Negative active material, electrochemical device, and electronic device

Abstract

The present application relates to a kind of negative electrode active material and the electrochemical device and electronic device comprising the negative electrode active material of this application.The negative electrode active material of the present application includes graphite and amorphous carbon, wherein, by Raman test, the negative electrode active material satisfies:1.6≤W D / W G ≤2.6, wherein, W D It is the half-peak width of D peak in 1340cm ‑1 -1370cm ‑1 In Raman spectrum, 40cm ‑1 ≤W D ≤100cm ‑1 , W G It is the half-peak width of G peak in 1570cm ‑1 -1590cm ‑1 In Raman spectrum, 15cm ‑1 ≤W G ≤50cm ‑1 .The negative electrode active material of the present application is surface treated, and its surface has higher surface lattice defect degree, can effectively improve its gram capacity and dynamics performance, to make the electrochemical device comprising the negative electrode active material have high energy density and electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to a negative electrode active material and an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Electrochemical devices (e.g., lithium ion batteries) are widely used due to their environmental friendliness, high working voltage, large specific capacity, and long cycle life, and have become the most promising new green chemical power source in the world. In recent years, medium and large size lithium ion batteries with high output characteristics have been developed and applied in electric vehicles (EV) and large-scale energy storage systems (ESS). With the wide application of lithium ion batteries, the range anxiety is gradually highlighted, and the improvement of energy density has become a key technical problem to be solved. Improving the active material in the electrode is one of the research directions to solve the above problems.

[0003] In the prior art, the specific capacity of the negative electrode material is improved by improving the graphitization degree of artificial graphite or using natural graphite to improve the energy density of the electrode assembly, but this will seriously affect the cycle performance, resulting in a trade-off between the two, and it is difficult to balance the overall performance of the lithium ion battery. SUMMARY

[0004] The present application provides a negative electrode active material, an electrochemical device and an electronic device comprising the same, in an attempt to solve at least one problem existing in the related art to at least some extent.

[0005] In a first aspect, the present application provides a negative electrode active material comprising graphite and amorphous carbon, wherein the negative electrode active material satisfies 1.6 ≤ W D / W G ≤ 2.6 by Raman test, wherein W D is the half-peak width of the D peak in the range of 1340 cm -1 to 1370 cm -1 , 40 cm -1 ≤ W D ≤ 100 cm -1 , W G is the half-peak width of the G peak in the range of 1570 cm -1 to 1590 cm -1 , 15 cm -1 ≤ W G ≤ 50 cm -1 . In the present application, the half-peak width of the D peak represents the surface grain size of the negative electrode active material, mainly reflecting the degree of defects of the surface lattice. The half-peak width of the G peak represents the crystallinity of the negative electrode active material. W D / W GWhen within the above range, the surface lattice defect degree of the negative electrode active material is large, and such surface lattice defects are beneficial to the rapid intercalation of active ions, thereby being able to improve the kinetic performance of the negative electrode active material; more importantly, such surface lattice defects are also able to store more active ions, thereby improving the gravimetric capacity of the negative electrode active material. In some embodiments, 1.7≤W D / W G ≤ 2.5. In some embodiments, 2≤W D / W G ≤2.5.

[0006] In some embodiments, 40 cm -1 ≤W D ≤60 cm -1 . In some embodiments, 15 cm -1 ≤W G ≤35 cm -1 .

[0007] In some embodiments, the negative electrode active material satisfies: 0.08≤ID / IG≤1.2, where ID is the intensity of the D peak, and IG is the intensity of the G peak. The ID / IG ratio can represent the crystal defect degree of the negative electrode active material, and the larger the value, the higher the defect degree. A high defect degree can increase the deintercalation channel of active ions, improve the deintercalation speed of active ions, and thereby improve the kinetic performance of the negative electrode active material. However, too many defects can cause the first coulombic efficiency, cycle, storage, and other performances of the electrochemical device to decrease. When the ID / IG ratio is within the above range, the electrochemical device can exhibit good kinetics, and its first coulombic efficiency cycle and other performances will not be significantly reduced. In some embodiments, 0.1≤ID / IG≤1.0.

[0008] In some embodiments, the specific surface area of the negative electrode active material is B1, where 0.8 cm 2 / g≤B1≤5.4 cm 2 / g. The smaller the specific surface area of the negative electrode active material, the smaller the area thereof in contact with the electrolyte, thereby reducing the active ions consumed by the electrochemical device when forming the SEI film for the first time, and increasing the first coulombic efficiency. However, when the specific surface area is too small, electrolyte infiltration and active diffusion become difficult, thereby affecting the kinetic performance of the electrochemical device. In some embodiments, 1.0 cm 2 / g≤B1≤4.5 cm 2 / g.

[0009] In some embodiments, the negative active material comprises basal planes and end planes, wherein the specific surface area of the basal planes accounts for 40% to 70% of the specific surface area of the negative active material. Lithium ions are mainly embedded in the interior through the end planes of graphite and some defect sites, and the electrolyte mainly reacts with graphite on the end planes to form SEI films; the higher the specific surface area of the basal planes, the fewer the side reactions, which can improve the first coulombic efficiency and cycle stability of the electrochemical device; but too high a proportion of basal planes will affect the kinetic performance. When the proportion of basal planes is within the above range, the electrochemical device can exhibit good first coulombic efficiency and cycle performance, and also take into account the kinetic performance. In some embodiments, the specific surface area of the basal planes accounts for 45% to 65% of the specific surface area of the negative active material.

[0010] In some embodiments, the negative active material comprises basal planes and end planes, wherein the roughness of the end planes is greater than the roughness of the basal planes.

[0011] In some embodiments, the most probable pore diameter of the negative active material is 2.5 nm to 3.5 nm. The most probable pore diameter of the negative active material represents the pore diameter at which the pore volume has the maximum change rate, i.e., the pore diameter corresponding to the strongest peak on the pore diameter-pore volume differential curve is called the most probable pore diameter. The most probable pore diameter of the negative active material in the present application is within the above range, which can store lithium to increase capacity on the one hand, and serve as a lithium intercalation channel to improve kinetic performance on the other hand; too large a pore diameter will lead to an increase in side reactions. In some embodiments, the most probable pore diameter of the negative active material is 2.7 nm to 3.3 nm.

[0012] In some embodiments, the pore volume of the most probable pore diameter of the negative active material accounts for 3% to 8% of the pore volume of the negative active material. In some embodiments, the pore volume of the most probable pore diameter of the negative active material accounts for 3.5% to 7% of the pore volume of the negative active material.

[0013] In some embodiments, the specific surface area of the negative active material after applying a pressure of 1 t is B2, wherein (B2-B1) / B1x100%≤80%. The specific surface area of the negative active material before and after applying pressure satisfies the above relationship, which indicates that the structure of the negative active material is stable, which is beneficial to improving the expansion performance of the electrochemical device during the cycle process.

[0014] In some embodiments, the mass content of oxygen element in the negative electrode active material is 2% to 5% by X-ray photoelectron spectroscopy. The surface oxygen element content can reflect the degree of surface lattice defects of the negative electrode active material to some extent. When the surface oxygen element content is too low, the surface does not form sufficient defects, which has no improvement effect on the specific capacity and kinetic performance of the material. When the surface oxygen element content is too high, the defects are too many, which leads to a decrease in the first coulombic efficiency and an increase in electrolyte consumption. When the oxygen element content is in the above range, the negative electrode active material has a suitable degree of surface crystal defects, which can exert the best improvement effect on the specific capacity and kinetics without affecting other performances. In some embodiments, the mass content of oxygen element in the negative electrode active material is 2.2% to 4.0%.

[0015] In some embodiments, the tap density of the negative electrode active material is 0.90 g / cm 3 to 1.05 g / cm 3 . In some embodiments, the 5t powder compaction density of the negative electrode active material is 1.9 g / cm 3 to 2.05 g / cm 3 . The increase in the powder compaction density enables the negative electrode active material to be used in the design of high compaction density electrode sheets, thereby improving the volumetric energy density of the electrochemical device. However, when the compaction density is too large, the interlayer slip of the negative electrode active material is too easy, the material becomes soft, the rebound of the electrode sheet is reduced, the pores formed by the internal particle accumulation are reduced, and thus the electrolyte infiltration and active ion diffusion become difficult, thereby affecting the performance of the electrochemical device.

[0016] In some embodiments, the preparation method of the negative electrode active material comprises the following steps:

[0017] S1: providing a graphite material;

[0018] S2: mixing the graphite material in S1 with a carbonaceous precursor to obtain a graphite material coated with a carbonaceous precursor;

[0019] S3: mixing the graphite material coated with a carbonaceous precursor in S2 with a bicarbonate salt to obtain a mixture, and heat-treating the mixture to obtain the negative electrode active material.

[0020] The preparation method of the negative electrode active material of the present application first coats a layer of carbonaceous precursor on the surface of the graphite material, which makes the subsequent reaction with gas easier. Secondly, a solid that can generate an oxidizing atmosphere by heat decomposition is selected to be mixed with the graphite material, which makes the oxidation reaction on the surface of the graphite more uniform and controllable. The obtained negative electrode active material has a moderate degree of surface oxidation, and has high specific capacity and excellent kinetic performance.

[0021] In a second aspect, the present application provides an electrochemical device, comprising a negative electrode, the negative electrode comprising 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 comprises the negative electrode active material of the first aspect.

[0022] In some embodiments, the specific surface area of the negative electrode active material is 4.35 cm 2 / g to 5.9 cm 2 / g.

[0023] In some embodiments, the reversible capacity of the coin cell composed of the negative electrode and lithium metal between 0.005 V and 2 V is C1 mAh / g, and the reversible capacity between 0 V and 2 V is C2 mAh / g, wherein C2-C1≥1.

[0024] In a third aspect, the present application provides an electronic device comprising the electrochemical device of the second aspect.

[0025] The present application can improve the kinetic performance of the negative electrode active material by oxidizing the surface of the negative electrode active material, which is beneficial to the rapid intercalation of active ions, can improve the kinetic performance of the negative electrode active material, can store more active ions, and improve the gravimetric capacity of the negative electrode active material, and thus the electrochemical device comprising the negative electrode active material has high energy density and electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] The drawings necessary for describing the embodiments of the present application or the prior art will be briefly described in the following in order to facilitate the description of the embodiments of the present application. Obviously, the drawings in the following description are only part of the embodiments in the present application. Other drawings of embodiments can still be obtained from the structures illustrated in these drawings without creative labor for those skilled in the art.

[0027] Figure 1 Raman spectra of the negative electrode active materials of the present application Example 9 and Comparative Example 1 are shown.

[0028] Figure 2 Pore size-pore volume differential curves of the negative electrode active materials of the present application Example 9 and Comparative Example 1 are shown.

[0029] Figure 3 SEM images of the negative electrode active material of the present application Example 9 are shown. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail in the following. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0031] 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 taken as a literal disclosure of each distinct endpoint in the range. To make clear that a range format is literal, the term "about" can be used with the range.

[0032] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "at least one of" or "one or more of" can mean any single one of the items in the list, or combinations of any of the items in the list. For example, if the list consists of A and B, then "at least one of A and B" means A alone, B alone, or A and B together. In another example, if the list consists of A, B, and C, then "at least one of A, B, and C" means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together. The item A can include an individual element or a plurality of elements. The item B can include an individual element or a plurality of elements. The item C can include an individual element or a plurality of elements.

[0033] I. Negative active material

[0034] The negative active material provided in the present application comprises graphite and amorphous carbon, wherein the negative active material satisfies 1.6≤W D / W G ≤2.6 by Raman test, wherein W D is a half-peak width of a D peak in a range of 1340 cm -1 to 1370 cm -1 , 40 cm -1 ≤W D ≤100 cm -1 , W G is a half-peak width of a G peak in a range of 1570 cm -1 to 1590 cm -1 , 15 cm -1 ≤W G ≤50 cm -1 . In the present application, the half-peak width of the D peak represents the surface grain size of the negative active material, and mainly reflects the defect degree of the surface lattice thereof. The half-peak width of the G peak represents the crystallinity of the negative active material. When W D / W G is within the above range, the surface lattice defect degree of the negative active material is large, and such surface lattice defect is beneficial to the rapid intercalation of active ions, thereby being capable of improving the kinetic performance of the negative active material. More importantly, such surface lattice defect is also capable of storing more active ions, thereby improving the gravimetric capacity of the negative active material. In some embodiments, W D / WG 1.65, 1.75, 1.85, 1.9, 1.95, 2.0, 2.05, 2.15, 2.25, 2.35, 2.45, 2.55, or a range of any two of these values. In some embodiments, 1.7 < W D / W G 2.5. In some embodiments, 2 < W D / W G 2.5.

[0035] In some embodiments, W D 42 cm -1 , 44 cm -1 , 46 cm -1 , 48 cm -1 , 50 cm -1 , 52 cm -1 , 54 cm -1 , 56 cm -1 , 58 cm -1 , 60 cm -1 , 65 cm -1 , 70 cm -1 , 75 cm -1 , 80 cm -1 , 85 cm -1 , 90 cm -1 , 95 cm -1 , or a range of any two of these values. In some embodiments, 40 cm -1 < W D < 60 cm -1 . W D Too high indicates that the material surface has too small grains, too many defects, leading to too many side reactions, and low first coulombic efficiency of the electrochemical device; too low indicates that the material surface treatment is not sufficient, and there are not enough defects to store lithium to enhance capacity, and the kinetics cannot be improved.

[0036] In some embodiments, W G 16 cm -1 , 17 cm -1 , 18 cm -1 , 19 cm -1 , 20 cm -1 , 21 cm -1 , 22 cm -1 , 23 cm -1 , 24 cm -1 , 25 cm -1 , 26 cm -1 , 27 cm -1 , 28 cm -1 , 29 cm-1 30 cm -1 31 cm -1 32 cm -1 33 cm -1 34 cm -1 37 cm -1 40 cm -1 43 cm -1 45 cm -1 47 cm -1 or a range consisting of any two of these values. In some embodiments, 15 cm -1 ≤ W G ≤ 35 cm -1 . W G too high indicates that the material has poor crystallinity, and the crystal structure is severely damaged, resulting in a significant decrease in the initial coulombic efficiency, and a decrease in the lithium storage sites between the active material layers, and a decrease in capacity; too low indicates that the material has good crystallinity and high graphitization, high capacity and high initial coulombic efficiency, but poor kinetics, and the electrochemical device is unstable during high-temperature cycling.

[0037] In some embodiments, the negative electrode active material satisfies: 0.08≤ID / IG≤1.2, wherein ID is the intensity of the D peak, and IG is the intensity of the G peak. The ID / IG ratio can represent the degree of crystal defects of the negative electrode active material, and the larger the value, the higher the degree of defects. A high degree of defects can increase the deintercalation channel of active ions and improve the deintercalation speed of active ions, thereby improving the kinetic performance of the negative electrode active material. However, too many defects can result in a decrease in the performance of the electrochemical device, such as the initial coulombic efficiency, cycle, and storage. When the ID / IG ratio is within the above range, the electrochemical device can exhibit good kinetics, and its initial coulombic efficiency, cycle, and other performances will not be significantly reduced. In some embodiments, ID / IG is 0.09, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, or a range consisting of any two of these values. In some embodiments, 0.1≤ID / IG≤1.0.

[0038] In some embodiments, the specific surface area of the negative electrode active material is B1, wherein 0.8 cm 2 / g≤B1≤5.4 cm 2 / g. The smaller the specific surface area of the negative active material, the smaller the area of the negative active material in contact with the electrolyte, thereby reducing the active ions consumed by the electrochemical device when forming the SEI film for the first time, and increasing the first coulombic efficiency. However, when the specific surface area is too small, the electrolyte infiltration and active diffusion become difficult, thereby affecting the kinetic performance of the electrochemical device. In some embodiments, B1 is 0.9 cm 2 / g, 1.1 cm 2 / g, 1.3 cm 2 / g, 1.5 cm 2 / g, 1.7 cm 2 / g, 2.0 cm 2 / g, 2.3 cm 2 / g, 2.5 cm 2 / g, 2.7 cm 2 / g, 3.0 cm 2 / g, 3.3 cm 2 / g, 3.5 cm 2 / g, 3.7 cm 2 / g, 4.0 cm 2 / g, 4.3 cm 2 / g, 4.7 cm 2 / g, 4.9 cm 2 / g, or a range consisting of any two of these values. In some embodiments, 1.0 cm 2 / g≤ B1≤ 4.5 cm 2 / g.

[0039] In some embodiments, the negative active material includes a base surface and an end surface, wherein the specific surface area of the base surface accounts for 40% to 70% of the specific surface area of the negative active material. The higher the specific surface area of the base surface, the fewer the side reactions, and the first coulombic efficiency and cycle stability of the electrochemical device can be improved; but when the proportion of the base surface is too high, the kinetic performance is affected. When the proportion of the base surface is within the above range, the electrochemical device can exhibit good first coulombic efficiency and cycle performance, and also take into account the kinetic performance. In some embodiments, the specific surface area of the base surface accounts for 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, or a range consisting of any two of these values, of the specific surface area of the negative active material. In some embodiments, the specific surface area of the base surface accounts for 45% to 65% of the specific surface area of the negative active material.

[0040] In some embodiments, the negative active material includes a base surface and an end surface, wherein the roughness of the end surface is greater than the roughness of the base surface. In some embodiments, as shown in FIG. 1, the roughness of the end surface (left side) of the negative active material is greater than the roughness of the base surface (right side). Figure 3 In some embodiments, the negative active material includes a base surface and an end surface, wherein the roughness of the end surface is greater than the roughness of the base surface. In some embodiments, as shown in FIG. 1, the roughness of the end surface (left side) of the negative active material is greater than the roughness of the base surface (right side).

[0041] In some embodiments, the most probable pore diameter of the negative active material is 2.5 nm to 3.5 nm. The most probable pore diameter of the negative active material represents the pore diameter at which the pore volume has the largest change rate with respect to the pore diameter. The most probable pore diameter of the negative active material of the present application is in the above range, which on the one hand can store lithium to increase the capacity, and on the other hand can serve as a lithium intercalation channel to improve the kinetic performance; a too large pore diameter will lead to an increase in side reactions. In some embodiments, the most probable pore diameter of the negative active material is 2.55 nm, 2.6 nm, 2.65 nm, 2.7 nm, 2.75 nm, 2.8 nm, 2.85 nm, 2.9 nm, 2.95 nm, 3.0 nm, 3.05 nm, 3.1 nm, 3.15 nm, 3.2 nm, 3.25 nm, 3.3 nm, 3.35 nm, 3.4 nm, 3.45 nm, or a range consisting of any two of these values. In some embodiments, the most probable pore diameter of the negative active material is 2.7 nm to 3.3 nm.

[0042] In some embodiments, the pore volume of the most probable pore diameter of the negative active material accounts for 3% to 8% of the pore volume of the negative active material. In some embodiments, the pore volume of the most probable pore diameter of the negative active material accounts for 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, or a range consisting of any two of these values, of the pore volume of the negative active material. In some embodiments, the pore volume of the most probable pore diameter of the negative active material accounts for 3.5% to 7% of the pore volume of the negative active material.

[0043] In some embodiments, the specific surface area of the negative active material after applying a pressure of 1 t is B2, wherein (B2-B1) / B1x100%≤80%. The specific surface area of the negative active material before and after applying the pressure satisfies the above relationship, which indicates that the structure of the negative active material is stable, and is beneficial to improving the expansion performance of the electrochemical device during the cycle process. In some embodiments, 10%≤(B2-B1) / B1x100%≤80%. In some embodiments, (B2-B1) / B1x100% is 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a range consisting of any two of these values.

[0044] In some embodiments, 4.0 cm 2 / g≤B2≤6.0 cm 2 / g. In some embodiments, B1 is 4.1 cm 2 / g, 4.3 cm 2 / g, 4.5 cm 2 / g, 4.7 cm 2 / g, 5.0 cm2 / g, 5.3 cm 2 / g, 5.5 cm 2 / g, 5.7 cm 2 / g, or a range consisting of any two of these values. In this application, B2 is the specific surface area after applying 1 t of pressure to the negative active material. The method of applying pressure to the negative active material is as follows: using an electronic pressure testing machine (SANS Longitudinal UTM7305), 1.0 ± 0.05 g of negative active material powder is placed on a mold with a diameter of 13 mm, 1 t of pressure is applied to the negative active material powder and maintained for 5 s, and after the pressure is released, the powder is removed.

[0045] In some embodiments, the mass content of oxygen element in the negative active material is 2% to 5% by X-ray photoelectron spectroscopy. The surface oxygen element content can reflect the degree of surface lattice defects of the negative active material to some extent. When the surface oxygen element content is too low, the surface does not form sufficient defects, and there is no improvement effect on the specific capacity and kinetic performance of the material. When the surface oxygen element content is too high, the defects are too many, which leads to a decrease in the first coulombic efficiency and an increase in electrolyte consumption. When the oxygen element content is in the above range, the negative active material has a suitable degree of surface crystal defects, which can exert the best improvement effect on the specific capacity and kinetics without affecting other performances. In some embodiments, the mass content of oxygen element in the negative active material is 2.1%, 2.3%, 2.5%, 2.7%, 3.0%, 3.3%, 3.5%, 3.7%, 3.9%, 4.3%, 4.5%, 4.7%, or a range consisting of any two of these values. In some embodiments, the mass content of oxygen element in the negative active material is 2.2% to 4.0%.

[0046] In some embodiments, the tap density of the negative active material is 0.90 g / cm 3 to 1.05 g / cm 3 . In some embodiments, the tap density of the negative active material is 0.90 g / cm 3 , 0.91 g / cm 3 , 0.92 g / cm 3 , 0.93 g / cm 3 , 0.95 g / cm 3 , 0.96 g / cm 3 , 0.97 g / cm 3 , 0.98 g / cm 3 , 0.99 g / cm 3 , 1.00 g / cm 3 , 1.01 g / cm 3 , 1.02 g / cm 3 , 1.03 g / cm3 1.04 g / cm3 3 or a range consisting of any two of these values.

[0047] In some embodiments, the 5t tap density of the negative electrode active material is 1.9 g / cm3 3 to 2.05 g / cm3 3 The tap density of the negative electrode active material is increased, and the negative electrode active material can be used for the design of high tap density electrode sheets, thereby improving the volumetric energy density of the electrochemical device. However, when the tap density is too large, the interlayer slip of the negative electrode active material is too easy, the material becomes soft, the rebound of the electrode sheet is reduced, the pores formed by the internal particle accumulation are reduced, and then the electrolyte infiltration and active ion diffusion become difficult, thereby affecting the performance of the electrochemical device. In some embodiments, the 5t tap density of the negative electrode active material is 1.90 g / cm3 3 1.92 g / cm3 3 1.93 g / cm3 3 1.94 g / cm3 3 1.96 g / cm3 3 1.97 g / cm3 3 1.98 g / cm3 3 1.99 g / cm3 3 2.01 g / cm3 3 2.02 g / cm3 3 2.03 g / cm3 3 2.04 g / cm3 3 or a range consisting of any two of these values.

[0048] In some embodiments, the method for preparing the negative electrode active material comprises the following steps:

[0049] S1: providing a graphite material;

[0050] S2: mixing the graphite material in S1 with a carbonaceous precursor to obtain a graphite material coated with the carbonaceous precursor;

[0051] S3: mixing the graphite material coated with the carbonaceous precursor in S2 with a bicarbonate salt to obtain a mixture, and heat treating the mixture to obtain the negative electrode active material.

[0052] The method for preparing the negative electrode active material of the present application first coats a layer of carbonaceous precursor on the surface of the graphite material, making it easier for subsequent reaction with gas; secondly, a solid that can generate an oxidizing atmosphere upon heating is selected to be mixed with the graphite material, making the oxidation reaction on the surface of the graphite more uniform and controllable, and the obtained negative electrode active material has a moderate degree of surface oxidation, and has high gravimetric capacity and excellent kinetic performance.

[0053] In some embodiments, the providing the graphite material in S1 comprises the following steps: mixing a graphite precursor with a binder to obtain a first mixture, performing a first heat treatment on the first mixture to obtain a graphite material precursor; performing a graphitization treatment on the graphite material precursor to obtain the graphite material.

[0054] In some embodiments, the graphite precursor is selected from at least one of coal tar pitch, coal-derived heavy oil, atmospheric residue, petroleum-derived heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenyl, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenyl ether, furfuryl alcohol resin, phenol formaldehyde resin, imide resin, and the like organic matter. In some embodiments, the graphite precursor is selected from at least one of petroleum coke or pitch coke. In some embodiments, the binder is selected from at least one of pitch, resin, or tar. In some embodiments, the binder is selected from high-temperature pitch. In some embodiments, the high-temperature pitch has a softening point of 200-250 °C, for example, 210 °C, 220 °C, or 240 °C. In some embodiments, the ratio of the graphite precursor to the binder is 1:(0.1-1), for example, 1:0.1, 1:0.2, 1:0.2, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or 1:0.9.

[0055] In some embodiments, the temperature of the first heat treatment is 450-550 °C, for example, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, or 540 °C. In some embodiments, the time of the first heat treatment is 1-5 h, for example, 2 h, 3 h, or 4 h. In some embodiments, the temperature of the graphitization treatment is 2500-3200 °C, for example, 2600 °C, 2700 °C, 2800 °C, 2900 °C, 3000 °C, or 3100 °C. In some embodiments, the time of the graphitization treatment is 10-200 h, for example, 20 h, 40 h, 60 h, 80 h, 100 h, 120 h, 140 h, 160 h, or 180 h.

[0056] In some embodiments, in S2, the carbonaceous precursor is selected from at least one of pitch, resin, or coal tar. In some embodiments, the pitch is selected from at least one of coal tar, tar light oil, tar middle oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, heavy oil. In some embodiments, the resin is selected from at least one of thermoplastic resin such as polyvinyl alcohol, polyacrylic acid, and thermosetting resin such as phenol formaldehyde resin, furan resin. In some embodiments, the pitch has a softening point of 40-90 °C, for example, 50 °C, 60 °C, 70 °C, or 80 °C.

[0057] In some embodiments, the temperature in S2 is from 50°C to 100°C, for example 60°C, 70°C, 80°C or 90°C. In some embodiments, in S2, the mass content of the carbonaceous precursor is from 0.1% to 15%, for example 1%, 3%, 5%, 7%, 9%, 10%, 12% or 14%, based on the mass of the graphitic material.

[0058] In some embodiments, in S3, the bicarbonate salt is selected from ammonium bicarbonate and / or sodium bicarbonate. In some embodiments, in S3, the mass content of the bicarbonate salt is from 0.5% to 15%, for example 1%, 3%, 5%, 7%, 9%, 10%, 12% or 14%, based on the mass of the graphitic material coated with the carbonaceous precursor. In some embodiments, the temperature of the heat treatment in S3 is from 50°C to 1000°C, for example 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 650°C, 700°C, 800°C or 900°C. In some embodiments, the time of the heat treatment in S3 is from 4h to 10h, for example 5h, 6h, 7h, 8h or 9h. In some embodiments, the heat treatment in S3 is carried out in an inert atmosphere, for example in nitrogen or argon.

[0059] II. Electrochemical devices

[0060] The electrochemical device of the present application comprises a negative electrode comprising 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 comprises the negative electrode active material of the first aspect.

[0061] In some embodiments, the specific surface area of the negative electrode active material is from 4.35 cm 2 / g to 5.9 cm 2 / g. In some embodiments, the specific surface area of the negative electrode active material is from 4.5 cm 2 / g, 4.7 cm 2 / g, 5.0 cm 2 / g, 5.3 cm 2 / g, 5.5 cm 2 / g, 5.7 cm 2 / g or a range defined by any two of these values. In the present application, the specific surface area of the negative electrode active material in the electrochemical device is the specific surface area measured after disassembling the negative electrode after the electrochemical device is discharged to 3V and scraping the powder on the negative electrode tab.

[0062] In some embodiments, the electrochemical device comprises a lithium ion battery, and the lithium ion battery has a reversible capacity of C1 mAh / g between 0.005 V and 2 V and a reversible capacity of C2 mAh / g between 0 V and 2 V, wherein C2 - C1 > 1. In some embodiments, C2 - C1 has a value of 1 mAh / g, 2 mAh / g, 3 mAh / g, 4 mAh / g, 5 mAh / g, 6 mAh / g, or a range defined by any two of these values. In the present application, the negative electrode of the coin cell is the negative electrode that is disassembled after the electrochemical device is discharged to a voltage of 3 V.

[0063] In some embodiments, the electrochemical device comprises a lithium ion battery, and the lithium ion battery has an expansion rate of less than 9% after 500 cycles at 25 °C. In some embodiments, the lithium ion battery has an expansion rate of less than 8% or less than 7%.

[0064] In some embodiments, the negative electrode active material layer further comprises a binder. In some embodiments, the binder comprises, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon.

[0065] In some embodiments, the negative electrode active material layer comprises a conductive material. In some embodiments, the conductive material comprises, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, or polyphenylene derivative.

[0066] In some embodiments, the negative electrode current collector comprises, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or polymer substrate coated with conductive metal.

[0067] The electrochemical device of the present application further comprises a positive electrode. The materials, compositions, and methods of manufacturing the positive electrode that can be used in the embodiments of the present application include any of the techniques disclosed in the prior art.

[0068] In some embodiments, the positive electrode comprises a current collector and a positive electrode active material layer on the current collector.

[0069] In some embodiments, the positive electrode active material comprises, but is not limited to, lithium cobalt oxide (LiCo02), lithium nickel cobalt manganese (NCM) ternary material, lithium iron phosphate (LiFeP04), or lithium manganate (LiMn204).

[0070] In some embodiments, the positive active material layer further includes a binder, and optionally, a conductive material. The binder improves the binding between the positive active material particles, and also improves the binding between the positive active material and the current collector.

[0071] In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0072] In some embodiments, the conductive material 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.

[0073] In some embodiments, the current collector can include, but is not limited to, aluminum.

[0074] The positive electrode can be prepared by a method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent can include, but is not limited to, N-methyl pyrrolidone.

[0075] The electrochemical device of the present application further includes an electrolyte. The electrolyte that can be used in the embodiments of the present application can be an electrolyte known in the art.

[0076] In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte according to the present application can be any organic solvent known in the art that can be used as a solvent of an electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and can be any electrolyte known in the art. The additive of the electrolyte according to the present application can be any additive known in the art that can be used as an additive of an electrolyte.

[0077] 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.

[0078] In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0079] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB).

[0080] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5-3 mol / L, 0.5-2 mol / L, or 0.8-1.5 mol / L.

[0081] The electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and it can be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, and the like.

[0082] For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a 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, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0083] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed of a mixture of a polymer and an inorganic substance.

[0084] The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from one or a combination of several 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 one or a combination of several of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0085] The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0086] In some embodiments, the electrochemical device of the present application includes, but is not limited to, a primary battery, or a secondary battery.

[0087] In some embodiments, the electrochemical device is a lithium secondary battery.

[0088] In some embodiments, the lithium secondary battery includes, but is 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.

[0089] III. Electronic device

[0090] The electronic device of the present application can be any device using the electrochemical device according to the embodiments of the present application.

[0091] In some embodiments, the electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, or a lithium ion capacitor, etc.

[0092] The preparation of the lithium ion battery is described below with the lithium ion battery as an example and in conjunction with specific embodiments, and those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0093] Example 1

[0094] Preparation of the lithium ion battery

[0095] 1. Preparation of the negative electrode

[0096] 1) Preparation of the negative electrode active material

[0097] S1: Petroleum coke is selected as the raw material, petroleum coke and high-temperature pitch with a softening point of 230°C are mixed at a ratio of 1:0.15, then heat treated at 550°C for 3 hours, and treated at 3000°C for graphitization for 150 hours to obtain a graphite active material;

[0098] S2: The graphite active material is then mixed with low-temperature pitch having a softening point of 70°C and heated to 80°C, wherein the mass ratio of the active material to the low-temperature pitch is 1:0.05, so that the pitch uniformly coats the surface of the graphite active material;

[0099] S3: The graphite active material coated with pitch is then mixed with ammonium bicarbonate at a weight ratio of 100:3 and placed in a box furnace at a loading rate of 50%, and heated to 300°C under a nitrogen atmosphere for 6 hours. The loading rate is the ratio of the amount of material added to the volume of the heating device furnace. The negative electrode active material is obtained.

[0100] 2) Preparation of the negative electrode

[0101] The negative electrode active material prepared above, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are dispersed in deionized water at a weight ratio of 97.7:1.2:1.1, and thoroughly mixed by stirring to obtain a negative electrode slurry. Acetylene black is coated on a copper foil to obtain a negative electrode current collector. The negative electrode slurry is coated on the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode.

[0102] 2) Preparation of the negative electrode

[0103] Lithium cobalt oxide (LiCoO2), acetylene black, and polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of N-methyl pyrrolidone (NMP) at a weight ratio of 96:2:2, and coated on an aluminum foil as a positive electrode current collector, dried, and cold-pressed to obtain a positive electrode.

[0104] 3) Preparation of the electrolyte

[0105] Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1 under a dry argon atmosphere, and LiPF6 is added and mixed uniformly. Fluoroethylene carbonate is added at a weight percentage of 3%, and hexanedinitrile is added at a weight percentage of 2% to obtain an electrolyte, wherein the concentration of LiPF6 is 1.15 mol / L.

[0106] 4) Preparation of the separator

[0107] A 12 μm thick porous polyethylene (PE) polymer film is used as the separator.

[0108] 5) Preparation of the lithium ion battery

[0109] The positive electrode, the separator, and the negative electrode are stacked in order, with the separator between the positive electrode and the negative electrode to serve as a separator. After the tab is welded, the bare cell is placed in an outer packaging foil aluminum plastic film, and the electrolyte prepared above is injected into the dried bare cell. After vacuum packaging, standing, formation, shaping, and capacity testing, a lithium ion battery is obtained.

[0110] Examples 2 to 16, Comparative Examples 1 to 2

[0111] Preparation of negative active material

[0112] The preparation process of the negative active material was similar to that of Example 1, except that the corresponding negative active material was prepared by adjusting the content of ammonium bicarbonate (the pitch-coated graphite active material was added in a weight ratio of 100: x with ammonium bicarbonate) and the heating temperature parameter in the preparation process S3, as shown in Table 1.

[0113] The preparation of the negative electrode, the positive electrode, the electrolyte, the separator, and the lithium ion battery was the same as that of Example 1.

[0114] Test method

[0115] 1. Raman spectrum test method

[0116] The Raman spectrum of the negative active material was tested using a laser microscopic confocal Raman spectrometer (HR Evolution): a small amount of powder was taken in the center of the sample groove and flattened with a glass sheet, and the laser parameters were set to 1800 gr / mm, 532 nm, 50%, 2s, and the sample Raman characteristic peak spectrum was tested.

[0117] 2. Test method for specific surface area of negative active material

[0118] The specific surface area of the negative active material was measured by nitrogen adsorption / desorption method using a specific surface area analyzer (Tristar II 3020M): the negative active material sample was dried in a vacuum drying oven, then loaded into a sample tube for measurement in the analyzer.

[0119] Confirmation of the proportion of basal planes of graphite: the end faces and basal planes of graphite have different adsorption energies for gases, the adsorption energy of the end face is 200-50 e / k, and the adsorption energy of the basal plane is generally 50-80 e / k. During the test of specific surface area, the proportion of basal planes can be obtained by fitting the specific surface area corresponding to different adsorption energies through software processing.

[0120] 3. Test method for gram capacity and initial coulombic efficiency of lithium ion battery

[0121] The lithium ion battery was discharged to 5.0 mV at 0.05C, to 5.0 mV at 50 μA, to 5.0 mV at 20 μA, and charged to 2.0 V at 0.1C, and the capacity of the lithium ion battery at this time was recorded as the gram capacity. The initial charging gram capacity divided by the initial discharging gram capacity is the initial coulombic efficiency. 0.05C refers to the current value at 0.05 times the design gram capacity, and 0.1C refers to the current value at 0.1 times the design gram capacity.

[0122] 4. Method for testing cycle thickness expansion rate of lithium ion battery

[0123] At 25℃, the thickness of the lithium ion battery at 3.95V is tested by using a micrometer, and is recorded as H0. The lithium ion battery is cycled at 1.5C rate for 500 cycles, and during the cycling, the thickness of the lithium ion battery at 4.45V is measured after every 50 cycles, and is recorded as Hn. n The cycle thickness expansion rate of the lithium ion battery is calculated by the following formula:

[0124] The cycle thickness expansion rate corresponding to the cycle number = (Hn-H0) / H0x100%. n

[0125] Test results

[0126] Table 1 shows the process parameters of the surface treatment of the negative electrode active material and the related performance test results.

[0127] Table 1

[0128]

[0129] As can be seen from Examples 1 to 4, Examples 5 to 8, Examples 9 to 12 and Examples 13 to 16, at a lower treatment temperature of 300℃, as the amount of ammonium bicarbonate added increases, the CO2 gas flow generated by decomposition increases, the half-peak width of the D peak and the G peak of the Raman spectrum of the negative electrode active material slightly increases, indicating that the degree of disorder of the active material surface increases, and the crystallinity slightly decreases, which is related to the slight oxidation of the active material surface and the destruction of the crystal structure. After increasing the treatment temperature, the effect of the gas flow is not obvious, indicating that under the premise of sufficient gas flow, the degree of oxidation reaction on the surface of the material is basically the same. In addition, from other performance parameters such as the specific surface area and the gravimetric capacity of the active material, the same conclusion is obtained. In addition, as can be seen from Examples 1 to 4, the first coulombic efficiency of the material is slightly improved, which is related to the slight oxidation at low temperature, which reduces some -OH functional groups on the surface of the graphite; these functional groups are more prone to side reactions with the electrolyte.

[0130] ​As can be seen from Example 2, Example 6, Example 10 and Example 14, when the amount of ammonium bicarbonate added is ensured to be consistent, the half-peak width of the D peak and the G peak in the Raman spectrum of the active material increases significantly after the temperature is raised (similar conclusions can also be drawn from Example 3, Example 7, Example 11 and Example 15, Example 4, Example 8, Example 12 and Example 16). Therefore, the increase in temperature plays a significant role in promoting the degree of surface oxidation. Moreover, as the temperature rises, the specific surface area of the active material increases significantly and the oxygen content rises significantly, indicating that after the oxidation reaction on the surface of the material, some C in the lattice is oxidized to form some pore structures. In addition, the proportion of basal planes decreases, indicating that most of the reactions occur on the edges of the graphite, resulting in an increase in the proportion of the specific surface area of the edges; and these pore structures can effectively store lithium, thereby significantly increasing the gram capacity of the material. However, due to the increase in the specific surface area, the side reactions between the active material and the electrolyte increase, which will affect the first coulombic efficiency as a whole.

[0131] As can be seen from Comparative Example 1 and Comparative Example 2, when the amount of ammonium bicarbonate added and the reaction temperature are reduced, the half-peak width of the G peak in the Raman spectrum of the active material is small, indicating that the peak shape is sharp and the material has high crystallinity; in addition, the specific surface area of the material is small and the gram capacity is low, indicating that the degree of oxidation reaction is weak. When the temperature and the amount of ammonium bicarbonate are increased, the oxidation reaction of the active material is abnormally severe, the peak intensity ratio of the D peak and the G peak in the Raman spectrum representing the degree of surface defects of the material increases significantly, the gram capacity increases more, but the first coulombic efficiency decreases significantly, which is not conducive to the improvement of the energy density of the lithium ion battery.

[0132] Table 2 shows the effects of heating time and sample loading amount in the heating device on the tap density, the compacted density, the specific surface area, the discharge capacity and the cycle thickness expansion rate of the negative electrode active material.

[0133] The negative electrode active materials in Examples 17-32 were prepared by adjusting the heating time and the loading rate in the furnace under a nitrogen atmosphere based on the negative electrode active material preparation conditions in Example 9.

[0134] The loading rate is the ratio of the actual volume of the powder loaded to the total volume of the furnace chamber of the heating device.

[0135] B1 is the specific surface area of the negative electrode active material before being pressed, and B2 is the specific surface area after being subjected to a pressure of 1 t. The method of applying pressure to the negative electrode active material is as follows: using an electronic pressure testing machine (Sage UTM7305), 1.0±0.05 g of negative electrode active material powder is placed on a mold with a diameter of 13 mm, a pressure of 1 t is applied to the negative electrode active material powder and maintained for 5 s, and after the pressure is released, the powder is taken out.

[0136] B11 is the specific surface area of the negative electrode sheet after the lithium ion battery is discharged to 3 V, disassembled, and the powder is scraped off. C1 is the gram capacity of the lithium ion battery after the lithium ion battery is discharged to 3 V, disassembled, and the Li sheet is assembled into a button half-cell, and then discharged to 5.0 mV; C2 is the gram capacity of the lithium ion battery after the lithium ion battery is discharged to 0 mV. The specific discharge process is as follows: discharged to 5.0 mV or 0 mV at 0.05 C, discharged to 5.0 mV or 0 mV at 50 μA, discharged to 5.0 mV or 0 mV at 20 μA, charged to 2.0 V at 0.1 C, and record the capacity of the lithium ion battery at this time as the gram capacity. 0.05 C refers to the current value at 0.05 times the design gram capacity, and 0.1 C refers to the current value at 0.1 times the design gram capacity.

[0137] Table 2

[0138]

[0139] It can be seen from Comparative Examples 17 to 20, Examples 21 to 24, Examples 25 to 28, and Examples 29 to 32 respectively that when the heating time is unchanged and the loading rate is increased, the tap density of the negative electrode active material is increased, the compacted density is decreased, and the C2-C1 capacity is decreased, indicating that the degree of oxidation of the negative electrode active material is slightly weakened. This is related to the fact that when the material loading amount is large, the powder is not fully contacted with the gas. In addition, the cycle expansion rate of the lithium ion battery containing the negative electrode active material is also slightly reduced, indicating that the degree of oxidation affects the structural stability of the material.

[0140] It can be seen from Comparative Examples 17, 21, 25, and 29, Examples 18, 22, 26, and 30, Examples 19, 23, 27, and 31, and Examples 20, 24, 28, and 32 respectively that when the reaction time is prolonged, the compacted density of the negative electrode active material is significantly increased, but the specific surface area change rate (B2-B1) / B1 of the material before and after being pressed is increased, and the expansion rate of the lithium ion battery is increased. In addition, the gram capacity of the negative electrode active material between 5.0 mV and 0 mV is significantly increased. The performance differences of the above negative electrode active materials are related to the degree and location of the oxidation reaction. After the oxidation reaction is intense, it is speculated that some dislocations and other defects on the surface of the negative electrode active material are reduced, so that the negative electrode active material is more likely to shrink and slip between layers after being pressed, resulting in an increase in the compacted density of the negative electrode active material powder. In addition, these oxidation reactions also react the binder between the secondary particles of the negative electrode active material, resulting in unstable secondary particle structures, which increases the expansion in the lithium ion battery.

[0141] References in the specification to "some embodiments," "particular embodiments," "one embodiment," "another embodiment," "an embodiment," "some aspects," "some alternatives," "one alternative," "certain embodiments," "certain alternatives," "some implementations," "some examples," "one example," "certain examples," or "an example" are not necessarily to the same embodiment or example, and such references mean at least one. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit and scope of the application. Thus, it is intended that the present application cover the modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

[0142] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes can be made to the embodiments in light of the teachings of the present disclosure, and it is understood that well-known elements have not been described in order to not obscure the present application.

Claims

1. A negative electrode active material comprising graphite and amorphous carbon, wherein, Raman spectroscopy revealed that the negative electrode active material satisfies the following condition: 1.6 ≤ W. D / W G ≤2.6, where W D 1340 cm⁻¹ in Raman spectrum -1 Up to 1370cm -1 The half-peak width of the inner D peak is 40 cm. -1 ≤W D ≤100cm -1 W G 1570 cm⁻¹ in the Raman spectrum -1 Up to 1590cm -1 Half-width of inner G peak: 15cm -1 ≤W G ≤50cm -1 The most probable pore size of the negative electrode active material is 2.55 nm to 3.45 nm; X-ray photoelectron spectroscopy shows that the mass content of oxygen in the negative electrode active material is 2.1% to 4.7%.

2. The negative electrode active material according to claim 1, characterized in that, 1.7≤W D / IN G ≤2.5。 3. 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 (i) to (iv): (i)2≤W D / IN G ≤2.5; (ii)40cm -1 ≤W D ≤60cm -1 ; (iii)15cm -1 ≤W G ≤35cm -1 ; (iv) The negative electrode active material satisfies: 0.08≤ID / IG≤1.2, where ID is the intensity of the D peak and IG is the intensity of the G peak.

4. 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 (v) to (viii): (v) The specific surface area of ​​the negative electrode active material is B1, wherein 0.8 cm² 2 / g≤B1≤5.4cm 2 / g, where B1 is the specific surface area of ​​the negative electrode active material before being subjected to pressure; (vi) The pore volume of the most probable pore size of the negative electrode active material accounts for 3% to 8% of the pore volume of the negative electrode active material; (vii) The negative electrode active material includes a base surface and an end surface, wherein the specific surface area of ​​the base surface accounts for 40% to 70% of the specific surface area of ​​the negative electrode active material; (viii) The negative electrode active material includes a base surface and an end surface, wherein the roughness of the end surface is greater than the roughness of the base surface.

5. The negative electrode active material according to claim 4, characterized in that, The negative electrode active material satisfies at least one of the following conditions (ix) to (xii): (ix)1.0cm 2 / g≤B1≤4.5cm 2 / g; (x) The most probable pore size of the negative electrode active material is 2.7 nm to 3.3 nm, and the pore volume of the most probable pore size of the negative electrode active material accounts for 3.5% to 7% of the pore volume of the negative electrode active material; (xi) The specific surface area of ​​the basal surface accounts for 45% to 65% of the specific surface area of ​​the active material; (xii) The specific surface area of ​​the negative electrode active material after applying a pressure of 1t is B2, wherein (B2-B1) / B1×100%≤80%.

6. 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 (xiv) to (xv): (xiv) The tap density of the negative electrode active material is 0.90 g / cm³. 3 Up to 1.05 g / cm 3 ; (xv) The compacted density of the 5t powder of the negative electrode active material is 1.9 g / cm³. 3 Up to 2.05 g / cm 3 .

7. The negative electrode active material according to claim 1, characterized in that, The preparation method of the negative electrode active material includes the following steps: S1: Provide graphite materials; S2: The graphite material in S1 is mixed with the carbonaceous precursor to obtain a graphite material coated with the carbonaceous precursor; S3: The graphite material coated with carbonaceous precursor in S2 is mixed with bicarbonate to obtain a mixture, and the mixture is heat-treated to obtain the negative electrode active material.

8. An electrochemical device comprising a negative electrode, the negative electrode comprising 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 comprises the negative electrode active material according to any one of claims 1-7.

9. The electrochemical device according to claim 8, characterized in that, The specific surface area B11 of the negative electrode active material is 4.35 cm². 2 / g to 5.9cm 2 / g, wherein B11 is the specific surface area measured by disassembling the negative electrode and scraping off the powder after the electrochemical device is discharged to 3V; and / or Charge-discharge tests were conducted using a coin cell composed of the negative electrode and lithium metal. The reversible capacity of the coin cell between 0.005V and 2V was C1 mAh / g, and the reversible capacity between 0V and 2V was C2 mAh / g, wherein C2-C1≥1.

10. An electronic device comprising the electrochemical device of claim 8 or 9.

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