Method for evaluating carbon content in lithium sulfide and application thereof

Abstract

The present application relates to the technical field of solid electrolyte, in particular to a method for evaluating carbon content in lithium sulfide and application thereof. The method for evaluating carbon content in lithium sulfide comprises: mixing lithium sulfide, a phosphorus source and an organic solvent and reacting, then performing solid-liquid separation to obtain a precursor; after sintering the precursor, a sulfide solid electrolyte is obtained; electronic conductivity of the sulfide solid electrolyte is tested; if the electronic conductivity of the sulfide solid electrolyte is higher than 1*10 ‑7 S / cm, it is determined that the carbon content in lithium sulfide is high and not suitable for preparing the sulfide solid electrolyte; otherwise, it is determined that the carbon content in lithium sulfide is low and suitable for preparing the sulfide solid electrolyte. The method can determine whether lithium sulfide is suitable as a raw material for preparing the sulfide solid electrolyte.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and more specifically, to a method for evaluating the carbon content in lithium sulfide and its application. Background Technology

[0002] Lithium sulfide (Li2S) is an important raw material for sulfide solid electrolytes. Currently, it is mainly prepared by reducing lithium sulfide precursors (one or more of lithium sulfate, lithium sulfite, lithium hydrogen sulfate, and lithium dithionate) at high temperature using a reducing agent. The reducing agent is generally a carbon-containing material (such as carbon, monosaccharides, or disaccharides). This method can yield high-purity lithium sulfide.

[0003] However, lithium sulfide prepared by this method will have a small amount of residual carbon remaining in the sulfide solid electrolyte, which can easily cause an increase in the electronic conductivity of the solid electrolyte and the resulting solid battery, posing a short circuit risk in solid battery applications.

[0004] Currently, the main method for testing the carbon content in lithium sulfide is through glow discharge plasma mass spectrometry. However, the equipment used in this method is expensive, and it has high requirements for the sample surface, which must be clean and free of oxidation. In actual testing, the sample is prone to deterioration, which is not conducive to the detection of carbon content.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a method for evaluating the carbon content in lithium sulfide. By testing the electronic conductivity of a sulfide solid electrolyte prepared from lithium sulfide, the carbon content in the lithium sulfide can be assessed, thereby determining whether the lithium sulfide is suitable as a raw material for preparing sulfide solid electrolytes. This evaluation method is low-cost and suitable for widespread use.

[0007] A second objective of this invention is to provide a method for evaluating the carbon content in lithium sulfide and its application in the preparation of sulfide solid electrolytes and solid-state batteries.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a method for evaluating the carbon content in lithium sulfide, comprising the following steps: mixing and reacting lithium sulfide, a phosphorus source, and an organic solvent, followed by solid-liquid separation to obtain a precursor; sintering the precursor to obtain a sulfide solid electrolyte; and performing an electronic conductivity test on the sulfide solid electrolyte; if the electronic conductivity of the sulfide solid electrolyte is higher than 1×10⁻⁶, the method is described in the original text. -7If the carbon content in the lithium sulfide is S / cm, it is determined that the lithium sulfide has a high carbon content and is not suitable for preparing sulfide solid electrolytes; conversely, if the carbon content in the lithium sulfide is low, it is determined that the lithium sulfide has a low carbon content and is suitable for preparing sulfide solid electrolytes.

[0010] Furthermore, the electronic conductivity test method includes: a battery mold comprising a shell with a cavity, a first electrode, and a second electrode, wherein the first electrode and the second electrode have the same cross-sectional area; inserting the first electrode into the cavity, adding the sulfide solid electrolyte into the cavity, then inserting the second electrode into the cavity and applying pressure to form a solid electrolyte layer of the sulfide solid electrolyte, which then contacts the first electrode and the second electrode at both ends, respectively, to obtain a battery cell; and using an electrochemical workstation, performing a chronoamperometry test on the battery cell to obtain a current-time curve. The current value corresponding to the last time point of the current-time curve is I, and the voltage measured by the chronoamperometry method is U. The resistance R of the sulfide solid electrolyte is calculated as R = U / I, where R is in Ω. Based on R, the electronic conductivity σ of the sulfide solid electrolyte is calculated as S / cm, where σ = (1 / R) × D / A, where D is the thickness of the solid electrolyte layer in the cell, in cm; and A is the contact area between the first electrode or the second electrode and the solid electrolyte layer, i.e., the cross-sectional area of ​​the first electrode or the second electrode, in cm². 2 .

[0011] Furthermore, 140–160 mg of the sulfide solid electrolyte is added to the battery mold.

[0012] Furthermore, the voltage measured by the chronoamperometry method is 0.8–1.2V.

[0013] Furthermore, the time for the chronoamperometry test is 3 to 200 hours.

[0014] Furthermore, the sampling interval for the chronoamperometry test is 1–20 s.

[0015] Furthermore, the chemical formula of the sulfide solid electrolyte is xLi₂S-(1-x)P₂S₅, where 0 <x<1。

[0016] Furthermore, the phosphorus source includes P2S5, P4S4, P4S5, P4S6, P4S7, and P4S. 10 At least one of them.

[0017] Furthermore, the organic solvent includes at least one of n-hexane, N-methylformamide, acetonitrile, tetrahydrofuran, and methyl propionate.

[0018] Furthermore, the reaction temperature is 15–35°C.

[0019] Furthermore, the reaction time is 0.5 to 36 hours.

[0020] Furthermore, the reaction is carried out under an inert atmosphere.

[0021] Furthermore, the solid-liquid separation method includes centrifugation at a speed of 10,000 to 15,000 r / min for 8 to 12 minutes.

[0022] Furthermore, the process prior to sintering includes a drying step at a temperature of 60–70°C.

[0023] Furthermore, the sintering temperature is 80–160°C.

[0024] Furthermore, the sintering time is 30–240 min.

[0025] Furthermore, the sintering is carried out under an inert atmosphere.

[0026] The present invention further provides the application of the method for evaluating the carbon content in lithium sulfide in the preparation of sulfide solid electrolytes and solid batteries.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The method for evaluating the carbon content in lithium sulfide provided by this invention can assess the carbon content in lithium sulfide by testing the electronic conductivity of the sulfide solid electrolyte prepared from lithium sulfide, and thus determine whether the lithium sulfide is suitable as a raw material for preparing sulfide solid electrolyte. This evaluation method is low in cost and provides accurate results. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is an exploded structural diagram of the battery mold provided by the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0032] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0035] In a first aspect, the present invention provides a method for evaluating the carbon content in lithium sulfide, which is also a method for determining whether lithium sulfide is suitable as a raw material for preparing sulfide solid electrolytes, specifically including the following steps:

[0036] Lithium sulfide, phosphorus source and organic solvent are mixed and reacted, followed by solid-liquid separation to obtain a precursor; the precursor is then sintered to obtain a sulfide solid electrolyte.

[0037] The electronic conductivity of the sulfide solid electrolyte was tested.

[0038] If the measured or calculated electronic conductivity of the sulfide solid electrolyte is higher than (i.e., greater than) 1 × 10⁻⁶ -7 If the carbon content in the lithium sulfide is S / cm, it is determined that the lithium sulfide has a high carbon content and is not suitable for preparing sulfide solid electrolytes.

[0039] Conversely (i.e., the measured electronic conductivity of the sulfide solid electrolyte is less than or equal to 10),-7 If the carbon content in the lithium sulfide is low (S / cm), it is determined that the lithium sulfide is suitable for preparing sulfide solid electrolytes.

[0040] This invention assesses the carbon content of lithium sulfide by testing its electronic conductivity, thereby determining whether the lithium sulfide is suitable as a raw material for preparing sulfide solid electrolytes. This assessment method is cost-effective in terms of equipment and labor, provides accurate results, and can be widely adopted.

[0041] Specifically, current technologies focus more on the ionic conductivity of solid electrolytes, which is generally around 10. -4 ~10 -3 While the S / cm ratio is considered, less attention is paid to electronic conductivity. In traditional liquid batteries, electrons can only be transported through the external circuit and cannot pass through the electrolyte between the positive and negative electrodes inside the battery. For solid electrolytes, electrons should also only be transported through the external circuit, with only ions transported internally. Therefore, electronic conductivity should be 3 to 4 orders of magnitude lower than ionic conductivity, i.e., less than or equal to 10. -7 S / cm. If the electronic conductivity of the solid electrolyte is too high, it will self-discharge, leading to a short circuit in the battery.

[0042] Therefore, this invention determines the quality of lithium sulfide used as a raw material for preparing sulfide solid electrolytes by testing the electronic conductivity of the sulfide-based solid electrolyte. This method is an auxiliary method for controlling the quality of raw materials used in the preparation of sulfide solid electrolytes.

[0043] In some specific embodiments, the test method for electronic conductivity testing includes:

[0044] Prepare the battery mold: The battery mold includes a housing with a cavity, a first electrode, and a second electrode, wherein the first electrode and the second electrode have the same dimensions and cross-sectional area. The inner diameter of the cavity is the same as the outer diameter of the first electrode and the second electrode.

[0045] The first electrode is inserted into the cavity, and then the sulfide solid electrolyte is added into the cavity. Next, the second electrode is inserted into the cavity, positioning the sulfide solid electrolyte between the first and second electrodes. Pressure is then applied to form a solid electrolyte layer, which fully contacts the first and second electrodes at both ends, thus obtaining a battery cell. The end surface of the first electrode is in complete contact with the sulfide solid electrolyte; that is, the contact area between the first electrode and the solid electrolyte layer is the cross-sectional area of ​​the first electrode. Similarly, the end surface of the second electrode is in complete contact with the sulfide solid electrolyte; that is, the contact area between the second electrode and the solid electrolyte layer is the cross-sectional area of ​​the second electrode.

[0046] like Figure 1 The diagram shown is an exploded view of the battery mold provided by the present invention.

[0047] An electrochemical workstation was used to perform chronoamperometry tests on the battery cell to obtain a current-time curve.

[0048] The current value corresponding to the last time point of the current-time curve is I, the voltage measured by the chronoamperometry is U, and the resistance R of the sulfide solid electrolyte is calculated, R = U / I, where the unit of R is Ω.

[0049] The electronic conductivity σ of the sulfide solid electrolyte is calculated based on R, where σ is in units of S / cm, and σ = (1 / R) × D / A, where D is the thickness of the solid electrolyte layer in the cell, in cm; and A is the contact area between the first electrode or the second electrode and the solid electrolyte layer, i.e., the cross-sectional area of ​​the first electrode or the second electrode, in cm². 2 .

[0050] In some specific embodiments, 140–160 mg (e.g., 145 mg, 150 mg, or 155 mg) of the sulfide solid electrolyte is added to the battery mold. Insufficient sulfide solid electrolyte will result in an electrolyte sheet that is too thin, causing direct contact and short circuit between the electrodes, leading to no test results. Excessive sulfide solid electrolyte will prevent some of the powder from being pressed into sheets, resulting in an actual sheet weight less than the tested weight. The specific amount can be adjusted according to the dimensions of the battery mold casing.

[0051] In some specific implementations, the voltage tested by the chronoamperometry method is 0.8 to 1.2V; including but not limited to the point value of any one of 0.8V, 0.9V, 1V, 1.1V, and 1.2V or the range between any two.

[0052] In some specific implementations, the chronoamperometry test time is 3 to 200 hours; including but not limited to point values ​​or ranges between any one of 3h, 8h, 12h, 15h, 24h, 48h, 50h, 56h, 64h, 72h, 80h, 100h, 120h, 130h, 150h, 160h, 180h, and 200h. The longer the test time, the more accurate the result; if the time is too short, the current value may not have converged to a stable value, thus failing to obtain an accurate electronic conductivity result.

[0053] In some specific embodiments, the sampling interval of the chronoamperometry test is 1 to 20 s, including but not limited to a point value of any one or a range value between any two of 1s, 2s, 3s, 5s, 6s, 7s, 8s, 10s, 12s, 13s, 15s, 18s and 20s.

[0054] In some specific embodiments, the sulfide solid electrolyte is added into a battery mold, after the test cell is placed stably, pressure is applied slowly to fix, clamp and stabilize the test cell, after the pressure is increased to 5 to 8 t and stabilized, the pressure is adjusted to 0.5 to 1.0 t.

[0055] In some specific embodiments, the chemical formula of the sulfide solid electrolyte is xLi2S-(1-x)P2S5, wherein 0<x<1, and x is, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.8.

[0056] It can be understood that different types of sulfide solid electrolytes have little difference in electronic conductivity, but the carbon content contained therein has a great influence on the electronic conductivity. Therefore, the method for evaluating the carbon content in lithium sulfide provided by the present invention can determine whether the carbon content of the corresponding lithium sulfide is too high and whether it is suitable as a raw material for preparing a sulfide solid electrolyte by measuring the electronic conductivity of different types of sulfide solid electrolytes.

[0057] In some specific embodiments, the phosphorus source includes P2S5, P4S4, P4S5, P4S6, P4S7 and P4S 10 at least one of.

[0058] In some specific embodiments, the organic solvent includes at least one of n-hexane, N-methylformamide, acetonitrile, tetrahydrofuran and methyl propionate.

[0059] In some specific embodiments, the reaction is carried out at room temperature, for example, the reaction temperature can be 15 to 35°C, such as 20°C, 25°C or 30°C, but not limited thereto.

[0060] In some specific embodiments, the reaction time is 0.6 to 36 h, for example, 1h, 2h, 4h, 8h, 12h or 24h.

[0061] In some specific embodiments, the reaction is carried out under an inert atmosphere.

[0062] In some specific embodiments, during the reaction, zirconium beads are added and oscillated with an oscillator, and the collision of zirconium beads can provide energy to the reaction system and homogenize the materials.

[0063] Understandably, based on the target chemical formula of the sulfide solid electrolyte, the molar ratio of each element can be determined, thereby determining the amount of lithium sulfide and phosphorus source to be used.

[0064] It is understood that the amount of organic solvent used has very little effect on the physicochemical properties of the obtained sulfide solid electrolyte. Therefore, the amount of organic solvent used can be any amount commonly used in the art, and this invention does not limit it.

[0065] In some specific embodiments, the solid-liquid separation method includes centrifugation, which comprises centrifuging at a speed of 10,000–15,000 r / min for 8–12 min. The speed includes, but is not limited to, any one of 10,000 r / min, 11,000 r / min, 12,000 r / min, 13,000 r / min, and 14,000 r / min, or a range between any two. The centrifugation time includes, but is not limited to, any one of 8 min, 9 min, 10 min, 11 min, and 12 min, or a range between any two.

[0066] In some specific embodiments, the apparatus used for solid-liquid separation includes a centrifuge.

[0067] In some specific embodiments, a drying step is included before sintering, and the drying temperature is 60-70°C; including but not limited to any one of 60°C, 62°C, 63°C, 65°C, 68°C, and 70°C, or any range between two of them.

[0068] In some specific embodiments, the sintering temperature is 80 to 160°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C or 150°C.

[0069] In some specific embodiments, the sintering time is 30 to 240 minutes, for example, 60 minutes, 120 minutes, 150 minutes or 200 minutes.

[0070] In some specific embodiments, the sintering is carried out under an inert atmosphere.

[0071] In some specific embodiments, the inert atmosphere includes at least one of a nitrogen atmosphere and an argon atmosphere.

[0072] Secondly, the present invention provides the application of the method for evaluating the carbon content in lithium sulfide in the preparation of sulfide solid electrolytes and solid batteries.

[0073] The method provided by this invention involves preparing lithium sulfide to be tested into a sulfide solid electrolyte and then performing an electronic conductivity test. Based on the electronic conductivity of the sulfide solid electrolyte, it can be determined whether lithium sulfide is suitable for preparing a sulfide solid electrolyte. This method is simple, easy to implement, low in cost, and easy to promote and use. It is beneficial for obtaining solid electrolytes and solid batteries with excellent electrochemical performance.

[0074] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0075] Example 1

[0076] The method for assessing the carbon content in lithium sulfide provided in this embodiment includes the following steps:

[0077] (1) Preparation of sulfide solid electrolyte 3 / 4Li2S-1 / 4P2S5: Under nitrogen atmosphere protection, lithium sulfide and phosphorus source P2S5 were added to 30 ml of n-hexane according to the target chemical formula ratio and stirred. 15 g of zirconium beads were added and shaken. The mixture was reacted at 30 °C for 12 h. After the reaction was completed, a precursor solution was obtained. The precursor solution was centrifuged at 12000 r / min for 10 min to separate the solid and liquid phases and obtain the precursor. The precursor was dried at 70 °C and then sintered at 100 °C for 3 h under nitrogen atmosphere protection. After cooling, the sulfide solid electrolyte was obtained.

[0078] (2) The above-mentioned sulfide solid electrolyte was tested for electronic conductivity using the following method: an electrochemical chronoamperometry test was performed using a simple battery mold. The simple mold included two electrodes of the same size (i.e., the same cross-sectional area) (i.e., the first electrode and the second electrode) and a hollow cylindrical polyurethane battery sleeve (i.e., a shell with a cavity). The hollow diameter inside the polyurethane battery sleeve was the same as the diameter of the two electrodes.

[0079] The method for preparing the battery cell includes: first, inserting one electrode into a polyurethane battery sleeve; then adding 150 mg of the aforementioned sulfide solid electrolyte into the polyurethane battery sleeve, followed by inserting the other electrode and initially compacting it. Afterwards, it is placed stably on a hydraulic press, and the pressure is slowly increased to 6 tons and then slowly decreased to 1 ton. The pressure is maintained during the pressure increase and decrease process. After compaction, a solid electrolyte layer is formed, resulting in the battery cell. The thickness of the solid electrolyte layer is D = 0.0700 cm. The contact area between the first or second electrode and the solid electrolyte layer (i.e., the cross-sectional area of ​​the first or second electrode) is A = 1.15 cm². 2 .

[0080] The SP-150e electrochemical workstation was connected to the two electrodes of the battery cell prepared above using wires, and a chronoamperometry test was performed. The chronoamperometry test parameters were: ① Voltage: 1V; ② Test time: 24h; ③ Sampling interval: 10s. After the test, the current-time curve was obtained.

[0081] The current value I corresponding to the last time point of the current-time curve is 6.25 × 10⁻⁶. -6 A. The voltage measured by the chronoamperometry method is U = 1V. Calculate the resistance of the sulfide solid electrolyte: R = U / I = 1.6 × 10⁻⁶ 5 Ω. The electronic conductivity of the sulfide solid electrolyte was calculated as σ = (1 / R) × D / A = 3.8 × 10⁻⁶. -7 S / cm.

[0082] The electronic conductivity of sulfide solid electrolytes is greater than 1×10⁻⁶. -7 The carbon content in the lithium sulfide sample was too high (S / cm), making it unsuitable for preparing sulfide solid electrolytes.

[0083] Example 2

[0084] The method for evaluating the carbon content in lithium sulfide provided in this embodiment is basically the same as that in Example 1. The difference is that the test parameters for the current-time curve are: ① Voltage: 1.2V; ② Test time: 48h; ③ Sampling interval: 20s.

[0085] In this embodiment, the current value I corresponding to the last time point of the current-time curve is 5.73 × 10⁻⁶. -5 A, thus the electronic conductivity of the sulfide solid electrolyte is calculated as σ = (1 / R) × D / A = 3.11 × 10⁻⁶. -6 S / cm.

[0086] The electronic conductivity of sulfide solid electrolytes is greater than 1×10⁻⁶. -7 The carbon content in the lithium sulfide sample was too high (S / cm), making it unsuitable for preparing sulfide solid electrolytes.

[0087] Example 3

[0088] The method for evaluating the carbon content in lithium sulfide provided in this embodiment is basically the same as that in Example 1. The difference is that a sulfide solid electrolyte 1 / 2Li2S-1 / 2P2S5 is prepared, and the amounts of lithium sulfide and phosphorus source to be tested are adjusted according to the proportion of the target chemical formula.

[0089] In this embodiment, the current value I corresponding to the last time point of the current-time curve is 6.79 × 10⁻⁶. -5A, thus the electronic conductivity of the sulfide solid electrolyte is calculated as σ = (1 / R) × D / A = 3.48 × 10⁻⁶. -6 S / cm.

[0090] The electronic conductivity of sulfide solid electrolytes is greater than 1×10⁻⁶. -7 The carbon content in the lithium sulfide sample was too high (S / cm), making it unsuitable for preparing sulfide solid electrolytes.

[0091] Example 4

[0092] The method for evaluating the carbon content in lithium sulfide provided in this embodiment is basically the same as that in Example 1. The difference is that the lithium sulfide to be tested is prepared by a different method than that in Example 1. That is, the carbon content in the lithium sulfide to be tested used in this embodiment is different from that in Example 1.

[0093] In this embodiment, the current value I corresponding to the last time point of the current-time curve is 4.22 × 10⁻⁶. -7 A, thus the electronic conductivity of the sulfide solid electrolyte is calculated as σ = (1 / R) × D / A = 2.39 × 10⁻⁶. -8 S / cm.

[0094] The electronic conductivity of sulfide solid electrolytes is less than 1×10⁻⁶. -7 Based on the S / cm, it was determined that the carbon content in the lithium sulfide to be tested was low, making it suitable for preparing sulfide solid electrolytes.

[0095] The carbon content in lithium sulfide used in each embodiment was tested using glow discharge plasma mass spectrometry to verify the accuracy of the above-mentioned method for assessing the carbon content in lithium sulfide. The carbon content test results are shown in Table 1.

[0096] Table 1. Carbon content test results

[0097]

[0098]

[0099] As shown in Table 1, the lithium sulfide used in Examples 1 to 3 had a high carbon content, which did not meet the standard for sulfide electrolytes, and the corresponding judgment results were accurate. The lithium sulfide used in Example 4 had a low carbon content, which met the standard for sulfide electrolytes, and the corresponding judgment results were accurate.

[0100] This demonstrates that the method for evaluating the carbon content in lithium sulfide provided by this invention can accurately assess whether lithium sulfide is suitable as a raw material for preparing sulfide solid electrolytes.

[0101] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for evaluating the carbon content in lithium sulfide, characterized in that, Includes the following steps: Lithium sulfide, phosphorus source and organic solvent are mixed and reacted, followed by solid-liquid separation to obtain a precursor; the precursor is then sintered to obtain a sulfide solid electrolyte. The electronic conductivity of the sulfide solid electrolyte was tested. If the electronic conductivity of the sulfide solid electrolyte is higher than 1×10 -7 If the carbon content in the lithium sulfide is S / cm, it is determined that the lithium sulfide has a high carbon content and is not suitable for preparing sulfide solid electrolytes; conversely, if the carbon content in the lithium sulfide is low, it is determined that the lithium sulfide has a low carbon content and is suitable for preparing sulfide solid electrolytes.

2. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, The test method for electronic conductivity includes: The battery mold includes a housing with a cavity, a first electrode, and a second electrode, wherein the first electrode and the second electrode have the same cross-sectional area. After inserting the first electrode into the cavity, the sulfide solid electrolyte is added into the cavity. Then, the second electrode is inserted into the cavity and pressure is applied to form a solid electrolyte layer of the sulfide solid electrolyte, which contacts the first electrode and the second electrode at both ends, respectively, to obtain a battery cell. An electrochemical workstation was used to perform chronoamperometry tests on the battery cell to obtain a current-time curve. The current value corresponding to the last time point of the current-time curve is I, the voltage measured by the chronoamperometry is U, and the resistance R of the sulfide solid electrolyte is calculated, R = U / I, and the unit of R is Ω; The electronic conductivity σ of the sulfide solid electrolyte is calculated based on R, where σ is in units of S / cm, and σ = (1 / R) × D / A, where D is the thickness of the solid electrolyte layer in the cell, in cm; and A is the contact area between the first electrode or the second electrode and the solid electrolyte layer, i.e., the cross-sectional area of ​​the first electrode or the second electrode, in cm². 2 .

3. The method for evaluating the carbon content in lithium sulfide according to claim 2, characterized in that, Add 140-160 mg of the sulfide solid electrolyte to the battery mold.

4. The method for evaluating the carbon content in lithium sulfide according to claim 2, characterized in that, At least one of the following conditions must be met: (1) The voltage measured by the chronoamperometry method is 0.8–1.2V; (2) The time for the chronoamperometry test is 3 to 200 hours; (3) The sampling interval of the chronoamperometry test is 1 to 20 seconds.

5. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, The chemical formula of the sulfide solid electrolyte is xLi₂S-(1-x)P₂S₅, where 0 <x<1。 6. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The phosphorus source includes P2S5, P4S4, P4S5, P4S6, P4S7 and P4S 10 At least one of them; (2) The organic solvent includes at least one of n-hexane, N-methylformamide, acetonitrile, tetrahydrofuran and methyl propionate.

7. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The reaction temperature is 15–35 °C; (2) The reaction time is 0.5 to 36 hours; (3) The reaction is carried out under an inert atmosphere.

8. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, The solid-liquid separation method includes centrifugation at a speed of 10,000 to 15,000 r / min for 8 to 12 minutes.

9. The method for evaluating the carbon content in lithium sulfide according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The sintering process includes a drying step, wherein the drying temperature is 60-70°C. (2) The sintering temperature is 80-160℃; (3) The sintering time is 30 to 240 minutes; (4) The sintering is carried out under an inert atmosphere.

10. The application of the method for evaluating the carbon content in lithium sulfide as described in any one of claims 1 to 9 in the preparation of sulfide solid electrolytes and solid-state batteries.

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