CN113066977A

CN113066977A - Negative electrode material, and electrochemical device and electronic device comprising same

Info

Publication number: CN113066977A
Application number: CN202110292208.5A
Authority: CN
Inventors: 金文博
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-03-18
Filing date: 2021-03-18
Publication date: 2021-07-02
Anticipated expiration: 2041-03-18
Also published as: CN113066977B

Abstract

The application relates to the technical field of energy storage, in particular to a negative electrode material, an electrochemical device comprising the same and electronic equipment. The present application provides an anode material comprising anode active particles, including: a first region including a region extending 0 μm to 0.5 μm from an intersection point of a diameter of a circumscribed circle of a cross-section of the anode active particle and a boundary of the cross-section toward a center of the circumscribed circle; a second region including a concentric circle of the circumscribed circle, the radius of the concentric circle being less than or equal to 0.5 μm; in the Raman spectrum of the negative active particle, the first region was 1350cm^‑1Peak intensity of_d1Relative to the reference point at 1575cm^‑1Peak intensity of_g1The ratio of which isR1, placing the second area at 1350cm^‑1Peak intensity of_d2Relative to the reference point at 1575cm^‑1Peak intensity of_g2When the ratio of R2 is defined as R2, the negative electrode material satisfies: r1 is more than or equal to R2, R1 is more than or equal to 0.2, and R2 is less than or equal to 0.35. The cathode material has good dynamic performance, can improve the low-temperature discharge performance of an electrochemical device, and improves the low-temperature discharge rate.

Description

Negative electrode material, and electrochemical device and electronic device comprising same

Technical Field

The present disclosure relates to the field of energy storage technologies, and more particularly, to an anode material, and an electrochemical device and an electronic apparatus including the same.

Background

Electrochemical devices such as lithium ion batteries have the advantages of environmental friendliness, high working voltage, high energy density, long cycle life and the like, and are widely applied to various fields such as mobile phones, computers, wearable equipment, consumer-grade unmanned aerial vehicles, electric tools, electric motorcycles, electric vehicles or large-scale energy storage devices. In recent years, with the expansion of the power market of lithium ion batteries, the performance requirements of batteries have been increased, and when the lithium ion batteries are applied to the fields of electric vehicles, electric tools and the like, low-temperature discharge performance becomes one of important indexes for investigating the performance of the batteries. Taking an electric vehicle or an electric tool as an example, the application scene is very wide, so that the use working conditions are complex and various, and the work under the low-temperature condition is difficult to avoid. However, the discharge performance of the lithium ion battery is a challenge at low temperature, and generally, the discharge capacity of the battery is lower than 25 ℃ at normal temperature at low temperature, which results in insufficient cruising ability of the electric vehicle or the electric tool at low temperature. Therefore, in order to meet the market demand, it is required to develop a battery having good discharge performance also under low temperature conditions. In the related art, the lithium intercalation path of lithium ions is shortened by reducing the graphite particle size, so that the purpose of improving the kinetics is achieved; however, this approach can result in a loss of energy density of the anode material, including compacted density, gram volume, etc. There are also some methods of direct coating of the negative electrode material, which can improve the kinetics of the negative electrode material, but they also result in a loss of energy density and higher cost.

Accordingly, there is a need for improvement in the negative electrode material in the related art and the electrochemical device and electronic apparatus using the same.

Disclosure of Invention

An object of the present application is to provide a negative electrode material, and an electrochemical device and an electronic apparatus including the same, which can improve low-temperature discharge performance of the electrochemical device in an attempt to solve at least one of the problems existing in the related art to at least some extent.

According to a first aspect of the present application, there is provided an anode material comprising an anode active particle, wherein the anode active particle includes: a first region including a diameter of a circle circumscribing a cross section of the anode active particle and a cross-sectional edgeThe intersection point of the boundary extends to the center of the external circle by 0 μm to 0.5 μm; a second region including concentric circles having a cross section of the circumscribed circle, the radius of the concentric circles being less than or equal to 0.5 μm; the first region is arranged at about 1350cm in Raman spectrum of the negative active particle^-1Peak intensity of_d1Relative to a distance of about 1575cm^-1Peak intensity of_g1The ratio of R1, the second region is set at about 1350cm^-1Peak intensity of_d2Relative to a distance of about 1575cm^-1Peak intensity of_g2When the ratio of R2 is defined as R2, the negative electrode material satisfies: r1 is more than or equal to R2, R1 is more than or equal to 0.2, and R2 is less than or equal to 0.35.

In some embodiments of the present application, the particle size distribution of the negative active particles satisfies the following relationship: dv99/Dv50-Dv90/Dv50 < 2.0, wherein the units of Dv99, Dv50, Dv90 and Dv50 are μm.

In some embodiments of the present application, the negative active particle satisfies the following relationship: 2.0-372 XG-C-8.0; wherein C is a gram capacity of the negative active particles in mAh/G, and G is a graphitization degree of the negative active particles.

In some embodiments of the present application, the negative active particle has a sphericity ratio satisfying: s50 ranges from 0.6 to 0.9; wherein S50 represents the shape factor value corresponding to a cumulative particle volume content of 50%.

In some embodiments of the present application, the anode active particles have an OI value satisfying: OI is less than or equal to 7.0; wherein OI is the ratio of the peak area C004 of the 004 surface and the peak area C110 of the 110 surface of the negative electrode active particle measured by an X-ray diffraction spectrum.

In some embodiments of the present application, the negative active particle satisfies at least one of conditions (a) to (e): (a) the compacted density CD of the negative active particles is more than or equal to 1.72, and the unit of the CD is g/cm³(ii) a The compacted density of the particles has an effect on the compacted density of the negative electrode, and a higher compacted density of the powder may ensure the compacted density of the negative electrode. (b) The specific surface area BET of the negative active particles is less than or equal to 2.5, and the unit of BET is m²(ii)/g; the low specific surface area can ensure the storage performance of the battery. (c)) The OI value of the negative active particles and the specific surface area BET of the negative active particles are satisfied, the OI is less than or equal to 5 multiplied by the BET, and the unit of the BET is m²(ii)/g; wherein, OI is the ratio of the peak area C004 of the 004 surface of the negative electrode active particle and the peak area C110 of the 110 surface of the negative electrode active particle obtained by X-ray diffraction spectrum determination, and BET is the specific surface area of the negative electrode active particle; the smaller the OI value, the lower the orientation degree of the material, which is beneficial to material dynamics, and the ball milling of the graphite by the FeO fine powder influences the specific surface area and the particle orientation degree of the graphite. (d) The mass content of sulfur element in the negative active particles is less than or equal to 100 ppm; (e) the negative active particles include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon.

According to a second aspect of the present application, there is provided an electrochemical device comprising an anode including an anode current collector and an anode active material layer provided on at least one surface of the anode current collector, wherein the anode active material layer includes the anode material as described above. The electrochemical device further includes a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

In some embodiments of the present application, Dv99 of the anode active particle and the thickness THK of the anode active material layer satisfy the following relationship: dv99 is less than or equal to 0.8THK is less than or equal to 65; where THK and Dv99 are in μm.

In some embodiments of the present application, the compacted density PD of the negative electrode ranges from: 1.45 to 1.75, the units of CD and PD are both g/cm³(ii) a And the PD and the compacted density CD of the anode active particles satisfy: PD is less than or equal to CD-0.9. Too low a cathode compaction density can cause the active material to fall off the substrate, and too high a cathode compaction density can affect the low temperature rate performance of the battery. In addition, the negative electrode compacted density is influenced by the powder compacted density, and the negative electrode compacted density corresponding to the higher powder compacted density can be higher, but the negative electrode compacted density cannot be too high, so that a better effect can be achieved when the PD is less than or equal to CD-0.9.

According to a third aspect of the present application, there is provided an electronic device comprising an electrochemical device according to the above-described embodiments of the present application.

The dynamic performance of the negative electrode material provided by the embodiment of the application can be improved, lithium dendrites are not easily formed during low-temperature charging, more electric quantity can be discharged during low-temperature discharging, and the low-temperature discharging multiplying power can be improved. Therefore, when an electrochemical device is operated under low temperature conditions, the use of the anode material of the present application can effectively improve the low temperature discharge performance of the electrochemical device. Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the figures can be obtained from the structures illustrated in these figures.

Fig. 1 is a Scanning Electron Microscope (SEM) picture of an anode material provided in an exemplary embodiment of the present application;

fig. 2 is a graph of discharge rate performance of a lithium ion battery according to an exemplary embodiment of the present disclosure.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

As used herein, the terms "about," "substantially," or "substantially" are used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the terms can refer to instances where the event or circumstance occurs precisely as well as instances where the event or circumstance occurs in close proximity. For example, when used in conjunction with numerical values, the term can refer to a range of variation that is less than or equal to ± 10% of the stated numerical value, such as less than or equal to ± 5%, less than or equal to ± 4%, less than or equal to ± 3%, less than or equal to ± 2%, less than or equal to ± 1%, less than or equal to ± 0.5%, less than or equal to ± 0.1%, or less than or equal to ± 0.05%.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if item A, B is listed, the phrase "at least one of A, B" means only a; only B; or A and B. In another example, if item A, B, C is listed, the phrase "at least one of A, B, C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

As used herein, "Dv 99" means a particle diameter of a material reaching 99% by volume accumulation from a small particle diameter side in a particle size distribution on a volume basis, that is, a volume of the material smaller than this particle diameter accounts for 99% of the total volume of the material. As used herein, "Dv 90" means a particle diameter of a material reaching 90% by volume accumulation from a small particle diameter side in a particle size distribution on a volume basis, that is, a volume of the material smaller than this particle diameter accounts for 90% of the total volume of the material. As used herein, "Dv 50" also referred to as "median particle diameter" means that the material reaches a particle diameter of 50% by volume cumulative from the small particle diameter side in the particle size distribution on a volume basis, i.e., the volume of the material smaller than this particle diameter accounts for 50% of the total volume of the material. In the negative electrode material, Dv50, Dv90, Dv99 of the negative electrode active particles may be measured by a method known in the art, for example, by a laser particle size analyzer (e.g., a malvern particle size tester).

First, negative electrode material

In some embodiments of the present invention, the,provided is an anode material including anode active particles, wherein the anode active particles include: a first region including a region extending 0 to 0.5 μm from an intersection of a diameter of a circumscribed circle of a cross-section of the anode active particle and a boundary of the cross-section toward a center of the circumscribed circle; a second region comprising concentric circles circumscribing the circle, the concentric circles having a radius less than or equal to 0.5 μm; the first region is located at about 1350cm in Raman spectrum (Raman spectrum) of the negative electrode active particle^-1Peak intensity of_d1Relative to a distance of about 1575cm^-1Peak intensity of_g1The ratio of R1, the second region is set at about 1350cm^-1Peak intensity of_d2Relative to a distance of about 1575cm^-1Peak intensity of_g2When the ratio of R2 is defined as R2, the negative electrode material satisfies: r1 is more than or equal to R2, R1 is more than or equal to about 0.2, and R2 is less than or equal to about 0.35.

Note that, herein, the shape of the cross section of the anode active particle is not limited. For example, in some cases, when the cross section is circular, the diameter of the circumscribed circle of the cross section is the diameter of the cross section, and the first region includes a region extending from 0 to 0.5 μm from the intersection of the diameter of the circumscribed circle of the cross section of the negative active particle and the boundary of the cross section toward the center of the circumscribed circle, meaning that the first region includes a region extending from 0 to 0.5 μm from the boundary point of the cross section of the negative active particle toward the center of the circle. In other cases, when the cross section is non-circular, further convex (or called convex polygon), the cross section has a plurality of vertices, and the circumscribed circle of the cross section refers to a circle intersecting at least two vertices of the cross section (because the shape of the cross section is irregular or diversified, the circumscribed circle needs to intersect two or more vertices), in other words, the circumscribed circle of the cross section can also be understood as a circle having a diameter between two points with the longest cross section.

The radius of the concentric circle of the circumscribed circle is smaller than that of the circumscribed circle. In some embodiments, R1 is greater than R2. In some embodiments, R1 may be enumerated as about 0.2, about 0.22, about 0.24, about 0.25, about 0.26, about 0.27, about 0.28, about 0.3, about 0.31, about 0.33, about 0.35, about 0.36, about 0.39, about 0.4, about 0.43, about 0.45, about 0.46, about 0.47, about 0.5, about 0.55, about 0.22, and the like. In some embodiments, R2 may be enumerated as about 0.35, about 0.33, about 0.3, about 0.28, about 0.26, about 0.25, about 0.24, about 0.2, about 0.18, about 0.16, about 0.15, about 0.12, about 0.11, about 0.1, and the like.

In the embodiment of the application, the Raman test equipment is a laser micro-confocal Raman spectrometer with the model of HR Evolution and the resolution of 0.02cm^-1. It is understood that in the Raman spectrum, at about 1350cm^-1The characteristic peak observed nearby is a D peak and is about 1575cm^-1The characteristic peak observed nearby is the G peak. However, the values may fluctuate slightly based on the difference in the instrumentation used or the effect of test errors or other relevant test factors, and thus the D peak may be at 1350cm^-1±50cm^-1The characteristic peak observed nearby, G peak may be 1575cm^-1±50cm^-1Characteristic peaks observed nearby. That is, the present application does not limit 1350cm^-1Or 1575cm^-1The values of (c) are acceptable within the allowable error range.

According to the anode material provided by the embodiment of the application, the first region of the anode active particles, namely the part relatively close to the surface layer, has the intensity ratio R1 (namely I) of the Raman spectrum D peak to the G peak_d1/I_g1) The ratio of the Raman spectrum D peak to G peak intensity R2 (i.e., I) to the second, central portion of the particle_d2/I_g2) Satisfies the relationship: r1 is more than or equal to R2, R1 is more than or equal to 0.20, and R2 is less than or equal to 0.35. Fig. 1 is a schematic cross-sectional view of an exemplary negative active particle, as shown in fig. 1, in which the first region is a portion of the negative active particle relatively close to the surface layer, for example, when an intersection of a diameter of a circle circumscribing a cross section of the negative active particle and a boundary of the cross section is regarded as an outermost point, a region extending 0 μm to 0.5 μm from the outermost point toward a center of the circle is a portion relatively close to the surface layer. The second region is a portion of the negative electrode active particle relatively close to the center, for example, the center of a circle circumscribing a cross section of the negative electrode active particle and a circle having a radius of not more than 0.5 μm with the center of the circle as a dot are taken as the center portion of the particle. Thereby, the negative electrodeThe strength ratio of the Raman spectrum D peak to the G peak of the surface layer part of the material particles is larger than that of R1, which shows that the surface layer atomic arrangement disorder degree is high, the number of lattice defects is more, the de-intercalation channel of lithium ions can be increased, the de-intercalation speed of the lithium ions is improved, the dynamic society of the negative electrode material is obviously improved, lithium dendrites are not easily formed during low-temperature charging, more electric quantity can be discharged during low-temperature discharging, and the low-temperature discharging multiplying power is improved. And the strength ratio of the Raman spectrum D peak to the G peak of the central part of the negative electrode material particle is smaller than that of R2, which shows that the central part has high crystallization degree, thereby being beneficial to improving the gram capacity and the compaction density of the active material and improving the energy density of the battery. Therefore, when the negative electrode material meets the conditions that R1 is not less than R2, R1 is not less than 0.20 and R2 is not more than 0.35, the negative electrode material has high dynamic performance, and is beneficial to improving the low-temperature discharge performance of an electrochemical device and improving the low-temperature discharge rate.

In some embodiments, the particle size distribution of the negative active particles satisfies the following relationship: dv99/Dv50-Dv90/Dv50 is equal to or less than 2.0, and the units of Dv99, Dv50, Dv90 and Dv50 are mum. In some embodiments, the particle size distribution of the negative active particles satisfies the following relationship: dv99/Dv50-Dv90/Dv50 is less than or equal to 1.8. In some embodiments, the particle size distribution of the negative active particles satisfies the following relationship: dv99/Dv50-Dv90/Dv50 is about 2.0, about 1.8, about 1.7, about 1.6, about 1.5, about 1.3, about 1.2, about 1.0, about 0.9, about 0.8, about 0.6, about 0.5, about 0.3, about 0.1, etc.

According to the embodiment of the application, in order to ensure that the granularity distribution of the material is narrow and avoid too many small particles and too many large particles, the range of the difference between Dv99/Dv50 and Dv90/Dv50 is defined. If the small particles are too large, the reactive sites of the active material and the electrolyte increase, consuming the electrolyte and causing a large number of side reactions, degrading the electrochemical properties such as storage and recycling. If the large particles are too large, the processability is reduced, and the surface of the negative electrode has bumps, which causes the consequences of lithium precipitation and the like, and reduces the battery performance. Therefore, by satisfying the difference between Dv99/Dv50 and Dv90/Dv50 of the active material: the Dv99/Dv50-Dv90/Dv50 is less than or equal to 2.0, so that the granularity distribution of the active material can be ensured to be in a narrower level, and the low-temperature rate capability of the electrochemical device is improved.

In some embodiments, the negative active particle satisfies the following relationship: 2.0-372 XG-C-8.0; wherein C is a gram capacity of the negative active particles in mAh/G, and G is a graphitization degree of the negative active particles. In some embodiments, the negative active particle satisfies the following relationship: 3.0-372 XG-C-7.0. In some embodiments, the negative active particle satisfies the following relationship: 372 xg-C is about 2.0, about 2.5, about 3.0, about 3.5, about 3.6, about 4.0, about 4.2, about 4.6, about 5.0, about 5.5, about 5.7, about 6.0, about 6.6, about 7.0, about 7.5, about 8.0, or a range consisting of any two of these values.

According to the embodiment of the present application, in order to ensure that the degree of crystallization of the active material is in an appropriate range, the gram capacity C and the graphitization degree G of the negative electrode active particle are defined to satisfy: 2.0-372 XG-C-8.0. Wherein 372 XG-C can be used for representing the difference value between the theoretical calculated capacity and the actual capacity of the active material, when the difference value is too small, the actual gram capacity is exerted to a higher degree, which indicates that the active material has high crystallization degree, and the high crystallization degree is not beneficial to dynamics, and the low-temperature discharge performance can be reduced. When the difference is too large, it indicates that the capacity exertion of the active material is low, resulting in low energy density of the battery. Therefore, the dynamic performance of the active material can be ensured by enabling the difference value between 372 XG and C to be in the range, and the low-temperature rate performance of the electrochemical device is favorably improved.

In some embodiments, the negative active particle has a sphericity ratio satisfying: the value range of S50 is 0.6-0.9; wherein S50 represents the shape factor value corresponding to a cumulative particle volume content of 50%. In some embodiments, the negative active particle has a sphericity ratio satisfying: s50 has a value in the range of 0.65 to 0.86. In some embodiments, the negative active particle has a sphericity ratio satisfying: s50 is about 0.6, about 0.65, about 0.66, about 0.67, about 0.68, about 0.7, about 0.73, about 0.75, about 0.78, about 0.8, about 0.82, about 0.85, about 0.86, about 0.88, about 0.9, or a range consisting of any two of these values.

It is understood that SQ represents a shape factor value corresponding to a cumulative particle volume content of Q%; when Q is 50, S50 represents a shape factor value corresponding to a cumulative particle volume content of 50%. Sphericity refers to the ratio of the circular perimeter of the equivalent projected area of a particle to the actual perimeter of its projection.

According to the embodiment of the application, in order to ensure the porosity and the compaction density of the negative electrode, the particle sphericity ratio of the negative electrode active particles is defined to satisfy: s50 is 0.60 to 0.90. The sphericity of the particles affects the arrangement of the particles in the negative electrode, which affects the porosity and compacted density of the negative electrode. If the particles are arranged too tightly, the porosity of the negative electrode is reduced, and the electrolyte is difficult to fully infiltrate, so that the dynamics of the battery is reduced, and the low-temperature discharge rate performance is reduced. If the particles are arranged too loosely, the compacted density of the negative electrode is low, and the adhesion of the negative electrode is weakened, which not only affects the capacity density of the battery, but also may cause the active material to fall off the negative electrode, thereby reducing the performance of the battery. Therefore, by making the sphericity ratio of the negative electrode active particles satisfy the value of S50 of 0.60 to 0.90, performance of the battery can be ensured.

In some embodiments, the negative active particles have a specific surface area BET of 2.5m or less²(ii) in terms of/g. In some embodiments, the negative active particles have a specific surface area BET of 2.0m or less²(ii) in terms of/g. In some embodiments, the negative active particle has a specific surface area BET of about 2.5m²G, about 2.2m²G, about 2.0m²G, about 1.8m²G, about 1.7m²A,/g, about 1.6m²G, about 1.5m²G, about 1.4m²G, about 1.2m²And/g, etc. The specific surface area BET of a material can be determined by methods known in the art, for example, by using a specific surface area analyzer (e.g., TriStar II specific surface analyzer).

According to the embodiment of the present application, in order to secure electrochemical properties such as storage of an electrochemical device, the specific surface area BET of the negative electrode active particle is defined to satisfy: BET is less than or equal to 2.5, and the unit of BET is m²(ii) in terms of/g. The BET of the active material reflects the surface state of the material, the BET is large, the surface reactivity of the material is high, the material is easy to react with an electrolyte, the storage performance is reduced, and even the performance of the whole battery is possibly reduced, so that the specific surface area of the negative active particles is required to be reducedThe BET is defined within the above suitable range.

In some embodiments, the anode active particles have an OI value that satisfies: OI is less than or equal to 7.0; wherein OI is a ratio of a peak area C004 of the 004 face and a peak area C110 of the 110 face of the negative electrode active particle measured by an X-ray diffraction (XRD) spectrum. That is, the OI value calculation formula is C004/C110, wherein C004 is the characteristic peak area intensity of the XRD spectrum line in the vicinity of 54.30 DEG to 54.60 DEG, and C110 is the characteristic peak area intensity of the XRD spectrum line in the vicinity of 77.35 DEG to 77.50 deg. In some embodiments, the anode active particles have an OI value that satisfies: OI is less than or equal to 6.0. In some embodiments, the anode active particles have an OI value that satisfies: OI is less than or equal to 5.0.

According to the embodiment of the application, in order to ensure the kinetics of the active material, the negative electrode active particle OI value is defined to be less than or equal to 7.0, the particle OI value represents the crystal orientation degree of the particles, and the higher the orientation degree is, the larger the OI value is, lithium ions can only enter and exit from the active material from a single direction, which is not beneficial to the extraction and extraction of the lithium ions. When the OI value is low, the uniformity of the crystal orientation degree is low, lithium ions can be de-embedded in all directions of the active material, the improvement of material dynamics is facilitated, the low-temperature discharge performance of the battery can be further improved, and therefore the OI value of active material particles is limited to be less than or equal to 7.0.

In some embodiments, the compacted density CD of the negative active particle satisfies: CD is more than or equal to 1.72, and the unit of CD is g/cm³. In some embodiments, the compacted density CD of the negative active particle satisfies: CD is more than or equal to 1.8. In some embodiments, the compacted density CD of the negative active particle is about 1.72, about 1.73, about 1.75, about 1.76, about 1.78, about 1.80, about 1.83, about 1.85, about 1.72, and the like.

According to the embodiment of the present application, in order to secure the energy density of the battery, the powder compacted density CD of the active material is defined to satisfy: CD is more than or equal to 1.72. The compacted density of the active material is in positive correlation with the compacted density of the negative electrode, and the greater the compacted density of the powder of the active material is, the higher the compacted density of the negative electrode can be, which is beneficial to improving the energy density of the battery, and therefore, the CD of the negative electrode active particles is limited within the appropriate range.

In some embodiments, the anode active particles have an OI value of ≦ 5 × BET. The smaller the OI value, the lower the orientation degree of the material, which is beneficial to material dynamics, and the ball milling of the graphite by the FeO fine powder influences the specific surface area and the particle orientation degree of the graphite.

In some embodiments, the sulfur element content in the negative active particles is 100ppm or less by mass. In some embodiments, the sulfur element content in the negative active particles is 80ppm or less by mass. In some embodiments, the elemental sulfur content of the negative active particle is about 100ppm, about 90ppm, about 88ppm, about 85ppm, about 80ppm, about 70ppm, about 60ppm, about 50ppm, about 40ppm, about 36ppm, about 30ppm, about 26ppm, about 20ppm, and the like, by mass. According to the embodiment of the application, in order to ensure the electrochemical stability of the negative active material, the content proportion of sulfur element S in the negative active particles is limited to be less than or equal to 100 ppm. In the negative active particles, the S element is an impurity element, which causes a side reaction with the electrolyte to generate by-products, thereby reducing the storage performance of the battery, generating gas, and reducing the cycle, resulting in the performance degradation of the battery.

Unless otherwise specified, various parameters referred to in this specification have the common meaning known in the art, and can be measured according to methods known in the art, and will not be described in detail herein.

In some embodiments, the negative active particles include a carbon material. In some embodiments, the carbon material comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon. In some embodiments, the negative active particles include natural graphite, artificial graphite, and combinations thereof. In some embodiments, the composite active particles may be graphite particles.

According to an embodiment of the present application, the negative active particle may be obtained by: selecting petroleum coke with a low volatile ratio as a raw material, crushing the petroleum coke into single particles, performing surface modification treatment after the single particles are converted into graphite through heat treatment, and finally obtaining the negative active particles. Of course, the preparation method of the anode active particle is not limited thereto, but may also be prepared by other methods well known in the art.

In some embodiments, the negative active particles are prepared by: the method comprises the steps of crushing raw coke to a certain range, wherein too small particle size can cause overlarge BET of a finished product to reduce the performances of storage, circulation and the like of a battery, and too large particle size can cause excessive loss of processability and dynamics of the finished product. FeO particles are small and high in hardness, the surfaces of raw coke particles can be roughened by ball milling, because FeO powder has friction action on the coke surfaces, a plurality of very tiny holes are formed on the coke surfaces, and part of FeO fine powder is embedded and attached to the surfaces of the coke particles under the action of pressure. In addition, ball milling also tends to make the particles more spherical, which increases the sphericity of the finished graphite. And after ball milling for 2h, performing low-temperature graphitization, wherein the graphitization temperature is 2500-2800 ℃, and the heat preservation time in the temperature range is not less than 36 h. FeO has a catalytic effect on the graphitization of the coke, and can promote the graphitization transformation of the coke, so that the crystallinity of the graphite is higher. The surface layer can be etched by oxygen atoms to form more defects, and the oxygen atoms are combined with carbon atoms on the surface layer part to form gas volatilization, so that the kinetics of the material can be improved. Iron compounds will also volatilize at high temperatures above 2500 c, thereby ensuring that the metal impurity content of the finished product remains low. Mixing the graphitized semi-finished product graphite with a certain proportion of asphalt, wherein the mass ratio of the semi-finished product graphite to the asphalt is (5-9): 1, adding a small amount of graphene powder, wherein the mass ratio of the graphene is 0.2-0.7%, the Dv50 particle size of the Dv50 asphalt is controlled to be less than 5 μm, and the asphalt type is medium-temperature asphalt with the softening point of less than 260 ℃. The three are uniformly mixed and then are subjected to heat treatment at 400-600 ℃, so that the asphalt is softened into sticky liquid and is uniformly mixed with the graphene powder, the sticky liquid can be coated on the surface of the semi-finished graphite under the stirring action, the semi-finished graphite has high surface roughness (for the reasons mentioned above) due to the ball milling effect, and the mixture of the asphalt and the graphene powder can be uniformly mixedEvenly and tightly attached to the surface of the graphite particles. After being stirred and mixed evenly, the mixture is heated to 1100 ℃ to 1300 ℃ for high-temperature carbonization treatment, so that the surface layer is carbonized and has graphitization transformation to a certain degree. The lithium ion releasing and embedding capacity of the amorphous carbon formed after carbonization is improved due to larger interlayer spacing, and the graphene has more defects (shown in I by Raman test)_dLarger), which is also beneficial to improving the lithium-releasing and-inserting capability of the material, and can obviously improve the dynamics of the material under the comprehensive action. The ball milling and shaping are carried out after the temperature reduction and cooling, the sphericity of the particles is improved, the specific surface area of the particles is reduced, and the surface defects can be caused (shown in the fact that Raman test is performed on I)_dLarger), thereby further improving the material dynamics, and then screening and demagnetizing to obtain the cathode material.

Two, electrochemical device

In some embodiments, the present application provides an electrochemical device including an anode, a cathode, an electrolyte, and a separator disposed between the cathode and the anode.

The electrochemical device of the present application may be a lithium ion battery, but may also be any other suitable electrochemical device. The electrochemical device in the embodiments of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors, without departing from the disclosure of the present application. In particular, the electrochemical device is a lithium secondary battery including, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The electrochemical device of the present application is an electrochemical device including a positive electrode having a positive electrode active material capable of occluding and releasing metal ions and a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, and is characterized by including any of the negative electrode materials described above.

The negative electrode material used in the electrochemical device of the present application is any of the negative electrode materials described above in the present application. In addition, the anode material used in the electrochemical device of the present application may further include other anode materials within a range that does not depart from the gist of the present application.

Negative electrode

In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the aforementioned negative electrode material.

In some embodiments, Dv99 of the anode active particle and the thickness THK of the (single-sided) anode active material layer satisfy the following relationship: dv99 is less than or equal to 0.8THK is less than or equal to 65; where Dv99 and THK are in μm. In some embodiments, Dv99 of the anode active particle and the thickness THK of the (single-sided) anode active material layer satisfy the following relationship: dv99 is less than or equal to 0.8THK is less than or equal to 45. In some embodiments, Dv99 is about 28 μm, about 30 μm, about 32 μm, about 35 μm, about 38 μm, about 40 μm, about 42 μm, about 43 μm, about 45 μm, or the like; 0.8THK is about 65 μm, about 55 μm, about 49 μm, about 48 μm, about 46 μm, about 45 μm, about 42 μm, about 40 μm, about 38 μm, about 35 μm, and the like.

According to the embodiment of the application, in order to ensure the processability of the active material, the Dv99 granularity of the active material is defined to satisfy the following conditions: dv99 is less than or equal to 0.8THK (i.e. 0.8 XTHK) is less than or equal to 65. When Dv99 is too large, the material is difficult to process, and an abnormality such as a convex spot is likely to occur on the surface of the negative electrode, and the negative electrode active material layer is more remarkably reduced as it becomes thinner. In addition, since the excessive Dv99 also deteriorates the filterability of the slurry and affects the production efficiency, the relationship between the Dv99 particle diameter of the anode active material and the thickness THK of the anode active material layer needs to be limited to the above-mentioned appropriate range.

In some embodiments, the compacted density PD of the negative electrode satisfies: PD is 1.45g/cm³To 1.75g/cm³. In some embodiments, the negative electrode has a compacted density, PD, of 1.50g/cm³To 1.65g/cm³. In some embodiments, the anode has a compacted density, PD, of about 1.45g/cm³About 1.50g/cm³About 1.52g/cm³About 1.56g/cm³About 1.58g/cm³About 1.60g/cm³About 1.62g/cm³About 1.65g/cm³About 1.67g/cm³About 1.68g/cm³About 1.70g/cm³About 1.75g/cm³Or a range of any two of these values.

In some embodiments, the compacted density PD of the negative electrode and the compacted density CD of the negative active particle satisfy: PD is less than or equal to CD-0.9, and the unit of PD and CD is g/cm³. Too little negative electrode compaction density PD can cause the active material to fall off the substrate, and too much negative electrode compaction density PD can reduce the low temperature rate performance of the battery. In addition, since the negative electrode compacted density PD is affected by the powder compacted density (i.e., CD), the higher the powder compacted density, the higher the corresponding negative electrode compacted density can be, but the negative electrode compacted density cannot be too high, and a better effect can be obtained when the PD is not more than CD-0.9.

In some embodiments, after the electrochemical device is cycled for N times, the disassembled negative electrode material still satisfies the characteristics of any of the previous embodiments, wherein N ≧ 0.

In some embodiments, the electrochemical device has a discharge rate at-10 ℃ of 80% or more; wherein the discharge rate is 1C discharge, and-10 ℃ discharge ratio (-10 ℃ discharge capacity/25 ℃ discharge capacity) × 100%).

According to the embodiment of the application, the negative electrode prepared by adopting the negative electrode material of any one of the above embodiments meets the condition that when the negative electrode compacted density PD ranges from 1.45 to 1.75, the unit of PD is g/cm³The electrochemical device is excellent in low-temperature discharge performance. The anode disassembled from the fresh battery and the anode disassembled after circulation still meet the compaction density range, and the anode material stripped and extracted from the anode still meets the anode material characteristics of any embodiment. If the compaction density of the negative electrode is too high, low-temperature dynamics can be reduced, and the discharge rate is influenced. The electrochemical device such as a lithium ion battery formed by matching the cathode with the anode, the electrolyte and the isolating membrane has excellent low-temperature discharge rate performance, and meets the condition that the discharge rate at minus 10 ℃ is more than or equal to 80 percent (the discharge rate is 1C discharge, and the discharge rate at minus 10 ℃ is (-10 ℃ discharge capacity/25 ℃ discharge capacity) multiplied by 100 percent). FIG. 2 is a graph of low temperature discharge rate performance vs. low temperature discharge rate performance for example 32 of the present invention and comparative example 1In contrast, as can be seen from fig. 2, the low-temperature discharge rate of the battery is significantly improved, and the-10 ℃ discharge rate of the sample of example 32 reaches 89.6%, which is greatly higher than 78.5% of the sample of comparative example 1, indicating that the negative electrode material and the electrochemical device comprising the same of the present invention have excellent low-temperature discharge performance.

In some embodiments, the negative active material layer further comprises a binder. The binder may include various binder polymers such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the negative electrode active material layer further includes a conductive agent to improve electrode conductivity. Any conductive material may be used as the conductive material as long as it does not cause a chemical change. Examples of conductive agents include, but are not limited to: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like; metal-based materials such as metal powders or metal fibers including copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives and the like; or mixtures thereof.

In some embodiments, the negative electrode current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymeric substrates coated with a conductive metal, and any combination thereof. In some embodiments, the negative current collector is a copper foil.

In some embodiments, the structure of the negative electrode is a negative electrode structure that can be used in electrochemical devices, as is known in the art.

In some embodiments, the method of preparing the negative electrode is a method of preparing a negative electrode that can be used in an electrochemical device, which is well known in the art. Illustratively, the negative electrode may be obtained by: the active material, the conductive agent, and the binder are mixed in a solvent, and the thickener may be heated as necessary to prepare an active material composition, and the active material composition is coated on the current collector. In some embodiments, the solvent may include, but is not limited to, water, N-methyl pyrrolidone.

Positive electrode

In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the negative electrode current collector, the positive electrode active material layer including a positive electrode active material. The specific kind of the positive electrode active material is not particularly limited and may be selected as desired.

In some embodiments, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive active material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive active material is selected from at least one of: lithium cobaltate (LiCoO)₂) Ternary lithium nickel manganese cobalt (NCM) and lithium manganate (LiMn)₂O₄) Lithium nickel manganese oxide (LiNi)_0.5Mn_1.5O₄) Or lithium iron phosphate (LiFePO)₄)。

In some embodiments, the positive active material layer further includes a binder, and optionally further includes a conductive material. The binder may improve the binding of the positive electrode active material particles to each other, and may improve the binding of the positive electrode active material to the positive electrode current collector. 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 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the positive electrode active material layer includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

In some embodiments, the positive current collector is a metal, for example including, but not limited to, aluminum foil.

In some embodiments, the structure of the positive electrode is a positive electrode structure that can be used in an electrochemical device, as is known in the art.

In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode that can be used in an electrochemical device, which is well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to, water, N-methylpyrrolidone, and the like.

Electrolyte solution

The electrolyte that may be used in the embodiments of the present application may be an electrolyte known in the art. The electrolyte may be classified into an aqueous electrolyte and a non-aqueous electrolyte, wherein an electrochemical device using the non-aqueous electrolyte may operate under a wider voltage window than the aqueous electrolyte, thereby achieving a higher energy density. In some embodiments, the non-aqueous electrolyte includes an organic solvent, an electrolyte, and an additive.

Electrolytes that may be used in the electrolytes of embodiments of the present application include, but are not limited to: inorganic lithium salts, e.g. LiClO₄、LiAsF₆、LiPF₆、LiBF₄、LiSbF₆、LiSO₃F、LiN(FSO₂)₂Etc.; organic lithium salts containing fluorine, e.g. LiCF₃SO₃、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 3-hexafluoropropane disulfonimide lithium, cyclic 1, 2-tetrafluoroethane disulfonimide lithium, LiPF₄(CF₃)₂、LiN(CF₃SO₂)(C4F₉SO₂)、LiC(CF₃SO₂)₃、LiPF₄(CF₃SO₂)₂、LiPF₄(C₂F₅)₂、LiPF₄(C₂F₅SO₂)₂、LiBF₂(CF₃)₂、LiBF₂(C₂F₅)₂、LiBF₂(CF₃SO₂)₂、LiBF₂(C₂F₅SO₂)₂(ii) a The dicarboxylic acid complex-containing lithium salt may, for example, be lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium tris (oxalato) phosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, or the like. The electrolyte may be used alone or in combination of two or more. For example, in some embodiments, the electrolyte comprises LiPF₆And LiBF₄Combinations of (a) and (b). In some embodiments, the electrolyte comprises LiPF₆。

In some embodiments, the concentration of the electrolyte is in the range of 0.8 to 3mol/L, such as in the range of 0.8 to 2.5mol/L, in the range of 0.8 to 2mol/L, in the range of 1 to 2mol/L, again, for example, 1, 1.15, 1.2, 1.5, 2, or 2.5 mol/L.

Additives that may be used in the electrolyte of the embodiments of the present application may be additives that can be used to improve the electrochemical performance of the battery, which are well known in the art. In some embodiments, the additive includes, but is not limited to, at least one of a polynitrile compound, a sulfur containing additive, fluoroethylene carbonate (FEC), 1, 3-Propane Sultone (PS), 1,4 butane sultone.

The organic solvent that may be used in the electrolyte of the embodiments of the present application may be any organic solvent known in the art. In some embodiments, organic solvents, including, but not limited to: a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. Among them, examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

In some embodiments the organic solvent comprises at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate.

The preparation method of the electrolyte in the embodiment of the application is not limited, and the electrolyte can be prepared in a conventional electrolyte mode. In some embodiments, the electrolytes of the present application can be prepared by mixing the components.

Isolation film

In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

For example, in some embodiments, the isolation film comprises a substrate layer. The substrate layer is a non-woven fabric, a membrane or a composite membrane with a porous structure. The material of the substrate layer may be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane.

At least one surface of the substrate layer is provided with a surface treatment layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles can be selected from one or more of alumina, silica, magnesia, titania, hafnia, stannic oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder can be selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

Third, application

In some embodiments, the present application provides an electronic device comprising the aforementioned electrochemical device.

According to the cathode material provided by the embodiment of the application, the low-temperature discharge performance of the electrochemical device can be improved, so that the electrochemical device manufactured by the method is suitable for electronic equipment in various fields, and is particularly suitable for electronic equipment with working requirements under low-temperature working conditions.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic apparatus known in the art. For example, the electronic devices include, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, lighting fixtures, toys, game machines, clocks, electric tools, flashlights, cameras, large household batteries, lithium ion capacitors, and the like. In addition, the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-exemplified electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.

The present application will be described in more detail with reference to specific examples and comparative examples, taking a lithium ion battery as an example, but the present application is not limited to these examples as long as the gist thereof is not deviated. In the following examples and comparative examples, reagents, materials and instruments used therefor were commercially available or synthetically available, unless otherwise specified.

Examples

The following describes performance evaluation according to examples and comparative examples of lithium ion batteries of the present application.

Preparation of lithium ion battery

1. Preparation of the negative electrode

The negative electrode active material graphite particles, the conductive agent, the binder Styrene Butadiene Rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in the solvent deionized water according to the weight ratio of 95.7: 1.5: 1.8: 1 to form uniform negative electrode slurry. And uniformly coating the negative electrode slurry on a copper foil of a negative current collector, drying, cold-pressing to form a negative active material layer, cutting and welding a tab to obtain the negative electrode.

In each of the examples and comparative examples described below, the difference in the preparation of the negative electrode is mainly in the difference in the negative electrode active material used, and details are shown in the tables described below.

Graphite particles of different particle sizes may be obtained by size reduction classification by any means known in the art. The thickness of the negative electrode active material layer is controlled by any means known in the art to obtain different gram capacity C and graphitization degree G, and the gram capacity C can be continuously changed by adjusting the particle size and the like.

2. Preparation of the Positive electrode

Lithium iron phosphate serving as a positive electrode active material, acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder are mixed according to a mass ratio of 96.3: 2.2: 1.5, mixing the mixture in a solvent N-methyl pyrrolidone (NMP), and fully and uniformly stirring the mixture in a vacuum stirrer to obtain the anode slurry. The anode material is coated on an anode current collector aluminum foil, dried and cold-pressed to form an anode active substance layer, and then the anode is obtained by cutting pieces and welding lugs. Wherein the anode active material is lithium iron phosphate (LiFePO)₄) Nickel cobalt manganese ternary material (NC)M), lithium cobaltate (LiCoO)₂) Lithium manganate (LiMn)₂O₄) One or a mixture of two or more of them. Because lithium iron phosphate has excellent stability and cycle performance, the structure is stable in the cycle process, the precipitated metal ions are few, the SEI film of the negative electrode cannot be damaged greatly, the surface defects of the active material of the negative electrode are more, the roughness is high, and the SEI film is easy to be damaged by the metal ions, so that the matched lithium iron phosphate positive active material can obtain better effect.

3. Preparation of the electrolyte

In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: EMC: DEC ═ 10: 30: 30: 30, then 2 percent of fluoroethylene carbonate and 2 percent of 1, 3-propane sultone are added, dissolved and fully stirred, and then lithium salt LiPF is added₆And mixing uniformly to obtain the electrolyte. Wherein LiPF₆The concentration of (2) is 1 mol/L.

4. Preparation of the separator

Polyethylene (PE) porous polymer films were used as separators.

5. Preparation of lithium ion battery

Stacking the obtained anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging foil aluminum-plastic film, injecting an electrolyte, and carrying out vacuum packaging, standing, formation and other process flows to obtain the lithium ion battery.

Second, testing method

Low-temperature discharge performance test of lithium ion battery

The low temperature discharge ratio test procedure is as follows:

(1) adjusting the furnace temperature to 25 ℃, and standing for 5 min; (2)0.5C DC to 2.5V;

(3) standing for 30 min; (4)0.2 CC to 3.6V, CV to 0.025C;

(5) standing for 10 min; (6)1.0C DC to 2.5V (reference capacity);

(7) standing for 10 min; (8)0.2 CC to 3.6V, CV to 0.025C;

(9) standing for 10 min; (10) adjusting the furnace temperature to 0 ℃, and standing for 60 min;

(11)1.0C DC to 2.5V; (12)0.2 CC to 3.6V, CV to 0.025C;

(13) standing for 10 min; (14)1.0C DC to 2.5V (0 ℃ discharge capacity);

(15) adjusting the furnace temperature to 25 ℃, and standing for 60 min; (16) and (5) finishing the test.

The discharge ratio at-10 ℃ of the lithium ion battery is (-10 ℃ discharge capacity/25 ℃ discharge capacity) × 100%).

Third, test results

Table 1 shows relevant performance parameters of the anode active materials in examples 1 to 12 and comparative examples 1 to 11 and performances of the corresponding batteries. In Table 1, examples 1 to 12 satisfy R1. gtoreq.R 2, and R1. gtoreq.0.20, and R2. ltoreq.0.35, while comparative examples 1 to 11 do not satisfy the above conditions. Wherein the first region is 1350cm^-1Peak intensity of_d1Relative to the reference point at 1575cm^-1Peak intensity of_g1The ratio of R1 to R1 is mainly influenced by the surface state of the graphitized semifinished product particles and the outer layer state of the finished product particles. The surface state of the particles of the finished product after ball milling can be changed by improving the mass ratio of the FeO fine powder, and the change of the addition ratio of the graphene also has an influence on the surface state of the outer layer of the finished product, and both the change and the influence on R1. When other conditions are consistent, the mass ratio of the FeO fine powder is improved from 0.3% to 1%, and the mass ratio of R1 is improved from 0.20 to 0.33. The mass ratio of the FeO fine powder is selected to be 0.7%, R1 is 0.33, on the basis, the amount of the added graphene powder is changed, R1 is also changed, and when the mass ratio of the graphene is increased from 0.2% to 0.7%, R1 is increased from 0.33 to 0.50. Placing the second region at 1350cm^-1Peak intensity of_d2Relative to the reference point at 1575cm^-1Peak intensity of_g2The ratio of R2 as R2 is mainly influenced by the degree of crystallinity of the graphitized semifinished particles, and R2 is smaller when the degree of crystallinity is high, and is larger conversely. The results of R2 can be varied by varying the graphitization temperature and varying the incubation time. The graphitization temperature is increased, the heat preservation time is prolonged, the graphitization degree of the particles is higher, and the crystallization is realizedHigher, defects are reduced and thus R2 is reduced, whereas R2 may be increased. When the holding time is kept constant (60 hours) and the graphitization temperature condition is increased from 2500 ℃ to 2800 ℃, R2 is reduced from 0.30 to 0.15. While maintaining the graphitization temperature at 2600 ℃, the incubation time was reduced from 60 hours to 36 hours and R2 was increased from 0.27 to 0.39. Table 1 shows the values of R1 and R2 controlled by controlling the ratio of FeO to graphene powder, graphitization temperature, and incubation time by the above method.

TABLE 1

Numbering	R1	R2	R1≥R2	Discharge ratio of-10 deg.C
					Example 1	0.20	0.11	Is that	82.6％
Example 2	0.22	0.12	Is that	82.8％
					Example 3	0.25	0.15	Is that	83.1％
Example 4	0.27	0.16	Is that	83.4％
					Example 5	0.31	0.18	Is that	83.5％
Example 6	0.33	0.20	Is that	83.3％
					Example 7	0.35	0.20	Is that	83.7％
Example 8	0.39	0.25	Is that	83.4％
					Example 9	0.43	0.28	Is that	83.9％
Example 10	0.46	0.30	Is that	83.7％
					Example 11	0.47	0.33	Is that	83.5％
Example 12	0.50	0.35	Is that	83.4％
					Comparative example 1	0.15	0.12	Is that	78.5％
Comparative example 2	0.18	0.13	Is that	77.5％
					Comparative example 3	0.17	0.22	Whether or not	76.8％
Comparative example 4	0.19	0.25	Whether or not	76.5％
					Comparative example 5	0.16	0.32	Whether or not	76.6％
Comparative example 6	0.17	0.35	Whether or not	76.3％
					Comparative example 7	0.24	0.33	Whether or not	76.7％
Comparative example 8	0.26	0.35	Whether or not	77.5％
					Comparative example 9	0.28	0.35	Whether or not	77.3％
Comparative example 10	0.45	0.42	Is that	77.8％
					Comparative example 11	0.47	0.44	Is that	77.5％

From table 1, it can be found that the batteries of examples 1 to 12 have good low-temperature discharge rate performance when the strength ratio of the Raman spectrum D peak to the G peak of the surface layer portion of the anode active material particles is larger than R1, and R1 is not less than R2, and R2 is not more than 0.35. The reason is that the atomic arrangement disorder degree of the surface layer is high, the number of lattice defects is large, the de-intercalation channels of lithium ions can be increased, the de-intercalation speed of the lithium ions is improved, the dynamic society of active materials is obviously improved, more electric quantity can be discharged during low-temperature discharge, and the low-temperature discharge multiplying power is improved. While comparative examples 1 to 11 are battery performances corresponding to the case where the active material does not satisfy the above conditions, it can be found that the low-temperature discharge rate performance is lowered. This is because when R1 is too small, lithium intercalation channels are insufficient in the surface layer of the active material, and rapid deintercalation of lithium ions cannot be achieved. When R1 is not more than R2, the internal defects of the active material are more, the lithium insertion bottleneck point of lithium ions is on the surface layer, and the low-temperature discharge rate cannot be fully exerted. In addition, when R2 is too large, it may result in a decrease in the compacted density and gram capacity of the active material, reducing the energy density of the battery. Therefore, when the active material meets the conditions that R1 is more than or equal to R2, R1 is more than or equal to 0.20, and R2 is less than or equal to 0.35, the battery matched with the active material can fully exert low-temperature discharge performance, and the low-temperature discharge rate is improved.

Table 2 shows relevant performance parameters of the negative electrode active materials of examples 13 to 17 and the corresponding performances of the batteries. Table 2 continuing to improve cell performance over example 9, to ensure a relatively narrow particle size distribution of the material, the difference between Dv99/Dv50 and Dv90/Dv50 for the active material was limited.

TABLE 2

Numbering	Dv99/Dv50	Dv90/Dv50	Dv99/Dv50-Dv90/Dv50	Discharge ratio of-10 deg.C
					Example 9	3.4	1.2	2.2	83.9％
Example 13	2.8	2.5	0.3	84.8％
					Example 14	3.1	2.2	0.9	85.2％
Examples15	3.4	2.1	1.3	85.4％
					Example 16	3.5	1.8	1.7	85.1％
Example 17	3.6	1.6	2.0	85.3％

From Table 2, it can be found that the-10 ℃ low-temperature discharge rate performance of examples 13 to 17 is improved compared with that of example 9 when Dv99/Dv50-Dv90/Dv50 is not more than 2.0. This is because the narrow particle size distribution of the active material avoids too many small particles and too many large particles. If the small particles are too large, the reactive sites of the active material and the electrolyte increase, consuming the electrolyte and causing a large number of side reactions, degrading the electrochemical properties such as storage and recycling. If the large particles are too large, the processability is reduced, and the surface of the negative electrode has bumps, which causes the consequences of lithium precipitation and the like, and reduces the battery performance. Therefore, the low-temperature rate performance of the battery can be improved by enabling the granularity of the active material to meet the Dv99/Dv50-Dv90/Dv50 ≤ 2.0.

Table 3 shows relevant performance parameters of the negative electrode active materials of examples 18 to 23 and the corresponding performances of the batteries. Table 3 to continue to improve the low-temperature discharge performance of the battery on the basis of example 15, in order to ensure that the degree of crystallization of the active material is in a suitable range, the relationship between the gram capacity C of the active material and the graphitization degree G is defined to be in a more suitable range.

TABLE 3

Numbering	G	C(mAh/g)	372×G-C	Discharge ratio of-10 deg.C
					Example 15	91.5％	339.2	1.2	85.4％
Example 18	91.2％	337.3	2.0	86.8％
					Example 19	92.5％	340.5	3.6	86.6％
Example 20	93.3％	342.5	4.6	86.5％
					Example 21	94.5％	345.8	5.7	86.1％
Example 22	95.6％	347.6	8.0	86.3％
					Example 23	95.4％	346.4	8.5	85.6％

It can be found from Table 3 that when 2.0. ltoreq. 372 XG-C. ltoreq.8.0 is satisfied, the low-temperature performance of the battery can be further improved, and the discharge rates at-10 ℃ in examples 18 to 22 are improved as compared with example 15. 372 xg-C may be used to represent the difference between the theoretical calculated capacity and the actual capacity of the active material, and when the difference is too small, the actual gram capacity exerts a high value, indicating that the active material has a high degree of crystallization, which is unfavorable for kinetics, and may degrade the low temperature discharge performance. As is clear from comparison of example 23 with examples 18 to 22, when the difference is too large, it is indicated that the capacity exertion of the active material is low, resulting in a low energy density of the battery, and thus the gram capacity C and the graphitization degree G defining the active material satisfy 2.0. ltoreq. 372 XG-C. ltoreq.8.0.

Table 4 shows relevant performance parameters of the negative electrode active materials of examples 24 to 32 and the corresponding performances of the batteries. Table 4 to continue to improve the low-temperature discharge performance of the battery on the basis of example 18, in order to secure the processability of the active material, Dv99 of the active material was defined within a suitable range. In order to secure electrochemical stability of the anode active material, the content of elemental sulfur S, which is an active material, is defined within a suitable range. In order to secure the energy density of the battery, the powder compaction density CD of the active material is defined within a suitable range.

TABLE 4

Numbering	Dv99	0.8THK	Content of S element (ppm)	CD(g/cm³)	Discharge ratio of-10 deg.C
						Example 18	54	51	155	1.70	86.8％
Example 24	32	38	132	1.70	87.5％
						Example 25	48	46	85	1.73	87.8％
Example 26	50	45	85	1.78	88.1％
						Example 27	42	56	122	1.78	88.4％
Example 28	50	65	126	1.83	88.3％
						Example 29	40	56	88	1.70	88.2％
Example 30	45	62	85	1.71	88.4％
						Example 31	38	45	30	1.76	89.0％
Example 32	43	53	36	1.85	89.6％

It can be found from table 4 that the-10 ℃ discharge rate performance of examples 24 to 32 is improved as compared with example 18 when none of examples 18 satisfies the above conditions. Wherein example 24 is an active material particle satisfying the condition that Dv99 is 0.8THK is 65 μm or less and the content ratio of S is 100ppm or less and CD is 1.72g/cm or more³In the case of (2), it was found that the low-temperature rate was improved because the material processing was difficult due to the large Dv99, and the negative electrode surface had abnormalities such as a projection, and the thinner the negative electrode active material layer was, the more remarkable the reduction was. In addition, too large a Dv99 also deteriorates filterability of the slurry, affecting production efficiency, and hence Dv 99. ltoreq.0.8 THK. ltoreq.65 μm is defined. Examples 25 and 26 are active materials satisfying Dv 99. ltoreq.0.8 THK.ltoreq.65 μm and satisfying the content ratio of S.ltoreq.100 ppm and CD.gtoreq.1.72 g/cm³In the case of (2), it was found that the discharge rate was improved at-10 ℃ compared with that of example 18, because the S element in the active material is an impurity element which occurs with the electrolyteSide reaction, which produces some by-products, reduces the storage performance and discharge performance of the battery, generates gas, reduces circulation and causes the performance reduction of the battery, thereby limiting the content proportion of sulfur element S of the active material to be less than or equal to 100 ppm. The compacted density of the active material is in positive correlation with the compacted density of the negative electrode, and the greater the compacted density of the powder of the active material is, the higher the compacted density of the negative electrode can be, which is beneficial to improving the energy density of the battery. When the active powder compaction is too low, the negative electrode tends to develop an overpressure, reducing kinetics, thus defining a CD ≥ 1.72, given in g/cm³. Examples 27 and 28 satisfy the discharge performance at Dv 99. ltoreq.0.8 THK. ltoreq.65 and CD. ltoreq.1.72, but do not satisfy the content ratio of S. ltoreq.100 ppm, examples 29 and 30 satisfy the discharge performance at Dv 99. ltoreq.0.8 THK. ltoreq.65 μm, and the content ratio of S. ltoreq.100 ppm, but do not satisfy the CD. ltoreq.1.72 g/cm³The discharge performance of the process is found to be improved compared with the discharge rate of the example 18 at minus 10 ℃. Examples 31 and 32 are the-10 ℃ discharge rate of the battery when all three conditions are met, and it can be seen that the-10 ℃ discharge rate performance of the battery performs best when all three conditions are met.

Table 5 shows relevant performance parameters of the negative electrode active materials of examples 33 to 50 and the corresponding battery performances. Table 5 to continue to improve the low-temperature discharge performance of the battery on the basis of example 32, the particle sphericity ratio of the active material is defined in order to secure the porosity and the compacted density of the negative electrode. In order to guarantee the electrochemical properties of the battery, such as storage, the specific surface area BET of the active material is defined. In order to ensure the kinetics of the active material, the particle OI value and the negative electrode compaction density PD of the active material are defined.

TABLE 5

Examples	S50	BET(m²/g)	OI value	PD(g/cm³)	Discharge ratio of-10 deg.C
						Example 32	0.53	2.7	8	1.78	89.6％
Example 33	0.55	1.6	5	1.60	90.9％
						Example 34	0.56	1.8	6	1.65	90.8％
Example 35	0.65	2.7	5	1.62	90.6％
						Example 36	0.73	2.9	5	1.62	90.7％
Example 37	0.66	1.6	8	1.67	90.6％
						Example 38	0.67	1.8	9	1.68	90.6％
Example 39	0.78	1.7	4	1.78	90.8％
						Example 40	0.82	1.7	5	1.79	90.7％
EXAMPLE 41	0.50	2.7	5	1.65	90.2％
						Example 42	0.55	3.1	5	1.70	90.1％
Example 43	0.66	2.8	8	1.68	90.3％
						Example 44	0.80	2.8	9	1.65	90.4％
Example 45	0.70	1.5	8	1.76	90.4％
						Example 46	0.86	1.8	8	1.78	90.5％
Example 47	0.60	1.6	4	1.45	91.2％
						Example 48	0.75	1.7	5	1.56	91.6％
Example 49	0.82	2.0	6	1.68	91.8％
						Example 50	0.90	2.5	7	1.75	91.3％

It can be seen from table 5 that, when none of examples 32 satisfies the above conditions, the-10 ℃ discharge rate is 89.2%, and the-10 ℃ discharge rate performance of examples 33 to 50 is improved. Examples 33 to 46 are discharge performances when at least one of the parameters does not satisfy the above conditions, and it can be found that the discharge rate at-10 ℃ is advantageous as compared with example 32. Examples 47 to 50 are examples each satisfying the above conditions, and it can be found that the low-temperature discharge performance of the battery is best exhibited when all four parameters are satisfied. This is because all of the above four conditions have an influence on the low-temperature discharge performance of the battery, and an appropriate parameter range promotes the exertion of the battery performance. The sphericity of the particles affects the arrangement of the particles in the negative electrode, which affects the porosity and compacted density of the negative electrode. Too close arrangement can reduce the porosity of the negative electrode, and the electrolyte is difficult to fully infiltrate, thereby reducing the dynamics of the battery and the low-temperature discharge rate performance. Too loose arrangement results in low compacted density of the negative electrode and weak adhesion of the negative electrode, which not only affects the capacity density of the battery but also may cause the active material to fall off from the negative electrode, reducing the performance of the battery. The active material BET reflects the surface state of the material, is larger, has higher surface reaction activity, is easy to reflect with an electrolyte, slightly reduces the storage performance, and severely reduces the performance of the whole battery. The particle OI value represents the degree of crystal orientation of the particle, and the higher the degree of orientation, the larger the OI value, the lithium ions can enter and exit the active material from only a single direction, which is not favorable for the deintercalation of lithium ions. When the OI value is low, the uniformity of the crystal orientation degree is low, lithium ions can be de-embedded in all directions of the active material, the improvement of material dynamics is facilitated, and the low-temperature discharge performance of the battery is further improved. Too high a cathode compaction can reduce low temperature kinetics and affect discharge rate, and too low a cathode compaction can cause the active material to fall from the cathode and affect battery stability.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An anode material comprising anode active particles, wherein the anode active particles comprise:

a first region including a region extending 0 μm to 0.5 μm from an intersection point of a diameter of a circumscribed circle of a cross-section of the anode active particle and a boundary of the cross-section toward a center of the circumscribed circle;

a second region including a concentric circle of the circumscribed circle, the radius of the concentric circle being less than or equal to 0.5 μm;

in the Raman spectrum of the negative active particle, the first region is 1350cm^-1Peak intensity of_d1Relative to the reference point at 1575cm^-1Peak intensity of_g1The ratio of the first region to the second region was set to R1, and the second region was set to 1350cm^-1Peak intensity of_d2Relative to the reference point at 1575cm^-1Peak intensity of_g2When the ratio of R2 is defined as R2, the negative electrode material satisfies:

r1 is more than or equal to R2, R1 is more than or equal to 0.2, and R2 is less than or equal to 0.35.

2. The anode material according to claim 1, wherein a particle size distribution of the anode active particles satisfies the following relationship:

Dv99/Dv50-Dv90/Dv50≤2.0；

wherein Dv99, Dv50, Dv90 and Dv50 are in μm.

3. The anode material according to claim 1, wherein the anode active particles satisfy the following relationship:

2.0≤372×G-C≤8.0；

wherein C is a gram capacity of the negative active particles in mAh/G, and G is a graphitization degree of the negative active particles.

4. The negative electrode material according to claim 1, wherein the negative electrode active particles have a sphericity ratio satisfying: s50 ranges from 0.6 to 0.9;

wherein S50 represents the shape factor value corresponding to a cumulative particle volume content of 50%.

5. The negative electrode material as claimed in claim 1, wherein the negative electrode active particles have an OI value satisfying: OI is less than or equal to 7.0;

wherein OI is the ratio of the peak area C004 of the 004 surface and the peak area C110 of the 110 surface of the negative electrode active particle measured by an X-ray diffraction spectrum.

6. The anode material according to any one of claims 1 to 5, characterized in that the anode active particles satisfy at least one of conditions (a) to (e):

(a) the compacted density CD of the negative active particles is more than or equal to 1.72, and the unit of the CD is g/cm³；

(b) The specific surface area BET of the negative active particles is less than or equal to 2.5m²In units of m,/g, BET²/g；

(c) The OI value of the negative active particles and the specific surface area BET of the negative active particles are satisfied, the OI is less than or equal to 5 multiplied by the BET, and the unit of the BET is m²/g；

(d) The mass content of sulfur element in the negative active particles is less than or equal to 100 ppm;

(e) the negative active particles include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon.

7. An electrochemical device comprising a negative electrode, characterized in that the negative electrode comprises a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material according to any one of claims 1 to 6.

8. The electrochemical device according to claim 7, wherein Dv99 of the anode active particle and a thickness THK of the anode active material layer satisfy the following relationship:

Dv99≤0.8THK≤65；

where THK is expressed in μm.

9. The electrochemical device according to claim 7 or 8, wherein the compacted density PD of the negative electrode satisfies: 1.45 or more and PD or less than 1.75, and the PD and the compacted density CD of the negative electrode active particles satisfy: PD is less than or equal to CD-0.9, CThe units of D and PD are both g/cm³。

10. An electronic device comprising the electrochemical device according to any one of claims 7 to 9.