Negative electrode active material, negative electrode piece containing the same, electrochemical apparatus and power consumption apparatus

Abstract

The present invention provides a negative electrode active material, a negative electrode piece containing the same, an electrochemical device, and a power consumption device. The negative electrode active material includes a hard carbon material, and the hard carbon material has an average lithium release potential of 0.15 V (vs. Li ) when used with a lithium metal counter electrode. + / Li)~0.40V(vs Li + / Li).

Description

Cross-reference of related applications

[0001] This invention claims priority to Chinese Patent Application No. 202211206036.6, filed on 30 September 2022, titled "Negative electrode active material, negative electrode piece containing the same, electrochemical apparatus and power consumption apparatus," all contents of said application are incorporated herein by reference. [Technical Field]

[0002] The present invention relates to the technical field of electrochemical batteries, and more specifically to a negative electrode active material, a negative electrode piece containing the same, an electrochemical apparatus, and a power consumption apparatus. [Background technology]

[0003] Rechargeable batteries, such as lithium-ion batteries, possess remarkable characteristics including high energy density, long cycle life, low pollution, and no memory effect. As a clean energy source, rechargeable batteries are becoming widespread in various applications, from electronic products to large-scale equipment such as electric vehicles, in order to adapt to sustainable development strategies for the environment and energy. This, in turn, demands for even higher energy density in rechargeable batteries.

[0004] Currently, graphite remains the primary negative electrode material for commercially available rechargeable batteries. Graphite offers advantages such as high conductivity and high stability. However, the theoretical capacity of graphite is approximately 372 mAh / g, and in recent years, development has almost reached its theoretical upper limit, making it difficult to further increase the energy density of lithium-ion batteries using graphite as the negative electrode material.

[0005] Therefore, developing negative electrode active materials to increase the energy density of secondary batteries is extremely important for the advancement of secondary batteries. [Overview of the project]

[0006] In view of the above-mentioned problems in the prior art, the present invention provides a negative electrode active material, a negative electrode piece containing the same, an electrochemical device, and a power consumption device. The negative electrode active material has a low lithium release average potential, thereby increasing the energy density of the negative electrode piece, the electrochemical device, and the power consumption device.

[0007] A first aspect of the present invention is a negative electrode active material, wherein the negative electrode active material includes a hard carbon material, and the average lithium release potential of the negative electrode active material with lithium metal as the counter electrode is 0.15V(vs Li + / Li)~0.40V(vs Li + The present invention provides a negative electrode active material in which the hard carbon material has multiple micropores such that the ratio is / Li.

[0008] In each embodiment, the O / C value, which is the ratio of the average number of moles of oxygen atoms to carbon atoms in the hard carbon material, is between 0.01 and 0.10.

[0009] In all embodiments, the O / C value of the hard carbon material is 0.02 to 0.07.

[0010] In any embodiment, the negative electrode active material is

number

[0011] In each embodiment, the X-ray diffraction pattern of the hard carbon material has a characteristic peak in the 18°–30° range, and the full width at half maximum of the characteristic peak is 4°–12°.

[0012] In any of the embodiments, the hard carbon material includes a core and a coating layer located on at least a part of the surface of the core, and abundant micropores are located within the core.

[0013] In any of the embodiments, the pore volume V of the micropores of the hard carbon material measured by the carbon dioxide gas adsorption method satisfies 0 cc / g < V ≤ 0.05 cc / g, and the diameter d nm of the micropores satisfies d nm ≤ 0.9 nm.

[0014] In any of the embodiments, the true density ρ g / cc of the hard carbon material measured by the n-butanol dipping method is 1.1 g / cc to 1.6 g / cc.

[0015] In any of the embodiments, D V 50 of the hard carbon material is 6 μm to 15 μm.

[0016] In any of the embodiments, the specific surface area of the hard carbon material is 2 m 2 / g to 10 m 2 / g.

[0017] A second aspect of the present invention is a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes the negative electrode active material of the first aspect, providing a negative electrode sheet.

[0018] In any of the embodiments, the negative electrode active material layer further includes artificial graphite, and the mass ratio A of the negative electrode active material to artificial graphite satisfies 0 < A ≤ 1 / 3.

[0019] In any of the embodiments, the compression density PD g / cm 3 of the negative electrode active material layer is 1.0 g / cm 3 to 1.7 g / cm 3 .

[0020] In any of the embodiments, the porosity of the negative electrode active material layer is 15% to 30%.

[0021] A third aspect of the present invention provides an electrochemical apparatus comprising the negative electrode piece described in the second aspect.

[0022] A fourth aspect of the present invention provides a power consumption device that includes the electrochemical apparatus described in the third aspect. [Brief explanation of the drawing]

[0023] [Figure 1] Figure 1 is a schematic diagram of an embodiment of the electrochemical apparatus of the present invention. [Figure 2] Figure 2 is an exploded view of an embodiment of the electrochemical apparatus of the present invention shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram of a power consumption device powered by an embodiment of the electrochemical apparatus of the present invention. [Figure 4] Figure 4 is a voltage-capacitance graph of a button battery corresponding to Embodiment 4 of the present invention. [Explanation of symbols]

[0024] 5 electrochemical apparatus, 51 case, 52 electrode assembly, 53 cover plate. [Modes for carrying out the invention]

[0025] Embodiments of the electrochemical apparatus and power consumption apparatus of the present invention will be described in detail below, with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of the same actual configuration may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and do not limit the subject matter described in the claims.

[0026] The “ranges” disclosed herein are limited in the form of lower and upper limits, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of a particular range. Ranges limited in this form may or may not include endpoints and can be arbitrarily combined. That is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is expected that this will be understood as the ranges 60-110 and 80-120. Also, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then all ranges such as 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are expected. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" in this specification means that all real numbers between "0 to 5" are listed, and "0 to 5" is an abbreviation for combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and selectable technical features of the present invention can be combined to form new technical solutions.

[0029] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0030] As described in the background information, developing negative electrode active materials to increase the energy density of secondary batteries is extremely important for the advancement of secondary batteries. Among the many negative electrode active materials awaiting development, hard carbon materials are attracting considerable attention due to their advantages such as high capacity per gram, good rate performance, and good low-temperature performance and cycle performance. In addition, hard carbon can be used as a negative electrode active material for both lithium-ion batteries and sodium-ion batteries, giving it a wide range of applications. However, conventional hard carbon materials have drawbacks such as high irreversible capacity and less-than-ideal capacity performance, so their application to lithium-ion or sodium-ion batteries is very limited in terms of improving battery energy density and is therefore insufficient for practical applications.

[0031] In view of this, the present inventors have conducted diligent research and have provided a negative electrode active material having a low lithium release average potential. By applying this negative electrode active material to a secondary battery, the energy density of the secondary battery can be increased.

[0032] negative electrode active material A first aspect of the present invention is a negative electrode active material, wherein the negative electrode active material includes a hard carbon material, and the hard carbon material has a lithium release average potential of 0.15V (vs Li) when a lithium metal is used as the counter electrode. + / Li)~0.40V(vs Li +The present invention provides a negative electrode active material having multiple micropores such that ( / Li) is the case. Although not intended to be limited to any theory or interpretation, the inventors have unexpectedly found that if a hard carbon material has multiple micropores, lithium ions can be intercalated into the micropores during the lithium intercalation process, thus providing reversible capacity. If a hard carbon material has a specific micropore structure such that the average lithium release potential of the hard carbon material with lithium metal as the counter electrode is within the relatively low range described above, the hard carbon material can have, on the one hand, high reversible capacity, particularly low-voltage platform capacity, and on the other hand, good lithium-ion diffusion dynamics performance. As a result, by applying the negative electrode active material of the present invention to a secondary battery, the secondary battery can be given high energy density, high initial Coulomb efficiency, and good cycle performance.

[0033] The specific micropore structure described above results in a lithium release average potential of 0.15V (vs Li) for hard carbon materials with lithium metal as the counter electrode. + / Li)~0.40V(vs Li + This is intended to represent any microporous structure in which the lithium emission average potential of a negative electrode active material with lithium metal as the counter electrode is 0.15 V (vs Li + / Li)~0.40V(vs Li + Hard carbon materials with specific microporous structures can be obtained in various ways, such as by using the formula / Li, but we will not be limited to these methods here.

[0034] In some embodiments, the O / C value, which is the ratio of the average number of moles of oxygen atoms to carbon atoms in a hard carbon material, may be between 0.01 and 0.10. For example, the O / C value of a hard carbon material may be 0.01, 0.02, 0.05, 0.07, 0.10, or within the range of any of the above values. Optionally, the O / C value of a hard carbon material may be between 0.02 and 0.07. For example, the O / C value of a hard carbon material may be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, or within the range of any of the above values. While not intended to limit to any particular theory or interpretation, when the O / C value of a hard carbon material is within the above appropriate range, the presence of a small amount of oxygen atoms is advantageous for the release of lithium ions within the micropores, thereby favoring the expression of the capacity of the negative electrode active material. Furthermore, if the O / C value falls within the appropriate range described above, the risk of irreversible capacity loss due to excess oxygen content can be reduced, thereby increasing the reversible capacity of the negative electrode active material. As a result, by applying the negative electrode active material of the present invention to a secondary battery, the energy density and initial Coulomb efficiency of the secondary battery can be further increased.

[0035] In some embodiments, the negative electrode active material is

number

[0036] In some embodiments, the X-ray diffraction (XRD) pattern of the hard carbon material may have characteristic peaks in the 18°–30° range with a full width at half maximum (FMAX) of 4°–12°. When the XRD diagram of the anode active material has these characteristic peaks, it indicates that the 002 lattice plane spacing of the hard carbon material is between 0.37 nm and 0.41 nm, which is much larger than that of graphite. This relatively large 002 lattice plane spacing contributes to the rapid release of lithium ions within the hard carbon material, thereby enhancing the reversible capacity and kinetic performance of the anode active material. As a result, applying the anode active material of the present invention to a secondary battery can improve the energy density and rate performance of the secondary battery.

[0037] In some embodiments, the hard carbon material may include a core and a coating layer located on at least a portion of the surface of the core, wherein the micropores are located within the core. The coating layer may be a dense coating layer that does not contain micropores. In some embodiments, the thickness of the coating layer may be 100 nm or less. In some embodiments, the coating layer may cover 50% or more of the surface area of ​​the core, 80% or more of the surface area, 90% or more of the surface area, or 100% of the surface area. When the hard carbon material has the above structure, the coating layer can effectively block contact between the inside of the micropores and the electrolyte by converting open micropores on the surface of the core into closed micropores, further reducing the irreversible loss of active ions due to the electrolyte forming an SEI film inside the micropores. As a result, by increasing the reversible capacity of the negative electrode active material, a secondary battery using the negative electrode active material can have a high energy density and a high initial Coulomb efficiency.

[0038] In some embodiments, the hard carbon material includes a core and a coating layer located on at least a part of the surface of the core. The pore volume V of the micropores of the hard carbon material measured by the carbon dioxide gas adsorption method can satisfy 0 cc / g < V ≤ 0.05 cc / g. When the hard carbon material includes a coating layer covering at least a part of the surface of the core, the coating layer can convert the open micropores on the core surface into closed micropores. When some of the micropores have a relatively small volume, not only is it difficult for carbon dioxide molecules to enter the micropores of the core for adsorption and desorption during the measurement process of carbon dioxide gas adsorption, but it is also difficult for them to be adsorbed into some of the micropores with a small volume. As a result, the volume of the micropores of the hard carbon material measured by the carbon dioxide gas adsorption method is within the relatively small range described above. When the volume of the micropores of the hard carbon material measured by the carbon dioxide gas adsorption method is within the relatively small range described above, on the one hand, the coating layer can effectively block the contact between the inside of the micropores and the electrolyte, thereby reducing the irreversible loss of active ions caused by the formation of the SEI film inside the micropores by the electrolyte. On the other hand, the small-volume micropores are advantageous for the deposition of lithium ions or sodium ions with a relatively small radius, thereby further increasing the lithium storage capacity / sodium storage capacity of the hard carbon material. As a result, by applying the negative electrode active material of the present invention to a secondary battery, the energy density and the initial Coulomb efficiency of the secondary battery can be further increased.

[0039] In some embodiments, the diameter d nm of the micropores can satisfy d nm ≤ 0.9 nm. When the diameter of the micropores is within the above appropriate range, it is advantageous for lithium ions (the ionic radius is about 76 pm) or sodium ions (the ionic radius is about 102 pm) to deposit and release smoothly inside the micropores, which is advantageous for improving the reversible capacity of the hard carbon particles. As a result, the negative electrode active material of the present invention can have a high reversible capacity, and thus, when applied to a secondary battery, the energy density of the battery can be increased.

[0040] In some embodiments, the true density ρ g / cc of the hard carbon material measured by the n-butanol dipping method may be 1.1 g / cc to 1.6 g / cc. The true density of the graphite material measured by the n-butanol dipping method is approximately 2.22 g / cc. In the anode active material of the present invention, the hard carbon material has a relatively large number of micropores and a relatively large 002 lattice plane spacing, thereby having both high capacity and a lower true density. As a result, by applying the anode active material of the present invention to a secondary battery, the mass energy density of the secondary battery can be further increased.

[0041] In some embodiments, the volume-average particle size D of the hard carbon material V 50 may be 6 μm to 15 μm. For example, D of hard carbon material V 50 may be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, or it may be within the range of any of the above values. Optionally, the hard carbon material may be primary particles. When the volume-average particle size of the hard carbon material is within the above appropriate range, on the one hand, the hard carbon material can have good electrolyte wettability, and on the other hand, by having a relatively small specific surface area, the active ions consumed by forming an SEI film on the surface of the hard carbon material during the initial charging process can be reduced. As a result, by applying the negative electrode active material of the present invention to a secondary battery, the secondary battery can have both good kinetic performance and high initial Coulomb efficiency.

[0042] In some embodiments, the specific surface area of ​​the hard carbon material is 2 m². 2 / g~10m 2 It may also be / g. For example, the specific surface area of ​​a hard carbon material is 2m². 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 The value may be / g, or it may be within the range of any of the above values. Generally, the larger the specific surface area of ​​the negative electrode active material particles, the larger the area of ​​the SEI film formed on the surface of the negative electrode active material particles during the initial charging process of the secondary battery, and the greater the loss of active ions. Also, the larger the specific surface area of ​​the negative electrode active material particles, the greater the amount of binder consumed to form the negative electrode active material layer, thus increasing the internal resistance of the negative electrode active material layer. If the specific surface area of ​​the hard carbon material is within the appropriate range above, applying it to a secondary battery allows the SEI film formed during the initial charging process to have an appropriate area while reducing the amount of binder used in the negative electrode active material layer. As a result, by reducing the loss of active ions and the internal resistance of the negative electrode active material layer, the initial Coulomb efficiency, energy density, cycle performance, and safety performance of the secondary battery can be improved.

[0043] As an example, the hard carbon material for the negative electrode active material of the present invention can be obtained by the following steps S10 to S40. Note that the hard carbon material for the negative electrode active material of the present invention can be obtained by various methods, and this example is not intended to limit the present invention, but merely to illustrate it.

[0044] S10. The hard carbon precursor material is placed in an oxygen-containing atmosphere, and the temperature of the reaction system is maintained at 100°C to 300°C to obtain the oxygen-added hard carbon precursor material.

[0045] In step S10, the hard carbon precursor material may be one or more selected from the group consisting of asphalt, biomass, and resin-based materials. The oxygen-containing atmosphere refers to an atmosphere containing oxygen gas. The oxygen-containing atmosphere may be, for example, compressed air, or a mixture of oxygen gas and an inert gas. In the mixture, the mass percentage of oxygen gas may be 1% to 100%. The gas flow rate of the oxygen-containing atmosphere may be 0.1 L / min to 5 L / min. The reaction time for step S10 may be 48 hours or less.

[0046] In S20, the oxygen-added hard carbon precursor material is placed in an inert atmosphere and heated to 450°C to 650°C at a heating rate of 0.5°C / min to 5°C / min. Then, the oxygen-added hard carbon precursor material is kept warm for a certain period of time to pre-carbonize it, thereby obtaining a pre-carbonized product.

[0047] In Step S20, the inert atmosphere can include an atmosphere that does not cause side reactions with the oxygen-granulated hard carbon precursor material, such as a nitrogen gas atmosphere, an argon gas atmosphere, or another noble gas atmosphere. The gas flow rate of the inert atmosphere may be 0.1 L / min to 5 L / min. In Step S20, the incubation time may be 1 hour to 4 hours.

[0048] In S30, the pre-carbonized product is placed in an inert atmosphere and heated to 700°C to 1600°C at a heating rate of 0.5°C / min to 10°C / min. After that, the product is kept warm for a certain period of time to further carbonize the pre-carbonized product and obtain the carbonized material.

[0049] In Step S30, the inert atmosphere can include an atmosphere that does not undergo side reactions with the pre-carbonization product, such as a nitrogen gas atmosphere, an argon gas atmosphere, or another noble gas atmosphere. The gas flow rate of the inert atmosphere may be 0.1 L / min to 5 L / min. In Step S30, the heating time may be 1 hour to 12 hours. In some examples, after obtaining the carbide, crushing and particle size classification treatments can be performed on the carbide to obtain carbide with a particle size within an appropriate range.

[0050] In S40, a hard carbon material is obtained by placing carbides in a reducing atmosphere, raising the temperature to 500°C to 1100°C at a heating rate of 0.5°C / min to 20°C / min, and then maintaining the temperature for a certain period of time.

[0051] In Step S40, the reducing atmosphere can be selected from atmospheres containing reducing gases, for example, a mixed gas of acetylene-argon with a mass percentage of 5% acetylene, or a mixed gas of methane-argon with a mass percentage of methane of 10%. The gas flow rate of the reducing atmosphere may be 0.1 L / min to 3 L / min. In Step S40, the heat retention time may be 0.1 hours to 8 hours.

[0052] In the above example, by applying an oxygenation treatment to the hard carbon precursor material, the oxygen content of the hard carbon precursor material can be increased, and the cross-linking structure inside the hard carbon precursor material can be altered. As a result, after carbonization, the material can have an appropriate microporous structure and a relatively high microporous content. By heat-treating the carbide in a reducing atmosphere, on the one hand, a dense coating layer can be formed on the surface of the carbide, resulting in a hard carbon material consisting of a core containing multiple micropores and a coating layer, and on the other hand, the oxygen content of the carbide can be reduced, bringing the O / C value of the hard carbon material within an appropriate range. As a result, the average lithium release potential of the hard carbon material with lithium metal as the counter electrode is 0.15V(vs Li + / Li)~0.40V(vs Li + A hard carbon material having multiple micropores can be prepared such that the ratio is / Li.

[0053] In this invention, the average lithium release potential of a hard carbon material with lithium metal as the counter electrode is of articulate significance and can be measured by methods known in the art. For example, a hard carbon material is uniformly mixed with an appropriate amount of binder, conductive agent, and solvent to obtain a negative electrode slurry; the negative electrode slurry is applied to the surface of a negative electrode current collector to obtain a negative electrode piece; a lithium metal piece is used as the positive electrode piece and assembled with the negative electrode piece to obtain a button cell; a charge-discharge cycle is performed on the button cell to determine the charging capacity and charging energy of the button cell; the charging capacity is divided by the charging energy to obtain the average lithium release potential of the hard carbon material.

[0054] In this invention, the O / C value of hard carbon materials has a well-known meaning in the art and can be measured by methods known in the art. For example, the O / C value of hard carbon materials can be measured using an elemental analyzer (Elementar Unicube).

[0055] In this invention, C1mAh and C0mAh have meanings that are well known in the art.

number

number

[0056] In this invention, the volume-average particle size D of the hard carbon materialV The value 50 has a well-known meaning in the field, representing that in a volume-based particle size distribution, 50% of the particles of hard carbon material have a particle size smaller than this value, and can be measured by methods known in the field. For example, it can be measured using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) by referring to GB / T19077-2016 Particle Size Distribution Laser Diffraction Method.

[0057] In this invention, the specific surface area of ​​a hard carbon material has a well-known meaning in the art and can be measured by methods known in the art. For example, the specific surface area of ​​a hard carbon material can be measured using a specific surface area analyzer (Tristar II 3020 M) by the nitrogen adsorption / desorption method.

[0058] In this invention, the pore diameter d nm of the hard carbon material has a well-known meaning in the art and can be measured by methods known in the art. For example, it can be measured using an ASAP2460 physical adsorption analyzer. Specifically, a powder of the negative electrode active material is taken, dried and degassed, and then the ASAP2460 physical adsorption analyzer is used to measure the amount of adsorption to carbon dioxide in a carbon dioxide atmosphere, adjusting different test pressures, and plotting adsorption and desorption isotherms. The pore shape is determined by the shape of the hysteresis loop, and the pore size distribution curve of the micropores is fitted using a DFT model to obtain the pore diameter d nm of the hard carbon material.

[0059] Negative electrode piece A second aspect of the present invention provides a negative electrode piece comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect of the present invention.

[0060] The negative electrode sheet of the present invention can have a high reversible capacity and good lithium ion diffusion kinetic performance by including the negative electrode active material of the first aspect of the present invention. As a result, by applying the negative electrode active material of the present invention to a secondary battery, the secondary battery can have a high energy density, a high initial Coulomb efficiency, and good cycle performance.

[0061] In the negative electrode sheet of the present invention, the negative electrode active material layer does not exclude other negative electrode active materials other than the negative electrode active material of the first aspect of the present invention.

[0062] In some embodiments, the negative electrode active material layer further includes artificial graphite, and the mass ratio A of the negative electrode active material to the artificial graphite can satisfy 0 < A ≤ 1 / 3. When the mass ratio of the negative electrode active material to the artificial graphite is within the above appropriate range, not only can the volume expansion rate of the negative electrode sheet in the fully charged state be reduced, but also the capacity of the negative electrode active material layer can be increased, and further the energy density of the secondary battery can be increased.

[0063] In some embodiments, the negative electrode active material layer further includes the above artificial graphite, and the compression density PD g / cm 3 of the negative electrode active material layer is 1.0 g / cm 3 ~1.7 g / cm 3 and may be.

[0064] In a negative electrode sheet prepared with a hard carbon material as a single negative electrode active material, the compression density of the negative electrode active material layer is often not as high as about 0.9 g / cm 3 ~1.2 g / cm 3 As a result, relatively large voids also exist in the hard carbon material after cold pressing. When mixed with an appropriate proportion of artificial graphite, the stacking of the negative electrode active material particles in the negative electrode active material layer becomes denser and can have the above relatively high compression density. As a result, by improving the content of the negative electrode active material in the negative electrode active material layer per unit volume, the secondary battery using the negative electrode sheet of the present invention can have a higher volume energy density.

[0065] In some embodiments, the negative electrode active material layer further contains the above-mentioned artificial graphite, and the porosity of the negative electrode active material layer may be 15% to 30%. When the porosity of the negative electrode active material layer is within the above appropriate range, the active material particles are sufficiently permeated into the electrolyte, improving the dynamic performance. If the porosity of the cross-section is too large, the contact points between the active material particles decrease, increasing the internal resistance of the secondary battery and also causing a loss of substrate energy density.

[0066] The present invention does not limit the negative electrode current collector of the negative electrode piece. Metal foil, porous metal plate, or composite current collector can be used. A composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. A composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)). As an example, the negative electrode piece may be a negative electrode piece of a lithium-ion battery, and the negative electrode current collector may be copper foil. As another example, the negative electrode piece may be a negative electrode piece of a sodium-ion battery, and the negative electrode current collector may be copper foil or aluminum foil.

[0067] In some embodiments, the negative electrode current collector has two opposing surfaces in the thickness direction, and the negative electrode active material layer may be installed on one surface of the negative electrode current collector or on both surfaces simultaneously. For example, the negative electrode current collector has two opposing surfaces in the thickness direction, and the negative electrode active material layer is installed on one or both of the two opposing surfaces of the negative electrode current collector.

[0068] In some embodiments, the negative electrode active material layer may optionally further contain a binder. The binder may be at least one selected from the group consisting of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic acid (esterified) styrene-butadiene rubber, epoxy resin, and nylon.

[0069] In some embodiments, the negative electrode active material layer may optionally further contain a conductive agent. The conductive agent is selected from carbon-based materials, metallic materials, and conductive polymers, or any combination of the above materials. As an example, the carbon-based material may be at least one selected from natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metallic material can be selected from metal powders and metal fibers. The conductive polymer may include polyphenylene derivatives.

[0070] In some embodiments, the negative electrode active material layer may optionally include other additives such as a thickening agent (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0071] In the present invention, the negative electrode pieces can be prepared according to conventional methods in the art. For example, the hard carbon and other selectable negative electrode active materials, conductive agents, binders, and thickeners are dispersed in a solvent which may be N-methylpyrrolidone (NMP) or deionized water to form a uniform negative electrode slurry, the negative electrode slurry is coated onto a negative electrode current collector, and the negative electrode pieces are obtained by processes such as drying and cold pressing.

[0072] Note that the parameters of each negative electrode active material layer provided by this invention refer to the parameter range of one negative electrode active material layer. When negative electrode active material layers are installed on both sides of the negative electrode current collector, if the parameters of either one of the negative electrode active material layers satisfy the requirements of this invention, it is considered to be within the scope of protection of this invention.

[0073] Furthermore, the negative electrode piece in the present invention does not exclude any additional functional layers other than the negative electrode active material layer. For example, in some embodiments, the negative electrode piece of the present invention further includes a conductive primer (e.g., consisting of a conductive agent and a binder) interposed between the negative electrode current collector and the negative electrode active material layer and placed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode piece of the present invention further includes a protective layer covering the surface of the negative electrode active material layer.

[0074] In this invention, the compressive density of the negative electrode active material layer has a meaning well known in the art and can be measured by methods known in the art. For example, a negative electrode piece (a negative electrode active material layer coated on both sides of a negative electrode current collector) with an area S is weighed with an electronic balance, its weight is taken as W1, and the thickness T1 of the negative electrode piece is measured with a micrometer; the negative electrode active material layer is washed off with a solvent, dried, the weight of the negative electrode current collector is measured as W2, and the thickness T2 of the negative electrode current collector is measured with a micrometer; the compressive density PD of the negative electrode active material layer installed on the negative electrode current collector side is PD = (W1 - W2) / [(T1 - T2) × S].

[0075] In this invention, the porosity of the negative electrode active material layer has a well-known meaning in the art and can be measured by methods known in the art. For example, the porosity of the negative electrode active material layer can be measured using a true density meter in accordance with the standard "Measurement of apparent density, true density and porosity of iron ore" GB / T24586-2009.

[0076] In this invention, the parameters of the negative electrode active material or the negative electrode active material layer may be measured by sampling during the battery preparation process, or by sampling from the prepared secondary battery.

[0077] When the above measurement samples are sampled from a prepared lithium-ion battery, they can be sampled, for example, according to the following steps (1) to (3).

[0078] (1) Discharge the lithium-ion battery (for safety reasons, the battery is generally fully discharged); disassemble the battery and remove the negative electrode piece, then immerse the negative electrode piece in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); after that, remove the negative electrode piece and dry it at a certain temperature and time (e.g., 60°C for 4 hours), and remove the negative electrode piece after drying. In this case, samples can be taken from the dried negative electrode piece to measure each of the parameters relating to the negative electrode active material layer of the present invention.

[0079] (2) The dried negative electrode piece from step (1) is fired at a certain temperature and time (for example, 400°C for 2 hours), and an arbitrary area is selected from the fired negative electrode piece to sample the negative electrode active material (it can be sampled by scraping with a blade).

[0080] (3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve) to obtain a sample that can be used to measure the parameters of each of the negative electrode active materials of the present invention.

[0081] Electrochemical apparatus A third aspect of the present invention provides an electrochemical apparatus, the electrochemical apparatus comprising any apparatus in which an electrochemical reaction occurs for the mutual conversion of chemical energy and electrical energy. The electrochemical apparatus may be a primary battery or a secondary battery, specific examples of which include all types of lithium primary batteries, lithium secondary batteries, sodium primary batteries and sodium secondary batteries.

[0082] In some embodiments, the electrochemical apparatus of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0083] [Negative electrode piece] The negative electrode piece used in the electrochemical apparatus of the present invention is a negative electrode piece according to a second embodiment of the present invention.

[0084] [Positive electrode piece] The materials, structure, and manufacturing method of the positive electrode piece used in the electrochemical apparatus of the present invention may include any prior art well known.

[0085] The positive electrode piece includes a positive electrode current collector and a positive electrode active material layer, which contains positive electrode active material and is placed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in the thickness direction of itself, and the positive electrode active material layer is placed on one or two of the two opposing surfaces of the positive electrode current collector.

[0086] In some embodiments, the positive electrode active material layer includes a positive electrode active material, the specific type of which is not particularly limited and can be selected as needed.

[0087] In some embodiments, the electrochemical device is a lithium-ion battery. The positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their modified compounds. In the electrochemical device of the present invention, the modified compounds of each of the above positive electrode active materials are obtained by doping modification, surface coating modification, or both doping modification and surface coating modification of the positive electrode active material. As an example, the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. As an example, the lithium-containing phosphates with an olivine structure may include one or more of lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, composite materials of lithium iron manganese phosphate and carbon, and their modified compounds. These positive electrode active materials may be used individually or in combination of two or more types.

[0088] In some embodiments, the electrochemical device is a sodium-ion battery. The positive electrode active material can be a positive electrode active material used in sodium-ion secondary batteries known in the art. For example, the positive electrode active material may include one or more of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. For example, the sodium transition metal oxide is, for example, Na 1-x Cu h Fe k Mn l M 1 m O 2-y (M 1is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, and satisfies 0 < x ≦ 0.33, 0 < h ≦ 0.24, 0 ≦ k ≦ 0.32, 0 < l ≦ 0.68, 0 ≦ m < 0.1, h + k + l + m = 1, 0 ≦ y < 0.2); Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2(M 2 is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn, and Ba, and satisfies 0 < z ≦ 0.1); Na a Li b Ni c Mn d Fe e O2(0.67 < a ≦ 1, 0 < b < 0.2, 0 < c < 0.3, 0.67 < d + e < 0.8, b + c + d + e = 1). As an example, the above polyanionic compound is, for example, A 1 f M 3 g (PO4) i O j X 1 3-j (A 1 is one or more of H, Li, Na, K, and NH4, M 3 is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more of F, Cl, and Br, and satisfies 0 < f ≦ 4, 0 < g ≦ 2, 1 ≦ i ≦ 3, 0 ≦ j ≦ 2); Na n M 4 PO4X 2 (M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, and satisfies 0 < n ≦ 2); Na p M 5 q (SO4)3(M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, and satisfies 0 < p ≦ 2, 0 < q ≦ 2); Na s Mnt Fe 3-t (PO4)2(P2O7) (satisfying 0 < s ≤ 4 and 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2 or 3).

[0089] As an example, the above Prussian blue compound is, for example, A 2 u M 6 v [M 7 (CN)6] W ·xH2O (A 2 is one or more of H + , NH4 + , alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, satisfying 0 < u ≤ 2, 0 < v ≤ 1, 0 < W ≤ 1, 0 < x < 6). For example, A 2 is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+ is one or more of them, and M 6 and M 7 are each independently cations of one or more transition metal elements among Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn and W. Preferably, A 2 is one or more of Li + , Na + and K + , and M 6 is a cation of one or more transition metal elements among Mn, Fe, Co, Ni and Cu, and M 7 is a cation of one or more transition metal elements among Mn, Fe, Co, Ni and Cu.

[0090] In some embodiments, the positive electrode active material layer may optionally further contain a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the positive electrode active material layer may optionally further contain a binder. As an example, the conductive agent can be selected from carbon-based materials, metallic materials, conductive polymers, and any combination of the above materials. For example, the carbon-based material may be at least one selected from natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metallic material can be selected from metal powders and metal fibers. The conductive polymer may include polyphenylene derivatives.

[0092] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, an aluminum foil can be used as the positive electrode current collector. A composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may be one or more selected from the group consisting of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate can be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0093] In the present invention, the positive electrode piece can be prepared according to methods commonly used in the art. For example, the positive electrode active material layer is usually obtained by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually obtained by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP).

[0094] The positive electrode piece of the present invention does not exclude any additional functional layers other than the positive electrode active material layer. For example, in some embodiments, the positive electrode piece of the present invention further includes a conductive primer (e.g., consisting of a conductive agent and a binder) interposed between the positive electrode current collector and the positive electrode active material layer and placed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode piece of the present invention further includes a protective layer covering the surface of the positive electrode active material layer.

[0095] [Electrolyte] The electrolyte plays the role of conducting active ions between the positive electrode and the negative electrode. The electrolyte used in the electrochemical apparatus of the present invention may be an electrolyte known in the prior art.

[0096] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives. The types of organic solvents, lithium salts, and additives are not particularly limited and can be selected as needed.

[0097] In some embodiments, the electrochemical apparatus is a lithium-ion battery, and the electrolyte salt may include a lithium salt. For example, the lithium salt may include, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatoborate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate). The above lithium salts may be used individually or in combination of two or more.

[0098] In some embodiments, the electrochemical device is a sodium-ion battery, and the electrolyte salt may include a sodium salt. For example, the sodium salt may be at least one selected from the group consisting of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0099] In some embodiments, the organic solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and dimethyl sulfone (ESE). The above organic solvents may be used individually or in combination of two or more. Optionally, two or more of the above organic solvents may be used simultaneously.

[0100] In some embodiments, the additives may include negative electrode film-forming additives and positive electrode film-forming additives, and may further include additives that can improve some of the battery's performance characteristics, such as additives that improve the battery's overcharge performance or additives that improve the battery's high-temperature or low-temperature performance.

[0101] As an example, the additive includes, but is not limited to, at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (DTD), propylene sulfate, ethylene sulfite (ES), 1,3-propanesultone (PS), 1,3-propensultone (PST), sulfonic acid ester cyclic quaternary ammonium salts, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0102] The electrolyte can be prepared according to the usual methods in the art. For example, an electrolyte can be obtained by uniformly mixing an organic solvent, an electrolyte salt, and any additives. The procedure for adding each material is not particularly limited. For example, the electrolyte salt and any additives can be added to the organic solvent and uniformly mixed to obtain the electrolyte. Alternatively, the electrolyte salt can be added to the organic solvent first, and then any additives can be added to the organic solvent and uniformly mixed to obtain the electrolyte.

[0103] [Separator] The separator is placed between the positive and negative electrode pieces and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through. The present invention does not particularly limit the type of separator, and any well-known porous separator with good chemical and mechanical stability can be selected.

[0104] In some embodiments, the material of the separator may be one or more selected from the group consisting of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited thereto. Optionally, the material of the separator may include polyethylene and / or polypropylene. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating layer and a metal oxide coating layer may also be provided on top of the separator.

[0105] In some embodiments, the electrode assembly can be fabricated by a winding process or a lamination process using a positive electrode piece, the negative electrode piece, and a separator.

[0106] The electrochemical apparatus of the present invention further includes an outer casing for packaging the electrode assembly and electrolyte. In some embodiments, the outer casing may be a rigid case such as a rigid plastic case, an aluminum case, or a steel case, or a soft bag such as a pouch-type soft bag. The material of the soft bag may be at least one of the following plastics: polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0107] The shape of the electrochemical apparatus of the present invention is not particularly limited and may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows an example of a rectangular electrochemical apparatus 5.

[0108] In some embodiments, referring to Figure 2, the casing includes a case 51 and a cover plate 53. The case 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates can surround and form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 is provided to cover the opening so as to close the housing cavity. The positive electrode piece, negative electrode piece and separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged within the housing cavity. The electrolyte permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the electrochemical apparatus 5 may be one or more, and those skilled in the art can select them according to their actual specific requirements.

[0109] In the above description of embodiments of the electrochemical apparatus, the beneficial effects that can be achieved by the electrochemical apparatus of the present invention were mainly explained using a secondary battery as a specific example. However, those skilled in the art will easily understand that, in the electrochemical apparatus of the present invention, the positive electrode current collector has high mechanical strength because the difference in thickness between any position in any cross-section of the positive electrode current collector is within an appropriate range, and furthermore, the electrochemical apparatus has high safety performance, so similar beneficial effects can be achieved when applied to other types of electrochemical apparatus.

[0110] power consumption equipment A fourth aspect of the present invention provides a power consumption device, the power consumption device comprising an electrochemical apparatus according to a third aspect of the present invention.

[0111] The power consumption device of the present invention is not particularly limited and can be used in any electronic device known in the prior art. In some embodiments, the power consumption device may include, but is not limited to, notebook computers, pen-input computers, mobile computers, e-book players, mobile phones, portable facsimile machines, portable copiers, portable printers, stereo headsets, video recorders, LCD televisions, portable cleaners, portable CD players, MiniDiscs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, auxiliary bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, strobes, cameras, large household storage batteries, and lithium-ion capacitors.

[0112] Figure 3 shows an example of a power-consuming device. This power-consuming device includes pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, etc. Examples

[0113] The following describes examples of the present invention. The examples described below are illustrative and are used only to interpret the present invention and should not be understood as limiting the present invention. Unless specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or in the product descriptions should be followed. Unless the manufacturer is specified for the reagents or equipment used, they are all common products that can be purchased commercially.

[0114] Example 1 Preparation of negative electrode active material 200g of phenolic resin powder was spread flat in a 25cm x 40cm stainless steel disc and placed in a vacuum oven. The oven was heated to 300°C and maintained for 3 hours while compressed air was continuously supplied to the oven at a flow rate of 3 L / min to obtain an oxygen-nominated hard carbon precursor material. Under a nitrogen atmosphere with a flow rate of 1 L / min, the oxygen-nominated hard carbon precursor material was heated to 600°C at a heating rate of 1°C / min and maintained for 2 hours to obtain a pre-carbonized product. Subsequently, under a nitrogen atmosphere with a flow rate of 1 L / min, the temperature was raised to 1100°C at a heating rate of 5°C / min and maintained for 2 hours, then crushed and classified to obtain carbides. 10g of the carbides was taken and heated to 600°C at a heating rate of 1°C / min under a mixed atmosphere of 5% wt methane and argon at a flow rate of 0.5 L / min and maintained for 2 hours to obtain a negative electrode active material.

[0115] Preparation of negative electrode piece A negative electrode slurry (solid content 40 wt%) was formed by dissolving the negative electrode active material, styrene-butadiene rubber (a binder), and sodium carboxymethylcellulose (CMC-Na) in deionized water in a weight ratio of 97:1.5:1.5. A 10 μm thick copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated onto the current collector of the negative electrode piece to a coating thickness of 50 μm. After drying at 85°C, the negative electrode piece was obtained by cold pressing, cutting, slitting, and drying under vacuum conditions at 120°C for 12 hours.

[0116] Preparation of positive electrode pieces Lithium cobalt oxide, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF), which are the positive electrode active materials, were mixed in a weight ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was uniformly stirred to obtain a positive electrode slurry. The positive electrode slurry (solid content 72 wt%) was uniformly coated onto aluminum foil, which is the positive electrode current collector, to a coating thickness of 80 μm. After drying at 85°C, the material was cold-pressed, cut, and slit, and then dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode piece.

[0117] Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) was added and mixed uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of fluoroethylene carbonate was 5%.

[0118] Preparation of separators A 7μm thick polyethylene (PE) was used as the separator.

[0119] Preparation of lithium-ion batteries The positive electrode piece, separator, and negative electrode piece were stacked and wound in this order to obtain an electrode assembly. The electrode assembly was placed in an outer casing, the electrolyte was injected, and after processes such as packaging, settling, chemical formation, and shaping, a lithium-ion battery was obtained. The design potential interval of the lithium-ion battery was set to 2.0V to 4.53V.

[0120] Examples 2-6 Following the preparation process for the negative electrode active material in Example 1, the heat retention time for the phenolic resin in the oven was adjusted to 6 hours, 9 hours, 12 hours, 16 hours, and 20 hours, respectively, during the preparation process of the negative electrode active material in Examples 2 to 6, and the negative electrode active materials of Examples 2 to 6 were prepared.

[0121] The preparation process for the negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery in Examples 2 to 6 was the same as in Example 1.

[0122] Examples 7-11 According to the preparation process of Example 1, as shown in Table 2, the hard carbon material D V The solution 50 was adjusted to prepare the negative electrode active material, negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery for Examples 7-11.

[0123] Examples 12-16 The negative electrode active material was a hard carbon material and artificial graphite. Following the preparation process of Example 1, the amounts of hard carbon material and artificial graphite used (the mass ratio of hard carbon was calculated based on the sum of the masses of the hard carbon material and artificial graphite, and the mass ratio of artificial graphite was also calculated based on the sum of the masses of the hard carbon material and artificial graphite) were adjusted as shown in Table 3, and the negative electrode active material, negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery of Examples 12 to 16 were prepared.

[0124] Comparative Example 1 Following the preparation process of Example 1, the negative electrode active material was made of artificial graphite, and the design potential interval of the lithium-ion battery was adjusted to 3.0V to 4.48V to prepare the negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery of Comparative Example 1.

[0125] Comparative Example 2 Following the preparation process of Example 1, the negative electrode active material was changed to Kuraray's TZ-509R hard carbon, and the negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery of Comparative Example 2 were prepared.

[0126] Comparative Example 3 Following the preparation process of Example 1, the negative electrode active material, negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery of Comparative Example 2 were prepared without oxygenation treatment of the phenolic resin.

[0127] Comparative Examples 4-5 According to the preparation process of Example 1, as shown in Table 1, the hard carbon material D V Formula 50 was prepared, and the negative electrode active material, negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery for Comparative Examples 4 and 5 were prepared.

[0128] Comparative Example 6 Following the preparation process of Example 1, the mass ratio of hard carbon material to artificial graphite (the mass percentage of hard carbon is calculated based on the sum of the masses of the hard carbon material and artificial graphite, and the mass percentage of artificial graphite is also calculated based on the sum of the masses of the hard carbon material and artificial graphite) was adjusted as shown in Table 1, and the negative electrode active material, negative electrode piece, positive electrode piece, electrolyte, separator, and lithium-ion battery of Comparative Example 6 were prepared.

[0129] Measuring part A completely discharged lithium-ion battery was disassembled, the negative electrode was removed, immersed in DMC (dimethyl carbonate) for 20 minutes, and then sequentially washed with DMC and acetone to remove the electrolyte and surface SEI film. After that, it was placed in an oven and baked at 80°C for 12 hours to obtain the treated negative electrode piece. The powder on the negative electrode piece was scraped off with a doctor blade, and the scraped powder was heat-treated in a tubular furnace at 400°C for 4 hours under argon gas atmosphere to remove the binder adhering to the surface of the negative electrode active material and obtain the negative electrode active material. The following measurements were performed on the obtained negative electrode active material layer and negative electrode active material.

[0130] (1)XRD measurement Measurement device: X-ray powder diffractometer (Model: Bruker D8 ADVANCE) Measurement parameters: Target material is CuK α The voltage and current were set to 40KV / 40mA, the scanning angle range to 5°~80°, the scanning step size to 0.00836°, and the time for each step size to 0.3s.

[0131] (2) Volume average particle size D V 50 measurements Measuring device: Malvern particle size analyzer (Mastersizer 2000E)

[0132] The negative electrode active material is dispersed in ethanol, a dispersant, and sonicated for 30 minutes. After that, the sample is placed in a Malvern particle size analyzer, and the hard carbon material D V I measured 50.

[0133] (3) Measurement of specific surface area Measuring device: Specific surface area analyzer (TristarII3020M) The specific surface area of ​​the negative electrode active material was measured using the nitrogen adsorption / desorption method as follows: The negative electrode active material was dried in a vacuum drying oven, placed in a sample tube, and measured with an analyzer.

[0134] (4) Measurement of volume per gram The negative electrode active material was mixed, applied, and dried to form the negative electrode piece, and the lithium piece was used as the positive electrode. The resulting button cell was then assembled and measured. The button battery was discharged to 0mV at 0.05C, discharged to 0mV at 50μA, discharged to 0mV at 10μA, and charged to 2.5V at 0.1C. The capacity of the button battery at this time was recorded, and this capacity was divided by the mass of the active material in the negative electrode piece to obtain the capacity per gram. 0.05C refers to a current value of 0.05 times the set capacity per gram, and 0.1C refers to a current value of 0.1 times the set capacity per gram. The initial efficiency was obtained by dividing the charging capacity by the discharge capacity. The average lithium release potential was obtained by dividing the charging capacity by the charging energy. The ratio C1 / C0 of the lithium release capacity per gram at 0V to 0.15V to the total capacity per gram was obtained by dividing the capacity per gram at the charging stage of 0V to 0.15V by the total charging capacity. Figure 4 is a voltage-capacity graph of a button battery corresponding to Example 4 of the present invention.

[0135] (5) Measurement of the pore size distribution of the negative electrode active material Measuring device: ASAP2460-Physical adsorption analyzer After taking a powder of the negative electrode active material and performing drying and degassing pretreatment, the amount of adsorption to carbon dioxide was measured using an ASAP2460 physical adsorption analyzer, with the measurement atmosphere being carbon dioxide and different test pressures adjusted. Adsorption and desorption isotherms were then plotted. The pore shape was determined by the shape of the hysteresis loop, and the pore size distribution curve of the micropores was fitted using a DFT model to calculate the pore volume V cc / g and the pore diameter d μm of the hard carbon material.

[0136] (6) Measurement of the true density of the negative electrode active material The powder of the negative electrode active material was taken, and the true density of the negative electrode active material was measured using n-butanol as the solvent, referring to the standard of "GB / T24203-2009 Method for determining the true density and true porosity of carbon materials - boiling method".

[0137] (7) Measurement of O / C value Measuring device: Elemental analyzer (Elementar Unicube) The negative electrode active material samples obtained by the above method were measured using the CHN mode and O mode of an elemental analyzer, respectively, to determine the mass content A of carbon and the mass content B of oxygen in the negative electrode active material, and the O / C value was found to be 0.75 × B / A.

[0138] (8) Measurement of the porosity of the negative electrode active material layer The negative electrode active material layer sample was prepared as a complete disk, and 30 samples were measured for each example or comparative example, with a volume of approximately 0.35 cm³ for each sample. 3 The porosity of the negative electrode active material layer was measured in accordance with the GB / T24586-2009 standard for "Measurement of apparent density, true density, and porosity of iron ore".

[0139] (9) Measurement of the compressive density of the negative electrode active material layer The negative electrode piece (with a negative electrode active material layer coated on both sides of the negative electrode current collector) after processing area S was weighed using an electronic balance, and its weight was defined as W1. The thickness T1 of the negative electrode piece was measured with a micrometer. The negative electrode active material layer was washed off with a solvent and dried. The weight of the negative electrode current collector was measured and defined as W2. The thickness T2 of the negative electrode current collector was measured with a micrometer. The compressed density PD of the negative electrode active material layer installed on the negative electrode current collector side was PD = (W1 - W2) / [(T1 - T2)·S].

[0140] (10) Measurement of the energy density of lithium-ion batteries Each group was given five lithium-ion batteries. First, the first charge and discharge cycle was performed at 25°C. Constant current and constant voltage charging was performed up to the upper voltage limit with a charging current of 0.5C, and then constant current discharge was performed up to the cutoff voltage with a discharge current of 0.2C. The energy density percentage of each example and comparative example compared to Comparative Example 1 was calculated. For a lithium-ion battery with graphite as the negative electrode active material, the maximum charge voltage was set to 4.48V and the maximum discharge voltage to 3.0V. For a lithium-ion battery in an example where pure hard carbon was used as the negative electrode active material, the maximum charge voltage was set to 4.53V and the maximum discharge voltage to 2.0V.

[0141] (11) Measurement of the cycle performance of lithium-ion batteries Each group was given five lithium-ion batteries. The lithium-ion batteries were repeatedly charged and discharged using the following steps, and the discharge capacity retention rate and thickness expansion rate of the lithium-ion batteries were calculated. First, at 25°C, the first charge and discharge cycle was performed. Constant current charging was performed with a charging current of 1C, and after reaching the upper voltage limit, it was converted to constant voltage charging. Then, constant current discharge was performed with a discharge current of 1C until the discharge cutoff voltage was reached, and the discharge capacity of the first cycle and the thickness of the fully charged lithium-ion battery were recorded. Subsequently, 800 charge and discharge cycles were performed, and the discharge capacity of the fully charged lithium-ion battery after the 800th cycle and the thickness of the fully charged lithium-ion battery were recorded. For lithium-ion batteries in examples where the negative electrode active material was graphite or a mixture of graphite, the upper charge voltage limit was set to 4.48V and the discharge cutoff voltage to 3.0V. For lithium-ion batteries in examples where the negative electrode active material was pure hard carbon, the upper charge voltage limit was set to 4.53V and the discharge cutoff voltage to 2.0V. Cycle capacity retention rate = (Discharge capacity at the 800th cycle / Discharge capacity at the first cycle) × 100% Cycle thickness expansion rate = (Thickness of a fully charged lithium-ion battery after 800 cycles - Thickness of a fully charged lithium-ion battery after the first cycle) / Thickness of a fully charged lithium-ion battery after the first cycle × 100%. The measurement data for each example and comparative example are shown in Tables 1 to 3.

[0142] [Table 1]

[0143] By comparing Examples 1 to 6 and Comparative Examples 1 to 3, it can be seen that by applying oxygen to the hard carbon material precursor, the hard carbon material has a higher capacity per gram and a higher ratio of lithium release capacity at 0V to 0.15V to the total capacity. This indicates that applying oxygen to the hard carbon material precursor effectively increases the pore content of the hard carbon material, further increasing the capacity per gram, and that the lithium-ion battery using this hard carbon material has the highest energy density.

[0144] [Table 2]

[0145] By comparing Examples 4, 7-11, Comparative Examples 4 and 5, it can be seen that hard carbon active materials that have been carbonized three times all have a specific surface area close to that of commercial graphite, and that by controlling the particle size of the hard carbon active material through crushing and sieving, the Dv50 and specific surface area of ​​the material can be effectively adjusted to further improve the initial efficiency and cycle performance of lithium-ion batteries. Furthermore, it can be seen that a relatively small particle size of the negative electrode active material increases the irreversible capacity of the first cycle of the lithium-ion battery, and that the sustained consumption of lithium ions during the cycle process affects the cycle performance of the lithium-ion battery.

[0146] [Table 3]

[0147] Examples 12 to 16, Comparative Example 1, and Comparative Example 6 show that as the mass ratio of hard carbon material increases, the compressive density of the negative electrode active material layer tends to decrease and the porosity of the negative electrode active material layer increases. Hard carbon not only has a low rate of volume expansion during the lithium release and storage processes, but it can also limit the volume expansion of graphite during the charge and discharge processes. Therefore, in examples with a high mass ratio of hard carbon, the corresponding lithium-ion batteries have a smaller cycle thickness expansion rate and a better cycle capacity retention rate. When the mass ratio of doped artificial graphite to hard carbon material is appropriate, the negative electrode piece can have a relatively high hard carbon content and a relatively high compressive density, so the energy density of the corresponding lithium-ion battery is also relatively higher.

[0148] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiment that has substantially the same configuration as the technical concept of the present invention and produces similar functions and effects is included within the scope of the present invention. Any other form constructed by combining some of the components of an embodiment, by implementing various modifications to the embodiments that a person skilled in the art could conceive of, without departing from the spirit of the present invention, is also included within the scope of the present invention.

Claims

1. It is a negative electrode active material, The negative electrode active material includes a hard carbon material. The hard carbon material has a plurality of micropores, The average lithium emission potential of the hard carbon material with lithium metal as the counter electrode is 0.15V to 0.40V. The pore volume V cc / g of the micropores of the hard carbon material, as measured by the carbon dioxide gas adsorption method, satisfies the condition 0 < V cc / g ≤ 0.05 cc / g. A negative electrode active material in which the diameter d nm of the micropores satisfies the condition d nm ≤ 0.9 nm.

2. The negative electrode active material according to claim 1, wherein the O / C value, which is the ratio of the number of moles of oxygen atoms to carbon atoms in the hard carbon material, is 0.01 to 0.

10.

3. The aforementioned negative electrode active material is [Math 1] Satisfying the condition, where C １ mAh / g represents the lithium release capacity of the hard carbon material at 0V to 0.15V when lithium metal is used as the counter electrode, C ０ The negative electrode active material according to claim 1 or claim 2, wherein mAh / g represents the total lithium release capacity of the hard carbon material when lithium metal is used as the counter electrode.

4. The hard carbon material comprises a core and a coating layer located on at least a portion of the surface of the core. The anode active material according to claim 1 or claim 2, wherein the plurality of micropores are located within the core.

5. The aforementioned negative electrode active material is (1) The hard carbon material has a true density ρ g / cc measured by the n-butanol dipping method of 1.1 g / cc to 1.6 g / cc. (2) D of the hard carbon material Ｖ 50 is between 6 μm and 15 μm. (3) The specific surface area of ​​the hard carbon material is 2 m² ２ / g to 10m ２ / g (4) The X-ray diffraction pattern of the hard carbon material has a characteristic peak in the 18° to 30° range, and the full width at half maximum of the characteristic peak is 4° to 12°, (5) The O / C value, which is the ratio of the number of moles of oxygen atoms to carbon atoms in the hard carbon material, is between 0.02 and 0.

07. A negative electrode active material according to claim 1 or claim 2, satisfying at least one of the following conditions.

6. A negative electrode piece comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material described in claim 1 or claim 2.

7. The aforementioned negative electrode active material layer is (1) The negative electrode active material layer further contains artificial graphite, and the mass ratio A of the negative electrode active material to the artificial graphite satisfies 0 < A ≤ 1 / 3. (2) Compression density PD g / cm³ of the negative electrode active material layer ３ 1.0 g / cm³ ３ ~1.7 g / cm ３ Being, and (3) The porosity of the negative electrode active material layer is 15% to 30%. The negative electrode piece according to claim 6, satisfying at least one of the following conditions.

8. An electrochemical apparatus comprising the negative electrode piece described in claim 6.

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