CN110797524B - Multi-element lithium-magnesium alloy cathode material for secondary battery and adaptive electrolyte thereof - Google Patents
Multi-element lithium-magnesium alloy cathode material for secondary battery and adaptive electrolyte thereof Download PDFInfo
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Abstract
The invention provides an oxidation-resistant easily-activated multi-element lithium-magnesium alloy cathode material for a secondary battery with high cycling stability and an adaptive electrolyte thereof, wherein the multi-element lithium-magnesium alloy is an alloy formed by lithium, magnesium and other alloy elements (one or more of calcium, strontium, barium, yttrium, lanthanum, cerium, aluminum, gallium, indium, silicon, tin, antimony and bismuth), the content of magnesium is 15-70 at.%, and the total content of the other alloy elements is 0.01-5 at.%; the electrolyte is a lithium salt organic ester solution containing an organic additive A and nitrate. The alloy elements are added into the metal lithium, and the pure lithium cathode is matched with the electrolyte containing the organic additive A and the nitrate, so that the problems of pulverization and dendritic crystal growth in the battery cycle process and restriction on the coulombic efficiency and the cycle life of the battery can be effectively solved. The multi-element lithium magnesium alloy has high activity, small polarization and air oxidation resistance, can be rolled into foil strips in a common air environment and used for battery assembly, and can be produced in a large scale with high efficiency and low cost.
Description
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to a multi-element lithium-magnesium alloy cathode material for a secondary battery and adaptive electrolyte thereof.
Background
The successful commercialization of lithium ion batteries has led to rapid development and significant advances in portable electronic products and electric transportation vehicles. However, with the development of science and technology, different industries put higher demands on battery performance, and the traditional graphite cathode (372mAh/g) has difficulty in meeting the demands of the new generation of high specific energy battery on cathode materials. The lithium metal negative electrode has high capacity (3860mAh/g), low potential (-3.040V vs standard hydrogen electrode) and low density (0.53g cm-2), and becomes an important negative electrode material for the development of next-generation high-specific-energy batteries. However, lithium metal has not been commercially used as a negative electrode for lithium batteries, mainly because of the following problems: (1) the volume change of the metallic lithium is very large in the charging and discharging processes, a surface solid electrolyte interface film (SEI) is easy to break, the surface lithium is unevenly deposited to form lithium dendrites during charging, the lithium dendrites are fused and separated to form dead lithium during discharging, so that the cyclic pulverization is caused, the polarization of the battery is increased, the negative electrode capacity is reduced, and the cycle life of the battery is prolonged; (2) lithium dendrites formed during charging of the metal lithium can pierce a diaphragm to cause short circuit failure of the battery, and potential dangers such as combustion and explosion are generated; (3) the metal lithium is easy to oxidize in the air, and the metal lithium foil strip cannot be rolled into a foil strip in a general air environment and used for battery assembly, so that the high-efficiency low-cost mass production of the metal lithium foil strip and the lithium battery is restricted.
To solve the problems faced by lithium metal anodes, researchers have tried many solutions:
1) and (5) modifying the electrolyte. Such as electrolyte additives, such methods aim to adjust the SEI film component on the surface of the lithium metal, or adjust the surface electric field and charge distribution of the lithium metal in the electrolyte, so as to achieve the effect of alleviating the generation of lithium dendrites. The lithium deposition under the method has a relieving effect on the generation of lithium dendrites under low current density and in a short time, but the lithium dendrites are difficult to effectively inhibit under high current density and long-time lithium deposition, for example, most additives are continuously consumed in the battery cycle process, and the electrochemical stability of long-time lithium deposition is influenced.
2) A solid electrolyte or a gel electrolyte, etc. is used. The electrolyte has certain strength and can prevent the lithium dendrite from puncturing the diaphragm, but because lithium ions are difficult to diffuse in the electrolyte, the power density of the battery is greatly reduced; and the interface impedance between the solid electrolyte and the lithium cathode is large, and the structure is unstable. In addition, the electrolyte has complicated preparation process and high price.
3) And coating and modifying the surface of the metal lithium. If the surface of the lithium metal is coated and modified by a polymer, the physical strength or chemical characteristics of the coating are utilized to relieve the generation of lithium dendrites. However, due to the limited insulation and strength of the coating, it is still difficult to effectively suppress the generation of lithium dendrites at high current density and for long-term lithium deposition.
4) And (4) alloying the negative electrode. Lithium deposited during charging forms intermetallic compounds (lithiated compounds) with silicon, aluminum, tin, boron and the like to avoid the formation of lithium dendrites, but the intermetallic compounds formed by lithium and silicon, aluminum, tin, boron and the like expand unevenly in volume by times and are easy to break and pulverize. Lithium and magnesium form a plastic solid solution, and the lithium and magnesium do not break, but the lithium magnesium alloy negative electrode in the prior art has insufficient effect of inhibiting lithium dendrite and is not resistant to air oxidation, thereby restricting practical application.
Therefore, a method which can effectively avoid pulverization of a metallic lithium negative electrode, inhibit growth of lithium dendrites and guarantee cycle stability and is suitable for industrial production in an air environment for a long time is not found at present.
Disclosure of Invention
In view of the above problems in the prior art, the present invention aims to provide a multi-element lithium magnesium alloy negative electrode material for a secondary battery (also referred to as lithium magnesium alloy negative electrode material or Li-Mg-M negative electrode in the present invention), and aims to provide a lithium magnesium alloy negative electrode material having oxidation resistance, activity and long-term cycling stability.
The second objective of the invention is to provide a modified electrolyte adapted to the multi-element lithium magnesium alloy negative electrode material, and the invention aims to provide an electrolyte which can be adapted to the multi-element lithium magnesium alloy negative electrode material, can generate cooperativity, and can significantly improve the cycle stability of a lithium secondary battery.
The third purpose of the invention is to provide an application method of the modified electrolyte adapted to the multi-element lithium magnesium alloy negative electrode material and the multi-element lithium magnesium alloy negative electrode material for adaptation and combination to obtain a lithium secondary battery.
The fourth purpose of the invention is to provide a lithium secondary battery comprising the modified electrolyte and the multi-element lithium-magnesium alloy negative electrode material, and the aim is to remarkably improve the cycle performance of the obtained lithium secondary battery through the cooperation of the electrolyte and the negative electrode.
A multi-element lithium-magnesium alloy negative electrode material (foil tape) for a secondary battery comprises a lithium-magnesium solid solution matrix and a Li-M intermetallic compound;
m is one or more elements of calcium, strontium, barium, yttrium, lanthanum, cerium, aluminum, gallium, indium, silicon, tin, antimony and bismuth;
the content of the magnesium is 15-70 at.%, and the total content of the M element is 0.01-5 at.%.
Based on long-term research and exploration on the lithium alloy negative electrode, the inventor finds that certain contradiction exists between the air resistance stability and the electrochemical activity of the lithium alloy negative electrode material, and the air resistance stability is the requirement of the lithium alloy negative electrode on extremely low cost and high efficiency industrial production and application. In order to solve the industrial problem that the lithium alloy cathode material is difficult to take air-resistant stability and electrochemical activity into consideration, the invention innovatively provides the multi-element lithium-magnesium alloy cathode material, which takes a lithium-magnesium solid solution with high magnesium content as a matrix to avoid air oxidation; the polarization is reduced by utilizing the activation effect of the Li-M intermetallic compound, and the lithium-ion battery has high electrochemical activity; meanwhile, the magnesium-lithium solid solution and the intermetallic compound porous skeleton formed in the charging and discharging processes of the alloy cathode can improve the deposition of lithium, greatly reduce the volume expansion and obviously improve the cycle stability.
According to the technical scheme of the lithium-magnesium alloy cathode material, magnesium is used as a main element in the industry, and the fact that the atomic content of magnesium is strictly controlled to be 15-70 at.% (converted into 38-88 wt.%), the air oxidation resistance effect can be remarkably improved, and the stability of the lithium-magnesium alloy cathode material in the air atmosphere is improved, so that a good basis is provided for production, assembly and application under conventional conditions.
The invention discovers that the problem of air oxidation resistance of the lithium negative electrode can be unexpectedly solved and the charge-discharge cycle stability of the lithium negative electrode can be improved by taking a lithium-magnesium solid solution as a matrix, taking magnesium as a main element and controlling the content of magnesium to be 15-70 at.%. The inventor researches and discovers that the content of magnesium is lower than 15 at.%, the multielement lithium magnesium alloy is easy to oxidize and unstable in the air, and the porous matrix of the negative electrode has low strength and low cycling stability during charge-discharge cycling after the secondary battery is assembled. The content of magnesium is higher than 70 at.%, and the lithium-magnesium alloy has large rolling processing deformation resistance and large charge-discharge polarization.
Preferably, the magnesium content is 15 to 50 at.%. Under such preferable conditions, it contributes to obtaining a negative electrode of good activity and excellent cyclability while ensuring stability against air.
The invention innovatively takes lithium-magnesium solid solution as a matrix, and further cooperates with the Li-M metal compound on the basis of strictly limiting the magnesium content, forms a magnesium-lithium solid solution and Li-M intermetallic compound porous network structure by utilizing the charging and discharging process, and further cooperates with the strict control of the proportion of Mg and M elements, so that the activity is further obviously improved, the polarization voltage is obviously reduced, and the cycling stability is improved under the condition of ensuring the air-resistant stability. Research shows that the charge-discharge polarization of the negative electrode is large in the absence of Li-M intermetallic compounds; in addition, the content of M needs to be controlled to be 0.01-5 at.%, and when the content of M exceeds 5 at.%, the rolling processing deformation resistance is large, the cracking is easy, and the volume expansion is large and the pulverization is easy during circulation; below 0.01 at.%, activation was not significant.
The multi-element lithium-magnesium alloy negative electrode material further controls the type of an M element on the basis of the necessary magnesium-lithium solid solution matrix, and is favorable for further improving the cycle performance.
Preferably, M is at least one element of calcium, strontium, barium, yttrium, lanthanum, cerium, gallium, indium, silicon, antimony and bismuth; more preferably at least one of calcium, strontium, barium, yttrium, lanthanum, cerium, gallium, indium, silicon, and antimony.
The invention also comprises a preparation method of the multi-element lithium-magnesium alloy negative electrode material for the secondary battery, which comprises the following steps:
(1) heating the metallic lithium to 200-800 ℃ in an environment with a dew point not higher than-50 ℃ and an oxygen content not higher than 10ppm, so that the metallic lithium is in a molten state; the environmental conditions are to avoid the change of the lithium metal and the moisture or oxygen in the air;
(2) adding magnesium and M element into molten metal lithium according to the atomic content ratio, preserving heat for 5-15 min, and uniformly mixing to form a molten alloy state;
(3) and (3) cooling the product obtained in the step (2) to room temperature, and rolling the product into a foil tape.
According to the preparation method, after magnesium and M alloy elements are added into molten metal lithium, the metal lithium can play a role of a cosolvent, so that the metal lithium, the magnesium and the M alloy elements can be well molten and mixed, and the alloy elements are uniformly distributed in the lithium to form molten alloy. In the process of solidifying and cooling the molten alloy, a lithium-magnesium solid solution matrix and an intermetallic compound communication network framework structure of lithium and alloy elements are formed. The foil tape obtained by the invention has good stability under the air condition, can assemble batteries under the air condition, and provides good conditions for industrial scale-up production.
The invention also provides a modified electrolyte adaptive to the multi-element lithium-magnesium alloy cathode material for the secondary battery, which comprises an ester solvent, a conductive lithium salt, an organic additive A and an inorganic additive B;
the organic additive A is at least one of organic matters with structural formulas of formula 1, formula 2 and formula 3;
the inorganic additive B is nitrate of alkali metal and alkaline earth metal.
The invention innovatively discovers that the modified electrolyte can be matched with the multi-element lithium-magnesium alloy cathode material, can generate complex surface conversion with the special cathode in the charging and discharging process, and can synergistically improve the cycle performance of the lithium secondary battery.
Preferably, the ester solvent is one or more selected from Propylene Carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC), and is preferably a mixed solution of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC).
The conductive lithium salt is one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide, lithium difluorophosphate, lithium bifluorosulfonimide, lithium bisoxalato borate and lithium difluorooxalato borate;
the inorganic additive B is one or more of lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate and barium nitrate.
Preferably, the concentration of lithium ions in the conductive lithium salt in the ester solvent is 0.5 to 2M/L (0.5 to 2mol/L), preferably 1M/L.
Preferably, the organic additive A is added in an amount of 5-35% by volume of the ester solvent.
Preferably, the concentration of the inorganic additive B is 0.01 to 0.4M/L.
The application of the modified electrolyte is to adapt the modified electrolyte and the multi-element lithium-magnesium alloy negative electrode material to assemble a lithium secondary battery. Namely, the special negative electrode and the special modified electrolyte are assembled into the same battery system at the same time to form the cooperatively matched lithium secondary battery.
The invention also provides a lithium secondary battery, which comprises a positive electrode, a negative electrode, electrolyte for soaking the positive electrode and the negative electrode, and a diaphragm for separating the positive electrode from the negative electrode, wherein the negative electrode is the multi-element lithium magnesium alloy negative electrode material, and the electrolyte is the modified electrolyte.
According to the lithium secondary battery, the problems of low coulombic efficiency, short service life and the like caused by pulverization and dendritic crystals of the metal lithium negative electrode material in the battery circulation process are effectively solved through the matching cooperation of the electrolyte and the multi-element lithium magnesium alloy negative electrode material, the polarization is small, and the lithium secondary battery is suitable for air environment industrial production.
In the lithium secondary battery, the materials such as the anode, the diaphragm and the like can be any materials known in the field of lithium secondary batteries. The positive electrode, the negative electrode, the modified electrolyte and the diaphragm can be assembled into the lithium secondary battery by adopting the conventional method.
Has the advantages that:
(1) the addition of the alloy elements in the lithium-magnesium metal alloy negative electrode material provided by the invention forms a lithium-magnesium solid solution matrix and an intermetallic compound of lithium and the alloy elements, lithium dissolved out from the lithium-magnesium solid solution matrix is converted into a magnesium-lithium solid solution during discharging, and the magnesium-lithium solid solution and the intermetallic compound jointly form a porous communicated framework, and metal lithium is deposited in the magnesium-lithium solid solution and the intermetallic compound porous framework during charging, so that the volume deformation of the negative electrode material is not caused during the charging and discharging circulation process, the actual surface area of a lithium negative electrode is greatly increased, the uneven degree of surface lithium deposition is reduced, and the fracture of an SEI film on the surface of lithium. In addition, compared with the interconnected network framework formed by the magnesium-lithium solid solution and the intermetallic compound alone, the porous interconnected network framework of the magnesium-lithium solid solution and the intermetallic compound has the following advantages:
(2) the magnesium-lithium solid solution has good plasticity, is used as a bonding agent for intermetallic compound (multi-lithiation) particles, reduces the brittleness of an intermetallic compound (multi-lithiation) particle network framework, and avoids the fragmentation and pulverization of the framework; pores formed by dissolving lithium in the magnesium-lithium solid solution phase are fine, the specific surface area is high, and lithium can be uniformly deposited on the surface of the magnesium-lithium solid solution phase; the lithium-magnesium solid solution alloy with high magnesium content is resistant to air oxidation, can be rolled into a foil tape in an air environment and assembled into a lithium battery, and is suitable for industrial production in the air environment; on the other hand, the interface electrochemical activity of the intermetallic compound and the lithium-magnesium solid solution matrix is high, and the lithium-magnesium solid solution alloy with high magnesium content has high electrochemical activity and can be charged and discharged preferentially; in addition, the intermetallic compound (multi-lithiation) particles can enhance the strength of the magnesium-lithium solid solution porous network, keep the shape of the porous framework from deforming in the charge-discharge cycle process and improve the cycle stability.
(3) The alloy elements in the multi-element lithium magnesium alloy cathode material and the addition of the organic additive A and the nitrate in the adaptive electrolyte can adjust the surface film component of the metal lithium from the internal and external aspects, regulate and control the surface electric field and the charge distribution of the metal lithium in the electrolyte, ensure that the lithium is uniformly deposited on the surface, and effectively inhibit the growth of lithium dendrites.
(4) The multielement lithium-magnesium alloy cathode material provided by the invention can be matched with the organic additive A and the nitrate in the electrolyte, so that the surface film component of the metal lithium can be adjusted, the film thickness can be controlled, and the polarization of the battery can be reduced.
(5) The multielement lithium-magnesium alloy cathode material and the adaptive electrolyte thereof provided by the invention are combined and applied to a lithium battery, so that the coulomb efficiency and the cycle life of the battery can be effectively improved.
(6) When the multi-element lithium-magnesium alloy cathode material and the adaptive electrolyte thereof provided by the invention are used for a metal lithium secondary battery, the cathode material can adopt a conventional lithium ion battery cathode material, an organic cathode material, a sulfur-containing cathode material and the like, and a special cathode material does not need to be additionally prepared.
Drawings
FIG. 1 is a graph showing the relationship between the time required for complete blackening of the surface of lithium magnesium (Li-Mg) and Li-Mg-M multi-element lithium magnesium alloy flakes in the air and the magnesium content (Li-Mg-M multi-element lithium magnesium alloy: when the magnesium content is 5 at.%, 10 at.%, and 15 at.%, M is Ca; when the magnesium content is 20 at.%, M is Al; when the magnesium content is 30 at.%, M is La; when the magnesium content is 50 at.%, M is Ba; when the magnesium content is 70 at.%, M is Y);
FIG. 2 shows the discharge performance of example 6 case 7 lithium nickel cobalt manganese oxide/Li-Mg-La cell.
Detailed Description
The present invention is further illustrated by the following specific examples, but the scope of the invention is not limited to the following examples.
Example 1
Heating metal lithium to 600 ℃ in an environment with a dew point not higher than-50 ℃ and an oxygen content not higher than 10ppm to enable the metal lithium to be in a molten state, respectively adding magnesium with different contents (shown in table 1) into the metal lithium, preserving the heat for 15min, uniformly mixing the metal lithium and the magnesium to form a molten alloy state, and then cooling the molten alloy state to room temperature to prepare the corresponding lithium-magnesium alloy material.
Heating metal lithium to 600 ℃ in an environment with a dew point of not higher than-50 ℃ and an oxygen content of not higher than 10ppm to enable the metal lithium to be in a molten state, respectively adding magnesium and other alloy elements with different contents (when the magnesium content is 5 at.%, 10 at.%, and 15 at.%, M is Ca; when the magnesium content is 20 at.%, M is Al; when the magnesium content is 30 at.%, M is La; when the magnesium content is 50 at.%, M is Ba; and when the magnesium content is 70 at.%, M is Y, the specific components are shown in Table 1), preserving heat for 15min, uniformly mixing to form a molten alloy state, and then cooling to room temperature to obtain the corresponding Li-Mg-M multi-element lithium magnesium alloy material.
And punching the two alloys into small round sheets with the diameter of 16mm in a glove box filled with argon in an anhydrous and oxygen-free manner, wherein the surfaces of the small round sheets are smooth and silvery white, then placing the alloy sheets in air with the temperature of 25 ℃ and the relative humidity of 50-60%, observing the gradual blackening process of the surfaces of the alloy sheets, and recording the time required for completely blackening the surfaces of the alloy sheets.
FIG. 1 is a graph showing the relationship between the time required for the surface of two types of alloy flakes to completely blacken in air and the magnesium content. As can be seen from the graph, for the lithium magnesium (Li-Mg) alloy, when the magnesium content in the alloy is increased, the passivation effect of the alloy surface is enhanced, the time required for the alloy flake surface to be completely blackened is increased, and when the magnesium content in the alloy is less than 15 at.%, the lithium magnesium alloy is easily oxidized and unstable in air; when the magnesium content in the alloy reached 15 at.%, the time required for the alloy flake surface to completely blacken was about 4 hours. For Li-Mg-M multi-element alloy, the time for completely blackening the surface of the alloy sheet and the change trend of the magnesium content are the same as those of the lithium-magnesium alloy, and the influence of the addition of the M element on the time for completely blackening the surface of the alloy is small. The results show that the lithium-magnesium solid solution alloy with high magnesium content and the Li-Mg-M multi-element alloy are resistant to air oxidation, can be rolled into a foil tape in an air environment and assembled into a lithium battery, and are suitable for industrial production in the air environment.
Example 2
In the absence of waterIn a glove box filled with argon in an oxygen-free manner, the lithium-magnesium alloy with different magnesium contents prepared in example 1 is punched into small round pieces with the diameters of 16mm as positive and negative electrodes, 1mol/L LiPF6 is dissolved in EC (electro magnetic compatibility)/DME (volume ratio 1:1:1) as electrolyte, Celgard 2325 with the diameter of 19mm as a diaphragm is packaged in a CR2032 button battery case, constant-current charge and discharge tests are carried out at constant temperature of 25 ℃ by using a blue-electricity battery test system, and the current density is 2mA/cm2The results of the tests are shown in Table 1, with charge and discharge being 2 hours each.
Comparative example 1
In a glove box filled with argon in an anhydrous and oxygen-free manner, a metal lithium foil is punched and cut into small round pieces with the diameter of 16mm as positive and negative poles, 1mol/L LiPF6 is dissolved in EC: EMC: DME (volume ratio of 1:1:1) as electrolyte, Celgard 2325 with the diameter of 19mm is used as a diaphragm and is packaged in a CR2032 button battery case, a constant-current charge-discharge test is carried out at constant temperature of 25 ℃ by using a blue-electricity battery test system (same as example 2), the current density is 2mA/cm2, the charge-discharge time is 2 hours respectively, and the test results are shown in Table 1
Example 3
Heating the metallic lithium to 600 ℃ in an environment with a dew point not higher than-50 ℃ and an oxygen content not higher than 10ppm to enable the metallic lithium to be in a molten state, respectively adding magnesium and other alloy elements (shown in table 1) with different contents, preserving heat for 15min, uniformly mixing to form a molten alloy state, and then cooling to room temperature to prepare the corresponding multi-element lithium-magnesium alloy material. In a glove box filled with argon in an anhydrous and oxygen-free manner, the material is punched into small round sheets with the diameter of 16mm as positive and negative electrodes, and 1mol/L LiPF6Dissolving in EC (ElectroMedia electronics) EMC (DME) (volume ratio 1:1:1) as electrolyte, packaging Celgard 2325 with diameter of 19mm as diaphragm in CR2032 button cell case, and performing constant current charge and discharge test at constant temperature of 25 deg.C by using blue cell test system (same as example 2), wherein current density is 2mA/cm2The charge and discharge time is 2 hours each, the test results are shown in Table 1,
from the results, only high-content magnesium is added, the electrochemical activity of the alloy electrode is reduced due to the passivation effect of magnesium, the polarization voltage is very high, and after a proper amount of other alloy elements are added, the formed intermetallic compound and the lithium-magnesium solid solution matrix have high interface electrochemical activity and can be charged and discharged preferentially, so that the lithium-magnesium solid solution alloy with high magnesium content has high electrochemical activity, and the polarization voltage is basically reduced to the level of a pure lithium electrode. Meanwhile, when the magnesium content is higher than 15 at.%, the addition of magnesium and other alloying elements increases the stable cycle time of the battery, as compared with comparative example 1; when the magnesium content is less than 15 at.%, the addition of magnesium and alloying elements does not significantly increase the battery stabilization cycle time, comparable to that of a pure lithium electrode battery.
Table 1 test results of comparative example 1, example 2 and example 3
Note: the stabilization cycle time is the time required for the metal electrode material to change (dendrite, pulverization, polarization, etc.) resulting in an increase in polarization voltage or cell failure.
Although the magnesium-lithium solid solution can improve the air oxidation resistance based on example 1, table 1 shows that the polarization voltage of the magnesium-lithium solid solution is significantly increased and the activity is low (experiments No. 1 to 7 in table 1 show); however, on the basis of the magnesium-lithium solid solution, by adding not more than 5 at.% of M (M is one or more of calcium, strontium, barium, yttrium, lanthanum, cerium, aluminum, gallium, indium, silicon, tin, antimony and bismuth), the problem of activity reduction caused by the magnesium-lithium solid solution can be remarkably solved, polarization is remarkably reduced, and the cycle stability is improved (No. 2-7 is compared with No. 8-22); it is further found that M is alkaline earth metal and rare earth metal, especially aluminum, gallium, indium, silicon, tin, antimony and other metals, and compared with some transition metals, the metal can still obtain better cycle performance under the condition of adding a small amount. In addition, the content of Mg needs to be strictly controlled between 15 to 70 at.%, and too high or too low is not favorable for performance (8 to 10 comparison).
Example 4
In a glove box filled with argon in an anhydrous and oxygen-free manner, a metal lithium foil sheet is punched and cut into small sheets with the diameter of 16mm as positive and negative electrodes, and 1mol/L LiPF is added6Dissolving in EC (EC), EMC and DME (volume ratio is 1:1:1), adding organic additives A with different volume contents and nitrates with different concentrations as electrolyte, taking Celgard 2325 with diameter of 19mm as a diaphragm, packaging in a CR2032 button battery case, and performing constant current charge and discharge test at constant temperature of 25 ℃ by using a blue battery test system with current density of 2mA/cm2The results of the tests are shown in Table 2, with charge and discharge being carried out for 2 hours each. The addition of organic additive a and nitrate increased the stable cycle time of the battery compared to comparative example 1.
Table 2 test results of example 4
The reference of the addition volume ratio of the organic additive A is a mixed solvent. The stable cycle time is the time required for the metal electrode material to change (dendrite, pulverization, polarization, etc.) and cause an increase in polarization voltage or battery failure.
Based on table 2, the cycle performance can be synergistically improved by the organic additives and the inorganic additives.
Example 5
In a glove box filled with argon in an anhydrous and oxygen-free manner, different multi-element lithium-magnesium alloy materials prepared in example 3 are punched into small round sheets with the diameter of 16mm as positive and negative electrodes, and 1mol/L LiPF6Dissolving in EC (electro magnetic compatibility): EMC (DME) (volume ratio 1:1:1), adding organic additives A with different volume contents and nitrates with different concentrations as electrolyte, taking Celgard 2325 with the diameter of 19mm as a diaphragm, packaging in a CR2032 button battery case, and performing constant-current charge and discharge test at constant temperature of 25 ℃ by using a blue battery test system (same as example 1) with the current density of 2mA/cm2Charging and discharging for 2 hours each, measuringThe test results are shown in Table 3. From the results, when the magnesium content is higher than 15 at.%, the combined action of the multi-element lithium-magnesium alloy negative electrode and the adaptive electrolyte can greatly improve the stable cycle time of the battery; when the magnesium content is less than 15 at.%, the addition of magnesium and alloying elements does not significantly increase the battery stabilization cycle time.
Table 3 test results of example 5
The reference of the addition volume ratio of the organic additive A is a mixed solvent.
The stable cycle time is the time required for the metal electrode material to change (dendrite, pulverization, polarization, etc.) and cause an increase in polarization voltage or battery failure.
Although the addition of the organic additive A alone can improve the cycle performance to some extent, the improvement effect is significantly lower than that of the organic additive A and the nitrate which are added together (cases 12 and 13 are compared).
The multielement cathode and the modified electrolyte have obvious cooperativity, and the cycle performance can be improved in multiples.
M is alkaline earth metal, rare earth metal and other metals, particularly aluminum, gallium, indium, silicon, tin, antimony and other metals, and better cycle performance can be obtained under the condition of adding a small amount of transition metal compared with certain transition metals (other cases are compared with 9/16).
Example 6
In a glove box filled with argon in a water-free and oxygen-free manner, the different multi-element lithium-magnesium alloy materials prepared in example 3 were punched into small round sheets with the diameter of 16mm as the negative electrode,1mol/L LiPF6Dissolving in EC (electro magnetic compatibility): DME (volume ratio is 1:1:1), adding organic additives A with different volume contents and nitrates with different concentrations as electrolyte, taking Celgard 2325 with the diameter of 19mm as a diaphragm, taking a nickel-cobalt lithium manganate pole piece with the diameter of 16mm as a positive pole, packaging in a CR2032 button battery case, and carrying out a multiplying power charge-discharge test at a constant temperature of 25 ℃ by using a blue battery test system, wherein the charge-discharge multiplying power is 0.2C, the charge voltage is 4.2v, the discharge voltage is 2.5v, and the test results are shown in Table 4. From the results, when the magnesium content in the multielement lithium magnesium alloy negative electrode is lower than 15 at.%, the strength of the negative electrode porous matrix is low during the charge and discharge cycles of the battery, so that the cycle stability is low; when the content of magnesium is higher than 15 at.%, the charge-discharge cycle stability of the battery is greatly improved, wherein when M elements are calcium, strontium, barium, yttrium, lanthanum, cerium, gallium, indium, silicon, antimony and bismuth, the charge-discharge cycle frequency of the battery can reach more than 1000.
Table 4 test results of example 6
The reference of the addition volume ratio of the organic additive A is a mixed solvent. The cycle number is the charge and discharge number of capacity fading to 80%.
Claims (9)
1. The multi-element lithium-magnesium alloy negative electrode material for the secondary battery is characterized by comprising a lithium-magnesium solid solution matrix and a Li-M intermetallic compound;
m is one or more elements of calcium, strontium, barium, yttrium, lanthanum, cerium, aluminum, gallium, indium, silicon, tin, antimony and bismuth; the content of the magnesium is 15-70 at.%, and the total content of M elements is 0.01-5 at.%;
wherein the lithium-magnesium solid solution matrix and the intermetallic compound of lithium and alloy elements form a connected network framework structure.
2. The multi-element lithium magnesium alloy negative electrode material for a secondary battery according to claim 1, wherein the magnesium content is 15 to 50 at.%.
3. The multi-element lithium magnesium alloy negative electrode material for secondary batteries according to claim 1,
m is at least one of calcium, strontium, barium, yttrium, lanthanum, cerium, gallium, indium, silicon and antimony.
4. The method for preparing the multi-element lithium-magnesium alloy negative electrode material for the secondary battery according to any one of claims 1 to 3, comprising the following steps:
(1) heating the metallic lithium to 200-800 ℃ in an environment with a dew point not higher than-50 ℃ and an oxygen content not higher than 10ppm, so that the metallic lithium is in a molten state;
(2) adding magnesium and M element into molten metal lithium according to the atomic content ratio, preserving heat for 5-15 min, and uniformly mixing to form a molten alloy state;
(3) and (3) cooling the product obtained in the step (2) to room temperature, and rolling the product into a foil tape.
5. A modified electrolyte adapted to the multi-element lithium-magnesium alloy negative electrode material for the secondary battery according to any one of claims 1 to 3 or the multi-element lithium-magnesium alloy negative electrode material for the secondary battery prepared by the preparation method according to claim 4, which is characterized by comprising an ester solvent, a conductive lithium salt, an organic additive A and an inorganic additive B;
the organic additive A is at least one of organic matters with structural formulas of formula 1, formula 2 and formula 3;
the inorganic additive B is nitrate of alkali metal and nitrate of alkaline earth metal.
6. The modified electrolyte of claim 5,
the ester solvent is one or more of ethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate and methyl ethyl carbonate;
the conductive lithium salt is one or more of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bistrifluoromethylsulfonyl imide, lithium difluorophosphate, lithium bifluorosulfonimide, lithium bisoxalato borate and lithium difluorooxalato borate;
the inorganic additive B is one or more of lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate and barium nitrate.
7. The modified electrolyte of claim 6, wherein the concentration of lithium ions in the conductive lithium salt in the ester solvent is 0.5 to 2M/L; the addition amount of the organic additive A is 5-35% of the volume of the ester solvent; the concentration of the inorganic additive B is 0.01-0.4M/L.
8. The use of the modified electrolyte according to any one of claims 5 to 7, wherein the modified electrolyte is adapted to the multi-element lithium magnesium alloy negative electrode material according to any one of claims 1 to 3 or the multi-element lithium magnesium alloy negative electrode material prepared by the preparation method according to claim 4 to assemble a lithium secondary battery.
9. A lithium secondary battery comprises a positive electrode, a negative electrode, electrolyte for soaking the positive electrode and the negative electrode, and a diaphragm for separating the positive electrode from the negative electrode, and is characterized in that the negative electrode is the multi-element lithium magnesium alloy negative electrode material of any one of claims 1 to 3 or the multi-element lithium magnesium alloy negative electrode material prepared by the preparation method of claim 4;
the electrolyte is the modified electrolyte as claimed in any one of claims 5 to 7.
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| CN111916721A (en) * | 2020-08-17 | 2020-11-10 | 哈尔滨工业大学 | Magnesium-sulfur secondary battery with magnesium-lithium alloy as negative electrode |
| CN113948693A (en) * | 2021-09-23 | 2022-01-18 | 西安交通大学 | Lithium indium alloy cathode material for lithium battery and preparation method thereof |
| CN113823840A (en) * | 2021-10-29 | 2021-12-21 | 中南大学 | Electrolyte for lithium metal cathode |
| CN114606418B (en) * | 2022-01-26 | 2022-09-09 | 广东工业大学 | Mg-Bi-In-Y anode material of magnesium air battery and preparation method and application thereof |
| CN114709494A (en) * | 2022-03-31 | 2022-07-05 | 青岛大学 | Water system zinc-double-halogen battery based on multi-electron conversion reaction and electrolyte thereof |
| CN115036470A (en) * | 2022-04-22 | 2022-09-09 | 青岛九环新越新能源科技股份有限公司 | High-magnesium-content lithium-magnesium alloy/copper composite foil negative electrode for inhibiting growth of lithium dendrite and preparation method thereof |
| CN114864866A (en) * | 2022-06-21 | 2022-08-05 | 合肥国轩高科动力能源有限公司 | Lithium-magnesium composite cathode, preparation method thereof, lithium-sulfur battery prepared by lithium-magnesium composite cathode and all-solid-state battery |
| EP4350796A1 (en) * | 2022-08-31 | 2024-04-10 | LG Energy Solution, Ltd. | Negative electrode for a lithium secondary battery, a method for preparing the same and a lithium secondary battery comprising the same |
| CN115786751B (en) * | 2022-11-15 | 2024-01-19 | 重庆天齐锂业有限责任公司 | Smelting method of lithium-magnesium-silicon alloy |
| CN117701928A (en) * | 2023-11-28 | 2024-03-15 | 西安工业大学 | Micro-nano LiSr alloy composite material, preparation method and application thereof |
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