nm, and the average particle size of transition metal oxide is 10nm to 1000nm; preferably, the average particle size of graphite is 20nm to 300nm, the average sheet size of graphene is 20nm to 500nm, the average length diameter of carbon nanotubes is 20nm to 500nm, the average particle size of lithium oxide is 20nm to 300nm, and the average particle size of transition metal oxide is 20nm to 300nm. Active ions are more easily diffused in the second region with an ordered structure, so increasing the contact area between the first region and the second region can increase the active ion diffusion coefficient in the negative electrode active material. When the size of the second active material is too large, the contact area between the first region and the second region is small, which is not conducive to the diffusion of active ions. When the size of the second active material is too small, the active material is prone to agglomeration, thereby affecting the rate performance, fast charging performance and cycle performance of the secondary battery.

[0042] In some embodiments, the average particle size of the graphite is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or a range consisting of any two of these values.

[0043] In some embodiments, the average sheet diameter of the graphene is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, or a range consisting of any two of these values.

[0044] In some embodiments, the carbon nanotubes have an average length diameter of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, or a range consisting of any two of these values.

[0045] In some embodiments, the average particle size of the lithium oxide is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or a range consisting of any two of these values.

[0046] In some embodiments, the average particle size of the transition metal oxide is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or a range consisting of any two of these values.

[0047] According to some embodiments of the present application, the second region is randomly distributed or layered within the composite particle. In some embodiments, the layered distribution is a single-layer distribution or a multi-layer distribution, and the multi-layer distribution is, for example, a double-layer distribution, a triple-layer distribution, or a quadruple-layer distribution. Different distribution patterns of the second region within the composite particle can effectively reduce the free path of active ions, increase the solid-phase transfer rate of active lithium ions, reduce the internal polarization of the negative electrode active material, and further improve the rate performance, fast charging performance, and cycle performance of the secondary battery.

[0048] According to some embodiments of the present application, the composite particles are primary particles. In some embodiments, the particle size of the composite particles satisfies 3μm≤Dv50≤12μm. In some embodiments, Dv50 is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or a range consisting of any two of these values. In the present application, Dv50 means that in the volume-based particle size distribution of the composite particles, 50% of the particles have a particle size less than this value. When the particle size of the composite particles is too large, the wetting effect of the electrolyte is poor. When the particle size of the composite particles is too small, the specific surface area increases, and more SEI films are formed on the surface of the composite particles during the first charge, which increases the consumption of active ions and affects the cycle performance and rate performance of the secondary battery.

[0049] According to some embodiments of the present application, the X-ray photoelectron spectrum of the negative electrode active material has a characteristic peak in the range of 283eV to 288eV. In the present application, the characteristic peak in the binding energy range of 283eV to 288eV corresponds to the characteristic peak of the disordered carbon structure in the first region.

[0050] According to some embodiments of the present application, the ID / IG of the negative electrode active material is 0.6 to 1.3, wherein ID represents the shift at 1300 cm during Raman spectroscopy testing. -1 to 1400cm -1 The peak intensity within the range, IG indicates that the Raman spectrum is shifted at 1550cm -1 to 1650cm -1 Peak intensity within the range.

[0051] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak within the range of 18° to 30° at 2θ. In the present application, the characteristic peak within the range of 18° to 30° at 2θ of the negative electrode active material corresponds to the disordered carbon structure in the first region. In some embodiments, the half-value width of the characteristic peak is 4° to 12°.

[0052] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in the range of 26° to 27° at 2θ. In the present application, the characteristic peak in the X-ray diffraction pattern of the negative electrode active material in the range of 26° to 27° at 2θ corresponds to graphite or carbon nanotubes (CNTs) having an ordered carbon structure in the second region.

[0053] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 2θ is 18° to 19°, 35° to 36°, or 43° to 44°. In the present application, the characteristic peak of the X-ray diffraction pattern of the negative electrode active material in the range of 2θ is 18° to 19°, 35° to 36°, or 43° to 44° corresponds to lithium titanate with an ordered structure in the second region. In some embodiments, the X-ray diffraction pattern of the negative electrode active material has obvious peaks at 2θ of 18.4°, 35.7°, and 43.3°, corresponding to lithium titanate with an ordered structure in the second region.

[0054] According to some embodiments of the present application, the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 2θ is 30° to 31°, 35° to 36°, 42.5° to 43.5°, 56.5° to 57.5°, or 62° to 63°. In the present application, the characteristic peak of the X-ray diffraction pattern of the negative electrode active material in the range of 2θ is 30° to 31°, 35° to 36°, 42.5° to 43.5°, 56.5° to 57.5°, or 62° to 63° corresponds to the ferrosoferric oxide with an ordered structure in the second region. In some embodiments, the X-ray diffraction pattern of the negative electrode active material has obvious peaks at 2θ of 30.2°, 35.5°, 43.1°, 57.1°, and 62.6°, corresponding to the ferrosoferric oxide with an ordered structure in the second region.

[0055] According to some embodiments of the present application, the specific surface area of ​​the negative electrode active material is 1 m 2 / g to 50m 2 In some embodiments, the specific surface area of ​​the negative electrode active material is 2.5 g / cm 2 、3 / cm 2 , 4g / cm 2 , 5g / cm 2 , 6g / cm 2 , 7g / cm 2 , 8g / cm 2 , 9g / cm 2 、10g / cm 2 , 12g / cm 2 , 15g / cm 2 , 20g / cm 2 , 25g / cm2 、30g / cm 2 、35g / cm 2 , 40g / cm 2 , 45g / cm 2 Or a range consisting of any two of these values. In some embodiments, the specific surface area of ​​the negative electrode active material is 2m 2 / g to 10m 2 When the specific surface area of ​​the negative electrode active material is too high, a large amount of SEI film is easily formed on its surface during the initial charge and discharge process of the secondary battery, resulting in a loss of secondary battery capacity. At the same time, negative electrode active materials with high specific surface area require more binder to be added to the negative electrode active material layer, which will increase the internal resistance of the negative electrode active material layer and affect the fast charging performance of the secondary battery.

[0056] According to some embodiments of the present application, the negative electrode active material may further include other negative electrode active materials in addition to the composite particles. The specific types of other negative electrode active materials are not subject to specific restrictions and can be selected according to needs. As an example, other negative electrode active materials include but are not limited to soft carbon such as natural graphite or artificial graphite, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure Li4Ti5O 12 , Li-Al alloy.

[0057] 2. Preparation method of composite particles

[0058] The method for preparing the negative electrode active material provided in this application comprises the following steps:

[0059] S1: mixing a second active material, a resin, a solvent, and an optional curing agent to form a second region to obtain a first mixed solution;

[0060] S2: Drying, for example, spray drying, the first mixed solution to obtain a precursor A containing a second active material;

[0061] S3: mixing the precursor A with the resin, the solvent, and the optional curing agent to obtain a second mixed solution;

[0062] S4: Drying, for example, spray drying the second mixed liquid to obtain precursor B;

[0063] S5: Carbonizing the precursor B to obtain the composite particles.

[0064] According to some embodiments of the present application, in S1, the mass ratio of the second active material, resin, solvent, and curing agent is a1:a2:a3:a4, wherein a1:a2 is 0.01 to 0.6; a3:a2 is 0.2 to 3; and a4:a2 is 0 to 0.5. In some embodiments, the mixing in S1 includes adding the second active material forming the second region to the solvent and dispersing it under ultrasound for, for example, 1 to 3 hours, followed by sequentially adding the resin and curing agent and mixing them under a stirrer for, for example, 0.5 to 3 hours.

[0065] According to some embodiments of the present application, in S3, the mass ratio of precursor A to resin, solvent and curing agent is b1:b2:b3:b4, wherein b2:b1 is 0.3 to 5; b3:b2 is 0.2 to 7; and b4:b2 is 0 to 0.5.

[0066] The method for preparing the composite particles provided in this application further comprises the following steps:

[0067] M1: mixing the second active material forming the second region, a resin, a solvent, hard carbon, and an optional curing agent to obtain a first mixed solution;

[0068] M2: Drying, for example, spray drying, the first mixed solution to obtain a precursor A1 containing a second active material;

[0069] M3: Mixing the precursor A1 with the resin, solvent, and optional curing agent to obtain a second mixed solution;

[0070] M4: Drying, for example, spray drying the second mixed liquid to obtain precursor B1;

[0071] M5: Carbonizing the precursor B1 to obtain the composite particles.

[0072] The method for preparing the composite particles provided in this application further comprises the following steps:

[0073] N1: mixing a second active material forming the second region, a resin, a solvent, hard carbon, and an optional curing agent to obtain a first mixed solution;

[0074] N2: drying, for example, spray drying, the first mixed solution to obtain precursor A2;

[0075] N3: Mixing the precursor A2 with the resin, the solvent, and the optional curing agent to obtain a second mixed solution;

[0076] N4: Drying, for example, spray drying, the second mixed liquid to obtain precursor B2;

[0077] N5: Mixing the precursor B2, the resin, the solvent, the second active material, and the optional curing agent to obtain a third mixed solution;

[0078] N6: Drying, for example, spray drying, the third mixed solution to obtain precursor C;

[0079] N7: Mixing the precursor C with the resin, the solvent, and the optional curing agent to obtain a fourth mixed solution;

[0080] N8: Drying, for example, spray drying, the fourth mixed solution to obtain precursor D;

[0081] N9: Optionally repeat steps N5 to N8 at least once to obtain precursor E;

[0082] N9: Carbonizing the precursor D or E to obtain the composite particles.

[0083] According to some embodiments of the present application, in M1 and N1, the mass ratio of the second active material, resin, solvent, curing agent, and hard carbon is c1:c2:c3:c4:c5, wherein c1:c2 is 0.01 to 3; c3:c2 is 0.2 to 7; c4:c2 is 0 to 0.5; and c5:c2 is 1 to 15. According to some embodiments of the present application, in N5, the mass ratio of the second active material, resin, solvent, curing agent, and precursor is d1:d2:d3:d4:d5, wherein d1:d2 is 0.01 to 3; d3:d2 is 0.2 to 7; d4:d2 is 0 to 0.5; and d5:d2 is 1 to 20. In some embodiments, the mixing in M1, N1 and N5 includes adding the second material forming the second region to the solvent and dispersing it under ultrasound, for example, for 1 to 3 hours, and then sequentially adding the resin, curing agent, hard carbon or precursor and mixing under a stirrer for 0.5 to 3 hours.

[0084] According to some embodiments of the present application, in M3, N3 and N7, the mass ratio of the precursor to the resin, solvent and curing agent is e1:e2:e3:e4, wherein e2:e1 is 0.1 to 1; e3:e2 is 0.5 to 3; and e4:2 is 0 to 0.5.

[0085] According to some embodiments of the present application, during spray drying, the inlet air temperature is set to 130°C to 300°C, and the outlet air temperature is set to 50°C to 150°C.

[0086] According to some embodiments of the present application, the carbonization includes a first carbonization and a second carbonization performed sequentially under an inert atmosphere. In some embodiments, the temperature of the first carbonization is 250° C. to 650° C. In some embodiments, the time of the first carbonization is 1 hour to 4 hours. In some embodiments, the temperature of the second carbonization is 700° C. to 1600° C. In some embodiments, the time of the second carbonization is 1 hour to 12 hours.

[0087] According to some embodiments of the present application, the resin includes at least one of a resol resin, an epoxy resin, a vinyl resin, a bismaleimide resin, a thermosetting polyimide resin, or a cyanate resin. In some embodiments, the solvent includes at least one of water, ethanol, methanol, acetone, dichloromethane, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, and the choice of the specific solvent is determined by the selected resin. In some embodiments, the curing agent includes at least one of ethylenetriamine, aminoethylpiperazine, m-phenylenediamine, diaminodiphenylmethane, and hexamethylenetetramine. In some embodiments, a curing agent may not be used, which is specifically determined by the selected resin system.

[0088] 3. Secondary batteries

[0089] The secondary battery provided in the present application includes a negative electrode, the negative electrode includes a negative electrode active material layer and a current collector, and the negative electrode active material layer includes the negative electrode active material according to the first aspect.

[0090] According to some embodiments of the present application, the porosity of the negative electrode active material layer is 10% to 50%. In some embodiments, the porosity of the negative electrode active material layer is 15%, 20%, 25%, 30%, 35%, 40%, 45% or a range consisting of any two of these values. In some embodiments, the porosity of the negative electrode active material layer is 15% to 35%. When the porosity of the negative electrode active material layer is within this range, the rate performance, fast charging performance and cycle performance of the secondary battery can be further improved. When the porosity of the negative electrode active material layer is too large, the contact points between the negative electrode active material particles are reduced, and the internal resistance of the secondary battery increases; when the porosity of the negative electrode active material layer is too small, it will lead to poor electrolyte wettability, the active ion transmission path becomes longer, and the active ions are hindered from shuttling between the positive and negative electrodes, so that the negative electrode plate that is not in contact with the electrolyte cannot participate in the electrochemical reaction inside the secondary battery. At the same time, the interface resistance of the secondary battery increases, affecting the rate performance, cycle performance, discharge capacity and service life of the secondary battery.

[0091] In some embodiments, the bonding force between the negative electrode active material layer and the current collector is 3N / m to 30N / m, for example, 5N / m, 10N / m, 15N / m, 20N / m or 25N / m. When the bonding force between the negative electrode active material layer and the current collector is within this range, the rate performance, fast charging performance and cycle performance of the secondary battery can be further improved. When the bonding force between the negative electrode active material layer and the current collector is too low, demolding and burrs are very likely to occur during the rolling or slitting process, leading to safety hazards of the secondary battery. When the bonding force between the negative electrode active material layer and the current collector is too high, the bonding strength between the active material and the current collector is too large, and the proportion of the binder is too high, which can easily lead to high internal resistance of the secondary battery, serious kinetic loss, and accelerated attenuation of long cycle performance.

[0092] In some embodiments, the negative electrode current collector comprises: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0093] In some embodiments, the negative electrode active material layer further comprises a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0094] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0095] The negative electrode of the present application can be prepared using methods known in the art. Typically, the negative electrode active material, optional conductive agent (e.g., carbon materials such as carbon black and metal particles), binder (e.g., SBR), and other optional additives (e.g., PTC thermistor material) are mixed together and dispersed in a solvent (e.g., deionized water). After stirring, the mixture is evenly coated on the negative electrode current collector and dried to obtain the negative electrode.

[0096] The secondary battery of the present application further includes a positive electrode, which includes a positive electrode current collector and a positive electrode active material layer, which includes a positive electrode active material, a binder, and a conductive agent.

[0097] According to some embodiments of the present application, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0098] According to some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In some embodiments, the binder includes a binder polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black or carbon fiber; a metal-based material such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0099] The positive electrode of the present application can be prepared by a method known in the art. Generally, the positive electrode active material, the conductive material and the binder are mixed together and dispersed in a solvent, stirred evenly and coated on the positive electrode current collector, and the positive electrode is obtained after drying. In some embodiments, the solvent may include, but is not limited to: N-methylpyrrolidone. The secondary battery of the present application also includes an isolating membrane. The material and shape of the isolating membrane used in the secondary battery of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolating membrane includes a polymer or inorganic substance formed from a material that is stable to the electrolyte of the present application.

[0100] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film may be used.

[0101] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0102] The secondary battery of the present application further comprises an electrolyte. The electrolyte that can be used in the present application can be an electrolyte known in the prior art.

[0103] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt and an optional additive. The organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. There is no restriction on the electrolyte used in the electrolyte according to the present application, and it may be any electrolyte known in the prior art. The additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0104] According to some embodiments of the present application, the secondary battery of the present application includes, but is not limited to: a lithium-ion battery or a sodium-ion battery. In some embodiments, the secondary battery includes a lithium-ion battery.

[0105] 4. Electronic Devices

[0106] The present application further provides an electronic device, which includes the secondary battery described in the third aspect of the present application.

[0107] The electronic devices or devices of the present application are not particularly limited. In some embodiments, the electronic devices of the present application include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0108] In the following examples and comparative examples, all reagents, materials and instruments used are commercially available unless otherwise specified.

[0109] Examples and Comparative Examples

[0110] Example 1

[0111] Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:1.4:1.6, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred to obtain a slurry. The slurry (solid content of 72 wt%) was evenly coated on the positive electrode current collector aluminum foil to a thickness of 80 μm. The sheet was then dried at 85°C, cold pressed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0112] Preparation of the negative electrode sheet: The composite particles, binder styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were dissolved in deionized water at a weight ratio of 97:1.5:1.5 to form a negative electrode slurry (solid content 40wt%). A 10μm-thick copper foil was used as the negative electrode current collector. The negative electrode slurry was coated onto the current collector to a thickness of 50μm. The sheet was then dried at 85°C, cold pressed, cut, and slit, and then dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0113] The composite particles were prepared by the following steps: preparing a mixed solution of nanographite microspheres with an average particle size of 100 nm with resol phenolic resin, ethanol, and hexamethylenetetramine in a mass ratio of 10:100:100:5 (first, the second active material, nanographite microspheres, were added to the ethanol solvent and dispersed under ultrasound for 2 hours, then the resol phenolic resin and hexamethylenetetramine were added in sequence and mixed under a stirrer for 1 hour), then spray-dried the mixed solution at an inlet air temperature of 200°C and an outlet air temperature of 130°C to obtain a precursor A containing the second active material. Precursor A obtained after a single spraying step was mixed with phenolic resin, ethanol, and hexamethylenetetramine in a mass ratio of 100:50:50:5 (precursor A, phenolic resin, ethanol, and hexamethylenetetramine were mixed under a stirrer for 1 hour), then spray-dried the mixed solution at an inlet air temperature of 200°C and an outlet air temperature of 130°C to obtain a precursor B. Precursor B was pre-carbonized at 600 °C for 1.5 h in a nitrogen atmosphere, and then carbonized at 1100 °C for 2 h in a nitrogen atmosphere to obtain Figure 6 The second active material with a similar structure in the left figure is nanographite, which is a composite particle with disordered distribution inside the composite particle.

[0114] Preparation of separator: The separator was 7 μm thick polyethylene (PE).

[0115] Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:PC:DEC=1:1:1, and then lithium salt LiPF6 and fluoroethylene carbonate are added and mixed evenly to obtain an electrolyte, wherein, based on the mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, and the mass percentage of fluoroethylene carbonate is 5%.

[0116] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets to act as an isolater, and wind them to obtain an electrode assembly. Place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80°C, inject the above-mentioned electrolyte and package it. After the formation, degassing, trimming and other process flows, a lithium-ion battery is obtained.

[0117] Example 2

[0118] The second active material in the composite particles of Example 2 is graphene, and the remaining parameters are the same as those of Example 1.

[0119] Example 3

[0120] The second active material in the composite particles of Example 3 is carbon nanotubes, and the other parameters are the same as those of Example 1.

[0121] Example 4

[0122] The second active material in the composite particles of Example 4 is lithium titanate, and the other parameters are the same as those of Example 1. Figure 1 As shown, after the composite particles obtained in this embodiment are ultra-thinly sectioned, clearly distinguishable lattice stripes can be observed under a high-resolution transmission electron microscope, wherein the areas with disordered stacking arrangements are the lattice stripes of the disordered carbon structure in the first area of ​​the composite particles, while the areas with neatly stacked arrangements are the lattice stripes of the ordered structure in the second area of ​​the composite particles.

[0123] like Figure 2 As shown, when observing the cross section of the negative electrode sheet containing the composite particles obtained in this embodiment under a scanning electron microscope, it can be seen that the dark gray part is hard carbon and the light gray part is lithium titanate particles, and the lithium titanate particles are randomly distributed inside the composite particles.

[0124] like Figure 3 As shown, the carbon fine spectrum of the X-ray electron spectrum of the composite particles obtained in this embodiment has a characteristic peak in the range of 283 eV to 288 eV, which corresponds to the characteristic peak of the disordered carbon structure in the first region.

[0125] like Figure 4 As shown in the Raman spectrum of the composite particles obtained in this application, ID / IG is about 0.7, where ID represents 1300 cm -1 to 1400cm -1 Peak intensity within the range, IG represents 1550cm -1 to 1650cm -1 Peak intensity within the range.

[0126] like Figure 5 As shown, the XRD spectrum of the composite particles obtained in this embodiment has sharp characteristic peaks in the ranges of 8° to 19°, 35° to 36°, and 43° to 44°, respectively, which correspond to lithium titanate with an ordered structure in the second region.

[0127] Example 5

[0128] The second active material in the composite particles of Example 5 is ferrosoferric oxide, and the other parameters are the same as those of Example 1.

[0129] Comparative Example 1

[0130] The composite particles of Comparative Example 1 were prepared without adding the second active material and were pure hard carbon materials. The remaining parameters were the same as those of Example 1.

[0131] Comparative Example 2

[0132] The negative electrode active material of Comparative Example 2 is artificial graphite.

[0133] Example 6

[0134] The second active material in the composite particles of Example 6 is graphite with an average particle size of 30 nanometers. The remaining parameters are the same as those of Example 1.

[0135] Example 7

[0136] The second active material in the composite particles of Example 7 is graphite with an average particle size of 300 nanometers. Other parameters are the same as those of Example 1.

[0137] Example 8

[0138] The second active material in the composite particles of Example 8 is graphite with an average particle size of 500 nanometers. The remaining parameters are the same as those of Example 1.

[0139] Example 9

[0140] The second active material in the composite particles of Example 9 is graphite with an average particle size of 1000 nanometers. The remaining parameters are the same as those of Example 1.

[0141] Example 10

[0142] The preparation method of the composite particles of Example 10 is as follows: a mixed solution of nano-lithium titanate microspheres with an average particle size of 100 nm and resol phenolic resin, ethanol, hexamethylenetetramine and hard carbon microspheres with a Dv50 of 8 μm is prepared in a mass ratio of 10:10:50:1:100 (first, the second active material nano-lithium titanate microspheres are added to ethanol and dispersed under ultrasound for 2 hours, and then the resol phenolic resin, hexamethylenetetramine and hard carbon microspheres are added in turn and mixed under a stirrer for 1 hour), and then the mixed solution is spray-dried, and the inlet air temperature is set to 200°C and the outlet air temperature is set to 130°C during spraying to obtain a precursor A1 containing the second active material. The precursor A1 obtained after one spraying was mixed with resol phenolic resin, ethanol and hexamethylenetetramine in a mass ratio of 100:50:50:5 (first, the precursor A1 was mixed with resol phenolic resin, ethanol and hexamethylenetetramine under a stirrer for 1 hour), and then the mixed solution was spray-dried. The air inlet temperature was set to 200°C and the air outlet temperature was set to 130°C during spraying to obtain precursor B1. The precursor B1 was pre-carbonized at 600°C for 1.5 hours under a nitrogen atmosphere, and then carbonized at 1100°C for 2 hours under a nitrogen atmosphere to obtain the same Figure 6 The second active material with a similar structure in the middle figure is nano-lithium titanate, and the nano-lithium titanate is distributed in layers inside the composite particles.

[0143] Example 11

[0144] The preparation concept of the composite particles of Example 11 is similar to that of Example 10, specifically as follows: a mixed solution of nano-lithium titanate microspheres with an average particle size of 100 nm and resol phenolic resin, ethanol, hexamethylenetetramine and hard carbon microspheres with a Dv50 of 5 μm is prepared in a mass ratio of 10:10:50:1:100 (first, the second active material nano-lithium titanate microspheres are added to ethanol and dispersed under ultrasound for 2 hours, and then resol phenolic resin, hexamethylenetetramine and hard carbon microspheres are added in turn and mixed under a stirrer for 1 hour), and then the mixed solution is spray-dried. During spraying, the inlet air temperature is set to 200°C and the outlet air temperature is set to 130°C to obtain a precursor A2 containing the second active material. Precursor A2, obtained after the first spraying, was mixed with resol phenolic resin, ethanol, and hexamethylenetetramine in a mass ratio of 100:25:25:2.5 (precursor A2, resol phenolic resin, ethanol, and hexamethylenetetramine were mixed under a stirrer for 1 hour). The mixed solution was then spray-dried with an inlet air temperature of 200°C and an outlet air temperature of 130°C to obtain precursor B2. Precursor B2, obtained after the second spraying, was mixed with nano-lithium titanate microspheres with an average particle size of 100 nm, resol phenolic resin, ethanol, and hexamethylenetetramine in a mass ratio of 100:10:10:50:1. The above mixing and spray-drying process was repeated to obtain precursor C. Precursor C, obtained after the third spraying, was mixed with resol phenolic resin, ethanol, and hexamethylenetetramine in a mass ratio of 100:25:25:2.5. The above mixing and spray-drying process was repeated to obtain precursor D. The precursor D was carbonized under the conditions similar to those in Example 10 to obtain Figure 6 The second active material with a similar structure in the right figure is nano-lithium titanate, and the nano-lithium titanate is distributed in a double-layered manner inside the composite particles.

[0145] Example 12

[0146] The preparation method of the composite particles of Example 12 is as follows: a mixed solution of nano-lithium titanate microspheres with an average particle size of 100 nm and resol phenolic resin, ethanol, hexamethylenetetramine and hard carbon microspheres with a Dv50 of 12 μm is prepared in a mass ratio of 10:5:50:0.5:100 (first, the nano-lithium titanate microspheres are added to ethanol and dispersed under ultrasound for 2 hours, and then the resol phenolic resin, hexamethylenetetramine and hard carbon microspheres are added in turn and mixed under a stirrer for 1 hour), and then the mixed solution is spray-dried, and the inlet air temperature is set to 200°C and the outlet air temperature is set to 130°C during spraying to obtain precursor E. After carbonizing precursor E under conditions similar to those in the above Example 10, composite particles are obtained in which the active material is nano-lithium titanate and the nano-lithium titanate is adsorbed and distributed on the surface of hard carbon.

[0147] Test Method

[0148] Negative electrode active material related parameter test

[0149] Take a fully discharged lithium-ion battery, disassemble it, remove the negative electrode, soak it in DMC (ethylene carbonate) for 20 minutes, then rinse it with DMC and acetone in turn to remove the electrolyte and the surface SEI film, then place it in an oven and bake it at 80°C for 12 hours to obtain the treated negative electrode sheet. Use a scraper to scrape off the powder on the negative electrode sheet, and heat treat the scraped powder at 400°C in a tube furnace under argon protection for 4 hours to remove the binder adhering to the surface of the negative electrode active material to obtain the negative electrode active material. The obtained negative electrode active material layer and negative electrode active material were tested as follows:

[0150] 1. TEM

[0151] The negative electrode active material was embedded and cured in epoxy resin, then sliced ​​into 50-70 nm sections using ultrathin sectioning to prepare the sample. High-magnification transmission electron microscopy was used to examine the cross-sections of the particle samples, observing the distribution of regions with long-range regular arrangement (i.e., the second region) and amorphous regions (without long-range regular lamellae and with disordered lamellae arrangement), i.e., the first region.

[0152] 2. SEM

[0153] Negative electrode ion milling (Cross-section) sample preparation process: Cut the negative electrode sheet after the above treatment into a size of 0.5cm×1cm, use conductive glue to stick the cut negative electrode on a 1cm×1.5cm silicon wafer carrier, and then use argon ion polishing (parameters: 8KV acceleration voltage, 4h per sample) to process one end of the negative electrode sheet. Argon ion polishing uses a high-voltage electric field to ionize argon gas to produce an ion state. The generated argon ions bombard the negative electrode surface at high speed under the action of the acceleration voltage, and erode the negative electrode sheet layer by layer to achieve the polishing effect.

[0154] The scanning electron microscope used in this application is the JSM-6360LV model of JEOL and its supporting X-ray spectrometer to analyze the cross-sectional morphology structure and element distribution of the polished negative electrode sheet and observe the distribution of the second region and the first region in the negative electrode active material.

[0155] 3. Surface defect

[0156] Laser microconfocal Raman spectroscopy was used to test the surface defects of the negative electrode active material. -1 The peak intensity ID at 1580 cm -1The ratio of the peak intensity IG at 1 / 2 (ID / IG) represents the surface defectivity of the sample. Each sample was tested at multiple potentials, and the standard deviation of the peak intensity IG at 1 / 2 (ID / IG) represents the uniformity of the surface defectivity across different regions. The average and standard deviation of the ID / IG ratios for the negative electrode active material were obtained by measuring 100 points of the unscreened negative electrode active material, obtaining the corresponding ID / IG values, and calculating the average and standard deviation of these 100 values.

[0157] 4. X-ray diffraction (XRD)

[0158] The negative electrode active material was tested by X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) with Cu Kα as the target; the voltage and current were 40 kV / 40 mA, the scanning angle range was 5° to 80°, the scanning step was 0.00836°, and the time per step was 0.3 s.

[0159] 5. X-ray Photoelectron Spectroscopy (XPS)

[0160] Perform an XPS full spectrum scan on the powder sample to identify the peaks for C1s, O1s, C(KLL), and O(KLL). High-resolution spectroscopy is then used to measure the chemical shifts of titanium, oxygen, and iron, with a scan width of 10 eV to 30 eV. Note that element binding energies must be charge-corrected, typically using C (285 eV), O (532 eV), or a fixed internal standard element for charge correction. Finally, the results are fitted using Xpeak software to obtain the final result.

[0161] 6. Particle size of negative electrode active material particles

[0162] The particle size of the negative electrode active material particles was tested using a Malvern particle size tester: the negative electrode active material was dispersed in an ethanol dispersant, and after ultrasonication for 30 minutes, the sample was added to the Malvern particle size tester to test the Dv50 of the negative electrode active material particles.

[0163] 7. Specific surface area of ​​negative electrode active material particles

[0164] The specific surface area of ​​the negative electrode active material was measured by nitrogen adsorption / desorption method using a specific surface area analyzer (Tristar II 3020M): the negative electrode active material sample was dried in a vacuum drying oven, then placed in a sample tube and measured in the analyzer.

[0165] 8. Gram capacity of negative electrode active material

[0166] The negative electrode active material was mixed, coated, and dried to form a negative electrode sheet. A lithium sheet was used as the positive electrode and assembled into a button cell for testing. The cell was discharged at 0.05C to 5.0mV, then at 50μA to 5.0mV, and finally at 10μA to 5.0mV. The cell was then charged at 0.1C to 2.0V. The capacity of the cell at this point was recorded (gram capacity).

[0167] Negative electrode related parameter test

[0168] 9. Porosity of the negative electrode active material layer

[0169] The negative electrode sheet after treatment was prepared into a complete round piece. 30 samples were tested for each embodiment or comparative example, and the volume of each sample was about 0.35 cm 3 The porosity of the negative electrode active material layer was tested according to the standard "GB / T24586-2009 Iron ore - Determination of apparent density, true density and porosity".

[0170] 10. Adhesion

[0171] The adhesion test between the negative electrode active material layer and the negative electrode current collector was conducted using an Instron 33652 instrument. A treated negative electrode sheet (30 mm wide x 100 mm to 160 mm long) was secured to a steel plate using double-sided tape (3M9448A, 20 mm wide x 90 mm to 150 mm long). A paper strip the same width as the negative electrode sheet was then secured to one side of the sheet using the tape. The tensile testing machine's stop was adjusted to the appropriate position. The paper strip was folded upward and slid 40 mm at a rate of 50 mm / min. The adhesion between the negative electrode active material layer and the negative electrode current collector was tested at a 180° angle (i.e., in the reverse direction of tension).

[0172] 11. Compaction density of negative electrode

[0173] Use an electronic balance to weigh a certain area S of the treated negative electrode sheet (the negative electrode current collector is coated with a negative electrode active material layer on both sides), and record the weight as W1. Use a ten-thousandth ruler to measure the thickness T1 of the negative electrode sheet. Use a solvent to wash off the negative electrode active material layer, dry it, measure the weight of the negative electrode current collector, record it as W2, and use a ten-thousandth ruler to measure the thickness T2 of the negative electrode current collector. Calculate the weight W0 and thickness T0 of the negative electrode active material layer provided on one side of the negative electrode current collector and the compaction density of the negative electrode active material layer by the following formula:

[0174] W0 = (W1 - W2) / 2; T0 = (T1 - T2) / 2; compacted density = W0 / (T0×S).

[0175] Lithium-ion battery related parameter testing

[0176] 12. Lithium-ion battery energy density

[0177] Five lithium-ion batteries from each group using all comparative examples and examples were sampled and the average value was calculated. First, the initial charge and discharge were performed in an environment of 25°C. Constant-current and constant-voltage charging was performed at a charging current of 0.5C until the upper voltage reached 4.48V. Then, constant-current discharge was performed at a discharge current of 0.2C, with a discharge cutoff voltage of 3V. The percentage increase in energy density for each example and comparative example relative to Comparative Example 2 was calculated.

[0178] 13. Lithium-ion battery cycle performance

[0179] Five lithium-ion batteries prepared using all comparative examples and examples were taken and the average value was calculated. The lithium-ion batteries were repeatedly charged and discharged using the following steps, and the cycle capacity retention rate and thickness expansion rate of the lithium-ion batteries were calculated.

[0180] First, in an environment of 25°C, the lithium-ion battery was charged and discharged for the first time. Constant current charging was performed at a charging current of 1C until the upper limit voltage of 4.48V was reached, and then constant voltage charging was switched. Then, constant current discharge was performed at a discharge current of 1C until the final voltage was 3V. The discharge capacity of the first cycle and the thickness of the fully charged lithium-ion battery were recorded. Then, 400 charge and discharge cycles were performed, and the discharge capacity and thickness of the fully charged lithium-ion battery were recorded at the 400th cycle.

[0181] Cycle capacity retention rate = (discharge capacity at the 400th cycle / discharge capacity at the first cycle) × 100%;

[0182] Cycle thickness expansion rate = (thickness of fully charged lithium-ion battery at the 400th cycle / thickness of fully charged lithium-ion battery at the first cycle) × 100%

[0183] 14. Lithium-ion battery charging rate performance

[0184] Take 5 lithium-ion batteries from each group and repeatedly charge and discharge the batteries using the following steps. Count the capacity (average value) at each charging stage and calculate the CC segment capacity ratio.

[0185] The specific steps are as follows: First, place the lithium-ion battery in a 25°C environment and let it sit for 1 hour. Perform constant current charging (CC) on the battery at a charging rate of 1C, charge to 4.48V and then switch to constant voltage charging (CV). Stop charging when the charging current is lower than 0.05C and let it sit for 5 minutes. Then discharge the battery to 3V at a constant current of 0.2C and let it sit for 5 minutes to ensure the integrity of the subsequent charging and discharging process. Then use different rates such as 0.2C, 0.5C, 1C, 2C, and 3C in turn according to the previous CC+CV charging mode to fully charge the battery. After leaving it for 5 minutes, discharge the battery capacity at a rate of 0.2C, and cycle once for each rate. Calculate the proportion of CC segment capacity at different charging rates. As shown in Table 2, the test is to fully charge the battery at a rate of 3C according to the previous CC+CV charging mode. The calculation formula is: CC segment capacity proportion (3C) = [CC segment charging capacity / (CC+CV) total charging capacity] × 100%

[0186] 15. Electrochemical Impedance Spectroscopy (EIS) and Lithium Ion Diffusion Coefficient

[0187] a) Preparation and lithium plating of a three-electrode battery: The preparation method is consistent with the above-mentioned lithium-ion battery. During the preparation of the lithium-ion battery, a copper wire was connected to the battery as a reference electrode. The negative electrode was lithium-plated at a current of 20 μA for 6 h. After lithium plating, EIS was measured at 25°C.

[0188] b) EIS test steps: The lithium-plated three-electrode battery was connected to the Bio-Logic VMP3B electrochemical workstation produced by Bio-Logitech, France, for testing. The test frequency range was 30mHz to 50kHz, and the amplitude was 5mV. After data collection, the impedance complex plane plot was used to analyze the data to obtain the impedance Rct data of the negative electrode of the lithium-ion battery.

[0189] c) Since the impedance of the battery is mainly determined by the mass transfer step under the action of low-frequency AC signal, the corresponding Warburg coefficient σ can be calculated based on the AC impedance spectrum curve, and then the differential value of the negative electrode potential and the battery state of charge can be calculated by the coulometric titration method. The lithium ion diffusion coefficient D of the corresponding battery state of charge is calculated by the following formula Li .

[0190]

[0191] Where V M is the average molar volume of the negative electrode active material; S is the effective area of ​​the negative electrode; F is the Faraday constant; the Warburg coefficient σ is calculated from the Z'-ω of the corresponding EIS curve -1 / 2 The slope value is determined.

[0192] The differential value of the negative electrode potential and the battery state of charge The test method is: charge the battery at 0.1C, charge for 1 hour, let it rest for 2 hours, measure the negative electrode open circuit voltage after the voltage stabilizes, and obtain the charging coulometric titration curve.

[0193] This application tests the lithium ion diffusion coefficient of the lithium ion battery when the state of charge is 90% for comparison.

[0194] Test results

[0195] Examples 1 to 5 and Comparative Examples 1 and 2 reflect the effects of the first region and the second region on the performance of lithium-ion batteries, wherein the second region is randomly distributed within the composite particles, and detailed data are shown in Table 1.

[0196] Table 1

[0197]

[0198] By comparing Examples 1 to 5 with Comparative Example 1, it can be seen that the lithium ion diffusion coefficients at 90% SOC of Examples 1 to 5 are all higher than those of Comparative Example 1. This indicates that the introduction of a structurally ordered second region into the composite particles comprising a disordered first region can effectively improve the solid-phase diffusion coefficient of lithium ions during the later stages of lithium insertion, while also minimizing internal polarization, thereby effectively improving the fast-charging, rate, and cycling performance of the lithium-ion battery. The ordered second active material has a higher density, so the negative electrode sheets of Examples 1 to 5 can achieve a higher compaction density during the cold pressing process than Comparative Example 1, ensuring a higher capacity for the negative electrode and improving the energy density of the lithium-ion battery.

[0199] Examples 1, 6, and 9 demonstrate the effect of the average particle size of the second active material on the performance of lithium-ion batteries. The second active material is nanographite, which is randomly distributed within the composite particles. Detailed data are shown in Table 2.

[0200] Table 2

[0201]

[0202] By comparing Example 1 and Examples 6 to 9, it can be seen that the introduction of the average particle size of the second active material nanographite affects the lithium ion diffusion coefficient and the fast charging capability of the lithium ion battery under high SOC, among which Example 1 in which the average particle size of the second active material nanographite is 100nm has the largest lithium ion diffusion coefficient under high SOC, and at the same time, it has the highest CC segment capacity when charged at a 3C rate, and has better fast charging capability.

[0203] Examples 4, 10, and 12 demonstrate the effect of the distribution of the second active material in the composite particles on the performance of lithium-ion batteries. The second active material is nano-lithium titanate with an average particle size of 100 nm. Detailed data are shown in Table 3.

[0204] Table 3

[0205]

[0206] By comparing Example 4 and Example 10 to Example 12, it can be seen that when the second active material is disordered or layered distributed inside the composite particles, the lithium ion diffusion coefficient under high SOC can be effectively improved, and the fast charging performance, rate performance and cycle performance of the secondary battery can be further improved.

[0207] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A negative electrode active material comprising a composite particle, wherein the composite particle consists of a first region and a second region, wherein: The first region has a disordered carbon structure, the second region has an ordered carbon structure and / or a metal oxide structure, and the surface of the composite particle includes the first region. The first region includes a first active material, the first active material includes hard carbon, The second region includes a second active material, wherein the second active material includes at least one of graphite, graphene, carbon nanotubes, lithium oxide, or transition metal oxide. The X-ray photoelectron spectrum of the negative electrode active material has a characteristic peak in the range of 283eV to 288eV; The ID / IG of the negative electrode active material is 0.6 to 1.3, wherein ID represents the shift at 1300 cm during Raman spectroscopy testing. -1 to 1400cm -1 The peak intensity within the range, IG indicates that the Raman spectrum is shifted at 1550cm -1 to 1650cm -1 Peak intensity within the range; The specific surface area of ​​the negative electrode active material is 1 m 2 / g to 50m 2 / g; The second active material satisfies at least one of the following conditions: (1) The average particle size of the graphite is 10 nm to 1000 nm; (2) The average sheet diameter of the graphene is 10 nm to 2000 nm; (3) The average length of the carbon nanotubes is 10 nm to 2000 nm; (4) The average particle size of the lithium oxide is 10 nm to 1000 nm; (5) The average particle size of the transition metal oxide is 10 nm to 1000 nm.

2. The negative electrode active material according to claim 1, characterized in that The second active material has a size of 10 nm to 2000 nm.

3. The negative electrode active material according to claim 1, characterized in that The second region is randomly distributed or layered inside the composite particle.

4. The negative electrode active material according to claim 1, characterized in that The composite particles are primary particles, and the particle size of the composite particles satisfies 3 μm≤Dv50≤12 μm.

5. 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 (d) to (g): (d) the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in the range of 18° to 30°, and the half-peak width of the characteristic peak is 4° to 12°; (e) the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in the range of 26° to 27°; (f) the X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 18° to 19°, 35° to 36°, or 43° to 44°; (g) The X-ray diffraction pattern of the negative electrode active material has a characteristic peak in at least one of the following ranges: 30° to 31°, 35° to 36°, 42.5° to 43.5°, 56.5° to 57.5°, or 62° to 63°. 6 . A secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode active material layer and a current collector, the negative electrode active material layer comprising the negative electrode active material according to claim 1 . 7 . An electronic device comprising the secondary battery according to claim 6 .

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