Cu + / li + double-ion conductor and high-power all-solid-state lithium battery

Abstract

A Cu+ / Li+ double-ion conductor and a high-power all-solid-state lithium battery, which belong to the technical field of solid-state lithium batteries. A Cu+ / Li+ double-ion conductor is constructed, and on the basis of the double-ion conductor, a high-speed ion pathway connecting a positive electrode active material and a composite positive electrode electrolyte is constructed, thereby realizing rapid migration of ions at an interface, and greatly improving the rate capability of a battery.

Description

A Cu + / Li + Dual ion conductor and high-power all-solid-state lithium battery Technical Field

[0001] The present invention relates to a Cu + / Li + Dual ion conductors and high-power all-solid-state lithium batteries belong to the field of solid-state lithium battery technology. Background Art

[0002] The most widely used power batteries on the market today are traditional liquid lithium-ion batteries, which present significant safety risks and limited energy density. Solid-state batteries, due to their superior safety and cycle performance, are widely considered one of the most promising secondary battery systems. Sulfide solid-state electrolytes, with their highest ionic conductivity and soft texture, are considered one of the most promising solid-state electrolytes. However, the current development of sulfide-based all-solid-state batteries is significantly limited by interface issues between sulfide electrolytes and traditional oxide cathodes.

[0003] Summary of the Invention

[0004] The technical problem addressed by this invention is that the interface between existing sulfide electrolytes and oxide cathodes limits the performance of sulfide all-solid-state lithium batteries. The present inventors unexpectedly discovered a composite cathode material constructed from sulfide materials that, when used in sulfide all-solid-state lithium batteries, exhibits dual-ion conductor properties, significantly improving battery performance.

[0005] A Cu + / Li + The dual ion conductor is a composite of Cu2S powder and sulfide electrolyte or halide electrolyte material.

[0006] The sulfide electrolyte is selected from at least one of LiPSX, LiPS, LiGePS, LiGePSI, LiSiPSCl, LiSiPSO, LiGeGaS or Li3InCl6, wherein X is selected from Cl, I or Br.

[0007] The halide electrolyte material is Li3InX, wherein X is selected from Cl, I or Br.

[0008] The weight ratio of the Cu2S powder to the electrolyte material is in the range of 7:3-5:5, preferably 6:4-5:5.

[0009] The above Cu + / Li + The preparation method of the dual ion conductor is to obtain it by mechanical ball milling mixing.

[0010] The ball milling process has a rotation speed of 100-300 rpm and a time of 2-6 h.

[0011] An all-solid-state lithium battery, comprising a positive electrode, an electrolyte and a negative electrode, wherein the positive electrode is the above-mentioned Cu + / Li + Dual ion conductor.

[0012] The electrolyte is made of inorganic electrolyte material.

[0013] Based on Cu + / Li + The working method of the all-solid-state lithium battery of the dual ion conductor is characterized by comprising the following steps: charging to convert the S in Cu2S into S 0 , while Cu + Transferred to the electrolyte in the composite positive electrode; then discharged to generate Cu and Li2S. Beneficial effects

[0014] The present invention constructs a Cu + / Li + Dual ion conductor, with the help of this dual ion conductor, we have constructed an ion high-speed path connecting the positive electrode active material and the composite positive electrode electrolyte, thereby achieving rapid ion migration at the interface, greatly improving the battery's rate performance, based on the specific ion transport synergy between Cu2S and sulfide electrolyte, making the capacity of the Cu2S positive electrode doubled. We use commercial Cu2S powder as the positive electrode active material, which is rich in Cu + and high electronic conductivity. By utilizing Cu + / Li + The dual ion conductor successfully realized the four-electron redox process of Cu2S (theoretical capacity: 672mAh / g). The battery system was at 60℃ and 20mA / cm 2 At an ultra-high current density of 10mA / cm, it still has a specific capacity of 229.9mAh / g, showing excellent kinetic performance. 2 At a current density of 3mA / cm2, the capacity retention rate of the 1500-cycle battery is as high as 93.2%. 2 At a current density of 1000 cycles, the capacity retention rate is as high as 93.3%, indicating that the battery system exhibits excellent cycle stability. In addition, the battery system also has excellent low-temperature performance and can operate normally at -60°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1: Cu + / Li +Schematic diagram of the crystal structure of a dual-ion conductor, which connects the cathode active material and the composite cathode electrolyte, enabling high-speed ion transport between the two.

[0016] Figure 2: a, AC impedance spectrum of SS-Li6PS5Cl-SS (SS: stainless steel) symmetric battery; b, AC impedance spectrum of SS-Cu6PS5Cl-SS (SS: stainless steel) symmetric battery.

[0017] Figure 3: a, Cu2S can be reversibly converted into S 0 , the process is through Cu + / Li + Double ion relay; b, Cu2S can be reversibly converted into Cu and Li2S, and this process can be achieved only by Li + Transmission implementation.

[0018] Figure 4: LiIn-LPSC-Cu2S all-solid-state battery at 0.1 mA / cm at 30°C 2 The charge and discharge curves.

[0019] Figure 5: a, First cycle charge capacity of LiIn|LPSC1.0|SE|pure Cu2S all-solid-state battery at a current density of 0.1 mA / cm 2 The battery was tested at 60℃, and the solid electrolyte SE used Li 5.5 PS 4.5 Cl 1.5 (LPSC1.5), Li 10 GeP2S 12 (LGPS), Li6PS5Cl(LPSC1.0), Li7P3S 11 (LPS7311), Li3InCl6 (LiInCl316); b, Arrhenius curves of five electrolytes, among which the ionic conductivity at 60 degrees is ranked as follows: LPSC1.5, LGPS, LPSC1.0, LPS7311, LiInCl316; c, histogram of the first-cycle charge capacity of the all-solid-state battery and the ionic conductivity of the electrolyte used, showing a linear relationship between the two.

[0020] Figure 6: Test results of different sulfide solid electrolytes.

[0021] Figure 7: SEM and energy spectrum analysis of a cross-section of a LiIn-LPSC-pure Cu2S all-solid-state battery. ac, SEM images and energy spectrum of the initial all-solid-state battery; df, SEM images and energy spectrum of the Cu and S all-solid-state battery after charging to 3.0V.

[0022] Figure 8: Characteristic points of subsequent ex situ XPS and ex situ XRD. 1, Initial state; 2, First cycle charge to 3.0 V; 3, First cycle discharge to 1.8 V; 4, First cycle discharge to 1.0 V; 5, Second cycle charge to 2.0 V; 6, Second cycle charge to 3.0 V.

[0023] Figure 9: Ex-situ XPS S 2p spectra of LiIn-LPSC-Cu2S all-solid-state batteries at different states.

[0024] Figure 10: Ex-situ XPS Cu 2p spectra of LiIn-LPSC-Cu2S all-solid-state batteries at different states.

[0025] Figure 11: Ex-situ XPS of Cu 2p in LiIn-LPSC-Cu2S all-solid-state batteries at different states 3 / 2 Spectrum.

[0026] Figure 12: Ex-situ XRD of LiIn-LPSC-Cu2S all-solid-state battery at different states.

[0027] Figure 13: LiIn-LPSC-Cu2S all-solid-state battery at 0.5 mA / cm at 60°C 2 The charge and discharge curves for the first three cycles of operation.

[0028] Figure 14: Cyclic voltammograms of the first three cycles of the LiIn-LPSC-Cu2S all-solid-state battery operating at 0.1 mV / s at 60°C.

[0029] Figure 15: Rate performance curve of LiIn-LPSC-Cu2S all-solid-state battery at 60°C.

[0030] Figure 16: LiIn-LPSC-Cu2S all-solid-state battery at 60°C at 10 mA / cm 2 Long cycle performance curve of operation.

[0031] Figure 17: Rate performance curve of LiIn-LPSC-Cu2S all-solid-state battery at 30°C.

[0032] Figure 18: LiIn-LPSC-Cu2S all-solid-state battery at 30°C at 3 mA / cm 2 Long cycle performance curve of operation

[0033] Figure 19: Rate performance curves of composite cathodes with three ratios at 60 degrees. DETAILED DESCRIPTION

[0034] Example 1

[0035] The process of the all-solid-state lithium battery with dual ion conductors in this patent:

[0036] Cu2S was used as the cathode active material. The composite cathode consisted of Cu2S:LPSC in a mass ratio of 6:4. The mixture was then mixed uniformly by low-speed ball milling. Specifically, the corresponding proportions of Cu2S and LPSC electrolyte were added to a zirconium dioxide ball mill at a controlled material-to-bead ratio of 1:50. The mixture was then milled at 150 rpm for 4 hours.

[0037] The process for assembling a solid-state lithium battery is as follows: First, approximately 150mg of LPSC powder is evenly added to a solid-state battery mold. The electrolyte sheet is then pressed using a hydraulic press, applying a pressure of 2 tons for 2 minutes. After the pressing process is complete, approximately 4mg of the composite cathode is evenly added to the electrolyte cathode side, and the pressing process is repeated. After the second pressing process is complete, a Li-In alloy anode is added to the cathode side of the mold, and an external pressure of approximately 10 MPa is applied to complete the battery assembly.

[0038] The battery test method and process are as follows: the battery is charged first and then discharged, and the voltage range is 1.0V-3.0V (V vs.Li / Li + ). Charge and discharge cycles were performed under different current densities and temperature conditions according to experimental requirements.

[0039] Example 2

[0040] Pure Cu2S powder was directly used as the positive electrode to assemble the battery. The other specific steps were the same as those in Example 1. The testing method was also the same as that in Example 1.

[0041] During the test, it was unexpectedly discovered that the all-solid-state lithium battery using Cu2S as the positive electrode active material exhibited significantly different performance from the liquid lithium battery. Cu2S can only release a specific capacity of 250mAh / g in the liquid battery, and there is only one charge and discharge platform. In the solid-state battery, Cu2S showed two sets of charge and discharge platforms, and had a high specific capacity of nearly 600mAh / g, which is more than double the capacity of Cu2S in the liquid state. The process also showed a smaller polarization voltage, indicating better kinetic performance; the charge and discharge curves of the two are compared in Figures 4 and 5, respectively. Figure 5 shows the charge and discharge voltage of Cu2S in a liquid organic electrolyte at room temperature at 0.1mA / cm 2 Based on this discovery, the applicant conducted in-depth research.

[0042] Figure 1 shows the constructed Cu + / Li + Schematic diagram of the crystal structure of a dual ion conductor, which constructs an ion path connecting the positive electrode active material and the composite positive electrode electrolyte, Cu + He Li +Figure 2 shows the AC impedance spectra of Li6PS5Cl (LPSC) and Cu6PS5Cl, whose ionic conductivities are 3.60mS / cm and 1.21mS / cm respectively, indicating that Cu + He Li + Capable of rapid migration of this universal anion.

[0043] Figure 3 shows the two stages of Cu2S redox and the ion migration in each stage. In stage 1, Cu2S can be reversibly converted into S 0 In this stage, the redox of S occurs, with two electron transfers. + The Li+ in the LPSC is transferred to the cathode, and the Li+ in the LPSC migrates to the anode to complete the ion transfer in the internal circuit. In the second stage, Cu2S is reversibly converted into Cu and Li2S, and the valence change of Cu is also accompanied by the transfer of two electrons. + Figure 4 shows the charge and discharge curves of the LiIn-LPSC-Cu2S all-solid-state battery, which can be clearly divided into two stages. The high voltage stage corresponds to the valence change of S, while the low voltage stage corresponds to the valence change of Cu.

[0044] For Example 2, this patent also tested different sulfide solid electrolytes, and used five electrolytes to assemble LiIn|LPSC1.0|SE|pure Cu2S all-solid-state batteries, where SE were LPSC1.5, LGPS, LPSC1.0, LPS7311, and LiInCl316. As shown in Figure 6, the negative electrode interface of the battery is the interface between LiIn alloy and LPSC1.0, so it has similar interface impedance. The pure Cu2S positive electrode can release a certain capacity, indicating that Cu + They can all migrate in these electrolytes, which include not only sulfide electrolytes but also halide electrolytes such as LiInCl316. We tested the ionic conductivity of these five electrolytes at different temperatures and plotted the Arrhenius curves of these electrolytes, where the shaded portion represents the ionic conductivity at 60 degrees Celsius. The order of ionic conductivity is LPSC1.5, LGPS, LPSC1.0, LPS7311, and LiInCl316. We plotted the first-cycle charge capacity of the all-solid-state battery and the ionic conductivity of the electrolyte into a bar graph, which showed a linear relationship, indicating that the lithium ion conductivity of Cu ions in the solid electrolyte is related to the solid electrolyte itself.

[0045] The battery assembled with pure Cu2S powder as the positive electrode has a first cycle charging curve of up to 244.2mAh / g, which is more than 2 / 3 of the theoretical capacity (theoretical capacity: 336mAh / g). + Migrated into the electrolyte layer. In order to characterize the Cu + To investigate the migration at the interface, we performed scanning electron microscopy and energy spectrum analysis on the cross section of the LiIn-LPSC-pure Cu2S all-solid-state battery. Figure 7 shows the characterization results. In the initial state, the energy spectrum signal of Cu can only be characterized in the Cu2S layer. When the battery is charged to 3.0V, a large amount of Cu energy spectrum signal can be characterized in the LPSC layer. Therefore, Cu + Able to migrate rapidly within the LPSC electrolyte anion framework.

[0046] For the reaction mechanism of the electrochemical process of the dual ion conductor material prepared in Example 1, we performed non-in situ characterization of the battery system. Figure 8 shows several characteristic points we tested: 1, initial state; 2, first cycle charge to 3.0V; 3, first cycle discharge to 1.8V; first cycle discharge to 1.0V; 5, second cycle charge to 2.0V; 6, second cycle charge to 3.0V. We first performed non-in situ XPS on these six points. Figure 9 shows the S 2p spectrum of non-in situ XPS. The S2p signal in the initial state is composed of Cu2S and PS4 3- When the first cycle is charged to 3.0V, the signal of Cu2S disappears, and S 0 The signal appears, indicating that Cu2S is converted into S during the first cycle of charging. 0 When the first cycle is discharged to 1.8V, S 0 The fitting peak of Cu2S disappears and the fitting peak of Li2S appears. When discharged to 1.0 V, the fitting peak of Cu2S disappears and the fitting peak of Li2S appears. During the charging process of the second cycle, the change of the fitting peak of S 2p is consistent with that of the first cycle.

[0047] The XPS spectrum of Cu 2p has little change except for the fourth characteristic point (Figure 10). This is because the Cu in the other five characteristic points is (+1) valence. Figure 11 shows the spectrum of Cu 2p3 / 2, where it can be seen that the peak position of the fitting peak of Cu has shifted to a certain extent. This is because the chemical environment of Cu has changed from the initial state of Cu in Cu2S to Cu in Cu x Li 6-x In PS5Cl, when the first cycle discharge reaches 1.0V, no metal Cu signal is detected. This is because Cu + When metallic Cu is formed, it migrates to the inside of the electrode, but the depth of XPS detection is shallow, only at the nanometer level. At this time, the weak Cu 2p signal can be attributed to a small amount of unreacted Cu2S.

[0048] Figure 3 shows the mechanism of the charge and discharge process of our battery system. Since Cu ions can migrate quickly in the solid electrolyte, we can achieve the valence change of S, which is impossible for Cu2S in liquid organic electrolytes. Therefore, in liquid organic electrolytes, due to the transmission of only Li ions, Cu2S can only achieve the valence change of Cu, which is a two-electron conversion reaction with a theoretical capacity of 336mAh / g. However, in the solid-state battery system, Cu2S can achieve a four-electron conversion reaction because the valence change of S is activated and the valence change of Cu is retained. It has a high theoretical capacity of 672mAh / g, which is twice that of Cu2S in liquid batteries.

[0049] In addition, we also used non-in situ XRD to characterize the composition evolution of the electrochemical process (Figure 12). In the initial state, the diffraction peak of the composite positive electrode is composed of the diffraction peaks of LPSC and Cu2S, among which the diffraction peak of Cu2S is weak, which is due to the poor crystallinity of Cu2S. When the first cycle is charged to 3.0V, the signal of Cu2S disappears. The surface Cu2S participates in the electrochemical reaction, but no S 0 The diffraction peak is due to the generation of S 0 It is usually amorphous. However, during the subsequent discharge process, when the discharge reaches 1.8V, the diffraction peak of Cu2S appears. When the discharge reaches 1.0V, the Cu2S signal disappears, and the signals of Li2S and Cu appear. This is consistent with the previous ex situ XPS results.

[0050] Figures 13-14 show the first three charge-discharge curves and cyclic voltammetry curves of the LiIn-LPSC-Cu2S all-solid-state battery, respectively. This shows that the electrochemical process consists of two groups of redox peaks, S 2- / S 0 and Cu + / Cu. Figure 15 shows the rate curve of the battery system at 60 degrees. The battery is at 20mA / cm 2 The battery system can contribute a specific capacity of 229.9 mAh / g at an ultra-high current, demonstrating excellent kinetic properties. Figure 16 shows the long-cycle performance curve of this battery system. The battery maintains a capacity of 93.2% after 1500 cycles at 60°C, demonstrating the system's excellent stability. The battery exhibits excellent electrochemical performance at room temperature (Figures 17-18).

[0051] In addition, this patent also compares the performance of different composite positive electrode material ratios. Three ratios of Cu2S to LPSC1.0 electrolyte were used to prepare three composite positive electrodes, namely 7:3, 6:4, and 5:5, which were recorded as Cu2S-73, Cu2S-64, and Cu2S-55 respectively. The rate curves of the composite positive electrodes with these ratios are shown in Figure 19. Among them, Cu2S-73 has the worst rate performance, and its specific capacity at low current is also significantly smaller than that of the composite positive electrodes with other ratios. This is because the Li ions in the electrolyte of the composite positive electrode are not enough to realize Li + / Cu + Cu2S-64 and Cu2S-55 exhibit similar rate performance, indicating that the lithium ions in the composite cathode are sufficient to achieve Li / Cu ion relay transport. Due to the high proportion of active material in the Cu2S-64 composite cathode, it has greater practical value.

Claims

1. A Cu + / Li + A dual ion conductor, characterized in that It is a composite of Cu2S powder and sulfide electrolyte or halide electrolyte material.

2. The Cu according to claim 1 + / Li + A dual ion conductor, characterized in that The sulfide electrolyte is selected from at least one of LiPSX, LiPS, LiGePS, LiGePSI, LiSiPSCl or LiSiPSOLiGeGaS, wherein X is selected from Cl, I or Br.

3. Cu according to claim 1 + / Li + A dual ion conductor, characterized in that The halide electrolyte material is Li3InX, wherein X is selected from Cl, I or Br.

4. The Cu according to claim 1 + / Li + A dual ion conductor, characterized in that The weight ratio of the Cu2S powder to the sulfide electrolyte material is in the range of 7:3-5:

5.

5. The Cu according to claim 4 + / Li + A dual ion conductor, characterized in that The weight ratio of the Cu2S powder to the sulfide electrolyte material is in the range of 6:4-5:

5.

6. The Cu according to claim 1 + / Li + A method for preparing a dual ion conductor, characterized in that: It is obtained by mechanical ball milling.

7. The preparation method according to claim 6, characterized in that: The ball milling process has a rotation speed of 100-300 rpm and a time of 2-6 hours.

8. An all-solid-state lithium battery, characterized in that: It comprises a positive electrode, an electrolyte and a negative electrode, wherein the positive electrode is the Cu as claimed in claim 1 + / Li + Dual ion conductor.

9. The all-solid-state lithium battery according to claim 8, characterized in that: The electrolyte used is an inorganic electrolyte material.

10. A Cu-based compound according to claim 1 + / Li + The working method of the all-solid-state lithium battery of the dual ion conductor is characterized in that: The steps include: charging to convert the S in Cu2S into S 0 , while Cu + Transferred to the electrolyte in the composite positive electrode; then discharged to generate Cu and Li2S.

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