A lithium-sulfur battery with internal short circuit warning and warning method thereof

Abstract

The present invention belongs to the field of lithium battery technology, and specifically relates to a lithium-sulfur battery with an early warning internal short circuit, and its preparation and early warning method. The present invention discloses a lithium-sulfur battery with an early warning internal short circuit, comprising a battery core located within a battery housing, wherein an electrolyte is disposed within the battery housing, and the battery core is composed of a sulfur positive electrode, an upper separator, a conductive separator, a lower separator, and a lithium negative electrode arranged in order from top to bottom. The present invention also discloses a method for early warning of an internal short circuit in a lithium-sulfur battery, comprising: detecting the electrode potential of the conductive separator as φ; detecting the electrode potential of the sulfur positive electrode as φ; + ; The final judgment is that: the state of the lithium-sulfur battery is that the negative electrode and the conductive separator are short-circuited; or the state of the lithium-sulfur battery is that the sulfur positive electrode and the conductive separator are short-circuited.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries and relates to a lithium-sulfur battery with early warning of internal short circuit and a preparation method and early warning method thereof. Background Art

[0002] Traditional lithium-ion batteries are approaching their energy density limit (~350Wh / kg), making it difficult to meet the demand for higher energy densities. Lithium-sulfur batteries, with a theoretical energy density of 2500Wh / kg, are a strong contender for achieving 500Wh / kg. Safety is a key consideration for any large-scale battery application, but as energy density increases, safety risks inevitably increase. Because the lithium anode and sulfur cathode easily melt, sublimate, and interact at high temperatures, the safety issues of lithium-sulfur batteries are particularly prominent.

[0003] Thermal runaway caused by abuse is the main cause of safety accidents of lithium-ion batteries. The occurrence of thermal runaway from abuse is usually related to internal short circuit. According to the literature (Research status and analysis for battery safety accidents in electric vehicles [J]. J. Mech. Eng, 2019, 55 (24): 93-104.), 78% of fire accidents in electric vehicles are caused by short circuit. Two preventive strategies are usually adopted to reduce potential risks: passive strategy and active strategy. Passive strategy refers to reducing the risk level when the danger occurs, while active strategy refers to avoiding the occurrence of hazards through effective diagnosis and prediction. If possible, the better option is to nip the danger in the bud, which means that detecting short circuit in the initial stage is crucial. At present, active strategies applied to short circuit warning are mainly targeted at traditional lithium-ion batteries. The shuttle effect existing in lithium-sulfur batteries will inevitably interfere with the detection signal, so whether these strategies can be directly transplanted into lithium-sulfur batteries remains to be verified. Compared with lithium-ion batteries, lithium-sulfur batteries are prone to generate lithium dendrites even in the absence of electrical abuse, which in turn triggers internal short circuit and thermal runaway of the battery. Even in all-solid-state batteries, lithium dendrites can still penetrate the solid electrolyte and cause internal short circuits. In lithium-ion batteries, the formation of lithium dendrites can be detected by the potential difference between the anode and lithium, but similar predictions cannot be achieved in lithium-sulfur batteries because the deposition potential of the lithium metal anode during charging is the same as the potential for dendrite growth. Although a lot of research has been done to inhibit the formation of dendrites, it is almost impossible to completely eliminate them. Therefore, there is an urgent need to develop short-circuit warning strategies for lithium-sulfur batteries. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a lithium-sulfur battery with an early warning internal short circuit and an early warning method thereof.

[0005] In order to solve the above problems, the present invention provides a lithium-sulfur battery with early warning of internal short circuit, including a battery core located in a battery shell, the battery core including a sulfur positive electrode and a lithium negative electrode, an electrolyte is provided in the battery shell, and the battery core is composed of a sulfur positive electrode, an upper diaphragm, a conductive separator, a lower diaphragm and a lithium negative electrode arranged in sequence from top to bottom; that is, the diaphragm is two layers, and the conductive separator is located between the two layers of diaphragms.

[0006] As an improvement of the lithium-sulfur battery with early warning internal short circuit of the present invention, the conductive separator has dual conductivity of ions and electrons.

[0007] Note: The conductive separator is porous and immersed in the electrolyte, so it can transmit ions; it is a conductor and therefore conducts electricity.

[0008] As a further improvement of the lithium-sulfur battery with early warning internal short circuit of the present invention, the conductive separator is any one of the following: a self-supporting conductive material, a conductive coating coated on a separator.

[0009] As a further improvement of the lithium-sulfur battery with internal short circuit warning of the present invention, when the conductive separator is a self-supporting conductive material, the self-supporting conductive material is at least one of a metal mesh, a metal foam, a carbon cloth, a carbon paper, a foamed carbon, a conductive composite foam, a porous metal foil, and an organic composite conductive film; the self-supporting conductive material needs to be cleaned and dried;

[0010] When the conductive spacer is a conductive coating applied on the diaphragm, the conductive coating is composed of a binder and a conductive agent, and the weight content of the conductive agent in the conductive coating is 50% to 90%; the thickness of the conductive coating is 1 to 5 μm; the conductive coating applied on the diaphragm needs to be mixed, coated and dried, and the drying temperature is 40 to 80°C.

[0011] Note: During actual preparation, the adhesive and conductive agent corresponding to the conductive coating are dissolved in a solvent and then coated. During the drying process after coating, the solvent is completely evaporated.

[0012] The binder is at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyacrylate, polytetrafluoroethylene, polyimide, polythiophene, polypyrrole, polyaniline, polyphenylene acetylene and epoxy resin;

[0013] The conductive agent is at least one of conductive carbon black, fullerene, carbon nanotube, carbon fiber, silver nanowire, copper nanowire, graphene, MXene, graphite and carbon aerogel.

[0014] As a further improvement of the lithium-sulfur battery with early warning internal short circuit of the present invention, the upper diaphragm and the lower diaphragm are any of the following:

[0015] Polypropylene porous membrane, polyethylene porous membrane, polyimide porous membrane, polyethylene terephthalate porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, cellulose porous membrane, glass fiber membrane, non-woven fabric, filter paper.

[0016] The present invention also provides a method for early warning of an internal short circuit in a lithium-sulfur battery as described above, comprising the following steps:

[0017] 1) Use the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and the electrode potential of the conductive spacer to φ;

[0018] 2) Use the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and detect the electrode potential of the sulfur positive electrode to φ + ;

[0019] 3) Comparing the electrode potential φ of the conductive separator with a preset stable electrode potential range (1.5 to 3.0 V) (the comparison result can be transmitted to the battery management system);

[0020] 4) The sulfur positive electrode potential φ + The derivative is compared with a preset value range of -1.0 to 1.0 (the comparison result can be transmitted to the battery management system;

[0021] The sulfur positive electrode potential φ during charging + The derivative is compared with the preset value range 2 (-0.005 to 0.005) (the comparison result can be transmitted to the battery management system);

[0022] 5) The battery management system determines:

[0023] Determine whether the electrode potential φ of the conductive separator obtained in step 3) is within the preset stable electrode potential range; determine whether the electrode potential φ of the sulfur positive electrode obtained in step 4) during the static state is within the preset stable electrode potential range; + Whether the derivative of is within the preset range 1; judging the sulfur positive electrode potential φ obtained in the charging process of step 4) + The derivative of is judged to be within the preset range 2;

[0024] If the judgment results of the above three are all yes, no output command;

[0025] On the contrary, when at least any one of the above three judgment results is negative, a power-off command is output;

[0026] 6) When at least any one of the judgment results in step 5) is negative, the electrode potential φ of the conductive spacer is compared with the electrode potential 0 of the reference electrode and the electrode potential φ of the sulfur positive electrode. + Make comparisons;

[0027] When the electrode potential φ of the conductive separator tends to the electrode potential 0 of the reference electrode, the state of the lithium-sulfur battery is determined to be a short circuit between the negative electrode and the conductive separator; conversely, when the electrode potential φ of the conductive separator tends to the electrode potential φ of the sulfur positive electrode, the state of the lithium-sulfur battery is determined to be a short circuit between the negative electrode and the conductive separator. + When the state of the lithium-sulfur battery is determined to be that the sulfur positive electrode and the conductive separator are short-circuited.

[0028] As an improvement to the early warning method for internal short circuit of the lithium-sulfur battery of the present invention:

[0029] In step 3), the preset stable electrode potential range is 1.5 to 3.0 V;

[0030] In step 4), the preset value range 1 is -1.0 to 1.0, and the preset value range 2 is -0.005 to 0.005.

[0031] As a further improvement to the early warning method for internal short circuit of the lithium-sulfur battery of the present invention:

[0032] The sulfur positive electrode potential φ during charging + When comparing the derivative with the preset value range 2, the 50mAh / g stage at the beginning and end of charging is excluded (i.e., taking the total capacity of 1500mAh / g as an example, the capacity stage selected for comparison is 50-1450mAh / g).

[0033] The short circuit warning strategy of the present invention is to introduce a conductive intermediate layer into the lithium-sulfur battery and detect its potential change.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The lithium-sulfur battery provided by the present invention can provide early warning of short circuits between the positive and negative electrodes and leave sufficient time to take measures, thereby effectively avoiding thermal runaway caused by short circuits;

[0036] (2) The preparation method provided by the present invention has a simple process, high requirements on equipment, and is easy to industrialize.

[0037] (3) The early warning method provided by the present invention is simple and accurate, and can identify the source of the short circuit and provide guidance for the measures to be taken. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0039] Figure 1 A schematic diagram of the structure of a lithium-sulfur battery with an internal short circuit warning;

[0040] Figure 2The voltage between the positive electrode and the conductive separator when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during the static state of Example 1;

[0041] V S represents the sulfur-conducting positive electrode potential, V SP Represents the conductive interlayer potential of carbon black.

[0042] Figure 3 is the derivative of the positive electrode and voltage when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during the static state of Example 1;

[0043] Figure 4 The voltage between the positive electrode and the conductive separator when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during the charge and discharge process of Example 1;

[0044] Figure 5 is the derivative of the positive electrode voltage when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during charging of Example 1;

[0045] Figure 6 The voltage between the positive electrode and the conductive separator when a short circuit is applied and removed between the sulfur positive electrode and the conductive separator during the static state of Example 1;

[0046] Figure 7 The voltage between the positive electrode and the conductive separator when a short circuit is applied and removed between the sulfur positive electrode and the conductive separator during the charge and discharge process of Example 1;

[0047] Figure 8 is the voltage between the second lithium negative electrode and the conductive separator during the lithium deposition process of Example 2;

[0048] Figure 9 is the voltage between the second lithium negative electrode and the conductive separator during the lithium deposition process of Example 3;

[0049] Figure 10 is the voltage between the second lithium negative electrode and the conductive separator during the lithium deposition process of Example 4;

[0050] Figure 11 is the voltage between the second lithium negative electrode and the conductive separator during the lithium deposition process of Example 5;

[0051] Figure 12 is the voltage between the second lithium negative electrode and the conductive separator during the lithium deposition process of Example 6;

[0052] Figure 13 is the voltage of the second lithium negative electrode during the lithium deposition process of Comparative Example 3;

[0053] Figure 14 is the voltage of the second lithium negative electrode during the lithium deposition process of Comparative Example 4. DETAILED DESCRIPTION

[0054] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0055] In the following examples, the sulfur positive electrode and lithium negative electrode are configured exactly as in conventional batteries. The thickness of the upper and lower separators are also exactly the same as those in conventional batteries, i.e., the thickness of the upper and lower separators is approximately 25 μm.

[0056] Example 1: A lithium-sulfur battery (full battery) with an early warning internal short circuit, comprising the following steps:

[0057] 1) Preparation of conductive layer coated diaphragm:

[0058] Conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 7:3, nitrogen-methyl pyrrolidone (N-methyl pyrrolidone) is added to the resulting mixture and stirred uniformly to obtain a conductive paste with a mass content of 10% of the mixture, that is, the solid content of the conductive paste is 10%;

[0059] The conductive slurry was coated on one side of the upper diaphragm (polypropylene porous membrane) with a 100 μm scraper to form a conductive barrier wet film with a thickness of 100 μm, and then transferred to a 60°C oven for drying for 1 hour to obtain a conductive barrier coated diaphragm composed of the upper diaphragm and the conductive barrier (the thickness of the conductive barrier is about 5 μm).

[0060] 2) Preparation of lithium-sulfur batteries:

[0061] A sulfur positive electrode is stacked on the surface of the upper diaphragm, and a conductive separator, a lower diaphragm, and a lithium negative electrode are stacked in sequence to form a battery core, which is then assembled in a conventional manner, that is, packaged in a glove box with an inert atmosphere: the battery core is encapsulated in a battery casing, the conductive separator is connected to the third electrode, and a conventional ether electrolyte (about 500 μL) is set in the battery casing; the battery core is in contact with the ether electrolyte.

[0062] Experiment 1: Testing method of lithium-sulfur battery:

[0063] 1) Test circuit connection:

[0064] Two battery test channels are used, namely battery test channel A and battery test channel B;

[0065] Use the counter electrode and reference electrode of battery test channel A to connect to the lithium negative electrode, and the working electrode and working sensing electrode to connect to the sulfur positive electrode; the voltage of the sulfur positive electrode is obtained by the working sensing electrode of test channel A;

[0066] The reference electrode of battery test channel B is connected to the lithium negative electrode, and the working sensing electrode is connected to the conductive spacer through the third electrode; the counter electrode and working electrode of battery test channel B are suspended in the air; the voltage of the conductive spacer is obtained by the working sensing electrode of test channel B.

[0067] 2) Negative electrode-conductive barrier short circuit test:

[0068] During the static state of the lithium-sulfur battery, a copper-zinc wire with a resistance of ~11.2Ω was used to create a short circuit between the lithium negative electrode and the conductive separator, and the voltage changes of the sulfur positive electrode and the conductive separator were recorded respectively.

[0069] During the charge and discharge process of the lithium-sulfur battery at 0.2C, a copper-zinc wire with a resistance of ~11.2Ω was used to create a short circuit between the lithium negative electrode and the conductive separator, and the voltage changes of the sulfur positive electrode and the conductive separator were recorded respectively.

[0070] The recorded data are Figure 2 and Figure 4 , V S represents the sulfur cathode potential, V SP Represents the potential of the carbon black conductive barrier layer; the sudden change of the voltage of the conductive barrier layer tending to 0 reflects the short circuit between the negative electrode and the conductive barrier layer.

[0071] 3) Positive electrode-conductive barrier short circuit test:

[0072] During the static state of the lithium-sulfur battery, a copper-zinc wire with a resistance of 11.2 Ω was used to create a short circuit between the sulfur cathode and the conductive separator, and the voltages and their derivatives were recorded.

[0073] During the charge and discharge process of the lithium-sulfur battery at 0.2C, a copper-zinc wire with a resistance of ~11.2Ω was used to create a short circuit between the sulfur positive electrode and the conductive separator, and the voltages and their derivatives of the sulfur positive electrode and the conductive separator were recorded respectively.

[0074] The recorded data are Figure 6 and Figure 7 , V S represents the sulfur cathode potential, V SP represents the potential of the carbon black conductive separator; the sudden change of the voltage of the conductive separator toward the sulfur positive electrode reflects the short circuit between the positive electrode and the conductive separator.

[0075] Example 2: A lithium-lithium battery:

[0076] 1) Preparation of conductive layer coated diaphragm:

[0077] Same as step 1) in Example 1.

[0078] 2) Assembly of symmetrical batteries:

[0079] The sulfur positive electrode is changed to lithium electrode 2, and the lithium negative electrode is used as lithium electrode 1;

[0080] Note: The lithium-lithium battery in Example 2 is a symmetrical battery, which is only used to meet the test requirements.

[0081] Experiment 2

[0082] 1) Test circuit connection:

[0083] Two battery test channels are used, namely battery test channel A and battery test channel B;

[0084] Connect the counter electrode and reference electrode of battery test channel A to lithium electrode 1, and the working electrode and working sensing electrode to lithium electrode 2; the voltage of lithium electrode 2 is obtained from the working sensing electrode of test channel A;

[0085] The reference electrode of battery test channel B is connected to lithium electrode 1, and the working sensing electrode is connected to the conductive spacer through the third electrode. The counter electrode and working electrode of battery test channel B are suspended in the air; the voltage of the conductive spacer is obtained by the working sensing electrode of test channel B.

[0086] 2) Lithium dendrite short circuit test:

[0087] The short-circuit process is that lithium dendrites continue to grow during the lithium deposition process on the lithium electrode, piercing the diaphragm and causing a short circuit.

[0088] At 1 mA / cm 2 Lithium deposition was performed at a current density of 100 nm and the voltages of the second lithium anode and the conductive separator were recorded simultaneously.

[0089] The recorded data is as follows Figure 8 , V Cu represents the potential of lithium electrode 2, V SP represents the potential of the carbon black conductive interlayer; the sudden change of the voltage of the conductive interlayer tending to 0 reflects that the lithium dendrites pierce the lower separator and form a short circuit with the conductive interlayer.

[0090] Example 3: A lithium-lithium battery:

[0091] 1) Preparation of conductive layer coated diaphragm:

[0092] The carbon nanotubes and polyvinylidene fluoride are mixed in a mass ratio of 7:3, and nitrogen-methyl pyrrolidone (N-methyl pyrrolidone) is added to the resulting mixture and stirred uniformly to obtain a conductive paste with a mass content of 2% of the mixture, that is, the solid content of the conductive paste is 2%;

[0093] The coating and drying process is the same as in Example 1;

[0094] 2) The assembly of the symmetrical battery is the same as that of Example 2.

[0095] The detection method refers to Experiment 2, and the results are:

[0096] The recorded data is as follows Figure 9 , V Cu represents the potential of lithium electrode 2, V CNT represents the potential of the carbon nanotube conductive spacer; the sudden change of the voltage of the conductive spacer tending to 0 reflects that the lithium dendrite pierces the lower separator and forms a short circuit with the conductive spacer.

[0097] Example 4: A lithium-lithium battery:

[0098] 1) Preparation of conductive layer coated diaphragm:

[0099] Graphite sheets and polyvinylidene fluoride are mixed in a mass ratio of 7:3, and nitrogen-methyl pyrrolidone (N-methyl pyrrolidone) is added to the resulting mixture and stirred uniformly to obtain a conductive paste with a mass content of 10% of the mixture, that is, the solid content of the conductive paste is 10%;

[0100] The coating and drying process is the same as in Example 1;

[0101] 2) The assembly of the symmetrical battery is the same as in Example 2.

[0102] The detection method refers to Experiment 2, and the results are:

[0103] The recorded data is Figure 10 , V Cu represents the potential of lithium electrode 2, V GF Represents the potential of the conductive interlayer of the graphite sheet; the sudden change of the voltage of the conductive interlayer tending to 0 reflects that the lithium dendrites pierce the lower diaphragm and form a short circuit with the conductive interlayer.

[0104] Example 5: A lithium-lithium battery:

[0105] 1) Preparation of self-supporting conductive materials:

[0106] The nickel foam was ultrasonically cleaned in ethanol for 5 min, then roller-pressed with a pressure of 2 MPa, and then transferred to a 60°C oven for drying for 1 h to obtain a self-supporting conductive material as a conductive spacer.

[0107] 2) Lithium-lithium battery preparation:

[0108] The second lithium electrode, the upper separator, the conductive separator, the lower separator, and the first lithium electrode are stacked in sequence to form a battery core, which is then assembled in a conventional manner, that is, packaged in a glove box with an inert atmosphere: the battery core is encapsulated in a battery casing, the conductive separator is connected to the third electrode, and a conventional ether electrolyte (about 500 μL) is set in the battery casing; the battery core is in contact with the ether electrolyte.

[0109] The detection method refers to Experiment 2, and the results are:

[0110] The recorded data is as follows Figure 11 , V Cu represents the potential of lithium electrode 2, V Foam Ni represents the potential of the nickel foam conductive interlayer; the sudden change of the conductive interlayer voltage toward 0 reflects that the lithium dendrites pierce the lower diaphragm and form a short circuit with the conductive interlayer.

[0111] Example 6: A lithium-lithium battery:

[0112] 1) Preparation of self-supporting conductive materials:

[0113] The copper mesh was ultrasonically cleaned in ethanol for 5 minutes and then transferred to a 60°C oven for drying for 1 hour to obtain a self-supporting conductive material as a conductive spacer.

[0114] 2) Lithium-lithium battery preparation:

[0115] Equivalent to Example 5.

[0116] The detection method refers to Experiment 2, and the results are:

[0117] The recorded data is as follows Figure 12 , V Cu represents the potential of lithium electrode 2, V Mesh Cu represents the potential of the conductive spacer of the copper mesh; the sudden change of the voltage of the conductive spacer tending to 0 reflects that the lithium dendrites pierce the lower diaphragm and form a short circuit with the conductive spacer.

[0118] Note: Examples 2 to 6 above simulate the situation in which a short circuit in a real battery is caused by the growth of lithium dendrites. Therefore, the short circuit between the lithium negative electrode and the conductive separator made of copper-zinc wire can better simulate the actual short circuit caused by lithium dendrites.

[0119] Comparative Example 1: Compared with Example 1, the conductive spacer is removed;

[0120] The details are as follows:

[0121] Cancel step 1) of Example 1;

[0122] The sulfur positive electrode, the upper separator, the lower separator, and the lithium negative electrode are stacked in sequence to form a battery core, and the rest is the same as step 2 of Example 1).

[0123] The detection methods of Experiment 3 and Comparative Example 1 are as follows:

[0124] 1) Test line connection:

[0125] Use a battery test channel with the counter electrode and reference electrode connected to the lithium negative electrode, and the working electrode and working sensing electrode connected to the sulfur positive electrode;

[0126] 2)Stationary and charge-discharge test:

[0127] When the lithium-sulfur battery is at rest and during charge and discharge at 0.2C, the positive and negative electrode voltages and their derivatives are recorded.

[0128] Since there is no conductive separator, there is no detectable signal, that is, there is no detectable signal showing whether the lower separator is pierced by lithium dendrites, so it is impossible to detect whether the lower separator is pierced.

[0129] Comparative Example 2: Compared with Example 1, the conductive spacer and the upper diaphragm are eliminated:

[0130] The details are as follows:

[0131] Cancel step 1) of Example 1;

[0132] The sulfur positive electrode, the lower separator, and the lithium negative electrode are stacked in sequence to form a battery core, and the rest is the same as step 2 of Example 1).

[0133] This comparative example 2 belongs to the prior art.

[0134] The testing method for Comparative Example 2 followed that of Experiment 3 above. The results showed that the sulfur positive electrode voltage showed no detectable warning signal before a short circuit occurred between the positive and negative electrodes. Therefore, compared to Example 1, the absence of the conductive separator and upper separator makes it impossible to determine the extent of separator failure before a short circuit occurs between the positive and negative electrodes in a lithium-sulfur battery.

[0135] Comparative Example 3: Compared with Example 2, the conductive spacer is removed; the rest is the same as Example 2.

[0136] The detection methods of Experiment 4 and Comparative Example 3 are as follows:

[0137] 1) Use the counter electrode and reference electrode of a battery test channel to connect to lithium electrode 1, and the working electrode and working sensing electrode to connect to lithium electrode 2;

[0138] 2) Lithium dendrite short circuit test:

[0139] At 1 mA / cm 2 Lithium deposition was performed at a current density of , and the voltage of the lithium electrode 2 was recorded simultaneously.

[0140] The recorded data is Figure 13 , V Cu Represents the potential of lithium electrode 2; since there is no conductive barrier, there is no detectable signal, so it is impossible to detect whether the lower membrane is punctured.

[0141] Comparative Example 4: Compared with Example 2, the conductive spacer and the upper diaphragm are removed; the rest are the same as Example 2.

[0142] The test method of comparative example 4 refers to the above experiment 4, and the results are as follows: the recorded data is Figure 14 , V Cu Represents the potential of the lithium electrode. There are no detectable warning signals before a short circuit occurs between the two electrodes. In other words, the voltage of the copper electrode shows no abnormality before a short circuit occurs. Therefore, it is impossible to determine the extent of separator failure before a short circuit occurs.

[0143] Early Warning Method Example 1: A method for early warning of an internal short circuit in a lithium-sulfur battery. Using the lithium-sulfur battery with the early warning internal short circuit described in Example 1, the test circuit connections are specifically as follows:

[0144] Two battery test channels are used, namely battery test channel A and battery test channel B;

[0145] The counter electrode and reference electrode of battery test channel A are connected to the lithium negative electrode, and the working electrode and working sensing electrode are connected to the sulfur positive electrode; the voltage of the sulfur positive electrode is obtained by the working sensing electrode of test channel A;

[0146] The reference electrode of battery test channel B is connected to the lithium negative electrode, and the working sensing electrode is connected to the conductive spacer through the third electrode; the counter electrode and working electrode of battery test channel B are suspended in the air; the voltage of the conductive spacer is obtained by the working sensing electrode of test channel B.

[0147] Therefore, according to the working sensing electrode of the test channel B, the electrode potential (voltage) of the conductive spacer can be obtained; according to the working sensing electrode of the test channel A, the electrode potential (voltage) of the sulfur positive electrode can be obtained;

[0148] Follow these steps in order:

[0149] 1) Using the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and the electrode potential of the detection conductive spacer to φ;

[0150] 2) Use the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and detect the electrode potential of the sulfur positive electrode to φ + ;

[0151] 3) Compare the electrode potential φ of the conductive spacer with the preset electrode potential range of 1.5 to 3.0 V, and transmit the comparison result to the battery management system;

[0152] 4) The sulfur positive electrode potential φ + The derivative is compared with a preset value range of -1.0 to 1.0, and the comparison result is transmitted to the battery management system;

[0153] The sulfur positive electrode potential φ during charging +The derivative of the battery is compared with a preset value range of -0.005 to 0.005, excluding the 50mAh / g stage at the beginning and end of charging (i.e., taking the total capacity of 1500mAh / g as an example, the capacity stage selected for comparison is 50 to 1450mAh / g), and the comparison result is transmitted to the battery management system;

[0154] 5) The battery management system determines:

[0155] Determine whether the electrode potential φ of the conductive separator obtained in step 3) is within the preset range (preset stable electrode potential range); determine whether the sulfur positive electrode potential φ obtained in step 4) during the static state is within the preset range (preset stable electrode potential range); + Whether the derivative of is within the preset range; judging step 4) the sulfur positive electrode potential φ obtained during the charging process + The derivative of is judged to be within the preset range;

[0156] If the above three conditions are met at the same time, that is, if the judgment results of the above three are all yes, no output command;

[0157] On the contrary, when at least any one of the above three conditions cannot be satisfied, that is, when the judgment result of at least any one of the above three conditions is negative, a power-off command is output.

[0158] 6) When the judgment result of step 5) is no, the electrode potential φ of the conductive spacer is compared with the electrode potential 0 of the reference electrode and the electrode potential φ of the sulfur positive electrode. + Make a comparison.

[0159] When the electrode potential φ of the conductive separator tends to the electrode potential 0 of the reference electrode, the state of the lithium-sulfur battery is determined to be a short circuit between the negative electrode and the conductive separator; conversely, when the electrode potential φ of the conductive separator tends to the electrode potential φ of the sulfur positive electrode, the state of the lithium-sulfur battery is determined to be a short circuit between the negative electrode and the conductive separator. + When the state of the lithium-sulfur battery is determined to be that the sulfur positive electrode and the conductive separator are short-circuited.

[0160] The short circuit warning strategy of the present invention is to introduce a conductive intermediate layer into the lithium-sulfur battery and detect its potential change. The recorded data is Figure 3 and Figure 5 Therefore, it is known that the short-circuit warning method can accurately detect the short-circuit state inside the battery, and the occurrence of thermal runaway accidents can be prevented by taking power-off measures.

[0161] Figure 2 and Figure 4 The voltages between the positive electrode and the conductive separator when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during the rest and charge-discharge processes of Example 1 are respectively; Figure 3 and Figure 5These are the derivatives of the positive electrode voltage when a short circuit is applied and removed between the lithium negative electrode and the conductive separator during the rest and charge processes of Example 1. It can be seen that, whether at rest or during charge and discharge, a short circuit between the lithium negative electrode and the conductive separator can be quickly and accurately detected by a sudden change in the conductive separator voltage or a sudden change in the sulfur positive electrode voltage derivative. Figure 6 and Figure 7 The voltages between the sulfur positive electrode and the conductive separator during the static state and the charge-discharge process in Example 1 are shown, respectively, when a short circuit is applied and removed between the sulfur positive electrode and the conductive separator. It can be seen that, whether static or during charge-discharge, a short circuit between the sulfur positive electrode and the conductive separator can be quickly and accurately detected by a sudden change in the conductive separator voltage. Therefore, a sudden change in the conductive separator voltage or a sudden change in the sulfur positive electrode voltage derivative can provide an early warning of an impending short circuit between the lithium negative electrode and the sulfur positive electrode, effectively preventing thermal runaway.

[0162] In Comparative Examples 1 and 2, however, there was no obvious sudden change in the voltage of the sulfur positive electrode before a short circuit occurred between the lithium negative electrode and the sulfur positive electrode, and no early warning of the internal short circuit could be given.

[0163] Figure 8 、 Figure 9 and Figure 10 The voltages between the second lithium electrode and the conductive separator during the lithium deposition process of Example 2, Example 3 and Example 4 are respectively, Figure 11 and Figure 12 The voltages of the second lithium electrode and the conductive separator during the lithium deposition process in Examples 5 and 6, respectively, are shown. It can be seen that the voltage of the conductive separator drops rapidly from 2.0-3.0V to nearly 0V before a short circuit occurs between the first and second lithium electrodes, indicating that lithium dendrites have pierced the underlying porous membrane and short-circuited the conductive separator. Therefore, internal short circuits caused by lithium dendrites in lithium-sulfur batteries can be warned by sudden voltage changes in the conductive separator.

[0164] Figure 13 and Figure 14 The voltages of the second lithium electrode during the lithium deposition process are shown in Comparative Example 3 and Example 4. It can be seen that before the short circuit occurs between the first and second lithium negative electrodes, no voltage anomalies are detected to provide an early warning of the occurrence of an internal short circuit.

[0165] In summary, by detecting the sudden change in the voltage of the conductive spacer or the sudden change in the inverse of the sulfur positive electrode voltage, the short circuit between the lithium negative electrode or the sulfur positive electrode and the conductive spacer can be detected quickly and accurately, thereby providing an early warning for the short circuit between the lithium negative electrode and the sulfur positive electrode, and effectively reducing the probability of thermal runaway.

[0166] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A lithium-sulfur battery with an internal short circuit warning, comprising a battery core located within a battery housing, the battery core comprising a sulfur positive electrode and a lithium negative electrode, and an electrolyte disposed within the battery housing, characterized in that: The battery core consists of a sulfur positive electrode, an upper separator, a conductive separator, a lower separator and a lithium negative electrode arranged in order from top to bottom; The conductive spacer has dual conductivity of ions and electrons; The early warning method for internal short circuit of lithium-sulfur battery includes the following steps: 1) Use the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and the electrode potential of the conductive spacer to φ; 2) Use the lithium negative electrode as the reference electrode, set the electrode potential of the reference electrode to 0, and detect the electrode potential of the sulfur positive electrode to φ + ; 3) Compare the electrode potential φ of the conductive spacer with the preset stable electrode potential range; The preset stable electrode potential range is 1.5~3.0 V; 4) The sulfur positive electrode potential φ + The derivative of is compared with a preset value range of one; The sulfur positive electrode potential during charging + The derivative of is compared with the preset value range 2; The preset value range 1 is -1.0~1.0, and the preset value range 2 is -0.005~0.005; The sulfur positive electrode potential φ during the charging process + When comparing the derivative with the preset value range 2, the initial and final stages of charging at 50 mAh / g are excluded; 5) Battery management system judgment: Determine whether the electrode potential φ of the conductive separator obtained in step 3) is within the preset stable electrode potential range; determine whether the electrode potential φ of the sulfur positive electrode obtained in step 4) during the static state is within the preset stable electrode potential range; + Whether the derivative of is within the preset value range 1; judging the sulfur positive electrode potential φ obtained in the charging process in step 4) + The derivative of is judged to be within the second preset value range; If the judgment results of the above three are all yes, no output command; On the contrary, when at least any one of the above three judgment results is negative, a power-off command is output; 6) When at least any one of the judgment results in step 5) is negative, the electrode potential φ of the conductive spacer is compared with the electrode potential 0 of the reference electrode and the electrode potential φ of the sulfur positive electrode. + Make comparisons; When the electrode potential φ of the conductive separator approaches the electrode potential 0 of the reference electrode, it is determined that the state of the lithium-sulfur battery is that the negative electrode and the conductive separator are short-circuited; On the contrary, when the electrode potential φ of the conductive separator tends to the electrode potential φ of the sulfur positive electrode + When the state of the lithium-sulfur battery is determined to be that the sulfur positive electrode and the conductive separator are short-circuited.

2. The lithium-sulfur battery with an internal short circuit warning according to claim 1, characterized in that: The conductive spacer is any one of the following: a self-supporting conductive material, a conductive coating coated on a diaphragm.

3. The lithium-sulfur battery with internal short circuit warning according to claim 2, characterized in that: When the conductive spacer is a self-supporting conductive material, the self-supporting conductive material is at least one of a metal mesh, a metal foam, a carbon cloth, a carbon paper, a foamed carbon, a conductive composite foam, a porous metal foil and an organic composite conductive film; When the conductive spacer is a conductive coating applied to the diaphragm, the conductive coating is composed of a binder and a conductive agent, and the weight content of the conductive agent in the conductive coating is 50% to 90%; the thickness of the conductive coating is 1 to 5 mm; The binder is at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyacrylate, polytetrafluoroethylene, polyimide, polythiophene, polypyrrole, polyaniline, polyphenylene acetylene and epoxy resin; The conductive agent is at least one of conductive carbon black, fullerene, carbon nanotube, carbon fiber, silver nanowire, copper nanowire, graphene, MXene, graphite and carbon aerogel.

4. The lithium-sulfur battery with an internal short circuit warning according to any one of claims 1 to 3, characterized in that: The upper diaphragm and the lower diaphragm are any of the following: Polypropylene porous membrane, polyethylene porous membrane, polyimide porous membrane, polyethylene terephthalate porous membrane, polytetrafluoroethylene porous membrane, polyvinylidene fluoride porous membrane, cellulose porous membrane, glass fiber membrane, non-woven fabric, filter paper.

Images