Lithium metal electrode material modified by a multifunctional interface layer, its preparation method and application

Abstract

The present invention discloses a lithium metal electrode material modified with a multifunctional interface layer, its preparation method and application. The present invention uses a simple one-step hot pressing method to prepare a metal lithium composite electrode material modified with a strontium nitride modified multifunctional interface layer. The thickness of the multifunctional interface layer of the composite electrode material is about 5 to 10 microns, and includes a fast ion conductor lithium nitride, a lithium strontium alloy lithiumophilic layer, and a strontium nitride powder buffer layer, which can effectively improve the deposition of lithium ions, relieve the growth of dendrites, and at the same time can also provide some space for lithium deposition to relieve the problem of the disconnection of the polymer electrolyte interface. The metal lithium composite electrode material modified with the multifunctional interface layer prepared by the present invention as the negative electrode of the battery can effectively improve the Coulomb efficiency and cycle life of the battery, improve the electrochemical performance of the battery, and has certain application potential in the high energy density lithium metal secondary battery system.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal composite anode materials, and specifically relates to the preparation of a composite electrode material for lithium metal and its application as an anode material for lithium metal solid-state batteries. Background Art

[0002] Lithium-ion batteries have been playing an important role in the energy storage field in the past three decades. However, the growing market demand has put forward higher requirements for the energy density and safety performance of the batteries. At the same time, the energy density of current commercial liquid lithium-ion batteries has approached the theoretical value, and their flammable organic electrolytes also pose a risk of combustion. Therefore, solid-state batteries have attracted extensive attention from researchers due to their high safety and potential to match lithium metal anodes. Lithium metal is known as the "holy grail" electrode because of its ultra-high specific capacity (3860 mAh / g), the lowest electrochemical potential for hydrogen (-3.04 V vs standard hydrogen electrode), and relatively low density, and it is currently the most promising anode material for high-energy batteries. Therefore, solid-state lithium metal batteries are expected to be commercialized as the next generation of high-energy density battery systems. Among the main development paths of solid electrolytes such as sulfides, oxides, and polymers, polymer-based solid electrolytes are considered to be the most commercially promising direction due to their low cost, easy manufacturing, and strong plasticity.

[0003] However, the uncontrollable growth of lithium dendrites and the problem of solid electrolyte interface contact have become the biggest obstacles to the commercial application of solid-state lithium metal batteries, and their specific manifestations are as follows: (1) The uncontrollable growth of lithium dendrites, accompanied by the fracture of dendrites and the accumulation of dead lithium, corresponds to electrode pulverization, volume expansion, and a decrease in the Coulombic efficiency of the battery. (2) After the dendrites of the lithium metal anode are peeled off, dendritic spaces will be left at the interface on the negative electrode side of the polymer-based solid electrolyte. After long-term cycling, the problem of interface disconnection will intensify, resulting in serious battery polarization and rapid capacity decay. Therefore, for the problems of dendrite growth and interface disconnection, the lithium metal electrode needs to be surface-modified to alleviate the impact on battery performance.

[0004] Therefore, the present invention designs a lithium metal electrode material with a multifunctional interface modification by adding strontium nitride to the original lithium metal sheet and preparing it by a one-step hot pressing method to improve the electrochemical performance of solid-state lithium metal batteries. Summary of the Invention

[0005] The object of the present invention is to provide a strontium nitride-modified multifunctional interfacial layer-modified lithium metal electrode material, its preparation method and application, aiming at the problems of dendrite growth of lithium metal anodes and interfacial contact on the negative electrode side of polymer-based solid electrolytes. The material prepared by this method, as the negative electrode material of a lithium metal battery, has the advantages of inhibiting lithium dendrite growth, alleviating the loss of contact on the negative electrode side of the polymer-based solid electrolyte, and simple preparation process.

[0006] The preparation method of the multifunctional interfacial layer-modified lithium metal electrode material of the present invention includes the following steps:

[0007] (1) Uniformly cover the surface of the lithium metal strip with strontium nitride powder;

[0008] (2) Mechanically press the lithium metal treated above;

[0009] (3) Perform high-temperature melting treatment on the pressed lithium metal composite material;

[0010] (4) After the material is cooled, the multifunctional interfacial layer-modified lithium metal electrode material can be obtained.

[0011] The following are the preferred technical solutions of the present invention:

[0012] In step (1), for the doped strontium nitride powder, the added mass ratio is strontium nitride: lithium metal = 0.5:1 to 3:1, preferably 0.5:1 to 2:1.

[0013] In step (2), the pressure range of the mechanical pressing is 2 - 10 MPa, further preferably 3 - 5 Mpa.

[0014] In step (2), the time of mechanical pressing is 2 min - 10 min, preferably 5 min.

[0015] In step (3), the temperature of the high-temperature melting treatment is 200°C - 450°C, preferably 250°C - 400°C.

[0016] In step (3), the time of the high-temperature melting treatment is 0.5 min - 5 min, preferably 1 min.

[0017] In step (3), the implementation process of the high-temperature melting treatment: Place the treated solid lithium metal on a heating table at 250°C - 400°C for 5 min - 10 min to melt it into a liquid state. The strontium nitride powder previously pressed on the surface of the lithium metal will undergo a chemical reaction with the molten lithium metal.

[0018] In step (4), the room-temperature cooling time of the material is 1 h - 5 h, preferably 2 h - 3 h.

[0019] Application of a lithium metal electrode material modified with a 5-10 μm multifunctional interfacial layer as a lithium metal negative electrode material. The strontium nitride modified lithium metal composite electrode consists of a heat treatment layer and a strontium nitride powder layer. The heat treatment layer is composed of lithium nitride and a lithium-strontium alloy obtained by reacting metallic lithium with strontium nitride powder at high temperature. The lithium metal composite electrode prepared by this method has the advantages of inhibiting dendrite growth and alleviating interfacial disconnection, and can be used as the negative electrode material of a metal lithium battery, having broad application prospects in fields such as small mobile electronic devices, electric vehicles, solar power generation, and aerospace.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The strontium nitride modified multifunctional interfacial layer modified lithium metal composite electrode prepared by the hot pressing method in one step in the present invention consists of a heat treatment layer and a strontium nitride powder layer. The heat treatment layer is composed of lithium nitride and a lithium-strontium alloy obtained by reacting metallic lithium with strontium nitride powder. The two-layer structure corresponds to different functions. The fast ion conductor lithium nitride in the heat treatment layer has the effect of accelerating the interfacial lithium ion reaction kinetics, while the lithium-strontium alloy as a lithiumophilic layer can guide the deposition of lithium ions. The combination of the two can improve the deposition of lithium ions, thereby alleviating the growth of dendrites; and the unreacted strontium nitride powder layer serves as a preset rigid skeleton, while guiding the shape of lithium deposition, it can also provide some space for lithium deposition to buffer the growth of dendrites and alleviate the interfacial disconnection of the polymer electrolyte. Therefore, using this electrode material as the negative electrode of the battery can effectively improve the Coulomb efficiency and cycle life of the battery, and at the same time reducing the electrode polarization can further improve the cycle stability of the battery.

[0022] In addition, the preparation method described in the present invention has the advantages of simple principle, high preparation efficiency, and easy control. Specifically, only by simply hot pressing the metallic lithium after adding the active particles, a lithium metal negative electrode with a multifunctional interface modification can be prepared in one step through a thermal reaction.

[0023] The present invention uses the hot pressing method to prepare a strontium nitride modified lithium metal composite electrode material in one step. The multifunctional interfacial layer of this composite electrode material includes a fast ion conductor lithium nitride, a lithium-strontium alloy lithiumophilic layer, and a strontium nitride powder buffer layer, which can effectively improve the deposition of lithium ions, alleviate the growth of dendrites, and at the same time can also provide some space for lithium deposition to alleviate the problem of interfacial disconnection of the polymer electrolyte. Improve the cycle stability and Coulomb efficiency of the battery. Therefore, the material prepared by the present invention can effectively improve the electrochemical performance of the lithium metal negative electrode and has certain application potential in a high energy density lithium metal secondary battery system. Description of the Drawings

[0024] Figure 1Cross-sectional scanning electron microscope image of the lithium metal composite electrode modified with the multifunctional interfacial layer prepared in Example 1;

[0025] Figure 2 Surface scanning electron microscope image of the lithium metal composite electrode modified with the multifunctional interfacial layer prepared in Example 1

[0026] Figure 3 Full cell cycling performance graph of the lithium metal composite electrode (LSN) modified with the multifunctional interfacial layer prepared in Example 1 and the lithium metal electrode (Li) prepared in Comparative Example 1 when paired with a lithium iron phosphate (LFP) polymer solid state battery. Detailed implementation manners

[0027] The effectiveness of the present invention will be described in detail below in combination with examples and comparative examples.

[0028] Example 1

[0029] In an argon glove box (both the water and oxygen content < 0.1 ppm), 1.5 mg of strontium nitride (Sr3N2) powder was evenly covered on the surface of the lithium sheet, and the covered area was a circle with a diameter of 10 mm, that is, the mass ratio of strontium nitride to metallic lithium added was 1:1. Then, a tablet press was used to press the lithium sheet, the pressure was set at 3 MPa, and the pressing time was 5 min. Then, the pressed lithium sheet was transferred to a heating table at 250 °C, heated at high temperature for 1 min, and after the molten reaction, the metallic lithium was cooled at room temperature of 25 °C for 1.5 h, and thus the metal lithium composite electrode material modified with the multifunctional interfacial layer modified by strontium nitride was obtained.

[0030] Example 2

[0031] In an argon glove box (both the water and oxygen content < 0.1 ppm), 3 mg of strontium nitride (Sr3N2) powder was evenly covered on the surface of the lithium sheet, and the covered area was a circle with a diameter of 10 mm, that is, the mass ratio of strontium nitride to metallic lithium added was 2:1. Then, a tablet press was used to press the lithium sheet, the pressure was set at 3 MPa, and the pressing time was 5 min. Then, the pressed lithium sheet was transferred to a heating table at 250 °C, heated at high temperature for 1 min, and after the molten reaction, the metallic lithium was cooled at room temperature of 25 °C for 1.5 h, and thus the metal lithium composite electrode material modified with the multifunctional interfacial layer modified by strontium nitride was obtained.

[0032] Example 3

[0033] In an argon glove box (with both water and oxygen contents < 0.1 ppm), 1.5 mg of strontium nitride (Sr3N2) powder was evenly covered on the surface of the lithium sheet. The covered area was a circle with a diameter of 10 mm, that is, the mass ratio of strontium nitride to metallic lithium was 2:1. Then, a tablet press was used to press the lithium sheet, with the pressure set at 3 MPa and the pressing time of 5 min. Subsequently, the pressed lithium sheet was transferred to a heating stage at 250 °C and heated at high temperature for 5 min. After the molten reaction, the metallic lithium was cooled at room temperature of 25 °C for 1.5 h, and then the metal lithium composite electrode material modified with strontium nitride and having a multifunctional interface layer was obtained.

[0034] Comparative Example 1

[0035] A lithium strip with a thickness of 300 μm (Zhongneng Lithium Industry) was milled into the required electrode size as the electrode for subsequent tests.

[0036] Performance Test

[0037] The lithium metal composite electrodes prepared in Example 1 and Example 2 above, and the pure lithium electrode of Comparative Example 1 were used as the negative electrode materials of the lithium metal solid-state battery. According to Figure 1 The cross-sectional scanning electron micrograph of Example 1 showed that its thickness was only 50 μm after pressing. Compared with the thickness of 300 μm in Comparative Example 1, the preparation process of the present invention greatly improved the utilization rate of metallic lithium and the overall energy density of the battery. According to Figure 2The surface scanning electron micrograph of Example 1 shows that the strontium nitride powder layer on the outermost layer of the electrode material is uniformly stacked in a granular shape. This morphology helps to guide the deposition of lithium, has a certain buffering effect on the growth of lithium dendrites, and alleviates the problem of interface disconnection of the polymer solid electrolyte. The polymer solid electrolyte is prepared by in-situ thermal polymerization. The liquid precursor of the electrolyte consists of 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1, adding 5 wt% fluoroethylene carbonate (FEC), the polymerization monomer polyethylene glycol diacrylate (PEGDA), and the initiator azobisisobutyronitrile (AIBN). In an argon glove box with a water and oxygen concentration less than 0.1 ppm, the symmetric battery is assembled in the order of the positive electrode shell, lithium metal composite electrode material (or pure lithium), electrolyte liquid precursor, cellulose ester membrane, lithium metal composite electrode material (or pure lithium), and negative electrode shell. The full battery is assembled in the order of the positive electrode shell, lithium iron phosphate positive electrode material, electrolyte liquid precursor, cellulose ester membrane, lithium metal composite electrode material (or pure lithium), and negative electrode shell. Finally, it is tightly sealed with a fully automatic sealing machine. The assembled battery is transferred to an oven at 70 °C and continuously heated for 2 h for in-situ curing of the electrolyte. After the battery is cooled to room temperature and left standing for 12 h, the constant current charge and discharge and electrochemical impedance tests are uniformly carried out using a Blue Power battery test system and an electrochemical workstation. The electrochemical tests are all carried out under the condition of 25 °C.

[0038] The performance test results are as follows:

[0039] The interfacial impedances of the lithium symmetric solid-state batteries assembled with the materials of Example 1, Example 2, Example 3, and Comparative Example 1 before cycling are 170 Ω, 215 Ω, 182 Ω, and 420 Ω, respectively. At a current density of 0.2 mA / cm 2 and a charge-discharge capacity of 0.2 mAh / cm 2Under the condition of capacity, the initial overpotentials of the lithium symmetric batteries assembled with the materials of Example 1, Example 2 and Comparative Example 1 were 24 mV, 35 mV, 28 mV and 77 mV respectively. After 50 cycles of activation in Example 1, the impedance decreased to about 42 Ω, and it stably cycled for 1300 h. The interfacial impedance was stable at about 26 Ω, the overpotential was maintained at about 10 mV, and there were no cases of sudden increase in polarization and short circuit. The activation time of Example 2 was relatively longer, and the activation ended after 80 cycles. The interfacial impedance decreased to about 38 Ω, and the overpotential was maintained at about 13 mV. A short circuit phenomenon occurred after 800 h of cycling. Example 3 had an overpotential close to that of Example 1, and the polarization suddenly increased after 1060 h of cycling, corresponding to the situation of the loss of contact of the solid electrolyte interface. In Comparative Example 1, a partial voltage drop phenomenon occurred after 100 h of cycling, corresponding to the soft short circuit of the battery caused by dendrite growth. After 200 cycles, the polarization also tended to increase. It can be seen that the prepared lithium metal composite electrode modified with strontium nitride modified multifunctional interfacial layer as the negative electrode material of the lithium metal solid battery has greatly reduced interfacial charge transfer impedance and excellent long cycle stability.

[0040] Furthermore, the materials of Example 1 and Comparative Example 1 were respectively assembled with a lithium iron phosphate positive electrode to form a solid-state lithium metal full battery for constant current cycling tests. Figure 3 The cycling performance of the two solid-state full batteries was recorded. After 200 cycles at a rate of 0.5C in Example 1, the capacity retention rate was still 77.2%, and the Coulomb efficiency was stable. In contrast, when Comparative Example 1 was tested at the same rate, after 55 cycles, the Coulomb efficiency fluctuated violently and the capacity decayed rapidly, corresponding to dendrite growth, accumulation of dead lithium and obstruction of the lithium ion transport path. It can be seen that the prepared lithium metal composite electrode modified with strontium nitride modified multifunctional interfacial layer as the negative electrode material of the lithium metal solid battery can alleviate dendrite growth and improve the cycle life of the battery.

[0041] It can be seen that the lithium metal composite electrode modified with strontium nitride modified multifunctional interfacial layer prepared by the present invention has the advantages of inhibiting dendrite growth, reducing interfacial impedance, high cycle life and high energy density. The mechanism of action is as follows: on the one hand, the fast ion conductor lithium nitride accelerates the interfacial lithium ion reaction kinetics and reduces the interfacial impedance, while the lithium-strontium alloy lithiophilic layer improves the deposition of lithium ions and alleviates the growth of dendrites. On the other hand, the unreacted strontium nitride powder layer acts as a pre-set rigid skeleton, which can guide the deposition shape of lithium while providing some space for lithium deposition to buffer the growth of dendrites and alleviate the loss of contact of the polymer electrolyte interface. In addition, the preparation method described in the present invention has the advantages of simple principle, high preparation efficiency and easy control.

[0042] Therefore, the lithium metal composite electrode modified with a multifunctional interface layer modified by strontium nitride prepared by the present invention has the characteristics of small interface impedance, excellent cycle stability and simple preparation, can effectively improve the coulombic efficiency and cycle life of the battery, enhance the electrochemical performance of the battery, and has certain application potential in high energy density lithium metal secondary battery systems.

Claims

1. A preparation method of a lithium metal electrode material modified with a multifunctional interface layer, characterized in that It includes the following steps: (1) Uniformly cover the strontium nitride powder on the surface of the lithium metal strip to obtain the treated lithium metal; The mass ratio of the strontium nitride to the lithium metal strip is 0.5-3:1; (2) Mechanically press the treated lithium metal to obtain the pressed lithium metal composite material; (3) Perform high-temperature melting treatment on the pressed lithium metal composite material; The temperature of the high-temperature melting treatment is 200°C - 450°C, and the time is 0.5 min - 5 min; (4) After the material is cooled for 1 h - 5 h, a lithium metal electrode material modified with a multifunctional interface layer is obtained; The multifunctional interface layer includes a fast ion conductor lithium nitride, a lithium-sr alloy lithium-philic layer, and a strontium nitride powder buffer layer.

2. The preparation method of the lithium metal electrode material modified by the multifunctional interface layer according to claim 1, characterized in that, In step (2), the pressure range of the mechanical pressing is 2-10 MPa.

3. The preparation method of the lithium metal electrode material modified by the multifunctional interface layer according to claim 1, wherein, In step (2), the time of the mechanical pressing is 2 min - 10 min.

4. The preparation method of the lithium metal electrode material modified by the multifunctional interface layer according to claim 1, characterized in that, In step (3), the implementation process of the high-temperature melting treatment: Place the pressed lithium metal composite material on a heating table at 250°C - 450°C for 5 min - 10 min to melt it into a liquid state. The strontium nitride powder previously pressed on the surface of the lithium metal will undergo a chemical reaction with the molten lithium metal.

5. The lithium metal electrode material modified with a multifunctional interface layer is prepared by the preparation method according to any one of claims 1 to 4.

6. Application of the lithium metal electrode material modified with a multifunctional interface layer according to claim 5 as a lithium metal negative electrode material.

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