CN103247822B - Lithium-sulfur secondary battery system - Google Patents

Abstract

The invention discloses a lithium-sulfur secondary battery system. The system includes a positive electrode, a negative electrode and an electrolyte, wherein the active material of the positive electrode is a carbon-sulfur composite material, the negative electrode uses a metal lithium sheet, and the electrolyte is a non-aqueous battery with a high salt concentration. Electrolyte, described high salt concentration non-aqueous electrolyte comprises lithium salt or sodium salt or lithium-sodium mixed salt and non-aqueous organic solvent; The molar ratio of described lithium salt or lithium-sodium mixed salt and non-aqueous organic solvent is 2-10 mol/ Lift. The present invention has the following remarkable advantages: since the electrolyte system effectively suppresses the dissolution of polysulfide ions in the electrolyte during charging and discharging of lithium-sulfur batteries, it avoids the shuttle effect of polysulfide ions dissolved in the electrolyte at the end of charging , thus preventing overcharging and increasing the Coulombic efficiency to over 99%. As a result, the battery cycle performance has also been greatly improved.

Description

Lithium sulfur secondary battery system

technical field

The invention belongs to the technical field of batteries, in particular to a lithium-sulfur secondary battery system.

Background technique

The current commercial use of lithium-ion battery cathode materials is mainly concentrated on transition metal lithium intercalation oxides, including cobalt, iron, nickel, manganese oxides and their doping compounds, but such compounds are limited by their own theoretical capacity. At present, the theoretical energy density of the commercialized system is around 600Wh/Kg. Although the industrial level continues to improve, the current power battery using this as the cathode material can achieve a maximum of 200Wh/Kg, and it is expected to reach 300Wh/Kg in the future, but the room for improvement has been limited. very limited. The development of future electric vehicles urgently requires a cathode material with higher energy density.

Due to its high specific capacity (S ₈ 1675mAh/g), the theoretical energy density can reach 2800Wh/kg, and it is considered to be the development direction of lithium secondary batteries in the future. Still in the laboratory stage. The main problem is that it cannot effectively suppress the dissolution of the intermediate products Li ₂ S ₈ , Li ₂ S ₆ , and Li ₂ S ₄ in the electrolyte during the charging and discharging process. Once the polysulfide ions dissolve in the electrolyte, a serious shuttle effect will occur during the charging process, resulting in low charge and discharge efficiency and large self-discharge, which will lead to deterioration of battery performance and short battery life. In addition, the shuttle effect will also lead to the deposition of non-conductive elemental sulfur or polysulfide compounds on the surface of the conductive agent during charging, which increases the resistance between the conductive agent particles and between the conductive agent and the current collector. And as the number of charge and discharge increases, the internal resistance of the battery continues to rise, the specific energy gradually decreases, and the cycle performance of the battery deteriorates rapidly. Therefore, as far as the current development of the system is concerned, how to suppress the shuttle effect has become the key to improving the coulombic efficiency of the system and the cycle life of the battery.

Since in the lithium-sulfur battery system, the active material of the positive electrode is elemental sulfur that does not contain lithium, the negative electrode uses metallic lithium, so safety performance will become a problem that must be solved for this system in the future. The main reason for the safety hazard of this system is that lithium dendrites are generated due to the uneven deposition of lithium metal in the negative electrode during the charging and discharging process, which easily causes internal short circuit of the battery and causes safety problems.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned problems in current lithium-sulfur batteries, and propose to replace the existing electrolyte system with an electrolyte system with high-concentration lithium salt as the electrolyte, so as to greatly reduce the solubility of polysulfide ions in the electrolyte, thereby achieving effective inhibition The shuttle effect improves the Coulombic efficiency of charge and discharge, and is expected to completely solve the problem of poor cycle performance of lithium-sulfur batteries.

The invention provides a secondary rechargeable lithium-sulfur battery system. The system includes a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode active material is a carbon-sulfur composite material, the negative electrode uses metal lithium sheets, and the electrolyte is a high-salt concentration Non-aqueous electrolyte, the high-salt-concentration non-aqueous electrolyte includes lithium salt or sodium salt or lithium-sodium mixed salt and non-aqueous organic solvent; the molar ratio of described lithium salt or lithium-sodium mixed salt to non-aqueous organic solvent is 3-9 mol/liter.

The present invention has the following significant advantages:

Since the electrolyte system effectively inhibits the dissolution of polysulfide ions in the electrolyte during charging and discharging of lithium-sulfur batteries, it avoids the shuttle effect of polysulfide ions dissolved in the electrolyte at the end of charging, thereby preventing overcharging. Increase Coulombic efficiency to over 99%. As a result, the battery cycle performance has also been greatly improved.

In addition, the addition of porous carbon and carbon nanotubes with a high specific surface area replaces the existing conductive additive acetylene black, so that the conductive additive also has a good adsorption effect on a small amount of polysulfide ions dissolved in the electrolyte, making the system in charge and discharge. The circulation and coulombic efficiency of the process are further improved. Moreover, by optimizing the conductive current collector and replacing the traditional aluminum foil with a layer of carbon coated on the aluminum foil, the interface performance between the active material and the current collector is improved to a certain extent, and the conductivity is improved.

In summary, by using a high-concentration non-aqueous organic electrolyte and using carbon with a high specific surface area (porous carbon or carbon nanotubes, etc.) that has a certain adsorption effect on polysulfide ions as a conductive additive, a layer of carbon The aluminum foil used as a current collector effectively solves some problems caused by the dissolution of polysulfide ions during the charging and discharging process, and the electrochemical performance of the lithium-sulfur battery is significantly improved.

Description of drawings

Fig. 1 is the cycle specific capacity and coulombic efficiency graph of embodiment 1 gained, and wherein the horizontal axis is the number of cycles (N), the left vertical axis is the charge-discharge specific capacity (mAh/g), and the right vertical axis is the coulombic efficiency (%); The inset is the charge-discharge curve of the system in the first week, where the horizontal axis is the charge-discharge specific capacity (mAh/g), and the vertical axis is the charge-discharge voltage (V). Test parameters: constant current test, voltage range 1-3V, charge and discharge rate is 0.2C.

Fig. 2 is in embodiment 2, adopts different concentrations of lithium salt electrolytes in the charge-discharge rate 0.2C cycle specific capacity comparison chart, wherein the horizontal axis is the number of cycles (N), and the vertical axis is the charge-discharge specific capacity (mAh/g );

Figure 3 is a comparison diagram of cycle coulombic efficiency at a charge-discharge rate of 0.2C using different concentrations of lithium salt electrolytes in Example 2, wherein the horizontal axis is the number of cycles (N), and the vertical axis is the coulombic efficiency (%);

Fig. 4 is the first-cycle charge-discharge curve of the carbon-sulfur composite material prepared by using 1# porous carbon in Example 2 and the carbon-sulfur ratio is 5:5, where the horizontal axis is the charge-discharge specific capacity (mAh/g) , the vertical axis is the charging and discharging voltage (V)

Fig. 5 is a comparison chart of the first week charge and discharge curves of the carbon-sulfur composite materials prepared by using 2# porous carbon and the carbon-sulfur ratios are 4:6, 3:7 and 2:8 in Example 2, wherein The horizontal axis is the charge-discharge specific capacity (mAh/g), and the vertical axis is the charge-discharge voltage (V).

Fig. 6 is a diagram of the cycle specific capacity of the lithium-sulfur battery in the first 100 cycles at a charge-discharge rate of 0.1C in Example 3, wherein the horizontal axis is the number of cycles (N), and the vertical axis is the charge-discharge specific capacity (mAh/g).

7 is a cycle specific capacity diagram of the lithium-sulfur battery in Example 4 at different charge-discharge rates, wherein the horizontal axis is the number of cycles (N), and the vertical axis is the charge-discharge specific capacity (mAh/g).

Fig. 8 is the first cycle charge and discharge graph of the lithium-sulfur battery with a charge and discharge rate of 0.2C at a high temperature of 50 degrees Celsius in Example 5, wherein the horizontal axis is the charge and discharge specific capacity (mAh/g), and the vertical axis is the charge and discharge Voltage (V).

detailed description

Example 1

The lithium-sulfur battery system simulates the battery, and the specific manufacturing process is as follows:

Positive electrode material and its pole piece production process:

The carbon-sulfur composite material uses 2# porous carbon. The specific parameters are as follows: specific surface area (m2/g): 1431, average pore diameter (nm): 3.8, pore volume (cc/g): 1.58

The preparation process of the cathode material is as follows:

Mix porous carbon 2# with elemental sulfur powder at a ratio of 4:6 by weight, seal the above carbon-sulfur composite material into an airtight argon-filled glass tube, and heat-treat the raw material at 155 degrees for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, carbon nanotubes and polyvinylidene fluoride (PVDF) according to the weight percentage of 8:1:1, and stir and mix them evenly with pyrrolidone as a dispersant. The aluminum foil coated with a layer of carbon is used as the current collector, the mixed slurry is evenly coated on the current collector, and then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

Electrolyte system:

The electrolytic solution adopts an organic electrolytic solution DOL:DME=1:1, the electrolyte concentration is 7mol/LLiTFSI respectively, and the water content of the obtained electrolytic solution is lower than 10ppm.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm. Using constant current charging and discharging, under the current of 0.2C, the charging and discharging voltage range is 1-3V for testing.

As shown in Figure 1, a high-concentration lithium salt system 7mol/LLiTFSI (DOL:DME=1:1) is used, the system electrolyte, and the battery’s electrochemical performance is excellent, mainly reflecting that the average Coulombic efficiency is greater than 99.5%, and it can be recharged after 90 weeks. The capacity retention rate can reach 81.2%.

Example 2

The lithium-sulfur battery system simulates the battery, and the specific manufacturing process is as follows:

Positive electrode material and its pole piece production process:

The carbon-sulfur composite material uses 1# porous carbon. The specific parameters are as follows: specific surface area (m2/g): 671, average pore diameter (nm): 2.5, pore volume (cc/g): 0.77

The carbon-sulfur composite material uses 2# porous carbon. The specific parameters are as follows: specific surface area (m2/g): 1431, average pore diameter (nm): 3.8, pore volume (cc/g): 1.58

The preparation process of the cathode material is as follows:

Mix porous carbon 1# with elemental sulfur powder at a weight percentage of 5:5, and porous carbon 2# and elemental sulfur powder at a weight percentage of 4:6, 3:7, and 2:8, respectively, and compound the above four kinds of carbon and sulfur The material was enclosed and sealed in an argon-filled glass tube, and the material was heat-treated at 155 degrees for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, acetylene black, and polyvinylidene fluoride (PVDF) according to the weight percentage of 8:1:1, and stir and mix them evenly with pyrrolidone as a dispersant. Using aluminum foil as a current collector, the mixed slurry is evenly coated on the current collector, then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

Electrolyte system:

The electrolytic solution adopts organic electrolytic solution DOL:DME=1:1, the electrolyte concentration is 2, 4, 5, 6 mol/LLiTFSI respectively, and the water content of the obtained electrolytic solution is lower than 10ppm.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm. Use constant current charge and discharge, and test the battery at a rate of 0.2C.

As shown in Figures 2 and 3, under the same condition of other positive and negative electrodes and assembly conditions, the electrochemical performance of the battery is significantly improved with the increase of lithium salt concentration, and the main performance In terms of cycle performance and Coulombic efficiency, and when the lithium salt concentration is larger than the solvent (6 mol/L) in volume ratio and weight ratio, the electrochemical improvement is particularly obvious.

In addition, Figure 4 and Figure 5 are the first cycle charge and discharge curves of the four carbon-sulfur composite materials described in Example 1. The charge and discharge current is set to 0.2C, and the charge and discharge voltage range is: 1.5-2.8V. By comparison, The specific capacity is uniformly calculated by elemental sulfur. Comparing the two figures, it can be found that as the sulfur content increases, the system contains more effective active substances, and the theoretical specific capacity of the composite material increases accordingly. However, since sulfur is an insulating substance, adding a large amount of sulfur To a certain extent, the actual specific capacity of the material will decrease and the chemical properties will deteriorate. As shown in Fig. 5, compared with Fig. 4, the sulfur content of the 2# porous carbon-supported active material is higher, and the composite specific capacity is the highest at the ratio of 4:6.

Example 3

The lithium-sulfur battery system simulates the battery, and the specific process is as follows:

Positive electrode material and its pole piece production process:

The preparation process of the carbon-sulfur composite material is as follows: the porous carbon 1# is mixed with sulfur powder at a weight percentage of 5:5, sealed and airtight in an argon-filled glass tube, and the raw material is treated at 155 degrees for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, sodium alginate and acetylene black according to the weight percentage of 7:2:1, and use deionized water as a dispersant to stir and mix them evenly. Using aluminum foil as a current collector, the mixed slurry is evenly coated on the current collector, then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

Electrolyte system:

The electrolytic solution adopts an organic electrolytic solution DOL:DME=1:1, the electrolyte is 6mol/LLiTFSI, and the water content of the obtained electrolytic solution is lower than 10ppm.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm. Use constant current charge and discharge, and test the battery at a rate of 0.1C.

As shown in Figure 6, the carbon-sulfur composite material using sodium alginate as the binder has good cycle performance under the electrolyte solution with high concentration of lithium salt.

Example 4

The lithium-sulfur battery system simulates the battery, and the specific manufacturing process is as follows:

Positive electrode material and its pole piece production process:

The carbon-sulfur composite material uses 2# porous carbon. The specific parameters are as follows: specific surface area (m2/g): 1431, average pore diameter (nm): 3.8, pore volume (cc/g): 1.58

The preparation process of the cathode material is as follows:

Mix porous carbon 2# with elemental sulfur powder at a ratio of 4:6 by weight, seal the above carbon-sulfur composite material into an airtight argon-filled glass tube, and heat-treat the raw material at 155 degrees for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, porous carbon 2# and polyvinylidene fluoride (PVDF) according to the weight percentage of 8:1:1, and stir and mix them evenly with pyrrolidone as a dispersant. The aluminum foil coated with a layer of carbon is used as the current collector, the mixed slurry is evenly coated on the current collector, and then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

Electrolyte system:

The electrolytic solution adopts an organic electrolytic solution DOL:DME=1:1, the electrolyte concentration is 6mol/LLiTFSI respectively, and the water content of the obtained electrolytic solution is lower than 10ppm.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm. Use constant current charge and discharge to test the battery.

As shown in Figure 7, the system uses a high-concentration lithium salt system 6mol/LLiTFSI (DOL:DME=1:1) system electrolyte, and the resulting battery has excellent rate performance, and the specific charging capacity can reach 0.2C in the first week ( 1333mAh/g), 0.5C (1120mAh/g) in the eleventh week, 1C (965mAh/g) in the twenty-first week, 2C (677mAh/g) in the thirty-first week and 5C (274mAh/g) in the forty-first week g).

Example 5

High lithium salt concentration electrolyte system and low lithium salt concentration system are used in the comparison experiment of lithium sulfur battery system:

High lithium salt concentration electrolyte system:

The electrolytic solution adopts an organic solvent DOL:DME=1:1, the electrolyte is 10mol/LLiTFSI, and the water content of the obtained electrolytic solution is lower than 10ppm.

The lithium-sulfur battery system simulates the battery, and the specific process is as follows:

Positive electrode material and its pole piece production process:

The preparation process of the carbon-sulfur composite material is as follows: the porous carbon and the sulfur powder are mixed at a weight percentage of 4:6, sealed and sealed in an argon-filled glass tube, and the raw material is treated at 155 degrees Celsius for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, acetylene black, and polyvinylidene fluoride (PVDF) according to the weight percentage of 8:1:1, and stir and mix them evenly with pyrrolidone as a dispersant. Using aluminum foil as a current collector, the mixed slurry is evenly coated on the current collector, then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm.

Using constant current charging and discharging, the battery is tested in a constant temperature high and low temperature box at a constant temperature of 50 degrees Celsius at a rate of 0.2C. As shown in Figure 8, a lithium-sulfur battery using an ether system electrolyte (10mol/L) with an ultra-high lithium salt concentration can work well at high temperatures, with normal charge-discharge curves in the first week and small polarization. The overcharge phenomenon caused by the shuttle effect is well suppressed, and the specific capacity is close to the design capacity.

Example 6

The lithium-sulfur battery system simulates the battery, and the specific process is as follows:

Positive electrode material and its pole piece production process:

The preparation process of the carbon-sulfur composite material is as follows: acetylene black and sulfur powder are mixed at a weight percentage of 4:6, sealed and airtight in an argon-filled glass tube, and the raw material is treated at 155 degrees for 24 hours.

Weigh a certain amount of carbon-sulfur composite material, acetylene black, and polyvinylidene fluoride (PVDF) according to the weight percentage of 8:1:1, and stir and mix them evenly with pyrrolidone as a dispersant. Using graphite paste as the current collector, the mixed slurry is evenly coated on the current collector, then dried and cut into pole pieces with the same shape and area. The negative pole piece is made of lithium metal.

Electrolyte system:

The 1# electrolyte adopts organic electrolyte diethylene glycol dimethyl ether (DGM), the electrolyte is 6mol/LLiFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The 2# electrolyte adopts organic electrolyte diethylene glycol dimethyl ether (DGM), the electrolyte is 5mol/LLiTFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The 3# electrolyte uses organic electrolyte shrinkage triethylene glycol dimethyl ether (TGDME), the electrolyte is 4mol/LLiFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The 4# electrolyte uses organic electrolyte tetraethylene glycol dimethyl ether (TEGDME), the electrolyte is 3mol/LLiTFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The 5# electrolyte adopts the organic electrolyte dimethyl sulfoxide (DMSO), the electrolyte is 6mol/LLiTFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The 6# electrolyte adopts organic electrolyte DOL:DME=1:1 (volume ratio), the electrolyte is 3mol/LLiTFSI and 3mol/LNaFSI, and the water content of the obtained electrolyte is lower than 10ppm.

The battery assembly uses a standard button cell CR2032, and the separator is glass fiber. The entire assembly process is completed in an argon glove box with a moisture content below 0.5ppm. Use constant current charge and discharge, and test the battery at a rate of 0.2C.

Above embodiment result is shown in the table below:

It can be seen from the results in Table 1 that the electrolyte system with high lithium salt concentration has the same effect after using other organic solvents. Therefore, for lithium-sulfur battery systems, high lithium salt concentration has a universal effect on improving battery performance.

In the above-mentioned embodiments, only a few non-aqueous organic solvents in the claims are listed. Of course, any one or more mixtures selected from ethers, sulfones, sulfates, alkoxysilanes, and nitriles can also be replaced.

The above-mentioned ether organic solvents include cyclic ethers and chain ethers; wherein, cyclic ethers include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL) Or 4-methyl-1,3-dioxolane (4-MeDOL); chain ethers include dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1, 2-Dimethoxypropane (DMP), diethylene glycol dimethyl ether (DGDME), triethylene glycol dimethyl ether (TGDME) or tetraethylene glycol dimethyl ether (TEGDME).

The aforementioned sulfone organic solvents include dimethylsulfoxide (DMSO), sulfolane (TMSO) or dimethylsulfone (MSM).

The above-mentioned sulfuric acid ester organic solvents include methyl sulfate, ethyl sulfate, dimethyl sulfate and diethyl sulfate.

The above-mentioned alkoxy silicon organic solvent has the following chemical structure: SiR ¹ R ² R ³ R ⁴ , wherein the substituents R ¹ , R ² , R ³ , and R ⁴ are the same or different, each independently selected from a hydrogen atom and a carbon atom, and the carbon atom is described as a saturated or unsaturated alkyl group of 1-10, and OC _x F _2x+1-y H _y , OCOC _x F _2x+1-y H _y , OSO ₂ C _x F _{2x+1- y} H _y and an ethoxy-based polymer group, wherein, x is an integer of 1-10, y is an integer greater than zero, and 2x+1-y is greater than or equal to zero; or, substituents R ¹ , R ² , R ³ and R ⁴ are the same or different, each independently replaced by F, C _x F _2x+1-y H _y , OC _x F _2x+1-y H _y , OCOC _x F _2x+1-y H _y , OSO ₂ C _x F _2x+1-y H _y , N(C _x F _2x+1-y H _y ) ₂ unsubstituted or monosubstituted or polysubstituted aryl, the aryl is phenyl and (or) naphthyl , or be F, C _x F _2x+1-y H _y , OC _x F _2x+1-y H _y , OCOC _x F _2x+1-y H _y , OSO ₂ C _x F _2x+1-y H _y , N(C _x F _2x+1-y H _y ) ₂ unsubstituted or monosubstituted or polysubstituted aromatic heterocyclic groups, the heterocyclic groups are pyridyl, pyridyl and (or) pyrimidyl; wherein , x is an integer of 1-10, y is an integer greater than zero, and 2x+1-y is greater than or equal to zero.

The above-mentioned alkoxy silicon organic solvent is selected from tetramethoxy silicon, ethyl triethoxy siloxane, ethyl triacetoxy siloxane, diphenyl methoxy siloxane, triethyl siloxane Oxyalkylfluoromethanesulfonates, and mixtures thereof.

The aforementioned nitrile organic solvents include propionitrile, malononitrile, methoxyacetonitrile, 3-methoxypropionitrile, and mixtures thereof.

In addition, the positive electrode of the embodiment of the present invention includes an active material, a conductive additive, and a binder; wherein, the active material is composed of a carbon-sulfur compound. In the embodiment of the present invention, the positive electrode only lists porous carbon as the carbon source. Of course, one or more of acetylene black, graphite, graphene, porous carbon, carbon nanotubes, carbon fibers, and nitrogen-doped carbon can also be used. Mixture composition.

The above-mentioned conductive additives are mainly composed of carbon materials. In the embodiments of the present invention, only acetylene black, carbon nanotubes and porous carbon are listed, and of course acetylene black, graphite, graphene, porous carbon, carbon nanotubes, and carbon fibers can also be used. , nitrogen-doped carbon, etc., are composed of one or more mixtures.

The above-mentioned binder can be composed of one or more mixtures of water-based binder sodium alginate, carboxymethyl cellulose (CMC), polytetrafluoroethylene PTFE, or a non-water-based binder polyvinylidene fluoride (PVDF ).

In addition, the lithium salt or sodium salt in the embodiment of the present invention only lists LiTFSI, LiFSI and NaTFSI. Of course, it can also be selected from LiNO ₃ , NaNO ₃ , LiCl, NaCl, LiBr, NaBr, LiI, NaI, Li ₂ CO ₃ , Na ₂ CO ₃ , Li ₂ SO , Na ₂ SO ₄ , LiCF ₃ SO ₃ , NaCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , NaC ₄ F ₉ SO ₃ , LiN(C _x F _2x+1 SO ₂ )( C _y F _2y+1 SO ₂ ) or NaN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ), where x and y are natural numbers, LiBF _z (CF ₃ ) _4-z , NaBF _z (CF ₃ ) _4-z , where z≤4 is a natural number, LiC(SO ₂ CF ₃ ) ₃ , NaC(SO ₂ CF ₃ ) ₃ , LiPF _a (CF ₃ ) _6-a , NaPF _a (CF ₃ ) _6-a , LiPF _b (C ₂ F ₅ ) _6-b , NaPF _b (C ₂ F ₅ ) _6-b , LiPF _c (iso-C ₃ F ₇ ) _6-c , NaPF _C . (iso-C ₃ F ₇ ) _6-c , where a, b, c≤6 are natural numbers.

Claims (14)

1. a lithium-sulfur secondary battery system, this system comprises positive pole, negative pole and electrolytic solution, wherein, positive active material is carbon sulphur matrix material, negative pole adopts metal lithium sheet, electrolytic solution is a kind of high salt concentration nonaqueous electrolyte, and described high salt concentration nonaqueous electrolyte comprises non-aqueous organic solvent, also comprises lithium salt or sodium salt or lithium sodium mixing salt; Described lithium salt or the lithium sodium mixing salt volumetric molar concentration scope in non-aqueous organic solvent is 5-10 mol/L; The carbon material that wherein carbon sulphur matrix material uses is that in acetylene black, graphite, Graphene, porous carbon, carbon nanotube, carbon fiber, nitrogen-doped carbon, one or more mixtures are formed.

2. battery system as claimed in claim 1, it is characterised in that, described non-aqueous organic solvent is selected from ether class, sulfone class, sulfuric acid ester, alkane oxygen silicon class, nitrile class and mixture thereof.

3. battery system as claimed in claim 1, it is characterised in that, described lithium salt or sodium salt are selected from LiNO₃��NaNO₃��LiCl��NaCl��LiBr��NaBr��LiI��NaI��Li₂CO₃��Na2CO₃��Li₂SO₄��Na2SO₄��LiCF₃SO₃��NaCF₃SO₃��LiC₄F₉SO₃��NaC₄F₉SO₃��LiN(C_xF_2x+1SO₂)(C_yF_2y+1SO₂) or NaN (C_xF_2x+1SO₂)(C_yF_2y+1SO₂), wherein, x and y is natural number, LiBF_z(CF₃)_4-z��NaBF_z(CF₃)_4-z, the wherein natural number of z��4, LiC (SO₂CF₃)₃��NaC(SO₂CF₃)₃��LiPF_a(CF₃)_6-a��NaPF_a(CF₃)_6-a��LiPF_b(C₂F₅)_6-b��NaPF_b(C₂F₅)_6-b��LiPF_c(iso-C₃F₇)_6-c��NaPF_c(iso-C₃F₇)_6-c, the wherein natural number of a, b, c��6.

4. battery system as claimed in claim 2, it is characterised in that, described ether organic solvent comprises ring-type ether and chain shape ether two class; Wherein, ring-type ether comprises tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxolanes or 4-methyl-1,3-dioxy pentamethylene; Chain shape ether comprises Methylal(dimethoxymethane), 1,2-glycol dimethyl ether, 1,2-Propanal dimethyl acetal, diglycol ethylene dme, contracting TRIGLYME or contracting tetraethyleneglycol dimethyl ether.

5. battery system as claimed in claim 2, it is characterised in that, described sulfone class organic solvent comprises dimethyl sulfoxide (DMSO), tetramethylene sulfone or dimethyl sulfone.

6. battery system as claimed in claim 2, it is characterised in that, described sulfuric acid ester organic solvent chemical general formula is R-O-SO₂-O-R', R are organic group, and R' is often proton or without group.

7. battery system as claimed in claim 2, it is characterised in that, described alkane oxygen silicon class organic solvent has and comprises chemical structure as follows: SiR¹R²R³R⁴, wherein, substituent R¹��R²��R³��R⁴Identical or different, it is selected from hydrogen atom and carbon atom independently of one another, and carbon atom is stated as the saturated of 1-10 or unsaturated alkyl and OC_xF_2x+1-yH_y��OCOC_xF_2x+1-yH_y��OSO₂C_xF_2x+1-yH_yWith the polymeric groups based on oxyethyl group, wherein, x is the integer of 1-10, y be greater than zero integer, and 2x+1-y is more than or equal to zero;Or, substituent R¹��R²��R³��R⁴Identical or different, independently of one another by F, C_xF_2x+1-yH_y��OC_xF_2x+1-yH_y�� OCOC_xF_2x+1-yH_y��OSO₂C_xF_2x+1-yH_y��N(C_xF_2x+1-yH_y)₂Not replacing monosubstituted or polysubstituted aryl, described aryl is phenyl and/or naphthyl, or is by F, C_xF_2x+1-yH_y��OC_xF_2x+1-yH_y��OCOC_xF_2x+1-yH_y��OSO₂C_xF_2x+1-yH_y��N(C_xF_2x+1-yH_y)₂Not replacing monosubstituted or polysubstituted aromatic heterocyclic radical, described heterocyclic radical is pyridyl, pyridyl and/or pyrimidyl; Wherein, x is the integer of 1-10, y be greater than zero integer, and 2x+1-y is more than or equal to zero.

8. battery system as claimed in claim 2, it is characterized in that, described alkane oxygen silicon class organic solvent is selected from tetramethoxy-silicane, ethyl triethoxy silicane oxygen alkane, ethyl triacetyl oxygen radical siloxane, diphenylmethyl oxygen radical siloxane, silicoheptane oxygen alkyl fluoride RF for methane sulfonates, and mixture.

9. battery system as claimed in claim 2, it is characterised in that, described nitrile class organic solvent comprises propionitrile, propane dinitrile, methoxyacetonitrile, 3-methoxypropionitrile and mixture thereof.

10. battery system as claimed in claim 1, it is characterised in that, described positive pole comprises active substance, conductive additive, tackiness agent and conductive current collector.

11. battery systems as claimed in claim 10, it is characterized in that, described conductive additive is mainly formed with carbon material, can be wherein one or more mixtures of carbon formation of acetylene black, graphite, Graphene, porous carbon, carbon nanotube, carbon fiber, N doping.

12. battery systems as claimed in claim 11, it is characterised in that, described tackiness agent can be aqueous adhesive sodium alginate, carboxymethyl cellulose, tetrafluoroethylene wherein one or more mixtures formation, it is also possible to be non-aqueous adhesive polyvinylidene difluoride (PVDF).

13. battery systems as claimed in claim 11, it is characterised in that, described conductive current collector can be metal aluminum foil or graphite felt, it is also possible to is the aluminium foil of one layer of carbon at surface-coated thickness equal one.

14. battery systems as claimed in claim 2, it is characterised in that, described sulfuric acid ester organic solvent comprises methyl sulfate, sulfovinic acid, methyl-sulfate and ethyl sulfate.