CN113443973B - Lithium squarate and preparation method and application thereof - Google Patents

Lithium squarate and preparation method and application thereof Download PDF

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CN113443973B
CN113443973B CN202011616037.9A CN202011616037A CN113443973B CN 113443973 B CN113443973 B CN 113443973B CN 202011616037 A CN202011616037 A CN 202011616037A CN 113443973 B CN113443973 B CN 113443973B
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lithium
squarate
reaction
freezing
temperature
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CN113443973A (en
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胡彦杰
江浩
李春忠
沈博磊
朱承贤
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East China University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/61—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C49/00—Ketones; Ketenes; Dimeric ketenes; Ketonic chelates
    • C07C49/587—Unsaturated compounds containing a keto groups being part of a ring
    • C07C49/703—Unsaturated compounds containing a keto groups being part of a ring containing hydroxy groups
    • C07C49/707—Unsaturated compounds containing a keto groups being part of a ring containing hydroxy groups a keto group being part of a three- to five-membered ring
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2601/00—Systems containing only non-condensed rings
    • C07C2601/04—Systems containing only non-condensed rings with a four-membered ring
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention discloses a lithium squarate and a preparation method and application thereof, which are characterized by comprising the following steps: mixing the lithium source water solution and the squaric acid water solution for reaction, further preparing a reaction product into powder, and sequentially dissolving with water, quickly freezing and freeze-drying. The lithium squarate is prepared by the preparation method, and the thickness of the lithium squarate is 50-100 nm. The preparation method disclosed by the invention is simple in process, and the uniform nanosheet with the thickness of 50-100 nm is obtained only through simple freeze-drying treatment. The decomposition voltage of the lithium squarate prepared by the method is greatly reduced, the electrochemical activity is greatly improved, and the lithium squarate can be used as a lithium supplement agent to be applied to a lithium-sulfur battery and/or a lithium ion battery.

Description

Lithium squarate and preparation method and application thereof
Technical Field
The invention belongs to the technical field of energy storage, and particularly relates to lithium squarate and a preparation method and application thereof.
Background
When the lithium ion battery is charged and activated in the first circle, lithium ions can be extracted from the positive electrode material and embedded into the negative electrode material. In this process, the battery consumes a part of lithium ions to form a solid electrolyte film (SEI film) on the surface of the negative electrode, and the consumed part of lithium ions is undoubtedly directly responsible for the loss of battery capacity. At present, graphite is used as a negative electrode of most commercial batteries on the market, and the irreversible capacity loss of the graphite is generally about 10%, which is acceptable, but for silicon-based and tin-based negative electrodes with high specific capacity, the irreversible capacity loss is generally more than 30%, which undoubtedly greatly limits the development of the electrode materials. The lithium replenishing technology can compensate the capacity loss, and the current lithium replenishing methods mainly comprise two methods, namely electrochemical lithium replenishing and lithium powder lithium replenishing. Electrochemical lithium supplementation is frequently used for basic research, and researchers make up for capacity loss in a full cell by pre-lithiating a negative electrode by an electrochemical method before assembling the full cell, but the operation method is complicated and thus difficult to industrialize. Lithium is supplemented by lithium powder, which is considered as the most promising industrialized method in a period of time, the lithium is supplemented by directly adding metal lithium powder into cathode slurry, but the metal lithium powder is expensive and very active in chemical property, and can be spontaneously combusted or even explode in a humid environment, and the cathode of the lithium ion battery at present adopts a water-based binder sodium carboxymethyl cellulose (CMC), so that the operation difficulty and risk of using the metal lithium powder in the current actual production are very high.
The traditional lithium supplement method is from the bottom of a negative electrode, and in order to overcome the problems of lithium supplement of the negative electrode, the lithium supplement of the positive electrode is researched in the field. The positive electrode lithium supplement has the advantages of relative stability, easy synthesis, low price, high lithium supplement capacity and the like, wherein the sacrificial lithium salt method generates lithium ions in the charging process and decomposes the lithium ions to form harmless gases such as nitrogen, carbon dioxide, carbon monoxide and the like, impurities which interfere the electrochemical reaction of an energy storage system cannot be introduced, and the method is gradually paid attention to by people. The specific capacity of the lithium squarate in the lithium salt is up to 440 milliampere per gram, the specific capacity of the lithium squarate is twice of that of the traditional anode material, and the lithium squarate is suitable for being used as a sacrificial lithium salt to compensate the irreversible capacity loss of lithium ions. However, since lithium squarate is an insulator and has low conductivity and ion mobility, it is necessary to reduce its size to enhance its electrochemical activity. The material prepared by the conventional means such as ball milling and aqueous solution rotary evaporation has overlarge size, and the electrochemical activity of the material is seriously influenced, which is shown in the aspects of high decomposition voltage, long-time activation with low multiplying power and the like.
CN110683944A discloses a squarate and a preparation method and application thereof, wherein a series of squarate is prepared by combining a ball milling method and an organic solvent, primary particles of the prepared material are small but have uneven size and are agglomerated, so that the overall structure of the material stays at a micron level, the decomposition voltage of the squarate is 4.1-4.8V, and the squarate cannot release all capacity under the cut-off voltage of 4.5V in a lithium-sulfur battery system, thereby limiting the application of the squarate in lithium-sulfur batteries and lithium ion batteries. In addition, carbon dioxide generated by the decomposition of lithium squarate is completely discharged out of the battery system, and the protective effect of carbon dioxide on the electrolyte is lost.
Disclosure of Invention
The invention aims to solve the technical problems that the preparation process of lithium squarate is complicated, the size of the prepared lithium squarate is mostly micron-sized, agglomeration is easy to occur, the electrochemical performance is low and the like in the prior art, and provides the lithium squarate, and a preparation method and application thereof.
The invention is realized by the following technical scheme:
the invention provides a preparation method of lithium squarate, which comprises the following steps: mixing the lithium source water solution and the squaric acid water solution for reaction, further preparing a reaction product into powder, and sequentially dissolving with water, quickly freezing and freeze-drying.
Preferably, the quick freezing comprises one or more of quick freezing by a refrigerator, quick freezing by liquid nitrogen and quick freezing by dry ice. More preferably, the quick freezing is liquid nitrogen quick freezing. The quick freezing can prepare white squaric acid lithium powder with uniform and fine particles.
Preferably, the temperature for quick freezing by the refrigerator is-20 ℃; the quick-freezing time of the refrigerator is 5-7 hours, for example 6 hours.
Preferably, the temperature of the liquid nitrogen quick freezing is-197 ℃; the time for quick freezing by liquid nitrogen is 1-10 min, for example 2 min.
Preferably, the temperature of the dry ice quick freezing is-78 ℃; the dry ice quick-freezing time is 20-40 min, such as 30 min.
Preferably, the freeze-drying time is 24-72 hours, and more preferably 48 hours.
Preferably, the temperature of the freeze drying is-10 ℃ to-50 ℃, more preferably-40 ℃ to-50 ℃.
Preferably, the further powdering of the reaction product is a concentration.
Preferably, the concentration temperature is 30-120 ℃, for example, 60 ℃.
Preferably, the mixing reaction is a metathesis reaction.
Preferably, the metathesis reaction is fed in a sequence in which the aqueous solution of the lithium source is added to the aqueous solution of the squaric acid.
Preferably, the molar ratio of the squaric acid to the lithium source in the raw materials for the double decomposition reaction is 1.1-1.5: 1; more preferably, the molar ratio of the squaraine to the lithium source is 1.1: 1. The squaric acid needs to be used in excess and subsequently excess squaric acid is removed by a solvent to ensure the purity of the lithium squarate.
Preferably, the lithium source in the raw material for the metathesis reaction is one or more of lithium carbonate, lithium bicarbonate, lithium sulfate and lithium hydroxide. More preferably, the lithium source is lithium carbonate.
Preferably, the temperature of the metathesis reaction is 20 ℃ to 60 ℃, such as 20 ℃, 30 ℃, 40 ℃, 50 ℃ and 60 ℃.
Preferably, the stirring time of the double decomposition reaction is 1-2 h.
Preferably, the stirring speed of the metathesis reaction is 300 r/min.
Preferably, the preparation method further comprises washing the lithium squarate powder with a washing solvent before the operation of dissolving with water. The cleaning solvent may be conventional in the art, and is preferably ethanol, acetone or other alcohols.
The invention also provides lithium squarate which is prepared by the preparation method of the lithium squarate.
Preferably, the lithium squarate is a nanosheet with a thickness of 50-100 nm.
The invention also provides an application of the lithium squarate as a lithium supplement agent in a lithium ion battery and/or a lithium sulfur battery.
The application method of the lithium squarate serving as a lithium supplement agent in the preparation of the lithium ion battery and/or the lithium sulfur battery generally comprises the following steps: (1) adding a positive electrode lithium supplement agent, (2) assembling the whole battery and (3) activating the lithium supplement agent.
Specifically, in the step (1), the operation and conditions for adding the positive electrode lithium supplement agent are conventional in the art. The addition of the positive electrode lithium supplement agent is to add a positive electrode material, lithium square oxide as the lithium supplement agent, a conductive agent and a binder into a solvent, grind the mixture to obtain viscous slurry, coat the slurry on a current collector, and dry the slurry to obtain a positive electrode plate with the lithium supplement agent, or coat the lithium square oxide slurry on the surface of the prepared positive electrode plate uniformly, and dry the slurry to obtain the positive electrode plate with the lithium supplement agent.
When the anode material in the step (1) is used for a lithium ion battery, the anode material is lithium iron phosphate; when the cathode material is used for a lithium-sulfur battery, the cathode material is a composite (S/pPAN) of sulfur and polyacrylonitrile.
The conductive agent in the step (1) is one or more of acetylene black, conductive carbon black, Ketjen black or CMK-3. When the conductive agent is used for a lithium ion battery, the conductive agent is Keqin black; when the conductive agent is used for a lithium-sulfur battery, the conductive agent is mesoporous carbon CMK-3.
In the step (1), the adhesive is one or more of polyvinylidene fluoride, carboxymethyl cellulose and polystyrene butadiene copolymer. When the binder is used for the lithium ion battery, the binder is polyvinylidene fluoride.
In the step (1), the solvent is 1-methyl-2-pyrrolidone and/or deionized water.
In the step (1), the current collector is an aluminum foil or a carbon-coated aluminum foil.
When the lithium supplement agent in the step (1) is used for a lithium ion battery, the ratio of the positive electrode material, the positive electrode lithium supplement agent, the conductive agent and the binder is 7.5:0.5:1: 1; when the lithium supplement agent is used for a lithium-sulfur battery, the ratio of the positive electrode material, the positive electrode lithium supplement agent, the conductive agent and the binder is 4:3:2: 1.
Specifically, in the step (2) full cell assembly, the operation and conditions of the full cell assembly are conventional in the art, and the full cell assembly is generally performed on a commercial negative electrode sheet and the positive electrode sheet obtained in the step (1).
Specifically, in the step (3), during the activation of the lithium supplement agent, the activation of the lithium supplement agent is a formation step in a lithium ion battery, which is a convention in the field, that is, the assembled battery is installed on a LAND battery test system, the full battery is activated in a certain current density and voltage interval, the charge cut-off voltage is 4.5V, and the battery activation is completed after the charging is completed.
The current density in the step (3) is 0.5C.
In the step (3), the voltage interval is 1-4.5V.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The positive progress effects of the invention are as follows:
(1) the preparation process of the squaric acid lithium is simple, and the squaric acid lithium obtained by simple freeze-drying treatment is a nanosheet with the thickness of 50-100 nm, so that the electrochemical activity of the squaric acid lithium is greatly improved.
(2) The squaric acid lithium prepared by the method has small size, greatly reduces the decomposition voltage of the squaric acid lithium, and can be applied to lithium-sulfur batteries and/or lithium ion batteries.
(3) According to the invention, carbon dioxide generated by decomposition of the lithium squarate cannot be completely discharged out of the electrolyte system, and part of the carbon dioxide is dissolved in the electrolyte to inhibit decomposition of the electrolyte, so that the stability of the electrolyte is ensured, and the flame retardance and the stability of the battery system are improved.
(4) The preparation method provided by the invention is low in cost, is suitable for mass production, can be directly applied to battery production without upgrading the conventional lithium ion battery or lithium sulfur battery production equipment, and improves the performance of the battery.
Drawings
FIG. 1 is a phase representation of lithium squarate prepared in Synthesis example 2 of the present invention;
FIG. 2 is a graph showing the morphology of lithium squarate prepared in comparative examples 1 and 2 and in Synthesis example 2 of the present invention, wherein FIG. (a) corresponds to comparative example 1, FIG. (b) corresponds to comparative example 2, and FIG. (c) corresponds to Synthesis example 2;
FIG. 3 is a graph showing electrochemical properties of lithium squarate prepared in comparative examples 1 and 2 and Synthesis example 2 according to the present invention;
FIG. 4 is a graph showing the test performance of lithium squarate prepared in comparative example 1 and Synthesis example 2 according to the present invention in a lithium ion battery;
FIG. 5 shows SEI film composition analysis in full cells containing lithium squarate of Synthesis example 2 of the present invention and full cells not containing lithium squarate of Synthesis example 2 of the present invention;
FIG. 6 is a graph showing the performance of lithium squarate prepared according to comparative example 1 and Synthesis example 2 of the present invention in a lithium sulfur battery electrolyte;
FIG. 7 is a graph showing the performance of lithium squarate prepared in Synthesis example 2 of the present invention in a lithium sulfur battery electrolyte;
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The reagents and starting materials used in the present invention are commercially available.
Comparative example 1
Comparative example 1 lithium squarate was prepared by ball milling, the specific procedure was as follows: 3.5359g of squaric acid and 2.2000g of lithium carbonate are added into 15mL of acetone, and ball milling and mixing are carried out, wherein the ball milling speed is 900rpm, the ball-material ratio is 2-10: 1, and the ball milling time is 30 min.
Comparative example 2
Comparative example 2 lithium squarate was prepared by rotary evaporation, the specific procedure was as follows: 0.5800g of squaric acid and 0.3695g of lithium carbonate were dissolved in 50ml of deionized water, respectively, and an aqueous solution of lithium carbonate was slowly added to the aqueous solution of squaric acid in a water bath at 60 ℃ and stirring was maintained for 2 hours after the addition was completed.
The solution was rotary evaporated at 60 ℃ until all water was evaporated to dryness to give a white powder. Then, the white powder is washed for 3 times by using absolute ethyl alcohol, and redundant squaraine is removed to obtain a pure phase of the lithium squaraine.
Synthesis example 1
Synthesis example 1 lithium squarate was prepared by quick freezing with a freezer, and the specific steps were as follows: 0.5800g of squaric acid and 0.3695g of lithium carbonate were dissolved in 50ml of deionized water, respectively, and an aqueous solution of lithium carbonate was slowly added to the aqueous solution of squaric acid in a water bath at 60 ℃ and stirred for 2 hours after the addition was completed.
The solution was rotary evaporated at 60 ℃ until all water was evaporated to dryness to give a white powder. Then, the white powder is washed for 3 times by using absolute ethyl alcohol, and redundant squaraine is removed to obtain a pure phase of the lithium squaraine.
Dissolving the pure lithium squarate phase in 20ml of deionized water, freezing for 6 hours in a freezer, and freeze-drying the quick-frozen solution for 48 hours at-40 ℃ to obtain the lithium squarate.
Synthesis example 2
Synthesis example 2 lithium squarate was prepared by liquid nitrogen flash freezing, and the specific steps were as follows: 0.5800g of squaric acid and 0.3695g of lithium carbonate were dissolved in 50ml of deionized water, respectively, and an aqueous solution of lithium carbonate was slowly added to the aqueous solution of squaric acid in a water bath at 60 ℃ and stirred for 2 hours after the addition was completed.
The solution was rotary evaporated at 60 ℃ until all water was evaporated to dryness to give a white powder. And then washing the white powder for 3 times by using absolute ethyl alcohol, and removing redundant squaraine to obtain a pure phase of the lithium squaraine.
Dissolving the pure lithium squarate phase in 20ml of deionized water, quickly freezing in liquid nitrogen for 2min, and freeze-drying the quick-frozen solution at-40 ℃ for 48h to obtain lithium squarate.
Performing characterization and performance test on the lithium squarate materials obtained in comparative example 1, comparative example 2, synthesis example 1 and synthesis example 2, wherein the characterization comprises SEM (scanning electron microscope), hydrogen spectrum, X-ray diffraction and infrared characterization, and instruments used for characterization are conventional in the field; the performance test comprises the following steps: testing a positive plate, testing a lithium ion battery, analyzing the SEI (solid electrolyte interphase) film component of the lithium ion full battery and testing the lithium sulfur battery;
the positive plate test comprises the following steps:
adding lithium squarate, CMK-3 and polyvinylidene fluoride into 1-methyl-2-pyrrolidone according to a ratio of 7:2:1, grinding to obtain black viscous slurry, coating the slurry on an aluminum foil, drying to obtain a lithium squarate electrode slice, and assembling metal lithium, a diaphragm and a lithium squarate electrode slice into a button battery, wherein the type of the button battery is CR2032, the type of the diaphragm is 2500, and an electrolyte is a 1mol/L lithium hexafluorophosphate solution (a solvent is a mixed solution of ethylene carbonate and dimethyl carbonate according to a volume ratio of 1: 1). After the assembly was completed, the cell was removed from the glove box, allowed to stand at 30 ℃ for 12 hours, and then tested on a Land test system.
The lithium ion battery test steps are as follows:
adding 75mg of lithium iron phosphate, 5mg of lithium squarate, 10mg of CMK-3 mesoporous carbon and 10mg of polyvinylidene fluoride into 1-methyl-2-pyrrolidone respectively, grinding to prepare black viscous slurry, coating the slurry on an aluminum foil, and drying to prepare a positive plate containing the lithium squarate;
and assembling the metal lithium, the diaphragm and the prepared positive plate into a button battery, wherein the model of the used button battery is CR2032, the model of the diaphragm is 2500, and the electrolyte is 1mol/L lithium hexafluorophosphate solution (the solvent is mixed solution of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1). After the assembly was completed, the cell was removed from the glove box, allowed to stand at 30 ℃ for 12 hours, and then tested on a Land test system.
The method for analyzing the SEI film component of the lithium ion full battery comprises the following steps:
and (3) respectively assembling the electrode plates containing lithium squarate and electrode plates not containing lithium squarate into a full cell, wherein the model of the used button cell is CR2032, the model of the used diaphragm is 2500, the electrolyte is 1mol/L lithium hexafluorophosphate solution (the solvent is mixed solution of ethylene carbonate and dimethyl carbonate according to the volume ratio of 1: 1), and the cathode is a commercial graphite electrode plate. After the assembly, the battery was removed from the glove box, allowed to stand at 30 ℃ for 12 hours, and then subjected to 5-cycle charge-discharge cycle on a Land test system, and then the battery was disassembled, and the negative electrode was subjected to XPS analysis.
The procedure for the lithium sulfur battery test was as follows:
adding S/pPAN (sulfur and cracked polyacrylonitrile composite), acetylene black and sodium carboxymethylcellulose into water according to the ratio of 8:1:1, grinding to obtain black viscous slurry, coating the slurry on an aluminum foil, drying to obtain an additive-free positive plate, adding lithium squarate, CMK-3 and polyvinylidene fluoride into 1-methyl-2-pyrrolidone according to the ratio of 7:2:1, grinding to obtain black viscous slurry, coating the slurry on the positive plate, and drying to obtain a positive plate covered with lithium squarate, wherein the process needs to ensure that the load capacity ratio of the positive material to the lithium squarate is 1: 1;
respectively adding silicon-carbon negative electrode powder, acetylene black and polyvinylidene fluoride into 1-methyl-2-pyrrolidone according to a certain proportion, grinding to obtain viscous slurry, coating the slurry on copper foil, and drying to obtain a negative electrode plate;
and assembling the prepared positive and negative pole pieces into a button battery, wherein the model of the used button battery is CR2032, the model of the diaphragm is 2500, and the electrolyte is 1mol/L lithium hexafluorophosphate solution (the solvent is a mixed solution of dimethyl carbonate and fluoroethylene carbonate in a volume ratio of 1: 1). And after the assembly is finished, the battery is moved out of the glove box, is kept stand for 6 hours at the temperature of 30 ℃ and is activated on a Land test system, the activation current is 0.05C, the activation voltage interval is 1-4.5V, and the working voltage after activation is 1-3V.
The characterization results are shown in figures 1-2, the test results of the positive plate are shown in figure 3, the test results of the lithium ion battery are shown in figure 4, the analysis results of the SEI film components in the lithium ion full battery are shown in figure 5, and the test results of the lithium sulfur battery are shown in figures 6-7.
Effect example 1
As can be seen from fig. 1(a), the hydrogen peak of squaric acid disappeared after the reaction with lithium carbonate, indicating the position where lithium completely replaced hydrogen, and as can be seen from fig. 1(b) and fig. 1(c), synthesis example 2 succeeded in synthesizing lithium squarate.
As can be seen from fig. 2(a), all the particles of the pure phase of lithium squarate prepared in comparative example 1 are tightly connected, and severe agglomeration occurs, resulting in that the particle size is in the order of micrometers in all dimensions; FIG. 2(b) is a plot of the lithium squarate prepared in comparative example 2, which is on a larger scale; FIG. 2(c) shows that the squaric acid lithium nanosheet prepared in synthetic example 2 is frozen in water due to the fact that the liquid nitrogen cooling speed is very high, most of the squaric acid lithium is not in time to precipitate and agglomerate, so that a uniform nanosheet structure is formed, the size is obviously reduced, and the nanosheet is in a sheet shape with the thickness of 50-100 nm.
Effect example 2
As can be seen from fig. 3, the decomposition voltage of the lithium squarate prepared in comparative example 1 is 4.1V, the decomposition voltage of the lithium squarate prepared in comparative example 2 is 4.2V, the lithium squarate prepared in synthesis example 2 has the lowest decomposition voltage of only 3.8V, and the lithium squarate prepared in synthesis example 2 has a much higher release capacity than those of comparative example 1 and comparative example 2 at 0.5C, which indicates that the lithium squarate prepared in synthesis example 2 has a high activation rate, can greatly shorten the first-turn synthesis time, has the highest electrochemical activity, and has more practical value.
It can be seen from fig. 4(a) that the decomposition voltage of lithium squarate prepared in synthesis example 2 in the lithium ion battery is still lower than that of comparative example 1. It can be seen from fig. 4(b) that the lithium squarate prepared in synthesis example 2 has better cycle performance and higher specific capacity than the lithium squarate prepared in comparative example 1.
Effect example 3
Fig. 5(a) and 5(b) are XPS spectra of F element, and fig. 5(C) and 5(d) are XPS spectra of C element. Wherein fig. 5(a) is an analysis of a negative electrode SEI film of a full cell to which lithium squarate is not added, and fig. 5(b) is an analysis of a negative electrode SEI film of a full cell to which a lithium squarate material prepared in synthesis example 2 is added, it can be seen that Li generated by decomposition of an electrolyte in fig. 5(a) x PF y /Li x POF y The content is obviously higher than that of FIG. 5 (b); fig. 5(c) is an analysis of a negative electrode SEI film of a full cell to which lithium squarate is not added, and fig. 5(d) is an analysis of a negative electrode SEI film of a full cell to which a lithium squarate material prepared in synthesis example 2 is added, and it can be seen that the SEI film of fig. 5(c) contains an organic component ROCO from an electrolyte 2 Li, while FIG. 5(d) shows the presence of lithium carbonate only, indicating the CO evolution upon addition of the lithium squarate of Synthesis example 2 2 The decomposition of the electrolyte is suppressed to make the electrolyte system more stable.
Effect example 4
As can be seen from fig. 6, lithium squarate prepared in comparative example 1 failed to release the full capacity at 4.5V and the battery system was destroyed when the voltage exceeded 4.5V in the lithium sulfur battery, whereas lithium squarate prepared in synthesis example 2 released just the full capacity at 4.5V and the battery system was not destroyed.
The lithium sulfur battery has high specific capacity, and the squaric acid lithium needs high loading capacity when applied to the lithium sulfur battery, so the squaric acid lithium cannot be directly added into slurry of the lithium sulfur battery and needs to be coated on the surface of the positive electrode of the lithium sulfur battery, otherwise, a large amount of gas generated in the lithium supplementing process can damage the structure of an electrode plate. Since the decomposition voltage of lithium squarate in the lithium-sulfur battery is increased by about 0.2V because no current collector is in direct contact with the current collector, and the electrolyte of the lithium-sulfur battery is strongly decomposed at 4.5V or more, the lithium squarate prepared in comparative example 1 cannot release the full capacity at the cut-off voltage of 4.5V in the lithium-sulfur battery system, while the lithium squarate can release the full capacity at 4.5V in the lithium-sulfur battery system due to the decomposition voltage of about 0.3V, which is lower than that of comparative example 1 and comparative example 2, in synthetic example 2, which indicates that the lithium squarate prepared in synthetic example 2 can also be used in the lithium-sulfur battery.
Fig. 7(a) is a charge-discharge graph of a sulfur positive electrode, which is free of lithium and requires discharging first to charge it with lithium. Fig. 7(b) is a charge-discharge curve diagram of a sulfur positive electrode to which lithium squarate is added, and the mixed electrode to which lithium squarate is added can be charged first to release lithium in the lithium squarate, and then the battery system is charged with lithium. Fig. 7(c) is a charge and discharge curve of a full battery in which a cathode is a mixed electrode and an anode is silicon carbon, and it can be seen that the lithium squarate material prepared in synthesis example 2 successfully provided lithium ions to a lithium-free system battery. Fig. 7(d) shows the cycle performance and the coulombic efficiency of the full cell, and it can be seen that the coulombic efficiency of the cell reaches 98.94% and almost remains unchanged after the lithium squarate prepared in synthesis example 2 is added, so the cell has excellent coulombic efficiency and cycle stability.
While specific embodiments of the invention have been described above, it will be understood by those skilled in the art that this is by way of example only, and that the scope of the invention is defined by the appended claims. Various changes or modifications to these embodiments may be made by those skilled in the art without departing from the principle and spirit of the invention, and these changes or modifications are within the scope of the invention.

Claims (11)

1. A preparation method of lithium squarate is characterized by comprising the following steps: mixing the lithium source aqueous solution and the squaric acid aqueous solution for reaction, further preparing a reaction product into powder, and sequentially dissolving the powder with water, quickly freezing and freeze-drying the powder;
the mixing reaction is a double decomposition reaction; the feeding sequence of the double decomposition reaction is to add the lithium source aqueous solution into the squaric acid aqueous solution;
the lithium source in the raw materials of the double decomposition reaction is one or more of lithium carbonate, lithium bicarbonate, lithium sulfate and lithium hydroxide;
the molar ratio of the squaric acid to the lithium source in the raw materials for the double decomposition reaction is 1.1-1.5: 1;
the operation of further powdering the reaction product is concentration;
the quick freezing comprises quick freezing by a refrigerator and/or quick freezing by liquid nitrogen;
the temperature of quick freezing by the refrigerator is-20 ℃; the quick-freezing time of the refrigerator is 5-7 hours;
the temperature of the liquid nitrogen quick freezing is-197 ℃; the time for quick freezing by using the liquid nitrogen is 1-10 min;
the freeze drying time is 24-72 hours; the temperature of the freeze drying is-10 ℃ to-50 ℃.
2. The method for preparing lithium squarate according to claim 1, wherein the flash freezing is liquid nitrogen flash freezing.
3. The method for preparing lithium squarate according to claim 2, wherein the time for quick freezing by the refrigerator is 6 hours;
and/or the time for quick freezing by using the liquid nitrogen is 2 min.
4. The method for preparing lithium squarate according to claim 1, wherein the freeze-drying time is 48 hours;
the temperature of the freeze drying is-40 ℃ to-50 ℃;
and/or the concentration temperature is 30-120 ℃.
5. The method of preparing lithium squarate according to claim 4, wherein the temperature of the concentration is 60 ℃.
6. The method of preparing lithium squarate according to claim 1, wherein the molar ratio of the squaric acid to the lithium source in the starting material for the metathesis reaction is 1.1: 1;
and/or the lithium source in the raw material of the double decomposition reaction is lithium carbonate.
7. The method of preparing lithium squarate according to claim 1, wherein the temperature of the metathesis reaction is 20 ℃ to 60 ℃;
and/or the stirring time of the double decomposition reaction is 1-2 h; the stirring speed of the double decomposition reaction is 300 r/min.
8. The method of preparing lithium squarate according to claim 7, wherein the metathesis reaction temperature is 20 ℃, 30 ℃, 40 ℃, 50 ℃ and 60 ℃.
9. The method for producing lithium squarate according to claim 1, further comprising, before the operation of dissolving with water, washing the lithium squarate powder with a washing solvent; the cleaning solvent is ethanol, acetone or other alcohols.
10. A lithium squarate produced by the method for producing lithium squarate according to any one of claims 1 to 9;
and/or the lithium squarate is a nanosheet with the thickness of 50-100 nm.
11. Use of the lithium squarate of claim 10 as a lithium replenisher in lithium ion batteries and/or lithium sulfur batteries.
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