Quantitative evaluation device and method for lithium ion solid-state electrolyte stability

Abstract

A kind of quantitative evaluation device and method of lithium ion solid-state electrolyte stability, comprising: from top to bottom sequentially arranged pressure machine upper hydraulic plate, pressure machine probe, upper pole, sample sleeve, lower pole and pressure machine lower hydraulic plate;Upper pole and lower pole are respectively provided with terminal post;Sample sleeve is placed with the sample to be measured;Pressure gauge connected with pressure machine probe;Electrochemical workstation connected with upper pole terminal post and lower pole terminal post respectively;The sample to be measured includes: from top to bottom sequentially arranged counter electrode, mixture of electrolyte to be measured and electronic conductor fiber, ion conductor layer a, ion conductor layer b and reference electrode.The quantitative evaluation device can solve the problem that the contact area between counter electrode and sample to be measured is small;The problem that sample to be measured is directly contacted with lithium metal, generates side reaction and interference signal;The problem that lithium ion migrates to the lithium foil on reference electrode to generate lithium dendrite and causes test interruption;The problem that the stability of electrolyte cannot be quantitatively analyzed.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion solid-state battery technology, and more specifically, to a quantitative evaluation device and method for the stability of lithium-ion solid-state electrolytes. Background Technology

[0002] Lithium-ion solid electrolytes are the core materials of lithium-ion solid-state batteries; meanwhile, the electrochemical window (electrochemical stability) of solid electrolytes is a key indicator. The electrochemical stability of solid electrolytes determines the voltage range in which they can be used, and ultimately affects the positive and negative electrode materials used with them, thus affecting the entire electrochemical system of the battery.

[0003] Currently, the publicly available evaluation methods for existing technologies mainly include:

[0004] 1. Battery assembly testing:

[0005] One current method for characterizing the electrochemical stability of solid-state electrolytes involves mixing the solid-state electrolyte with positive or negative electrode materials, assembling it into a battery, and then testing the ICE (initial charge / discharge efficiency), CE (coulombic efficiency), and cycle capacity retention during the entire battery charge-discharge process to determine whether the solid-state electrolyte can withstand the voltage range during battery charge-discharge. However, this method has the following drawbacks: mixing the solid-state electrolyte with positive or negative electrode materials and then conducting charge-discharge tests complicates the system, making it impossible to directly determine the stable voltage range of the electrolyte; furthermore, this method increases the electrolyte / active material interface, which may mask the intrinsic stability signal of the electrolyte due to side reactions at the interface; secondly, this method is time-consuming, requiring 20 hours of cycling at 0.1C in the first week to obtain ICE data, and subsequent long-cycle tests can take several months, which is not conducive to high-throughput screening of solid-state electrolyte materials.

[0006] 2. Electrolyte stability was tested using CV (voltammetric cycling).

[0007] The electrolyte to be tested was assembled as follows Figure 1The structure is tested; (1) - counter electrode, which is an electronic conductor and ion-blocking electrode, and remains stable within the test voltage range, is generally made of stainless steel; (2) test sample, which is the solid electrolyte powder material to be tested pressed into a sheet in a mold; (3) - reference electrode, which serves to provide a reference voltage, is required to be an electronic conductor and be able to maintain its own potential unchanged within the test range, and not change its potential with the insertion of lithium ions, and lithium foil is generally used as the reference electrode. After assembling the electrolyte material to be tested according to the above method, the above structure is generally tested using an electrochemical workstation; specifically, the CV method is used, that is, a continuously and steadily increasing voltage is applied to the counter electrode, for example, the voltage is increased from 2.5V to 4.5V at an increase rate of 5mV / S, and the change of current is recorded during this process. However, this method has the following drawbacks: (1) Since the decomposition of solid electrolytes at different voltages mainly occurs at the interface with the electronic conductor, in this method, the decomposition of solid electrolytes only occurs at the interface between the electrode and the sample to be tested; the contact area at the interface is a two-dimensional plane, so the contact area is small, and the electrical signal generated by the decomposition of solid electrolytes is small and not easy to capture. (2) The sample to be tested is in direct contact with the lithium foil used as the reference electrode. However, due to the low potential (0V Vs.Li) and extremely active chemical properties of lithium metal, most solid electrolytes are thermodynamically unstable to lithium metal (some oxide electrolytes, almost all sulfide electrolytes and halide electrolytes). Therefore, the side reaction generated at the interface between the reference electrode and the sample to be tested will interfere with the electrical signal and cause the test signal to fluctuate and become unstable, ultimately leading to inaccurate judgment. (3) When the sample decomposes, lithium ions migrate to the lithium foil used as the reference electrode. On the one hand, this intensifies the interfacial reaction between lithium metal and the electrolyte. On the other hand, due to the low potential of lithium, lithium ions are more likely to deposit directly on the lithium foil and generate lithium dendrites. When the lithium dendrites grow and pierce the sample, electron conduction occurs between the reference electrode and the counter electrode, resulting in a zero potential difference between the two electrodes, making the sample untestable. (4) During the CV method test using an electrochemical workstation, the voltage rises at a constant rate. However, due to electrode polarization, the current signal response lags behind the corresponding voltage, causing the measured current signal to shift towards higher voltages. Consequently, the measured electrochemical window is wider than its actual window. (5) This method is a qualitative analysis of electrolyte stability and cannot perform quantitative analysis, especially for solid electrolytes with different specific surface areas, densities, particle sizes, and compositions.

[0008] In summary, there is currently no rapid, convenient, and quantitative testing device or method for the electrochemical stability of solid electrolytes. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a quantitative evaluation device and method for the stability of lithium-ion solid electrolytes, which can solve the following technical problems: (1) the problem of small contact area between the counter electrode and the sample to be tested, which is a two-dimensional plane; (2) the problem of side reactions and interference signals generated when the sample to be tested directly contacts the lithium metal used as the reference electrode; (3) the problem of lithium dendrites generated when lithium ions migrate to the lithium foil of the reference electrode, causing test interruption; (4) the problem of wide test values ​​caused by current hysteresis in the CV test method; (5) the problem of the inability to quantitatively analyze the stability of electrolytes.

[0010] This invention provides a quantitative evaluation device for the stability of lithium-ion solid electrolytes, comprising:

[0011] The press consists of, from top to bottom, an upper hydraulic plate, a press probe, an upper electrode, a sample sleeve, a lower electrode, and a lower hydraulic plate; the upper and lower electrodes are each equipped with a terminal block; the sample to be tested is placed inside the sample sleeve.

[0012] The pressure gauge connected to the press probe;

[0013] An electrochemical workstation connected to the upper and lower electrode terminals respectively;

[0014] The sample to be tested includes:

[0015] The components arranged from top to bottom are: counter electrode, mixture of electrolyte and electronic conductor fiber, ion conductor layer a, ion conductor layer b, and reference electrode.

[0016] Preferably, the material of the counter electrode is selected from carbon-coated aluminum foil, aluminum foil, gold foil, platinum foil, steel foil, or carbon-coated steel foil.

[0017] Preferably, the electrolyte to be tested is a lithium-ion conductor;

[0018] The electronic conductivity of the electronic conductor fiber is >10. 5 S / cm;

[0019] The surface area ratio of the electrolyte to be tested to the surface area of ​​the electronic conductor fiber is 1:(50-100).

[0020] Preferably, the electronic conductor fiber is selected from one or more of metal fibers, Ketjen Black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers.

[0021] Preferably, the ionic conductivity of the ion conductor layer a is >10. -4 S / cm, electronic conductivity <10 -8S / cm, Young's modulus less than 25GPa, and able to withstand oxidation cutoff voltage ≥4.5V;

[0022] The ionic conductivity of the ion conductor layer b is >10. -4 S / cm, electronic conductivity <10 -8 S / cm, Young's modulus less than 25GPa, and the reduction cutoff potential it can withstand is ≤0.6V.

[0023] Preferably, the reference electrode is made of In. x -Li y , where 5:95≤x:y≤45:55.

[0024] This invention also provides a quantitative evaluation method for the stability of lithium-ion solid electrolytes, comprising the following steps:

[0025] The quantitative evaluation device for the stability of lithium-ion solid electrolytes using the above technical solution involves sequentially placing an ion conductor layer b, an ion conductor layer a, and a mixture of the electrolyte to be tested and electronic conductor fibers inside a sample sleeve. The counter electrode and reference electrode are then placed on either side of the electronic conductor fiber mixture and the ion conductor layer b, respectively, and pressed. Subsequently, the electrochemical stability is tested using an electrochemical workstation under continuous pressure. The quantitative evaluation of the stability of the lithium-ion solid electrolyte is achieved by measuring the integral area of ​​the response current and voltage.

[0026] Preferably, the process of sequentially setting the ion conductor layer b, the ion conductor layer a, and the mixture of the electrolyte to be tested and the electronic conductor fiber specifically involves:

[0027] First, the components of ion conductor layer b are placed in the sample sleeve and pressed for the first time to form ion conductor layer b. Then, the components of ion conductor layer a are placed on top of ion conductor layer b in the sample sleeve and pressed for the second time to form ion conductor layer a. Finally, the mixture of the electrolyte to be tested and the electronic conductor fiber is placed on top of ion conductor layer a in the sample sleeve and pressed for the third time.

[0028] The pressure of the first compression is 50MPa to 600MPa, and the time is 1min to 5min;

[0029] The pressure of the second pressing is 50MPa to 600MPa, and the time is 1min to 5min;

[0030] The pressure of the third pressing is 50MPa to 600MPa, and the time is 1min to 5min.

[0031] Preferably, the pressing pressure is 50MPa to 600MPa, and the pressing time is 1min to 5min;

[0032] The value of the continuous pressure is 10MPa to 600MPa.

[0033] Preferably, in the process of testing electrochemical stability, the voltage increase adopts a cyclic testing method of step increase-constant voltage stabilization-step increase-constant voltage stabilization; the specific process of step increase-constant voltage stabilization-step increase-constant voltage stabilization is as follows: at the initial voltage U1, a constant time t is maintained, then the voltage is increased to the second stage voltage U2, U2 = U1 + ΔU, at the U2 voltage, a constant time t is maintained, then the voltage is increased to the third stage voltage U3, U3 = U2 + ΔU, and so on until the voltage reaches the cutoff voltage U to be tested. n =U 截止 –U0.

[0034] This invention provides a quantitative evaluation device for the stability of lithium-ion solid electrolytes, comprising: a hydraulic platen of a press, a press probe, an upper electrode, a sample sleeve, a lower electrode, and a lower hydraulic platen of a press, arranged sequentially from top to bottom; the upper electrode and the lower electrode are respectively provided with terminals; the sample to be tested is placed inside the sample sleeve; a pressure gauge connected to the press probe; and an electrochemical workstation connected to the terminals of the upper electrode and the lower electrode, respectively; the sample to be tested comprises: a counter electrode, a mixture of the electrolyte to be tested and electronic conductor fibers, an ion conductor layer a, an ion conductor layer b, and a reference electrode, arranged sequentially from top to bottom. Compared with the prior art, the quantitative evaluation device provided by the present invention adopts a structure and connection relationship that achieves better overall interaction and can solve the following technical problems: (1) the problem of small contact area between the counter electrode and the sample to be tested, which is a two-dimensional plane; (2) the problem of the sample to be tested directly contacting the lithium metal used as the reference electrode, resulting in side reactions and interference signals; (3) the problem of lithium ions migrating to the lithium foil of the reference electrode and generating lithium dendrites, causing test interruption; (4) the problem of current hysteresis in the CV test method leading to a wide test value; (5) the problem of the inability to quantitatively analyze the stability of the electrolyte.

[0035] Furthermore, the quantitative evaluation method for the stability of lithium-ion solid electrolytes provided by this invention has simple and easy-to-operate process steps. The stability between different electrolytes can be quantitatively compared by the integral area of ​​the response current and voltage. Moreover, this method is fast and convenient, and can achieve high-throughput testing of different types of electrolytes. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of electrolyte assembly when using CV testing to assess electrolyte stability in existing technologies.

[0037] Figure 2 A schematic diagram of the structure of the quantitative evaluation device for the stability of lithium-ion solid electrolyte provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of a partially magnified structure of the sample to be tested in the quantitative evaluation device for the stability of lithium-ion solid electrolytes provided in an embodiment of the present invention.

[0039] Figures 4-5 The graph shows the test results of electrochemical stability in Example 1 of this invention;

[0040] Figures 6-7 The graph shows the test results of electrochemical stability in Example 2 of this invention;

[0041] Figure 8 This is a graph showing the test results of electrochemical stability in Example 3 of the present invention;

[0042] Figure 9 This is a graph showing the test results of electrochemical stability in Example 4 of the present invention;

[0043] Figure 10 This is a graph showing the test results of electrochemical stability in Example 5 of the present invention;

[0044] Figure 11 The graph shows the test results of electrochemical stability in Example 6 of this invention;

[0045] Figure 12 The graph shows the test results of electrochemical stability in Comparative Example 1. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0047] This invention provides a quantitative evaluation device for the stability of lithium-ion solid electrolytes, comprising:

[0048] The press consists of, from top to bottom, an upper hydraulic plate, a press probe, an upper electrode, a sample sleeve, a lower electrode, and a lower hydraulic plate; the upper and lower electrodes are each equipped with a terminal block; the sample to be tested is placed inside the sample sleeve.

[0049] The pressure gauge connected to the press probe;

[0050] An electrochemical workstation connected to the upper and lower electrode terminals respectively;

[0051] The sample to be tested includes:

[0052] The components arranged from top to bottom are: counter electrode, mixture of electrolyte and electronic conductor fiber, ion conductor layer a, ion conductor layer b, and reference electrode.

[0053] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of the quantitative evaluation device for the stability of lithium-ion solid electrolyte provided in an embodiment of the present invention; wherein, 1 is the upper hydraulic plate of the press, 2 is the press probe, 3 is the upper electrode terminal, 4 is the upper electrode, 5 is the sample sleeve, 6 is the sample to be tested, 7 is the lower electrode terminal, 8 is the lower electrode, 9 is the lower hydraulic plate of the press, 10 is the pressure gauge, and 11 is the electrochemical workstation.

[0054] Figure 2 In the image, a magnified view of a localized structure of sample 6 is shown below. Figure 3 As shown; where 12 is the counter electrode, 13 is a mixture of the electrolyte to be tested and the electronic conductor fiber (17 is the electrolyte particle to be tested, 18 is the electronic conductor fiber), 14 is the ion conductor layer a, 15 is the ion conductor layer b, and 16 is the reference electrode.

[0055] In this invention, the quantitative evaluation device for the stability of lithium-ion solid electrolyte includes, from top to bottom, an upper hydraulic plate of a press, a press probe, an upper electrode column, a sample sleeve, a lower electrode column, and a lower hydraulic plate of a press, as well as a pressure gauge and an electrochemical workstation.

[0056] In this invention, the upper hydraulic plate and the lower hydraulic plate of the press are used to apply pressure, and there are no special limitations on this.

[0057] In this invention, the press probe is connected to the pressure gauge and is used to control the value of the pressure applied by the press.

[0058] In this invention, the upper electrode and the lower electrode are respectively provided with terminals; wherein, the upper electrode terminal is preferably connected to the positive terminal of the electrochemical workstation, and the lower electrode terminal is preferably connected to the negative terminal of the electrochemical workstation.

[0059] In this invention, the sample sleeve contains a sample to be tested; the sample to be tested includes:

[0060] The components arranged from top to bottom are: counter electrode, mixture of electrolyte and electronic conductor fiber, ion conductor layer a, ion conductor layer b, and reference electrode.

[0061] In this invention, the material of the counter electrode is preferably selected from carbon-coated aluminum foil, aluminum foil, gold foil, platinum foil, steel foil, or carbon-coated steel foil, and more preferably carbon-coated steel foil. In this invention, the counter electrode must be stable within the electrolyte electrochemical stability test voltage range, not decompose, and be chemically inert, and must be able to make good contact with the mixture of the electrolyte to be tested and the electronic conductor fiber.

[0062] In this invention, the electrolyte to be tested is preferably a lithium-ion conductor; the lithium-ion conductor contains lithium, and lithium-ion migration dominates its ionic conductivity. Specifically, the electrolyte to be tested can be: oxide electrolytes, such as LATP, LLZO, LLTO, etc.; polymer electrolytes, such as PEO+LiTFSI, PVdF+LiFSI, etc.; sulfide electrolytes, such as Li 10 SnP2S 12 Li3PS4, Li7P3S 11 Li 10 GeP2S 12 Li6PS5Cl, etc.

[0063] In this invention, the electronic conductivity of the electronic conductor fiber is >10. 5 S / cm; the electronic conductor fiber is preferably selected from one or more of metal fibers, Ketjen Black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers, more preferably single-walled carbon nanotubes or vapor-grown carbon fibers, and even more preferably single-walled carbon nanotubes. This invention does not impose any special restrictions on the source of the electronic conductor fiber; commercially available products or homemade products well known to those skilled in the art can be used.

[0064] In this invention, the electronic conductor fiber is used to construct a three-dimensional electronic conductivity network in the electrolyte sample to be tested, so that the surface of the electrolyte sample particles is in full contact with the electronic conductor.

[0065] In this invention, the surface area ratio of the electrolyte to be tested to the surface area of ​​the electronic conductor fiber is preferably 1:(50-100).

[0066] In this invention, the ion conductor layer a serves to conduct lithium ions and block electron transport; specifically, it is a lithium ion conductor and an electronic insulator; preferably, the ion conductivity of the ion conductor layer a is >10. -4 S / cm, electronic conductivity preferably <10 -8 S / cm; To maintain good contact at the interface, the Young's modulus of the ion conductor layer a is preferably less than 25 GPa; at the same time, the ion conductor layer a has the ability to withstand the upper limit of the cutoff voltage within the range of the voltage to be measured, and the oxidation-resistant cutoff voltage it can withstand is preferably ≥4.5V.

[0067] In this invention, the composition of the ion conductor layer a is preferably Li3ErCl6, Li3GdCl6, Li4MgCl6, Li3ScCl6, Li3AlCl6 or Li3GaCl6.

[0068] In this invention, the ion conductor layer b serves to conduct lithium ions and block electron transport; specifically, it is a lithium ion conductor and an electronic insulator; preferably, the ion conductivity of the ion conductor layer b is >10. -4 S / cm, electronic conductivity preferably <10 -8 S / cm; To maintain good contact at the interface, the Young's modulus of the ion conductor layer b is preferably less than 25 GPa; Simultaneously, the ion conductor layer b has the ability to withstand the reference electrode potential, therefore, when the reference electrode uses In... x -Li y When (5:95≤x:y≤45:55), the potential of the reference electrode is 0.6V, so the reduction resistance cutoff potential that the ion conductor layer b can withstand is preferably ≤0.6V.

[0069] In this invention, the composition of the ion conductor layer b is preferably Li3ErS3, In-Li9, or Li3YS3.

[0070] In this invention, the reference electrode plays the role of maintaining a constant potential during the test, and it should have the following characteristics: (1) the lithium ion insertion potential is ≥0.1V to avoid the generation of lithium dendrites when the potential is close to 0V; (2) the potential does not change with the insertion of lithium ions during the test; (3) the potential provided by the reference electrode should be within the stable range of the ion conductor layer b; (4) the reference electrode is an electronic conductor and also has the function of absorbing lithium ions. The absorption function can be realized by alloying, insertion, or reduction.

[0071] In this invention, the reference electrode is preferably made of In. x -Li y Wherein, 5:95≤x:y≤45:55; In a preferred embodiment of the present invention, the reference electrode is made of In-Li9, In-Li4 or In2-Li3.

[0072] The quantitative evaluation device provided by this invention adopts a specific structure and connection relationship to achieve better overall interaction and can solve the following technical problems: (1) the problem of small contact area between the counter electrode and the sample to be tested, which is a two-dimensional plane; (2) the problem of the sample to be tested directly contacting the lithium metal used as the reference electrode, resulting in side reactions and interference signals; (3) the problem of lithium ions migrating to the lithium foil of the reference electrode and generating lithium dendrites, causing test interruption; (4) the problem of current hysteresis in the CV test method leading to a wide test value; (5) the problem of the inability to quantitatively analyze the stability of the electrolyte.

[0073] This invention also provides a quantitative evaluation method for the stability of lithium-ion solid electrolytes, comprising the following steps:

[0074] The quantitative evaluation device for the stability of lithium-ion solid electrolytes using the above technical solution involves sequentially placing an ion conductor layer b, an ion conductor layer a, and a mixture of the electrolyte to be tested and electronic conductor fibers inside a sample sleeve. The counter electrode and reference electrode are then placed on either side of the electronic conductor fiber mixture and the ion conductor layer b, respectively, and pressed. Subsequently, the electrochemical stability is tested using an electrochemical workstation under continuous pressure. The quantitative evaluation of the stability of the lithium-ion solid electrolyte is achieved by measuring the integral area of ​​the response current and voltage.

[0075] In this invention, the process of sequentially setting the mixture of ion conductor layer b, ion conductor layer a, and the electrolyte to be tested and the electronic conductor fiber is preferably as follows:

[0076] First, the components of ion conductor layer b are placed in the sample sleeve and pressed for the first time to form ion conductor layer b. Then, the components of ion conductor layer a are placed on top of ion conductor layer b in the sample sleeve and pressed for the second time to form ion conductor layer a. Finally, the mixture of the electrolyte to be tested and the electronic conductor fiber is placed on top of ion conductor layer a in the sample sleeve and pressed for the third time.

[0077] In this invention, the pressure of the first pressing is preferably 50MPa to 600MPa, more preferably 100MPa to 300MPa, and the time is preferably 1min to 5min, more preferably 2min.

[0078] In this invention, the pressure of the second pressing is preferably 50MPa to 600MPa, more preferably 100MPa to 200MPa, and the time is preferably 1min to 5min, more preferably 2min.

[0079] In this invention, the pressure of the third pressing is preferably 50MPa to 600MPa, more preferably 200MPa to 300MPa, and the time is preferably 1min to 5min, more preferably 2min.

[0080] Then, the present invention places the counter electrode and the reference electrode on both sides of the electronic conductor fiber mixture and the ion conductor layer b, respectively. Specifically, the counter electrode is placed on one side of the electronic conductor fiber mixture and the reference electrode is placed on the other side of the ion conductor layer b, and then pressed. The pressing pressure is preferably 50MPa to 600MPa, more preferably 50MPa to 100MPa.

[0081] After assembling the above structure (pressing the multi-layer block according to the above steps), the present invention uses a press to apply continuous pressure to the above structure, and uses an electrochemical workstation to test the electrochemical stability under this pressure; the value of the continuous pressure (controlled by a pressure gauge) is preferably 10MPa to 600MPa, more preferably 20MPa to 30MPa.

[0082] In this invention, during the electrochemical stability testing process using an electrochemical workstation, to avoid interference from the hysteresis of the response current relative to the voltage, the voltage increase preferably employs a cyclic testing method of step increase-constant voltage stabilization-step increase-constant voltage stabilization, rather than a continuous increase in voltage. Specifically, the step increase-constant voltage stabilization-step increase-constant voltage stabilization process is preferably as follows: a constant time t is maintained at the initial voltage U1, then the voltage is increased to the second stage voltage U2, where U2 = U1 + ΔU; a constant time t is maintained at voltage U2, then the voltage is increased to the third stage voltage U3, where U3 = U2 + ΔU; this cycle is repeated until the voltage reaches the required cutoff voltage U. n =U 截止 –U0. In a preferred embodiment of the present invention, the voltage boosting procedure is set as follows: the voltage is kept constant at an initial voltage U1 for 2 seconds, then boosted to a second-stage voltage U2, where U2 = U1 + ΔU; the voltage is kept constant at U2 for 2 seconds, then boosted to a third-stage voltage U3, where U3 = U2 + ΔU; this cycle is repeated until the voltage reaches the cutoff voltage U to be tested. n =U 截止 –U0; wherein the voltage constant time is preferably 0.5S to 5S, and ΔU is preferably 1 to 10mV.

[0083] In this invention, the potential of the reference electrode relative to Li is U0, when In within the above-mentioned ratio range is used. x -Li y At that time, U0 = 0.6V (Vs.Li).

[0084] The quantitative evaluation method for the stability of lithium-ion solid electrolytes provided by this invention has simple and easy-to-operate process steps. The stability between different electrolytes can be quantitatively compared by the integral area of ​​the response current and voltage. Moreover, this method is fast and convenient, and can achieve high-throughput testing of different types of electrolytes.

[0085] This invention provides a quantitative evaluation device and method for the stability of lithium-ion solid electrolytes, which can quantitatively determine the stability of electrolytes and has the following beneficial effects:

[0086] (1) A three-dimensional conductive network is constructed inside the electrolyte particles to ensure that the electrolyte is sufficiently degraded within the voltage range to be tested, thus avoiding problems such as insufficient response current and insufficient contact caused by two-dimensional planar contact in traditional testing methods.

[0087] (2) The reference electrode uses an electrode with a high lithium intercalation potential and a stable lithium intercalation potential; avoids the decomposition of lithium metal at low potential caused by contact between the electrolyte and lithium metal, and avoids the formation of lithium dendrites during the test.

[0088] (3) The lithium-ion conductive layers a and b are respectively made of lithium-ion conductors with high voltage resistance and low voltage resistance to ensure that there is no interference signal caused by the decomposition of substances other than the electrolyte to be tested.

[0089] (4) A combination of a press and a pressure gauge is used during the test to ensure that the pressure is constant and the particles are in close contact due to external pressure, so as to ensure that the contact condition is not changed due to volume changes during the test.

[0090] (5) The voltage during the test is increased by step-stabilization-step increase-stabilization in a cycle to ensure that the electrolyte degradation reaction is fully carried out under a specific voltage and to reduce the test results that are higher than the actual values ​​caused by the current response lag.

[0091] (6) The stability of different electrolytes can be quantitatively compared by the integral area of ​​the response current and voltage. This method is fast and convenient and can achieve high-throughput testing of different types of electrolytes.

[0092] This invention provides a quantitative evaluation device for the stability of lithium-ion solid electrolytes, comprising: a hydraulic platen of a press, a press probe, an upper electrode, a sample sleeve, a lower electrode, and a lower hydraulic platen of a press, arranged sequentially from top to bottom; the upper electrode and the lower electrode are respectively provided with terminals; the sample to be tested is placed inside the sample sleeve; a pressure gauge connected to the press probe; and an electrochemical workstation connected to the terminals of the upper electrode and the lower electrode, respectively; the sample to be tested comprises: a counter electrode, a mixture of the electrolyte to be tested and electronic conductor fibers, an ion conductor layer a, an ion conductor layer b, and a reference electrode, arranged sequentially from top to bottom. Compared with the prior art, the quantitative evaluation device provided by the present invention adopts a specific structure and connection relationship to achieve better overall interaction and can solve the following technical problems: (1) the problem of small contact area between the counter electrode and the sample to be tested, which is a two-dimensional plane; (2) the problem of the sample to be tested directly contacting the lithium metal used as the reference electrode, resulting in side reactions and interference signals; (3) the problem of lithium ions migrating to the lithium foil of the reference electrode and generating lithium dendrites, causing test interruption; (4) the problem of current hysteresis in the CV test method leading to a wide test value; (5) the problem of the inability to quantitatively analyze the stability of the electrolyte.

[0093] Furthermore, the quantitative evaluation method for the stability of lithium-ion solid electrolytes provided by this invention has simple and easy-to-operate process steps. The stability between different electrolytes can be quantitatively compared by the integral area of ​​the response current and voltage. Moreover, this method is fast and convenient, and can achieve high-throughput testing of different types of electrolytes.

[0094] To further illustrate the present invention, the following embodiments will be described in detail.

[0095] Example 1

[0096] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of the quantitative evaluation device for the stability of lithium-ion solid electrolyte provided in an embodiment of the present invention, wherein 1 is the upper hydraulic plate of the press, 2 is the press probe, 3 is the upper electrode terminal, 4 is the upper electrode, 5 is the sample sleeve, 6 is the sample to be tested, 7 is the lower electrode terminal, 8 is the lower electrode, 9 is the lower hydraulic plate of the press, 10 is the pressure gauge, and 11 is the electrochemical workstation.

[0097] Figure 2 In the image, a magnified view of a localized structure of sample 6 is shown below. Figure 3 As shown; where 12 is the counter electrode, 13 is a mixture of the electrolyte to be tested and the electronic conductor fiber (17 is the electrolyte particle to be tested, 18 is the electronic conductor fiber), 14 is the ion conductor layer a, 15 is the ion conductor layer b, and 16 is the reference electrode.

[0098] The working process (quantitative evaluation method) of the lithium-ion solid electrolyte stability quantitative evaluation device provided in this embodiment of the invention is as follows:

[0099] (1) Weigh 0.1g of Li3YS3 and place it in the sample sleeve 5. Use the upper and lower pressure heads to apply a pressure of 300MPa in the press for 2min to press Li3YS3 into a block, which is layer 15.

[0100] (2) Weigh 0.1g of Li3ScCl6 and place it on top of layer 15 in sample sleeve 5. Apply a pressure of 200MPa for 2min using the upper and lower pressure heads in the press to press the block of Li3ScCl6 into layer 14.

[0101] (3) The specific surface area of ​​the solid electrolyte particle Li6PS5Cl was measured using a specific surface area analyzer and was B. E (7.3m 2 / g), and the specific surface area of ​​CNTs was tested to be B. C (2100m 2 / g); The ratio of solid electrolyte to single-arm carbon nanotubes is calculated according to the area ratio, such as weighing the solid electrolyte as W. E (1g), then the corresponding surface area is S E (7.3cm 2 The surface area ratio of the single-arm carbon nanotube to the surface area of ​​the solid electrolyte is 50:1, so weigh 0.1738g of the corresponding carbon nanotube; after weighing the solid electrolyte and the corresponding single-arm carbon nanotube, use a planetary ball mill to mix and disperse them.

[0102] The mass of the mixture of electrolyte and conductive carbon is W. M(0.1g); the corresponding electrolyte surface area is S E-M (6.22m 2 The weighed mixture is placed on layer 14 in sample sleeve 5, and a pressure of 200 MPa is applied in the press for 2 minutes using upper and lower pressure heads to press the sample into a block of layer 13.

[0103] (4) Place the counter electrode 12 (carbon-coated stainless steel foil) and the reference electrode 16 (In-Li4) on both sides of layer 13 and layer 15 respectively, and press them with a pressure of 50 MPa using a press.

[0104] (5) After the above structure is assembled, a press is used to apply a continuous pressure of 30 MPa to the above structure.

[0105] (6) The above-mentioned test samples were tested using an electrochemical workstation to test the electrochemical stability of the test samples between 2.5 and 4.3 V (Vs.Li).

[0106] In Example 1, U1 = 2.5V – U0 = 2.5 – 0.6 = 1.9V.

[0107] The voltage is kept constant at an initial voltage U1 = 1.9V for 2 seconds, then increased to the second stage voltage U2, where U2 = U1 + ΔU, and ΔU = 5mV. This voltage is then kept constant at U2 for 2 seconds, then increased to the third stage voltage U3, where U3 = U2 + ΔU. This cycle is repeated until the voltage reaches the required cutoff voltage U. n U n =U 截止 –U0=4.3–0.6=3.7V.

[0108] Test results are as follows Figure 4 As shown.

[0109] To achieve quantitative comparison between different test samples, integral calculations are performed on the region enclosed by the response current curve and the voltage coordinate axis, such as... Figure 5 The shaded area is shown in the figure.

[0110] When quantitatively comparing the voltage stability of different electrolytes, the surface area of ​​the electrolytes in layer 13 must be the same, and the other test conditions must be the same; and the stability of various different electrolytes within the test voltage range can be determined by quantitative comparison of the integrated area.

[0111] Example 2

[0112] The quantitative evaluation device for the stability of lithium-ion solid electrolytes described in Example 1 operates as follows:

[0113] (1) Weigh 0.1g of Li3YS3 and place it in the sample sleeve 5. Use the upper and lower pressure heads to apply a pressure of 100MPa in the press for 2min to press Li3YS3 into a block, which is layer 15.

[0114] (2) Weigh 0.1g of Li3ScCl6 and place it on top of layer 15 in sample sleeve 5. Use the upper and lower pressure heads to apply a pressure of 100MPa in the press for 2min to press the block of Li3ScCl6 into layer 14.

[0115] (3) The specific surface area of ​​the solid electrolyte particles Li was tested using a specific surface area analyzer. 10 GeP2S 12 The specific surface area is B E (8m 2 / g), and the specific surface area of ​​CNTs was tested to be B. C (2100m 2 / g); The ratio of solid electrolyte to single-arm carbon nanotubes is calculated according to the area ratio, such as weighing the solid electrolyte as W. E (1g), then the corresponding surface area is S E (8m 2 The surface area ratio of the single-arm carbon nanotube to the surface area of ​​the solid electrolyte is 50:1; then weigh 0.19g of the corresponding single-arm carbon nanotube; after weighing the solid electrolyte and the corresponding single-arm carbon nanotube, disperse them using a planetary ball mill.

[0116] The mass of the mixture of electrolyte and conductive carbon is W. M (0.1g), the corresponding electrolyte surface area is S E-M (6.72m 2 / g); The weighed mixture is placed on layer 14 in sample sleeve 5, and a pressure of 300MPa is applied in the press for 2 minutes using upper and lower pressure heads to press the sample into a block of layer 13.

[0117] (4) Place the counter electrode 12 (carbon-coated stainless steel foil) and the reference electrode 16 (In-Li4) on both sides of layer 13 and layer 15 respectively, and press them with a pressure of 100MPa using a press.

[0118] (5) After the above structure is assembled, a press is used to apply a continuous pressure of 20 MPa to the above structure.

[0119] (6) The above-mentioned test samples were tested using an electrochemical workstation to test the electrochemical stability of the test samples between 2.5 and 3.5 V (Vs.Li).

[0120] In Example 2, U1 = 2.5V – U0 = 2.5 – 0.6 = 1.9V.

[0121] The voltage is kept constant at an initial voltage U1 = 1.9V for 1 second, then increased to the second stage voltage U2, where U2 = U1 + ΔU, and ΔU = 1mV. This voltage is then kept constant at U2 for 1 second, then increased to the third stage voltage U3, where U3 = U2 + ΔU. This cycle is repeated until the voltage reaches the required cutoff voltage U. n U n =U 截止 –U0=3.5–0.6=2.9V.

[0122] Test results are as follows Figure 6 As shown.

[0123] To achieve quantitative comparison between different test samples, integral calculations are performed on the region enclosed by the response current curve and the voltage coordinate axis, such as... Figure 7 The shaded area is shown in the figure.

[0124] When quantitatively comparing the voltage stability of different electrolytes, the surface area of ​​the electrolytes in layer 13 must be the same, and the other test conditions must be the same; and the stability of various different electrolytes within the test voltage range can be determined by quantitative comparison of the integrated area.

[0125] Example 3

[0126] The method provided in Example 2 is used, except that the solid electrolyte particles to be tested use Li 10 SnP2S 12 .

[0127] Test results are as follows Figure 8 As shown.

[0128] Under the same test conditions as in Example 2, the integral curve of the electrolyte response current and voltage in Example 3 can be obtained. By quantitatively comparing the integral areas in Example 2 and Example 3, a quantitative judgment on the stability of different electrolytes within the voltage range to be tested can be obtained.

[0129] Example 4

[0130] The method provided in Example 2 is used, except that vapor-grown carbon fibers are used instead of single-arm carbon nanotubes as the three-dimensional conductive framework.

[0131] Test results are as follows Figure 9 As shown.

[0132] Under the same test conditions as in Example 2, the integral curve of the electrolyte response current and voltage in Example 4 can be obtained. By quantitatively comparing the integral areas in Example 2 and Example 4, a quantitative judgment on the stability of different electrolytes within the voltage range to be tested can be obtained.

[0133] Example 5

[0134] The method provided in Example 2 is used, except that the ion conductor layer a is composed of Li3ErCl6.

[0135] Test results are as follows Figure 10 As shown.

[0136] Under the same test conditions as in Example 2, the integral curve of the electrolyte response current and voltage in Example 5 can be obtained. By quantitatively comparing the integral areas in Example 2 and Example 5, a quantitative judgment on the stability of different electrolytes within the voltage range to be tested can be obtained.

[0137] Example 6

[0138] The method provided in Example 2 is used, except that the ion conductor layer b is composed of In-Li9.

[0139] Test results are as follows Figure 11 As shown.

[0140] Under the same test conditions as in Example 2, the integral curve of the electrolyte response current and voltage in Example 6 can be obtained; by quantitatively comparing the integral areas in Example 2 and Example 6, a quantitative judgment on the stability of different electrolytes within the voltage range to be tested can be obtained.

[0141] Comparative Example 1

[0142] Comparative Example 1 and Example 2 used the exact same test electrolyte, the only difference being that Comparative Example 1 did not use the method described in Example 2 of this invention. See [link to Comparative Example 1]. Figure 1 As shown, the testing method is as follows:

[0143] (1) Weigh the electrolyte Li to be tested 10 GeP2S 12 A sample weighing 0.1g is placed in sample sleeve 5, and a pressure of 300MPa is applied in the press for 2 minutes using the upper and lower pressure heads to compress the sample into a block.

[0144] (2) Place the stainless steel foil counter electrode and the reference electrode Li on both sides of the electrolyte to be tested, and press them with a pressure of 100 MPa using a press.

[0145] (3) After the above structure is assembled, a press is used to apply a continuous pressure of 20 MPa to the above structure.

[0146] (4) The above-mentioned test samples were tested using an electrochemical workstation to test the electrochemical stability of the test samples between 2.5 and 3.5 V (Vs.Li).

[0147] The initial voltage U1 = 2.5V is continuously increased at a rate of 1mV / s until the voltage reaches 3.5V.

[0148] Test results are as follows Figure 12 As shown.

[0149] A comparison of the test results of Example 2 and Comparative Example 1 shows that the response current of Example 2 is more significant. This is because a three-dimensional conductive framework was constructed in Example 2. Compared with the two-dimensional contact plane in Comparative Example 1, Example 2 allows the electrolyte to degrade sufficiently under the corresponding voltage, thereby generating a more significant response signal, which is beneficial for the accurate observation and statistical analysis of the electrical signal.

[0150] Comparing Example 2 and Comparative Example 1, the electrolyte in Example 2 exhibited significant response signal peaks at 2.75V and 3.25V, while these were not observed in Comparative Example 1. This is because the voltage step test conditions in Example 2 allow sufficient time for the electrolyte to degrade, decompose, and for ions and electrons to migrate and voltage polarization to be eliminated, thus clearly distinguishing the location of the electrolyte decomposition peaks. In Comparative Example 1, on the one hand, the continuous increase in voltage resulted in a delayed current response from the degradation reaction; on the other hand, the electrolyte was in direct contact with lithium metal, and the thermodynamic instability between the sulfide electrolyte and lithium metal led to unavoidable side reactions. The resulting interference signals also masked part of the response signal, blurring the final results.

[0151] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantitative evaluation device for the stability of lithium-ion solid electrolytes, characterized in that, include: The press consists of, from top to bottom, an upper hydraulic plate, a press probe, an upper electrode, a sample sleeve, a lower electrode, and a lower hydraulic plate; the upper and lower electrodes are each equipped with a terminal block; the sample to be tested is placed inside the sample sleeve. The pressure gauge connected to the press probe; An electrochemical workstation connected to the upper and lower electrode terminals respectively; The sample to be tested includes: The components arranged from top to bottom are: counter electrode, mixture of electrolyte to be tested and electronic conductor fiber, ion conductor layer a, ion conductor layer b, and reference electrode. The electronic conductivity of the electronic conductor fiber is >10. 5 S / cm; The surface area ratio of the electrolyte to be tested to the surface area of ​​the electronic conductor fiber is 1:(50~100). The ionic conductivity of the ion conductor layer a is >10. -4 S / cm, electronic conductivity <10 -8 S / cm, Young's modulus less than 25GPa, and able to withstand oxidation cutoff voltage ≥4.5V; The ionic conductivity of the ion conductor layer b is >10. -4 S / cm, electronic conductivity <10 -8 S / cm, Young's modulus less than 25GPa, and the reduction cutoff potential it can withstand is ≤0.6V.

2. The quantitative evaluation device for the stability of lithium-ion solid electrolytes according to claim 1, characterized in that, The material of the counter electrode is selected from carbonized aluminum foil, aluminum foil, gold foil, platinum foil, steel foil, or carbonized steel foil.

3. The quantitative evaluation device for the stability of lithium-ion solid electrolytes according to claim 1, characterized in that, The electrolyte to be tested is a lithium-ion conductor.

4. The quantitative evaluation device for the stability of lithium-ion solid electrolytes according to claim 1, characterized in that, The electronic conductor fiber is selected from one or more of the following: metal fiber, Ketjen Black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers.

5. The quantitative evaluation device for the stability of lithium-ion solid electrolytes according to claim 1, characterized in that, The reference electrode is made of In. x -Li y , where 5:95≤x:y≤45:

55.

6. A quantitative evaluation method for the stability of lithium-ion solid electrolytes, characterized in that, Includes the following steps: The quantitative evaluation device for the stability of lithium-ion solid electrolytes according to any one of claims 1 to 5 is used. An ion conductor layer b, an ion conductor layer a, and a mixture of the electrolyte to be tested and electronic conductor fibers are sequentially arranged inside a sample sleeve. The counter electrode and reference electrode are then placed on either side of the electronic conductor fiber mixture and the ion conductor layer b, respectively, and pressed. Subsequently, the electrochemical stability is tested using an electrochemical workstation under continuous pressure. The quantitative evaluation of the stability of the lithium-ion solid electrolyte is achieved by measuring the integral area of ​​the response current and voltage.

7. The quantitative evaluation method for the stability of lithium-ion solid electrolytes according to claim 6, characterized in that, The process of sequentially setting the ion conductor layer b, the ion conductor layer a, and the mixture of the electrolyte to be tested and the electronic conductor fiber is as follows: First, the components of ion conductor layer b are placed in the sample sleeve and pressed for the first time to form ion conductor layer b. Then, the components of ion conductor layer a are placed on top of ion conductor layer b in the sample sleeve and pressed for the second time to form ion conductor layer a. Finally, the mixture of the electrolyte to be tested and the electronic conductor fiber is placed on top of ion conductor layer a in the sample sleeve and pressed for the third time. The pressure of the first compression is 50MPa~600MPa, and the time is 1min~5min; The pressure of the second pressing is 50MPa~600MPa, and the time is 1min~5min; The pressure of the third pressing is 50MPa~600MPa, and the time is 1min~5min.

8. The quantitative evaluation method for the stability of lithium-ion solid electrolytes according to claim 6, characterized in that, The pressing pressure is 50MPa~600MPa, and the time is 1min~5min; The value of the continuous pressure is 10MPa~600MPa.

9. The quantitative evaluation method for the stability of lithium-ion solid electrolytes according to claim 6, characterized in that, During the electrochemical stability test, the voltage increase adopts a cyclic test method of step increase-constant voltage stabilization-step increase-constant voltage stabilization. Specifically, the step increase-constant voltage stabilization-step increase-constant voltage stabilization process involves: maintaining a constant voltage U1 for a time t, then increasing to the second stage voltage U2, where U2 = U1 + ΔU; maintaining a constant voltage U2 for a time t, then increasing to the third stage voltage U3, where U3 = U2 + ΔU; and repeating this cycle until the voltage reaches the required cutoff voltage U. n =U 截止 –U0.

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