Negative pole piece, secondary battery, battery pack and energy storage system

Abstract

The invention provides a negative pole piece, a secondary battery, a battery pack and an energy storage system, the secondary battery comprises the negative pole piece, the negative pole piece comprises a fluorine-doped coal-based carbon material, the fluorine-doped coal-based carbon material has a pore structure, and the internal specific surface area of the fluorine-doped coal-based carbon material can be 1500m < 2 > / g to 2500m < 2 > / g, so that the fluorine-doped coal-based carbon material has a large number of pores, and the pore structure is uniform. More active sites are provided, so that the specific capacity of the negative pole piece can be improved, and the first effect of the secondary battery is improved; moreover, because the negative pole piece is doped with the fluorine element, the fluorine element reacts with the electrolyte to form a passivation film containing fluoride on the surface of the negative pole piece, and the passivation layer is an excellent conductor of an electronic insulator and active ions, the active ions can be freely embedded into and separated from the negative pole piece through the passivation layer; therefore, the first efficiency and the cycling stability of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, a battery pack, and an energy storage system. Background Technology

[0002] Secondary batteries can include sodium-ion batteries, lithium-ion batteries, or potassium-ion batteries. Taking sodium-ion batteries as an example, the negative electrode can include a current collector and an active material disposed on the current collector. The active material can be made of coal-based hard carbon, which has a lower cost, thus reducing the manufacturing cost of sodium-ion batteries. However, coal-based hard carbon has a relatively complete crystal structure, making it difficult to form abundant pores during cross-linking or carbonization. This makes it difficult to provide sufficient active sites for sodium ion storage, resulting in a lower specific capacity of the negative electrode and a reduced initial efficiency of the sodium-ion battery. Summary of the Invention

[0003] This application provides a negative electrode sheet, a secondary battery, a battery pack, and an energy storage system to improve the specific capacity of the negative electrode sheet and enhance the initial efficiency of the secondary battery.

[0004] In a first aspect, embodiments of this application provide a secondary battery, which includes a negative electrode sheet comprising a fluorine-doped coal-based carbon material. The fluorine-doped coal-based carbon material has a porous structure, and its internal specific surface area can be 1500 m². 2 / g to 2500m 2 / g, for example, but not limited to: 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 Other dimensions, such as g, can be determined based on actual conditions. When the internal specific surface area of ​​fluorine-doped coal-based carbon material is within the above range, it indicates that the fluorine-doped coal-based carbon material has a large number of pores, providing more active sites, thereby improving the specific capacity of the negative electrode and the first-time efficiency of the secondary battery. Furthermore, due to the doping of fluorine, the fluorine reacts with the electrolyte to form a passivation film containing fluoride on the surface of the negative electrode. This passivation layer is an electronic insulator and an excellent conductor of active ions (such as sodium ions, lithium ions, and potassium ions). Therefore, active ions can freely insert and extract from the negative electrode through this passivation layer, thereby improving the first-time efficiency and cycle stability of the secondary battery.

[0005] Optionally, the pore size of the pore structure can be from 0.7 nm to 1.2 nm, such as, but not limited to, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, etc., and can be determined according to the actual situation. When the pore size of the pore structure is within the above range, it indicates that the pore structure is relatively small and mostly closed pores. Closed pores can provide active sites, and the increase in the number of closed pores increases the number of active sites, improving the storage capacity of active ions and providing more stable kinetic performance. This can further improve the specific capacity of the negative electrode and further improve the first-stage efficiency of the secondary battery. It should be understood that the more closed pores in fluorine-doped coal-based carbon materials, the faster the liquid-phase conduction speed of active ions and the better the kinetic performance, and vice versa.

[0006] Optionally, the mass ratio of fluorine to carbon can be (5-10):100, such as, but not limited to, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, etc., which can be determined according to the actual situation. Although a higher fluorine content results in higher initial efficiency and cycle stability of the secondary battery, it also increases the manufacturing difficulty and cost. Therefore, setting the mass ratio of fluorine to carbon within the above range can reduce manufacturing difficulty and cost while improving the initial efficiency and cycle stability of the secondary battery.

[0007] Optionally, the interlayer spacing of the fluorine-doped coal-based carbon material can be from 0.34 nm to 0.35 nm, such as, but not limited to, 0.341 nm, 0.342 nm, 0.343 nm, 0.344 nm, 0.345 nm, 0.346 nm, 0.347 nm, 0.348 nm, 0.349 nm, 0.35 nm, and other sizes, which can be determined according to the actual situation. When the interlayer spacing of the fluorine-doped coal-based carbon material is within the above range, it indicates that the fluorine-doped coal-based carbon material has a high interlayer density, which can reduce the volume of the negative electrode sheet, thereby increasing the volumetric energy density of the negative electrode sheet, thus improving the energy density of the secondary battery and improving the performance of the secondary battery.

[0008] Optionally, when performing Raman spectroscopy on fluorine-doped coal-based carbon materials, the obtained spectrum contains D3 and G peaks, and the ratio of the peak area of ​​D3 peak to the peak area of ​​G peak in the Raman spectrum of fluorine-doped coal-based carbon materials can be 2 to 3. The ratio of the peak area of ​​D3 peak to the peak area of ​​G peak reflects the number of closed pores in the fluorine-doped coal-based carbon materials. When the ratio is 2 to 3, it indicates that a large number of closed pores have formed in the fluorine-doped coal-based carbon materials. Therefore, based on the ratio of the peak area of ​​D3 peak to the peak area of ​​G peak, the fluorine-doped coal-based carbon materials in this embodiment have a large number of closed pores, increasing the number of active sites and improving the storage capacity of active ions, thereby further improving the specific capacity of the negative electrode and further improving the first-stage efficiency of the secondary battery.

[0009] Optionally, the content of elements other than carbon, fluorine, and oxygen in the fluorine-doped coal-based carbon material is no more than 0.5%, such as, but not limited to, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc., which can be determined according to the actual situation and are not specifically limited here. The elements other than carbon, fluorine, and oxygen in the fluorine-doped coal-based carbon material can be referred to as impurities. When the impurity content is within the above range, it indicates that the impurity content in the fluorine-doped coal-based carbon material is low, at least four times lower than the minimum impurity content of 2% in current coal-based carbon materials. Therefore, it can effectively improve the problem of severe decomposition side reactions between coal-based carbon materials and electrolytes, thereby improving the cycle stability of the secondary battery.

[0010] Optionally, the fluorine-doped coal-based carbon material can be selected from at least one of other coal-based carbon materials such as fluorine-doped lignite, fluorine-doped anthracite, and fluorine-doped bituminous coal. As long as it is a coal-based carbon material that can be used to make a negative electrode sheet, it is applicable in the embodiments of this application.

[0011] Secondly, embodiments of this application also provide a negative electrode sheet, which may include a fluorine-doped coal-based carbon material. The fluorine-doped coal-based carbon material has a porous structure, and the internal specific surface area of ​​the fluorine-doped coal-based carbon material is 1500 m². 2 / g to 2500m 2 / g, which can not only improve the initial efficiency of the secondary battery, but also the cycle stability of the secondary battery.

[0012] It should be understood that since the principle of this negative electrode plate in solving the problem is similar to that of the aforementioned secondary battery, the implementation and technical effects of this negative electrode plate can be found in the implementation and technical effects of the aforementioned secondary battery, and the repetition will not be repeated.

[0013] Thirdly, embodiments of this application also provide a battery pack, which may include: a housing and a plurality of secondary batteries, each secondary battery being disposed within the housing, wherein the secondary batteries are as described in the first aspect and any embodiment thereof. Thus, by improving the performance of the secondary batteries, the performance of the battery pack will also be enhanced.

[0014] It should be understood that since the principle by which this battery pack solves the problem is similar to that of the aforementioned secondary battery, the implementation and technical effects of this battery pack can be found in the implementation and technical effects of the aforementioned secondary battery, and the repetitions will not be repeated.

[0015] Fourthly, embodiments of this application also provide an energy storage system, which includes a battery pack and a power converter as described in the third aspect above. The power converter is used to convert AC power output from an external AC power source into DC power for output to the battery pack, and / or, the power converter is used to convert DC power output from the battery pack into AC power for output to a load or the power grid. Thus, by improving the performance of the battery pack, the performance of the energy storage system is also improved.

[0016] It should be understood that since the principle of this energy storage system in solving the problem is similar to that of the aforementioned battery pack, the implementation and technical effects of this energy storage system can be found in the implementation and technical effects of the aforementioned battery pack, and the repetition will not be repeated. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the energy storage system provided in the embodiments of this application;

[0018] Figure 2 This is a schematic diagram of the battery pack structure provided in an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application;

[0020] Figure 4 The first charge-discharge curve and cycle curve provided for embodiments of this application;

[0021] Figure 5 A schematic diagram illustrating the formation principle of fluorine-doped coal-based carbon materials provided in the embodiments of this application;

[0022] Figure 6 Characterization data of fluorine content provided for embodiments of this application;

[0023] Figure 7 Raman spectra of fluorine-doped coal-based carbon materials provided in embodiments of this application;

[0024] Figure 8The small-angle X-ray diffraction pattern of the fluorine-doped coal-based carbon material provided in the embodiments of this application;

[0025] Figure 9 The X-ray diffraction pattern of the fluorine-doped coal-based carbon material provided in the embodiments of this application is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the application will now be described in further detail with reference to the accompanying drawings.

[0027] It should be noted that the same reference numerals in the accompanying drawings of this application denote the same or similar structures, and therefore repeated descriptions of them will be omitted. Terms expressing position and direction described in this application are illustrative based on the accompanying drawings, but may be modified as needed, and all such modifications are included within the scope of protection of this application. The accompanying drawings of this application are for illustrating relative positional relationships only and do not represent actual scale.

[0028] To facilitate understanding of the technical solutions provided in the embodiments of this application, the application scenarios will be explained first below.

[0029] The technical solutions provided in this application can be widely applied in energy storage systems. These energy storage systems can be used, but are not limited to, in scenarios such as residential energy storage, site energy, smart photovoltaics, and data center energy, for storing electrical energy and providing it externally. See also... Figure 1 The diagram shows the architecture of an energy storage system. The energy storage system may include: a battery cluster and a power converter 200. The battery cluster includes multiple battery packs 100 connected in series. Figure 1 The diagram shows only one battery pack 100 as an example. The power converter 200 can convert the AC power output from an external AC power source (such as the power grid 300) into DC power and output it to the battery pack 100 in the battery cluster to charge the battery pack 100. It can also convert the DC power output from the battery pack 100 in the battery cluster into AC power and output it to the load 400 or the power grid 300 to discharge the battery pack 100.

[0030] See Figure 2 The schematic diagram of the battery pack 100 shown indicates that the battery pack 100 may include: a housing 101 and multiple secondary batteries 102. Each secondary battery 102 is disposed within the housing 101. The secondary batteries 102 can be connected in series, in parallel, or a combination of series and parallel connections to give the battery pack 100 a high capacity and high voltage, thus making it suitable for various application scenarios. For each secondary battery 102, as follows... Figure 3The schematic diagram of the secondary battery 102 shown indicates that the secondary battery 102 may include: a positive electrode 11, a negative electrode 12, a battery separator 13, and an electrolyte 14. The battery separator 13 is disposed between the positive electrode 11 and the negative electrode 12, and the electrolyte 14 wets the positive electrode 11, the battery separator 13, and the negative electrode 12. Furthermore, the secondary battery may be, but is not limited to, sodium-ion batteries, lithium-ion batteries, or potassium-ion batteries, or other types of secondary batteries. Taking a sodium-ion battery as an example, the negative electrode may include a current collector and an active material disposed on the current collector. The active material may be made of coal-based hard carbon, as coal-based hard carbon has a lower cost, thus reducing the manufacturing cost of sodium-ion batteries. However, the lattice structure of coal-based hard carbon is relatively complete, making it difficult to form abundant pores during cross-linking or carbonization, which makes it difficult to provide sufficient active sites for sodium ion storage, resulting in a lower specific capacity of the negative electrode and a reduced initial efficiency of the secondary battery. It should be understood that the specific capacity of the negative electrode refers to the number of sodium ions that can be accommodated per unit mass of the active material in the negative electrode. The specific capacity mentioned below refers to the specific capacity of the negative electrode.

[0031] Based on this, this application provides a secondary battery, which includes a negative electrode sheet comprising a fluorine-doped coal-based carbon material. The fluorine-doped coal-based carbon material has a porous structure, and its internal specific surface area can be 1500 m². 2 / g to 2500m 2 / g, for example, but not limited to: 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 Other dimensions, such as / g, can be determined based on actual conditions. When the internal specific surface area of ​​fluorine-doped coal-based carbon materials is within the above range, it indicates that the fluorine-doped coal-based carbon materials have a large number of pores, providing more active sites, thereby improving the specific capacity of the negative electrode and the first-stage efficiency of the secondary battery. For example, the specific capacity of the negative electrode can reach up to 410 mAh / g. Figure 4As shown in (a); and, due to the doping of fluorine, the fluorine reacts with the electrolyte to form a passivation film containing fluoride on the surface of the negative electrode. This passivation layer is an electronic insulator and an excellent conductor of active ions (such as sodium ions, lithium ions, and potassium ions), so active ions can freely insert and extract from the negative electrode through this passivation layer, thereby improving the battery's initial efficiency and cycle stability; for example, the initial efficiency of a secondary battery can be increased to 93%, and the performance retention rate can be greater than 90% after 2000 cycles, such as... Figure 4 As shown in (b) of the diagram.

[0032] It should be understood that specific surface area refers to the total surface area of ​​a unit mass of powder. Specific surface area includes external specific surface area and internal specific surface area. Internal specific surface area refers to the total internal surface area of ​​a unit mass of powder, while external specific surface area refers to the total external surface area of ​​a unit mass of powder. Unless otherwise specified, specific surface area is the sum of internal and external specific surface areas.

[0033] It should also be understood that the fluorine-doped coal-based carbon materials provided in the embodiments of this application can be used not only in secondary batteries, but also in capacitors or other devices that require fluorine-doped coal-based carbon materials as negative electrode plates.

[0034] For example, the pore size of the pore structure can be from 0.7 nm to 1.2 nm, such as, but not limited to, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, etc., which can be determined according to the actual situation. When the pore size of the pore structure is within the above range, it indicates that the pore structure is relatively small and mostly closed pores. Closed pores can provide active sites. Increasing the number of closed pores increases the number of active sites, improves the storage capacity of active ions, and also has more stable kinetic performance, thereby further improving the specific capacity of the negative electrode and further improving the first-stage efficiency of the secondary battery. It should be understood that the more closed pores in fluorine-doped coal-based carbon materials, the faster the liquid phase conduction speed of active ions and the better the kinetic performance, and vice versa.

[0035] It should be understood that the relationship between aperture and specific capacity (i.e., Relationship 1) is as follows:

[0036]

[0037] Where C represents specific capacity, V pore Indicates the volume of the hole. The pore size represents the amount of active ions that can be accommodated in the pore, and is simply referred to as pore capacity. According to Equation 1, it can be found that the pore size is inversely proportional to the specific capacity. The smaller the pore size, the higher the specific capacity, and vice versa. Therefore, when the pore size of the pore structure is between 0.7 nm and 1.2 nm, the negative electrode can have a high specific capacity.

[0038] When Raman spectroscopy was performed on fluorine-doped coal-based carbon materials, the obtained spectra showed D3 and G peaks. The ratio of the peak area of ​​D3 peak to the peak area of ​​G peak in the Raman spectrum of fluorine-doped coal-based carbon materials could be 2 to 3. The ratio of the peak area of ​​D3 peak to the peak area of ​​G peak reflects the number of closed pores in the fluorine-doped coal-based carbon materials. When the ratio is 2 to 3, it indicates that a large number of closed pores have been formed in the fluorine-doped coal-based carbon materials. Therefore, judging from the ratio of the peak area of ​​D3 peak to the peak area of ​​G peak, the fluorine-doped coal-based carbon materials in this embodiment have a large number of closed pores, which increases the number of active sites and improves the storage capacity of active ions, thereby further improving the specific capacity of the negative electrode and further improving the first-stage efficiency of the secondary battery.

[0039] The interlayer spacing of fluorine-doped coal-based carbon materials can be from 0.34 nm to 0.35 nm, such as, but not limited to, 0.341 nm, 0.342 nm, 0.343 nm, 0.344 nm, 0.345 nm, 0.346 nm, 0.347 nm, 0.348 nm, 0.349 nm, 0.35 nm, and other sizes, which can be determined according to the actual situation. When the interlayer spacing of fluorine-doped coal-based carbon materials is within the above range, it indicates that the fluorine-doped coal-based carbon materials have high interlayer density, which can reduce the volume of the negative electrode sheet, thereby increasing the volumetric energy density of the negative electrode sheet, thus improving the energy density of the secondary battery and improving the performance of the secondary battery.

[0040] The mass ratio of fluorine to carbon can be (5-10):100, such as, but not limited to, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, etc., which can be determined according to the actual situation. While a higher fluorine content results in better initial efficiency and cycle stability of the secondary battery, it also increases manufacturing difficulty and costs. Therefore, setting the mass ratio of fluorine to carbon within the above range can reduce manufacturing difficulty and costs while improving the initial efficiency and cycle stability of the secondary battery.

[0041] Current coal-based carbon materials contain numerous impurities, such as silicon, calcium, aluminum, sulfur, and other elements. These impurities can trigger severe decomposition side reactions between the coal-based carbon material and the electrolyte in the negative electrode, leading to a continuous decrease in the amount of coal-based carbon material and ultimately reducing the cycle stability of the secondary battery. Therefore, the cycle stability of the secondary battery can be improved by reducing the impurity content in the coal-based carbon material. In the fluorine-doped coal-based carbon material provided in this application embodiment, the content of elements other than carbon, fluorine, and oxygen is no more than 0.5%, such as, but not limited to, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc., which can be determined according to the actual situation and are not specifically limited here. In fluorine-doped coal-based carbon materials, elements other than carbon, fluorine, and oxygen can be referred to as impurities or impurity elements. When the impurity content is within the above range, it indicates that the impurity content in the fluorine-doped coal-based carbon material is low. Compared with the impurity content of at least 2% in current coal-based carbon materials, it is reduced by at least four times. Therefore, it can effectively improve the problem of severe decomposition side reactions between coal-based carbon materials and electrolytes, thereby improving the cycle stability of secondary batteries.

[0042] For example, the fluorine-doped coal-based carbon material can be selected from at least one of other coal-based carbon materials such as fluorine-doped lignite, fluorine-doped anthracite, and fluorine-doped bituminous coal. As long as it is a coal-based carbon material that can be used to make a negative electrode sheet, it is applicable in the embodiments of this application.

[0043] Based on the above, this application also provides a method for preparing fluorine-doped coal-based carbon materials, which may include: (see above) Figure 5 As shown, the carbon chain end groups of the coal-based carbon material precursor include at least one of hydroxyl and carboxyl groups. When the coal-based carbon material precursor is mixed with a fluorinating agent, the fluorine element in the fluorinating agent combines with the hydrogen element in the hydroxyl and carboxyl groups to form hydrofluoric acid, causing the hydroxyl groups in the carbon chain end groups to form -O. - Carboxyl group forms -COO - Because of -O - and -COO - It has high activity, so the two ends of the same carbon chain or the ends of different carbon chains will cross-link, realizing the edge cross-linking of carbon sheets and forming an intermediate. The intermediate is heat-treated, and after the heat treatment is carried out for a preset time, a decontaminant is introduced. The decontaminant reacts with the impurity elements in the intermediate to form volatile substances and salts. The volatile substances will be removed from the intermediate, and the salts will be removed by washing, thereby obtaining fluorine-doped coal-based carbon materials.

[0044] Therefore, the process of pore formation and impurity removal can be completed in one step to produce fluorine-doped coal-based carbon materials, achieving in-situ purification. This not only improves the production efficiency of fluorine-doped coal-based carbon materials, but also gives them a large number of closed pores, effectively reducing the impurity content. When this fluorine-doped coal-based carbon material is applied to the negative electrode of a secondary battery, it can improve the performance of the secondary battery.

[0045] For example, the impurity remover may include, but is not limited to, HCl. In this case, the sulfur element in the intermediate can be volatilized as H2S, and the salts formed by silicon, calcium, and aluminum with chlorine can be washed away, thereby effectively removing impurities from fluorine-doped coal-based carbon materials. Furthermore, the timing or preset time for introducing the impurity remover can be set according to actual needs, as long as it ensures that the impurity remover can form volatile substances and salts with the impurities; no specific limitation is made here. In this embodiment, the types of salts formed by silicon, calcium, and aluminum with chlorine are not limited; the type of salt needs to be determined based on factors such as the valence state of each element and the stability of the salt.

[0046] For example, the manufacturing method may specifically include the following steps:

[0047] Step 1: Mix the fluorinating agent of the powder with the coal-based carbon material precursor of the powder at a mass ratio of 0.05:1 to 10:1 to obtain a mixed powder. Then, disperse the mixed powder in a dispersion solution to obtain a dispersion liquid. After drying the dispersion liquid, obtain a mixed solid. The dispersion solution can be a solution capable of dispersing the mixed powder, such as, but not limited to, a water-alcohol solution. The drying temperature can be determined according to the composition of the dispersion solution to facilitate the evaporation of the dispersion solution and leave the mixed powder. Alternatively, the mixed powder can be mixed evenly to obtain the mixed solid.

[0048] Step 2: Perform heat treatment and purification on the mixed solid to obtain fluorine-doped coal-based carbon material. The heat treatment may include multiple stages, and the treatment temperature of each stage may be different, with the later stage having a higher treatment temperature than the earlier stage, so as to facilitate the stepwise heating treatment of the mixed solid. For example, but not limited to, the heat treatment includes two stages, with the first stage having a treatment temperature of 800℃ to 1000℃ and the second stage having a treatment temperature of 1200℃ to 1600℃. The purification temperature may not be higher than the temperature of the heat treatment, for example, but not limited to, a purification temperature of 200℃ to 600℃.

[0049] In this way, the product does not need to be removed from the cavity after pore creation, and purification can be achieved in situ, which avoids product contamination and can also improve production efficiency.

[0050] The secondary battery will be described below with reference to specific embodiments.

[0051] The specific manufacturing process of fluorine-doped coal-based carbon materials:

[0052] Step 1: Crush the coal-based carbon material precursor, such as lignite, to a particle size of D50 of less than 5μm. Mix the fluorinating agent with the crushed coal-based carbon material precursor at a certain mass ratio (i.e., fluorine-to-coal ratio), and disperse it in a water-alcohol mixture. After stirring, a uniformly dispersed dispersion is obtained. The dispersion is dried at a certain temperature to obtain a mixed solid.

[0053] Step 2: The mixed solid is placed in a high-temperature atmosphere furnace, heated to a low temperature in an inert atmosphere and held at that temperature for a certain period of time. Then, it is further heated to a high temperature and held at that temperature for a certain period of time. Afterward, it is cooled to the purification temperature, and HCl gas is introduced into the furnace under an inert atmosphere for a certain period of time. The furnace is then cooled to room temperature to obtain powder. The powder is washed and dried to obtain fluorine-doped coal-based carbon material.

[0054] The manufacturing process of a secondary battery: The negative electrode is made from the obtained fluorine-doped coal-based carbon material, and the positive electrode is then made to form a secondary battery.

[0055] Technical parameters of each embodiment and comparative example:

[0056] Example 1: The fluorinating agent was NaF, the fluorine-to-coal ratio was 3:1, the low temperature was 1000℃, the high temperature was 1400℃, the purification temperature was 400℃, and the concentration of HCl was 30%.

[0057] Example 2: The difference from Example 1 is that the fluorinating agent is Na2SiF6, the fluorine-to-coal ratio is 5:1, and the low temperature is 900℃;

[0058] Example 3: The difference from Example 1 is that the fluorine-to-coal ratio is 0.5:1;

[0059] Example 4: The difference from Example 1 is that the fluorine-to-coal ratio is 10:1 and the high temperature is 1600℃;

[0060] Example 5: The difference from Example 1 is that the purification temperature is 200℃;

[0061] Example 6: The difference from Example 1 is that the concentration of HCl is 10%;

[0062] Example 7: The difference from Example 1 is that the concentration of HCl is 0, that is, no HCl gas is introduced;

[0063] Example 8: The difference from Example 1 is that the concentration of HCl is 2%;

[0064] Comparative Example 1: The difference from Example 1 is that no fluorinating agent is used; the coal-based carbon material precursor is directly subjected to heat treatment and purification.

[0065] Comparative Example 2: The difference from Example 1 is that the fluorine-to-coal ratio is 0.05:1;

[0066] Comparative Example 3: The difference from Example 1 is that the fluorinating agent is mixed with the crushed coal-based carbon material precursor at a certain mass ratio (i.e., fluorine-to-coal ratio) to obtain a mixed solid.

[0067] Characterization data: The characterization results of each embodiment and comparative example are shown in Table 1 below, and as shown in... Figures 6 to 9 As shown in Table 1, D3 / G represents the ratio of the peak area of ​​peak D3 to the peak area of ​​peak G.

[0068] Table 1

[0069]

[0070] exist Figure 6 middle, Figure 6 (a) in the image represents a scanning electron microscope (SEM) image of a fluorine-doped coal-based carbon material. Figure 6 (b) in the diagram is the distribution of element C. Figure 6 (c) in the diagram represents the distribution of element F. Figure 6 (d) in the figure is a comparison chart of the content of each element, from Figure 6 The results shown indicate that fluorine is uniformly distributed in fluorine-doped coal-based carbon materials, achieving uniform doping, and the F / C ratio can reach 5% to 10%, while the O / C ratio can reach 3% to 5%.

[0071] Figure 7 The Raman spectra show only D1 and G peaks in the undoped coal-based carbon material, indicating the absence of lamellar edge crosslinking structures. In the spectrum of the fluorine-doped coal-based carbon material, D1, D2, D3, and G peaks appear, with D3 peak being relatively high. The D3 peak indicates the presence of sp... 3 Carbon components, while sp 3 The carbon composition indicates that a lamellar edge cross-linked structure was formed in the precursor of the coal-based carbon material, thus demonstrating that the introduction of fluorinating agents can promote the formation of a large number of closed pores.

[0072] Figure 8 The small-angle X-ray diffraction pattern, analyzed from the curves, indicates an aperture of approximately 0.7 nm to 1.2 nm, and an internal specific surface area of ​​1500 m². 2 / g to 2500m 2 / g indicates that the closed pores in fluorine-doped coal-based carbon materials are small in size and numerous in number.

[0073] Figure 9The X-ray diffraction pattern shows that the interlayer spacing of the fluorine-doped coal-based carbon material is approximately 0.34 nm to 0.35 nm, which can be calculated by converting the C peak marked by the dashed line in the figure. This indicates that the interlayer density of the fluorine-doped coal-based carbon material is higher.

[0074] Test data: The test results of each embodiment and comparative example are shown in Table 2 below, where cycle stability refers to the number of charge-discharge cycles when SOH decreases from 100% to 80%.

[0075] Table 2

[0076] First effect Specific capacity (mAh / g) Cyclic stability (number of cycles) Example 1 93％ 410 2000 Example 2 91％ 390 2000 Example 3 89％ 370 1500 Example 4 90％ 430 1300 Example 5 93％ 410 1500 Example 6 93％ 406 1400 Example 7 85％ 380 400 Example 8 88％ 385 500 Comparative Example 1 70％ 230 500 Comparative Example 2 75％ 280 700 Comparative Example 3 73％ 300 800

[0077] From the results given in Tables 1 and 2 above, the following conclusions can be drawn:

[0078] 1. In Example 7, since no HCl gas was introduced, the obtained fluorine-doped coal-based carbon material was not purified, resulting in an impurity content as high as 2%. When the HCl concentration was 2%, corresponding to Example 8, the impurity content decreased to 1.5%. When the HCl concentration was 10%, corresponding to Example 6, the impurity content decreased to 0.1%. Therefore, increasing the HCl concentration can effectively reduce the impurity content in the fluorine-doped coal-based carbon material. Furthermore, the cycle stability of Example 7 was 400 cycles, Example 8 was 500 cycles, Example 6 was 1400 cycles, and when the HCl concentration in Example 1 increased to 30%, the cycle stability of Example 1 increased to 2000 cycles. Based on this, it can be determined that introducing HCl gas can reduce the impurity content in the fluorine-doped coal-based carbon material and increase the cycle stability of the secondary battery.

[0079] 2. By comparing Comparative Example 1, Comparative Example 2, Example 1, and Example 3, it can be concluded that with the increase of the fluorine-to-coal ratio, the internal specific surface area of ​​the fluorine-doped coal-based carbon material gradually increases, the pore size shows a decreasing trend, the F / C ratio gradually increases, and the D3 / G ratio gradually increases. This indicates that with the increase of the fluorine-to-coal ratio, the number of closed pores in the fluorine-doped coal-based carbon material gradually increases, the pore size of the closed pores becomes smaller, and the F content gradually increases, thereby gradually increasing the initial efficiency, specific capacity, and cycle stability of the secondary battery.

[0080] 3. By comparing Comparative Example 3 with Example 1, it can be found that the number of closed pores in the fluorine-doped coal-based carbon material after dispersion treatment with water-alcohol mixture is significantly increased and the pore size of the closed pores is smaller. The amount of F doped in is also increased. This is because dispersion treatment with water-alcohol mixture can achieve full mixing of coal-based carbon material precursor and fluorinating agent, so that F can be more uniformly dispersed in the mixed solid. Therefore, during heat treatment, F element can play a uniform role, resulting in more and smaller closed pores, improving the first efficiency, specific capacity and cycle stability of secondary battery.

[0081] 4. By comparing Example 1 and Example 5, it was found that the purification temperature of 200℃ or 400℃ had little difference in its impact on the parameters of fluorine-doped coal-based carbon materials and the performance of secondary batteries. Therefore, in order to reduce production costs and avoid energy waste, the purification temperature can be appropriately reduced.

[0082] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A secondary battery, characterized in that, The electrode includes a negative electrode sheet comprising a fluorine-doped coal-based carbon material having a porous structure and an internal specific surface area of ​​1500 m². 2 / g to 2500m 2 / g.

2. The secondary battery as described in claim 1, characterized in that, The pore size of the pore structure is from 0.7 nm to 1.2 nm.

3. The secondary battery as described in claim 1 or 2, characterized in that, The mass ratio of fluorine to carbon is (5-10):

100.

4. The secondary battery according to any one of claims 1-3, characterized in that, The interlayer spacing of the fluorine-doped coal-based carbon material is 0.34 nm to 0.35 nm.

5. The secondary battery according to any one of claims 1-4, characterized in that, The ratio of the peak area of ​​the D3 peak to the peak area of ​​the G peak in the Raman spectrum of the fluorine-doped coal-based carbon material is 2 to 3.

6. The secondary battery according to any one of claims 1-5, characterized in that, The content of elements other than carbon, fluorine, and oxygen in the fluorine-doped coal-based carbon material is no more than 0.5%.

7. The secondary battery according to any one of claims 1-6, characterized in that, The fluorine-doped coal-based carbon material is selected from at least one of fluorine-doped lignite, fluorine-doped anthracite, and fluorine-doped bituminous coal.

8. A negative electrode sheet, characterized in that, This includes fluorine-doped coal-based carbon materials, wherein the fluorine-doped coal-based carbon materials have a porous structure and an internal specific surface area of ​​1500 m². 2 / g to 2500m 2 / g.

9. A battery pack, characterized in that, include: The enclosure and a plurality of secondary batteries as described in any one of claims 1-7, each of the secondary batteries being disposed within the enclosure.

10. An energy storage system, characterized in that, The energy storage system includes a battery pack and a power converter as described in claim 9, wherein the power converter is used to convert AC power output from an external AC power source into DC power output to the battery pack, and / or, the power converter is used to convert DC power output from the battery pack into AC power output to a load or the power grid.

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