Hard carbon material and preparation method therefor, and secondary battery and electric apparatus

Abstract

Provided in the present disclosure are a hard carbon material and a preparation method therefor, and a secondary battery and an electric apparatus. An XRD diffraction pattern of the hard carbon material includes a first diffraction peak, the first diffraction peak being located at a position where 2θ=26±0.5°.

Description

Hard carbon material and preparation method thereof, secondary battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202410269844.X, application date March 8, 2024, and invention name “Hard carbon material and preparation method thereof, secondary battery and electrical device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the technical field of lithium batteries, and in particular to a hard carbon material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. With the application and promotion of secondary batteries, people have increasingly higher requirements for the energy density, cycle performance, and high-rate charging performance of secondary batteries. As an important component of secondary batteries, the performance of the negative electrode active material affects the performance of the secondary battery to a certain extent. Currently, hard carbon is commonly used as the negative electrode active material of secondary batteries. However, when used as the negative electrode active material, hard carbon has a low reversible gram capacity, which leads to a low first coulombic efficiency of the battery.

[0005] Summary of the Invention

[0006] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a hard carbon material and its preparation method, a secondary battery and an electrical device, wherein the hard carbon material has an increased reversible gram capacity and an improved first coulombic efficiency when used as a negative electrode material of a secondary battery.

[0007] In order to achieve the above object, a first aspect of the present disclosure provides a hard carbon material, wherein an XRD diffraction pattern of the hard carbon material comprises a first diffraction peak located at 2θ of 26±0.5°.

[0008] In this disclosure, the presence of the first diffraction peak reflects the presence of a relatively highly ordered graphite microcrystal structure within the hard carbon material. The presence of this highly ordered graphite microcrystal structure can reduce the content of non-hexacyclic defects within the nanoscale periphery of the structure, thereby facilitating the release of active ions and achieving both high reversible gram capacity and first coulombic efficiency.

[0009] In some embodiments, the XRD diffraction pattern of the hard carbon material further includes a second diffraction peak; the second diffraction peak is located at 2θ of 23.5±0.6°; and the peak intensity ratio X between the first diffraction peak and the second diffraction peak satisfies the following relationship: 0.95≤X≤1.05.

[0010] The XRD diffraction peaks of the hard carbon material provided by the present invention satisfy that the peak intensity ratio X of the first diffraction peak to the second diffraction peak is in the range of 0.95≤X≤1.05, reflecting that the defect content in the hard carbon material is in a suitable range relative to the content of the graphite microcrystalline structure, which is beneficial to improving the reversible gram capacity, first coulombic efficiency and discharge gram capacity.

[0011] In some embodiments, the peak intensity ratio X of the first diffraction peak to the second diffraction peak satisfies the following relationship: 0.995≤X≤1.031. When the peak intensity ratio X of the first diffraction peak to the second diffraction peak is within the above range, it is more conducive to improving the reversible gram capacity, the first coulombic efficiency, and the discharge gram capacity.

[0012] In some embodiments, the hard carbon material has an I D / I G is 0.8-1.1; among them, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at I D / I G Within the above range, it reflects that the carbon surface of the material has a high degree of disorder, more surface defects, and suitable reaction activity.

[0013] In some embodiments, the half-width at half maximum of the second diffraction peak is greater than the half-width at half maximum of the first diffraction peak. The half-width at half maximum of the second diffraction peak is greater than the half-width at half maximum of the first diffraction peak, reflecting that the second diffraction peak is a broad peak and the first diffraction peak is a sharp peak, that is, the structure corresponding to the first diffraction peak is relatively ordered.

[0014] In some embodiments, the hard carbon material has a BET specific surface area of ​​0.1 m 2 / g-15m 2 The specific surface area of ​​the hard carbon material is within the above range, which can reduce the consumption of active ions during the first charge and is beneficial to improving the first coulombic efficiency of the secondary battery.

[0015] In some embodiments, the hard carbon material satisfies at least one of the following:

[0016] (1) The compaction density of the hard carbon material under 50000N is 0.83g / cm3 -1.15g / cm 3 When the compaction density of the hard carbon material powder is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and thus improve the kinetic performance of the secondary battery.

[0017] (2) The tap density of the hard carbon material is 0.62 g / cm 3 -0.95g / cm 3 When the tap density of the hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0018] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm.

[0019] (4) The volume distribution particle size Dv90 of the hard carbon material is 8 μm to 15 μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above ranges, it is beneficial to reduce the specific surface area of ​​the hard carbon material and the occurrence of side reactions, thereby improving the initial coulombic efficiency of the secondary battery. It can also shorten the bulk phase transmission path of active ions, thereby improving the dynamic performance of the secondary battery.

[0020] A second aspect of the present disclosure further provides a method for preparing a hard carbon material, the method comprising: polymerizing a polymerizable monomer containing an iron source to form a hard carbon material precursor; and carbonizing the hard carbon material precursor to obtain the hard carbon material.

[0021] The present invention discloses that an iron source is added to the raw materials when preparing a hard carbon material precursor. Therefore, during the carbonization process, through the induction effect of iron, a certain amount of uniformly distributed graphite microcrystalline structure with relatively high order is formed in the bulk phase of the hard carbon material, thereby reducing the content of non-hexamembered ring defects in the hard carbon material. In this way, more active ions can be reversibly deintercalated, which is beneficial to the reversible gram capacity and first coulomb efficiency of the secondary battery.

[0022] In some embodiments, the iron source is added in an amount of 0.03 wt% to 0.3 wt% of the elemental iron based on the total weight of the polymerized monomers. Adding the iron source within this range allows for an appropriate amount of defects in the hard carbon material, which is beneficial for balancing the reversible gram capacity and first coulombic efficiency of the secondary battery.

[0023] In some embodiments, the amount of the iron source added is 0.15 wt% to 0.21 wt% based on the total weight of the polymerized monomers. The amount of the iron source added within the above range is further beneficial for balancing the reversible gram capacity and the first coulombic efficiency of the secondary battery.

[0024] In some embodiments, the hard carbon material precursor includes at least one of a phenolic resin, an epoxy resin, and a furan resin. These precursors are thermosetting resins with a high degree of crosslinking, which prevents melting during subsequent heating, which could lead to iron displacement and agglomeration, thereby facilitating uniform defect reduction.

[0025] In some embodiments, the iron source is FeCl3 and / or FeCl2. Ionic iron can be evenly dispersed in the monomer, which is beneficial to the uniform reduction of defects.

[0026] In some embodiments, the polymerization is carried out under alkaline conditions, which is beneficial for increasing the rate of the polymerization reaction.

[0027] In some embodiments, the polymerization is carried out in the presence of aqueous ammonia; based on the total weight of the polymerized monomers, the aqueous ammonia is added in an amount of 0.022 wt% to 0.044 wt% in terms of ammonia.

[0028] In some embodiments, the amount of ammonia added is 0.031 wt% to 0.035 wt% based on the total weight of the polymerized monomers. When the amount of ammonia added to the ammonia during the polymerization process is within this range, the hard carbon material precursor has an appropriate degree of crosslinking and does not precipitate ionic iron due to excessive alkalinity, thereby preventing the precursor from being ineffective.

[0029] In some embodiments, the polymerization is carried out at 120° C. to 160° C. for 0.5 h to 2 h.

[0030] In some embodiments, the polymerization is performed at 135-145° C. When the polymerization is performed under the above conditions, the hard carbon material precursor has an appropriate crosslinking degree and does not break the solidified crosslinking bonds, so that the precursor does not melt during the subsequent carbonization process.

[0031] In some embodiments, the carbonization treatment is performed in an inert atmosphere at 1000°C to 1800°C for 1 to 12 hours, with the temperature ramped at a rate of 2°C / min to 20°C / min. During the carbonization process, heteroatoms such as H and O are removed from the precursor to form a stable hard carbon skeleton, while the iron source is reduced to elemental iron.

[0032] In some embodiments, after the carbonization treatment, a deashing treatment is further performed. The deashing treatment comprises washing the hard carbon material with an acid at room temperature to 95° C.; the acid comprises at least one of hydrochloric acid, nitric acid, sulfuric acid, hypochlorous acid, hydrofluoric acid, and perchloric acid. Deashing can remove residual Fe in the hard carbon material.

[0033] A third aspect of the present disclosure provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the hard carbon material described in the first aspect, or comprises the hard carbon material obtained by the preparation method described in the second aspect.

[0034] The negative electrode film layer in the secondary battery disclosed herein includes the hard carbon material provided by the present disclosure, which can effectively improve the reversible gram capacity and the first coulombic efficiency of the secondary battery.

[0035] A fourth aspect of the present disclosure provides an electric device including the secondary battery according to the third aspect of the present disclosure.

[0036] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is an X-ray diffraction spectrum of a hard carbon material according to an embodiment of the present disclosure.

[0038] FIG2 is a peak fitting diagram of a schematic X-ray diffraction spectrum of a hard carbon material.

[0039] FIG3 is a scanning electron microscope image of a hard carbon material according to an embodiment of the present disclosure.

[0040] FIG. 4 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0041] FIG. 5 is an exploded view of the battery cell shown in FIG. 4 according to an embodiment of the present disclosure.

[0042] FIG6 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0043] FIG. 7 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0044] FIG. 8 is an exploded view of the battery pack shown in FIG. 7 according to an embodiment of the present disclosure.

[0045] FIG9 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0046] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0047] Below, embodiments of the hard carbon material and its preparation method, secondary battery, and electrical device disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary lengthiness in the following description and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0048] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is also expected that the scope of 60-110 and 80-120 is understood to be.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3,1-4,1-5,2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0052] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0053] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0054] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0055] Currently, hard carbon is generally used as the negative electrode active material of secondary batteries. However, when hard carbon is used as the negative electrode active material, the reversible capacity is low, which leads to low first coulombic efficiency of the secondary battery.

[0056] In view of this, embodiments of the present disclosure provide a new hard carbon material, which, as a negative electrode material for a secondary battery, has a high reversible gram capacity and a high first coulombic efficiency.

[0057] Hard carbon materials

[0058] A first aspect of the embodiments of the present disclosure provides a hard carbon material, wherein an XRD diffraction pattern of the hard carbon material comprises a first diffraction peak located at 2θ of 26±0.5°.

[0059] Conventional hard carbon materials are composed of twisted graphite-like sheets stacked together, exhibiting a structural characteristic of short-range order and long-range disorder, often referred to as a "house of cards" model. The XRD spectrum of conventional hard carbon materials shows a broad peak at 2θ of 20°-30°, corresponding to different interlayer spacings between sheets. Unlike the carbon layer structure in graphite materials, these sheets of hard carbon materials include non-six-membered ring defects such as five-membered rings and seven-membered rings. The presence of these defects can promote the embedding of active ions. However, too many defects will result in a relatively high energy barrier for active ions to overcome when they are released. The embedding and release of active ions adsorbed at some sites are irreversible, thus affecting the reversible gram capacity and first coulombic efficiency.

[0060] Unlike conventional hard carbon materials, the hard carbon material disclosed herein exhibits a first diffraction peak at 26±0.5° (2θ) when measured by XRD. This corresponds to a spacing between (002) planes in the lamellar structure within the range of approximately 0.337 nm to 0.349 nm. This first diffraction peak reflects the presence of a relatively highly ordered graphite microcrystal structure within the hard carbon material. The presence of this highly ordered graphite microcrystal structure reduces the content of non-hexacyclic defects within the nanometer-scale periphery of the structure, thereby facilitating the release of active ions and achieving both high reversible gram capacity and initial coulombic efficiency.

[0061] When the first diffraction peak exists in the XRD spectrum of the hard carbon material, it reflects that the content of defects in the hard carbon material is relatively reduced.

[0062] In some embodiments, the XRD diffraction pattern of the hard carbon material further includes a second diffraction peak; the second diffraction peak is located at 2θ of 23.5±0.6°; and the peak intensity ratio X between the first diffraction peak and the second diffraction peak satisfies the following relationship: 0.95≤X≤1.05.

[0063] The second diffraction peak reflects the house-of-cards lamellar structure in the hard carbon material, in which there are defect structures other than six-membered rings. The second diffraction peak is a broad peak with the maximum peak intensity occurring at 2θ of 23.5±0.6°. The corresponding interplanar spacing of the 002 crystal plane is greater than 0.37nm. The presence of the second diffraction peak can be due to active ions (such as Na + ) provides the necessary mass transfer channels, enabling active ions to be embedded and extracted during the charge and discharge process, contributing to the gram capacity of the material.

[0064] The XRD diffraction peaks of the hard carbon material provided by the present disclosure satisfy that the peak intensity ratio X of the first diffraction peak to the second diffraction peak is in the range of 0.95≤X≤1.05, reflecting that the defect content in the hard carbon material is in a suitable range relative to the content of the graphite microcrystalline structure. On the one hand, there are enough defects in the hard carbon material to facilitate the adsorption of active ions and promote the embedding of active ions in the graphite-like layered structure. At the same time, the content of defects is controlled in a suitable range to facilitate the escape of active ions and improve the discharge gram capacity. On the other hand, the content of the graphite microcrystalline structure is within a suitable range, which is conducive to reducing the impact on the gram capacity of the hard carbon material, thereby simultaneously improving the reversible gram capacity and the first coulomb efficiency of the secondary battery. Therefore, the hard carbon material provided by the present disclosure can balance the relationship between the sodium intercalation gram capacity, the first coulomb efficiency and the reversible gram capacity, that is, under the premise of ensuring a good sodium intercalation capacity, the first coulomb efficiency and the reversible gram capacity are improved.

[0065] In some embodiments, the peak intensity ratio X of the first diffraction peak to the second diffraction peak satisfies the following relationship: 1.018≤X≤1.033. When the peak intensity ratio X of the first diffraction peak to the second diffraction peak is within the above range, it is more conducive to improving the reversible gram capacity, the first coulombic efficiency, and the discharge gram capacity.

[0066] In some embodiments, the hard carbon material has an I D / I G is 0.8-1.1; among them, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 For example, the G peak intensity of the hard carbon material is D / I G is 0.8, 0.9, 1.0, 1.1, or any value within the range formed by any two of these values. D / I G Within the above range, it reflects that the carbon on the surface of the material is highly disordered, has many surface defects, and has suitable reactivity. It also reflects that the typical graphite structure does not exist on the surface of the material.

[0067] In some embodiments, the XRD diffraction pattern of the hard carbon material has no characteristic peak in the range of 2θ of 52°-57°, that is, the diffraction peak of the (004) crystal plane does not exist in the hard carbon material of the present disclosure, which further reflects that the hard carbon material does not have a typical graphite structure, but presents an overall disordered structure.

[0068] In some embodiments, the half-width of the second diffraction peak is greater than the half-width of the first diffraction peak. The half-width of the second diffraction peak is greater than the half-width of the first diffraction peak, reflecting that the second diffraction peak is a wide peak and the first diffraction peak is a sharp peak. Exemplarily, in the calibrated spectrum, the half-width of the second diffraction peak is in the range of 4°-8°, for example, 6°; the half-width of the first diffraction peak is in the range of 0.2°-1°, for example, 0.4°. The half-width of the second diffraction peak is within the above range, reflecting that the material has the typical characteristics of a hard carbon material. The half-width of the first diffraction peak is within the above range, reflecting that the material contains a graphite microcrystalline structure with relatively uniform interlayer spacing and relatively high order.

[0069] In some embodiments, the hard carbon material has a BET specific surface area of ​​0.1 m 2 / g-15m 2 The specific surface area of ​​the hard carbon material is within the above range, which can reduce the consumption of active ions during the first charge and is beneficial to improving the first coulombic efficiency of the secondary battery.

[0070] In some embodiments, the hard carbon material satisfies at least one of the following:

[0071] (1) The compaction density of the hard carbon material under 50000N is 0.83g / cm 3 -1.15g / cm 3 When the compaction density of the hard carbon material powder is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and thus improve the kinetic performance of the secondary battery.

[0072] (2) The tap density of the hard carbon material is 0.62 g / cm 3 -0.95g / cm 3 When the tap density of the hard carbon material is within the above range, it is beneficial to increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery.

[0073] (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm.

[0074] (4) The volume distribution particle size Dv90 of the hard carbon material is 8 μm to 15 μm. When the volume distribution particle sizes Dv50 and Dv90 of the hard carbon material particles are within the above ranges, it is beneficial to reduce the specific surface area of ​​the hard carbon material and the occurrence of side reactions, thereby improving the initial coulombic efficiency of the secondary battery. It can also shorten the bulk phase transmission path of active ions, thereby improving the dynamic performance of the secondary battery.

[0075] In some embodiments, the hard carbon material includes C, H, and O, wherein the C content is 94%-98%, the O content is 0.3%-4.5%, and the H content is less than 1.5%. The hard carbon material is primarily composed of C, H, and O, which helps reduce the defect content caused by other heteroatoms, thereby improving the reversible gram capacity and first coulombic efficiency of the secondary battery.

[0076] In other embodiments, the hard carbon material includes doping elements, such as a certain amount of N, S, etc. The present disclosure has no particular limitation on the type and content of the doping elements, which can be added as needed.

[0077] In this disclosure, XRD diffraction patterns of hard carbon materials can be measured using an X-ray diffractometer in accordance with JIS K 0131-1996. The test conditions are as follows: the hard carbon material is prepared using a flat plate method, using CuKα radiation as the radiation source, a copper target as the anode target, a voltage of 40 kV, a current of 40 mA, a 1 mm anti-scatter slit, a 2θ scanning range of 20°-80°, a step size of 0.01671°, a step duration of 0.24 s, and a scan rate of 4° / min. The test instrument can be a Bruker D8 Discover X-ray diffractometer.

[0078] In the present disclosure, the XRD diffraction spectrum of the hard carbon material can be fitted, and the second diffraction peak (peak A) and the first diffraction peak (peak B) that overlap with each other in the XRD spectrum of the hard carbon material of one embodiment shown in FIG1 can be decomposed into two independent peaks (as shown in FIG2 ). Specifically, through the Lorentz calibration, the Lorentz calibration data as shown in FIG2 is obtained, and further through the Lorentz calibration data, it can be known that there are two diffraction peaks near 15-35°, the peak angle of one peak is at about 25°, and the peak angle of the other peak is at about 26°. Next, Gaussian distribution is used to fit the peak angles of the two peaks to obtain the first fitting peak and the second fitting peak. In this way, the half-height width b of the first diffraction peak can be obtained based on the second fitting peak, and the half-height width a of the second diffraction peak can be obtained based on the first fitting peak.

[0079] In the present disclosure, the I of the hard carbon material D / I G The value can be tested using Raman spectrometer, I D The Raman spectrum of the material is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of the material is 1580±50cm -1 The test conditions are: excitation wavelength 532nm, grating 600 lines, objective lens 50 times, integration time 10s, accumulation times 3 times, surface scanning, obtain 100 points of D peak and G peak intensity, calculate 100 points of I D / I G , remove the largest and smallest 30 I D / I G The average value of the remaining 40 points is the I D / I G The testing instrument may be a Horiba LabRAM HR800 Raman spectrometer.

[0080] In this disclosure, the BET surface area of ​​hard carbon materials is generally known in the art and can be measured using instruments and methods known in the art. For example, the surface area can be measured using nitrogen adsorption surface area analysis and calculated using the BET (Brunauer Emmett Teller) method, as described in GB / T 19587-2017. The testing instrument can be a Micromeritics Tri-Star 3020 surface area pore size analyzer.

[0081] In this disclosure, the compacted density of hard carbon materials is a well-known term in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine) in accordance with GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and placed on a plate with a bottom area of ​​1.327 cm 2 In the mold, pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the powder compaction density of the material under 50000N pressure.

[0082] In this disclosure, the tap density of hard carbon materials is generally known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester, such as that described in GB / T 5162-2006. A Dandong Better BT-301 tester can be used, using the following test parameters: vibration frequency of 250 ± 15 times / minute, amplitude of 3 ± 0.2 mm, number of vibrations of 5000, and a 25 mL graduated cylinder.

[0083] In this disclosure, the volume distribution particle sizes Dv50 and Dv90 of hard carbon materials are generally known in the art and represent the particle sizes corresponding to the 50% and 90% cumulative volume distribution percentages, respectively. These can be measured using instruments and methods known in the art. For example, measurements can be made using a laser particle size analyzer in accordance with GB / T 19077-2016. The measuring instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0084] In the present disclosure, the elements and content distribution of the hard carbon material can be measured using instruments and methods known in the art. For example, the elements and content of the hard carbon material can be measured using inductively coupled plasma atomic emission spectrometry according to EPA 6010D-2014.

[0085] In the present disclosure, the microstructure of the hard carbon material can be observed by a scanning electron microscope or a transmission electron microscope.

[0086] Preparation method of hard carbon material

[0087] A second aspect of the disclosed embodiments provides a method for preparing the hard carbon material, comprising: polymerizing a polymerizable monomer containing an iron source to form a hard carbon material precursor; and carbonizing the hard carbon material precursor to obtain the hard carbon material.

[0088] The present invention uses a polymer as a precursor (i.e., a carbon source) and adds an iron source to the raw materials when preparing a hard carbon material precursor. Therefore, during the carbonization process, through the induction effect of iron, a certain amount of uniformly distributed graphite microcrystalline structure with relatively high order is formed in the bulk phase of the hard carbon material, thereby reducing the content of non-hexamembered ring defects in the hard carbon material. In this way, more active ions can be reversibly deintercalated, which is beneficial to the reversible gram capacity and first coulomb efficiency of the secondary battery.

[0089] In some embodiments, the iron source is added in an amount of 0.03 wt% to 0.3 wt% (calculated as elemental iron) based on the total weight of the polymerized monomers. Alternatively, the iron source is added in an amount of 0.15 wt% to 0.21 wt% (calculated as elemental iron) based on the total weight of the polymerized monomers. Adding an iron source within this range allows for an appropriate amount of defects in the hard carbon material, which is beneficial for balancing the reversible gram capacity and first coulombic efficiency of the secondary battery.

[0090] In some embodiments, the hard carbon material precursor includes at least one of a phenolic resin, an epoxy resin, and a furan resin. These precursors are thermosetting resins with a high degree of crosslinking, which prevents melting during subsequent heating, which could lead to iron displacement and agglomeration, thereby facilitating uniform defect reduction.

[0091] In some embodiments, the iron source is FeCl3 and / or FeCl2. Ionic iron can be evenly dispersed in the monomer, which is beneficial to the uniform reduction of defects.

[0092] In other embodiments, for example, in order to introduce other elements such as sulfur and nitrogen in appropriate amounts, other iron-containing salts such as sulfates and nitrates may be used alone or in combination.

[0093] In some embodiments, the polymerization is carried out under alkaline conditions. Carrying out polymerization under alkaline conditions is beneficial to increasing the rate of the polymerization reaction and increasing cross-linking. The alkaline conditions can be adjusted by adding an alkaline substance.

[0094] In a specific embodiment, the polymerization is carried out in the presence of aqueous ammonia, because the ammonia in the aqueous ammonia is easily volatilized and will not remain in the final hard carbon material, thereby not introducing nitrogen.

[0095] In some embodiments, the amount of ammonia added is 0.022 wt% to 0.044 wt% (or optionally 0.031 wt% to 0.035 wt%), based on the weight of the polymerized monomers. When the amount of ammonia added to the ammonia during the polymerization process is within this range, the hard carbon material precursor has an appropriate degree of crosslinking and does not precipitate ionic iron due to excessive alkalinity, thereby rendering it ineffective.

[0096] In some embodiments, the polymerization is performed at 120-160° C., optionally 135-145° C., for 0.5-2 hours. Under the above conditions, the hard carbon material precursor has an appropriate degree of crosslinking, and the solidified crosslinking bonds are not broken, so that the precursor does not melt during the subsequent carbonization process.

[0097] In some embodiments, the heating rate during the polymerization process is 2°C / min-10°C / min, and optionally, the heating rate during the polymerization process is 4°C / min-6°C / min. When the heating rate during the polymerization process is within the above range, the polymerization reaction proceeds in an orderly manner, thereby forming a hard carbon material precursor with a moderate degree of curing.

[0098] In some embodiments, the carbonization treatment is performed under an inert atmosphere at 1000°C to 1800°C for 1 to 12 hours; optionally, the temperature is increased at a rate of 2°C / min to 20°C / min. During the carbonization process, the precursor removes heteroatoms such as H and O, forming a stable hard carbon skeleton, while simultaneously reducing the iron source to elemental iron.

[0099] In some embodiments, the inert atmosphere may be, for example, at least one of nitrogen, argon, helium, or neon. Optionally, the inert atmosphere is nitrogen or argon.

[0100] In some embodiments, after the carbonization treatment, a deashing treatment is further performed, wherein the deashing treatment comprises washing the hard carbon material with an acid at room temperature to 95° C. Since residual Fe in the hard carbon material may catalyze the decomposition of the electrolyte, deashing can remove the residual Fe in the hard carbon material.

[0101] The present disclosure does not particularly limit the acid used in the deashing treatment. Exemplarily, the acid includes at least one of hydrochloric acid, nitric acid, sulfuric acid, hypochlorous acid, hydrofluoric acid, and perchloric acid. Depending on the type of acid used, the concentration of the appropriate acid can be determined.

[0102] In some embodiments, the hard carbon material is washed with acid for 1 hour to 12 hours, and the number of washing times is 1 to 5 times.

[0103] The preparation method of the hard carbon material will be described in more detail below by taking the hard carbon material precursor as phenolic resin as an example.

[0104] In some embodiments, polymerizing a monomer containing an iron source to form a hard carbon material precursor comprises the following steps 1) and 2):

[0105] 1) Liquid phase mixing and dispersion of reaction materials

[0106] First, a certain amount of iron source (such as FeCl3) is added to a formaldehyde aqueous solution (for example, a mass concentration of 40%) and stirred for 0.5-2 hours to form a uniformly dispersed mixed solution 1; then a certain amount of phenol is added to the mixed solution 1 (the molar ratio of formaldehyde to phenol is determined according to the desired degree of cross-linking, for example, the molar ratio of formaldehyde to phenol is 9:7) and stirred at room temperature for 0.5-4 hours to form a mixed solution 2.

[0107] FeCl3 can be thermally reduced at high temperature to form elemental Fe nanocrystals during the subsequent solidification process. The presence of nano-sized elemental Fe is conducive to inducing the ordering of the local carbon skeleton at the nanoscale, thereby reducing defects within this scale range.

[0108] In some embodiments, the amount of FeCl3 added is 0.09 wt% to 0.9 wt% of the total amount of phenol and formaldehyde. The amount of FeCl3 added within the above range is conducive to appropriately reducing defects.

[0109] 2) Curing

[0110] A certain amount of aqueous ammonia is added to mixed solution 2, mixed evenly, and then heated to the curing temperature (within the range of 120°C-160°C) for 0.5-2 hours until completely cured to form a phenolic resin. The heating process can be controlled at a certain heating rate, for example, 5°C / min, to ensure orderly curing.

[0111] In some embodiments, ammonia as a catalyst can increase the curing reaction rate and crosslinking rate. The amount of ammonia added to the ammonia solution can be 0.02wt%-0.05wt% of the amount of phenol. Within this range, the ammonia solution can have a suitable catalytic effect and prevent large-scale agglomeration of FeCl3, which is beneficial for its performance.

[0112] In some embodiments, after forming the hard carbon precursor, the following steps 3) and 4) may be further included.

[0113] 3) Vacuum drying

[0114] Vacuum drying can be performed at about 60°C-100°C.

[0115] 4) Crushing

[0116] The product obtained by drying in step 3) is crushed by ball milling. Conventional methods can be used for ball milling.

[0117] In some embodiments, the hard carbon material precursor is subjected to a carbonization treatment (step 5 below)) to obtain the hard carbon material.

[0118] 5) High temperature carbonization

[0119] The product obtained by crushing in the above step 4) is heated to 1000-1800° C. at a heating rate of 2-20° C. / min in a tube furnace under a nitrogen atmosphere or an argon atmosphere, and sintered for 1-12 hours.

[0120] In some embodiments, after the carbonization step, a deashing and drying step is further included.

[0121] 6) Deliming

[0122] The product after carbonization treatment in the above step 5) is soaked in an acidic aqueous solution at room temperature-95°C for 1-12 hours, and repeated 1-5 times to remove Fe element in the product, and finally washed with water to remove acid.

[0123] 7) Drying

[0124] The product obtained in step 6) is dried to obtain a hard carbon material. Drying can also be performed under vacuum.

[0125] The preparation method using epoxy resin or furan resin as a precursor is similar to the method using phenolic resin as a precursor. The main difference is the different reactive monomers. Epoxy resin generally refers to the condensation product of epichlorohydrin and bisphenol A or polyol. Similarly, the iron source and the alkaline substance can be dissolved in different polymer monomers respectively, for example, the iron source is dissolved in bisphenol A or polyol, the fatty amine curing agent is first added to the epichlorohydrin, and finally the two monomers are mixed for curing. Furan resin is a general term for resins containing furan rings in the molecular structure, such as furfuryl alcohol resin, furfural-acetone resin, furfural-acetone-formaldehyde resin, etc. For the case of multiple reactants, the iron source and the alkaline substance can be similarly dissolved in different polymer monomers and then mixed and cured. For the case of one reactant, such as furfural resin, the reactants can be divided into two parts, the iron source and the alkaline substance are dissolved separately, and then mixed and cured.

[0126] secondary batteries

[0127] According to a third aspect of the embodiments of the present disclosure, a secondary battery is provided. The secondary battery of the present disclosure will be described below with reference to the accompanying drawings as appropriate.

[0128] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. Each of these is described below.

[0129] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0130] [Negative electrode]

[0131] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0132] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0133] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the negative electrode active material includes the hard carbon material provided in the above embodiment or the hard carbon material prepared according to the preparation method of the above embodiment.

[0135] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0136] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0139] [Positive electrode]

[0140] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material according to the first aspect of the present disclosure.

[0141] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0142] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] In some embodiments, the battery cell is a sodium ion battery, and the positive electrode active material can be a positive electrode active material for sodium ion batteries known in the art. As an example, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, etc., but the present disclosure is not limited to these materials, and other traditionally known materials that can be used as positive electrode active materials for sodium ion batteries can also be used. For example, as an optional technical solution of the present disclosure, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 <x≤1。

[0144] As an optional technical approach of the present disclosure, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n-A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- The polyanionic compound can also be a compound with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4) n- The halogen can be at least one of F, Cl and Br. The polyanionic compound can also be a compound with sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- Valence state: Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ The halogen can be at least one of F, Cl and Br. Examples of polyanionic compounds are NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1). The Prussian blue compound can be a compound having sodium ions, transition metal ions and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. For example, the Prussian blue compound is Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 <a≤2,0<b<1,0<c<1。

[0145] In other embodiments, the battery cell may also be a lithium-ion battery, and the positive electrode active material may be a positive electrode active material for lithium-ion batteries known in the art.

[0146] In the list of positive electrode active materials in this disclosure, the molar content of oxygen is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0147] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0148] In some embodiments, the positive electrode film layer may further include a conductive agent. For 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.

[0149] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0150] [Electrolytes]

[0151] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0152] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0153] In some embodiments, when the battery cell is a sodium ion battery, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorooxalatoborate, sodium dioxalatoborate, sodium difluorophosphate, sodium difluorodioxalatophosphate, and sodium tetrafluorooxalatophosphate.

[0154] In some embodiments, when the battery cell is a lithium ion battery, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0155] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0156] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0157] [Isolation film]

[0158] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0159] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0160] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0161] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0162] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0163] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG4 shows a battery cell 5 with a square structure as an example.

[0164] In some embodiments, referring to Figure 5, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0165] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0166] Figure 6 shows an example battery module 4. Referring to Figure 6 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0167] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0168] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0169] Figures 7 and 8 illustrate an example battery pack 1. Referring to Figures 7 and 8 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0170] Electrical devices

[0171] A fourth aspect of an embodiment of the present disclosure further provides an electrical device. The secondary battery of the present disclosure will be described below with reference to the accompanying drawings as appropriate.

[0172] The electrical device mentioned in the embodiments of the present disclosure includes the secondary battery provided by the present disclosure. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0173] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0174] Figure 9 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0175] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0176] Example

[0177] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0178] Example 1

[0179] Preparation of hard carbon materials:

[0180] 1) adding a certain amount of FeCl3 to a 40% formaldehyde aqueous solution and stirring for 1 hour to form a uniformly dispersed mixed solution 1, then adding a certain amount of phenol to the mixed solution 1 and stirring at room temperature for 2 hours to form a mixed solution 2; wherein the amount of FeCl3 added is 0.03 wt% in terms of elemental iron;

[0181] 2) Then, a certain amount of aqueous ammonia (mass concentration 40%) was added to the mixed solution 2, stirred for 0.5 h, and then heated to 140° C. at a heating rate of 5° C. / min and maintained for 2 h until completely solidified; wherein the amount of aqueous ammonia added was 0.033 wt % in terms of ammonia;

[0182] 3) drying the solidified product obtained in step 2) under vacuum at 80° C. for 12 h;

[0183] 4) The dried product obtained in step 3) was subjected to ball milling using zirconia ball milling beads and a zirconia ball milling jar. When the mass ratio of the ball milled material to the ball milling beads reached 1:3, the ball milling speed was 800 rpm, and the ball milling time was 8 hours, the ball milling beads were removed to obtain a crushed product.

[0184] 5) heating the crushed product in step 4) to 1600° C. at a heating rate of 10° C. / min under an argon atmosphere and maintaining the temperature for 6 h to obtain a carbonized product;

[0185] 6) The carbonized product obtained in step 5) was pickled with an aqueous sulfuric acid solution at a temperature of 50° C. for 4 hours, and the washing process was repeated 3 times;

[0186] 7) The product after acid washing in step 6) was vacuum dried at 80° C. for 12 h to obtain a hard carbon material.

[0187] Hard carbon material related tests:

[0188] 1) XRD test

[0189] The hard carbon material prepared in Example 1 was prepared using a flat plate method, using CuKα radiation as the radiation source, a copper target as the anode target, a voltage of 40 kV, a current of 40 mA, a 1 mm anti-scatter slit, a 2θ scanning range of 20°-80°, a step size of 0.01671°, a step duration of 0.24 s per step, and a scan rate of 4° / min. The test instrument can be a Bruker D8 Discover X-ray diffractometer.

[0190] Figure 1 is the XRD diffraction spectrum of the hard carbon material. As shown in Figure 1, the XRD spectrum of the hard carbon material includes a first diffraction peak B and a second diffraction peak A, wherein the second diffraction peak A is located at 2θ of 24.9°, and the first diffraction peak B is located at 2θ of 26.3°, and the peak intensity ratio X of the first diffraction peak B to the second diffraction peak A is 0.956.

[0191] 2) Micromorphology test

[0192] A scanning electron microscope (ZEISS SSEM) was used to observe the hard carbon material particles and take SEM photos. The test was conducted with reference to JY / T010-1996.

[0193] FIG3 is a scanning electron microscope image of the hard carbon material. As shown in FIG3 , the hard carbon material is in an irregular granular shape, and the particle size thereof is about 4-10 μm.

[0194] Preparation of button half-cell:

[0195] The hard carbon material prepared in Example 1 was thoroughly stirred and mixed with a binder of styrene-butadiene rubber (SBR), a thickener of sodium carboxymethyl cellulose (CMC-Na), and a conductive agent of carbon black in an appropriate amount of deionized water in a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry was evenly coated on the surface of the negative electrode current collector copper foil, dried in an oven, and sliced ​​for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then NaPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Afterwards, a metal sodium sheet was used as the counter electrode and a glass fiber film was used as the separator to assemble a CR2430 button cell in an argon-protected glove box.

[0196] Button half-cell performance test

[0197] At 25°C, the button half-cell prepared above was first discharged at a current density of 10 mA / g to 0 V, and the first-cycle discharge gram capacity (i.e., discharge gram capacity) of the button half-cell was recorded. Then, the button half-cell was charged at a current density of 10 mA / g to 2.0 V, and the first-cycle charge gram capacity (i.e., reversible gram capacity) of the button cell was recorded.

[0198] First coulombic efficiency (%) = first cycle charging capacity / first cycle discharging capacity × 100%.

[0199] Examples 2-7

[0200] A hard carbon material was prepared in a similar manner to Example 1 and assembled into a button-type half-cell. The only difference was that the amount of Fe added was adjusted during the preparation of the hard carbon material to obtain hard carbon materials with different X values. See Table 1 for details.

[0201] Comparative Example 1

[0202] A hard carbon material was prepared in a similar manner to Example 1 and assembled into a button-type half-cell, the only difference being that FeCl 3 was not added during the preparation of the hard carbon material. See Table 1 for details.

[0203] The test results of the button-type half-cells prepared in Examples 1-7 and Comparative Example 1 are shown in Table 1 below.

[0204] Table 1:

[0205] As can be seen from Table 1 above, when the Fe content is between 0.03wt% and 0.3wt%, the peak intensity ratio X between the first and second diffraction peaks of the prepared hard carbon material is within a range of 0.95-1.05, significantly improving the initial coulombic efficiency and reversible gram capacity while also achieving a high discharge gram capacity. Without wishing to be bound by theory, this may be because when the iron content is within this range, it can effectively reduce non-hexacyclic ring defects, which is beneficial for achieving a high reversible gram capacity, a high initial coulombic efficiency, and a high discharge gram capacity. In Comparative Example 1, where X is less than 0.95, the discharge gram capacity is high, but the initial coulombic efficiency is too low.

[0206] Examples 8-11

[0207] A hard carbon material was prepared in the same manner as in Example 1 and assembled into a button-type half-cell. The only difference was that the amount of ammonia added to the ammonia water was adjusted during the preparation of the hard carbon material to obtain hard carbon materials with different X values. See Table 2 for details.

[0208] The test results of the button-type half-cells prepared in Examples 8-11 are shown in Table 2. In addition, for the convenience of comparison, the data of Example 4 are also shown in Table 2.

[0209] Table 2:

[0210] As shown in Table 2, when the amount of ammonia added to the aqueous solution is between 0.022 wt% and 0.044 wt%, the peak intensity ratio (X) of the first to second diffraction peaks of the prepared hard carbon material is within a range of 0.95 to 1.05, significantly improving the initial coulombic efficiency and reversible gram capacity while also achieving a high discharge gram capacity. Without wishing to be bound by theory, this may be because when the amount of ammonia added to the aqueous solution is within this range, the hard carbon material precursor has an appropriate degree of crosslinking and does not cause ionic Fe precipitation, thereby enhancing the ordering effect.

[0211] Examples 12-15

[0212] The hard carbon material was prepared in the same manner as in Example 1 and assembled into button-type half-cells. The only difference was that the curing temperature was adjusted during the preparation of the hard carbon material to obtain hard carbon materials with different X values. See Table 3 for details.

[0213] The test results of the button-type half-cells prepared in Examples 12-15 are shown in Table 3. In addition, for the convenience of comparison, the data of Example 4 are also shown in Table 3.

[0214] Table 3:

[0215] As can be seen from Table 3 above, when the curing temperature is within the range of 120°C-160°C, the peak intensity ratio X between the first and second diffraction peaks of the prepared hard carbon material is within the range of 0.95-1.05, significantly improving the initial coulombic efficiency and reversible specific capacity while also achieving a high discharge specific capacity. Without wishing to be bound by theory, this may be because when the curing temperature is within this range, the formed hard carbon material precursor has an appropriate degree of crosslinking, and melting does not cause the displacement and agglomeration of iron, nor does it break the curing crosslinks, which is conducive to the Fe element-induced effect, thereby facilitating the improvement of the reversible specific capacity and initial coulombic efficiency, while also achieving a high discharge specific capacity.

[0216] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A hard carbon material, wherein an XRD diffraction pattern of the hard carbon material comprises a first diffraction peak, wherein the first diffraction peak is located at 2θ of 26±0.5°.

2. The hard carbon material according to claim 1, wherein The XRD diffraction pattern of the hard carbon material further comprises a second diffraction peak; the second diffraction peak is located at 2θ of 23.5±0.6°; The peak intensity ratio X between the first diffraction peak and the second diffraction peak satisfies the following relationship: 0.95≤X≤1.

05.

3. The hard carbon material according to claim 2, wherein The peak intensity ratio X between the first diffraction peak and the second diffraction peak satisfies the following relationship: 0.995≤X≤1.

031.

4. The hard carbon material according to claim 2 or 3, wherein The hard carbon material I D / I G 0.8-1.1; Among them, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

5. The hard carbon material according to any one of claims 2 to 4, wherein The half-height width of the second diffraction peak is greater than the half-height width of the first diffraction peak.

6. The hard carbon material according to any one of claims 1 to 5, wherein The specific surface area of ​​the hard carbon material is 0.1 m 2 / g-15m 2 / g.

7. The hard carbon material according to any one of claims 1 to 6, wherein The hard carbon material satisfies at least one of the following: (1) The compaction density of the hard carbon material under 50000N is 0.83g / cm 3 -1.15g / cm 3 ; (2) The tap density of the hard carbon material is 0.62 g / cm 3 -0.95g / cm 3 ; (3) The volume distribution particle size Dv50 of the hard carbon material is 3.0 μm-7.9 μm; (4) The volume distribution particle size Dv90 of the hard carbon material is 8 μm-15 μm.

8. A method for preparing a hard carbon material, the method comprising: polymerizing a polymerizable monomer containing an iron source to form a hard carbon material precursor; The hard carbon material precursor is carbonized to obtain the hard carbon material.

9. The preparation method according to claim 8, wherein Based on the total weight of the polymerized monomers, the added amount of the iron source calculated as iron element is 0.03 wt% to 0.3 wt%.

10. The preparation method according to claim 8 or 9, wherein Based on the total weight of the polymerized monomers, the added amount of the iron source calculated as iron element is 0.16 wt%-0.22 wt%.

11. The preparation method according to any one of claims 8 to 10, wherein The hard carbon material precursor includes at least one of phenolic resin, epoxy resin, and furan resin.

12. The preparation method according to any one of claims 8 to 11, wherein The iron source is FeCl3 and / or FeCl2.

13. The preparation method according to any one of claims 8 to 12, wherein The polymerization is carried out under alkaline conditions.

14. The preparation method according to any one of claims 8 to 13, wherein The polymerization is carried out in the presence of aqueous ammonia; based on the total weight of the polymerized monomers, the aqueous ammonia is added in an amount of 0.022 wt% to 0.044 wt% in terms of ammonia.

15. The preparation method according to any one of claim 14, wherein Based on the total weight of the polymerized monomers, the amount of the ammonia water added as ammonia is 0.031 wt% to 0.035 wt%.

16. The preparation method according to any one of claims 8 to 15, wherein The polymerization is carried out at 120° C. to 160° C. for 0.5 h to 2 h.

17. The preparation method according to claim 16, wherein The polymerization was carried out at 135°C-145°C.

18. The preparation method according to any one of claims 8 to 17, wherein The carbonization treatment is carried out in an inert atmosphere at 1000° C. to 1800° C. for 1 hour to 12 hours; The carbonization treatment is carried out at a heating rate of 2°C / min-20°C / min.

19. The preparation method according to any one of claims 8 to 18, wherein After the carbonization treatment, a deashing treatment is further included, and the deashing treatment includes: The hard carbon material is washed with an acid at room temperature to 95° C.; the acid comprises at least one of hydrochloric acid, nitric acid, sulfuric acid, hypochlorous acid, hydrofluoric acid and perchloric acid.

20. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the hard carbon material according to any one of claims 1 to 7, or comprises the hard carbon material obtained according to the preparation method according to any one of claims 8 to 19.

21. An electric device comprising the secondary battery according to claim 20.

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