CN111370791B - Lithium-sulfur battery formation method and lithium-sulfur battery prepared by formation method - Google Patents

Abstract

The invention discloses a lithium-sulfur battery formation method and a lithium-sulfur battery prepared by the formation method, comprising the following steps: and (3) after the lithium-sulfur battery is injected with liquid and sealed, transferring the lithium-sulfur battery into a formation cabinet for formation, exhausting air and sealing for the second time. According to the invention, by a high-frequency symmetrical/asymmetrical charge-discharge formation method, the high-surface-load S/C electrode of the high-sulfur lithium-sulfur battery is soaked with electrolyte in a short time, the dissolution of lithium polysulfide is effectively inhibited, the loss of active substances in the air extraction/secondary sealing process is avoided, and the problems of low capacity, poor cycle stability and the like of the lithium-sulfur battery after formation are effectively solved.

Description

A lithium-sulfur battery formation method and a lithium-sulfur battery prepared by the formation method

Technical field

The invention belongs to the technical field of lithium-sulfur batteries, and specifically relates to a lithium-sulfur battery formation method and a lithium-sulfur battery prepared by the formation method.

Background technique

With the continuous advancement of science and technology and the improvement of people's living standards, higher requirements have been placed on the performance of rechargeable secondary power supply products. Among them, lithium-sulfur batteries with sulfur as the positive electrode, lithium metal as the negative electrode, and lithium-ion organic solvents as the electrolyte have ultra-high capacities and energy densities of 1675mAh g ^-1 and 2600Wh kg ^-1 , and are considered to be the second most powerful battery after lithium-ion batteries. The high-specific energy secondary battery system closest to commercialization. In addition, lithium-sulfur batteries have the advantages of wide source of positive active material (elementary sulfur), low price, and environmental friendliness, making them one of the most promising energy storage systems after lithium-ion batteries. Currently, many governments around the world are strongly supporting the technological development of lithium-sulfur batteries.

However, the commercialization of lithium-sulfur batteries is still hampered by many problems, such as the low conductivity of the cathode active material, lithium polysulfide dissolving and migrating in the electrolyte, and then reacting with the metallic lithium anode to produce a "shuttle effect", and metallic lithium dendrites. The generation of crystals, etc. In response to these problems, researchers have used various carbon materials to increase the conductivity of the cathode, inhibited the shuttle of lithium polysulfide through physical and chemical adsorption methods, and built an SEI film on the surface of the lithium metal anode through in-situ and ex-situ methods. . To a certain extent, the cycle problem of lithium-sulfur batteries is solved.

At the same time, in lithium-sulfur batteries, the formation method will also significantly affect battery performance. Formation is an extremely important process in the manufacturing process of lithium-sulfur batteries. During the formation, the electrolyte infiltrates the S/C positive electrode. At the same time, the battery undergoes self-discharge, and lithium polysulfide dissolves from the positive electrode into the electrolyte. If the formation method is improper, the S positive electrode will not be fully infiltrated, or the lithium polysulfide will be excessively dissolved in the electrolyte and extracted during the secondary sealing, resulting in the loss of active materials. Therefore, the formation method greatly affects the cycle performance of lithium-sulfur batteries.

In view of this, it is indeed necessary to provide a formation method for lithium-sulfur batteries, especially in the case of high sulfur content and high surface loading. In order to meet the requirements for cell performance, it can also save time, improve production efficiency and reduce production costs. The high-frequency symmetric/asymmetric charge-discharge formation method fully infiltrates the S/C electrode and the electrolyte in a short period of time, and at the same time "locks" the lithium polysulfide on the positive electrode side to prevent it from dissolving in the electrolyte and improve the lithium-sulfur content. Battery capacity development and cycle stability.

Contents of the invention

In order to solve the above shortcomings and shortcomings of the prior art, the purpose of the present invention is to provide a formation method for lithium-sulfur batteries to meet the requirements for cell performance, save formation time, and improve production efficiency. The S/C electrode and the electrolyte are fully infiltrated in a short period of time, while the lithium polysulfide is "locked" on the positive electrode side, suppressing the loss of active materials and improving the capacity and cycle stability of the lithium-sulfur battery after formation.

In order to achieve the above-mentioned object of the invention, on the one hand, the invention provides a lithium-sulfur battery formation method. The steps of the lithium-sulfur battery formation method are as follows:

A lithium-sulfur battery formation method includes the following steps: after injecting liquid and sealing the lithium-sulfur battery, transfer it to a formation cabinet for formation, exhausting, and secondary sealing.

Preferably, in the above lithium-sulfur battery formation method, the positive electrode of the lithium-sulfur battery is composed of one or more of sulfur element, sulfur-containing composite materials, lithium polysulfide Li ₂ S _x and composite materials thereof. ;

The negative electrode of a lithium-sulfur battery is composed of one or more of metallic lithium, lithium metal alloy, lithium-containing composite materials, graphite, and silicon-carbon materials;

The electrolyte form of lithium-sulfur batteries is liquid, gel or solid, and the solute is one or more of LiTFSI, LiFSI and LiPF ₆ ;

The solvent used in the liquid electrolyte is an ether solvent or an ester solvent;

The solid electrolyte is polymethyl methacrylate, polyethylene terephthalate, polyoxyethylene gel polymer electrolyte, polyoxyethylene, polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride, One or more compounds of acrylonitrile-based all-solid polymer electrolyte, LiBH ₄ fast ion conductor, Li ₃ N, LISICIN, Li ₂ SP ₂ S ₅ glass ceramic electrolyte;

The separator of a lithium-sulfur battery is composed of one or more of polyethylene, polypropylene, polyvinylidene fluoride, and polymethylmethacrylate.

Preferably, in the above-mentioned lithium-sulfur battery formation method, the ether solvent is ethylene glycol dimethyl ether, diglyme, tetraethylene glycol dimethyl ether, and 1,3-dioxopentane. ring, one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,4-tetrafluoropropyl ether; the ester solvent is ethylene carbonate, propylene carbonate, One or more components of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

Preferably, in the above-mentioned lithium-sulfur battery formation method, the steps of the formation are as follows: under the temperature condition of 0-60°C, the lithium-sulfur battery that has been left standing after liquid injection is discharged with a current of 1-200mA g ^-1 , the time is 1-7200s, and the charging time is 1-7200s with the same current. After 1-20000 cycles, the same current is used to charge to full power 2.5-3.4V.

Preferably, in the above-mentioned lithium-sulfur battery formation method, the steps of the formation are as follows: under the conditions of 25-45°C, the lithium-sulfur battery that has been left standing after liquid injection is discharged with a current of 5-50mA g ^-1 , The time is 5-1800s, and the charging time is 5-1800s with the same current. After 50-10000 cycles, the same current is used to charge to full power 2.6-3.0V.

Preferably, in the above-mentioned lithium-sulfur battery formation method, the single discharge capacity of the battery should be greater than or equal to the charging capacity.

A lithium-sulfur battery is formed by any one of the above lithium-sulfur battery formation methods.

Compared with the existing technology, the present invention has the following beneficial effects: the lithium-sulfur battery formation method of the present invention uses small current and high frequency to perform symmetrical/asymmetric charge and discharge, so that the S/C positive electrode and the electrolyte are fully infiltrated, while inhibiting the activity The dissolution of the material lithium polysulfide during the formation process improves the battery liquid retention capacity and the utilization rate of active materials during the formation process. At the same time, the formation time is reduced, production efficiency is improved, and production costs are saved. The lithium-sulfur battery of the present invention adopts the lithium-sulfur battery formation method of the present invention for formation treatment, thereby improving the discharge capacity and cycle stability of the lithium-sulfur battery of the present invention.

Description of the drawings

The present invention will be further described below in conjunction with the accompanying drawings and examples. In the accompanying drawings:

Figure 1 is a comparison chart of the first cycle performance of lithium-sulfur soft pack batteries prepared in Examples 2 and 6 and Comparative Examples 1, 2, 4 and 5.

Figure 2 is a comparison chart of the cycle performance of lithium-sulfur soft pack batteries prepared in Example 2 and Comparative Examples 1-5.

Detailed ways

The present invention will be described in further detail below with reference to the examples and drawings, but the implementation of the present invention is not limited thereto.

Example 1

(1) Assemble the S/C positive electrode, lithium negative electrode and carbon-coated separator in a laminated manner to assemble a Li-S soft-packed battery cell with a battery capacity of 1.1Ah. After entering the shell, inject the electrolyte. The electrolyte composition is 1mol/L LiTFSI (lithium bistrifluoromethylsulfonimide) dissolved in DME (ethylene glycol dimethyl ether) and DOL (dioxolane), add 2 %LiNO ₃ .

(2) After sealing, let it sit for 2 hours and transfer to the forming cabinet. Use 25mA current to discharge for 1800s, charge for 1800s, and cycle 50 times.

(3) Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 2

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 360s and charge for 360s. Charge and discharge cycles 250 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05 C).

Example 3

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 180s and charge for 180s. Charge and discharge cycles 500 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 4

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 18s and charge for 18s. Charge and discharge cycles 5,000 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 5

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 45°C, use 50mA current to discharge for 1800s (0.5h), charge for 1728s (0.46h), and charge and discharge 50 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 6

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 180s (0.05h), charge for 165s (about 0.046h), and charge and discharge 500 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 7

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 18s (0.005h), charge for 16s (about 0.0046h), and charge and discharge 5000 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Example 8

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was: seal and let stand for 2 hours, then transfer to the formation cabinet. At 25℃, use 25mA current to discharge for 9s (0.0025h), charge for 8s (about 0.0023h), and charge and discharge 10,000 times. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Comparative example 1

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was as follows: after sealing, the battery was left to stand at 25°C for 50 hours. Perform air extraction and secondary sealing, and then transfer to the test cabinet for cycle testing (0.05C).

Comparative example 2

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was as follows: after sealing, the battery was left to stand at 25°C for 120 hours. Perform air extraction and secondary sealing, and then transfer to the test cabinet for cycle testing (0.05C).

Comparative example 3

Lithium-sulfur batteries were prepared according to the method described in Example 1. The formation procedure was as follows: after sealing, the battery was left to stand at 25°C for 360 hours. Perform air extraction and secondary sealing, and then transfer to the test cabinet for cycle testing (0.05C).

Comparative example 4

Prepare the lithium-sulfur battery according to the method described in Example 1. The formation procedure is: after sealing, let it stand at 25°C for 2 hours, and then transfer it to the formation cabinet. Discharge to 1.6V using 0.01C (16.75mA g ^-1 ) current. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Comparative example 5

Prepare the lithium-sulfur battery according to the method described in Example 1. The formation procedure is: after sealing, let it stand at 25°C for 2 hours, and then transfer it to the formation cabinet. Use 0.01C (16.75mA g ^-1 ) current to discharge to 1.6V and then charge to 2.6V. Transfer the lithium-sulfur battery from the formation cabinet, perform air extraction and secondary sealing, and then transfer it to the test cabinet for cycle testing (0.05C).

Effect comparison:

(1) Compare the first cycle discharge curves of the lithium-sulfur soft pack batteries prepared in Examples 2, 6 and Comparative Examples 1, 2, 4, and 5. The results are shown in Figure 1. It can be seen from Figure 1 that the discharge capacity of the comparative examples is low. Among them, the capacities of comparative examples 1 and 2 are only 737.0 and 781.3mAh g ^-1 respectively due to poor electrode wettability. This shows that even if the electrode is left standing for 120 hours, the electrode cannot be fully infiltrated and exert the corresponding capacity; the capacities of Comparative Examples 4 and 5 are 998.1 and 969.4mAh g ^-1 respectively, and they are discharged or discharged/charged at 0.01C for one week, and the time consumption is respectively At 86 and 164 hours, the wettability was significantly improved. However, during this process, a large number of polysulfide ions on the positive electrode were dissolved into the electrolyte and shuttled. During the secondary sealing process of the battery, the wettability was extracted from the battery along with the electrolyte, resulting in the formation of active substances. Loss. Example 2 was formed through high-frequency symmetrical charging and discharging. The charging and discharging were carried out 250 times at a current of 25mA and a time of 0.1h. Since the electrode wettability was greatly improved and the dissolution of lithium polysulfide was suppressed, the discharge capacity of the first cycle was increased to 1218.1mAhg ^-1 . Example 6 was formed through high-frequency asymmetric charge and discharge, with a current of 25mA, a discharge time of 0.05h, and a charging time of 0.046h, and was charged and discharged 500 times. During this process, the electrode wettability was further improved, and at the same time, the dissolved amount of Lithium sulfide is "locked" on the positive electrode side to prevent it from dissolving into the electrolyte. Therefore, the capacity is once again increased to 1317.3mAh g ^-1 .

(2) Compare the cycle performance of the lithium-sulfur soft pack batteries prepared in Example 2 and Comparative Examples 1-5. The results are shown in Figure 2. As can be seen from Figure 2: Comparative Examples 1 and 2 have a short standing formation time and low active material loss, so that the battery capacity can be stabilized at around 1000mAh g ^-1 . However, due to poor electrode wettability, the capacity quickly decays; In Comparative Example 3, the standing formation time was increased to 360 hours. The long formation time resulted in a large amount of active material loss, so the battery capacity was inhibited. After Comparative Examples 4 and 5 were formed through 0.01C discharge/discharge, the battery capacity was low during 30 cycles and the attenuation was serious. In Example 2, after high-frequency symmetrical charging and discharging, the battery capacity stabilized at around 1000mAh g ^-1 , and the discharge specific capacity of 976.9mAh g ^-1 was still maintained after 30 cycles. It can be seen that after high-frequency charging and discharging, the capacity and stability of the battery are significantly improved.

Claims (2)

1. A lithium-sulfur battery formation method, characterized by comprising the following steps: after injecting liquid and sealing the lithium-sulfur battery, transfer it to a formation cabinet for formation, exhausting, and secondary sealing; The steps of the formation are as follows: under the conditions of 25-45°C, the lithium-sulfur battery left standing after injection is discharged with a current of 5-50mA g ^-1 for a time of 5-1800s, and then charged with the same current for a time of 5-1800s. It takes 5-1800s, and after 50-10000 cycles, it is charged to full power 2.6-3.0V with the same current; The single discharge capacity of the battery should be greater than or equal to the charging capacity; The positive electrode of the lithium-sulfur battery is composed of one or more of sulfur element, sulfur-containing composite materials, lithium polysulfide Li ₂ S _x and composite materials thereof; The negative electrode of a lithium-sulfur battery is composed of one or more of metallic lithium, lithium metal alloy, lithium-containing composite materials, graphite, and silicon-carbon materials; The electrolyte form of lithium-sulfur batteries is liquid, gel or solid, and the solute is one or more of LiTFSI, LiFSI and LiPF ₆ ; The solvent used in liquid electrolyte is ether solvent or ester solvent; The solid electrolyte is polymethyl methacrylate, polyethylene terephthalate, polyoxyethylene gel polymer electrolyte, polyoxyethylene, polymethyl methacrylate, polyvinylidene fluoride, polyacrylonitrile-based One or more composites of all-solid polymer electrolyte, LiBH ₄ fast ion conductor, Li ₃ N, LISICIN, Li ₂ SP ₂ S ₅ glass ceramic electrolyte; The separator of the lithium-sulfur battery is composed of one or more of polyethylene, polypropylene, polyvinylidene fluoride, and polymethylmethacrylate; The ether solvents are ethylene glycol dimethyl ether, diglyme, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,1,2,2-tetrafluoroethyl -One or more of 2,2,3,4-tetrafluoropropyl ether; the ester solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate one or more components. 2. A lithium-sulfur battery, characterized in that it is formed by the lithium-sulfur battery formation method according to claim 1.