Electrochemical device and electronic device

Abstract

The present invention discloses an electrochemical device and an electronic device. An electrochemical device comprises: a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the electrolyte comprises dimethyl carbonate, vinylene carbonate and a carboxylic acid ester compound; based on the mass of the electrolyte, the mass content of dimethyl carbonate is A%, the mass content of vinylene carbonate is B%, and the mass content of the carboxylic acid ester compound is C%, satisfying: the value range of A / (B+C) is 4 to 12.53; the value range of A is 8.35 to 25.05; the carboxylic acid ester compound is any one of methyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and vinyl methacrylate, or a mixture of two or more thereof; the amount of organic matter dissolved from the sintered molded body in the diaphragm is less than 150ppm. The electrolyte of the present invention can improve the high temperature and room temperature cycle performance of the electrochemical device, while reducing the internal resistance of the electrochemical device.

Description

[0001] This application claims priority to patent application No. 202110592885.9 (the filing date of the prior application is May 28, 2021, the name of the invention is A non-aqueous electrolyte for lithium batteries, a preparation method thereof, and a lithium-ion battery, and the applicant is Envision Power Technology (Jiangsu) Co., Ltd.). Technical Field

[0002] The present invention relates to the technical field of electrolytes, and in particular to an electrochemical device and an electronic device. Background Art

[0003] Because lithium-ion batteries have the important advantages of high voltage and high capacity, as well as long cycle life and good safety performance, they have broad application prospects in portable electronic devices, electric vehicles, space technology, defense industry and many other fields.

[0004] Electrolyte is the "blood" of lithium batteries and one of the four key raw materials of lithium batteries. It is the carrier of ion transmission in the battery and plays the role of conducting lithium ions between the positive and negative electrodes. It has an important impact on the energy density, specific capacity, operating temperature range, cycle life, and safety performance of lithium batteries.

[0005] In order to develop a suitable high-performance electrolyte, suitable electrolyte additives are often added to the electrolyte. Commonly used electrolyte additives include boron additives, organophosphorus additives, carbonate additives, carboxylate additives, sulfur-containing additives, ionic liquid additives, etc.

[0006] At present, as the demand for fast charging of lithium-ion batteries becomes increasingly strong, it is necessary to introduce dimethyl carbonate DMC on the basis of using sufficient negative electrode film-forming additives to obtain better wettability and lithium ion transmission performance for the electrode. Summary of the invention

[0007] In view of the deficiencies of the prior art, the object of the present invention is to provide an electrochemical device and an electronic device. The electrolyte of the present invention can improve the high temperature and room temperature cycle performance of the electrochemical device and reduce the internal resistance of the electrochemical device.

[0008] One of the purposes of the present invention is to provide an electrolyte. To achieve this purpose, the present invention adopts the following technical solutions:

[0009] An electrolyte comprising dimethyl carbonate, vinylene carbonate and a carboxylic acid ester compound;

[0010] Based on the mass of the electrolyte, the mass content of dimethyl carbonate is A%, the mass content of vinylene carbonate is B%, and the mass content of the carboxylic acid ester compound is C%, satisfying:

[0011] The value range of A is 0 to 60, and the value range of A / (B+C) is 4 to 20.88.

[0012] The electrolyte of the present invention can improve the high temperature and room temperature cycle performance of the electrochemical device and reduce the internal resistance of the electrochemical device by using dimethyl carbonate, vinylene carbonate and carboxylic acid ester compounds in combination and adjusting the dosage ratio of the three.

[0013] The value range of A is 5 to 60, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, etc.

[0014] The value range of A / (B+C) is 4 to 20.88, for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, etc.

[0015] As a preferred solution, the value range of A / (B+C) is 5 to 8.

[0016] As a preferred solution, the value range of A is 8 to 42.

[0017] The carboxylate compound is a compound represented by formula (I):

[0018]

[0019] R 1 , R 3 , R 4 are each independently selected from hydrogen, substituted or unsubstituted C 1-12 The hydrocarbon group; R 2 Selected from C 1-12 The substituted or unsubstituted hydrocarbon group, when substituted, has a halogen atom as the substituent.

[0020] As an illustration, C 1-12 The hydrocarbon group refers to a hydrocarbon group having 1 to 12 carbon atoms.

[0021] The compound represented by the formula (I) is dimethyl fumarate Methyl Methacrylate Dimethyl maleate 1,1,1,3,3,3-Hexafluoroisopropyl methacrylate Vinyl Methacrylate Any one or a mixture of two or more of the above. A typical but non-limiting combination of the mixture is a mixture of two, three, four or five, such as a mixture of dimethyl fumarate and methyl methacrylate, a mixture of dimethyl fumarate and dimethyl maleate, a mixture of dimethyl fumarate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, a mixture of dimethyl fumarate and vinyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, and dimethyl maleate, a mixture of dimethyl fumarate, methyl methacrylate, and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, and vinyl methacrylate, a mixture of methyl methacrylate, dimethyl maleate, and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, and vinyl methacrylate, a mixture of methyl methacrylate, dimethyl maleate, and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and methyl methacrylate. A mixture of methyl methacrylate, dimethyl maleate, and vinyl methacrylate, a mixture of dimethyl maleate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and vinyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, dimethyl maleate, and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, dimethyl maleate, and vinyl methacrylate, a mixture of methyl methacrylate, dimethyl maleate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and vinyl methacrylate, a mixture of dimethyl fumarate, methyl methacrylate, dimethyl maleate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and vinyl methacrylate.

[0022] A second object of the present invention is to provide an electrochemical device comprising a positive electrode, a negative electrode, a separator and the electrolyte described in one of the objects.

[0023] The electrochemical device of the present application includes any device that generates an electrochemical reaction, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0024] In some embodiments, the electrochemical device of the present application is an electrochemical device having a positive electrode having a positive electrode active material capable of occluding and releasing metal ions and a negative electrode having a negative electrode active material capable of occluding and releasing metal ions.

[0025] The positive electrode comprises a positive electrode active material, and the positive electrode active material is selected from any one of lithium iron phosphate, lithium nickel transition metal composite oxide, and lithium nickel manganese composite oxide with a spinel structure, or a mixture of two or more thereof.

[0026] The negative electrode includes a negative electrode active material and a current collector, and the negative electrode active material includes graphite.

[0027] The negative electrode further comprises a carbon material, and the carbon material is selected from any one of acetylene black, conductive carbon black, carbon fiber, carbon nanotube and Ketjen black, or a mixture of two or more thereof.

[0028] The chlorine content in the diaphragm is less than or equal to 20ppm, specifically 3ppm, 4ppm, 5ppm, 6ppm, etc. Preferably, the chlorine content in the diaphragm is 7ppm to 20ppm, for example, 7ppm, 8ppm, 9ppm, 10ppm, 11ppm, 12ppm, 13ppm, 14ppm, 15ppm, 16ppm, 17ppm, 18ppm, 19ppm, 20ppm, etc. If the chlorine content in the diaphragm is too low, the effect of chlorine on the battery will be reduced, but it is difficult to further reduce the chlorine content due to the current diaphragm process; if the chlorine content in the diaphragm exceeds 20ppm, the polymerization reaction of SVC and additives will be quenched, which has a negative impact on battery performance.

[0029] A third object of the present invention is to provide an electronic device, which includes the electrochemical device described in the second object.

[0030] The electronic devices include but are not limited to the following types, such as laptop computers, pen-type computers, mobile computers, electronic book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The electrolyte of the present invention can improve the high temperature and room temperature cycle performance of the electrochemical device and reduce the internal resistance of the electrochemical device by using dimethyl carbonate, vinylene carbonate and carboxylic acid ester compounds in combination and adjusting the dosage ratio of the three. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0034] Unless otherwise specified, various raw materials of the present invention can be purchased from the market or prepared according to conventional methods in the art.

[0035] The electrolyte of the present invention, dimethyl carbonate, vinylene carbonate and carboxylic acid ester compounds;

[0036] Based on the mass of the electrolyte, the mass content of dimethyl carbonate is A%, the mass content of vinylene carbonate is B%, and the mass content of carboxylic acid ester compounds is C%, satisfying:

[0037] The value range of A is 5 to 60, and the value range of A / (B+C) is 4 to 20.88.

[0038] In the present invention, the electrochemical device is a lithium ion battery, and the lithium ion battery is a primary lithium battery or a secondary lithium battery, comprising: a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0039] The preparation method of the secondary lithium battery of the present invention is as follows:

[0040] (1) LFP (LiFePO 4 ) Preparation of positive electrode:

[0041] The positive electrode active material (LiFePO 4 ), polyvinylidene fluoride as a binder and SuperP as a conductive agent are mixed in a weight ratio of 97:2:1, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under a vacuum mixer until the system becomes uniform and transparent to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on an aluminum foil; the aluminum foil is dried at room temperature and then transferred to an oven for drying, and then cold pressed and cut to obtain a positive electrode (pole piece);

[0042] (2) Preparation of graphite negative electrode:

[0043] Artificial graphite is used as the negative electrode active material, Super P is used as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) is used as the thickener, and styrene-butadiene rubber (SBR) is used as the binder, and the mixture is mixed in a mass ratio of 96:1:1:2, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; the copper foil is dried at room temperature and then transferred to an oven for drying, and then cold pressed and cut to obtain a negative electrode (pole sheet);

[0044] (3) Preparation of electrolyte:

[0045] In an argon atmosphere glove box with a water content of <10ppm, battery-grade ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a ratio to form an organic solvent. Other components are quantitatively added according to the electrolyte composition described in the table below, mixed evenly, and an electrolyte is obtained. The content of each component in the table is the weight percentage calculated based on the total weight of the electrolyte; "DMC" described below as an electrolyte component is dimethyl carbonate, "DTD" is vinyl sulfate, and "VC" is vinylene carbonate.

[0046] (4) Preparation of isolation membrane:

[0047] Polypropylene film is used as the isolation film;

[0048] (5) Preparation of secondary batteries:

[0049] A 12 μm thick polypropylene film (PP) was used as a separator. The positive electrode, separator, and negative electrode prepared above were stacked in sequence, so that the separator was placed between the positive and negative electrodes to play a role of isolation. Then, the aluminum-plastic film was wrapped outside, transferred to a vacuum oven for drying at 120°C, and the electrolyte prepared above was injected at 3.0 g / Ah, then sealed, and the electrolyte was formed, and finally a soft-pack battery (i.e., lithium-ion battery) with a capacity of 1 Ah was prepared.

[0050] The lithium ion battery prepared by the present invention has a negative electrode gram capacity of 350 mAh / g, a liquid injection coefficient of 3 g / Ah, a battery core capacity of 1 Ah, a negative electrode mass of 3 g, and an electrolyte mass of 3 g.

[0051] The formation conditions of the electrolyte in the iron-lithium battery cell of the present invention are as follows.

[0052] The specific steps of forming the electrolyte in the iron-lithium battery cell are: after the electrolyte is injected, maintain a hot pressing environment of 0.1MPa, charge at 0.02C for 17min at 45°C in a static state, and then charge to 0.3Ah at 0.02C after standing for 5min, then cut off the air bag and vacuum package, and stand at room temperature for 48h to complete the formation of the electrolyte.

[0053] Among them, in the example of the present invention, the compounds represented by formula (I) are the following five types, compound 1 is methyl methacrylate, compound 2 is dimethyl fumarate, compound 3 is dimethyl maleate, compound 4 is 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and compound 5 is vinyl methacrylate.

[0054] The secondary battery of the present invention can be tested by the following method:

[0055] (1) Secondary battery cycle test

[0056] In an oven at a specified temperature (room temperature 25°C or high temperature 45°C), cyclic charge and discharge are performed at a current of 1C in a specified potential range, and the discharge capacity of each cycle is recorded. The test is terminated when the battery capacity reaches 80% of the first cycle capacity.

[0057] (2) Secondary battery DC resistance (DCR) test

[0058] At a specified temperature, when the battery is discharged to 50% SOC (state of charge, reflecting the remaining capacity of the battery) at a current of 1C, the current is increased to 4C and maintained for 30s. The difference between the updated stable voltage and the original platform voltage is detected. The ratio of its value to the 3C current value is the DC resistance of the battery. The DCR test result after the battery is fully charged for the first time is the initial DCR of the battery.

[0059] (3) Secondary battery high temperature storage capacity retention test

[0060] After the secondary battery is fully charged, it is placed in a constant temperature box at 60°C, taken out after 30 days, and discharged to the cut-off voltage at a rate of 0.33C after cooling to room temperature, and the percentage of its capacity relative to the initial discharge capacity is compared.

[0061] Among them, the cut-off voltage of charge and discharge is as follows: LFP-graphite is 2.5V to 3.65V.

[0062] (4) The amount of organic matter dissolved from the sintered body in the diaphragm was tested by the following method:

[0063] 10 g of the sintered molded body and 40 mL of hexane for PCB test manufactured by Wako Pure Chemical Industries, Ltd. were added to a 180 mL SUS container and sealed. The entire SUS container was immersed in a 70°C water bath, extracted for 2 hours while vibrating at a speed of 50 min-1, and then immersed in 20°C water for rapid cooling. The supernatant was filtered using a glass syringe equipped with a 0.2 micron filter (PTFE) to prepare a sample. For standard substances with carbon atoms of 12 and 14, special n-dodecane and n-tetradecane manufactured by Wako Pure Chemical Industries, Ltd. were dissolved in hexane for PCB test manufactured by Wako Pure Chemical Industries, Ltd. and used as standard substances. For standard substances with carbon atoms of 16 to 34, ASTM D5442C16-C44Qualitative RetentionTime Mix manufactured by Sigma Aldrich was dissolved in hexane for PCB test manufactured by Wako Pure Chemical Industries, Ltd. and used as standard substances.

[0064] The above sample was measured using a gas chromatograph GC-2014AF manufactured by Shimadzu Corporation. As a column, a glass column of 3 mmφ×1.5 m filled with Silicone OV-1 (3%) / CW80-100 mesh / AW-DMCS treated by Shinwa Chemical Co., Ltd. was used. The conditions were set as follows: the temperature was an injection temperature of 350°C, a detection temperature of 350°C, and after holding at an initial temperature of 100°C for 2 minutes, the temperature was increased at 10°C / min and held at 330°C for 20 minutes. The amount of hydrocarbon components with a carbon number of 12 or more and 34 or less was calculated based on the relative ratio of the peak area of ​​the detection peak obtained from the sample at the same holding time to the peak area of ​​the detection peak of the above standard reagent (6 wtppm each for C12 to 20, 8.3 wtppm each for C22 to C34), and classified into the following three levels.

[0065] ○: Dissolution amount is less than 150ppm

[0066] △: Dissolution amount is greater than or equal to 150ppm and less than 300ppm

[0067] ×: Dissolution amount is greater than or equal to 300 ppm

[0068] The electrolyte compositions of Examples 1 to 8 of the present invention and Comparative Example 1 are shown in Table 1-1. Lithium-ion batteries were prepared using the above preparation method, and their performance was tested. The test results are shown in Table 1-2.

[0069] Table 1-1

[0070]

[0071] Table 1-2

[0072]

[0073] It can be seen from the data in Table 1-2 that when the amount of negative electrode film-forming additive is fixed, with the addition of dimethyl carbonate, the high temperature cycle and room temperature cycle performance of the battery are improved, especially the room temperature cycle, which is significantly improved. At the same time, the addition of DMC effectively reduces the initial DCR and improves the high temperature capacity retention rate to a certain extent. Based on this, we can find that the effect is better when the mass content of DMC and the mass content of the negative electrode film-forming additive (VC+Compound 1) A / (B+C) is 4.18-20.88.

[0074] In order to further explore the impact of this ratio and performance, we kept the amount of DMC added unchanged and changed the content of the negative electrode film-forming additive (VC + compound 1). We found that the effect was better when the ratio was 4.05-8.35, taking into account both high-temperature and room-temperature cycle performance, while effectively reducing DCR and improving capacity retention.

[0075] Example 9 to Example 12

[0076] The electrolyte compositions of Examples 9 to 12 differ from those of Example 3 in that the types of compounds represented by formula (I) are different. Example 3 uses compound 1, Example 9 uses compound 2, Example 10 uses compound 3, Example 11 uses compound 4, and Example 12 uses compound 5. The others are the same as those of Example 3.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 3 is that the compound represented by formula (I) is not added, and the reduced amount of the compound represented by formula (I) is added to VC.

[0079] The lithium ion battery was prepared by the above preparation method, and its performance was tested. The test results are shown in Table 2.

[0080] Table 2

[0081]

[0082]

[0083] It can be seen from the data in Table 2 that, compared with Comparative Example 3 without adding the compound represented by formula (I), Examples 3, 9 to 12, using different types of compounds represented by formula (I), can make the high temperature, room temperature cycle performance, high temperature storage performance of the battery better, and the resistance lower.

[0084] The difference between Examples 13 to 14 and Example 2 is that the amount of organic matter dissolved from the sintered molded body by the diaphragms used therein is different. The dissolution amount in Example 2 is 75 ppm, that in Example 14 is 203 ppm, and that in Example 15 is 800 ppm. The rest are the same as in Example 2.

[0085] The lithium ion battery was prepared by the above preparation method, and its performance was tested. The test results are shown in Table 3.

[0086] Table 3

[0087]

[0088] After adding DMC, the electrolyte's ability to wet the diaphragm is greatly enhanced, so the organic dissolution of the diaphragm itself will also increase, affecting the battery performance. Therefore, it is necessary to select a diaphragm with low organic dissolution. From the data in Table 3, it can be seen that the less organic matter is dissolved from the sintered molded body of the diaphragm, the better the overall battery performance.

[0089] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0090] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0091] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0092] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An electrochemical device, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises dimethyl carbonate, vinylene carbonate and a carboxylic acid ester compound; Based on the mass of the electrolyte, the mass content of dimethyl carbonate is A%, the mass content of vinylene carbonate is B%, and the mass content of the carboxylic acid ester compound is C%, satisfying: The value range of A / (B+C) is 4 to 12.53; the value range of A is 8.35 to 25.05; The carboxylate compound is any one of methyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and vinyl methacrylate, or a mixture of two or more thereof; The amount of organic matter eluted from the sintered compact in the separator is less than 150 ppm.

2. The electrochemical device according to claim 1, characterized in that The positive electrode comprises a positive electrode active material; the positive electrode active material is selected from any one of lithium iron phosphate, lithium nickel transition metal composite oxide, and lithium nickel manganese composite oxide with a spinel structure, or a mixture of two or more thereof.

3. The electrochemical device according to claim 1 or 2, characterized in that: The negative electrode includes a negative electrode active material and a current collector, and the negative electrode active material includes graphite.

4. An electronic device, characterized in that: An electrochemical device comprising any one of claims 1 to 3.

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