Negative electrode material, secondary battery, and electronic device

Abstract

Provided is a negative electrode material including a carbon-based material, wherein the surface average roughness of the negative electrode material is Ra, 1.2 nm ≤ Ra ≤ 30 nm. The negative electrode material of the present application has high gravimetric capacity and excellent kinetic performance, and thus a secondary battery including the negative electrode material has both high energy density and fast charging performance. Also provided is a secondary battery including 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 continuous updating and iteration of consumer electronics, the performance requirements of lithium ion batteries are also getting higher and higher, among which the energy density and fast charging capability of lithium ion batteries are usually the key indicators affecting product experience. Artificial graphite, as the main negative electrode material used in lithium ion batteries, can improve the energy density and fast charging performance of lithium ion batteries by improving its specific capacity and kinetic performance.

[0003] Conventional artificial graphite often improves the specific capacity by increasing the graphitization degree of the precursor, but this way of improving the specific capacity is limited, and the graphite under this way has a very regular crystal structure inside and on the surface, which is not conducive to the rapid diffusion of lithium ions, and thus increases the difficulty of lithium ion diffusion and deteriorates the kinetic performance. Therefore, it is of great significance to develop new technical means to greatly improve the specific capacity and kinetic performance of graphite. SUMMARY

[0004] In view of the above problems existing in 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 specific capacity and excellent kinetic performance, thereby enabling the secondary battery comprising the same to have high energy density and fast charging performance.

[0005] In a first aspect, the present application provides a negative electrode material comprising a carbon-based material, wherein the surface average roughness of the negative electrode material is Ra, 1.2 nm≤Ra≤30 nm. The surface layer carbon atoms of the negative electrode material are consumed to different degrees by reaction, and the surface will form a corresponding wrinkle structure, which exhibits a certain roughness on the surface of the negative electrode material. The wrinkle structure on the surface of the negative electrode material of the present application can provide a large number of adsorption sites for lithium ions, thereby improving the specific capacity of the negative electrode material. At the same time, the surface wrinkle structure can also promote the diffusion of lithium ions on the basal plane of the negative electrode material, thereby improving the kinetic performance of the negative electrode material. In addition, the negative electrode material of the present application can expose more end faces, which is conducive to the rapid intercalation of lithium ions and can further improve its kinetic performance. Ra is within the above range, the negative electrode material has a suitable wrinkle structure, which can effectively improve the specific capacity and improve the kinetic performance, thereby obtaining a secondary battery with high energy density and fast charging performance, while not affecting its initial efficiency, storage, cycle and other electrical properties. In some embodiments, 5 nm≤Ra≤25 nm.

[0006] 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 material satisfies 2≤C004 / C110≤7, as tested by X-ray diffraction method. The C004 crystal face of the negative electrode material is parallel to the basal plane direction, and the C110 crystal face is perpendicular to the basal plane direction. The ratio of C004 / C110 can represent the degree of crystal face orientation of the negative electrode material. The larger the ratio of C004 / C110, the greater the proportion of crystal faces parallel to the basal plane in the negative electrode material, which is more unfavorable for the intercalation of lithium ions and results in greater expansion during the cycle process. If the ratio of C004 / C110 is too small, the electrode sheet has a higher risk of deformation during the cycle process. When the ratio of C004 / C110 is within the above range, the negative electrode material has a suitable degree of crystal face orientation, and the secondary battery can exhibit good kinetics without a significant decrease in energy density. In some embodiments, 2≤C004 / C110≤5.

[0007] In some embodiments, the average stacking thickness of the negative electrode material along the c-axis direction is Lc, and 20nm≤Lc≤35nm, as tested by X-ray diffraction method. In some embodiments, the average stacking thickness of the negative electrode material along the a-axis direction is La, and 95nm≤La≤150nm, as tested by X-ray diffraction method. The values of Lc and La of the negative electrode material represent the degree of graphitization thereof. The smaller the values of Lc and La, the smaller the gravimetric capacity of the negative electrode material. When the values of Lc and La are too high, although the gravimetric capacity of the negative electrode material increases, its cycle performance decreases. When the values of Lc and La are within the above range, the negative electrode material has a high gravimetric capacity without a significant decrease in cycle performance. In some embodiments, 23nm≤Lc≤32nm. In some embodiments, 98nm≤La≤145nm.

[0008] In some embodiments, the half-peak width of the 002 crystal face diffraction peak of the negative electrode material is Fw, and 0.28°≤Fw≤0.35°, as tested by X-ray diffraction method. The smaller the Fw, the larger the grain size of the negative electrode material, and the higher the corresponding gravimetric capacity, but the worse the cycle expansion. The larger the Fw, the smaller the grain size of the negative electrode material, and the lower the gravimetric capacity. When the Fw is within the above range, the negative electrode material has a high gravimetric capacity without a significant decrease in cycle performance. In some embodiments, 0.28°≤Fw≤0.32°.

[0009] In some embodiments, the Dv50 of the negative electrode material satisfies: 6 nm≤Dv50≤15 nm. In some embodiments, the Dv99 of the negative electrode material satisfies: 15 nm≤Dv99≤42 nm. The particle size Dv50 and Dv99 of the negative electrode material affect the size of its surface roughness. The smaller the particle, the larger the reaction contact area of the negative electrode material, the deeper the degree of carbon atom reaction, and the higher the surface roughness, but the initial efficiency and cycle capacity retention of the negative electrode material are also lower. The larger the particle, the more difficult the reaction of the negative electrode material during processing, the smaller the surface roughness, and there is no obvious improvement effect on its specific capacity and kinetics, and the particle is too large to make the slurry processing performance of the negative electrode material worse. When the Dv50 and Dv99 of the negative electrode material are within the above range, the secondary battery including the negative electrode material has both high energy density and fast charging performance, and its electrical properties such as initial efficiency, storage, and cycle are not reduced. In some embodiments, 8 nm≤Dv50≤13 nm. In some embodiments, 20 nm≤Dv99≤35 nm.

[0010] In some embodiments, the tap density (TD) of the negative electrode material is greater than or equal to 0.80 g / cm3. 3 A too low tap density can cause the negative electrode material to have poor slurry dispersibility during the preparation of the secondary battery, so that the slurry is prone to sedimentation, resulting in uneven coating thickness and affecting the electrical properties of the secondary battery. In some embodiments, the tap density of the negative electrode material is 0.80 g / cm3 3 to 1.5 g / cm3 3 .

[0011] In some embodiments, the carbon-based material includes artificial graphite and / or natural graphite.

[0012] In some embodiments, the preparation method of the negative electrode material includes: heating and reacting the pretreated graphite material with (NH4)2S2O8 under liquid phase conditions, wherein the mass ratio of the added (NH4)2S2O8 is 1% to 6%.

[0013] In some embodiments, the reaction time of the heating reaction of the carbonaceous material with (NH4)2S2O8 is 6 to 12 h.

[0014] In some embodiments, the reaction temperature of the heating reaction of the carbonaceous material with (NH4)2S2O8 is 80°C to 150°C.

[0015] In a second aspect, the present application provides a secondary battery, which includes a negative electrode, the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes the negative electrode material of the first aspect.

[0016] In some embodiments, the mass content of the negative material is w, based on the mass of the negative active material, wherein 70%≤w≤100%. In some embodiments, 80%≤w≤100%. The negative material with Ra size in the range of 1.2 nm to 30 nm can significantly improve the specific capacity and kinetic performance, and thus the proportion thereof in the negative active material can be more than 70% to effectively improve the energy density and fast charging performance of the secondary battery.

[0017] In some embodiments, the expansion rate of the negative electrode is less than or equal to 30%. The negative material exposes more crystal faces after processing, so that the expansion of the particles in the negative electrode sheet is in multiple directions, and the negative material with Ra in the range of 1.2 nm to 30 nm can to some extent alleviate the expansion rate of the electrode sheet.

[0018] In some embodiments, the compaction density of the negative electrode is greater than or equal to 1.48 g / cm 3 In some embodiments, the sheet resistance of the negative electrode is less than or equal to 0.50 Ω / cm.

[0019] In a third aspect, the present application provides an electronic device comprising the secondary battery of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the negative material of Example 21 of the present application.

[0021] Figure 2 SEM image of the negative material of Comparative Example 1 of the present application.

[0022] Figure 3 Charge-discharge curves of lithium ion batteries of Example 19 and Comparative Example 1 of the present application are shown.

[0023] Figure 4 Irreversible lithium loss of lithium ion batteries of Example 1 and Comparative Example 1 of the present application is shown.

[0024] Figure 5 DCR curves of lithium ion batteries of Example 32 and Comparative Example 1 of the present application are shown. DETAILED DESCRIPTION

[0025] For the sake of brevity, the present application has only specifically disclosed some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, as can any upper limit be combined with any other upper limit to form a range not explicitly recited. Moreover, each individual disclosed point or single numerical value can itself be combined as a lower limit or upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0026] In the description of the present application, unless otherwise stated, "above", "below" include the number.

[0027] Unless otherwise defined, the terms used in the present application have the meanings commonly understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the method given in the examples of the present application).

[0028] The list of items connected by the terms "at least one of", "at least one", "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0029] The present application is further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0030] I. Negative electrode material

[0031] The negative electrode material provided in the present application comprises a carbon-based material, wherein the surface average roughness of the negative electrode material is Ra, 1.2 nm≤Ra≤30 nm. The surface layer carbon atoms of the negative electrode material are consumed to different degrees by reaction, and the corresponding wrinkle structure is formed on the surface, which shows that the negative electrode material has a certain roughness. The wrinkle structure on the surface of the negative electrode material can provide a large number of adsorption sites for lithium ions, thereby improving the gram capacity of the negative electrode material. At the same time, the surface wrinkle structure can also promote the diffusion of lithium ions on the basal plane of the negative electrode material, thereby improving the kinetic performance of the negative electrode material. In addition, the negative electrode material of the present application can expose more end faces, which is beneficial to the rapid insertion of lithium ions and can further improve the kinetic performance. When Ra is within the above range, the negative electrode material has a suitable wrinkle structure, which can effectively improve the gram capacity and improve the kinetic performance, so as to obtain a secondary battery with high energy density and fast charging performance, while the electrical properties such as initial efficiency, storage and cycle are not affected. In some embodiments, Ra is 1.5 nm, 2 nm, 3 nm, 4 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, 15 nm, 15.5 nm, 16 nm, 16.5 nm, 17 nm, 17.5 nm, 18 nm, 18.5 nm, 19 nm, 19.5 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, or a range consisting of any two of these values. In some embodiments, 5 nm≤Ra≤25 nm.

[0032] In some embodiments, the ratio of the diffraction peak area C004 of the 004 crystal plane to the diffraction peak area C110 of the 110 crystal plane of the negative electrode material satisfies 2≤C004 / C110≤7, as tested by X-ray diffraction method. The C004 crystal plane of the negative electrode material is parallel to the basal plane direction, and the C110 crystal plane is perpendicular to the basal plane direction. The ratio of C004 / C110 can represent the degree of crystal plane orientation of the negative electrode material. The larger the ratio of C004 / C110, the greater the proportion of the crystal plane parallel to the basal plane in the negative electrode material, which is more unfavorable for the insertion of lithium ions and has a larger expansion during the cycle process. If the ratio of C004 / C110 is too small, the electrode sheet has a higher risk of deformation during the cycle process. When C004 / C110 is within the above range, the negative electrode material has a suitable degree of crystal plane orientation, and the secondary battery can exhibit good kinetics without a significant reduction in energy density. In some embodiments, C004 / C110 is 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, or a range consisting of any two of these values. In some embodiments, 2≤C004 / C110≤5.

[0033] In some embodiments, the average packing thickness of the negative electrode material along the c-axis direction is Lc, 20 nm≤Lc≤35 nm, as tested by X-ray diffraction method. In some embodiments, Lcis 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, or a range consisting of any two of these values. In some embodiments, the average packing thickness of the negative electrode material along the a-axis direction is La, 95 nm≤La≤150 nm, as tested by X-ray diffraction method. In some embodiments, Lais 100 nm, 103 nm, 105 nm, 107 nm, 110 nm, 113 nm, 115 nm, 117 nm, 120 nm, 123 nm, 125 nm, 127 nm, 130 nm, 143 nm, 145 nm, 147 nm, or a range consisting of any two of these values. The Lcand Lavalues of the negative electrode material represent the degree of graphitization thereof, and the smaller the Lcand Lavalues, the smaller the gravimetric capacity of the negative electrode material. When the Lcand Lavalues are too high, although the gravimetric capacity of the negative electrode material becomes larger, its cycle performance decreases. When the Lcand Lavalues are within the above ranges, the negative electrode material has a high gravimetric capacity while its cycle performance does not decrease significantly. In some embodiments, 23 nm≤Lc≤32 nm. In some embodiments, 98 nm≤La≤145 nm.

[0034] In some embodiments, the half-peak width of the 002 crystal face diffraction peak of the negative electrode material is Fw, 0.28°≤Fw≤0.35°, as tested by X-ray diffraction method. In some embodiments, Fwis 0.285°, 0.29°, 0.295°, 0.3°, 0.305°, 0.31°, 0.315°, 0.325°, 0.33°, 0.335°, 0.34°, 0.345°, or a range consisting of any two of these values. The smaller the Fw, the larger the grain size of the negative electrode material, and the higher the corresponding gravimetric capacity, but the worse the cycle expansion. The larger the Fw, the smaller the grain size of the negative electrode material, and the lower the gravimetric capacity thereof. When the Fwis within the above range, the negative electrode material has a high gravimetric capacity while its cycle performance does not decrease significantly. In some embodiments, 0.28°≤Fw≤0.32°.

[0035] In some embodiments, the Dv50 of the negative electrode material satisfies: 6 nm≤Dv50≤15 nm. In some embodiments, the Dv50 is 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11 nm, 11.5 nm, 12 nm, 12.5 nm, 13 nm, 13.5 nm, 14 nm, 14.5 nm, or a range consisting of any two of these values. The Dv99 of the negative electrode material satisfies: 15 nm≤Dv99≤42 nm. In some embodiments, the Dv99 is 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, or a range consisting of any two of these values. The particle size Dv50 and Dv99 of the negative electrode material affect the size of its surface roughness. The smaller the particle, the larger the reaction contact area of the negative electrode material, the deeper the degree of carbon atom reaction, and the higher the surface roughness, but the initial efficiency and cycle capacity retention rate of the negative electrode material are also lower. The larger the particle, the more difficult the reaction of the negative electrode material during processing, the smaller the surface roughness, and there is no obvious improvement effect on its specific capacity and kinetics, and the particle is too large, which also makes the slurry processing performance of the negative electrode material worse. When the Dv50 and Dv99 of the negative electrode material are within the above ranges, the secondary battery including the negative electrode material has both high energy density and fast charging performance, and its electrical properties such as initial efficiency, storage, and cycle are not reduced. In some embodiments, 8 nm≤Dv50≤13 nm. In some embodiments, 20 nm≤Dv99≤35 nm. In this application, Dv50 represents that 50% of the particles in the particle size distribution of the negative electrode material on a volume basis have a particle size less than this value. Dv99 represents that 99% of the particles in the particle size distribution of the negative electrode material on a volume basis have a particle size less than this value.

[0036] In some embodiments, the tap density of the negative electrode material is greater than or equal to 0.80 g / cm3. 3 A tap density that is too low can cause the negative electrode material to have poor slurry dispersibility during the preparation of the secondary battery, making the slurry prone to sedimentation, resulting in uneven coating thickness, and thus affecting the electrical properties of the secondary battery. In some embodiments, the tap density of the negative electrode material is 0.90 g / cm3, 1.0 g / cm3, 1.1 g / cm3, 1.2 g / cm3, 1.3 g / cm3, 1.4 g / cm3, 1.5 g / cm3, or a range consisting of any two of these values. 3 3 3 3 3 3

[0037] In some embodiments, the carbon-based material includes a graphite material, and the graphite material includes artificial graphite and / or natural graphite.

[0038] ​​​​​​In some embodiments, the method for preparing the negative electrode material comprises: heating the surface-preprocessed graphite material with (NH4)2S2O8 under liquid phase conditions, wherein the mass ratio of (NH4)2S2O8 added is 1% to 6%. In some embodiments, the mass ratio of (NH4)2S2O8 is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range between any two of these values. In this application, the mass ratio of (NH4)2S2O8 is the mass ratio of (NH4)2S2O8 to the mass of the surface-preprocessed graphite material. In some embodiments, the liquid phase conditions can be provided by water, an alcohol solution, or an organic solvent.

[0039] In some embodiments, the reaction time for heating the surface-preprocessed graphite material with (NH4)2S2O8 is 6h to 12h. In some embodiments, the reaction time for heating is 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, or a range between any two of these values.

[0040] In some embodiments, the reaction temperature for heating the surface-preprocessed graphite material with (NH4)2S2O8 is 80℃ to 150℃. In some embodiments, the reaction temperature for heating is 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, or a range between any two of these values.

[0041] In some embodiments, the surface-preprocessing method is to perform carbonization on the surface-coated graphite material at 900℃-1200℃, such as 1000℃, under inert atmosphere conditions, for example, for 4h, and then perform 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 includes one of high-temperature gas phase reaction, liquid phase heating reaction, and high-temperature solid phase reaction, wherein the gas source used in the high-temperature gas phase reaction includes one of oxygen-containing atmosphere, carbon dioxide, nitrogen dioxide, and methane, the reactant used in the liquid phase heating reaction includes one of H2O2, concentrated sulfuric acid, and nitric acid, and the reactant used in the high-temperature solid phase reaction includes one of potassium permanganate, ammonium bicarbonate, and sodium bicarbonate.

[0042] Secondary battery

[0043] The secondary battery provided in the present application comprises a negative electrode, the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises the negative electrode material of the first aspect.

[0044] In some embodiments, the mass content of the negative material is w, based on the mass of the negative active material, wherein 70%≤w≤100%. In some embodiments, w is 70%, 75%, 80%, 85%, 90%, 95%, or a range consisting of any two of these values. In some embodiments, 80%≤w≤100%. Negative materials with Ra sizes in the range of 1.2 nm to 30 nm can significantly improve the gravimetric capacity and kinetic performance, and thus a proportion of 70% or more in the negative active material can effectively improve the energy density and fast-charging performance of the secondary battery.

[0045] In some embodiments, the expansion rate of the negative electrode is less than or equal to 30%. In the present application, the expansion rate of the negative electrode = 100% x (T2-T1) / T1, wherein T1 is the thickness of the negative electrode at 0% state of charge of the secondary battery, and T2 is the thickness of the negative electrode at 100% state of charge of the secondary battery. The negative material exposes more crystal faces after processing, causing the particles in the negative electrode sheet to expand in multiple directions, and the negative material with Ra in the range of 1.2 nm to 30 nm can to some extent alleviate the expansion rate of the electrode sheet.

[0046] In some embodiments, the compaction density of the negative electrode is greater than or equal to 1.48 g / cm 3 In the present application, the compaction density of the negative electrode is the compaction density of the negative electrode at 50% state of charge of the secondary battery. In some embodiments, the sheet resistance of the negative electrode is less than or equal to 0.50 Ω / cm.

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

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

[0049] In some embodiments, the conductive agent comprises, 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 fibers, 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.

[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 employ 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, polyolefin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fiber; a metal-based material such as a metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

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

[0054] For example, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a non-woven 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 non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0055] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0056] The secondary battery of this application also includes an electrolyte. The electrolyte that can be used in this application can be any electrolyte known in the prior art.

[0057] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives. The organic solvent in the electrolyte of this application can be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte of this application; it can be any electrolyte known in the prior art. The additives in the electrolyte of this application can be any additives known in the prior art that can be used as electrolyte additives. 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 ether solvents, such as at least one selected from 1,3-dioxane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate 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 comprising 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 computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, 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 player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, a lithium ion capacitor, and the like.

[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] 1. Preparation of graphite material

[0066] The graphite material used in the present application includes artificial graphite and / or natural graphite, wherein the artificial graphite is obtained by graphitizing carbonaceous raw materials such as needle coke, petroleum coke, pitch coke, and biomass at high temperature, and the natural graphite is obtained by spheroidizing natural flake graphite.

[0067] 2. Surface pretreatment of graphite material

[0068] A certain amount of the above graphite material is weighed, and first subjected to surface pretreatment. The pretreatment method is to carbonize the graphite material at 1000°C in an inert atmosphere for 4h after coating the graphite material on the surface. 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). Then, surface etching reaction is performed, and the reaction mode includes one of high-temperature gas phase reaction, liquid phase heating reaction, and high-temperature solid phase reaction. In the high-temperature gas phase reaction, the gas source includes one of oxygen-containing atmosphere, carbon dioxide, nitrogen dioxide, and methane. In the liquid phase heating reaction, the reactant includes one of H2O2, (NH4)2S2O8, concentrated sulfuric acid, and nitric acid. In the high-temperature solid phase reaction, the reactant includes one of potassium permanganate, ammonium bicarbonate, and sodium bicarbonate.

[0069] The preparation method of Example 1 is as follows: 3 kg of artificial graphite material is weighed, mixed uniformly with pitch as a coating agent (the mass ratio of pitch to artificial graphite is 3:97), and then carbonized at 1000°C under a nitrogen atmosphere for 4 hours to obtain a surface pretreated product; the surface pretreated product is made into a slurry with a solid content of 10%, 1% (mass ratio of the surface pretreated product) of (NH4)2S2O8 is added, then reacted at 80°C for 6 hours, and finally filtered, washed and dried to obtain a carbon-based material, i.e. a negative electrode active material.

[0070] Preparation of the negative electrode

[0071] The above negative electrode material, binder styrene-butadiene rubber (abbreviated as SBR), thickening agent sodium carboxymethyl cellulose (abbreviated as CMC) are mixed in a weight ratio of 97:1.5:1.5, and then fully stirred in a proper amount of deionized water solvent to form a uniform negative electrode slurry; the slurry is coated on a current collector Cu foil with a conductive coating thickness of 1 μm, dried, cold-pressed, and a negative electrode sheet is obtained.

[0072] Preparation of the positive electrode

[0073] Lithium cobalt oxide (chemical formula: LiCoO2) is selected as the positive electrode active material, which is fully stirred and mixed with conductive agent acetylene black and binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96.3:2.2:1.5 in a proper amount of N-methyl pyrrolidone (abbreviated as NMP) solvent to form a uniform positive electrode slurry; the slurry is coated on an Al foil current collector, dried, cold-pressed, and a positive electrode sheet is obtained.

[0074] Preparation of the electrolyte

[0075] In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC=1:3:3:3, then fluoroethylene carbonate and 1,3-propane sultone are added, dissolved and fully stirred, and then lithium salt LiPF6 is added, and the mixture is uniformly mixed to obtain an electrolyte. The mass percentage of LiPF6 is 12.5%, the mass percentage of fluoroethylene carbonate is 2%, and the mass percentage of 1,3-propane sultone is 2%, and the mass percentages of the substances are calculated based on the mass of the electrolyte.

[0076] Preparation of the separator film

[0077] A polyethylene (PE) porous polymer film with a thickness of 7 μm is used as the separator film, and the porosity is 35%.

[0078] Preparation of the lithium ion battery

[0079] 1) Preparation of button lithium ion battery

[0080] The negative electrode was cut into a Φ(diameter) = 14 mm disc as a working electrode, a Φ(diameter) = 18 mm lithium metal sheet was used as a reference electrode, and the two were separated by a Φ(diameter) = 20 mm separator film. An appropriate amount of electrolyte was added, and a CR2430 type button lithium ion battery was assembled.

[0081] 2) Preparation of soft package lithium ion battery

[0082] The positive electrode, separator, and negative electrode were stacked in order, with the separator between the positive electrode and the negative electrode to act as a separator, and then wound to obtain an electrode assembly. After welding the tabs, the electrode assembly was placed in an outer packaging foil aluminum plastic film, and the electrolyte prepared above was injected into the dried electrode assembly. After vacuum packaging, standing, formation, shaping, capacity testing, and other processes, a soft package lithium ion battery was obtained.

[0083] Examples 2 to 11, Comparative Examples 1 to 5

[0084] Preparation of negative electrode material

[0085] The preparation process of the negative electrode material was similar to that of Example 1, except that the mass ratio of (NH4)2S2O8 added was adjusted to prepare the corresponding negative electrode material. The specific preparation parameters are shown in Table a:

[0086] Table a

[0087]

[0088]

[0089] The preparation of the negative electrode and the button battery and lithium ion battery was the same as in Example 1.

[0090] Examples 12 to 23

[0091] Preparation of negative electrode material

[0092] The preparation process of the negative electrode material was similar to that of Example 8, except that the reaction time was adjusted to adjust the C004 / C110 value of the negative electrode material. The specific preparation parameters are shown in Table b:

[0093] Table b

[0094]

[0095] Examples 24 to 30

[0096] The preparation process of the negative electrode material is similar to that of Example 21, except that the C004 / C110 value of the negative electrode material is adjusted by adjusting the reaction temperature. The specific preparation parameters are shown in Table C.

[0097] Table C

[0098]

[0099] The negative electrode and the preparation of the button cell and the lithium ion battery are the same as those of Example 21.

[0100] Examples 31 to 36

[0101] Preparation of the negative electrode material

[0102] The preparation process of the negative electrode material is the same as that of Example 27.

[0103] Preparation of the negative electrode

[0104] The preparation process of the negative electrode is similar to that of Example 27, except that the graphite negative electrode material and the conventional artificial graphite are used as the negative electrode active material, and the mass ratio of the graphite negative electrode material to the negative electrode active material is 95%, 90%, 85%, 80%, 75%, and 70%, respectively.

[0105] The preparation of the button cell and the lithium ion battery is the same as that of Example 27.

[0106] Test method

[0107] 1. Dv50, Dv99 test

[0108] The particle size of the negative electrode material is measured by using a Malvern particle size tester: the negative electrode material is dispersed in a dispersing agent (ethanol), and after ultrasonic treatment for 30 minutes, the sample is added to the Malvern particle size tester, and the test is started. The Dv50 of the negative electrode material is the particle size at which the volume accumulation is 50% from the small particle size side in the volume-based particle size distribution of the negative electrode material; at the same time, the Dv99 of the negative electrode material is the particle size at which the volume accumulation is 99% from the small particle size side in the volume-based particle size distribution of the negative electrode material.

[0109] 2. Test of the average surface roughness of the negative electrode material

[0110] The surface roughness R1, R2, …, Rn of the negative electrode material is tested by atomic force microscopy (AFM) in an area of 15 μm x 15 μm on the surface of the negative electrode material. 100 The arithmetic average roughness Ra of its surface is Ra = (R1 + R2 + … + Rn) / 100. 1+ R1 + R2 + … + Rn. 2+ 100

[0111] 3. XRD test of the negative electrode material​​

[0112] The (004) face diffraction pattern and the (110) face diffraction pattern in the X-ray diffraction pattern of the negative electrode material are tested according to the People's Republic of China mechanical industry standard JB / T 4220-2011 "Determination of lattice parameters of artificial graphite". The test conditions are as follows: X-ray uses CuKα radiation, and the CuKα radiation is removed by a filter or a monochromator. The working voltage of the X-ray tube is (30-35) kV, and the working current is (15-20) mA. The scanning speed of the counter is 1 / 4 (°) / min. When recording the 004 diffraction pattern, the scanning range of the diffraction angle 2θ is 53°-57°. When recording the 110 diffraction pattern, the scanning range of the diffraction angle 2θ is 75°-79°. The peak area obtained from the (004) face diffraction pattern is denoted as C004. The peak area obtained from the (110) face diffraction pattern is denoted as C110.

[0113] The negative electrode active material graphite is tested by using an X-ray powder diffractometer, the target material is CuKα; the voltage and current are 40KV / 40mA, the scanning angle range is 5° to 80°, the scanning step length is 0.00836°, and the time for each step length is 0.3s. According to the obtained X-ray diffraction pattern, the full width at 50% between the lowest and highest points of the peak intensity of the 002 peak is denoted as Fw. La is the average size of the graphite crystallite along the a-axis direction, La=Kλ / β(2θ) / cosβ. K=scherrer constant (K=0.9), β is the half-peak width of the 100 crystal face diffraction peak, λ is the wavelength (0.154056), and θ is the 100 crystal face diffraction peak maximum peak intensity position angle. Lc is the average stacking thickness of the graphite crystallite along the c-axis direction, Lc=Kλ / α(2θ) / cosα. K=scherrer constant (K=0.9), α is the half-peak width of the 002 peak, λ is the wavelength (0.154056), and θ is the 002 peak maximum peak intensity position angle.

[0114] 4. Tap density test of negative electrode material

[0115] The tap density is the mass per unit volume of the powder in the container after being vibrated under specified conditions, and the unit is g / cm 3 .

[0116] The test method is to fix a graduated cylinder containing a certain mass of powder on a mechanical vibration device, the vibration motor drives the mechanical vibration device to vibrate vertically up and down, the graduated cylinder containing the powder vibrates periodically with the mechanical vibration device, as the number of vibrations increases, the powder in the graduated cylinder is gradually vibrated and compacted, after the number of vibrations reaches the set number, the mechanical vibration device stops vibrating, and the volume of the graduated cylinder is read. According to the definition of density: mass divided by volume, the density of the vibrated and compacted powder is calculated. The specific process parameters are: vibration frequency: 5000 times; vibration frequency: 250±15 times / min; ambient temperature: 15℃ to 28℃.

[0117] 5. Gram capacity test

[0118] Place the button cell on the blue test instrument for testing, the test procedure is to discharge to 5mv at 0.05C, stand for 5min, discharge to 5mv at 0.05mA, discharge to 5mv at 0.01mA, charge to 2.0V at 0.1C to obtain the charge capacity, and finally divide by the active material weight to obtain the gram capacity of the negative electrode material. The first efficiency can be obtained by comparing the charge capacity with the discharge capacity.

[0119] 6. Irreversible Li loss rate test

[0120] Test the fast charging performance of the button cell, the test procedure is as follows:

[0121] 1) The test temperature is set at 25℃;

[0122] 2) Stand for 10min;

[0123] 3) Discharge to 3.0V at 0.025C;

[0124] 4) Stand for 10min;

[0125] 5) Charge to 4.48V at 3C, constant voltage to 0.025C;

[0126] 6) Stand for 10min;

[0127] 7) Discharge to 3.0V at 0.025C;

[0128] 8) Stand for 10min;

[0129] 9) Cycle 10 times for steps 5)-8);

[0130] Record the capacity of the last cycle as D10, and the capacity of the first cycle as C1, the irreversible Li loss rate Q is expressed as: Q=(C1-D10) / C1×100%.

[0131] 7. Lithium ion battery DCR direct current impedance test

[0132] 1) Test temperature is 25°C;

[0133] 2) Rest for 60 min;

[0134] 3) 0.5C CC (constant current) to 4.48V, CV (constant voltage) to 0.025C;

[0135] 4) Rest for 10 min;

[0136] 5) 0.1C DC (direct current) to 3V;

[0137] 6) Rest for 10 min;

[0138] 7) 0.5C CC to 4.48V, CV to 0.025C;

[0139] 8) Rest for 1 h;

[0140] 9) 0.1C DC to 10s;

[0141] 10) 1C DC to 1s;

[0142] 11) Rest for 1 h;

[0143] 12) 0.5C DC to 6 min;

[0144] 13) If voltage < 2.5V, go to step 15;

[0145] 14) Repeat step 8 to step 13 for 26 times;

[0146] 15) Rest for 10 min;

[0147] 16) 0.5C CC to 3.95V, CV to 0.025C;

[0148] 17) Rest for 10 min;

[0149] Take the impedance DCR of the battery at 70% SOC, and the test is over.

[0150] Test results

[0151] Table 1 shows the effect of the surface average roughness Ra of the negative electrode material on the performance of lithium ion batteries.

[0152] Table 1

[0153]

[0154] From the data in Table 1, it can be seen that when Ra satisfies the range 1.2 nm≤Ra≤30 nm, the negative electrode material has higher gram capacity and initial efficiency, and lower DCR and Li loss rate. When Ra is below 1.2 nm, the gram capacity of the negative electrode material is relatively low, and the DCR and Li loss rate are relatively high. When Ra is above 30 nm, the initial efficiency of the negative electrode material decreases, which will adversely affect the energy density and cycle performance of the lithium ion battery.

[0155] Table 2 further studies the influence of the ratio of the diffraction peak area of the 004 crystal plane to the diffraction peak area of the 110 crystal plane C004 / C110 of the negative electrode material, the average stacking thickness of the negative electrode material along the c-axis direction Lc, the average stacking thickness of the negative electrode material along the a-axis direction La, and the half-peak width of the 002 crystal plane diffraction peak on the performance of the lithium ion battery on the basis of Example 8.

[0156] Table 2

[0157]

[0158] From the data in Table 2, it can be seen that C004 / C110 represents the orientation degree of the crystal plane of the negative electrode material. The smaller the value, the better the isotropy of the negative electrode material, which is beneficial to the embedding of lithium ions from multiple directions, thereby improving the kinetic performance. However, too small C004 / C110 will increase the risk of deformation of the electrode sheet during the cycle process. When C004 / C110 is 2 to 5, it is more appropriate. In addition, when Lc satisfies 23.0 nm≤Lc≤32.0 nm, La satisfies 98.0 nm≤La≤145 nm, and Fw satisfies 0.280°≤Fw≤0.320°, the negative electrode material has higher gram capacity.

[0159] Table 3 further studies the influence of the size of Dv50 and Dv99 of the negative electrode material on the performance of the lithium ion battery on the basis of Example 21.

[0160] Table 3

[0161]

[0162]

[0163] As can be seen from Examples 21, 24 to 26 in Table 3, as Dv50 and Dv99 decrease, the initial efficiency of the negative electrode material tends to decrease. It is presumed that because the reaction contact area of the negative electrode material increases, the degree of carbon atom reaction deepens, and the surface roughness increases, the side reaction between the negative electrode material and the electrolyte intensifies, thereby causing the initial efficiency to decrease. As can be seen from Examples 21, 27 to 30, as Dv50 and Dv99 increase, the surface average roughness Ra of the negative electrode material gradually decreases, and the level of the gravimetric capacity tends to decrease. It is presumed that because the particles increase, the negative electrode material is more difficult to react during processing, the surface roughness is smaller, and the adsorption sites of lithium ions decrease, thereby causing the improvement effect on the gravimetric capacity to weaken. At the same time, too large particles can also make the negative electrode slurry processing performance poor, causing particle scratches in the coating process of a thin electrode sheet, and causing the performance to decrease. The tap density (TD) of the reaction material in the slurry processing process, as the degree of reaction increases, the surface groups of the material increase, and the material is easy to uniformly disperse in the slurry. In summary, it is more appropriate to limit the range of Dv50 to 8 nm to 13 nm, the range of Dv99 to 20 nm to 35 nm, and TD≥0.80 g / cm3. 3

[0164] Table 4 further studies the influence of the mass ratio w of the above-mentioned graphite negative electrode material in the negative electrode active material on the performance of the lithium ion battery based on Example 27.

[0165] Table 4

[0166]

[0167] As can be seen from the data in Table 4, when the graphite ratio w satisfying 1.2 nm≤Ra≤30 nm is more than 80%, the negative electrode sheet has a higher gravimetric capacity, a smaller negative electrode expansion rate, a lower DCR, and a lower Li loss rate. It is presumed that because the graphite negative electrode material satisfying 1.2 nm≤Ra≤30 nm has a higher gravimetric capacity than conventional graphite, and its C004 / C110 is also smaller than conventional graphite, the expansion of the electrode sheet after lithium intercalation is in multiple directions, so the negative electrode expansion rate can be alleviated. In addition, it is also more conducive to the intercalation of lithium ions from multiple directions, thereby improving the kinetic performance. Therefore, limiting the graphite ratio w satisfying 1.2 nm≤Ra≤30 nm to be more than 80% can obtain a better improvement effect.

[0168] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above-mentioned embodiments cannot be interpreted as a limitation of the present application, and changes, substitutions, and modifications can be made to the embodiments without departing from the spirit, principles, and scope of the present application.​

Claims

1. A negative electrode active material, the negative electrode active material being a graphite material, wherein, The surface average roughness of the graphite material is Ra, and 1.2 nm≤Ra≤30 nm; The ratio of the 004 crystal face diffraction peak area C004 to the 110 crystal face diffraction peak area C110 of the graphite material satisfies 2≤C004 / C110≤7 through X-ray diffraction testing.

2. The negative active material according to claim 1, wherein, 5 nm≤Ra≤25 nm.

3. The negative active material according to claim 1, wherein, The negative electrode active material satisfies at least one of conditions (i) to (iv) below: (i) The average stacking thickness of the negative electrode active material along the c-axis direction is Lc, and 20 nm≤Lc≤35 nm, and the average stacking thickness of the negative electrode active material along the a-axis direction is La, and 95 nm≤La≤150 nm, through X-ray diffraction testing; (ii) The half-peak width of the 002 crystal face diffraction peak of the negative electrode active material is Fw, and 0.28°≤Fw≤0.35°, through X-ray diffraction testing; (iii) The Dv50 of the negative electrode active material satisfies 6 nm≤Dv50≤15 nm, and the Dv99 of the negative electrode active material satisfies 15 nm≤Dv99≤42 nm; (iv) the tap density of the negative electrode active material is greater than or equal to 0.80 g / cm3 3 .

4. The negative active material according to claim 3, wherein, The negative electrode active material satisfies at least one of conditions (v) to (viii) below: (v) 23 nm≤Lc≤32 nm, and 98 nm≤La≤145 nm; (vi) 0.28°≤Fw≤0.32°; (vii) 8 nm≤Dv50≤13 nm, and 20 nm≤Dv99≤35 nm; (viii) the tap density of the negative electrode active material is 0.80 g / cm 3 up to 1.5 g / cm 3 .

5. The negative active material according to any one of claims 1 to 3, wherein, 2≤C004 / C110≤5.

6. The negative active material according to any one of claims 1 to 3, wherein, The graphite material includes natural graphite and / or artificial graphite.

7. A method for producing the negative electrode active material according to any one of claims 1 to 3, wherein The preparation method includes: heating and reacting the pretreated graphite material with (NH4)2S2O8 under liquid phase conditions, wherein the mass ratio of the added (NH4)2S2O8 is 1% to 6%.

8. A secondary battery comprising a negative electrode, the negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising the negative electrode active material according to any one of claims 1-6.

9. The secondary battery according to claim 8, wherein The negative electrode satisfies at least one of conditions (xi) to (xiii) below: (xi) The expansion rate of the negative electrode is less than or equal to 30%; (xii) the compacted density of the negative electrode is greater than or equal to 1.48 g / cm 3 ; (xiii) The sheet resistance of the negative electrode is less than or equal to 0.50 Ω / cm.

10. An electronic device comprising the secondary battery according to any one of claims 8-9.

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