Se-doped solid-state electrolyte, preparation method and application thereof

Abstract

The application discloses a Se-doped solid electrolyte and a preparation method and application thereof, and belongs to the field of electrochemical energy storage batteries. By doping Se elements in a sulfur-based solid electrolyte, the interface stability of the electrolyte can be greatly improved, and the electrolyte can also have the effect of a protective layer. After the Se-doped solid electrolyte is coated on the surface of lithium cobaltate, a uniform coating layer can be formed on the surface of the lithium cobaltate, and the oxygen loss problem of the lithium cobaltate during high-voltage cycling can be slowed down, so that the lithium cobaltate after coating has good Li + conductivity, and the specific capacity and cycle performance are also improved. The process of coating the Se-doped solid electrolyte on the lithium cobaltate is simple, does not need a complex treatment process, has strong accessibility, and can be directly applied to the primary sintering and secondary sintering process of the lithium cobaltate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage batteries, in particular to a Se-doped solid-state electrolyte and a preparation method and application thereof. BACKGROUND

[0002] Lithium-ion batteries (LIBs) are still lagging behind the increasing demand for high energy density batteries as the preferred energy storage system for portable electronic products and electric vehicles. As the positive material of rechargeable LIBs, lithium cobalt oxide dominates in 3C electronic devices due to its high tap density; however, lithium cobalt oxide in practical application only develops 1 / 2 of its theoretical capacity (about 140 mAh·g-1), which means that only half of the Li + is separated from lithium cobalt oxide; although charging lithium cobalt oxide to a high voltage can increase the energy density by more than 40%, the redox of oxygen ions at a high voltage contributes to the capacity, and the migration of oxygen ions in a high oxidation state leads to severe oxygen loss of lithium cobalt oxide during high-voltage cycling, which not only hinders the conduction of lithium ions due to the irreversible phase transition of the positive material, but also causes the oxidation and decomposition of the carbonate electrolyte, thereby leading to a sharp decline in the cycle life of the battery.

[0003] To solve the problem of cycle life decay of the battery, strategies have been developed, including morphology design, element doping and coating. Se, as a special element in the human body with the function of "anti-aging", can capture excess oxygen ion radicals in the human metabolism process, thereby delaying cell aging; by virtue of the unique feature of Se in capturing oxygen ion radicals, Se treatment can slow down the oxygen loss of lithium cobalt oxide during high-voltage cycling; CN110668509A discloses the preparation of Se-coated lithium cobalt oxide, which is blended and sintered with elemental Se, the process is simple, but the SeO + layer formed by elemental Se in the subsequent sintering process has poor ion / Li + conductivity, in addition, the trace Se coating in lithium cobalt oxide is in the form of "island" coating, and there is still a bare lithium cobalt oxide surface directly in contact with the electrolyte; these problems will increase the electrochemical polarization of the lithium cobalt oxide positive material, leading to a decrease in the specific capacity and a decrease in the cycle stability of the material.

[0004] Therefore, it is one of the difficulties to achieve stable cycling of lithium cobalt oxide at a high voltage to construct a uniform Se coating layer on the surface of lithium cobalt oxide while not reducing the ion / Li + conductivity of lithium cobalt oxide. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a Se-doped solid-state electrolyte which can uniformly coat the surface of lithium cobalt oxide, and the coated lithium cobalt oxide can maintain good ion / Li +Se-doped solid electrolyte, preparation method and application thereof

[0006] To achieve the above object, the technical scheme adopted by the present application is as follows: a Se-doped solid electrolyte, the chemical composition of the Se-doped solid electrolyte is Li 6+x P 1-x Se x S5X2 or Li 6+x P 1-x Se x S 5-2x X1 2x X2, wherein 0 < x < 1; X1 is O or S, and X2 is at least one of F, Cl, Br and I.

[0007] The Se-doped solid electrolyte of the present application, by doping Se element in the sulfur-based solid electrolyte, makes the electrolyte not only maintain the excellent ion / Li + conductivity of the sulfur-based solid electrolyte, but also greatly improves the interface stability of the electrolyte through the doping of Se element, and at the same time, the sulfur-based solid electrolyte also has the function of protective layer, so that the lithium cobaltate can be stably cycled at high voltage.

[0008] Another object of the present application is to provide a preparation method of the Se-doped solid electrolyte, comprising the following steps: weighing the materials Li2S, SeX1, P2S5 and LiX2 according to the stoichiometric ratio, pre-mixing, and crushing the mixed materials to obtain the Se-doped solid electrolyte.

[0009] Preferably, the stoichiometric ratio of the materials is Li2S:SeX1:P2S5:LiX2=(5-6):(0-1):2:1, and the inventors have found through experiments that, under this stoichiometric ratio, the materials can not only ensure sufficient Li + delivery, but also control the cost of producing the Se-doped solid electrolyte.

[0010] Preferably, the materials are placed in a high-energy ball mill and ball-milled under inert atmosphere, the high-energy ball milling is a crushing method combining physical and chemical methods, which can realize uniform dispersion and mixing of different components, and in the present application, the materials are fully mixed by high-energy ball milling, which not only realizes the chemical activation and crushing effect of the materials, but also enables alloying between the materials, so that a dense coating layer can be formed in the subsequent sintering process, thereby improving the Li + conductivity.

[0011] More preferably, the ball-to-material mass ratio of the ball milling is 15 70:1, and the inventors have found through experiments that, within this range, the mixing efficiency of the materials is the highest, and neither over-crushing occurs nor metal loss of the high-energy ball mill is caused.

[0012] More preferably, the inert atmosphere is nitrogen or argon.

[0013] More preferably, the ball milling medium of the ball milling is zirconium oxide.

[0014] Most preferably, the diameter of the zirconium oxide is 5-15mm, the inventors use the ball milling medium with the diameter to grind the material more fully according to the hardness of the material.

[0015] The application also provides the use of the Se-doped solid electrolyte in coating lithium cobalt oxide material.

[0016] Preferably, the step of coating the lithium cobalt oxide material with the Se-doped solid electrolyte is: coating the Se-doped solid electrolyte and the lithium cobalt oxide material under an inert atmosphere, and performing low-temperature sintering under an inert atmosphere, and then grinding and sieving after cooling to obtain the lithium cobalt oxide material with a coating layer of Se-doped solid electrolyte.

[0017] More preferably, the mass percentage of Se in the Se-doped solid electrolyte in the lithium cobalt oxide material is: 0<Se≤1%.

[0018] More preferably, the lithium cobalt oxide material includes at least one of cobalt carbonate, cobalt hydroxide, tricobalt tetraoxide, and lithium cobalt oxide.

[0019] Most preferably, the preparation method of the lithium cobalt oxide material is: after uniformly mixing the raw materials, placing them in a tube furnace, heating at a rate of 1-3℃ / min to 550-650℃, maintaining the temperature for 1-3h, then heating at a rate of 1-3℃ / min to 850-950℃, maintaining the temperature for 9-11h, naturally cooling, and then rolling and sieving to obtain the lithium cobalt oxide primary sintering product.

[0020] More preferably, the coating method is coating with a coating fusion machine.

[0021] Most preferably, the rotation speed of the coating fusion machine is 40-60Hz, and the coating time is 2-8min, which can make the coating more sufficient under the coating parameters.

[0022] More preferably, the inert atmosphere during the coating is nitrogen or argon.

[0023] More preferably, the process parameters of the low-temperature sintering are: increasing the temperature to 400-800℃ at a rate of 2-10℃ / min, maintaining the temperature for 6-8h, and then cooling.

[0024] The beneficial effects of the present application are that the present application provides a Se-doped solid-state electrolyte, by doping Se element in the sulfur-based solid-state electrolyte, the interface stability of the electrolyte can be greatly improved, and the electrolyte can also have the function of protective layer, after being coated on the surface of lithium cobaltate, a uniform coating layer can be formed on the surface of lithium cobaltate, and the oxygen loss problem of lithium cobaltate during high-voltage cycling can be slowed down, so that the lithium cobaltate after coating has good + electrical conductivity, and the specific capacity and cycle performance are also improved; the process of coating the Se-doped solid-state electrolyte on the lithium cobaltate is simple, does not need complex processing process, has strong accessibility, and can be directly applied to the primary sintering and secondary sintering process of lithium cobaltate. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The SEM image of the Se-doped solid-state electrolyte coated on lithium cobaltate in Example 1. DETAILED DESCRIPTION

[0026] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific examples.

[0027] Example 1

[0028] An embodiment of the Se-doped solid-state electrolyte according to the present application, the preparation method of the Se-doped solid-state electrolyte according to the present embodiment is as follows: Li2S, Se, P2S5 and LiCl solid powders are weighed according to the stoichiometric ratio of 5:0.45:2:1, preliminarily mixed in a plastic bag, then poured into a high-energy ball mill, stirred at a speed of 450 rmp under nitrogen atmosphere for 8h, and sieved to obtain a Se-doped solid-state electrolyte with a mass percentage of 5%.

[0029] The preparation method of the Se-doped solid-state electrolyte coated on lithium cobaltate according to the present embodiment comprises the following steps:

[0030] (1) 100g of tricobalt tetraoxide is weighed and uniformly mixed with 45.3g of lithium carbonate, then placed in a tube furnace, heated to 600℃ at a rate of 2℃ / min, kept for 2h, then heated to 900℃ at a rate of 2℃ / min, kept for 10h, naturally cooled, and then rolled and sieved to obtain a pure-phase lithium cobaltate primary sintering product.

[0031] (2) Take 100 g of the pure-phase lithium cobalt oxide once-sintered product in step (1) and 6 g of Se-doped solid electrolyte, coat in a fusion coater at a frequency of 50 Hz for 3 min, then place in a tube furnace filled with nitrogen, heat to 550°C at a rate of 2°C / min, keep for 10 h, then heat to 700°C at a rate of 2°C / min, keep for 10 h, after natural cooling, roll and sieve, complete the coating of Se-doped solid electrolyte on lithium cobalt oxide, i.e. obtain high-voltage lithium cobalt oxide with a mass percentage of 0.3%, the SEM image of the high-voltage lithium cobalt oxide is shown in FIG. 2. Figure 1

[0032] Example 2

[0033] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, Se is replaced by SeS2, and the remaining steps are consistent with Example 1.

[0034] Example 3

[0035] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, Se is replaced by SeO2, and the remaining steps are consistent with Example 1.

[0036] Example 4

[0037] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, Li2S, Se, P2S5 and LiCl solid powders are taken according to the stoichiometric ratio of 6:1:2:1, and the remaining steps are consistent with Example 1.

[0038] Example 5

[0039] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, LiCl is replaced by LiF, and the remaining steps are consistent with Example 1.

[0040] Example 6

[0041] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, LiCl is replaced by LiBr, and the remaining steps are consistent with Example 1.

[0042] Example 7

[0043] The difference between this embodiment and Example 1 is only that in the preparation method of the Se-doped solid electrolyte, LiCl is replaced by LiI, and the remaining steps are consistent with Example 1.

[0044] Example 8

[0045] ​The difference between this embodiment and embodiment 1 is only that the mass of the Se-doped solid electrolyte weighed in the preparation method of the Se-doped solid electrolyte is 20 g, and the remaining steps are consistent with embodiment 1, and a high-voltage type lithium cobaltate with 1% Se by mass is prepared.

[0046] Comparative example 1

[0047] The difference between this comparative example and embodiment 1 is only that only elemental Se is used to coat the lithium cobaltate primary sintering product, and the mass of the elemental Se is 0.3 g, i.e. a lithium cobaltate coated with 0.3% Se by mass is obtained.

[0048] Comparative example 2

[0049] The difference between this comparative example and embodiment 1 is only that the lithium cobaltate primary sintering product is directly placed in a tube furnace filled with nitrogen, heated to 300°C at a rate of 2°C / min, and kept at this temperature for 2 h, then heated to 700°C at a rate of 2°C / min, and kept at this temperature for 10 h, and after natural cooling, the product is rolled and sieved, i.e. pure-phase lithium cobaltate is obtained.

[0050] Effect example

[0051] The lithium cobaltate materials in the above embodiment 1-2 and comparative examples 1-2 are prepared into electrode sheets, and a button cell is prepared with lithium sheets as the counter electrode for electrochemical testing, and the results are shown in Table 1 below.

[0052] Among them, CC and DC respectively represent the capacity of the first full charge of the battery and the capacity discharged after the first full charge, and CE% represents the initial efficiency, i.e. the ratio of the capacity discharged after the first full charge of the battery to the capacity of the first full charge.

[0053] Table 1

[0054]

[0055] As shown in Table 1, after the Se-doped sulfur-based solid electrolyte in embodiments 1 and 2 is coated on the surface of the lithium cobaltate material, the charge and discharge capacity and the cycle performance of the lithium cobaltate material are both significantly improved, and the cycle retention rate of embodiment 1 reaches 86.6%, and the initial efficiency reaches 94.6%; while in comparative example 1, only Se is used to coat the lithium cobaltate, the capacity of the first full charge is increased, but the first discharge capacity is low, resulting in a final initial efficiency of only 91.7%, which is significantly lower than that of embodiments 1 and 2, and the cycle stability is also lower than that of embodiments; in comparative example 2, since the blank lithium cobaltate is used, the first charge capacity and the first discharge capacity are both significantly reduced, and the cycle stability is <70%, only 67.1%.

[0056] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the protection scope of the present application, and although the present application has been described in detail with reference to the preferred embodiments, it should be appreciated by those skilled in the art that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. Use of a Se-doped solid-state electrolyte in a coated lithium cobalt oxide material, characterized in that, The chemical composition of the Se-doped solid electrolyte is Li 6+x P 1-x Se x S5X2 or Li 6+x P 1-x Se x S 5-2x X1 2x X2, wherein 0 < x < 1; X1 is O or S, and X2 is at least one of F, Cl, Br, and I; the mass percentage of Se in the Se-doped solid electrolyte in the lithium cobaltate material is 0 < Se ≤ 1%. The preparation steps of the Se-doped solid-state electrolyte coated lithium cobaltate material are: coating Se-doped solid-state electrolyte and lithium cobaltate material under inert atmosphere, sintering under inert atmosphere, and grinding and screening after cooling to obtain the lithium cobaltate material with Se-doped solid-state electrolyte coating layer.

2. Use of Se-doped solid-state electrolyte according to claim 1, characterized in that, The method comprises the following steps: weighing materials Li2S, SeX1, P2S5 and LiX2 according to stoichiometric ratio, pre-mixing, and grinding the mixed materials to obtain the Se-doped solid-state electrolyte.

3. Use of Se-doped solid-state electrolyte according to claim 2, characterized in that, The stoichiometric ratio of the materials is Li2S:SeX1:P2S5:LiX2=(5-6):(0-1):2:

1.

4. Use of Se-doped solid state electrolyte according to claim 2, wherein The materials are ball milled in a high-energy ball mill.

5. Use of Se-doped solid state electrolyte according to claim 4, characterized in that, The ball milling ball-to-material mass ratio is 15-70:

1.

6. Use of Se-doped solid state electrolyte in coating of lithium cobalt oxide material as claimed in claim 1, wherein, The lithium cobaltate material comprises at least one of cobalt carbonate, cobalt hydroxide, tricobalt tetraoxide and lithium cobaltate.

7. Use of Se-doped solid state electrolyte in coating of lithium cobalt oxide material as claimed in claim 1, wherein the coating is applied on the surface of the lithium cobalt oxide material. The sintering process parameters are: increasing the temperature to 400-800℃ at a heating rate of 2-10℃ / min, keeping the temperature for 6-8h, and then cooling.

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