Negative electrode material, secondary battery, and electronic device

Abstract

Provided is a negative electrode material comprising a carbon-based material, which satisfies S1 / S2≥20%, S2 / S≥15% by nitrogen adsorption-desorption testing; wherein S1 represents the adsorption volume of pores with a pore diameter of less than or equal to 2 nm in the negative electrode material, 0.0003 cm 3 / g≤S1≤0.001 cm 3 / g; S2 represents the adsorption volume of pores with a pore diameter of greater than 2 nm and less than or equal to 10 nm in the negative electrode material, 0.0008 cm 3 / g≤S1≤0.0025 cm 3 / g; and S represents the adsorption volume of pores with a pore diameter of less than or equal to 30 nm in the negative electrode material. The negative electrode material of the present application has high gravimetric capacity and excellent kinetic performance, and thus a secondary battery comprising the negative electrode material has both high energy density and fast charging performance. Also provided is a secondary battery comprising the negative electrode material.

Description

TECHNICAL FIELD

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

[0002] With the wide application of lithium ion secondary batteries in the fields of consumer electronics, electric vehicles, electric tools, energy storage, etc., the market requirements for the performance of lithium ion secondary batteries are also getting higher and higher. Among them, in order to meet the as long as possible endurance time and short charging time of various products, it is required that the lithium battery has as high as possible energy density and kinetic performance. As the most commonly used negative electrode material of lithium battery, graphite can usually improve the energy density of lithium battery by improving the gram capacity and powder compaction density of graphite, and improve the kinetic performance of lithium battery by adjusting the specific surface area, defect content and structure orientation of graphite. The existing technology is difficult to ensure that the kinetic performance is considered while improving the energy density, and the improvement effect of energy density is not significant, so it is particularly important to develop graphite negative electrode that can meet the requirements of lithium battery with higher energy density and kinetic performance. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a negative electrode material and a secondary battery comprising the same. The negative electrode material of the present application has high gram capacity and excellent kinetic performance, thereby making the secondary battery comprising the same have high energy density and fast charging performance.

[0004] In a first aspect, the present application provides a negative electrode material comprising a carbon-based material, which satisfies S1 / S2≥20% and S2 / S≥15% by nitrogen adsorption-desorption test; wherein S1 represents the adsorption volume of pores with a pore size less than or equal to 2 nm in the negative electrode material, 0.0003 cm 3 / g≤S1≤0.001 cm 3 / g; and S2 represents the adsorption volume of pores with a pore size greater than 2 nm and less than or equal to 10 nm in the negative electrode material, 0.0008 cm 3 / g≤S1≤0.0025 cm 3 / g; S represents the adsorption volume of pores with a pore size less than or equal to 30 nm in the negative electrode material. The conventional graphite negative electrode material is intercalated with lithium in the interlayer, and the lithium intercalation capacity is limited. The inventors of the present application found that, by treating the surface of a carbon-based material such as graphite to form a nano-sized pore structure, a new lithium storage mechanism, i.e., pore adsorption storage of lithium, can be introduced, and the lithium intercalation capacity of graphite can be greatly improved, and a higher gram capacity can be obtained compared with conventional graphite. Among them, micropores with a pore size of less than 2 nm have the most significant effect on improving the gram capacity, followed by mesopores with a pore size ranging from 2 to 10 nm. In addition, the porous structure can also provide abundant deintercalation sites for lithium ions, shorten the transmission distance of lithium ions, and reduce the diffusion resistance of lithium ions, so that the material has good kinetic performance. The present application limits the adsorption volume of pores with a pore size of less than 2 nm and the adsorption volume of pores with a pore size greater than 2 nm and less than or equal to 10 nm in the negative electrode material to the above range, so that the negative electrode material has a suitable number and size of nano-pore structures, which can improve the gram capacity of graphite while improving the kinetic performance, thereby obtaining a secondary battery with high energy density and fast charging performance.

[0005] In some embodiments, 20%≤S1 / S2≤60%. In some embodiments, 30%≤S1 / S2≤50%. In some embodiments, 15%≤S2 / S≤50%. When the pore size or the number of pores is too large, the specific surface area of the negative electrode material increases rapidly, and the active area exposed to the electrolyte environment is also larger, which causes more side reactions and the formation of SEI film, resulting in excessive irreversible capacity loss, thereby affecting the capacity of the secondary battery. At the same time, excessive consumption of electrolyte will cause the reduction of the cycle life of the battery. When the number of pores is too small, the introduced pore intercalation capacity is too low, and the lithium ion deintercalation sites are not significantly different from conventional graphite materials, thereby failing to achieve the purpose of improving the energy density and kinetic performance of the secondary battery.

[0006] In some embodiments, 0.006 cm 3 / g≤S≤0.008 cm 3 / g. When S is too large, the degree of reaction of the material is too high, the number of pores formed on the surface is too large, and the pore size is too large, which causes excessive side reactions to occur, resulting in excessive irreversible Li consumption; and when S is too small, the effect of providing adsorption sites for lithium ions and accelerating the diffusion of lithium ions cannot be achieved.

[0007] In some embodiments, the carbon-based material includes a graphite material, and the graphite material includes natural graphite and / or artificial graphite.

[0008] In some embodiments, the surface oxygen element mass content of the negative electrode material is w, 1%≤w≤6% by X-ray photoelectron spectroscopy test. The surface oxygen element content can reflect the nano-pore structure of the negative electrode material to some extent. When the surface oxygen element content is too low, the nano-pore structure is not formed on the surface, and the specific capacity and kinetic performance of the material are not improved. When the surface oxygen element content is too high, too many pores and oxygen-containing functional groups are formed, which leads to the decrease of the initial efficiency and the increase of the electrolyte consumption. When the oxygen element content is in the above range, the negative electrode material has a nano-pore structure with appropriate quantity and size, which can exert the best specific capacity and kinetic improvement effect without affecting other performances. In some embodiments, 2%≤w≤5%.

[0009] In some embodiments, the specific surface area of the negative electrode material is A, 3.0m 2 / g≤A≤8.0m 2 / g. When the specific surface area is in the above range, the size and proportion of the pore structure formed on the surface of the negative electrode material are moderate, which can exert the best specific capacity and kinetic improvement effect without affecting other performances. In some embodiments, 3.0m 2 / g≤A≤6.0m 2 / g.

[0010] In some embodiments, the powder compaction density of the negative electrode material is C, 1.9g / cm 3 ≤C≤2.1g / cm 3 . The increase of the powder compaction density C of the negative electrode material can be used for the design of the electrode sheet with high compaction density, thereby improving the volume energy density of the secondary battery. However, when C is too large, the interlayer slip of the negative electrode material is too easy, the material texture 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 lithium ion diffusion become difficult, thereby affecting the performance of the secondary battery. In some embodiments, 1.95g / cm 3 ≤C≤2.05g / cm 3 .

[0011] In some embodiments, the negative electrode active material satisfies 0.1≤Id / Ig≤0.5 by Raman test, wherein Id is the intensity of the 1350cm -1 peak in the Raman spectrum, and Ig is the intensity of the 1580cm -1The intensity of the peak. The Id / Ig ratio can represent the defect content of the surface of the negative electrode material, and the larger the value, the higher the defect content. High defect content can promote the rapid deintercalation of lithium ions, thereby improving the kinetic performance of the negative electrode material. However, too many defects can reduce the initial efficiency, cycle performance, and the like of the secondary battery. When the Id / Ig ratio is within the above range, the secondary battery can exhibit good kinetics, and the initial efficiency, cycle performance, and the like will not be significantly reduced. In some embodiments, 0.2≤Id / Ig≤0.4.

[0012] In some embodiments, the preparation method of the negative electrode material comprises: subjecting the surface pretreated graphite material to heat treatment in an oxidizing atmosphere, in particular a low-concentration oxidizing atmosphere, wherein the temperature of the heat treatment is 200-500°C.

[0013] In some embodiments, the oxidizing atmosphere comprises O2 / N2 mixed gas. In some embodiments, the flow rate of the oxidizing atmosphere during the heat treatment is 6-10 L / min. In some embodiments, the time of the heat treatment is 2-5 h. In some embodiments, the O2 volume concentration in the O2 / N2 mixed gas is 1-5%.

[0014] In a second aspect, the present application provides a secondary battery comprising a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material of the first aspect.

[0015] In some embodiments, the compaction density of the negative electrode is P, and 1.75 g / cm 3 ≤P≤1.85 g / cm 3 When the compaction density of the negative electrode is too high, the internal pores of the negative electrode are reduced, and the electrolyte is difficult to infiltrate, resulting in reduced kinetic performance. When the compaction density of the negative electrode is within the above range, the negative electrode sheet has a higher compaction density than a relatively conventional design, which can improve the volume energy density of the secondary battery, and will not affect the kinetic performance of the secondary battery.

[0016] In some embodiments, the ratio of the 004 crystal face diffraction peak area C004 to the 110 crystal face diffraction peak area C110 of the negative electrode satisfies 8≤C004 / C110≤18, as tested by X-ray diffraction method. When the C110 crystal face and the C004 crystal face of the negative electrode satisfy the above relationship while meeting the high compaction density design, the effective intercalation of lithium ions can be ensured.

[0017] In a third aspect, the present application provides an electronic device comprising the secondary battery of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The pore size distribution of the negative electrode material of Example 7 and Comparative Example 1 of the present application is shown.

[0019] Figure 2 Charge-discharge curves of lithium-ion batteries of Example 2 and Comparative Example 3 of the present application are shown.

[0020] Figure 3 Irreversible lithium loss of lithium-ion batteries of Example 15 and Comparative Example 1 of the present application are shown.

[0021] Figure 4 SEM image of the negative electrode material of Example 13 of the present application. DETAILED DESCRIPTION

[0022] For the sake of brevity, the present application often discloses only certain specific combinations and sub-combinations of various alternatives. However, a person of ordinary skill in the art will understand that the application is not limited to the specific combinations and sub-combinations disclosed, but extends to all possible combinations and sub-combinations, and that the full scope of the application is defined by the appended claims.

[0023] In the description of the present application, the terms "upper" and "lower" are used with reference to the orientation of the figures, unless otherwise indicated.

[0024] Unless otherwise indicated, the terms used in the present application have the commonly understood meanings as understood by one of ordinary skill in the art. Unless otherwise indicated, the numerical values of the various parameters set forth in the present application can be measured using any of the various methodologies commonly used in the art (e.g., can be tested according to the methods given in the examples of the present application).

[0025] The use of the terms "at least one", "one or more", or "and / or" in the context of describing the application should not be interpreted as being restricted to only one element of a listing of elements, unless otherwise indicated. Rather, the phrase "at least one of A and B" should be interpreted to mean that A alone, B alone, or A and B together are possible under the recitation. The phrases "at least one of A, B, and C" and "at least one of A, B, or C" should be interpreted to mean that 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 are possible under the recitation. The phrases "at least one of A, B, and C" and "at least one of A, B, or C" should be interpreted to mean that 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 are possible under the recitation. The phrase "at least one of A, B, and C" and "at least one of A, B, or C" should be interpreted to mean that 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 are possible under the recitation.

[0026] The present application is further illustrated below in connection with specific embodiments. It is understood that these embodiments are merely illustrative of the present application and should not be construed as limiting the scope of the present application.

[0027] I. Negative electrode material

[0028] The negative electrode material provided in the present application comprises a carbon-based material, and through nitrogen adsorption and desorption testing, the negative electrode material satisfies: S1 / S2≥20%, S2 / S≥15%; wherein S1 represents the adsorption volume of pores with a pore size less than or equal to 2 nm in the negative electrode material, 0.0003 cm 3 / g≤S1≤0.001 cm 3 / g; S2 represents the adsorption volume of pores with a pore size greater than 2 nm and less than or equal to 10 nm in the negative electrode material, 0.0008 cm 3 / g≤S1≤0.0025 cm 3 / g; S represents the adsorption volume of pores with a pore size less than or equal to 30 nm in the negative electrode material. The conventional graphite negative electrode material is intercalated with lithium, and its lithium intercalation capacity is limited. The inventors of the present application found through research that by treating the surface of a carbon-based material such as graphite to form a nano-sized pore structure, a new lithium storage mechanism, i.e., pore adsorption lithium storage, can be introduced, which can greatly improve the lithium intercalation capacity of graphite and obtain a higher gram capacity compared to conventional graphite. Among them, micropores with a pore size of less than 2 nm have the most significant effect on gram capacity improvement, followed by mesopores with a pore size ranging from 2 to 10 nm. In addition, the porous structure can also provide abundant deintercalation sites for lithium ions, shorten the transmission distance of lithium ions, and reduce the diffusion resistance of lithium ions, so that the material has good kinetic performance. The present application limits the adsorption volume of pores with a pore size less than 2 nm and the adsorption volume of pores with a pore size greater than 2 nm and less than or equal to 10 nm in the negative electrode material to the above range, so that the negative electrode material has a suitable number and size of nano-pore structures, which can improve the gram capacity of graphite while improving the kinetic performance, thereby obtaining a secondary battery with high energy density and fast charging performance.

[0029] In some embodiments, 20%≤S1 / S2≤60%. In some embodiments, S1 / S2 is 23%, 25%, 27%, 29%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, 50%, 53%, 55%, 57%, or a range consisting of any two of these values. In some embodiments, 30%≤S1 / S2≤50%.

[0030] In some embodiments, 15%≤S2 / S≤50%. In some embodiments, S2 / S is 17%, 20%, 23%, 25%, 27%, 29%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, or a range consisting of any two of these values.

[0031] When the number of pores or pore diameters is too large, the specific surface area of the negative material increases rapidly, and the active area exposed to the electrolyte environment is also larger, which causes more side reactions and the formation of SEI films, resulting in excessive irreversible capacity loss, thereby affecting the capacity of the secondary battery. At the same time, excessive consumption of electrolyte will cause the reduction of the cycle life of the battery. When the number of pores is too small, the introduced pore lithium intercalation capacity is too low, and the lithium ion deintercalation site has no significant difference from conventional graphite materials, so as to fail to achieve the purpose of improving the energy density and kinetic performance of the secondary battery.

[0032] In some embodiments, S1 is 0.00035 cm 3 / g, 0.0004 cm 3 / g, 0.00045 cm 3 / g, 0.0005 cm 3 / g, 0.00055 cm 3 / g, 0.0006 cm 3 / g, 0.00065 cm 3 / g, 0.0007 cm 3 / g, 0.00075 cm 3 / g, 0.0008 cm 3 / g, 0.00085 cm 3 / g, 0.0009 cm 3 / g, 0.0095 cm 3 / g, or a range consisting of any two of these values. In some embodiments, S2 is 0.0008 cm 3 / g, 0.0009 cm 3 / g, 0.001 cm 3 / g, 0.0011 cm 3 / g, 0.0012 cm 3 / g, 0.0013 cm 3 / g, 0.0014 cm 3 / g, 0.0015 cm 3 / g, 0.0016 cm 3 / g, 0.0017 cm 3 / g, 0.0018 cm 3 / g, 0.0018 cm 3 / g, 0.002 cm 3 / g, 0.0021 cm 3 / g, 0.0022 cm 3 / g, 0.0023 cm 3 / g, 0.0024 cm 3 / g, or a range consisting of any two of these values.

[0033] In some embodiments, S is in the range of 0.006 cm / g 3 / g≤S≤0.008 cm / g 3 In some embodiments, S is 0.0061 cm / g 3 / g, 0.0062 cm / g 3 / g, 0.0063 cm / g 3 / g, 0.0064 cm / g 3 / g, 0.0065 cm / g 3 / g, 0.0066 cm / g 3 / g, 0.0067 cm / g 3 / g, 0.0068 cm / g 3 / g, 0.0069 cm / g 3 / g, 0.007 cm / g 3 / g, 0.0071 cm / g 3 / g, 0.0072 cm / g 3 / g, 0.0073 cm / g 3 / g, 0.0074 cm / g 3 / g, 0.0075 cm / g 3 / g, 0.0076 cm / g 3 / g, 0.0077 cm / g 3 / g, 0.0078 cm / g 3 / g, 0.0079 cm / g 3 / g, or a range consisting of any two of these values. If S is too large, the material reacts too much, the surface forms too many pores with too large a pore size, and too many side reactions occur, resulting in too much irreversible Li consumption. If S is too small, the effects of providing adsorption sites for lithium ions and speeding up the diffusion of lithium ions cannot be achieved.

[0034] In some embodiments, the carbon-based material comprises a graphite material, which includes natural graphite and / or artificial graphite.

[0035] In some embodiments, the surface oxygen element mass content of the negative electrode material is w, 1%≤w≤6% by X-ray photoelectron spectroscopy. In some embodiments, w is 1.3%, 1.5%, 1.7%, 1.9%, 2.3%, 2.5%, 2.7%, 3.0%, 33%, 35%, 37%, 4.0%, 4.3%, 4.5%, 4.7%, 4.9%, 5.3%, 5.5%, 5.7%, or a range consisting of any two of these values. The surface oxygen element content can reflect the nanopore structure of the negative electrode material to some extent. When the surface oxygen element content is too low, no nanopore structure is formed on the surface, and the material has no improvement effect on the specific capacity and kinetic performance. When the surface oxygen element content is too high, too many pores and oxygen-containing functional groups are formed, which leads to a decrease in the initial efficiency and an increase in the electrolyte consumption. When the oxygen element content is in the above range, the negative electrode material has a suitable number and size of nanopore structures, which can exert the best improvement effect on the specific capacity and kinetics without affecting other performances. In some embodiments, 2%≤w≤5%.

[0036] In some embodiments, the specific surface area of the negative electrode material is A, 3.0m 2 / g≤A≤8.0m 2 / g. In some embodiments, A is 3.5g / cm 2 , 4g / cm 2 , 4.5g / cm 2 , 5g / cm 2 , 5.5g / cm 2 , 6.5g / cm 2 , 7g / cm 2 , 7.5g / cm 2 , or a range consisting of any two of these values. When the specific surface area is in the above range, the size and proportion of the pore structure formed on the surface of the negative electrode material are moderate, which can exert the best improvement effect on the specific capacity and kinetics without affecting other performances. In some embodiments, 3.0m 2 / g≤A≤6.0m 2 / g.

[0037] In some embodiments, the powder compaction density of the negative electrode material is C, 1.9g / cm 3 ≤C≤2.1g / cm 3 . In some embodiments, C is 1.92g / cm 3 , 1.94g / cm 3 , 1.96g / cm 3 , 1.98g / cm 3 , 2.0g / cm 3 , 2.02g / cm 3 , 2.04g / cm 32.06 g / cm 3 2.08 g / cm 3 Or a range of any two of these values. Increasing the powder compaction density C allows for the use of high compaction density electrode designs in the negative electrode material, thereby improving the volumetric energy density of the secondary battery. However, when C is too high, interlayer slippage in the negative electrode material becomes too easy, the material becomes softer, resulting in reduced electrode rebound and fewer pores formed by internal particle accumulation. This, in turn, makes electrolyte wetting and lithium-ion diffusion more difficult, thus affecting the performance of the secondary battery. In some embodiments, 1.95 g / cm³... 3 ≤C≤2.05g / cm 3 .

[0038] In some embodiments, the negative electrode active material satisfies the following condition by Raman spectroscopy: 0.1 ≤ Id / Ig ≤ 0.5, where Id is the Raman spectral density at 1350 cm⁻¹. -1 The peak intensity, Ig is the peak intensity at 1580 cm⁻¹ in the Raman spectrum. -1 The peak intensity. In some embodiments, Id / Ig is a range of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or any combination of these values. The Id / Ig ratio characterizes the defect content on the surface of the negative electrode material; a higher value indicates a higher defect content. A high defect content can promote rapid lithium-ion insertion and extraction, thereby improving the kinetic performance of the negative electrode material. However, excessive defects can lead to a decrease in the first-efficiency and cycle performance of the secondary battery. When the Id / Ig ratio is within the above range, the secondary battery exhibits good kinetics, and its first-efficiency and cycle performance are not significantly reduced. In some embodiments, 0.2 ≤ Id / Ig ≤ 0.4.

[0039] In some embodiments, the method for preparing the negative electrode material comprises: 1. Graphite material preparation. The graphite material comprises artificial graphite and / or natural graphite, wherein the artificial graphite is obtained by high-temperature graphitization of carbonaceous raw materials such as needle coke, petroleum coke, pitch coke, and biomass. The natural graphite is obtained by spheroidization of natural flake graphite. 2. Surface pretreatment of the graphite material. A certain amount of the graphite material in step 1 is first subjected to surface pretreatment. The surface pretreatment method is that the graphite material is coated and then carbonized at 900-1200°C, for example 1000°C, in an inert atmosphere, for example for 4h, and then subjected to a surface etching reaction. The coating agent used is at least one of pitch, tar, and resin organic matter, and the mass ratio of the coating agent to the graphite material is (1-5):(99-95). The etching reaction method comprises one of high-temperature gas phase reaction, liquid phase heating reaction, and high-temperature solid phase reaction. The gas source used in the high-temperature gas phase reaction comprises one of an oxygen-containing atmosphere, carbon dioxide, nitrogen dioxide, and methane. The reactant used in the liquid phase heating reaction comprises one of H2O2, (NH4)2S2O8, concentrated sulfuric acid, and nitric acid. The reactant used in the high-temperature solid phase reaction comprises one of potassium permanganate, ammonium bicarbonate, and sodium bicarbonate. 3. Heat treatment process. The graphite material after surface pretreatment is subjected to heat treatment in an oxidizing atmosphere to obtain the carbon-based material of the present application, wherein the heat treatment temperature is 200-500°C. The carbon-based material prepared by the surface treatment process forms a nano-sized pore structure, introduces a new lithium storage mechanism, i.e. hole adsorption lithium storage, greatly improves the lithium intercalation capacity of the carbon-based material, and obtains a higher gram capacity than conventional graphite. In addition, the surface porous structure formed by heat treatment also provides abundant deintercalation sites for lithium ions, shortens the transmission distance of lithium ions, reduces the diffusion resistance of lithium ions, enables the material to have good kinetic performance, and thus improves the fast-charging performance of the secondary battery.

[0040] In some embodiments, the heat treatment temperature is 230°C, 250°C, 270°C, 300°C, 330°C, 350°C, 370°C, 400°C, 430°C, 450°C, 470°C, or a range consisting of any two of these values.

[0041] In some embodiments, the flow rate of the oxidizing atmosphere during the heat treatment process is 6-10 L / min, for example 6.5 L / min, 7 L / min, 7.5 L / min, 8 L / min, 8.5 L / min, 9 L / min, or 9.5 L / min. In some embodiments, the heat treatment time is 2-5h, for example 2.5h, 3h, 3.5h, 4h, or 4.5h.

[0042] In some embodiments, the oxidizing atmosphere comprises O2 / N2 mixed gas. In some embodiments, the volume concentration of O2 in the oxidizing atmosphere is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values.

[0043] Secondary battery

[0044] The secondary battery provided in the present application comprises a negative electrode, the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material of the first aspect.

[0045] In some embodiments, the compaction density of the negative electrode is P, and 1.75 g / cm 3 ≤ P ≤ 1.85 g / cm 3 In some embodiments, P is 1.76 g / cm 3 , 1.77 g / cm 3 , 1.78 g / cm 3 , 1.79 g / cm 3 , 1.80 g / cm 3 , 1.81 g / cm 3 , 1.82 g / cm 3 , 1.83 g / cm 3 , 1.84 g / cm 3 , or a range consisting of any two of these values. When the compaction density of the negative electrode is too high, the internal pores of the negative electrode are reduced, and the electrolyte is difficult to infiltrate, resulting in reduced kinetic performance. When the compaction density of the negative electrode is within the above range, the negative electrode sheet has a higher compaction density than a relatively conventional design, which can improve the volumetric energy density of the secondary battery, and will not affect the kinetic performance of the secondary battery.

[0046] In some embodiments, the ratio of the diffraction peak area of the 004 crystal face C004 to the diffraction peak area of the 110 crystal face C110 of the negative electrode satisfies 8 ≤ C004 / C110 ≤ 18, as tested by X-ray diffraction method. In some embodiments, C004 / C110 is 9, 10, 11, 12, 13, 14, 15, 16, 17, or a range consisting of any two of these values. When the C110 crystal face and the C004 crystal face of the negative electrode satisfy the above relationship while meeting the high compaction density design, the effective intercalation of lithium ions can be ensured.

[0047] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode current collector comprises a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, a polymer substrate coated with a conductive metal, or any combination thereof.

[0048] In some embodiments, the negative active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0049] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymers are polyphenylene derivatives.

[0050] The secondary battery of the present application further includes a cathode including a cathode current collector and a cathode active material layer including a cathode active material, a binder, and a conductive agent.

[0051] According to some embodiments of the present application, the cathode current collector can be a metal foil or a composite current collector. For example, an aluminum foil can be used. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0052] According to some embodiments of the present application, the cathode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganate, spinel lithium nickel manganate, and lithium titanate. In some embodiments, the binder includes a binder polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fibers; a metal-based material, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as polyphenylene derivatives; or mixtures thereof.

[0053] The secondary battery of the present application further includes a separator. The material and shape of the separator used in the secondary battery of the present application are not particularly limited and can be any of those known in the art. In some embodiments, the separator includes a polymer or inorganic material formed of a material stable to the electrolyte of the present application.

[0054] 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.

[0055] The surface treatment layer is provided on at least one surface of the substrate layer and can be a polymer layer or an inorganic layer, or a layer formed of a mixture of a polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0056] The secondary battery of the present application further includes an electrolyte. The electrolyte used in the present application can be any of those known in the art.

[0057] According to some embodiments of the present application, the electrolyte solution includes an organic solvent, a lithium salt, and an optional additive. The organic solvent in the electrolyte solution of the present application can be any organic solvent known in the art as a solvent for an electrolyte solution. The electrolyte used in the electrolyte solution according to the present application is not limited and can be any electrolyte known in the art. The additive of the electrolyte solution according to the present application can be any additive known in the art as an additive for an electrolyte solution. In some embodiments, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate. In some embodiments, the organic solvent includes an ether-based solvent, for example, including at least one of 1,3-dioxolane (DOL) and dimethoxyethane (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-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). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0058] According to some embodiments of the present application, the secondary battery of the present application includes, but is not limited to, a lithium ion battery or a sodium ion battery. In some embodiments, the secondary battery includes a lithium ion battery.

[0059] III. Electronic device

[0060] The present application further provides an electronic device including the secondary battery of the second aspect of the present application.

[0061] The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, 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 player, 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 home-use large-sized storage battery, and a lithium ion capacitor, etc.

[0062] In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0063] Examples and Comparative Examples

[0064] Example 1

[0065] Preparation of negative electrode material

[0066] 5 kg of artificial graphite was weighed, wherein the artificial graphite was obtained by graphitizing pitch coke at 3000°C, then pitch was used as a coating agent to mix uniformly with the artificial graphite (the mass ratio of pitch to artificial graphite was 3:97), then the surface pretreated product was obtained by carbonizing the mixture at 1000°C under nitrogen atmosphere for 4h; then the surface pretreated product was loaded into an atmosphere furnace, the O2 / N2 mixed gas atmosphere with an O2 volume concentration of 1% was adjusted to a flow rate of 6L / min, the furnace temperature was 200°C, and finally the reaction was carried out for 2h to obtain the carbon-based material, i.e. the negative electrode active material.

[0067] Preparation of negative electrode

[0068] The above negative electrode material, binder styrene-butadiene rubber (abbreviated as SBR), thickening agent sodium carboxymethyl cellulose (abbreviated as CMC) were mixed in a weight ratio of 97:1.5:1.5, and then a proper amount of deionized water solvent was added to fully stir and mix, so as to form a uniform negative electrode slurry; the slurry was coated on a current collector Cu foil with a conductive coating thickness of 1μm, and then dried and cold-pressed to obtain a negative electrode sheet.

[0069] Preparation of electrolyte

[0070] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC=1:3:3:3, then fluoroethylene carbonate and 1,3-propane sultone were added, dissolved and fully stirred, then lithium salt LiPF6was added, and the mixture was uniformly mixed to obtain an electrolyte. The mass percentage of LiPF6was 12.5%, the mass percentage of fluoroethylene carbonate was 2%, and the mass percentage of 1,3-propane sultone was 2%, and the mass percentages of the substances were calculated based on the mass of the electrolyte.

[0071] Preparation of separator film

[0072] A porous polyethylene (PE) film with a thickness of 7μm was used as a separator film, and the porosity was 35%.

[0073] Preparation of button cell

[0074] The prepared negative electrode, lithium sheet, separator, electrolyte, steel sheet, foamed nickel and button cell shell were assembled together to obtain a button cell.

[0075] Examples 2 to 10, Comparative Examples 1 to 5

[0076] Preparation of negative electrode material

[0077] The negative electrode material was prepared in a similar manner to Example 1, except that the atmosphere flow rate, temperature and treatment time were adjusted to prepare the corresponding negative electrode material. The specific preparation parameters are shown in Table a:

[0078] Table a

[0079]

[0080] The negative electrode and button cell were prepared in the same manner as in Example 1.

[0081] Examples 11 to 20

[0082] Preparation of negative electrode material

[0083] The negative electrode material was prepared in a similar manner to Example 10, except that the O2 / N2 mixed gas flow rate and O2 volume concentration of the mixed gas were adjusted to adjust the content of surface oxygen elements of the negative electrode material. The specific preparation parameters are shown in Table b:

[0084] Table b

[0085]

[0086] The negative electrode and button cell were prepared in the same manner as in Example 10.

[0087] Examples 21 to 25

[0088] Preparation of negative electrode material

[0089] The negative electrode material was prepared in a similar manner to Example 13, except that the treatment time was adjusted to adjust the specific surface area of the negative electrode material. The specific preparation parameters are shown in Table c:

[0090] Table c

[0091]

[0092] The negative electrode and button cell were prepared in the same manner as in Example 13.

[0093] Examples 26 to 30

[0094] The negative material was prepared in a similar manner to Example 25, except that the powder compaction density of the negative material was adjusted by adjusting the treatment temperature and O2 / N2 mixed gas flow rate. The specific preparation parameters are shown in Table d:

[0095] Table d

[0096]

[0097] The negative electrode and button cell were prepared in a similar manner to Example 25.

[0098] Examples 31 to 39

[0099] The negative material was prepared in a similar manner to Example 27, except that the Id / Ig of the negative material was adjusted by adjusting the O2 volume concentration and flow rate of the O2 / N2 mixed gas. The specific preparation parameters are shown in Table e:

[0100] Table e

[0101]

[0102] The negative electrode and button cell were prepared in a similar manner to Example 27.

[0103] Test method

[0104] 1. Negative material pore size distribution test

[0105] 1) Weigh 20 to 30 g of the negative material sample for tabletting, and then weigh 1.5 to 3.5 g for loading into the test sample tube after tabletting;

[0106] 2) The sample was degassed at 200°C for 2 h;

[0107] 3) Then high-purity nitrogen was introduced, and the sample was adsorbed with nitrogen at a liquid nitrogen temperature environment until adsorption saturation;

[0108] 4) The obtained N2 adsorption / desorption curve was used to extract data according to the BJH model to obtain the BJH pore size distribution curve, and the adsorption volume of the pores corresponding to the pore size range could be obtained by calculating the integral area corresponding to different pore size ranges.

[0109] 2. Surface oxygen element content test

[0110] The sample was tested by X-ray photoelectron spectroscopy scanning using an XSAM-800 photoelectron spectrometer, Al Kα radiation was used as the main excitation light source, and the O1s spectrum binding energy shift was corrected by C1s standard binding energy 284.5 eV.

[0111] 3. Powder compaction density test

[0112] The test standard of powder compaction density refers to GB / T 24533-2009 "Lithium ion battery graphite negative electrode material". The specific test method is as follows:

[0113] 1.0000±0.0500g of the negative electrode material sample is weighed and placed in the test mold (CARVER #3619 (13mm)), and then the sample is placed in the test equipment, the test equipment is a three-dimensional UTM7305 test tonnage of 0.3t, 0.5t, 0.75t, 1.0t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, 5.0t, the pressure increasing rate is 10mm / min, the pressure holding time is 30s, the pressure releasing rate is 30mm / min, and the pressure releasing holding time is 10s.

[0114] In this application, the powder compaction density is the compaction density measured after 5t pressure release. The calculation formula of the compaction density is: compaction density = material mass / (material force area x sample thickness).

[0115] 4. Negative electrode material Raman test

[0116] The negative active material is scanned by a laser microscopic confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Co., Ltd.) to obtain the g peak and the g peak of all particles in the area range. The data is processed by LabSpec software to obtain the peak intensity of each particle d peak and g peak, which are Id and Ig respectively. The frequency of Id / Ig is counted with a step of 0.02 to obtain the normal distribution graph, and the (Id / Ig)max, (Id / Ig)min of these particles are counted, and the average value of Id / Ig is calculated, which is the Id / Ig value of the negative active material. The laser wavelength of the Raman spectrometer can be in the range of 532nm to 785nm.

[0117] d peak: generally at 1350cm -1 , caused by the symmetric stretching vibration mode of sp2 carbon atoms in the aromatic ring (structural defects);

[0118] g peak: appears at 1580cm -1 , caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of E2g optical phonon at the center of the Brillouin zone (carbon atom in-plane vibration).

[0119] 5. Capacity test

[0120] The button cell is placed on a blue electric tester for testing. The testing procedure is as follows: discharging to 5mv at 0.05C, standing for 5min, discharging to 5mv at 0.05mA, discharging to 5mv at 0.01mA, charging to 2.0V at 0.1C to obtain the charging capacity, and finally dividing by the active material weight to obtain the gram capacity of the negative electrode material; dividing the charging capacity by the discharging capacity to obtain the initial efficiency of the negative electrode material.

[0121] 6. Irreversible Li loss rate test

[0122] The button cell is subjected to fast charging performance test, and the testing procedure is as follows:

[0123] 1) The testing temperature is set at 25℃;

[0124] 2) Standing for 10min;

[0125] 3) Discharging to 3.0V at 0.025C;

[0126] 4) Standing for 10min;

[0127] 5) Charging to 4.48V at 3C, and constant voltage to 0.025C;

[0128] 6) Standing for 10min;

[0129] 7) Discharging to 3.0V at 0.025C;

[0130] 8) Standing for 10min;

[0131] 9) Cycling 10 times according to steps 5)-8);

[0132] The capacity of the last cycle is recorded as D10, the capacity of the first cycle is recorded as C1, and the irreversible Li loss rate Q is expressed as: Q=(C1-D10) / C1x100%.

[0133] Test results

[0134] Table 1 shows the influence of BJH pore size distribution of the negative electrode material on the performance of lithium ion batteries, wherein S1 is the adsorption volume of pores with a pore size less than or equal to 2nm, S2 is the adsorption volume of pores with a pore size greater than 2nm and less than or equal to 10nm, and S is the adsorption volume of pores with a pore size less than or equal to 30nm.

[0135] Table 1

[0136]

[0137]

[0138] As can be seen from the data in Table 1, when S1 satisfies 0.0003cm 3 / g≤S1≤0.001 cm 3 / g, S2 satisfies 0.0008 cm 3 / g≤S2≤0.0025 cm 3 / g, S1 / S2 satisfies S1 / S2≥20%, and S2 / S satisfies S2 / S≥15%, the graphite negative electrode has higher gram capacity, which is beneficial to prepare secondary batteries with high energy density, and the irreversible Li loss rate of the secondary battery is smaller when charged at a large rate, which indicates that the secondary battery has more excellent fast charging performance.

[0139] Table 2 further studies the influence of the surface oxygen element content on the performance of lithium ion batteries on the basis of Example 10.

[0140] Table 2

[0141]

[0142]

[0143] It can be seen from the data in Table 2 that when the surface oxygen element content w≤2%, the gram capacity of the negative electrode material is not significantly improved and the kinetics is not significantly improved. When the surface oxygen element content is≥5%, the gram capacity of the negative electrode material is actually reduced. It is speculated that because there are too many oxygen-containing functional groups on the surface of the negative electrode material, the side reaction between the negative electrode material and the electrolyte is increased, so that the initial efficiency is too low, the actual reversible lithium ions are reduced, and then the energy density of the secondary battery and the electrolyte consumption in the cycle process are affected. When the surface oxygen element content satisfies the relationship 2%≤w≤5%, the material has high gram capacity and excellent kinetic performance at the same time.

[0144] Table 3 further studies the influence of the specific surface area A of the negative electrode material on the performance of lithium ion batteries on the basis of Example 13.

[0145] Table 3

[0146]

[0147] It can be seen from the data in Table 3 that when the specific surface area A satisfies the relationship 3m 2 / g≤A≤6m 2 / g, the negative electrode material has very high gram capacity, and the secondary battery has good fast charging performance. The specific surface area of the negative electrode material of Example 23 to Example 25 is larger, and the active area exposed to the electrolyte environment is too high, so that too many side reactions occur, thereby showing low initial efficiency, so that the reversible capacity is reduced.

[0148] Table 4 further studies the influence of the powder compaction density C of the negative electrode material on the performance of lithium ion batteries on the basis of Example 25.

[0149] Table 4

[0150]

[0151]

[0152] From the data in Table 4, it can be seen that the powder compaction density C satisfies the relationship 1.95 g / cm3 3 ≤ C ≤ 2.05 g / cm3 3 The negative electrode materials of the corresponding embodiments all have high gram capacity, in addition, when the powder compaction density is too high, the interlayer slip of the graphite negative electrode material is more prone to occur, thereby reducing the rebound of the electrode sheet after cold pressing and reducing the internal porosity, which will affect the kinetic performance, and the irreversible Li loss will correspondingly increase, so the Li loss of Example 28 to Example 30 is higher than that of Example 25 to Example 27.

[0153] Table 5 further studies the influence of the size of Id / Ig of the negative electrode material on the performance of the lithium ion battery on the basis of Example 27.

[0154] Table 5

[0155]

[0156] From the data in Table 5, it can be seen that when the Id / Ig of the negative electrode material is ≤0.02, the surface treatment degree is too shallow, and no pore and defect structure is formed, thereby showing low gram capacity and high fast-charging irreversible Li loss. When the Id / Ig exceeds 0.4, the surface defect structure is too much, although it can improve the fast-charging irreversible Li loss to a certain extent, but the excessive defects on the surface are prone to side reactions of the electrolyte, resulting in excessive Li consumption during the first charging process, low first efficiency, and thereby low gram capacity. The Id / Ig satisfies the relationship 0.2 ≤ Id / Ig ≤ 0.4, which can satisfy that the material has high gram capacity while having good kinetic performance.

[0157] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be interpreted as a limitation of the present application, and the embodiments can be changed, replaced and modified without departing from the spirit, principles and scope of the present application.

Claims

1. A negative electrode material, comprising a carbon-based material, wherein the negative electrode material satisfies: S1 / S2≥ 20%, S2 / S≥ 15%; 20%≤ S1 / S2≤ 60%; and / or 15%≤ S2 / S≤ 50%, through nitrogen adsorption-desorption test. wherein, S1 represents the adsorption volume of pores having a pore diameter of less than or equal to 2 nm in the negative electrode material, 0.0003 cm 3 / g ≤ S1 ≤ 0.001 cm 3 / g; S2 represents the adsorption volume of pores having a pore diameter of greater than 2 nm and less than or equal to 10 nm in the negative electrode material, 0.0008 cm 3 / g ≤ S2 ≤ 0.0025 cm 3 / g; S represents the adsorption volume of pores having a pore diameter of less than or equal to 30 nm in the negative electrode material.

2. The negative electrode material of claim 1, wherein, The carbon-based material comprises natural graphite and / or artificial graphite.

3. The negative electrode material of claim 1, wherein, 30% < S1 / S2 < 50%; and / or 0.006 cm 3 / g < S < 0.008 cm 3 / g.

4. The negative electrode material according to any one of claims 1 to 3, wherein, The negative electrode material satisfies at least one of the following conditions (i) to (iv):

5. The negative electrode material according to any one of claims 1 to 3, wherein, (i) The surface oxygen element mass content of the negative electrode material is w, 1%≤ w≤ 6%, through X-ray photoelectron spectroscopy test; The negative electrode material satisfies at least one of the following conditions (v) to (viii): (ii) the specific surface area of the negative electrode material is A, 3.0 m 2 / g≤ A≤ 8.0 m 2 / g; (iii) the powder compaction density of the negative electrode material is C, 1.9 g / cm 3 / ≤ C≤ 2.1 g / cm 3 ; (iv) The negative electrode active material satisfies 0.1 < Id / Ig < 0.5 by Raman measurement, where Id is the intensity of a 1350 cm -1 peak in a Raman spectrum, and Ig is the intensity of a 1580 cm -1 peak in the Raman spectrum. (iv) The negative electrode active material satisfies 0.1 < Id / Ig < 0.5 by Raman measurement, where Id is the intensity of a 1350 cm -1 peak in a Raman spectrum, and Ig is the intensity of a 1580 cm -1 peak in the Raman spectrum.

6. The negative electrode material of claim 5, wherein, (v) 2%≤ w≤ 5%; (viii) 0.2≤ Id / Ig≤ 0.

4. (vi) 3.0 m 2 / g ≤ A ≤ 6.0 m 2 / g; (vii) 1.95 g / cm 3 / ≤ C ≤ 2.05 g / cm 3 ; The preparation method of the negative electrode material comprises: heat treating a surface pretreated graphite material in an oxidizing atmosphere, wherein the temperature of the heat treatment is 200℃ to 500℃.

7. The negative electrode material according to any one of claims 1 to 3, wherein 8.A secondary battery, comprising a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material according to any one of claims 1-7. The ratio of the 004 crystal face diffraction peak area C004 to the 110 crystal face diffraction peak area C110 of the negative electrode satisfies 8≤ C004 / C110≤ 18, through X-ray diffraction test.

9. The secondary battery according to claim 8, wherein The compaction density of the negative electrode is P, 1.75 g / cm 3 / ≤ P≤ 1.85 g / cm 3 ; and / or 10.An electronic device, comprising the secondary battery according to claim 8 or 9. ​

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