CN112820858A - Lithium metal negative electrode protected by phosphorus-sulfur-based interfacial film and preparation method thereof - Google Patents
Lithium metal negative electrode protected by phosphorus-sulfur-based interfacial film and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a lithium metal negative electrode protected by a phosphorus-sulfur-based interfacial film and a preparation method thereof, belonging to the technical field of battery materials. The preparation method of the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film provided by the invention comprises the following steps: mixing phosphorus-containing compound and Li2And S and elemental sulfur are added into an organic solvent to react and dissolve, and a lithium sheet is soaked in the solution to react for a certain time, so that the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film is obtained. The side reaction between the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film and the electrolyte is effectively reduced, and the lithium metal deposition is more uniformThe interface impedance of the battery and the overpotential of the lithium symmetric battery are reduced, the shuttle effect of polysulfide can be inhibited when the lithium symmetric battery is used for the lithium sulfur battery, the cycle stability of the lithium sulfur battery is improved, and the preparation process is simple, green and environment-friendly.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a lithium metal negative electrode protected by a phosphorus-sulfur-based interfacial film and a preparation method thereof.
Background
The lithium-sulfur battery has high theoretical specific energy of 2600Wh/kg, and has become a hot research point for next-generation high specific energy lithium secondary batteries. However, in practical application, the lithium-sulfur battery has the problems of low coulombic efficiency, fast capacity fading, large potential safety hazard and the like, and the problems are mostly related to complex lithium-sulfur chemical reaction and can be attributed to the following points: (1) the electronic insulativity of sulfur and lithium sulfide causes low utilization rate of active substance sulfur; (2) the shuttle effect is serious, so that the loss of sulfur active substances and lithium active substances is caused, a large amount of electrolyte is consumed, and the coulomb efficiency and the circulation stability of the lithium-sulfur battery are reduced; (3) the lithium metal negative electrode has high activity, is used together with inflammable organic electrolyte, has large potential safety hazard, and easily forms dendritic lithium which continuously grows through a diaphragm to cause internal short circuit and cause thermal runaway of the battery; (4) severe lithium negative electrode corrosion and electrolyte consumption are major causes of battery failure.
The improvement of the cycling stability of the lithium metal negative electrode is one of the important aspects for solving the problems, and researches show that the establishment of a stable electrode/electrolyte interface film on the surface of the lithium metal negative electrode can effectively reduce the side reaction on the surface of the negative electrode, stabilize lithium deposition and inhibit the growth of lithium dendrites. The in-situ modified solid electrolyte interfacial film can be prepared by electrolyte additives and cosolvents, and lithium nitrate, polysulfide, lithium difluoro-oxalato-borate and the like are reported as the electrolyte additives. After the battery is assembled or in the battery circulation process, the modified additive reacts with lithium metal to form a passive film on the surface of the negative electrode, so that the corrosion of polysulfide to the lithium metal negative electrode is reduced. In addition, it is also feasible to prepare an artificial solid electrolyte interface film on the surface of metallic lithium in advance, and this can be done by inorganic compounds (e.g., Li)3N、LiF、Al2O3) Polymers (e.g. PVDF, PVA) and inorganic/organic composite modifications. These compounds are generally capable of reacting with lithium metalA fast ion conductor should be generated to improve the transmission of lithium ions and make the lithium deposition more uniform; and the inorganic component generally has good mechanical hardness, can physically inhibit the growth of dendrites, and the organic component generally has good toughness, so that the mechanical stability of the solid electrolyte interfacial film is improved.
It has been studied to form Li on the surface of the negative electrode by reacting polyphosphoric acid with lithium metal3PO4However, the ionic conductivity of this compound is not high, and the preparation process using polyphosphoric acid is not environmentally friendly.
Disclosure of Invention
The invention provides a lithium metal cathode protected by a phosphorus-sulfur-based interface film and a preparation method thereof, the preparation process of the lithium metal cathode is simple and environment-friendly, the modified lithium metal cathode improves the coulomb efficiency and the cycle stability of a lithium-sulfur battery, and reduces the interface impedance of the battery and the overpotential of a lithium symmetric battery.
The invention firstly provides a preparation method of a lithium metal negative electrode protected by a phosphorus-sulfur-based interfacial film, which comprises the following steps:
(1) mixing phosphorus-containing compound and Li2S and elemental sulfur are added into an organic solvent to react and dissolve to obtain a solution;
(2) and (2) soaking a lithium sheet in the solution obtained in the step (1), and taking out the lithium sheet after soaking to obtain the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film.
In the above preparation method, in the step (1), the phosphorus-containing compound is P2S3、P4S16、P2S5、P2O3、P2O5、P2Se5、PCl3、PCl5、PF5、PBr3、PBr5、PI3At least one of (1).
The phosphorus-containing compound and the Li2The molar ratio of S is 1: 1-4; the ratio of the total amount of the active ingredients can be 1: 2-3.
The Li2The molar ratio of S to the elemental sulfur is 1-10: 1; specifically, the ratio can be 3-6: 1, 4:1 or 5: 1.
The Li2S is inThe molar concentration in the organic solvent is 0.01-0.1 mol/L; specifically, the concentration of the water is 0.05 to 0.07 mol/L.
The organic solvent is at least one of 1, 3-dioxolane, 1, 2-dimethoxyethane, tetrahydrofuran and triglyme.
Specifically, the organic solvent is 1, 3-dioxolane, 1, 2-dimethoxyethane, tetrahydrofuran or a mixture of 1, 3-dioxolane and 1, 2-dimethoxyethane.
In the preparation method, in the step (1), the reaction and dissolution time is 10-48 h; specifically, the time can be 10-20 h, 10h, 15h or 16 h.
The reaction dissolution is carried out under stirring.
The reaction dissolution temperature is room temperature; specifically, the room temperature is 15-35 ℃ which is known to those skilled in the art.
In the preparation method, in the step (2), the soaking time is 1-10 hours; specifically, the time can be 1-5 h, 1h, 2h or 4 h.
The soaking is carried out at room temperature; specifically, the room temperature is 15-35 ℃ which is known to those skilled in the art.
The preparation method is carried out in a glove box filled with argon (H)2O<1ppm，O2<1ppm) was carried out.
In the preparation method, in the step (2), the step of removing the oxide film on the surface of the lithium sheet is further included;
and taking out the lithium sheet and then standing the lithium sheet until the residual solvent is completely volatilized.
The lithium sheet is in the shape of a metal lithium electrode commonly used in the art; specifically, the lithium sheet is round, rectangular, square or strip-shaped; the thickness of the lithium sheet is 0.2-1 mm.
The lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film prepared by the preparation method also belongs to the protection scope of the invention.
The application of the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film in the preparation of the battery also belongs to the protection scope of the invention.
The invention also provides a battery containing the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film.
Specifically, the battery is a lithium-sulfur battery.
The invention has the following advantages:
(1) the method adopts a composite solution of sulfide and phosphide to pretreat the metal lithium, and the metal lithium reacts on the surface of the lithium metal to form a fast ion conductor passivation layer before the battery is assembled, and the passivation layer is tightly contacted with a lithium metal cathode;
(2) a layer of phosphorus-sulfur-based compound fast ion conductor inorganic solid electrolyte interface film is formed on the surface of the lithium metal negative electrode, the interface impedance is reduced from 200 omega to 3 omega by the interface film, and the lithium metal negative electrode is beneficial to the transmission of lithium ions and the improvement of the electrochemical performance of the negative electrode; the interface film blocks the contact between the electrolyte and the metal lithium, thereby reducing side reactions and enabling the deposition of the lithium metal to be more uniform; compared with lithium metal, the phosphorus-sulfur-based compound has higher Young modulus, can physically inhibit the formation of lithium dendrites, improves the cycling stability of the metal lithium, maintains the overpotential of the assembled lithium symmetric battery at 9mV after cycling for 300h, and increases the overpotential of the lithium symmetric battery assembled by a blank metal lithium cathode to 52 mV;
(3) the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film is assembled with the lithium-sulfur battery, so that the shuttle effect of polysulfide is inhibited, the consistency of the charge-discharge curve of the lithium-sulfur battery is better, and the cycle stability and the coulomb efficiency of the lithium-sulfur battery are improved;
(4) the preparation method of the lithium metal cathode protected by the phosphorus-sulfur-based interface film is simple to operate, avoids the defects of consumption of electrolyte components by the in-situ solid electrolyte interface film and the like, can effectively ensure the cycling stability of the battery, is green and environment-friendly, and is easy for large-scale production.
Drawings
Fig. 1 is a graph of impedance of a lithium metal negative electrode protected with a phosphorus sulfur based interfacial film prepared in example 1 and a lithium symmetric battery using blank lithium metal.
Fig. 2 is a graph of cycling performance and local voltage for lithium metal negative electrodes protected with a phosphorus sulfur based interfacial film prepared in example 1 and for a lithium symmetric cell using a blank lithium metal.
Fig. 3 is a graph comparing discharge capacity versus cycle performance of lithium metal negative electrodes protected using the phosphorus sulfur-based interfacial film prepared in example 1 and lithium sulfur batteries using blank lithium metal.
FIG. 4 is an SEM image of the deposition profile of the negative electrode after 50 weeks of cycling of the lithium sulfur battery of example 1; where a in fig. 4 is blank lithium metal and b in fig. 4 is a lithium metal negative electrode protected by a phosphorus sulfur based interfacial film.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.
The experimental procedures in the following examples are conventional unless otherwise specified.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
The thickness of the PP separator in the following examples was 30 μm and was purchased from Celgard.
Assembly and testing of lithium sulfur batteries prepared in the following examples: and (2) mixing sulfur powder and a carbon nano tube according to a mass ratio of 7: 3 heating to 155 ℃, keeping the temperature for 10 hours, melting and mixing to obtain a sulfur-carbon composite material, uniformly stirring the sulfur-carbon composite material, conductive carbon black and a binder LA132 according to the mass ratio of 80:12:8 to prepare slurry, and coating the slurry on an aluminum foil current collector to obtain the sulfur anode. The electrolyte consists of lithium bis (trifluoromethylsulfonyl) imide, lithium nitrate and a mixed solvent of 1:1 by volume of ethylene glycol dimethyl ether and 1, 3-dioxolane, wherein the concentration of the lithium bis (trifluoromethylsulfonyl) imide is 1mol/L, and the concentration of the lithium nitrate is 0.2 mol/L. The diaphragm adopts a PP diaphragm, the negative electrode adopts a lithium metal negative electrode or blank metal lithium protected by the phosphorus-sulfur-based interfacial film prepared in the embodiment, and the CR2016 type lithium-sulfur battery is formed in a glove box. The assembled lithium sulfur battery was subjected to electrochemical performance testing at room temperature using a blue test system.
Assembly and testing of lithium symmetric cells of the following examples: the electrolyte consists of lithium bis (trifluoromethylsulfonyl) imide, lithium nitrate and a mixed solvent of 1:1 by volume of ethylene glycol dimethyl ether and 1, 3-dioxolane, wherein the concentration of the lithium bis (trifluoromethylsulfonyl) imide is 1mol/L, and the concentration of the lithium nitrate is 0.2 mol/L. The diaphragm adopts a PP diaphragm. The positive electrode and the negative electrode both adopt the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film prepared in the embodiment or the positive electrode and the negative electrode both adopt blank metal lithium, and a CR2025 type lithium symmetrical battery is formed in a glove box. And (3) carrying out electrochemical performance test on the assembled lithium symmetrical battery at room temperature by adopting a blue testing system.
In the following examples, the glove box was an argon-filled glove box (H)2O<1ppm，O2<1ppm)。
Example 1
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.5mm, and cutting into wafers with the diameter of 11mm for later use;
(2) in the glove box 0.555g P was placed2S5、0.276g Li2S and 0.048g of elemental sulfur are added into 100mL of 1, 3-dioxolane, and the mixture is stirred for 10 hours to be completely reacted and dissolved;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 2h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. From the test results of fig. 1, it can be seen that the interfacial resistance of the lithium symmetric battery using the blank lithium metal negative electrode is 200 Ω, compared to only 3 Ω of the lithium symmetric battery using the lithium metal negative electrode protected by the phospho-sulfur-based interfacial film, which facilitates lithium ion transport and makes the lithium metal deposition more uniform. The cycling test of the lithium symmetric battery is performed, and according to the test result shown in fig. 2, the overpotential of the lithium symmetric battery using the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9mV after cycling for 300 hours, while the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 52mV after cycling for 300 hours, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the desorption of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. According to the test results shown in fig. 3, the first cycle specific discharge capacity of the lithium-sulfur battery using the lithium metal negative electrode protected by the boundary film of phosphorus-sulfur is 771.9mAh/g, and the specific discharge capacity after 50 cycles is 589.2mAh/g, compared with the specific discharge capacity of the lithium-sulfur battery using the blank lithium metal after 50 cycles of only 470.1mAh/g, which is lower than the specific discharge capacity of the lithium metal negative electrode protected by the boundary film of phosphorus-sulfur during the whole cycle; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
As can be seen from a in FIG. 4, the blank lithium metal shows the morphological characteristics of porous dispersion on the surface after circulation, and a moss-like lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, as shown in b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Example 2
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.6mm, and cutting into wafers with the diameter of 11mm for later use;
(2) in the glove box 0.555g P was placed2S5、0.288g Li2S and 0.04g of elemental sulfur are added into 100mL of 1, 2-dimethoxyethane and stirred for 10 hours to be completely reacted and dissolved;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 1h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test results are similar to fig. 1, with the interface impedance of the lithium symmetric cell using the blank lithium metal negative electrode being 203 Ω, compared to only 4 Ω for the lithium symmetric cell using the lithium metal negative electrode protected with the phospho-sulfur based interfacial film, which facilitates lithium ion transport and more uniform lithium metal deposition. The cycling test of the lithium symmetric battery is performed, the test result is similar to that shown in fig. 2, the overpotential of the lithium symmetric battery with the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9.5mV after the lithium symmetric battery is cycled for 300 hours, the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 53mV after the lithium symmetric battery is cycled for 300 hours, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the extraction of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test result is similar to that shown in fig. 3, the first cycle discharge specific capacity of the lithium-sulfur battery using the lithium metal cathode protected by the phosphorus-sulfur interface film is 772.2mAh/g, and the discharge specific capacity after 50 cycles is 589.5mAh/g, compared with the discharge specific capacity of the lithium-sulfur battery using the blank lithium metal after 50 cycles is only 471.3mAh/g, which is lower than the discharge specific capacity of the lithium metal cathode protected by the phosphorus-sulfur interface film in the whole cycle process; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
The test result is similar to a in fig. 4, the blank lithium metal shows the morphological characteristic of porous dispersion on the surface after circulation, and a moss-shaped lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, the result is similar to b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Example 3
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.5mm, and cutting into wafers with the diameter of 11mm for later use;
(2) in the glove box 0.555g P was placed2S5、0.288g Li2S and 0.04g of elemental sulfur are added into a mixed solution of 50mL of 1, 2-dimethoxyethane and 50mL of 1, 3-dioxolane, and stirred for 15 hours to be completely reacted and dissolved;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 1h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test results are similar to fig. 1, with the interface impedance of the lithium symmetric cell using the blank lithium metal negative electrode being 202 Ω, compared to only 4 Ω for the lithium symmetric cell using the lithium metal negative electrode protected with the phospho-sulfur based interfacial film, which facilitates lithium ion transport and more uniform lithium metal deposition. The cycling test of the lithium symmetric battery is performed, the test result is similar to that shown in fig. 2, the overpotential of the lithium symmetric battery with the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9.3mV after the lithium symmetric battery is cycled for 300h, the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 54mV after the lithium symmetric battery is cycled for 300h, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the extraction of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test result is similar to that shown in fig. 3, the first cycle discharge specific capacity of the lithium-sulfur battery using the lithium metal cathode protected by the phospho-sulfur interface film is 772.5mAh/g, and the discharge specific capacity after 50 cycles is 590.1mAh/g, compared with the previous cycle discharge specific capacity of the lithium-sulfur battery using the blank lithium metal is only 470.8mAh/g after 50 cycles, and the discharge specific capacity is lower than that of the lithium metal cathode protected by the phospho-sulfur interface film in the whole cycle process; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
The test result is similar to a in fig. 4, the blank lithium metal shows the morphological characteristic of porous dispersion on the surface after circulation, and a moss-shaped lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, the result is similar to b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Example 4
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.4mm, and cutting into a wafer with the diameter of 11mm for later use;
(2) in the glove box 0.555g P was placed2S5、0.296g Li2S and 0.034g of elemental sulfur are added into 100mL of tetrahydrofuran, and the mixture is stirred for 15 hours to be completely reacted and dissolved;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 4h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test results are similar to fig. 1, with the interface impedance of the lithium symmetric cell using the blank lithium metal negative electrode being 203 Ω, compared to only 3.5 Ω for the lithium symmetric cell using the lithium metal negative electrode protected with the phospho-sulfur based interface film, which facilitates lithium ion transport and more uniform lithium metal deposition. The cycling test of the lithium symmetric battery is performed, the test result is similar to that shown in fig. 2, the overpotential of the lithium symmetric battery with the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9.6mV after the lithium symmetric battery is cycled for 300h, the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 53mV after the lithium symmetric battery is cycled for 300h, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the extraction of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test result is similar to that shown in fig. 3, the first cycle discharge specific capacity of the lithium-sulfur battery using the lithium metal cathode protected by the phosphorus-sulfur interface film is 773.1mAh/g, and the discharge specific capacity after 50 cycles is 589.7mAh/g, compared with the previous cycle discharge specific capacity of the lithium-sulfur battery using the blank lithium metal is only 471.8mAh/g after 50 cycles, and the discharge specific capacity is lower than that of the lithium metal cathode protected by the phosphorus-sulfur interface film in the whole cycle process; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
The test result is similar to a in fig. 4, the blank lithium metal shows the morphological characteristic of porous dispersion on the surface after circulation, and a moss-shaped lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, the result is similar to b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Example 5
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.6mm, and cutting into wafers with the diameter of 11mm for later use;
(2) 1.59g P in the glove box4S16、0.288g Li2S and 0.04g of elemental sulfur are added into 100mL of tetrahydrofuran, and the mixture is stirred for 16 hours to be completely reacted and dissolved;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 2h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test results are similar to fig. 1, with the interface impedance of the lithium symmetric cell using the blank lithium metal negative electrode being 204 Ω, compared to only 3.4 Ω for the lithium symmetric cell using the lithium metal negative electrode protected with the phospho-sulfur based interface film, which facilitates lithium ion transport and more uniform lithium metal deposition. The cycling test of the lithium symmetric battery is performed, the test result is similar to that shown in fig. 2, the overpotential of the lithium symmetric battery with the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9.7mV after the lithium symmetric battery is cycled for 300h, the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 55mV after the lithium symmetric battery is cycled for 300h, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the desorption of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test result is similar to that in fig. 3, the first cycle discharge specific capacity of the lithium-sulfur battery using the lithium metal cathode protected by the phosphorus-sulfur interface film is 771.5mAh/g, and the discharge specific capacity after 50 cycles is 587.9mAh/g, compared with the specific discharge capacity of the lithium-sulfur battery using the blank lithium metal after 50 cycles is only 470.2mAh/g, and the discharge specific capacity of the lithium metal cathode protected by the phosphorus-sulfur interface film is lower in the whole cycle process; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
The test result is similar to a in fig. 4, the blank lithium metal shows the morphological characteristic of porous dispersion on the surface after circulation, and a moss-shaped lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, the result is similar to b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Example 6
(1) Removing an oxide film on the surface of lithium metal in a glove box, rolling the lithium metal to the thickness of 0.4mm, and cutting into a wafer with the diameter of 11mm for later use;
(2) 1.59g P in the glove box4S16、0.296g Li2S and 0.034g of elemental sulfur were added to a mixed solution of 50mL of 1, 2-dimethoxyethane and 50mL of 1, 3-dioxolane, and the mixture was stirred for 10 hours to completely reactDissolving;
(3) and (3) putting 10mL of the solution in a weighing bottle in a glove box, soaking a lithium sheet in the solution for reaction for 1h, taking out the lithium sheet, and standing until the residual solvent is completely volatilized to obtain the lithium metal cathode protected by the phosphorus-sulfur-based interfacial film.
Two sets of lithium symmetric cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test results are similar to fig. 1, with the interface impedance of the lithium symmetric cell using the blank lithium metal negative electrode being 202 Ω, compared to only 3.2 Ω for the lithium symmetric cell using the lithium metal negative electrode protected with the phospho-sulfur based interface film, which facilitates lithium ion transport and more uniform lithium metal deposition. The cycling test of the lithium symmetric battery is performed, the test result is similar to that shown in fig. 2, the overpotential of the lithium symmetric battery with the lithium metal negative electrode protected by the phosphorus-sulfur-based interface film is still kept at 9.2mV after the lithium symmetric battery is cycled for 300h, the overpotential of the lithium symmetric battery assembled by the blank lithium metal negative electrode is increased to 54mV after the lithium symmetric battery is cycled for 300h, and the phosphorus-sulfur-based interface film is beneficial to the deposition and the extraction of lithium ions, so that the cycling stability of the metal lithium negative electrode is improved.
Two sets of lithium sulfur cells were assembled, differing only in that: one group uses lithium metal negative electrodes protected with a phospho-sulfur based interfacial film and one group uses blank metal lithium. The test result is similar to that shown in fig. 3, the first cycle discharge specific capacity of the lithium-sulfur battery using the lithium metal negative electrode protected by the phosphorus-sulfur interface film is 771.7mAh/g, and the discharge specific capacity after 50 cycles is 588mAh/g, compared with the lithium-sulfur battery using the blank lithium metal, the discharge specific capacity after 50 cycles is only 470.6mAh/g, and the discharge specific capacity is lower than that of the lithium metal negative electrode protected by the phosphorus-sulfur interface film in the whole cycle process; this is because the phosphorus sulfur based interfacial film suppresses the shuttling effect of polysulfides, reducing active species loss.
The test result is similar to a in fig. 4, the blank lithium metal shows the morphological characteristic of porous dispersion on the surface after circulation, and a moss-shaped lithium reaction area is observed after amplification, which indicates that the lithium metal is seriously corroded. However, after the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film is cycled, the result is similar to b in fig. 4, the lithium metal is deposited flatly and is tightly stacked on the surface of the electrode, and the compact lithium deposition morphology is beneficial to reducing the contact between the electrolyte and the active metal lithium, inhibiting the growth of lithium dendrites and improving the long cycle stability of the lithium metal electrode.
Claims (9)
1. A preparation method of a lithium metal negative electrode protected by a phosphorus-sulfur-based interfacial film comprises the following steps:
(1) mixing phosphorus-containing compound and Li2S and elemental sulfur are added into an organic solvent to react and dissolve to obtain a solution;
(2) and (2) soaking a lithium sheet in the solution obtained in the step (1), and taking out the lithium sheet after soaking to obtain the lithium metal negative electrode protected by the phosphorus-sulfur-based interfacial film.
2. The method of claim 1, wherein: in the step (1), the phosphorus-containing compound is P2S3、P4S16、P2S5、P2O3、P2O5、P2Se5、PCl3、PCl5、PF5、PBr3、PBr5、PI3At least one of;
the phosphorus-containing compound and the Li2The molar ratio of S is 1: 1-4;
the Li2The molar ratio of S to the elemental sulfur is 1-10: 1;
the Li2The molar concentration of S in the organic solvent is 0.01-0.1 mol/L.
3. The production method according to claim 1 or 2, characterized in that: the organic solvent is at least one of 1, 3-dioxolane, 1, 2-dimethoxyethane, tetrahydrofuran and triglyme.
4. The production method according to any one of claims 1 to 3, characterized in that: in the step (1), the reaction and dissolution time is 10-48 h.
5. The production method according to any one of claims 1 to 4, characterized in that: in the step (2), the soaking time is 1-10 h.
6. The production method according to any one of claims 1 to 5, characterized in that: the whole process of the preparation method is carried out in a glove box filled with argon;
in the step (2), the method further comprises the step of removing the oxide film on the surface of the lithium sheet;
and taking out the lithium sheet and then standing the lithium sheet until the residual solvent is completely volatilized.
7. The lithium metal negative electrode protected by the phosphorus sulfur based interfacial film prepared by the preparation method of any one of claims 1 to 6.
8. A battery comprising a lithium metal negative electrode protected by a phosphorus sulfur based interfacial film as claimed in claim 7.
9. The battery of claim 8, wherein: the battery is a lithium sulfur battery.
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