Lithium metal negative electrode and preparation method thereof, and lithium battery

Abstract

The application relates to the technical field of lithium batteries, in particular to a lithium metal negative electrode and a preparation method thereof and a lithium battery. The lithium metal negative electrode preparation method comprises the following steps: firstly, dimethyl terephthalate and an aliphatic diol are mixed, a catalyst is added, and the reaction environment atmosphere, air pressure and temperature are controlled to prepare a crosslinked polymer precursor; secondly, the crosslinked polymer precursor is treated to obtain a carbon skeleton material; thirdly, the lithium metal and the carbon skeleton material are mixed and treated at a certain proportion to obtain modified lithium metal; and finally, the modified lithium metal is made into a lithium metal negative electrode. The lithium metal negative electrode preparation method provided by the application can obtain a fiber network material with a suitable structure and a carbon skeleton material with active sites, the carbon skeleton material is compounded with the lithium metal to form a fiber reinforced network structure, so that the tensile strength and the elongation at break of the lithium metal negative electrode are significantly improved, the processing performance of the lithium metal negative electrode is greatly improved, the service life of the battery is prolonged, and the industrial production is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium metal negative electrode and a preparation method thereof, and a lithium battery. BACKGROUND

[0002] With the increasing demand for energy, lithium metal batteries are considered as the ideal choice for the next generation of high-energy-density energy storage systems due to their ultra-high theoretical specific capacity (3860 mAh / g) and extremely low electrode potential, and have shown great application potential in electric vehicles, portable electronic devices, and large-scale energy storage. However, lithium metal batteries face many challenges in practical application, one of which is the insufficient stretchability and ductility of lithium metal electrodes, which is one of the key factors restricting their commercialization process.

[0003] Currently, during the charging and discharging process of traditional lithium metal electrodes, the uneven growth of lithium dendrites will generate a large stress on the electrode. These stresses can easily cause the electrode to deform and break, thereby damaging the internal structure of the battery, causing short circuits, shortening the cycle life of the battery, and other problems. In addition, the existing lithium metal electrode has low tensile strength, and is difficult to withstand external pressure and impact during battery assembly and use, which can easily cause damage, reduce production efficiency, increase manufacturing costs, and affect the overall performance and safety of the battery. SUMMARY

[0004] In order to solve the technical problems of low tensile strength of the lithium metal negative electrode of the lithium battery, easy damage under impact, affecting production efficiency and overall performance of the battery, the present application provides a novel lithium metal negative electrode and a preparation method thereof, and a lithium battery.

[0005] In order to solve the above technical problems, the present application provides a preparation method of a lithium metal negative electrode, which comprises the following steps: mixing dimethyl terephthalate and aliphatic diol according to a molar ratio of 1:(1.05-1.3), and continuing to add a catalyst accounting for 0.01%-0.05% of the total mass percentage in the mixture of dimethyl terephthalate and aliphatic diol;

[0006] After adding the catalyst, the mixture is stirred at a temperature of 120-160 DEG C, and then the reaction temperature is gradually increased to 170-200 DEG C and maintained at 170-200 DEG C for 1-3 h; and

[0007] The ambient pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190-250 DEG C, and the reaction is continued for 1.5-3 h, and the polyester oligomer is obtained after the reaction is completed;

[0008] The polyester oligomer is mixed with citric acid ester and a catalyst, and then gradually heated and the ambient pressure is gradually reduced under an inert atmosphere to obtain a cross-linked polymer precursor; the cross-linked polymer precursor is dried and subjected to carbonization treatment and acid pickling under an inert atmosphere, and then subjected to low-temperature activation treatment to obtain a carbon skeleton material; wherein the carbonization treatment is carried out in an atmosphere of a mixture of nitrogen and oxygen, the oxygen content in the mixture of nitrogen and oxygen is 3%-7% by volume fraction, and the carbonization treatment is carried out at a temperature of 300-600°C; the low-temperature activation treatment is carried out at a temperature of 250-400°C for 0.5-3h; and the lithium metal and the carbon skeleton material are mixed in a certain proportion to obtain modified lithium metal, and the modified lithium metal is made into a lithium metal negative electrode.

[0009] Preferably, the aliphatic diol includes any one or a combination of ethylene glycol, propylene glycol, and butanediol; and / or the catalyst is tetrabutyl titanate.

[0010] Preferably, after the reaction system is vacuumized and the ambient pressure is reduced to 1000-5000 Pa while being heated to 190-250°C, the reaction is continued for 1.5-3h, and the polyester oligomer is obtained after the reaction is completed, the method further comprises the following steps: the polyester oligomer is mixed with citric acid ester at a molar ratio of 1:(1-1.2), and a catalyst is added, and the whole feeding and mixing process is carried out in an inert atmosphere; the polyester oligomer, citric acid ester, and catalyst are continuously stirred while being purged with inert gas, the temperature is increased to a first temperature, then the temperature is continuously increased to a second temperature and maintained for 1-3h, and then the temperature is continuously increased to a third temperature; and the temperature is maintained at the third temperature, the ambient pressure is gradually reduced from normal pressure to below 100 Pa, the reaction is stopped when the reaction reaches a preset condition, and a cross-linked polymer precursor is obtained.

[0011] Preferably, in the step of continuously stirring the polyester oligomer, citric acid ester, and catalyst while being purged with inert gas, the temperature is increased to a first temperature, then the temperature is continuously increased to a second temperature and maintained for 1-3h, and then the temperature is continuously increased to a third temperature, the third temperature is greater than the second temperature, and the second temperature is greater than the first temperature, and the temperature difference between the first temperature and the second temperature and the temperature difference between the second temperature and the third temperature are both 5-30°C.

[0012] Preferably, the drying of the cross-linked polymer precursor comprises the following steps: vacuum drying at a temperature of 70-90°C for 2-6h to remove unreacted substances remaining on the cross-linked polymer precursor.

[0013] Preferably, the lithium metal and the carbon skeleton material are mixed at a mass ratio of (90-99):(1-10) and are subjected to mixing and processing in a double roller mill to obtain modified lithium metal.

[0014] Preferably, the double roller machine comprises front wheels and rear wheels, the rotation speed of the front wheels is 12 rpm-20 rpm, the rotation speed ratio of the front wheels to the rear wheels is 1.1-1.3, and the mixing temperature is 30℃-50℃; and / or the roller gap between the front wheels and the rear wheels is set to 0.5mm-2mm.

[0015] To solve the above technical problems, the present application provides a lithium metal negative electrode prepared by the above-mentioned lithium metal negative electrode preparation method, which comprises lithium metal and carbon skeleton material, and the mass ratio of lithium metal to carbon skeleton material is (90-99):(1-10).

[0016] To solve the above technical problems, the present application provides a lithium battery comprising a positive electrode, a solid-state electrolyte and the above-mentioned lithium metal negative electrode, wherein the solid-state electrolyte is arranged between the positive electrode material and the lithium metal negative electrode.

[0017] Compared with the prior art, the lithium metal negative electrode and its preparation method and the lithium battery provided by the present application have the following beneficial effects:

[0018] The present application provides a lithium metal negative electrode preparation method, which provides a cross-linked polymer precursor prepared by mixing dimethyl terephthalate and aliphatic diol, adding a catalyst and controlling the reaction environment atmosphere, gas pressure and temperature; then carbonizing the cross-linked polymer precursor to obtain a carbon skeleton material; mixing lithium metal and the carbon skeleton material in a certain proportion to obtain modified lithium metal; and preparing a lithium metal negative electrode from the modified lithium metal. Through the structural design of the cross-linked polyester, the present application successfully prepares a carbon skeleton material with abundant active sites, thereby improving the tensile strength and elongation at break of the lithium metal, greatly improving the processability of the lithium metal, and improving the battery life. The cross-linking points of the cross-linked polyester prepared by the present application cannot be completely deoxidized and carbonized during the carbonization process, so they still have part of the active sites, which can form covalent bonds during the rolling process of the lithium battery, thereby greatly improving the compatibility of the two phases of lithium metal and carbon skeleton material.

[0019] After the lithium metal is compounded with the carbon skeleton material, the high-strength carbon material acts as a "skeleton" to bear the main load, and the reaction sites remaining on the carbon skeleton material bond the two phases well, and the interface of the two phases is combined as a whole, which is beneficial to the conduction of stress and realizes the synergistic optimization of strength and rigidity. After the carbon skeleton material is compounded with the modified lithium metal, the surface properties and structural strength of the lithium metal are obviously improved, which avoids the defects of surface mutual bonding and easy tearing of the lithium metal during the processing of the lithium metal, and makes the lithium metal more suitable for industrial production. At the same time, after the carbon skeleton material is strengthened, the lithium metal negative electrode is more beneficial to resist the volume expansion caused by the deintercalation of lithium ions during the charge and discharge cycle, thereby improving the cycle life of the battery.

[0020] Meanwhile, the carbon skeleton material can be obtained by pre-preparation, and the lithium metal is mixed with the carbon skeleton by mixing treatment, which is conducive to the industrial large-scale preparation of the lithium metal negative electrode, and by limiting the specific mixing performance, the stability of the product prepared can be further improved, the production yield can be improved, the production cost can be reduced, and the commercial application of the lithium metal battery can be promoted.

[0021] The application further limits the molar ratio of the dimethyl terephthalate to the aliphatic diol to 1:(1.05-1.3); and / or the aliphatic diol includes any one or a combination of several of ethylene glycol, propylene glycol, and butanediol. By limiting the dimethyl terephthalate and the aliphatic diol, the design of the cross-linked polyester structure can be better optimized, so that a better cross-linked network can be provided for the carbon skeleton fiber structure obtained by subsequent carbonization and activation.

[0022] The application further adjusts the environmental air pressure and temperature to obtain the polyester oligomer in the step of mixing the dimethyl terephthalate and the aliphatic diol according to the preset ratio, and then putting the preset amount of catalyst for mixing. In the application, the polyester synthesis is a condensation reaction. The initial temperature is low, the solid reactant dimethyl terephthalate is first dissolved in the diol to improve the reaction rate. Then the temperature is further increased to promote the molecular chain growth. If the preparation method of increasing the temperature in advance is adopted, the side reaction will increase, which will hinder the formation of the product.

[0023] The application further limits the polyester oligomer and the citrate to be weighed according to a preset ratio, and a catalyst is added, and the whole mixing process is maintained in an inert atmosphere; the polyester oligomer, the citrate, and the catalyst are continuously stirred, and inert gas is blown at the same time, the temperature is increased to a first temperature, then slowly increased to a second temperature and maintained for 1-3 hours, and then the temperature is continuously increased to a third temperature; and the reaction temperature is maintained at the third temperature, the gas pressure of the reaction environment is gradually reduced from normal pressure to below 100 Pa by vacuumizing, and the reaction is stopped when the reaction reaches the preset condition, and the cross-linked polymer precursor is obtained. In the above step, the third temperature > the second temperature > the first temperature, and the temperature difference between the first temperature and the second temperature and the temperature difference between the second temperature and the third temperature are both 5-30℃. In the application, the slow heating method is adopted, and the purpose is also to hope that under the action of the polyester oligomer, the citrate, and the catalyst, the cross-linked polymer can be orderly and slowly generated by controlling the temperature, the gas pressure, and the reaction environment atmosphere, so that the cross-linked polymer precursor with a cross-linked network structure can be prepared by a simple and controllable preparation method, and a basis is provided for the subsequent setting of the carbon skeleton fiber structure.

[0024] The step of obtaining the carbon skeleton material by drying the cross-linked polymer precursor, carbonizing the cross-linked polymer precursor in an inert atmosphere, acid washing, and then activating in the present application is further limited as follows: vacuum drying the cross-linked polymer precursor at a temperature of 70-90 DEG C for 2-6 hours to remove unreacted substances remaining on the cross-linked polymer precursor; carbonizing the cross-linked polymer precursor after removing impurities and moisture, the carbonization environment is a mixture of nitrogen and oxygen, and the temperature is raised to the carbonization temperature, and then the polyester polymer carbonization product is obtained after maintaining for a predetermined time; and then the polyester polymer carbonization product is acid washed, washed, and then activated to obtain a carbon skeleton material. In the specific limiting conditions of the above steps, the integrity of the cross-linked network of the carbon skeleton can be maintained while avoiding the breaking of the cross-linked network due to carbonization and activation.

[0025] In the present application, the modified lithium metal is obtained by mixing the lithium metal and the carbon skeleton material in a certain proportion, and the modified lithium metal is made into a lithium metal negative electrode. The lithium metal and the carbon skeleton material are mixed in a double roller machine at a mass ratio of (90-99):(1-10) to obtain the modified lithium metal. The double roller machine is used for mixing, which can utilize the shearing force of mixing. By limiting the ratio of lithium metal to carbon skeleton material, the effective active area in the lithium metal negative electrode obtained can be ensured.

[0026] In the present application, the double roller machine includes front wheels and rear wheels, the rotation speed of the front wheels is 12 rpm-20 rpm, the rotation speed ratio of the front wheels to the rear wheels is (1.1-1.3):1, and the mixing temperature is 30 DEG C-50 DEG C. By limiting the above parameters, the material can be prevented from being excessively sheared or under-mixed, the mixing stability and uniformity can be improved, the processing performance can be ensured, and the lithium metal can be softened without melting. Further, the roller distance between the front wheels and the rear wheels is set to 0.5 mm-2 mm, which is beneficial to precisely control the product thickness and adapt to multiple scene requirements.

[0027] The present application provides a lithium metal negative electrode prepared by the above-mentioned lithium metal negative electrode preparation method. In the lithium metal negative electrode, the mass ratio of the lithium metal to the carbon skeleton material is (90-99):(1-10). The lithium metal negative electrode provided by the present application has good ductility, which can make the lithium metal negative electrode itself have the performance of buffering volume expansion, and can also improve the stability of the interface layer and the stability and service life of the lithium metal negative electrode. By preparing a fiber network material and active sites with a suitable structure, the tensile strength and elongation at break of the lithium metal electrode sheet prepared by mixing the lithium metal and the carbon skeleton material can be significantly improved.

[0028] The lithium battery provided by the present application comprises a positive electrode, a solid-state electrolyte and a lithium metal negative electrode as described above, wherein the solid-state electrolyte is arranged between the positive electrode material and the lithium metal negative electrode. In the prior art, the performance of the lithium metal electrode is improved by changing the electrolyte composition, introducing a solid electrolyte or optimizing the electrode structure, but the existing technology only has the problems of limited enhancement effect and difficulty in realizing uniform dispersion by means of composite enhancement, and cannot effectively meet the actual demand.

[0029] The lithium metal negative electrode provided by the present application is used in a lithium battery, and the lithium metal negative electrode has good ductility, so that the performance and safety of the lithium battery can be effectively improved. The good ductility of the lithium metal negative electrode can also make the lithium metal negative electrode remain intact under the action of external force other than extrusion, so that the integrity of the electrode structure can be maintained and the service life of the lithium battery can be prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the experimental examples of the present application, the drawings needed in the experimental examples or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some experimental examples of the present application, and other drawings can also be obtained according to these drawings without creative labor for those skilled in the art.

[0031] Figure 1 is a step flow diagram of the preparation method of the lithium metal negative electrode provided by the first embodiment of the present application.

[0032] Figure 2 is Figure 1 is a specific step flow diagram of step S1 shown in the present application.

[0033] Figure 3 is Figure 1 is a specific step flow diagram of step S2 shown in the present application.

[0034] Figure 4 is Figure 1 is a specific step flow diagram of step S3 shown in the present application.

[0035] Figure 5 is Figure 4 is a specific step flow diagram of step S32 shown in the present application.

[0036] Figure 6 is a structural diagram of the lithium battery provided by the third embodiment of the present application.

[0037] Figure 7 is a stress-strain curve diagram after the tensile test experiment of experimental example 6 and comparative example 1 provided by the present application.

[0038] Figure 8 is a graph showing the relationship between the cycle life and the capacity retention rate of the battery with a capacity loss of 20% under the 1C charge-discharge condition of Experimental Example 6 and Comparative Example 1 according to the present application.

[0039] Explanation of the drawings:

[0040] 30, lithium battery; 31, lithium metal negative electrode; 32, positive electrode; 33, solid-state electrolyte. DETAILED DESCRIPTION

[0041] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0042] In the experimental examples provided by the present application, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined according to A. However, it should also be understood that the determination of B according to A does not mean that B is determined only according to A, but B can also be determined according to A and / or other information.

[0043] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. Those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0044] In various embodiments of the present application, it should be understood that the size of the serial number of the above processes does not mean the inevitable sequence of execution, and the execution sequence of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0045] In the flowcharts and block diagrams in the drawings of the present application, the methods and possible implemented architectures, functions and operations according to various embodiments of the present application are illustrated. In this regard, each block in the flowchart or block diagram can represent a part of a step. It should also be noted that in some alternative implementations, the functions indicated in the blocks can also occur in a different order from that indicated in the drawings. For example, two blocks indicated in succession can actually be executed substantially in parallel, and sometimes they can be executed in reverse order, which is determined based on the functions involved.

[0046] Please refer to Figure 1The application provides a lithium metal negative electrode preparation method, and specific steps are as follows:

[0047] Step S1: dimethyl terephthalate and aliphatic diol are mixed according to a preset ratio, then a preset amount of catalyst is added for mixing, and then the environmental air pressure and temperature are adjusted to obtain polyester oligomer; the polyester oligomer is mixed with citrate and catalyst, then the mixture is gradually heated and the environmental air pressure is reduced under an inert atmosphere, and finally a cross-linked polymer precursor is obtained;

[0048] Step S2: the cross-linked polymer precursor is dried and subjected to carbonization treatment and acid pickling under an inert atmosphere, and then is subjected to activation treatment to obtain a carbon skeleton material; and

[0049] Step S3: lithium metal and the carbon skeleton material are mixed according to a proportion to obtain modified lithium metal, and the modified lithium metal is made into a lithium metal negative electrode.

[0050] The lithium metal negative electrode preparation method provided by the application can obtain a fiber network material with a suitable structure and a carbon skeleton material with active sites, and the carbon skeleton material is compounded with the lithium metal to form an effective fiber reinforcement effect, thereby significantly improving the tensile strength of the lithium metal electrode.

[0051] In the above step S1, dimethyl terephthalate and aliphatic diol are further included. In the application, dimethyl terephthalate and aliphatic diol are used as reactants, and are mixed according to a molar ratio of 1:(1.05-1.3). Specifically, the molar ratio of dimethyl terephthalate:aliphatic diol can be 1:(1.05-1.2), 1:(1.1-1.3) or 1:(1.1-1.2), and further, the molar ratio of dimethyl terephthalate:aliphatic diol can also be 1:1.1, 1:1.15, 1:1.2 or 1:1.3.

[0052] Among them, the aliphatic diol includes any one or a combination of several of ethylene glycol, propylene glycol and butanediol.

[0053] In some specific experimental examples, the aliphatic diol includes ethylene glycol, propylene glycol and butanediol. Specifically, the aliphatic diol includes ethylene glycol:propylene glycol:butanediol=1:0.6:0.4 in a molar ratio.

[0054] By using the above method, the carbon skeleton material with rich active sites can be obtained, thereby improving the tensile strength and elongation at break of the lithium metal negative electrode, greatly improving the processing performance, and prolonging the service life of the battery.

[0055] The tensile strength of the lithium metal negative electrode refers to the maximum tensile stress that the lithium metal negative electrode can withstand during the stretching process (before breaking), reflecting the ability of the lithium metal negative electrode to resist "tensile failure".

[0056] The elongation at break of the lithium metal negative electrode refers to the percentage of the total elongation of the gauge length to the original gauge length when the lithium metal negative electrode is stretched to break. The elongation at break (δ) = [(gauge length after breaking L1- original gauge length L0) / original gauge length L0] × 100%. The elongation at break reflects the "ductility" of the lithium metal negative electrode, that is, the plastic deformation ability of the lithium metal negative electrode.

[0057] Please refer to Figure 2 The preparation path of the cross-linked polyester polymer is further limited to the following steps: dimethyl terephthalate is first subjected to dehydration and polycondensation with ethylene glycol, propylene glycol, and butanediol to form an oligomer (molecular weight of about 1,000), which specifically includes the following steps:

[0058] In step S11, a catalyst accounting for 0.01%-0.05% of the total mass is continuously added to the mixture of dimethyl terephthalate and aliphatic diol. The catalyst is preferably tetrabutyl titanate.

[0059] In step S12, after the catalyst is added, the mixture is stirred at a temperature of 120-160°C, and then the reaction temperature is gradually increased to 170-200°C and maintained at 170-200°C for 1-3h.

[0060] In step S13, the environmental pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190-250°C, and the reaction is continued for 1.5-3h. After the reaction is completed, a polyester oligomer is obtained.

[0061] It can be understood that the polyester oligomer is a linear polyester oligomer, wherein the main chain is alternately connected by "terephthalic acid units-aliphatic diol units". The polyester is synthesized by polycondensation reaction, which needs to exclude small molecule byproducts. The initial temperature is low, and the solid reactant dimethyl terephthalate is first dissolved in aliphatic diol to improve the reaction efficiency. Then, the reaction generates small molecule byproduct methanol, and after continuous removal of methanol, further heating is needed to promote molecular chain growth. Early temperature rise will cause an increase in side reactions, hindering the formation of products.

[0062] In some specific embodiments, under the action of a catalyst (such as tetrabutyl titanate), dimethyl terephthalate reacts with excess aliphatic diol (commonly used ethylene glycol EG) to directly generate an oligomer. At higher temperatures and higher vacuum degrees, the molecular chain continuously grows to form long-chain polyester molecules (PET).

[0063] The role of the catalyst tetrabutyl titanate [Ti(OCH3)4] in this process is to activate the carbonyl group of dimethyl terephthalate, promote the step-by-step substitution of the methoxy group (-OCH3) by the hydroxyethyl group (-CH2CH2OH) of ethylene glycol, and further accelerate the reaction speed.

[0064] In the present application, the degree of polymerization of the prepared polyester oligomer is generally 5-30, which is lower than that of ordinary high molecular weight polyesters, and the molecular weight is smaller. The ends of the molecular chain still retain part of the hydroxyl group (-OH), which can be further reacted with isocyanate, acid anhydride, etc. for subsequent modification (such as preparation of high crosslinking polyester).

[0065] In the above step S11, the total mass percentage refers to the percentage of the total mass of the input raw materials, wherein the input raw materials refer to the mixture of dimethyl terephthalate and aliphatic diol, and the total mass after adding the catalyst. The input catalyst accounts for 0.01%-0.05% of the total mass, wherein the catalyst can also be specifically inputted in the range of 0.01%-0.03%, 0.02%-0.04%, 0.03%-0.05% of the total mass of the catalyst. Specifically, the input catalyst accounts for 0.01%, 0.03% or 0.05% of the total mass, etc.

[0066] In the above step S12, after adding the catalyst, heating and stirring can also be carried out at a temperature of 120℃-140℃ or 130℃-150℃ or 140℃-160℃. Specifically, the heating and stirring temperature is 120℃, 130℃ or 140℃, etc.

[0067] Further, after mixing uniformly, the reaction temperature is gradually increased to 180℃-190℃, and the temperature is maintained for 1.5-2.5h; specifically, the reaction temperature is gradually increased to 180℃, 185℃ or 190℃, and the temperature is maintained for 2h. The specific temperature and time can be determined based on the actual reaction condition.

[0068] In the above step S13, the reaction system refers to the comprehensive body of the reaction environment, the reactant mixture, the reaction intermediate substance, etc. The reactant mixture includes reaction precursors, reaction intermediates and reaction final products.

[0069] In the above step S13, the reaction system can be vacuumed, and the environmental pressure is reduced to 1000-5000 Pa, that is, the environmental pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190℃-220℃, 200℃-220℃ or 210℃-250℃. Specifically, the increased temperature range is 190℃, 193℃, 194℃, 197℃ or 200℃. The specific temperature is related to the environmental pressure of the actual reaction system.

[0070] In some embodiments, the step S13 above can be twice heated, once from 190-200°C, and the second time, after the reactant mixture in the reaction system stops boiling violently, the temperature is raised to 220-230°C, and then maintained at a higher temperature for 2-3h.

[0071] It can be understood that after the reactant mixture in the reaction system stops boiling violently, the temperature can be further raised to 225-245°C or 235-250°C, and the reaction is continued for 2-3h, and the polyester oligomer is obtained after the reaction is completed. Specifically, after the reaction system stops boiling violently, the temperature is raised to 230-240°C, 225-245°C or 235-250°C, and the reaction is continued for 2-3h

[0072] Please continue to combine Figure 2 After the polyester oligomer is obtained by completing the step 13 above, and before the crosslinked polymer precursor is formed by polycondensation with trimethyl citrate, the following steps are further included:

[0073] Step S14, the polyester oligomer and the citrate are mixed in a molar ratio of 1:(1-1.2), and a catalyst is added, and the whole feeding and mixing is carried out in an inert atmosphere;

[0074] Step S15, continue to stir the polyester oligomer, citrate and catalyst, and at the same time, inert gas is blown, the temperature is raised to a first temperature, then the temperature is continuously raised to a second temperature and maintained for 1-3h, and then the temperature is continuously raised to a third temperature; and

[0075] Step S16, the temperature is maintained at the third temperature, the environmental pressure is gradually reduced from normal pressure to 100Pa or below, and when the reaction reaches the preset condition, the reaction is stopped, and the crosslinked polymer precursor is obtained.

[0076] In the step S14 above, the molar ratio of the polyester oligomer to the citrate is 1:(1-1.2), and the molar ratio of the two can also be 1:(1-1.1), 1:(1.08-1.2), further, the molar ratio of the polyester oligomer to the citrate is 1:1, 1:1.05, 1:1.07, 1:1.1, 1:1.15 or 1:1.2.

[0077] The citrate includes any one or a combination of several of trimethyl citrate (TMC), triethyl citrate (TEC) and the like.

[0078] In the above steps, the citrate is selected as trimethyl citrate, and the ratio between the polyester oligomer and the trimethyl citrate is 1:1.05 molar ratio.

[0079] In the step S15, the catalyst is selected from tetrabutyl titanate with a monomer mass of 0.01%-0.03%. Specifically, the tetrabutyl titanate with a monomer mass of 0.01%, a monomer mass of 0.015%, a monomer mass of 0.02%, or a monomer mass of 0.03% can be selected.

[0080] In the step S14 and the step S15, the inert atmosphere is selected from nitrogen, argon, and the like.

[0081] In the step S15, the third temperature is greater than the second temperature, and the second temperature is greater than the first temperature. In some embodiments, the temperature difference between the first temperature and the second temperature and the temperature difference between the second temperature and the third temperature are both 5-30°C. Specifically, the first temperature is 170-185°C, the second temperature is 190-210°C, and the third temperature is 210-230°C.

[0082] In some embodiments, the first temperature is 180°C, the second temperature is 200°C, and the third temperature is 220°C. Alternatively, the first temperature is 180°C, the second temperature is 190°C, and the third temperature is 210°C.

[0083] In the step S15, after the temperature is increased to the first temperature, the temperature is increased from room temperature to the first temperature at a rate of 3-10°C / s. Then, the temperature is increased to the second temperature and maintained for 1-3 hours. In this case, the temperature is increased slowly at a rate of 0.1-2°C / s. Then, the temperature is increased from the second temperature to the third temperature at a rate of 3-10°C / s. The different temperature ranges have different rates of temperature increase, which can ensure that the reaction between the polyester oligomer, the citrate ester, and the catalyst is sufficient. The different temperatures can have different effects: for example, the first temperature range can activate the reaction and mix the reactants uniformly, the second temperature range can effectively control the reaction rate and ensure sufficient reaction, and the third temperature range can facilitate the reaction.

[0084] In the step S16, while the temperature is maintained at the third temperature, the environmental pressure is gradually decreased from normal pressure to 100 Pa or less. The normal pressure is 101.325 kPa, and the rate of decrease of the environmental pressure can be 50-5000 Pa / min, which can be determined based on the reaction state.

[0085] It can be understood that, at the initial stage of the reaction, the viscosity of the mixture of the polyester oligomer, the citrate ester and the catalyst added is low, and as the temperature rises, the molecular chain continuously increases during the reaction, and the long-chain molecular chains intertwine with each other, at this time the viscosity of the system continues to slowly rise as the reaction continues. The reaction reaches the preset condition, that is, when the polymer reaction system appears "climbing pole effect", the reaction is stopped. That is, when the polymer reaction system appears "climbing pole effect", it is considered that the preset condition is reached, and at this time the related reaction is stopped.

[0086] In some specific implementation schemes, the polymerization reaction needs to be judged by observing whether the polymer climbs the pole to determine whether the reaction endpoint is reached, that is, whether the reaction reaches the preset condition is determined based on the judgment. Because after the polymer climbs the pole, part of the reaction system is suspended and no longer fully contacts the reactor wall, it is difficult to further increase the molecular weight by continuing the reaction, therefore, when the polymer reaction system appears "climbing pole effect", the reaction can be selected to be terminated. It can be understood that, this "climbing pole effect" phenomenon was first discovered by Weissenberg in 1948, and is also known as Weissenberg Effect or normal stress effect in the academic field. Its basic performance is that when a rotating rod is immersed in a polymer solution or melt, the fluid climbs along the rod to form a convex liquid surface to overcome the centrifugal force, which is in sharp contrast to the characteristics of Newtonian fluid flowing outward due to inertial force.

[0087] Please refer to Figure 3 In the above step S2, after the cross-linked polymer precursor is dried and carbonized under an inert atmosphere, and acid washing, an activation treatment is performed to obtain a carbon skeleton material, which specifically includes the following steps:

[0088] Step S21, vacuum drying at a temperature range of 70-90°C for 2-6h to remove unreacted substances remaining on the cross-linked polymer precursor;

[0089] Step S22, carbonization treatment is performed on the cross-linked polymer precursor after impurities and moisture are removed, the carbonization environment atmosphere is a mixed gas of nitrogen and oxygen, and after being heated to a carbonization temperature, the carbonization temperature is maintained for a predetermined time to obtain a polyester polymer carbide; and

[0090] Step S23, the polyester polymer carbide is subjected to acid washing, washing and then activation to obtain a carbon skeleton material.

[0091] The combination of the unique structure design of the cross-linked polyester and the carbonization process makes the carbon skeleton material retain part of the reactive sites. Among them, the reactive sites include part of the residual hydroxyl groups, carbonyl groups and other oxygen-containing groups.

[0092] In the step S21, the temperature range is 70-90°C, which can also be 70-80°C, 76-90°C or 76-85°C, and in particular, the corresponding temperature in step S21 is 70°C, 80°C, 85°C or 90°C. The time for vacuum drying can be 2-5h, 4-6h or 3-5h, and in particular, the time for vacuum drying is 4h, 5h or 6h, etc.

[0093] In the step S22, the oxygen content in the mixed gas of nitrogen and oxygen is 3%-7% by volume, and in particular, the oxygen content can also be 3%-5%, 4%-6% or 5%-7% by volume, and can also be 3%, 4%, 5% or 6%. The selection of the oxygen content in the mixed gas of nitrogen and oxygen provides environmental protection for “structural stability” and “functional group optimization”: nitrogen can be used to inhibit excessive oxidation and reduction, and oxygen with a volume fraction of 3%-7% can be used to moderately control the type and distribution of functional groups. The two work together to ultimately achieve the goal of “continuous porous carbon skeleton + uniform distribution of lithiumophilic functional groups”, thereby meeting the core needs of lithium metal reinforced materials.

[0094] In particular, the residual unreacted substance is an unreacted small molecule impurity.

[0095] In the step S22, the carbonization temperature is a medium-low temperature. The carbonization temperature is between 300-600°C, and in particular, the carbonization temperature is between 300-410°C, 400-460°C, 400-550°C and 540-600°C. Further in particular, the carbonization temperature is 400°C, 450°C, 500°C or 550°C, etc. The temperature range of 300-600°C belongs to the medium-low temperature interval, and the thermal effect in the medium-low temperature interval can achieve “selective carbonization”, which can preliminarily form the carbon skeleton and retain the integrity of the cross-linked network; it can also efficiently retain the lithiumophilic functional groups (-OH, C=O, -COOH), which can be more easily covalently connected with the lithium battery anode material during subsequent rolling processing, thereby greatly improving the compatibility between lithium metal and the carbon skeleton material. However, high-temperature carbonization will destroy these active sites.

[0096] In the step S22, the heating rate is a constant rate, and the heating rate is 0.5-2°C / min, and in particular, the heating rate can be 0.5-1°C / min, 0.8-1.5°C / min or 1.1-2°C / min, and further, the heating rate can be 0.5°C / min, 1°C / min, 1.8°C / min or 2°C / min.

[0097] After reaching the carbonization temperature, the holding time is 20 min-50 min, specifically, the holding time can also be 20 min-40 min, 30 min-50 min or 20 min-35 min, and further, the holding time can also be 20 min, 30 min, 40 min or 50 min, etc.

[0098] In the above step S23, the polyester polymer carbonization product is subjected to acid pickling, wherein the acid liquid can be dilute nitric acid, dilute sulfuric acid, dilute hydrochloric acid, etc., and the acid liquid concentration is 0.05 mol / L-0.5 mol / L, specifically, the acid liquid concentration can also be 0.1 mol / L-0.3 mol / L, 0.1 mol / L-0.5 mol / L or 0.08 mol / L-0.15 mol / L, specifically, the acid liquid concentration can also be specifically 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L or 0.5 mol / L.

[0099] Further, the polyester polymer carbonization product is subjected to acid pickling by soaking in the acid liquid, and the soaking time is 3 h-6 h, 3 h-5 h or 4 h-6 h, specifically, the soaking time is 3 h, 4 h, 4.5 h, 5 h, 5.5 h and 6 h.

[0100] In the above step S23, after the soaking is completed, the residual acid liquid on the reactant is further washed until the washing liquid is neutral or weakly acidic, and then the washing is stopped.

[0101] In the above step S23, finally, the washed product is subjected to low-temperature activation under an inert gas atmosphere to obtain a carbon skeleton material, wherein the low-temperature activation refers to keeping at 250℃-400℃ for 0.5 h-3 h.

[0102] The low-temperature activation temperature is specifically 300℃-400℃, 280℃-350℃ or 300℃-400℃, specifically, the low-temperature activation temperature can further be 300℃, 310℃, 350℃ or 400℃. The low-temperature activation keeping time is 0.5 h-3 h, which can also be specifically 0.5 h-2 h, 1 h-3 h or 2 h-3 h, and can also be specifically 0.6 h, 1 h, 2 h, 2.7 h or 3 h. In a specific embodiment of the present application, the core of low-temperature activation at 250℃-400℃ under a nitrogen atmosphere is “cleaning the surface + preserving the functional groups + stabilizing the structure”, rather than the traditional activation “pore making”; if the low-temperature activation treatment is not performed, impurities will be left, functional groups will be lost, and the skeleton stability will be reduced, ultimately losing the enhancement effect on lithium metal; the selection of the activation temperature needs to strictly match the thermal stability of the precursor and the functional group preservation requirement, and the effect of low-temperature activation is optimal at a temperature of 250℃-400℃.

[0103] It can be understood that in the step S1 and the step S2 of the method disclosed in the present application, the inert gas mentioned can be any one or a combination of nitrogen and argon.

[0104] Please continue to refer to Figure 4 In the step S3, the modified lithium metal is obtained by mixing the lithium metal and the carbon skeleton material in a certain proportion, and the specific step of manufacturing the lithium metal negative electrode from the modified lithium metal can further include:

[0105] In the step S31, the lithium metal and the carbon skeleton material are mixed in a mass ratio of (90-99):(1-10), and are processed by mixing in a double roller machine to obtain the modified lithium metal; and

[0106] In the step S32, the modified lithium metal is processed to obtain the lithium metal negative electrode.

[0107] In the step S31-S32, the carbon skeleton material is formed by carbonization processing from the original cross-linked polyester polymer. The combination of the unique structure design of the cross-linked polyester and the carbonization process makes the carbon skeleton material retain part of the reactive sites, which can greatly enhance the structure enhancement effect of the lithium metal.

[0108] In the step S31, specifically, the mass ratio of the lithium metal to the carbon skeleton material can be 90:10-95:5, 90:10-93:7, or 93:7-99:1, and further, the mass ratio of the lithium metal to the carbon skeleton material can be 90:10, 91:9, 93:7, 95:5, 96:4, 97:3, and 99:1.

[0109] Specifically, the two rollers of the double roller mixer usually rotate at different speeds, thereby generating strong shear force. This speed difference is represented by the friction ratio, which is the ratio of the speed of the front roller to the speed of the rear roller. In the present application, the speed of the front roller is 12 rpm-20 rpm, and the speed ratio of the front roller to the rear roller is (1.1-1.3):1. Specifically, the speed ratio of the front roller to the rear roller can be 1.1:1, 1.15:1, 1.2:1, 1.21:1, 1.26:1, 1.29:1, and 1.3:1, etc., which can be adjusted according to the mixing requirements.

[0110] Specifically, the speed of the front roller can also be 12 rpm-16 rpm, 14 rpm-20 rpm, and 13 rpm-18 rpm, and the speed of the front roller can be specifically 12 rpm, 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, or 20 rpm, wherein rpm represents revolutions per minute.

[0111] The mixing temperature is 30-50℃, specifically 30-45℃, 35-48℃ or 36-50℃, etc. The specific mixing temperature can also be 30℃, 31℃, 33℃, 38℃, 40℃, 42℃, 45℃ or 50℃, etc.

[0112] In order to better control the progress of double-roller mixing, the roller gap between the front wheel and the rear wheel is set to 0.5-2mm, and further the roller gap is 0.8-1.5mm, 0.5-1.2mm or 1-2mm, which can be: specifically, the roller gap can be 0.5mm, 1mm, 1.5mm or 2mm.

[0113] The mixing time is 10-30min, specifically the mixing time can also be 10-25min, 15-30min, 18-24min. Further, the specific mixing time can also be 10min, 15min, 18min, 20min, 24min, 28min or 30min.

[0114] It can be understood that in some other embodiments of the present application, the step S31 can also use other types of mixing equipment to mix the lithium metal and the carbon skeleton material in a mass ratio of (90-99):(1-10) to obtain modified lithium metal. However, the modified lithium metal obtained after the mixing processing by the double-roller machine has the best performance.

[0115] As shown in Figure 5 The step S32 can further include:

[0116] Step S321, first make the modified lithium metal into a sheet; and

[0117] Step S322, cut to the size required by the lithium battery, that is, make the lithium metal negative electrode.

[0118] Specifically, in the above step S321, the modified lithium metal can be prepared by cold rolling forming, and the corresponding cold rolling temperature is room temperature or a temperature lower than room temperature, such as 25℃, 20℃, 18℃, 15℃, 10℃ or 5℃, 3℃ or 0℃, etc.

[0119] It can be understood that the mixing through the foregoing step S31 has obtained the modified lithium metal with good processability, and in the subsequent step S32, only the thickness and size of the modified lithium metal are adjusted. In some specific embodiments of the present application, the rolling roller adopts a mirror roller, the cold rolling temperature of which is as defined above, and the thickness of the sheet of the modified lithium metal after passing through the roller can be 0.5 mm-5 mm, and the rolling speed is 0.1 m / s-5 m / s. The thickness and cold rolling speed of the specific sheet can be adjusted based on the size and thickness requirements of the lithium metal negative electrode to be formed, and are determined by the forming material application and the like, and the above content is only an example.

[0120] It can be understood that in another specific embodiment, the modified lithium metal obtained after step S31 is further made into a required lithium metal negative electrode, and the subsequent step can be replaced by other methods, such as being made into a lithium metal negative electrode by static pressure pressing, mold pressing and the like.

[0121] It can be understood that in the present application, the tensile strength of the lithium metal negative electrode prepared in steps S1-S3 in the above lithium metal negative electrode preparation method can be greater than 6.2 MPa, and can reach 8.7 MPa. The tensile strength of the unmodified lithium metal is only 1.4 MPa. It can be seen that the lithium metal after mixing and processing has excellent mechanical properties, and the tensile strength is increased to 6.2 MPa-8.7 MPa, the lithium metal and the surface of the carbon skeleton material are no longer bonded to each other, and the lithium metal negative electrode can be quickly rolled and die cut. The description that the lithium metal and the surface of the carbon skeleton material are no longer bonded to each other can be understood as follows: after the lithium metal is added to the carbon skeleton material, the surface morphology of the lithium metal is changed, and the surface adhesion of the carbon skeleton material is reduced. Therefore, it is described that the lithium metal and the surface of the carbon skeleton material are no longer bonded to each other.

[0122] In order to further meet the use scenarios of different lithium batteries, the lithium metal negative electrode can be cut into any special shape by die cutting, and can be further prepared in cooperation with a curved battery or a flexible battery.

[0123] In the present application, although the mass fraction of the carbon skeleton material in the lithium metal negative electrode is not large, it has a significant effect on improving the ductility of the lithium metal negative electrode.

[0124] It can be understood that in the present application, the rotation speed, speed ratio, and roll gap can form a synergistic relationship, and thus a lithium metal negative electrode material with the required properties can be stably prepared. Through the structural design of the cross-linked polyester, the carbon skeleton material with rich active sites is successfully prepared, thereby improving the tensile strength of the lithium metal negative electrode, and further improving the processing performance and the service life of the lithium battery with the lithium metal negative electrode.

[0125] The lithium metal negative electrode preparation method provided in the embodiment can obtain the carbon skeleton material in advance, and the lithium metal and the carbon skeleton are mixed and cold-rolled, which is beneficial to the industrialized large-scale preparation of the lithium metal negative electrode, and by limiting the specific mixing performance, the stability of the product prepared can be further improved, the production yield is improved, and the production cost is reduced.

[0126] The lithium metal negative electrode is prepared by the lithium metal negative electrode preparation method in the first embodiment. In the lithium metal negative electrode, lithium metal is the main body, and a small amount of carbon skeleton is added. In the lithium metal negative electrode, the mass ratio of the lithium metal to the carbon skeleton material is (90-99):(1-10).

[0127] Further, in the lithium metal negative electrode, the mass ratio of the lithium metal to the carbon skeleton material can also be (90:10)-(95:5), (90:10)-(93:7), or (93:7)-(99:1); specifically, the mass ratio of the lithium metal to the carbon skeleton material is 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, or 99:1, etc. In the present application, although the mass ratio of the carbon skeleton material in the lithium metal negative electrode is not large, it has a significant effect on improving the ductility of the lithium metal negative electrode.

[0128] Specifically, by preparing the carbon skeleton material with a structure-adapted fiber network and active sites, and compounding it with lithium metal, an effective fiber reinforcement effect can be formed, thereby significantly improving the tensile strength of the lithium metal electrode. The fiber network refers to a cross-linked polymer network structure, and part of the active sites are still retained after carbonization; the reaction active sites include part of the residual hydroxyl, carbonyl and other oxygen-containing groups.

[0129] The cross-linking point of the cross-linked polyester prepared by the lithium metal negative electrode preparation method claimed in the first embodiment cannot be completely deoxidized and carbonized in the carbonization process, and therefore still has part of the active sites, which can form covalent connection when the lithium battery is rolled, thereby greatly improving the compatibility of the two phases. When the lithium metal is compounded with the carbon skeleton material, the high-strength carbon skeleton material acts as a "skeleton" to bear the main load, the reaction sites remaining on the carbon skeleton material bond the lithium metal and the carbon skeleton well, and the interface of the two is combined as a whole, thereby facilitating the conduction of stress and realizing the synergistic optimization of strength and rigidity.

[0130] The melting point of lithium metal is about 180℃, therefore, the lithium metal negative electrode prepared based on the above-mentioned lithium metal negative electrode preparation method, wherein the lithium metal is softer and has certain ductility under the reaction environment with a mixing temperature of 30-50℃ than at room temperature. In the lithium metal negative electrode provided in the present application, lithium metal is the main body and the carbon skeleton material is a small amount of additive. Due to the addition of the carbon skeleton, the lithium metal negative electrode has better tensile strength.

[0131] Further, the surface properties and structural strength of the lithium metal negative electrode obtained by compounding lithium metal with the carbon skeleton material are obviously improved, the problem of mutual adhesion and easy tearing of the surface of the lithium metal negative electrode in the processing process is avoided, and the lithium metal negative electrode is more beneficial to industrial production.

[0132] In the prior art, the lithium metal will have significant volume change during the charging and discharging of the lithium battery. If the lithium metal with poor ductility is used as the negative electrode, the rigid structure of the lithium metal negative electrode cannot adapt to the volume fluctuation, and great internal stress is easily generated, thereby causing the negative electrode material to crack and the interface stability to decrease. In the present application, due to the addition of the carbon skeleton material, the lithium metal negative electrode claimed in the present application is more beneficial to resist the volume expansion caused by the deintercalation of lithium ions during the charging and discharging cycle, thereby improving the cycle life of the battery.

[0133] Other related limitations of the carbon skeleton fiber structure 21 formed by the extension of the carbon skeleton material are the same as those in the first embodiment, and will not be described here.

[0134] The lithium metal negative electrode provided in the present embodiment can well solve this problem. The good ductility can make the lithium metal negative electrode itself have the performance of buffering the volume expansion, and can also improve the stability of the interface layer, thereby improving the stability and service life of the lithium metal negative electrode.

[0135] Please refer to Figure 6 The third embodiment of the present application provides a lithium battery 30 with the above-mentioned lithium metal negative electrode 31, wherein the lithium metal negative electrode 31 serves as the negative electrode of the lithium battery 30. The lithium battery further comprises a positive electrode 32 and a solid-state electrolyte 33, wherein the solid-state electrolyte 33 is arranged between the positive electrode 32 and the lithium metal negative electrode 31.

[0136] The lithium battery 30 further comprises a shell 34 for accommodating the lithium metal negative electrode 31, the solid-state electrolyte 33 and the positive electrode 32.

[0137] The material of the positive electrode 32 can be any one or a combination of several of ternary layered oxides, lithium cobaltate (LiCoO2, LCO), spinel lithium manganate (LiMn2O4, LMO), lithium iron phosphate (LiFePO4, LFP) and the like.

[0138] The material of the solid-state electrolyte 33 can be selected from any one or a combination of oxide solid-state electrolyte, sulfide solid-state electrolyte, polymer solid-state electrolyte, halide solid-state electrolyte, etc.

[0139] The processed lithium metal negative electrode 31, together with the positive electrode 32 and the solid-state electrolyte 33, forms a solid-state-lithium metal battery, i.e., the lithium battery 30. The cycle life of the lithium battery 30 provided in the embodiment is increased to 600-800 cycles.

[0140] Other limitations related to the lithium metal negative electrode 31 are the same as in the first embodiment described above, and will not be repeated here.

[0141] In the embodiment, the lithium metal negative electrode 31 prepared by the lithium metal negative electrode preparation method provided in the first embodiment has good ductility, so that the lithium metal negative electrode 31 can be used to prepare special-shaped lithium batteries without being limited by the lithium metal negative electrode.

[0142] The common method in the prior art is to change the composition of the electrolyte, introduce a solid electrolyte, or optimize the electrode structure to improve the performance of the lithium metal electrode. However, the existing technology only has limited enhancement effect and is difficult to achieve uniform dispersion through composite enhancement, which cannot effectively meet the actual demand.

[0143] In the lithium battery 30 provided in the present application, the lithium metal negative electrode 31 has good ductility, so that it can meet the preparation and assembly requirements of special-shaped batteries such as flexible batteries and curved batteries. In addition, the lithium metal negative electrode 31 with good ductility can "fill" the interface gap by deforming itself, and even form a closer physical contact with the solid-state electrolyte under a certain pressure, thereby reducing the interface impedance and improving the rate performance of the battery.

[0144] The lithium metal negative electrode 31 provided in the present application is used in the lithium battery 30. Since the lithium metal negative electrode 31 has good ductility, the performance and safety of the lithium battery 30 can be effectively improved. The good ductility of the lithium metal negative electrode 31 also allows the lithium metal negative electrode 31 to remain intact under the action of external forces other than extrusion, thereby maintaining the integrity of the electrode structure and prolonging the service life of the lithium battery 30.

[0145] In order to better illustrate the performance of the lithium metal negative electrode prepared by the technical solution protected by the present application, the present application further provides the following specific experimental examples and comparative examples as specific examples of the lithium metal negative electrode and the preparation method thereof.

[0146] Experimental Example 1

[0147] A lithium metal negative electrode preparation method comprises the following steps: first, preparing a cross-linked polyester polymer, then obtaining a carbon skeleton material, mixing lithium metal with the carbon skeleton material, and then obtaining the lithium metal negative electrode.

[0148] The preparation of the cross-linked polymer precursor comprises the following steps:

[0149] The reactant molar ratio is dimethyl terephthalate:aliphatic diol = 1:1.1 (wherein the aliphatic diol includes ethylene glycol, propylene glycol, and butanediol, and the molar ratio of ethylene glycol:propylene glycol:butanediol is 1:0.6:0.4). A total of 0.03% of the catalyst tetrabutyl titanate is added to the raw materials, heated and stirred at 150°C, and after the mixture is uniformly mixed, the reaction temperature is gradually increased to 180°C, and the reaction is continued for 2 hours.

[0150] The reaction system is vacuumed, the environmental air pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190°C. After the system stops boiling violently, the temperature is increased to 225°C and the reaction is continued for 2 hours. After the reaction is completed, the polyester oligomer is obtained.

[0151] The polyester oligomer and trimethyl citrate are weighed according to a molar ratio of 1:1.05, and a catalyst tetrabutyl titanate with a monomer mass of 0.02% is added. Nitrogen is introduced to ensure an inert atmosphere. After stirring and nitrogen purging, the raw materials are heated to 180°C, then slowly heated to 200°C, and the reaction is continued for 2 hours. The temperature is then increased to 220°C, the reaction environment is gradually reduced from normal pressure to below 100 Pa, and the reaction is stopped when the preset conditions are reached. The cross-linked polymer precursor is obtained.

[0152] The carbon skeleton material is prepared by the following steps:

[0153] The cross-linked polymer precursor (from Experimental Example 1) is first vacuum dried at 80°C for 4 hours to remove residual unreacted small molecule impurities, and then placed in an oven for low-temperature carbonization in a nitrogen and oxygen mixed gas environment, wherein the volume fraction of oxygen is 5%. The temperature is increased to 450°C at a rate of 1°C / min, and the temperature is maintained for 30 minutes after reaching the target temperature.

[0154] The low-temperature carbonized material is subjected to dilute nitric acid pickling (acid concentration is 0.1 mol / L, and soaking time is 3-6 hours), and the pickling is stopped when the washing liquid is neutral or weakly acidic.

[0155] Finally, the material is subjected to low-temperature activation (in a N2 atmosphere, maintained at 300°C for 1 hour) to obtain the carbon skeleton material.

[0156] The lithium metal negative electrode is prepared by the following steps:

[0157] The lithium metal and the carbon skeleton material (selected from Experimental Example 4) are mixed and processed in a double roller at a mass ratio of 95:5, the front wheel rotation speed is 5 rpm, the speed ratio is 1.1, the temperature is 20℃, the roller distance is 2 mm, and the mixing time is 25 minutes. The modified lithium metal after mixing and processing is cold-rolled into a sheet, and is cut and trimmed into the size required by the lithium battery, that is, the lithium metal negative electrode is prepared.

[0158] Experimental Example 2

[0159] The difference from Experimental Example 1 is only that the preparation steps of the cross-linked polymer precursor are as follows: the reactant molar ratio is dimethyl terephthalate: aliphatic diol = 1:1.1 (wherein the aliphatic diol includes ethylene glycol, propylene glycol, and butanediol, and the molar ratio is ethylene glycol: propylene glycol: butanediol = 1:0.5:0.5). The total mass of the catalyst tetrabutyl titanate is 0.05% of the total mass of the raw materials, heated and stirred at 150℃, and after the mixture is uniform, the reaction temperature is gradually increased to 180℃, and the reaction is carried out for 1h.

[0160] The reaction system is vacuumed, the environmental air pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190℃ at the same time. After the system stops boiling violently, the temperature is increased to 240℃ and the reaction is continued for 1.5h. The polyester oligomer is obtained after the reaction is completed.

[0161] The above polyester oligomer and trimethyl citrate are weighed according to a molar ratio of 1:1.08, and the catalyst tetrabutyl titanate is added in an amount of 0.02% of the mass of the monomers. Nitrogen is introduced to ensure an inert atmosphere. Stirring, nitrogen blowing, heating the raw materials to 180℃, slowly increasing the temperature to 200℃, and then continuing to increase the temperature to 220℃. The reaction environment is gradually reduced from normal pressure to below 100 Pa. When the reaction reaches the preset condition, the reaction is stopped, and the cross-linked polymer precursor is obtained.

[0162] Experimental Example 3

[0163] The difference from Experimental Example 1 is only that the preparation steps of the cross-linked polymer precursor are as follows: the reactant molar ratio is dimethyl terephthalate: aliphatic diol = 1:1.1 (wherein the aliphatic diol includes ethylene glycol, propylene glycol, and butanediol, and the molar ratio is ethylene glycol: propylene glycol: butanediol = 1:0.55:0.45). The total mass of the catalyst tetrabutyl titanate is 0.04% of the total mass of the raw materials, heated and stirred at 150℃, and after the mixture is uniform, the reaction temperature is gradually increased to 180℃, and the reaction is carried out for 1.5h.

[0164] The reaction system is vacuumed, the environmental air pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190℃ at the same time. After the system stops boiling violently, the temperature is increased to 240℃ and the reaction is continued for 1.5h. The polyester oligomer is obtained after the reaction is completed.

[0165] The above polyester oligomer and trimethyl citrate are weighed according to a molar ratio of 1:1.1, and a catalyst tetrabutyl titanate with a mass of 0.03% of the monomer is added. Nitrogen is introduced to ensure an inert atmosphere. After the raw materials are heated to 180°C, the temperature is slowly increased to 190°C, and the reaction is continued for 2 hours. The temperature is then increased to 210°C, and the reaction environment is gradually reduced from normal pressure to below 100 Pa. When the reaction reaches the preset condition, the reaction is stopped, and a cross-linked polymer precursor is obtained.

[0166] Experimental Example 4

[0167] The difference between it and the above Experimental Example 2 is only that the preparation steps of the carbon skeleton material are as follows: the cross-linked polymer precursor is first vacuum dried at 90°C for 3h to remove residual unreacted small molecule impurities, and then placed in a furnace for low-temperature carbonization in a nitrogen and oxygen mixed gas atmosphere, wherein the volume fraction of oxygen is 5%, and the temperature is increased to 500°C at a rate of 1.5°C / min. After reaching the target temperature, it is kept for 40 min.

[0168] The low-temperature carbonized material is subjected to dilute nitric acid pickling (acid concentration is 0.1 mol / L, soaking time is 3-6h), and the washing is stopped when the washing liquid is neutral or weakly acidic.

[0169] Finally, the material is subjected to low-temperature activation (atmosphere is N2, maintained at 300°C for 1h) to obtain a carbon skeleton material.

[0170] Experimental Example 5

[0171] The difference between it and the above Experimental Example 1 is only that the preparation steps of the carbon skeleton material are as follows: the cross-linked polymer precursor is first vacuum dried at 100°C for 2h to remove residual unreacted small molecule impurities, and then placed in a furnace for low-temperature carbonization in a nitrogen and oxygen mixed gas atmosphere, wherein the volume fraction of oxygen is 5%, and the temperature is increased to 550°C at a rate of 2°C / min. After reaching the target temperature, it is kept for 45 min.

[0172] The low-temperature carbonized material is subjected to dilute nitric acid pickling (acid concentration is 0.1 mol / L, soaking time is 3-6h), and the washing is stopped when the washing liquid is neutral or weakly acidic.

[0173] Finally, the material is subjected to low-temperature activation (atmosphere is N2, maintained at 300°C for 1h) to obtain a carbon skeleton material.

[0174] Experimental Example 6

[0175] The difference between it and the above Experimental Example 4 is only that the reaction steps of lithium metal and the carbon skeleton material are as follows:

[0176] The lithium metal and carbon skeleton material were mixed and processed in a double roller machine at a mass ratio of 90:10, with a front wheel speed of 15 rpm, a speed ratio of 1.2, a temperature of 40°C, a roller distance of 1 mm, and a mixing time of 20 minutes. The modified lithium metal after mixing and processing was cold-rolled into a sheet, and cut into the required size for lithium batteries by die cutting, i.e., a lithium metal negative electrode was prepared.

[0177] Experimental Example 7

[0178] The difference from Experimental Example 5 described above is only that the reaction step of the lithium metal and the carbon skeleton material is as follows:

[0179] The lithium metal and carbon skeleton material were mixed and processed in a double roller machine at a mass ratio of 93:7, with a front wheel speed of 10 rpm, a speed ratio of 1.15, a temperature of 50°C, a roller distance of 1.5 mm, and a mixing time of 15 minutes. The modified lithium metal after mixing and processing was cold-rolled into a sheet, and cut into the required size for lithium batteries by die cutting, i.e., a lithium metal negative electrode was prepared.

[0180] Comparative Example 1

[0181] The lithium metal material was pressed to form a lithium metal sheet.

[0182] The material tensile strength test was performed on the above Experimental Examples 1-7 and Comparative Example 1 to test the material properties of the lithium metal negative electrode prepared based on the above method.

[0183] Experimental scheme: Tensile strength (Rm) refers to the maximum engineering stress that the lithium metal sample can withstand before breaking under uniaxial tensile load. The calculation formula is:

[0184] Rm = Fm / S0

[0185] Where: Fm: maximum tensile force before sample breaks (unit: N); S0: original cross-sectional area of sample (unit: mm², which needs to be accurately calculated according to the shape of the sample)

[0186] After the test, the axial tensile force was applied by the material testing machine, and the load-displacement data was recorded synchronously, which was converted into stress-strain curve, and finally the key test indicators of tensile strength were extracted.

[0187] The lithium metal negative electrode provided in the above Experimental Examples 1-7 was tested, and was assembled into a 58 Ah capacity battery cell through the preparation process of solid-state battery; at the same time, the unmodified lithium metal negative electrode in Comparative Example 1 was prepared into a battery through the same process.

[0188] Experimental method: under the same 1C charge-discharge condition, the cycle life of the battery was tested. Taking the capacity loss of 20% as the cut-off condition, the cycle life of the modified lithium metal battery can reach 680-732 cycles, while the unmodified lithium battery can only reach 193 cycles of cycle life.

[0189] Table 1 is the experimental data of lithium metal negative electrode prepared in experimental examples 1-7 and comparative example 1

[0190]

[0191] The tensile strength of the lithium metal negative electrode in comparative example 1 is extremely low (1.4 MPa), which means that the material has poor rigidity and weak plastic deformation resistance, and its overall performance is significantly inferior to that of experimental examples 1-7.

[0192] See Figure 7 The stress-strain curve (Stress-Strain Curve) is shown in the following table 1 and figure 1. Comparing comparative example 1 with experimental example 6, the tensile strength of experimental example 6 changes with the gradual increase of tensile strain. When the tensile strain is between 0%-6%, the tensile strength rapidly increases from 0Mpa to 8.3Mpa (peak); then, when the tensile strain is between 6%-20%, the tensile strength gradually decreases from 8Mpa to about 6.3Mpa; when the tensile strain is between 20%-59%, the tensile strength slowly increases from 6.3Mpa to about 7.8Mpa. It can be seen that the material obtained by experimental example 6 can maintain a relatively stable tensile strength. Compared with experimental example 6, the tensile strength of comparative example 1 only has a significant increase when the tensile strain is between 0%-3%, specifically from 0Mpa to 1Mpa, and then the tensile strain increases, and the change of the corresponding tensile strength is small. As shown in table 1 and Figure 7 It can be seen that the tensile strength of experimental example 6 is significantly better than that of comparative example 1. It can be seen that the tensile strength and ductility of the lithium metal negative electrode prepared by the lithium metal negative electrode preparation method of the present application are significantly improved.

[0193] Further, experimental example 6 and comparative example 1 are compared, as shown in Figure 8 Experimental method: under the same 1C charge-discharge condition, the cycle life of the battery was tested. Taking the capacity loss of 20% as the cut-off condition, the cycle life of the modified lithium metal battery can reach 732 cycles, while the unmodified lithium battery in comparative example 1 has a rapid capacity retention rate and can only reach 193 cycles of cycle life.

[0194] It can be known from the above experiments that, compared with the comparative example 1, the material tensile strength and capacity retention rate of the lithium metal negative electrode prepared by the experimental examples 1-7 of the application are obviously improved. Specifically, the effective fiber reinforcing effect can be formed, so as to significantly improve the tensile strength of the prepared lithium metal negative electrode. After the lithium metal is compounded with the carbon skeleton material, the high-strength carbon material acts as a "skeleton" to bear the main load, the reaction sites reserved on the carbon skeleton material well bond the two phases, and then the interface of the two phases is combined as a whole, which is beneficial to the stress conduction, and realizes the strength and rigidity synergistic optimization. After the lithium metal is compounded with the carbon skeleton material, the surface properties and structural strength of the obtained lithium metal negative electrode are obviously improved, the defects of surface mutual adhesion and easy tearing in the processing of the lithium metal negative electrode are avoided, and the lithium metal negative electrode is more beneficial to large-scale industrialized production.

[0195] The lithium metal negative electrode and the preparation method thereof and the lithium battery disclosed in the above experimental examples of the application are described in detail, and the principles and implementation manners of the application are described by applying specific examples. The above experimental examples are only used to help understand the method of the application and the core idea thereof; meanwhile, for the general skilled person in the art, the specific implementation manners and application ranges will be changed according to the idea of the application. In conclusion, the content of the specification should not be understood as the limitation of the application, and any modification, equivalent replacement and improvement within the principles of the application should be included in the protection scope of the application.

Claims

1. A method of preparing a lithium metal anode, characterized by: The preparation method of the lithium metal negative electrode comprises the following steps: mixing dimethyl terephthalate and aliphatic diol according to a molar ratio of 1:(1.05-1.3), continuously adding a catalyst accounting for 0.01%-0.05% of the total mass percentage in the mixture of dimethyl terephthalate and aliphatic diol; After the catalyst is added, the mixture is stirred at a temperature of 120-160 DEG C, the reaction temperature is gradually increased to 170-200 DEG C, and the temperature is maintained at 170-200 DEG C for 1-3 h; and The ambient pressure is reduced to 1000-5000 Pa, and the temperature is increased to 190-250 DEG C, and the reaction is continued for 1.5-3 h, and the polyester oligomer is obtained after the reaction is completed; The polyester oligomer is mixed with citric acid ester and a catalyst, and then the crosslinked polymer precursor is obtained by gradually increasing the temperature and reducing the ambient pressure in an inert atmosphere; The crosslinked polymer precursor is dried and subjected to carbonization treatment and acid pickling in an inert atmosphere, and then subjected to low-temperature activation treatment to obtain a carbon skeleton material; wherein the carbonization treatment is carried out in a mixed gas of nitrogen and oxygen, the oxygen content in the mixed gas of nitrogen and oxygen is 3%-7% by volume fraction, and the carbonization treatment is carried out at a temperature of 300-600 DEG C; the low-temperature activation treatment is carried out at a temperature of 250-400 DEG C for 0.5-3 h; and The lithium metal is mixed with the carbon skeleton material in a certain proportion to obtain modified lithium metal, and the modified lithium metal is made into a lithium metal negative electrode.

2. The method of claim 1, wherein the lithium metal anode is prepared by: The aliphatic diol includes any one or a combination of the following three: ethylene glycol, propylene glycol, and butanediol; and / or the catalyst is tetrabutyl titanate.

3. The method of claim 1, wherein the lithium metal anode is prepared by: After the above-mentioned step of reducing the ambient pressure to 1000-5000 Pa, increasing the temperature to 190-250 DEG C, continuing the reaction for 1.5-3 h, and obtaining the polyester oligomer after the reaction is completed, the following steps are further included: The polyester oligomer is mixed with citric acid ester according to a molar ratio of 1:(1-1.2), and a catalyst is added, and the whole feeding and mixing process is carried out in an inert atmosphere; The polyester oligomer, citric acid ester, and catalyst are continuously stirred, and inert gas is blown at the same time, the temperature is increased to a first temperature, then the temperature is continuously increased to a second temperature and maintained for 1-3 h, and then the temperature is continuously increased to a third temperature; and The temperature is maintained at the third temperature, the ambient pressure is gradually reduced from normal pressure to below 100 Pa, and the reaction is stopped when the reaction reaches the preset condition, and the crosslinked polymer precursor is obtained.

4. The method of claim 3, wherein the lithium metal negative electrode is prepared by: In the above-mentioned step of continuously stirring the polyester oligomer, citric acid ester, and catalyst, and blowing inert gas at the same time, increasing the temperature to a first temperature, then continuously increasing the temperature to a second temperature and maintaining for 1-3 h, and then continuously increasing the temperature to a third temperature, the third temperature > the second temperature > the first temperature, and the temperature difference between the first temperature and the second temperature and the temperature difference between the second temperature and the third temperature are both 5-30 DEG C.

5. The method of claim 1, wherein the lithium metal anode is prepared by: The above-mentioned drying of the crosslinked polymer precursor specifically comprises the following steps: Vacuum drying is performed at a temperature range of 70-90 DEG C for 2-6 hours to remove unreacted substances remaining on the crosslinked polymer precursor.

6. The method of claim 1, wherein the lithium metal anode is prepared by: The lithium metal and the carbon skeleton material are mixed in a mass ratio of (90-99):(1-10) and are processed by mixing in a double roller to obtain a modified lithium metal.

7. The method of claim 6, wherein the lithium metal anode is prepared by: The double roller comprises front wheels and rear wheels, the rotation speed of the front wheels is 12-20 rpm, the rotation speed ratio of the front wheels to the rear wheels is (1.1-1.3):1, and the mixing temperature is 30-50 DEG C; and / or the roller distance between the front wheels and the rear wheels is set to 0.5-2 mm.

8. A lithium metal anode, characterized by: The lithium metal negative electrode is prepared by the method of any one of claims 1-7, and comprises lithium metal and a carbon skeleton material, the mass ratio of the lithium metal to the carbon skeleton material being (90-99):(1-10).

9. A lithium battery, characterized by: The lithium battery comprises a positive electrode, a solid-state electrolyte, and the lithium metal negative electrode of claim 8, wherein the solid-state electrolyte is arranged between the positive electrode material and the lithium metal negative electrode.

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