Lithium metal negative electrode sheet, lithium metal battery, and electric device

Abstract

The application provides a lithium metal negative electrode sheet, a lithium metal battery and a power utilization device. The lithium metal negative electrode sheet comprises a lithium metal body and a modification layer with a three-dimensional porous structure arranged on the surface of the lithium metal body, the modification layer comprises a polymer with a three-dimensional network structure and lithium nitrate, there is lithium nitrate in the pores of the modification layer, and the XRD pattern of the modification layer exists wide characteristic peaks at positions of 5-10° and 20-25° in 2θ. The application constructs a stable interface modification layer on the surface of the lithium metal, the modification layer has the effects of inhibiting the growth of lithium dendrites and slowing down the volume expansion of the lithium metal in the cycle process, so that the cycle performance of the lithium metal battery is improved.

Description

Technical Field

[0001] This application relates to the field of lithium metal battery technology, and in particular to a lithium metal anode sheet, a lithium metal battery, and an electrical device. Background Technology

[0002] With the increasing demands for vehicle range in the new energy vehicle sector, the development of high-energy-density batteries to replace current lithium-ion batteries has become more urgent. Lithium metal, due to its extremely high theoretical specific capacity (3860 mAh / g), has become the most promising anode material. Batteries combining lithium metal anodes and ternary cathodes are expected to achieve an energy density of 500 Wh / kg. However, in practical applications, the excessive growth of lithium dendrites and the volume expansion of lithium metal can lead to internal short circuits, hindering the practical application and industrial production of lithium metal batteries. Summary of the Invention

[0003] The purpose of this application is to overcome the problem of poor cycle performance of lithium metal batteries caused by lithium dendrite growth and lithium metal volume expansion.

[0004] To achieve the above objectives, a first aspect of this application provides a lithium metal anode sheet, the lithium metal anode sheet comprising a lithium metal body and a modification layer having a three-dimensional porous structure disposed on the surface of the lithium metal body, the modification layer comprising a polymer having a three-dimensional network structure and lithium nitrate, the pores of the modification layer containing lithium nitrate, and the XRD pattern of the modification layer having broad characteristic peaks at positions of 2θ of 5–10° and 20–25° respectively.

[0005] As an embodiment of this application, the thickness of the modified layer is 0.1 to 5 μm.

[0006] As an embodiment of this application, the elastic modulus of the modified layer is 3 to 8 GPa.

[0007] As an embodiment of this application, the mass percentage of lithium nitrate in the modified layer is 30-50%.

[0008] As an embodiment of this application, the ionic conductivity σ of the modified layer is 0.1 to 1.05 mS / cm.

[0009] As an embodiment of this application, the thermal decomposition temperature of the modified layer is 300-400°C.

[0010] As an embodiment of this application, the raw materials for preparing the three-dimensional network structure polymer include cage-like silsesquioxane and a crosslinking agent.

[0011] As an embodiment of this application, the molecular formula of the cage-like silsesquioxane is (RSiO). 3 / 2)n, where n is 8, 10 or 12, and at least 2 of the n R bases contain functional groups with double bonds.

[0012] As an embodiment of this application, the crosslinking agent includes an alkane having at least two double bonds, an epoxy group, or a mercapto group.

[0013] A second aspect of this application provides a lithium metal battery, the lithium metal battery comprising the lithium metal negative electrode sheet described in the first aspect of this application.

[0014] A third aspect of this application provides an electrical device comprising the lithium metal battery described in the second aspect of this application.

[0015] Compared with the prior art, the beneficial effects of this application are:

[0016] This application provides a lithium metal anode sheet, comprising a modification layer with a three-dimensional porous structure. The modification layer contains a polymer with a three-dimensional network structure and lithium nitrate. Lithium nitrate is present in the pores of the modification layer, and the XRD pattern of the modification layer exhibits broad characteristic peaks at 2θ positions of 5–10° and 2θ positions of 20–25°. This application improves the cycle performance of lithium metal batteries by constructing a stable interface modification layer on the lithium metal surface. This modification layer inhibits lithium dendrite growth and slows down volume expansion during lithium metal cycling. Attached Figure Description

[0017] Figure 1 The image shows the XRD pattern of the modified layer described in Example 1. Detailed Implementation

[0018] To better illustrate the purpose, technical solution, and advantages of this application, specific embodiments will be used to further describe this application below. However, these embodiments do not limit this application in any way. Unless otherwise specified, the reagents, methods, and equipment used in this application are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this application are commercially available.

[0019] An embodiment of this application provides a lithium metal anode sheet, which includes a lithium metal body and a modification layer with a three-dimensional porous structure disposed on the surface of the lithium metal body. The modification layer contains a polymer with a three-dimensional network structure and lithium nitrate. The pores of the modification layer contain lithium nitrate. The XRD pattern of the modification layer has broad characteristic peaks at positions of 2θ of 5-10° and 20-25°, respectively.

[0020] It should be noted that the broad characteristic peaks described in this application are also called amorphous characteristic peaks.

[0021] In some embodiments, the thickness of the modification layer is 0.1–5 μm. For example, the thickness of the modification layer can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any two of the above values. A thickness within the above range can further improve the cycle performance of the battery.

[0022] In some embodiments, the elastic modulus of the modified layer is 3–8 GPa. Exemplarily, the elastic modulus of the modified layer can be 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, or any two of the above values. During the elastic deformation stage of a material, its stress and strain are directly proportional (i.e., they conform to Hooke's Law), and this proportionality constant is called the elastic modulus. In this application, the elastic modulus of the modified layer is within the above range, which can further suppress the growth of lithium dendrites, thereby improving the cycle performance of lithium metal batteries.

[0023] In some embodiments, the mass percentage of lithium nitrate in the modified layer is 30% to 50%. For example, the mass percentage of lithium nitrate in the modified layer is 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or any two of the above values. Maintaining a lithium nitrate mass percentage within the above range ensures that the lithium nitrate concentration in the electrolyte remains at an appropriate level throughout the lithium metal battery's lifespan, thereby improving the cycle performance of the lithium metal battery.

[0024] In some embodiments, the ionic conductivity σ of the modified layer is 0.1–1.05 mS / cm. For example, the ionic conductivity σ of the modified layer is 0.1 mS / cm, 0.2 mS / cm, 0.3 mS / cm, 0.4 mS / cm, 0.5 mS / cm, 0.6 mS / cm, 0.7 mS / cm, 0.8 mS / cm, 0.9 mS / cm, 1.0 mS / cm, 1.05 mS / cm, or any two of the above values. An ionic conductivity σ of the modified layer within the above range indicates that the modified layer possesses good ion-conducting properties.

[0025] In some embodiments, the thermal decomposition temperature of the modified layer is 300–400°C. For example, the thermal decomposition temperature of the modified layer is 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, or a range consisting of any two of the above values. The fact that the thermal decomposition temperature of the modified layer is within the above range indicates that the modified layer of this application has excellent thermal stability, thereby improving the cycle performance of lithium metal batteries.

[0026] In some embodiments, the raw materials for preparing the three-dimensional network polymer include cage-like silsesquioxanes and crosslinking agents.

[0027] In some embodiments, the method for preparing the lithium metal anode sheet includes the following steps:

[0028] S1. Dissolve cage-type silsesquioxane, crosslinking agent and lithium nitrate in an organic solvent, add photoinitiator, stir at room temperature to obtain precursor solution;

[0029] S2. The precursor solution is coated onto the lithium metal substrate, irradiated with ultraviolet light, and then dried to obtain the lithium metal anode sheet.

[0030] By dissolving cage-like silsesquioxane, a crosslinking agent, and lithium nitrate in an organic solvent, adding a photoinitiator, and then irradiating with ultraviolet light, a polymer with a three-dimensional network structure is prepared by reacting the cage-like silsesquioxane with the crosslinking agent. This results in a three-dimensional porous modified layer with lithium nitrate adsorbed in its pores. Based on the concentration gradient, the adsorbed lithium nitrate can be slowly released into the electrolyte. Furthermore, the three-dimensional porous structure of the modified layer effectively adsorbs the electrolyte, which is beneficial for uniform lithium deposition. The porous structure also provides space for lithium volume expansion. In addition, the three-dimensional network structure of the polymer results in broad characteristic peaks in the XRD pattern of the modified layer at 2θ positions of 5–10° and 20–25°, respectively, giving the modified layer excellent mechanical properties and good thermal stability. Therefore, using the lithium metal anode sheet described in this application can significantly improve cycle performance.

[0031] In some embodiments, the cage-like silsesquioxane has the molecular formula (RSiO). 3 / 2 )n, where n is 8, 10 or 12, and at least 2 of the n R bases contain functional groups with double bonds.

[0032] In some embodiments, R is one of -CH=CH2, -CH(O)CH-, and CH2=CH-COO-(CH2)3-.

[0033] In some embodiments, the crosslinking agent comprises an alkane having at least two double bonds, an epoxy group, or a mercapto group. An alkane having at least two double bonds or an epoxy group can react with the double bonds on a cage-like silsesquioxane, while an alkane having at least two mercapto groups can undergo an "enthiol addition" reaction with the double bonds on a cage-like silsesquioxane, thereby preparing a polymer with a three-dimensional network structure.

[0034] In some embodiments, the crosslinking agent includes at least one selected from 1,2-ethylenedithiol, 1,3-propanedithiol, 1,4-phenyldithiol, and 1,6-hexyldithiol.

[0035] In some embodiments, the photoinitiator includes benzoin dimethyl ether.

[0036] Embodiments of this application also provide a lithium metal battery, which includes the lithium metal negative electrode. Due to the use of the lithium metal negative electrode of this application, the lithium metal battery of this application exhibits excellent cycle performance.

[0037] This application also protects electrical devices that include the aforementioned lithium metal batteries. These electrical devices include backup power supplies, motors, electric vehicles, electric motorcycles, electric bicycles, bicycles, power tools, and large household batteries, etc.

[0038] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0039] Example 1

[0040] Example 1 provides a lithium metal battery, the preparation method of which includes the following steps:

[0041] S1. Take 0.633g of octavinyl cage-type silsesquioxane, 0.377g of 1,2-ethylenedithiol and 1.000g of LiNO3, dissolve them in 100mL of THF solution, then add 0.02g of initiator benzoin dimethyl ether (DMPA), stir at room temperature until completely dissolved to obtain a precursor solution;

[0042] S2. Drop 30 μL of the precursor solution obtained above onto a lithium sheet with a diameter of 15.6 mm, then irradiate with ultraviolet light for 5 min, and then dry under vacuum at room temperature for 24 h to obtain a lithium metal anode sheet with a modified layer.

[0043] S3. Assemble a lithium metal anode sheet with a modified layer, an NCM cathode sheet, a Celgard 2320 separator, and an electrolyte into a lithium metal battery.

[0044] The preparation method of NCM positive electrode is as follows:

[0045] The positive electrode active material NCM811, conductive agent Super P, CNT, and binder PVDF were mixed in a mass ratio of 95:2:0.5:2.5. NMP solvent was added and stirred until the system was homogeneous and viscous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto a current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. It was then cut into appropriate sizes to form the positive electrode sheet, with a positive electrode surface capacity of 4.5 mAh / cm². 2 The concentration of LiPF6 in the electrolyte is 1M, the organic solvent is a mixture of EC, DMC and EMC with a volume ratio of 1:1:1, and the additive is 10% FEC.

[0046] Example 2

[0047] Example 2 provides a lithium metal battery, which differs from Example 1 in that the volume of the solution used for drop coating is 10 μL.

[0048] Example 3

[0049] Example 3 provides a lithium metal battery, which differs from Example 1 in that the volume of the solution used for drop coating is 5 μL.

[0050] Example 4

[0051] Example 4 provides a lithium metal battery, which differs from Example 1 in that the volume of the solution used for drop coating is 1 μL.

[0052] Example 5

[0053] Example 5 provides a lithium metal battery, which differs from Example 1 in that 0.063g of Vi-POSS, 0.037g of 1,2-ethylenedithiol, and 0.100g of LiNO3 are dissolved in 100mL of THF solution, and then 0.002g of initiator benzoin dimethyl ether (DMPA) is added. The mixture is stirred at room temperature until it is completely dissolved and homogeneous to obtain a precursor solution. 5μL of the obtained precursor solution is drop-coated onto a lithium sheet with a diameter of 15.6mm, and then irradiated with an ultraviolet lamp for 5min. After that, it is dried under vacuum at room temperature for 24h to obtain a lithium metal anode sheet with a modified layer.

[0054] Example 6

[0055] Example 6 provides a lithium metal battery, which differs from Example 1 in that the mass of LiNO3 in the precursor solution is 0.67g.

[0056] Example 7

[0057] Example 7 provides a lithium metal battery, which differs from Example 1 in that the mass of LiNO3 in the precursor solution is 0.5g.

[0058] Example 8

[0059] Example 8 provides a lithium metal battery, which differs from Example 1 in that 1,2-ethylenedithiol in the raw materials is replaced with 1,3-propanedithiol.

[0060] Example 9

[0061] Example 9 provides a lithium metal battery, which differs from Example 1 in that 1,2-ethanedithiol in the raw materials is replaced with 1,4-phenyldithiol.

[0062] Example 10

[0063] Example 10 provides a lithium metal battery, which differs from Example 8 in that the mass of LiNO3 in the precursor solution is 0.5g.

[0064] Comparative Example 1

[0065] Comparative Example 1 provides a lithium metal battery, which differs from Example 1 in that it uses a lithium sheet without a modification layer as the negative electrode.

[0066] The lithium metal anode sheets and lithium metal batteries obtained in Examples 1-10 and Comparative Example 1 were characterized and tested. The specific characterization and testing items and methods are as follows:

[0067] The modified layers were tested using X-ray diffraction. The results showed that the XRD patterns of the modified layers obtained in each embodiment all exhibited broad characteristic peaks at positions of 5–10° and 20–25°. Figure 1 This is the XRD pattern of the modified layer obtained in Example 1.

[0068] Cycling performance: The lithium metal battery was first charged to 4.25V at a constant current and constant voltage of 0.1C, and then discharged to 2.8V at a rate of 0.1C for 2 cycles; then it was charged to 4.25V at a constant current and constant voltage of 0.5C and discharged to 2.8V at 0.5C for long-term cycle testing, and the capacity retention rate after 100 cycles was recorded in Table 1.

[0069] Lithium dendrites: After fully discharging the battery after 100 cycles, the negative electrode was removed and its surface morphology and uniformity were observed using a scanning electron microscope (SEM). Lithium dendrites exhibited dendritic or filamentous morphology. The growth status of lithium dendrites was determined based on the proportion of the total area occupied by the lithium dendrite morphology in the 500X SEM image. A proportion of 0% indicates no dendrites, 0-30% indicates a small amount, 30-60% indicates a moderate amount, and 60-100% indicates a severe amount.

[0070] 0.5C specific capacity: Select the first cycle of discharge at 0.5C to 2.8V and read the specific capacity data.

[0071] Elastic modulus: Lithium sheets and modified lithium sheets were tested using a nanoindenter. The elastic modulus test results were calculated from the curve of force versus indentation depth.

[0072] Ionic conductivity: The modification layer material on the lithium metal anode sheet described in Examples 1 to 10 was scraped off with a scraper, and then the obtained powder material was pressed into a sheet, soaked in the corresponding electrolyte for 1 hour, removed and wiped dry of residual electrolyte on the surface, and the impedance R of the sheet was tested by electrochemical AC impedance spectroscopy. Finally, the ionic conductivity was calculated according to σ = d / RA, where d is the thickness of the sheet and A is the area of ​​the sheet.

[0073] Thermal stability: The modification layer material on the lithium metal anode sheet described in Examples 1 to 10 was scraped off with a scraper, and the obtained powder material was subjected to thermogravimetric analysis (TG). The powder was heated in an N2 atmosphere at a temperature range of 30 to 700 °C at a heating rate of 10 °C / min. The thermal decomposition temperature was recorded in Table 1.

[0074] Table 1. Parameters of the lithium metal anode sheets described in Examples 1-10

[0075]

[0076] Note: *Data refers to the elastic modulus of lithium sheets.

[0077] Table 2. Performance test results of lithium metal batteries prepared in Examples 1-10 and Comparative Example 1.

[0078]

[0079]

[0080] The results above show that:

[0081] As can be seen from the above embodiments and comparative examples, by providing a modification layer containing the modification layer described in this application on the surface of the lithium metal body, the cycle performance of the lithium metal battery can be improved.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A lithium metal negative electrode sheet, characterized by, The lithium metal negative electrode sheet comprises a lithium metal body and a modification layer with a three-dimensional porous structure arranged on the surface of the lithium metal body, the modification layer comprises a polymer with a three-dimensional network structure and lithium nitrate, there is lithium nitrate in the pores of the modification layer, the XRD pattern of the modification layer has a characteristic peak at positions of 5-10° and 20-25° in 2θ respectively, the thickness of the modification layer is 0.1-5 μm. The preparation raw material of the polymer with the three-dimensional network structure comprises a cage silsesquioxane and a crosslinking agent. The cage silsesquioxane has a molecular formula of (RSiO 3 / 2 ) n wherein n is 8, 10 or 12, and at least two of the n R groups contain a functional group having a double bond; The crosslinking agent comprises an alkane with at least two double bonds, an epoxy group or a mercapto group.

2. The lithium metal negative electrode sheet according to claim 1, wherein The elastic modulus of the modification layer is 3-8 GPa.

3. The lithium metal negative electrode sheet of claim 1, wherein, The mass ratio of lithium nitrate in the modification layer is 30-50 %.

4. The lithium metal negative electrode sheet of claim 1, wherein, The ionic conductivity σ of the modification layer is 0.1-1.05 mS / cm. And / or, the thermal decomposition temperature of the modification layer is 300-400 °C.

5. A lithium metal battery, characterized in that, The lithium metal negative electrode sheet comprises the lithium metal negative electrode sheet according to any one of claims 1-4.

6. An electrical device, characterized by The lithium metal battery comprises the lithium metal battery according to claim 5.

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