Organic composite solid electrolyte and preparation method thereof, and battery

Abstract

The present invention belongs to the field of lithium-ion battery materials, and discloses an organic composite solid electrolyte, including a negative electrode side solid electrolyte and a second solid electrolyte attached to one side of the negative electrode side solid electrolyte; the negative electrode side solid electrolyte includes a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride) and a polymer; the second solid electrolyte includes a second lithium salt and a polymer. During the cycle, PTCDA in the solid electrolyte spontaneously reacts with lithium metal to form an organic SEI film, increasing the interfacial contact between lithium metal and the solid electrolyte. In addition, the PTCDA molecule contains a large number of carbonyl groups, which increases the lithium ion binding sites, increases the lithium ion conductivity in the electrolyte, reduces the internal resistance of the battery, and improves the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery materials and relates to a solid electrolyte, in particular to a lithium ion battery composite solid electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely favored in the fields of transportation, electronic communications, etc. due to their high energy density and long cycle life. However, due to the flammable liquid electrolyte, lithium batteries are prone to explosion and combustion when they are in thermal runaway. Therefore, how to improve the safety of lithium-ion batteries is one of the problems that need to be solved urgently.

[0003] Solid electrolytes can solve the problem of unstable and explosive liquid electrolytes, and most solid electrolytes have flame retardant properties. At the same time, the mechanical strength of solid electrolytes is significantly greater than that of liquid electrolytes, and the growth of lithium dendrites can be effectively suppressed during the cycle, making solid electrolytes widely concerned. Solid electrolytes are generally divided into sulfide solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. Each solid electrolyte has certain advantages and disadvantages, but current research data shows that it is difficult for a single solid electrolyte to take into account all kinds of characteristics, thus affecting battery performance. Summary of the invention

[0004] In view of the above problems existing in the prior art, in the first aspect, the present invention provides an organic composite solid electrolyte; in the second aspect, the present invention provides a method for preparing an organic composite solid electrolyte; in the third aspect, the present invention provides a battery.

[0005] In a first aspect, the present invention provides an organic composite solid electrolyte, comprising a negative electrode side solid electrolyte and a second solid electrolyte attached to one side of the negative electrode side solid electrolyte; the negative electrode side solid electrolyte comprises a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride) and a polymer; the second solid electrolyte comprises a second lithium salt and a polymer.

[0006] Preferably, the first lithium salt and the second lithium salt are different.

[0007] Preferably, the first lithium salt includes one or more of LiBOB (lithium bis(oxalatoborate), LiDFOB (lithium difluorooxalatoborate), and LiODFP (lithium difluorobis(oxalatophosphate)); the second lithium salt is one or more of LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethylsulfonyl imide), LiBF4 (lithium tetrafluoroborate), and LiPF6 (lithium hexafluorophosphate).

[0008] Preferably, the thickness of the solid electrolyte on the negative electrode side is 60-150 μm; the total thickness of the organic composite solid electrolyte is greater than the thickness of the solid electrolyte on the negative electrode side, and the organic composite solid electrolyte is 120-300 μm.

[0009] In a second aspect, the present invention provides a method for preparing an organic composite solid electrolyte, comprising the following steps:

[0010] Step 1, mixing a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride), a polymer and a solvent to obtain a solution A, and drying the solution A under an inert atmosphere to obtain a negative electrode side solid electrolyte;

[0011] Step 2, mixing the second lithium salt, the polymer and the solvent to obtain a solution B, pouring the solution B onto one side of the solid electrolyte on the negative electrode side and drying it under an inert atmosphere to obtain an organic composite solid electrolyte.

[0012] Preferably, in step 1 and step 2, the polymers are one or both of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) and PVDF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene).

[0013] Preferably, in step 1 and step 2, the solvent is one or more of DMF (dimethylformamide), THF (tetrahydrofuran), and NMP (N-methylpyrrolidone).

[0014] Preferably, in step 1, the mass ratio of the polymer, the first lithium salt, and PTCDA is 1:0.8-1.1:0.05-0.2.

[0015] Preferably, in step 2, the mass ratio of the polymer to the second lithium salt is 1:0.8-1.1.

[0016] Preferably, in step 1 and step 2, the mass ratio of the polymer to the solvent is 1:10-40.

[0017] Preferably, in step 1 and step 2, during drying, the mixture is first dried at room temperature for 24 hours, and then heated to 60° C. and dried for 24 hours.

[0018] Compared with the prior art, one or more technical solutions provided by the present invention have at least one of the following beneficial technical effects:

[0019] (1) The solid electrolyte on the negative electrode side includes PTCDA. During the cycle, PTCDA spontaneously reacts with lithium metal to form an organic SEI film, which increases the interfacial contact between lithium metal and the solid electrolyte. In addition, the PTCDA molecule contains a large number of carbonyl groups, which increases the lithium ion binding sites, increases the lithium ion conductivity in the electrolyte, reduces the internal resistance of the battery, and improves the battery's cycle stability.

[0020] (2) Use different lithium salts to prepare the negative electrode solid electrolyte membrane and the second solid electrolyte, and utilize the different potential stabilities of different lithium salts to form SEI / CEI films with different properties on the positive electrode side and the negative electrode side, thereby generating a stable interface film during the electrochemical reaction and improving the cycle stability and high-voltage performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The cycle performance diagram of the battery made of the composite solid electrolyte prepared in Examples 1-2, Examples 5-6, and Comparative Examples 1-3;

[0022] Figure 2 This is a voltage window test diagram of a battery assembled with the composite solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0023] The present invention provides the following specific technical solutions.

[0024] In a first aspect, the present invention provides an organic composite solid electrolyte, comprising a negative electrode side solid electrolyte and a second solid electrolyte connected to one side of the negative electrode side solid electrolyte; the negative electrode side solid electrolyte comprises a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride) and a polymer; the solid electrolyte comprises a second lithium salt and a polymer.

[0025] The inventors have found through research that during the cycle process, PTCDA spontaneously reacts with lithium metal to form an organic SEI film, which increases the interfacial contact between lithium metal and the solid electrolyte. In addition, the PTCDA molecule contains a large number of carbonyl groups, which increases the lithium ion binding sites, increases the lithium ion conductivity in the electrolyte, reduces the internal resistance of the battery, and improves the cycle stability of the battery.

[0026] Preferably, the first lithium salt and the second lithium salt are different.

[0027] The inventors have found that using different lithium salts to prepare negative electrode solid electrolyte membranes and solid electrolytes, and utilizing the different potential stabilities of different lithium salts to form SEI / CEI films with different properties on the positive and negative electrode sides, can improve the cycle stability and high-voltage performance of the battery.

[0028] Preferably, the first lithium salt includes one or more of LiBOB (lithium bis(oxalatoborate), LiDFOB (lithium difluorooxalatoborate), and LiODFP (lithium difluorobis(oxalatophosphate)); the second lithium salt is one or more of LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethylsulfonyl imide), LiBF4 (lithium tetrafluoroborate), and LiPF6 (lithium hexafluorophosphate).

[0029] Preferably, the thickness of the solid electrolyte on the negative electrode side is 60-150 μm; the thickness of the second solid electrolyte is 50-150 μm.

[0030] In actual situations, the thickness of the negative electrode side solid electrolyte and the second solid electrolyte can be selected according to actual conditions, and the above range is only a preferred range proposed by the inventor.

[0031] In a first aspect, the present invention provides a method for preparing an organic composite solid electrolyte, comprising the following steps:

[0032] Step 1, mixing a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride), a polymer and a solvent to obtain a solution A, and drying to obtain a negative electrode side solid electrolyte;

[0033] Step 2: Mix the second lithium salt, the polymer and the solvent to obtain a solution B, pour the solution B onto the solid electrolyte on the negative electrode side, and dry it to obtain an organic composite solid electrolyte.

[0034] Preferably, in step 1 and step 2, the polymers are one or both of PVDF-HFP and PVDF-CTFE.

[0035] Preferably, in step 1 and step 2, the solvent is one or more of DMF, THF and NMP.

[0036] Preferably, in step 1, the mass ratio of the polymer, the first lithium salt, and PTCDA is 1:0.8-1.1:0.05-0.2.

[0037] Preferably, in step 2, the mass ratio of the polymer to the second lithium salt is 1:0.8-1.1.

[0038] Preferably, in step 1 and step 2, the mass ratio of the polymer to the solvent is 1:10-40.

[0039] The inventors have found through research that in the actual preparation process, the contents of polymer or lithium salt in the two layers of solid electrolyte are preferably similar. If the content of the polymer or lithium salt is too different or the concentration difference is too large, it will easily lead to rapid migration of lithium salt and loss of the double-layer characteristics.

[0040] Preferably, in step 1 and step 2, solution A or solution B is dried; more preferably, during drying, the solution is first dried at room temperature for 24 hours, and then the temperature is raised to 60° C. and dried for 24 hours.

[0041] In order to make the technical problems to be solved, technical solutions and technical advantages of the present invention more clear, they will be described in detail below with reference to specific examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0043] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0044] Embodiment 1:

[0045] (1) 0.09 g LiBOB, 0.01 g LiDFOB, 0.1 g PVDF-HFP, and 0.012 g PTCDA were dissolved in 3.0 g DMF and stirred thoroughly to obtain solution A. Solution A was then poured onto a Teflon plate and dried at 25 °C for 24 h in an atmosphere where the water and oxygen contents were both less than 0.01 ppm, and then dried at 60 °C for 24 h to obtain a negative electrode side solid electrolyte with a thickness of 110 μm.

[0046] (2) Take 0.1gLiFSI and 0.1gPVDF-HFP and dissolve them in 3.0gDMF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with a water and oxygen content of less than 0.01ppm, and then dry it at 60°C for 24h to obtain an organic composite solid electrolyte with a thickness of 100μm.

[0047] Comparative Example 1:

[0048] (1) 0.09 g LiBOB, 0.01 g LiDFOB, and 0.1 g PVDF-HFP were dissolved in 3.0 g DMF and stirred thoroughly to obtain solution A. Solution A was then poured onto a Teflon plate and dried at 25 °C for 24 h in an atmosphere where the water and oxygen contents were both less than 0.01 ppm, and then dried at 60 °C for 24 h to obtain a negative electrode side solid electrolyte with a thickness of 110 μm.

[0049] (2) Take 0.1gLiFSI and 0.1gPVDF-HFP and dissolve them in 3.0gDMF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with a water and oxygen content of less than 0.01ppm, and then dry it at 60°C for 24h to obtain an organic composite solid electrolyte with a thickness of 100μm.

[0050] Comparative Example 2:

[0051] Take 0.1gLiFSI and 0.1gPVDF-HFP and dissolve them in 3.0gDMF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with water and oxygen contents less than 0.01ppm, and then dry it at 60°C for 24h to obtain a solid electrolyte with a thickness of 210μm.

[0052] Comparative Example 3:

[0053] 0.1g LiBOB, 0.1g PVDF-HFP, and 0.012g PTCDA were dissolved in 3.0g DMF, and the solution A was obtained after sufficient stirring. Then, the solution A was poured onto a Teflon plate, and dried at 25°C for 24h under an atmosphere with water and oxygen contents less than 0.01ppm, and then dried at 60°C for 24h to obtain a solid electrolyte with a thickness of 210μm.

[0054] Embodiment 2:

[0055] (1) 0.1 g LiFSI, 0.1 g PVDF-HFP, and 0.012 g PTCDA were dissolved in 3.0 g THF, and the solution A was obtained after sufficient stirring. Solution A was then poured onto a Teflon plate, and dried at 25 °C for 24 h in an atmosphere where the water and oxygen contents were both less than 0.01 ppm, and then dried at 60 °C for 24 h to obtain a 90 μm thick negative electrode side solid electrolyte.

[0056] (2) Take 0.1gLiFSI and 0.1gPVDF-HFP and dissolve them in 3.0gTHF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with water and oxygen contents less than 0.01ppm, and then dry it at 60°C for 24h to obtain an organic composite solid electrolyte with a thickness of 100μm.

[0057] Embodiment 3:

[0058] (1) 1.1 g of LiDFOB, 1 g of PVDF-HFP, and 0.2 g of PTCDA were dissolved in 40 g of DMF and stirred thoroughly to obtain solution A. Then 3 g of solution A was poured onto a Teflon plate and dried at 25 °C for 24 h in an atmosphere where the water and oxygen contents were both less than 0.01 ppm, and then dried at 60 °C for 24 h to obtain a 60 μm thick negative electrode solid electrolyte.

[0059] (2) Take 1.1g LiTFSI and 1g PVDF-HFP and dissolve them in 40g DMF. After fully stirring and dissolving, obtain solution B. Then take 3g solution B and pour it on the solid electrolyte on the negative electrode side. Dry it at 25℃ for 24h in an argon atmosphere with water and oxygen content less than 0.01ppm, and then dry it at 60℃ for 24h to obtain an organic composite solid electrolyte with a thickness of 50μm.

[0060] Embodiment 4:

[0061] (1) Take 0.8g LiODFP, 1g PVDF-HFP, and 0.05g PTCDA and dissolve them in 10g NMP. Stir thoroughly to obtain solution A. Then take 3g solution A and pour it on a Teflon plate. Dry it at 25℃ for 24h in an atmosphere with water and oxygen content less than 0.01ppm, and then dry it at 60℃ for 24h to obtain a negative electrode side solid electrolyte with a thickness of 150μm.

[0062] (2) Take 0.8g LiBF4 and 1g PVDF-HFP and dissolve them in 10g NMP. After fully stirring and dissolving, obtain solution B. Then take 3g solution B and pour it on the solid electrolyte on the negative electrode side. Dry it at 25℃ for 24h in an argon atmosphere with water and oxygen content less than 0.01ppm, and then dry it at 60℃ for 24h to obtain an organic composite solid electrolyte with a thickness of 150μm.

[0063] Embodiment 5:

[0064] (1) 0.1 g LiBOB, 0.1 g PVDF-HFP, and 0.012 g PTCDA were dissolved in 3.0 g THF and stirred thoroughly to obtain solution A. Solution A was then poured onto a Teflon plate and dried at 25 °C for 24 h in an atmosphere where the water and oxygen contents were both less than 0.01 ppm, and then dried at 60 °C for 24 h to obtain a 90 μm thick negative electrode side solid electrolyte.

[0065] (2) Take 0.1g LiBOB and 0.1g PVDF-HFP and dissolve them in 3.0g THF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with a water and oxygen content of less than 0.01ppm, and then dry it at 60°C for 24h to obtain an organic composite solid electrolyte with a thickness of 100μm.

[0066] Embodiment 6:

[0067] (1) 0.09g LiFSI, 0.01g LiDFOB, 0.1g PVDF-HFP, and 0.012g PTCDA were dissolved in 3.0g DMF and stirred thoroughly to obtain solution A. Solution A was then poured onto a Teflon plate and dried at 25°C for 24h in an atmosphere where the water and oxygen contents were both less than 0.01ppm, and then dried at 60°C for 24h to obtain a negative electrode side solid electrolyte with a thickness of 110μm.

[0068] (2) Take 0.1g LiBOB and 0.1g PVDF-HFP and dissolve them in 3.0g DMF. After fully stirring and dissolving, obtain solution B. Then pour solution B on the solid electrolyte on the negative electrode side, and dry it at 25°C for 24h in an argon atmosphere with a water and oxygen content of less than 0.01ppm, and then dry it at 60°C for 24h to obtain an organic composite solid electrolyte with a thickness of 100μm.

[0069] The solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were used as electrolytes in the battery, a lithium sheet with a diameter of 16 mm was used as the negative electrode, a commercial six-series (622) ternary positive electrode material was mixed with a conductive agent, acetylene black (AB), and a binder, polyvinylidene fluoride (PVDF), at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was used as a solvent. The mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 hours to obtain a slurry. The slurry was coated on a current collector aluminum foil using an automatic coating machine, placed flat on a tempered glass and transferred to a vacuum drying oven at 85°C for 4 hours, and a circular pole piece with a diameter of 12 mm was punched and dried at 105°C in a vacuum drying oven for 4 hours. The pole piece was placed in a glove box filled with argon atmosphere with a water content and an oxygen content of less than 0.01 ppm for 4 hours to reduce the moisture adsorbed by the pole piece during the transfer process, and then assembled into a CR2032 button battery in the glove box.

[0070] The batteries assembled from the solid electrolytes prepared in Examples 1-2, Examples 5-6 and Comparative Examples 1-3 were aged for 12 hours and then subjected to charge and discharge tests at different potentials. The discharge specific capacity of the battery after 300 cycles at a current density of 1.0C at a voltage of 2.8-4.5V was as follows: Figure 1 .

[0071] Depend on Figure 1 It can be seen that by comparing the cycle curves of the battery assembled with the solid electrolytes prepared in Example 1 and Comparative Examples 1 to 3, it can be seen that the specific capacity and cycle stability of the composite solid electrolyte provided by the present invention are better; by comparing the cycle curves of the battery assembled with the solid electrolytes prepared in Example 1 and Example 2, it can be reflected from the side that when the lithium salts used in the two layers of electrolytes in the composite solid electrolyte are different, its electrochemical window and cycle stability are further improved.

[0072] The solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were assembled into batteries and then subjected to cyclic voltammetry testing at a scan rate of 1.0 mV / s.

[0073] The solid electrolyte was cut into 16 mm discs and equipped with a 2032 button cell with a stainless steel / electrolyte / stainless steel structure. EIS test was performed on an electrochemical workstation to obtain Rs. The ionic conductivity was calculated by σ=L / RsS (L is the electrolyte thickness and S is the contact area).

[0074] Table 1 Voltage window and ionic conductivity of batteries assembled from solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 3

[0075]

[0076] It can be seen from Table 1 that the ionic conductivity of the composite solid electrolyte provided by the present invention is greatly improved.

[0077] Figure 2 The voltage window test diagram of the battery assembled with the composite solid electrolyte prepared in Examples 1 to 6 and Comparative Examples 1 to 3 is shown in FIG. Figure 2 It can be seen that the voltage window of the battery assembled with the solid electrolyte prepared in Example 1 is higher than the voltage window of the battery assembled with the solid electrolyte prepared in Comparative Examples 1 to 3, indicating that the combined effect of the layered structure and PTCDA effectively improves the voltage window of the material and can improve the stability of the battery under high voltage conditions.

[0078] The voltage window of the battery assembled with the solid electrolyte prepared in Example 1 is higher than the voltage window of the battery assembled with the solid electrolyte prepared in Example 2, indicating that the lithium salts used in the two layers of solid electrolytes in the composite solid electrolyte are different, and its interface voltage adaptability is better.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An organic composite solid electrolyte, characterized in that: It includes a negative electrode side solid electrolyte and a second solid electrolyte attached to one side of the negative electrode side solid electrolyte; the negative electrode side solid electrolyte includes a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride) and a polymer; the second solid electrolyte includes a second lithium salt and a polymer; The first lithium salt and the second lithium salt are different; The first lithium salt includes one or more of LiBOB (lithium bis(oxalatoborate), LiDFOB (lithium difluorooxalatoborate), and LiODFP (lithium difluorobis(oxalatophosphate)); the second lithium salt includes one or more of LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethylsulfonyl imide), LiBF4 (lithium tetrafluoroborate), and LiPF6 (lithium hexafluorophosphate).

2. A method for preparing an organic composite solid electrolyte, characterized in that: The method for preparing the organic composite solid electrolyte according to any one of claim 1 comprises the following steps: Step 1, mixing a first lithium salt, PTCDA (3,4,9,10-tetracarboxylic anhydride), a polymer and a solvent to obtain a solution A, and drying the solution A under an inert atmosphere to obtain a negative electrode side solid electrolyte; Step 2, mixing the second lithium salt, the polymer and the solvent to obtain a solution B, pouring the solution B onto one side of the solid electrolyte on the negative electrode side and drying it under an inert atmosphere to obtain an organic composite solid electrolyte.

3. The method for preparing an organic composite solid electrolyte according to claim 2, characterized in that: In step 1 and step 2, the polymers are either or both of PVDF-HFP and PVDF-CTFE.

4. The method for preparing an organic composite solid electrolyte according to claim 2, characterized in that: In step 1 and step 2, the solvent is one or more of DMF, THF and NMP.

5. The method for preparing an organic composite solid electrolyte according to claim 2, characterized in that: In step 1, the mass ratio of the polymer, the first lithium salt, and PTCDA is 1:0.8-1.1:0.05-0.

2.

6. The method for preparing an organic composite solid electrolyte according to claim 2, characterized in that: In step 2, the mass ratio of the polymer to the second lithium salt is 1:0.8-1.

1.

7. The method for preparing an organic composite solid electrolyte according to claim 2, characterized in that: In step 1 and step 2, the mass ratio of the polymer to the solvent is 1:10-40.

8. A battery comprising the organic composite solid electrolyte according to claim 1 or the organic composite solid electrolyte prepared by the preparation method according to any one of claims 2 to 6.

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