High-voltage fast-charge lithium ion battery and electrolyte

Abstract

Provided are a high-voltage fast-charge lithium ion battery and an electrolyte. The electrolyte comprises a basic solvent, a lithium salt, a functional additive, a polymer electrolyte and a nano inorganic filler, wherein the basic solvent is dispersed in the polymer electrolyte to form a gel polymer electrolyte; the lithium salt, the functional additive and the nano inorganic filler are dispersed in the gel polymer electrolyte; the polymer electrolyte is selected from polyethylene oxide; the nano inorganic filler is formed by compounding boehmite and aluminum oxide according to the mass ratio of (8:1)-(10:1); and the basic solvent is prepared from the following raw materials in parts by weight: 50-60 parts of ethylene carbonate, 10-15 parts of fluorinated ethylene carbonate, 8-10 parts of acrylonitrile and 3-5 parts of methyl ethylene oxide.

Description

High-voltage fast-charging lithium ion battery and electrolyte TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary battery materials. More specifically, it relates to a high-voltage fast-charging lithium ion battery and electrolyte. BACKGROUND

[0002] Under high-voltage conditions, the electrolyte of a lithium battery may face various failure problems, which are mainly related to the chemical stability of the electrolyte, the interface reaction, and the performance of the additives. TECHNICAL PROBLEM

[0003] The following are some common failure problems:

[0004] 1. Oxidative decomposition of solvents: Under high-voltage conditions, solvent molecules in the electrolyte may undergo oxidation reactions on the positive electrode surface, leading to the decomposition of the solvent and the formation of unstable decomposition products. This decomposition consumes lithium ions in the electrolyte, reducing the number of available lithium ions in the battery, thereby reducing the capacity and cycle life of the battery.

[0005] 2. Formation of unstable solid electrolyte interface (SEI): On the negative electrode surface, especially the lithium metal negative electrode, the electrolyte may participate in the formation of the SEI layer. If the SEI layer is formed unevenly or is unstable, it may cause the interface impedance to increase during the battery cycle, affecting the charge-discharge efficiency and cycle stability of the battery.

[0006] 3. Thermal stability problem of electrolyte: High-voltage electrolyte may be more prone to thermal decomposition at high temperatures (high temperatures generated by fast charging of the battery), producing gas, which may cause the battery to swell, leak, or even cause a safety accident.

[0007] 4. Failure of electrolyte additives: In order to improve the performance of the electrolyte, some functional additives are usually added. Under high-voltage conditions, these additives may fail to effectively inhibit the decomposition of the electrolyte or stabilize the electrode interface.

[0008] 5. Structural changes of positive electrode materials: Under high-voltage, the positive electrode material may undergo structural changes such as phase transition, release of lattice oxygen, etc., which may damage the structural stability of the positive electrode material and affect the stability of the electrolyte.

[0009] 6. Compatibility problem between electrolyte and electrode material: High-voltage electrolyte needs to have good compatibility with electrode materials. If the electrolyte and electrode materials undergo undesirable chemical reactions, it may cause the battery performance to decline.

[0010] To solve these problems, researchers are developing new high-voltage electrolyte systems, such as using new solvents, improving additives, designing more stable SEI / CEI interfaces, and other strategies to improve the stability of electrolytes under high-voltage conditions and the overall performance of the battery. Technical solutions

[0011] The technical problem to be solved by the present application is to overcome the problem that the existing electrolyte system for lithium ion batteries cannot be effectively compatible under the condition of higher voltage window and fast charging, and to provide a high-voltage fast-charging type lithium ion battery and electrolyte.

[0012] The purpose of the present application is to provide a high-voltage fast-charging type lithium ion battery electrolyte.

[0013] Another purpose of the present application is to provide a high-voltage fast-charging type lithium ion battery.

[0014] The above purposes of the present application are achieved by the following technical solutions:

[0015] A high-voltage fast-charging type lithium ion battery electrolyte, comprising a base solvent, a lithium salt, a functional additive, a polymer electrolyte, and a nano-inorganic filler;

[0016] The base solvent is dispersed in the polymer electrolyte to form a gel-state polymer electrolyte;

[0017] The lithium salt, the functional additive, and the nano-inorganic filler are dispersed in the gel-state polymer electrolyte;

[0018] The polymer electrolyte is selected from polyethylene oxide;

[0019] The nano-inorganic filler includes boehmite.

[0020] The above scheme uses a gel-state polymer electrolyte as a basic electrolyte under a high-voltage use scenario, and adds a nano-inorganic filler to the gel-state polymer electrolyte, the added nano-inorganic filler can form a stable physical interface with lithium salt in the electrolyte in the network skeleton of the polymer electrolyte, thereby effectively inhibiting the oxidative decomposition of the polymer electrolyte and the liquid solvent dispersed therein under high voltage, thereby allowing the electrolyte to work normally in a wider voltage range; in addition, by using boehmite as an inorganic filler, it can cooperate with polyethylene oxide to build an electrolyte skeleton with excellent liquid retention capacity, and the mechanical stability and thermal stability of the electrolyte skeleton are significantly improved due to the addition of boehmite, thereby making the overall shape of the gel-state electrolyte stable and reliable under high voltage or fast charging. In addition, boehmite is often used in the surface coating of lithium battery separators, and the physical interface formed on the surface of polyethylene oxide can also improve the wetting ability of the liquid solvent to polyethylene oxide, thereby improving the overall lithium ion transmission capacity of the product and effectively protecting the fast charging performance of the product.

[0021] Further, the basic solvent is prepared from the following raw materials by weight: 50-60 parts of ethylene carbonate, 10-15 parts of fluorinated ethylene carbonate, 8-10 parts of acrylonitrile, and 3-5 parts of methyl oxirane.

[0022] Further, the functional additive includes film-forming protective additive vinyl sulfate, overcharge protective additive DTD, and flame-retardant additive trimethyl phosphate; wherein the mass ratio of the vinyl sulfate, the DTD, and the trimethyl phosphate is 4:1:3; the amount of the functional additive is 8-10% of the mass of the solvent.

[0023] Further, the nano-inorganic filler is compounded from boehmite and alumina in a mass ratio of 8:1-10:1.

[0024] Further, in the nano-inorganic filler, the D50 of the boehmite is 60-80 nm; the D50 of the alumina is 0.3-0.4 times that of the boehmite.

[0025] Further, the addition amount of the nano-inorganic filler is 6-8% of the mass of the polymer electrolyte.

[0026] The above technical solution selects a filler system mixed from boehmite and alumina, and controls the particle size and addition amount of the two, which cooperates in the gel-state electrolyte to regulate the transmission behavior of lithium ions, making the transmission of lithium ions more uniform, effectively avoiding the formation of lithium dendrites during fast charging, and effectively improving the fast charging performance of lithium battery products.

[0027] Further, the lithium salt is selected from any one or a combination of two of LiPF6, LiTFSI, and LiDFOB; and the concentration of the lithium salt in the electrolyte for lithium ion battery is 1.2-1.4 mol / L.

[0028] A high-voltage fast-charging lithium ion battery, comprising a positive electrode, a negative electrode, a separator, and the electrolyte for lithium ion battery according to any one of claims 1-7;

[0029] The separator is composed of a base film and a PVDF glue layer sprayed on the surface of the base film, the PVDF glue layer is coated on both surfaces of the base film, and the base film is a porous PP or PE film.

[0030] The electrolyte for lithium ion battery is distributed on both surfaces of the separator and adheres to the positive electrode and the negative electrode, respectively.

[0031] Further, the thickness of the base film is 5-6 μm, the thickness of a single layer of the PVDF glue layer is 2.0-2.5 μm, and the thickness of a single layer of the electrolyte for lithium ion battery is 8-12 μm.

[0032] Further, the thickness of the electrolyte for lithium ion battery on the side of the positive electrode is 8-9 μm, and the thickness of the electrolyte for lithium ion battery on the side of the negative electrode is 10-12 μm. Beneficial effects

[0033] The above scheme further provides electrolyte layers with different thicknesses on both sides of the base film. Specifically, the electrolyte layer on the side of the positive electrode is relatively thin, and the electrolyte layer on the side of the negative electrode is relatively thick. The advantage of this is that, during fast charging, lithium ions are released from the positive electrode material and embedded in the negative electrode material. At this time, the release rate of lithium ions from the positive electrode is significantly higher than the embedding rate in the negative electrode. This is also the reason why the conventional fast-charging bottleneck is often in the negative electrode. The inventors have found that, for the gel electrolyte used in the present application, when the electrolyte layer on the side of the positive electrode is relatively thin, the probability of oxidation on the side of the positive electrode can be reduced under the condition of voltage rise. The thicker electrolyte layer on the side of the negative electrode can provide better lithium ion storage capacity and avoid the accumulation of lithium ions on the surface of the negative electrode, thereby preventing lithium precipitation. Embodiments of the present application

[0034] The present application will be further described in conjunction with specific examples. Unless otherwise specified, the reagents, methods, and equipment used in the present application are conventional reagents, methods, and equipment in the technical field.

[0035] Unless otherwise specified, the reagents and materials used in the following examples are commercially available. Example 1

[0036] Preparation of electrolyte for lithium ion battery:

[0037] Polyethylene oxide and N-methyl pyrrolidone (NMP) are mixed in a container at a mass ratio of 1:8, stirred at a speed of 400 r / min by a stirrer, then heated under stirring to completely dissolve the polyethylene oxide to obtain a polyethylene oxide solution; for example, the lithium ion battery is a 4.5V lithium ion battery.

[0038] After the polyethylene oxide solution is cooled to room temperature, nano-inorganic fillers are continuously added to the container containing the polyethylene oxide solution under stirring, then ultrasonic dispersion is performed at an ultrasonic frequency of 65 kHz for 45 min to obtain a dispersion liquid;

[0039] The dispersion liquid is poured into a flat mold, cast coated, and vacuum dried to remove NMP to obtain an electrolyte film; a lithium salt is added in a base solvent at a concentration of 1.2 mol / L, then a functional additive is added in an amount of 8% of the mass of the base solvent, and then stirred and mixed by a stirrer at a speed of 600 r / min for 4 h to obtain an electrolyte solution;

[0040] The obtained electrolyte film is immersed in the electrolyte solution to allow the electrolyte film to absorb the obtained electrolyte solution, and then taken out after continuous immersion at room temperature for 8 h to obtain an electrolyte for a lithium ion battery;

[0041] The nano-inorganic fillers are compounded by boehmite and aluminum oxide at a mass ratio of 8:1;

[0042] The D50 of the boehmite in the nano-inorganic fillers is 60 nm; the D50 of the aluminum oxide is 0.3 times that of the boehmite;

[0043] The addition amount of the nano-inorganic fillers is 6% of the mass of the polymer electrolyte (polyethylene oxide);

[0044] The base solvent is prepared from the following raw materials in parts by weight: 50 parts of ethylene carbonate, 10 parts of fluorinated ethylene carbonate, 8 parts of acrylonitrile, and 3 parts of methyl oxirane;

[0045] The functional additives include film-forming protective additive vinyl sulfate, overcharge protective additive DTD, and flame-retardant additive trimethyl phosphate; the mass ratio of the vinyl sulfate, the DTD, and the trimethyl phosphate is 4:1:3;

[0046] The lithium salt is selected from LiPF6;

[0047] Composition of lithium ion battery:

[0048] Select NCM as the positive active material, Ni:Co:Mn=5:3:2; select artificial graphite as the negative active material;

[0049] The separator is composed of a base film and a PVDF adhesive layer sprayed on the surface of the base film, the PVDF adhesive layer is coated on both surfaces of the base film, and the base film is a porous PP film;

[0050] The thickness of the base film is 5μm, and the single-layer thickness of the PVDF adhesive layer is 2.0μm;

[0051] The lithium ion battery electrolyte is distributed on both surfaces of the separator and is attached to the positive and negative electrodes respectively; the thickness of the lithium ion battery electrolyte on the positive electrode side is 8μm, and the thickness of the lithium ion battery electrolyte on the negative electrode side is 10μm. Example 2

[0052] Preparation of lithium ion battery electrolyte:

[0053] Polyethylene oxide and N-methyl pyrrolidone (NMP) were mixed in a container at a mass ratio of 1:9, stirred at a speed of 500r / min with a stirrer, then heated under stirring to completely dissolve the polyethylene oxide, obtaining a polyethylene oxide solution;

[0054] After the polyethylene oxide solution was cooled to room temperature, nano-inorganic fillers were continuously added to the container containing the polyethylene oxide solution under stirring, then ultrasonic dispersion was carried out at an ultrasonic frequency of 70kHz for 50min to obtain a dispersion liquid;

[0055] The dispersion liquid was poured into a flat mold, cast coated, and then vacuum dried to remove NMP, obtaining an electrolyte film; lithium salt was added in the base solvent at a concentration of 1.3mol / L, then functional additives were added in an amount of 9% of the mass of the base solvent, and then stirred at a speed of 700r / min with a stirrer for 5h to obtain an electrolyte solution;

[0056] The obtained electrolyte film was immersed in the electrolyte solution to allow the electrolyte film to absorb the electrolyte solution, and then taken out after continuous immersion at room temperature for 10h, obtaining a lithium ion battery electrolyte;

[0057] The nano-inorganic fillers are compounded by boehmite and alumina at a mass ratio of 9:1;

[0058] The D50 of the boehmite in the nano-inorganic fillers is 70nm; the D50 of the alumina is 0.35 times that of the boehmite;

[0059] The addition amount of the nano-inorganic fillers is 7% of the mass of the polymer electrolyte (polyethylene oxide).

[0060] The base solvent is prepared from the following raw materials in parts by weight: 55 parts of ethylene carbonate, 12 parts of fluorinated ethylene carbonate, 9 parts of acrylonitrile, 4 parts of methyl oxirane;

[0061] The functional additives include film-forming protective additives vinyl sulfate, overcharge protective additives DTD, and flame-retardant additives trimethyl phosphate; wherein the mass ratio between the vinyl sulfate, the DTD and the trimethyl phosphate is 4:1:3;

[0062] The lithium salt is selected from LiTFSI;

[0063] Composition of the lithium ion battery:

[0064] NCM is selected as the positive electrode active material, Ni:Co:Mn=5:3:2; artificial graphite is selected as the negative electrode active material;

[0065] The separator is composed of a base film and a PVDF adhesive layer sprayed on the surface of the base film, the PVDF adhesive layer is coated on both surfaces of the base film, and the base film is a porous PE film;

[0066] The thickness of the base film is 5.5 μm, and the single-layer thickness of the PVDF adhesive layer is 2.2 μm;

[0067] The lithium ion battery electrolyte is distributed on both surfaces of the separator and is attached to the positive electrode and the negative electrode respectively; the thickness of the lithium ion battery electrolyte on the positive electrode side is 8.5 μm, and the thickness of the lithium ion battery electrolyte on the negative electrode side is 11 μm. Example 3

[0068] Preparation of the lithium ion battery electrolyte:

[0069] Polyethylene oxide and N-methyl pyrrolidone (NMP) are mixed in a container in a mass ratio of 1:10, stirred with a stirrer at a speed of 600 r / min, then heated under stirring to completely dissolve the polyethylene oxide, and a polyethylene oxide solution is obtained;

[0070] After the polyethylene oxide solution is cooled to room temperature, nano-inorganic fillers are continuously added to the container containing the polyethylene oxide solution under stirring, and then ultrasonic dispersion is carried out at an ultrasonic frequency of 75 kHz for 60 min to obtain a dispersion liquid;

[0071] The dispersion liquid is poured into a flat mold, cast coated, and vacuum dried to remove NMP to obtain an electrolyte film; a lithium salt is added in a base solvent at a concentration of 1.4 mol / L, and a functional additive is added in an amount of 10% of the mass of the base solvent, followed by stirring at a stirring speed of 800 r / min for 6 h to obtain an electrolyte solution;

[0072] The obtained electrolyte film is immersed in the electrolyte solution to allow the electrolyte film to absorb the obtained electrolyte solution, and the electrolyte film is taken out after being immersed at room temperature for 12 h to obtain an electrolyte for a lithium ion battery;

[0073] The nanometer inorganic filler is compounded by boehmite and aluminum oxide at a mass ratio of 10:1.

[0074] The D50 of the boehmite in the nanometer inorganic filler is 80 nm, and the D50 of the aluminum oxide is 0.4 times that of the boehmite.

[0075] The addition amount of the nanometer inorganic filler is 8% of the mass of the polymer electrolyte (polyethylene oxide).

[0076] The base solvent is prepared from the following raw materials in parts by weight: 60 parts of ethylene carbonate, 15 parts of fluorinated ethylene carbonate, 10 parts of acrylonitrile, and 5 parts of methyl oxirane.

[0077] The functional additive includes film-forming protective additive vinyl sulfate, overcharge protective additive DTD, and flame-retardant additive trimethyl phosphate; the mass ratio of the vinyl sulfate, the DTD, and the trimethyl phosphate is 4:1:3.

[0078] The lithium salt is selected from LiDFOB.

[0079] The composition of the lithium ion battery is as follows:

[0080] NCM is selected as the positive active material, and the ratio of Ni:Co:Mn is 5:3:2; artificial graphite is selected as the negative active material.

[0081] The separator is composed of a base film and a PVDF adhesive layer sprayed on the surface of the base film, the PVDF adhesive layer is coated on both surfaces of the base film, and the base film is a porous PP film.

[0082] The thickness of the base film is 6 μm, and the thickness of a single layer of the PVDF adhesive layer is 2.5 μm.

[0083] The electrolyte for the lithium ion battery is distributed on both surfaces of the separator and is attached to the positive electrode and the negative electrode, respectively; the thickness of the electrolyte for the lithium ion battery on the positive electrode side is 9 μm, and the thickness of the electrolyte for the lithium ion battery on the negative electrode side is 12 μm. Example 4

[0084] The difference between this example and Example 1 is that no alumina is added, and the rest of the conditions remain unchanged. Example 5

[0085] The difference between this example and Example 1 is that the D50 of the boehmite and the alumina are both 60 nm, and the rest of the conditions remain unchanged. Example 6

[0086] The difference between this example and Example 1 is that the lithium ion battery electrolyte is distributed on both surfaces of the separator and is attached to the positive electrode and the negative electrode respectively; the thickness of the lithium ion battery electrolyte on the positive electrode side is 10 μm, and the thickness of the lithium ion battery electrolyte on the negative electrode side is 8 μm, and the rest of the conditions remain unchanged. Example 7

[0087] The difference between this example and Example 1 is that the lithium ion battery electrolyte is distributed on both surfaces of the separator and is attached to the positive electrode and the negative electrode respectively; the thickness of the lithium ion battery electrolyte on the positive electrode side is 8 μm, and the thickness of the lithium ion battery electrolyte on the negative electrode side is 8 μm, and the rest of the conditions remain unchanged.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that no nano-inorganic filler is added, and the rest of the conditions remain unchanged.

[0090] The products obtained in Examples 1-7 and Comparative Example 1 are subjected to performance testing, and the specific testing methods and testing results are as follows:

[0091] Cycle performance test:

[0092] According to the formula of the foregoing examples or comparative examples, lithium ion batteries are prepared into soft pack batteries with a capacity of 5 Ah in a glove box;

[0093] At 25°C, after the battery is fixed in volume, the battery is charged at a rate of 0.33C and discharged at a rate of 0.5C to perform full charge and full discharge cycle test until the capacity of the battery decays to 80% of the initial capacity, the charging and discharging is stopped, and the cycle number is recorded; the specific test results are shown in Table 1;

[0094] During the full charge process, first, constant current charging is performed at a charge rate of 0.33C, then constant voltage charging is continued until the current is lower than 0.025C, the charging is stopped, and it is considered as full charge; during the full discharge process, after discharging at a discharge rate of 0.5C to a cut-off voltage of 2.8V, it is left for 30 min.

[0095] Table 1: Cycle performance test results

[0096]

[0097] From the test results in Table 1, it can be seen that the product obtained by the application can still maintain excellent cycle performance under high voltage use.

[0098] High-rate charge performance test:

[0099] According to the formula of the foregoing examples or comparative examples, the lithium ion battery was prepared into a soft package battery with a capacity of 5 Ah in a glove box;

[0100] At 25℃, after the battery was fixed in volume, the battery was charged at a rate of 3C and discharged at a rate of 1C to perform full charge and full discharge cycle test until the capacity of the battery was attenuated to 80% of the initial capacity, the charge and discharge was stopped, and the cycle number was recorded; the specific test results are shown in Table 2.

[0101] During the full charge process, first, constant current charging was performed at a rate of 3C, then constant voltage charging was performed until the current was lower than 0.025C, and the charging was stopped, which was regarded as full charge; during the full discharge process, the battery was discharged at a rate of 1C until the cut-off voltage was 2.8V, and then the battery was rested for 30 min.

[0102] Table 2: High-rate charge performance test results

[0103]

[0104] From the test results in Table 2, it can be seen that the product obtained by the application can still maintain excellent cycle performance when charging and discharging at a high rate.

[0105] The foregoing examples are preferred embodiments of the application, but the embodiments of the application are not limited by the foregoing examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the application shall be equivalent replacement modes and shall be included in the protection scope of the application.

Claims

1. An electrolyte for a high-voltage fast-charging lithium ion battery, characterized by comprising The lithium ion battery electrolyte comprises a base solvent, a lithium salt, a functional additive, a polymer electrolyte, and a nano inorganic filler. The base solvent is dispersed in the polymer electrolyte to form a gel-state polymer electrolyte. The lithium salt, the functional additive, and the nano inorganic filler are dispersed in the gel-state polymer electrolyte. The polymer electrolyte is selected from polyethylene oxide. The nano inorganic filler is compounded by boehmite and alumina at a mass ratio of 8:1-10:

1.

2. The electrolyte for high-voltage fast-charging lithium-ion batteries according to claim 1, characterized in that, The functional additive comprises film-forming protective additive vinyl sulfate, overcharge protective additive DTD, and flame-retardant additive trimethyl phosphate.

3. A high-voltage fast-charging lithium ion battery, characterized in that, The mass ratio of the vinyl sulfate, the DTD, and the trimethyl phosphate is 4:1:

3. The amount of the functional additive is 8-10% of the mass of the solvent. The D50 of the boehmite in the nano inorganic filler is 60-80 nm.

4. The high voltage fast-charge lithium-ion battery of claim 3, wherein, The D50 of the alumina is 0.3-0.4 times that of the boehmite.

5. The high voltage fast-charge lithium-ion battery of claim 4, wherein, The amount of the nano inorganic filler is 6-8% of the mass of the polymer electrolyte. The lithium salt is selected from any one or a combination of two of LiPF6, LiTFSI, and LiDFOB. The concentration of the lithium salt in the lithium ion battery electrolyte is 1.2-1.4 mol / L. The lithium ion battery comprises a positive electrode, a negative electrode, a separator, and the lithium ion battery electrolyte according to any one of claims 1-2. The separator comprises a base film and a PVDF adhesive layer sprayed on the surface of the base film. The PVDF adhesive layer is coated on both surfaces of the base film. The base film is a porous PP or PE film. The lithium ion battery electrolyte is distributed on both surfaces of the separator and is attached to the positive electrode and the negative electrode, respectively. The thickness of the base film is 5-6 μm. The single-layer thickness of the PVDF adhesive layer is 2.0-2.5 μm. The single-layer thickness of the lithium ion battery electrolyte is 8-12 μm. The thickness of the lithium ion battery electrolyte on the side of the positive electrode is 8-9 μm. The thickness of the lithium ion battery electrolyte on the side of the negative electrode is 10-12 μm.

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