Negative active material, negative electrode sheet, and energy storage device
By optimizing the pore structure and particle size distribution of the negative electrode active material, the balance between lifespan and capacity performance of energy storage devices has been solved, achieving superior cycle performance and capacity levels.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAMEN HITHIUM ENERGY STORAGE TECHNOLOGY CO LTD
- Filing Date
- 2023-09-18
- Publication Date
- 2026-06-23
AI Technical Summary
Existing technologies struggle to maintain the capacity performance of energy storage devices while extending their lifespan, which can easily affect the overall performance of these devices.
By optimizing the pore structure of the negative electrode active material, controlling the pore volume ratio and particle size distribution of micropores, mesopores and macropores, ensuring 0.5%≤V1/V2≤2%, 30%≤V2/(V2+V3)≤50%, and controlling the ratio of V2/(V2+V3) to (Dv99-Dv90)/Dv99 within the range of 0.8 to 1.5, the lithium-ion channels and lithium source consumption are optimized.
It significantly improves the cycle performance and rate performance of energy storage devices, extends their service life, and maintains high capacity performance, with a cycle performance of over 99.7%.
Smart Images
Figure CN117117143B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a negative electrode active material, a negative electrode sheet, and an energy storage device. Background Technology
[0002] With the explosive growth of the energy storage market, the market demands increasingly higher lifespans for energy storage devices. Although there are currently some ways to improve the lifespan of energy storage devices, it is easy to compromise the capacity performance of the devices while improving their lifespan, making it difficult to simultaneously ensure the overall performance of the energy storage devices during use. Summary of the Invention
[0003] To address the aforementioned technical problems, this application discloses a negative electrode active material, a negative electrode sheet, and an energy storage device. By optimizing and controlling the negative electrode active material in the negative electrode sheet, the service life of the energy storage device can be improved, while simultaneously enhancing its stability and rate performance.
[0004] In a first aspect, this application provides a negative electrode active material, the negative electrode active material comprising a porous structure having micropores, mesopores and macropores, wherein the pore volume of the negative electrode active material satisfies the following relationship: 0.5% ≤ V1 / V2 ≤ 2%, and 30% ≤ V2 / (V2+V3) ≤ 50%;
[0005] V1 is the pore volume of the micropores in the negative electrode active material, V2 is the pore volume of the intermediate pores in the negative electrode active material, and V3 is the pore volume of the macropores in the negative electrode active material.
[0006] Furthermore, the ratio between V2 / (V2+V3) and (Dv99-Dv90) / Dv99 ranges from 0.8 to 1.5, where Dv99 refers to the particle size value corresponding to the cumulative particle size distribution percentage of the negative electrode active material reaching 99%, and Dv90 refers to the particle size value corresponding to the cumulative particle size distribution percentage of the negative electrode active material reaching 90%.
[0007] Furthermore, 0.34≤(Dv99-Dv90) / Dv99≤0.36.
[0008] Preferably, 20μm≤Dv90≤30μm, 30μm≤Dv99≤40μm.
[0009] Preferably, 0.5% ≤ V1 / V2 ≤ 0.6%.
[0010] Preferably, 46% ≤ V2 / (V2+V3) ≤ 48%.
[0011] Furthermore, 0.00001cm 3 / g≤V1≤0.00004cm3 / g, 0.001cm 3 / g≤V2≤0.0025m 3 / g, 0.0026cm 3 / g≤V3≤0.004cm 3 / g.
[0012] Further, the proportion of the negative electrode active material in the first particle size range to the total negative electrode active material is x, the proportion of the negative electrode active material in the second particle size range to the total negative electrode active material is y, and the proportion of the negative electrode active material in the third particle size range to the total negative electrode active material is z. The particle size of the negative electrode active material satisfies the following relationship: 8.4≤x / z≤25.0, 2.8≤y / z≤11.7; the first particle size range is greater than or equal to 0.6μm and less than or equal to 2.5μm, the second particle size range is greater than 2.5μm and less than 7.5μm, and the third particle size range is greater than or equal to 7.5μm and less than or equal to 30μm.
[0013] Furthermore, 0.59≤x≤0.75, 0.20≤y≤0.35, 0.03≤z≤0.07.
[0014] Furthermore, the specific surface area of the negative electrode active material is 1.1 m². 2 / g~2.0m 2 / g.
[0015] Secondly, embodiments of this application provide a negative electrode sheet, the negative electrode sheet including a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the negative electrode active material as described in the first aspect.
[0016] Thirdly, an energy storage device is provided in the embodiments of this application, the energy storage device comprising the negative electrode active material as described in the first aspect, or the energy storage device comprising the negative electrode sheet as described in the second aspect.
[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0018] After extensive research, this application found that when the pore volume of various types of pores in the negative electrode active material meets the requirements of 0.5% ≤ V1 / V2 ≤ 2% and 30% ≤ V2 / (V2+V3) ≤ 50%, on the one hand, the proportion of micropores, mesopores and macropores in terms of pore size and pore volume is more conducive to improving the abundance of lithium-ion channels, but without causing excessive increase in specific surface area and excessive consumption of lithium source in the SEI film stage. On the other hand, the particle size ratio of micropores and mesopores is conducive to providing good kinetic performance and reducing the occurrence of side reactions. Thus, by controlling the pore volume and particle size distribution of the aforementioned micropores, mesopores and macropores, the cycle performance and rate performance of the negative electrode sheet using this negative electrode material can be improved. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0020] Figure 1 These are cycle performance test diagrams of the negative electrode sheets of Embodiment 1 and Comparative Example 1 of this application. Detailed Implementation
[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.
[0023] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.
[0024] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.
[0025] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.
[0026] The technical solution of the present invention will be further described below with reference to the embodiments and accompanying drawings.
[0027] This application provides a negative electrode active material, a negative electrode sheet, and an energy storage device to further improve the service life of the energy storage device while ensuring its high capacity performance.
[0028] In a first aspect, embodiments of this application provide a negative electrode active material, which includes a porous structure having micropores, mesopores, and macropores. The pore volume of the negative electrode active material satisfies the following relationship: 0.5% ≤ V1 / V2 ≤ 2%, and 30% ≤ V2 / (V2+V3) ≤ 50%; where V1 is the pore volume of the micropores in the negative electrode active material, V2 is the pore volume of the mesopores in the negative electrode active material, and V3 is the pore volume of the macropores in the negative electrode active material.
[0029] The negative electrode active material in this application embodiment is a porous structure simultaneously possessing micropores, mesopores, and macropores, such as graphite material simultaneously possessing micropores, mesopores, and macropores. Here, micropores refer to pores with a diameter less than 2 nm, mesopores refer to pores with a diameter greater than or equal to 2 nm and less than or equal to 50 nm, and macropores refer to pores with a diameter greater than 50 nm and less than 500 nm. It is understood that 0.5% ≤ V1 / V2 ≤ 2% includes any value within this ratio range, for example, V1 / V2 is 0.5, 0.8, 1, 1.2, 1.5, 1.8, or 2. 30% ≤ V2 / (V2+V3) ≤ 50% includes any value within this ratio range, for example, V2 / (V2+V3) is 30%, 32%, 35%, 38%, 40%, 42%, 45%, 47%, or 50%.
[0030] The pores with different volumes in the negative electrode active material can provide channels for lithium ion insertion and extraction, but they can also cause more consumption of lithium source during the formation of SEI film. Therefore, it is not always better to have larger pore size or larger pore volume. Instead, the pore volume of micropores, mesopores and macropores needs to be optimized and controlled to enable the negative electrode sheet using the negative electrode active material to have better cycle performance and rate performance, thereby enabling the energy storage device using the negative electrode sheet to have a longer service life and better capacity performance.
[0031] After extensive research, this application found that when 0.5% ≤ V1 / V2 ≤ 2% and 30% ≤ V2 / (V2+V3) ≤ 50%, the proportion of micropores, mesopores, and macropores in terms of pore size and pore volume is more conducive to improving the abundance of lithium-ion channels, but without causing excessive increase in specific surface area and excessive consumption of lithium source in the SEI film stage. Thus, by controlling the pore volume of the aforementioned micropores, mesopores, and macropores, the cycle performance and rate performance of the anode sheet using this anode material can be improved.
[0032] Specifically, when V1 / V2 is less than 0.5% and V2 / (V2+V3) is less than 30%, the porosity of the entire negative electrode active material decreases, and the pore structure of the negative electrode active material is dominated by macropores. Although more macropores can reduce the consumption of lithium source, this reduces the channels for lithium ion insertion and extraction, weakens the kinetic performance, increases the internal resistance, and has a significant impact on the cycle life of the negative electrode sheet. When V1 / V2 is greater than 2% and V2 / (V2+V3) is greater than 50%, the pore structure of the negative electrode active material is characterized by more mesopores and micropores and a significant reduction in the amount of macropores. However, this leads to a significant increase in the specific surface area of the negative electrode active material, which in turn increases the consumption of lithium source during the SEI film formation stage, affecting the initial coulombic efficiency of the energy storage device and thus affecting the cycle life of the energy storage device.
[0033] Furthermore, the ratio between V2 / (V2+V3) and (Dv99-Dv90) / Dv99 ranges from 0.8 to 1.5. That is, 0.8 ≤ [V2 / (V2+V3)] / [(Dv99-Dv90) / Dv99] ≤ 1.5. Here, the ratio between the pore volume ratio of the mesopores and macropores and the particle size ratio of the negative electrode active material ranges from 0.8 to 1.5, including any value within this range. For example, [V2 / (V2+V3)] / [(Dv99-Dv90) / Dv99] can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, or 1.5.
[0034] Based on controlling the pore volumes of micropores, mesopores, and macropores within the aforementioned ranges, further controlling the ratio of the pore volume of mesopores and macropores to the particle size of the negative electrode active material within the aforementioned range allows the particle size distribution and pore volume characteristics of the negative electrode active material to provide suitable lithium-ion channels and a specific surface area for consuming lithium sources, thereby further promoting a balanced improvement in the cycle performance and capacity level of the energy storage device. When the aforementioned ratio is below 0.8, the particle size distribution of the negative electrode active material contains more large particles, and the porous structure is dominated by macropores. This material structure characteristic results in fewer lithium-ion channels and poorer kinetic performance. When the aforementioned ratio is above 1.5, the particle size distribution of the negative electrode active material contains too few large particles, and the porous structure is dominated by mesopores. This significantly increases the specific surface area of the negative electrode active material, making it easier to consume more lithium sources during SEI film formation, affecting the initial coulombic efficiency, and also significantly impacting the cycle performance of the energy storage device.
[0035] The following section provides further explanation of the pore volume of various types of pores and the particle size distribution of the negative electrode active material.
[0036] Furthermore, 0.5% ≤ V1 / V2 ≤ 0.6%, 46% ≤ V2 / (V2+V3) ≤ 50%, and 0.34 ≤ (Dv99-Dv90) / Dv99 ≤ 0.36.
[0037] By further controlling the ratio of micropores to mesopores to 0.5%–0.6%, and further controlling the proportion of mesopores in the total pore volume of mesopores and macropores to 46%–48%, and when 0.34≤(Dv99-Dv90) / Dv99≤0.36, both the proportion of pore volume of mesopores, micropores, and macropores in the negative electrode active material and the particle size distribution of the negative electrode active material can better balance the wetting reaction channels provided to lithium ions and the consumption of lithium source when forming the SEI film. As a result, the capacity retention rate of the energy storage device after 600 cycles is as high as 99.7% or more, and the specific capacity of the energy storage device does not show significant decay.
[0038] Furthermore, 0.00001cm 3 / g≤V1≤0.00004cm 3 / g, 0.001cm 3 / g≤V2≤0.0025m 3 / g, 0.0026cm 3 / g≤V3≤0.004cm 3 / g. When the pore volumes of micropores, mesopores, and macropores in the negative electrode active material of this application are set within the above-mentioned ranges, it is more advantageous to obtain the pore volume structure characteristics under the aforementioned conditions of 0.5%≤V1 / V2≤0.6% and 46%≤V2 / (V2+V3)≤50%. This helps to optimize the electrochemical performance of the negative electrode active material by rapidly screening porous structures with these pore volumes, thereby optimizing the cycle performance and capacity level of the energy storage device.
[0039] Furthermore, 20μm≤Dv90≤30μm, 30μm≤Dv99≤40μm. When the negative electrode active material of this application limits its Dv90 and Dv99 particle size distribution to the above range, it is more advantageous to obtain the particle size structure characteristics under the aforementioned condition of 0.34≤(Dv99-Dv90) / Dv99≤0.36. This helps to optimize the electrochemical performance of the negative electrode active material by rapidly screening negative electrode active materials with these specified particle sizes, thereby optimizing the cycle performance and capacity level of the energy storage device.
[0040] In addition to controlling the pore volume ratio of different types of micropores, mesopores, and macropores, this application finds that when the particle size distribution of the negative electrode active material is further controlled within a specific range, it can further ensure that the negative electrode active material has fewer side reactions, stronger kinetic performance, and a higher compaction density. Specifically, the proportion of the negative electrode active material in the first particle size range is x, the proportion of the negative electrode active material in the second particle size range is y, and the proportion of the negative electrode active material in the third particle size range is z. The particle size of the negative electrode active material satisfies the following relationship: 8.4 ≤ x / z ≤ 25.0, 2.8 ≤ y / z ≤ 11.7; the first particle size range is greater than or equal to 0.6 μm and less than or equal to 2.5 μm, the second particle size range is greater than 2.5 μm and less than 7.5 μm, and the third particle size range is greater than or equal to 7.5 μm and less than or equal to 30 μm.
[0041] When x / z is greater than 25.0 or y / z is less than 2.8, the particle size of the negative electrode active material is too small and the specific surface area is too large, which easily leads to side reactions. When x / z is less than 25.0 or y / z is greater than 2.8, it easily affects the kinetic performance of the negative electrode active material, leading to lithium plating. Therefore, given that the negative electrode active material already possesses a specific micropore, mesopore, and macropore volume distribution, further controlling the particle size distribution within the aforementioned ranges is beneficial for controlling a more suitable lithium source consumption level, further improving kinetic performance, and reducing the occurrence of side reactions.
[0042] For example, x / z can be 8.4, 9.0, 9.5, 10.0, 10.5, 11.0, 12.0, 15.0, 18.0, 20.0, 21.0, 22.0, 24.0, or 25.0. For example, y / z can be 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, or 11.7.
[0043] Furthermore, 0.59≤x≤0.75, 0.20≤y≤0.35, and 0.03≤z≤0.07. When x, y, and z are limited to the above ranges in the negative electrode active material of this application embodiment, it is more advantageous to ensure that the particle size distribution of micropores and mesopores satisfies 8.4≤x / z≤25.0 and 2.8≤y / z≤11.7. This facilitates the optimization of the electrochemical performance of the negative electrode active material by rapidly screening negative electrode active materials with these specified particle sizes, thereby optimizing the cycle performance and capacity level of the energy storage device. For example, x is 0.59, 0.60, 0.62, 0.65, 0.67, 0.70, 0.72, or 0.75; y is 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, or 0.35; and z is 0.03, 0.04, 0.05, 0.065, or 0.07.
[0044] Furthermore, the specific surface area of the negative electrode active material is 1.1 m². 2 / g~2.0m 2 / g. The specific surface area of the negative electrode active material is 1.1m². 2 / g~2.0m 2 This includes any point within this numerical range, for example, the specific surface area of the negative electrode active material is 1.1 m². 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.45m 2 / g, 1.6m 2 / g, 1.65m 2 / g, 1.7m 2 / g, 1.72m 2 / g, 1.75m 2 / g, 1.8m 2 / g, 1.90m 2 / g or 2.0m 2 / g.
[0045] Secondly, embodiments of this application provide a negative electrode sheet, the negative electrode sheet including a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the negative electrode active material as described in the first aspect.
[0046] In this embodiment, the current collector can be a copper foil current collector. An active material layer can be disposed on one or both sides of the current collector to participate in the electrochemical reaction. Furthermore, the active material layer can include the negative electrode active material described in the first aspect, as well as functional additives such as binders and conductive agents.
[0047] Thirdly, embodiments of this application provide an energy storage device, which includes the negative electrode active material as described in the first aspect. This energy storage device can be a power battery such as a lithium battery or a sodium battery. Taking a lithium battery as an example, the lithium battery may further include a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive and negative electrode. The positive electrode, negative electrode, and separator are assembled to form a battery cell. The electrolyte is used to inject liquid into the battery cell and wet the positive and negative electrode. The negative electrode may be the negative electrode described in the second aspect, and the active material layer of the negative electrode includes the negative electrode active material described in the first aspect.
[0048] The technical solutions of the embodiments of this application will be further described below with reference to more specific examples.
[0049] Example 1
[0050] This embodiment provides a negative electrode sheet, which includes a current collector and an active material layer disposed on the surface of the current collector. The active material layer includes a negative electrode active material, which comprises graphite having micropores, mesopores, and macropores. The micropore volume V1 of the negative electrode active material is 0.00001165 cm³. 3 / g, mesopore volume V2 of the negative electrode active material = 0.00233cm³ 3 / g, the macropore volume V3 of the negative electrode active material is 0.00272cm³. 3 / g, the Dv90 of the negative electrode active material is 22.1μm, the Dv99 of the negative electrode active material is 34.2μm, and the specific surface area of the negative electrode active material is 1.67m². 2 / g. Wherein, the proportion of the negative electrode active material in the first particle size range among all negative electrode active materials is x, where x is 0.65; the proportion of the negative electrode active material in the second particle size range among all negative electrode active materials is y, where y is 0.31; and the proportion of the negative electrode active material in the third particle size range among all negative electrode active materials is z, where z is 0.004. The first particle size range is greater than or equal to 0.6 μm and less than or equal to 2.5 μm; the second particle size range is greater than or equal to 2.5 μm and less than 7.5 μm; and the third particle size range is greater than or equal to 7.5 μm and less than or equal to 30 μm.
[0051] The preparation method of this negative electrode sheet includes the following steps: dissolving 10 wt% aqueous carboxymethyl cellulose binder in water, adding 10 wt% carbon black conductive agent and 80 wt% of negative electrode active material particles with the above-mentioned pore volume, particle size distribution, and specific surface area to form a uniformly dispersed slurry. The slurry is uniformly coated onto the surface of a copper foil current collector and transferred to a vacuum drying oven for drying to obtain the negative electrode sheet. The negative electrode sheet is then rolled and punched to obtain a disc-shaped negative electrode sheet for preparing coin cells.
[0052] Example 2
[0053] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0054] Example 3
[0055] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0056] Example 4
[0057] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0058] Example 5
[0059] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0060] Example 6
[0061] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0062] Example 7
[0063] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0064] Example 8
[0065] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0066] Example 9
[0067] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0068] Example 10
[0069] The only difference between this embodiment and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0070] Comparative Example 1
[0071] The only difference between this comparative example and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0072] Comparative Example 2
[0073] The only difference between this comparative example and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0074] Comparative Example 3
[0075] The only difference between this comparative example and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0076] Comparative Example 4
[0077] The only difference between this comparative example and Example 1 is the pore volume, particle size distribution, and specific surface area of the negative electrode active material, as detailed in Table 1.
[0078] The following describes the testing of the pore volume, particle size distribution, and specific surface area of the negative electrode active materials in the above embodiments and comparative examples.
[0079] (1) Using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000), the particle size distribution and specific surface area were measured according to the particle size distribution laser diffraction method GB / T19077-2016, and Dv99 and Dv90 were obtained.
[0080] (2) Pore volume measurement: The pore volume was measured using a TriStar 3030 fully automated surface area and porosity analyzer. The specific test method is as follows: 2g of the negative electrode active material sample from the above examples and comparative examples was taken and degassed at 200℃ for 12 hours. The degassed sample was then placed into the sample tube of the surface area analyzer, and the pore volume and specific surface area were measured.
[0081] The test results are detailed in Table 1 below.
[0082] Table 1. Microstructure test results of negative electrode active materials in Examples 1 to 10 and Comparative Examples 1 to 4
[0083]
[0084]
[0085] The following describes the performance testing of the negative electrode active material.
[0086] Preparation of the positive electrode: Lithium iron phosphate, PVDF binder, and SP conductive agent were dispersed in NMP solvent at a mass ratio of 95.5:2:2.5 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil and dried. The coating weight of the positive electrode active material layer was 254 mg / 1540.25 mm. 2 After rolling, slitting, and cutting, the positive electrode sheet is obtained.
[0087] Electrolyte preparation: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the above mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.
[0088] Assembling coin cells: Using a 12μm thick polyethylene separator as the separator, the electrode plates, separator, and positive electrode plate from the above embodiments and comparative examples are stacked in sequence, with the separator positioned between the positive electrode plate and the electrode plates. The electrolyte described above is added to assemble the cells. Cycle performance tests are then performed on the cells.
[0089] The cycle performance test process included: at 25°C, the batteries prepared using the negative electrode sheets of the above-described examples and comparative examples were charged to 3.65V at a constant power of 1P, and then discharged to 2.5V at a constant power of 1P. The discharge capacity was recorded as the initial capacity. This cycle was repeated until the capacity of the lithium battery was less than 80% of the initial capacity, and the number of cycles was recorded. The test results are shown in Table 2 and Appendix. Figure 1 As shown.
[0090] Table 2 shows the pore volume ratio and cycle performance test results for the embodiments and comparative examples.
[0091]
[0092]
[0093] By comparing Examples 1 to 10 and Comparative Examples 1 to 4, it can be seen that when the pore volume between micropores, mesopores, and macropores in the negative electrode active material satisfies 0.5% ≤ V1 / V2 ≤ 2% and 30% ≤ V2 / (V2+V3) ≤ 50%, the cycle performance of the energy storage device can be significantly improved while maintaining a high specific capacity of over 345 mAh / g. The embodiments of this application can improve the cycle performance to over 98%, or even over 99%, which can well meet the requirements for extending the service life of the energy storage device. Especially through... Figure 1 The cycle performance test results of Example 1 and Comparative Example 1 show that the negative electrode active material of this application embodiment can significantly improve the cycle performance of the energy storage device.
[0094] In Comparative Examples 1, 3, and 4, the V1 / V2 ratio is greater than 2%, and the V2 / (V2+V3) ratio is greater than 50%. This indicates an excessive proportion of mesopores and micropores in the overall negative electrode active material, resulting in a significant increase in specific surface area. This leads to excessive lithium source consumption during SEI film formation on the negative electrode, resulting in insufficient initial coulombic efficiency and capacity retention in the energy storage device. In Comparative Example 2, the V1 / V2 ratio is less than 0.5%, and the V2 / (V2+V3) ratio is less than 30%. This indicates an excessive number of macropores in the overall negative electrode active material, providing fewer lithium-ion channels and resulting in insufficient kinetics, which still affects the cycle performance of the energy storage device.
[0095] Further comparisons of Examples 1 and 2, and Examples 3 and 4, reveal that when the pore volume among micropores, mesopores, and macropores in the negative electrode active material is further controlled at 0.5% ≤ V1 / V2 ≤ 0.6% and 46% ≤ V2 / (V2+V3) ≤ 48%, and the relationship between pore volume and particle size satisfies the ratio between V2 / (V2+V3) and (Dv99-Dv90) / Dv99 being in the range of 1.3 to 1.4, the cycle performance of the energy storage device can be further improved to over 99.7% while maintaining a high capacity level. This indicates that the negative electrode active material with the above-mentioned pore volume and particle size distribution characteristics has superior capacity and cycle performance.
[0096] Further comparisons of Examples 1 to 4, 5, and 6 reveal that while the pore volume and particle size distribution of the negative electrode active materials in Examples 5 and 6 also satisfy 0.5% ≤ V1 / V2 ≤ 2% and 30% ≤ V2 / (V2+V3) ≤ 50%, the ratio of V2 / (V2+V3) to (Dv99-Dv90) / Dv99 exceeds the range of 0.8 to 1.5. Although these examples also exhibit a cycle retention rate of over 99% for 600 cycles, Example 1 demonstrates a superior cycle retention rate of over 99.7%. Therefore, when the ratio of V2 / (V2+V3) to (Dv99-Dv90) / Dv99 is further satisfied within the range of 0.8 to 1.5, a cycle retention rate of over 99.7% can be achieved while maintaining a high specific capacity level.
[0097] Further comparison of Examples 1 to 6 and Examples 7 to 10 reveals that although the pore volume and particle size distribution of the negative electrode active materials in Examples 7 to 10 also meet the requirements of 0.5% ≤ V1 / V2 ≤ 2% and 30% ≤ V2 / (V2+V3) ≤ 50%, the x / z range exceeds 8.4–25.0 or the y / z range exceeds 2.8–11.7. While these materials also exhibit cycle performance exceeding 98%, Examples 1 to 8 demonstrate superior cycle performance exceeding 99%. Therefore, further satisfying x / z of 8.4–25.0 and y / z of 2.8–11.7 is advantageous for achieving a cycle retention rate exceeding 99% while maintaining a high specific capacity.
[0098] Comparing Examples 1 and 7, it is evident that when x / z is less than 8.4, the proportion of large particles in the negative electrode material is too high, resulting in a large particle size and insufficient kinetics, leading to lithium plating and thus reduced battery cycle performance. Comparing Examples 1 and 8, it is evident that when x / z is greater than 25.0, the proportion of fine powder in the negative electrode material is too high, increasing side reactions and reducing battery cycle performance. Comparing Examples 1 and 9, it is evident that when y / z is less than 2.8, the particle size distribution in the negative electrode material is mismatched, resulting in a high proportion of large particles, insufficient kinetics, and lithium plating, thus reducing battery cycle performance. Comparing Examples 1 and 10, it is evident that when y / z is greater than 11.7, the particle size distribution in the negative electrode material is mismatched, resulting in a high proportion of small particles, a high specific surface area, excessive lithium consumption, and increased side reactions, thus reducing battery cycle performance.
[0099] The above provides a detailed description of the negative electrode active material, negative electrode sheet, and energy storage device disclosed in the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions, preparation methods, and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.
Claims
1. A negative electrode active material, characterized in that, The negative electrode active material comprises a porous structure having micropores, mesopores, and macropores. The pore volume of the negative electrode active material satisfies the following relationship: 0.5%≤V1 / V2≤2%, and 30%≤V2 / (V2+V3)≤50%; wherein, V1 is the pore volume of the micropores in the negative electrode active material, V2 is the pore volume of the mesopores in the negative electrode active material, and V3 is the pore volume of the macropores in the negative electrode active material. The micropores are pores with a diameter of less than 2 nm, the mesopores are pores with a diameter of greater than or equal to 2 nm and less than or equal to 50 nm, and the macropores are pores with a diameter of greater than 50 nm and less than 500 nm.
2. The negative electrode active material according to claim 1, characterized in that, The ratio between V2 / (V2+V3) and (Dv99-Dv90) / Dv99 ranges from 0.8 to 1.5, where Dv99 refers to the particle size value corresponding to the cumulative particle size distribution percentage of the negative electrode active material reaching 99%, and Dv90 refers to the particle size value corresponding to the cumulative particle size distribution percentage of the negative electrode active material reaching 90%.
3. The negative electrode active material according to claim 2, characterized in that, 0.34≤(Dv99-Dv90) / Dv99≤0.
36.
4. The negative electrode active material according to claim 2, characterized in that, 20 μm≤Dv90≤30μm, 30 μm≤Dv99≤40μm.
5. The negative electrode active material according to claim 1, characterized in that, 0.5%≤V1 / V2≤0.6%.
6. The negative electrode active material according to claim 1, characterized in that, 46%≤V2 / (V2+V3)≤48%.
7. The negative electrode active material according to claim 1, characterized in that, 0.00001 cm 3 / g≤V1≤0.00004cm 3 / g,0.001 cm 3 / g≤V2≤0.0025m 3 / g,0.0026 cm 3 / g≤V3≤0.004 cm 3 / g。 8. The negative electrode active material according to any one of claims 1 to 7, characterized in that, The proportion of the negative electrode active material in the first particle size range is x, the proportion of the negative electrode active material in the second particle size range is y, and the proportion of the negative electrode active material in the third particle size range is z. The particle size of the negative electrode active material satisfies the following relationship: 8.4 ≤ x / z ≤ 25.0, 2.8 ≤ y / z ≤ 11.
7. The first particle size range is greater than or equal to 0.6 μm and less than or equal to 2.5 μm, the second particle size range is greater than 2.5 μm and less than 7.5 μm, and the third particle size range is greater than or equal to 7.5 μm and less than or equal to 30 μm.
9. The negative electrode active material according to claim 8, characterized in that, 0.59≤x≤0.75, 0.20≤y≤0.35, 0.03≤z≤0.
07.
10. The negative electrode active material according to any one of claims 1 to 7, characterized in that, The specific surface area of the negative electrode active material is 1.1 m². 2 / g~2.0 m 2 / g.
11. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer including the negative electrode active material as described in any one of claims 1 to 10.
12. An energy storage device, characterized in that, The energy storage device includes the negative electrode active material as described in any one of claims 1 to 10.