Low-temperature-resistant cycle-resistant lithium battery electrolyte additive and preparation method thereof

Abstract

The invention provides a low-temperature-resistant cycle-resistant lithium battery electrolyte additive and a preparation method thereof. The low-temperature-resistant cycle-resistant lithium battery electrolyte additive comprises the following raw materials: a novel lithium salt, a carbonate solvent and a composite additive, according to the low-temperature-resistant cycle-resistant lithium battery electrolyte additive disclosed by the invention, the charge-discharge performance of a lithium battery at a low temperature can be improved, and the battery can still keep good performance after multiple cycles and has good stability in a high-temperature environment.

Description

Technical Field

[0001] The invention relates to lithium battery technology, and in particular to a low-temperature and cycle-resistant lithium battery electrolyte additive and a preparation method thereof. Background Art

[0002] As an advanced electrochemical energy storage device, lithium batteries have occupied an important position in the modern energy field since their introduction due to their many significant advantages. Their operating voltage is usually between 3.0-4.2V, which is significantly higher than traditional lead-acid batteries (about 2V) and nickel-metal hydride batteries (about 1.2V). The higher operating voltage means that lithium batteries can provide greater power at the same current output, thus providing strong support for the efficient operation of various devices.

[0003] In terms of energy density, lithium batteries are particularly outstanding. High energy density enables lithium batteries to store more electrical energy in a smaller volume and weight, which is of decisive significance for the lightweight design of portable electronic products such as smartphones and laptops, as well as the long driving range requirements of electric vehicles. In addition, lithium batteries also have a good cycle life. Under normal use conditions, lithium batteries can undergo hundreds or even thousands of charge and discharge cycles while still maintaining a high capacity retention rate. In low temperature environments, the charging process of lithium batteries faces many challenges. First, low temperatures will cause the viscosity of the electrolyte solution to increase significantly. For example, when the temperature drops from 25°C to -20°C, the viscosity of carbonate electrolyte solutions may increase several times. High-viscosity electrolytes will hinder the migration speed of lithium ions in them, making the diffusion of lithium ions from the positive electrode to the negative electrode extremely slow. This is like swimming in a viscous liquid. The movement of ions is greatly resisted, making it difficult for the charging current to pass through the electrolyte to the negative electrode smoothly, resulting in difficulty in charging. Under low temperature conditions, the deintercalation process of lithium ions in the positive electrode material and the intercalation process of lithium ions in the negative electrode material will become slow. Taking graphite negative electrode as an example, the kinetic energy barrier of lithium ion embedding reaction between graphite layers increases at low temperature, making it difficult for lithium ions to embed into graphite lattice quickly and effectively. At the same time, low temperature may cause changes in the crystal structure of electrode materials, such as lattice distortion, further reducing the electrode material's capacity and reactivity for lithium ions, making it difficult for the charging process to proceed normally. The impact of low temperature on the discharge capacity of lithium batteries mainly comes from the following aspects. First, the migration rate of lithium ions slows down at low temperature, which makes it impossible for lithium ions released from the negative electrode to migrate to the positive electrode through the electrolyte in time during the discharge process, resulting in a decrease in the electrochemical reaction rate inside the battery and a decrease in the amount of electricity available for output. For example, in a low temperature environment, the discharge current of the battery may be limited and cannot reach the level at room temperature, thus affecting the normal use of the equipment. Second, low temperature will increase the internal resistance of the battery. On the one hand, the increase in electrolyte viscosity leads to an increase in ion conduction resistance; on the other hand, the electronic conductivity of the electrode material at low temperature will also decrease, especially some positive electrode materials with semiconductor properties, whose electronic transmission performance will deteriorate at low temperature. The increase in the internal resistance of the battery means that during the discharge process, more electrical energy will be consumed in the form of heat energy on the internal resistance instead of being effectively output to external devices, thereby reducing the discharge capacity of the battery. In addition, low temperatures may also lead to poor interfacial compatibility between electrode materials and electrolytes. At low temperatures, some unstable intermediates or side reaction products may form on the electrode surface. These substances will cover the electrode surface, hindering the transmission of lithium ions and the electrochemical reaction, further reducing the discharge capacity of the battery. The charging and discharging process under low temperature conditions will cause irreversible damage to the positive and negative electrode materials, electrolytes, and electrode / electrolyte interfaces of the battery.During the charging process, lithium dendrites are easily formed on the negative electrode surface due to the uneven deposition of lithium ions. The growth of lithium dendrites will not only destroy the structural integrity of the negative electrode material, causing its capacity to decay, but may also pierce the separator and cause an internal short circuit in the battery, thus rendering the battery inoperable. The cycle life of lithium batteries in low temperature environments will be greatly shortened.

[0004] Lithium batteries are widely used in portable electronic products and electric vehicles due to their high operating voltage, high energy density, long cycle life and low cost. However, problems such as difficulty in charging, low discharge capacity and short life under low temperature conditions greatly limit their application in low temperature environments.

[0005] In summary, the problem to be solved by the present invention is to develop a lithium battery electrolyte additive that can improve battery performance at low temperatures, can be cycled multiple times, and has good chemical stability under high temperature environments. Summary of the invention

[0006] Purpose of the invention:

[0007] The purpose of the present invention is to provide a low-temperature and cycle-resistant lithium battery electrolyte additive to improve the charge and discharge performance of the lithium battery at low temperatures. The battery can still maintain good performance after multiple cycles and also has good chemical stability in high temperature environments.

[0008] The technical solution of the present invention:

[0009] A low-temperature-resistant and cycle-resistant lithium battery electrolyte additive, characterized in that the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive comprises the following raw materials: a new type of lithium salt, a carbonate solvent, and a composite additive.

[0010] Furthermore, the raw materials for preparing the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive include, by percentage, 100%, 10-15% of the new lithium salt, 80-85% of the carbonate solvent, and 5-10% of the composite additive.

[0011] Furthermore, the novel lithium salt is a mixture of one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate.

[0012] Furthermore, the carbonate solvent is a mixture of cyclic carbonate and linear carbonate; the mass ratio of the cyclic carbonate to the linear carbonate is 1:2.5-4.

[0013] Furthermore, the cyclic carbonate is a mixture of one or more of vinylene carbonate, fluoroethylene carbonate, and propylene carbonate; the linear carbonate is a mixture of one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0014] Furthermore, the composite additive is a mixture of 1,3-propane sultone and chlorine trifluoride-hectorite; the mass ratio of the 1,3-propane sultone to chlorine trifluoride-hectorite is 2-4:1.

[0015] Further, the preparation of the chlorine trifluoride-hectorite comprises the following steps:

[0016] S1: drying the hectorite at 100-200°C for 2-4 hours to remove moisture and setting aside;

[0017] S2: putting the hectorite dried in step S1 into a reaction container, and then slowly introducing chlorine trifluoride into the reaction container, controlling the reaction temperature to 80-120° C., the reaction pressure to 1-5 atm, and reacting for 12-24 hours;

[0018] S3: After the reaction in step S2 is completed, chlorine trifluoride-hectorite is obtained by filtering, centrifuging, washing and drying.

[0019] Furthermore, the mass ratio of hectorite to chlorine trifluoride in step S2 is 1:0.5-2.

[0020] The present invention also discloses a method for preparing a low-temperature-resistant and cycle-resistant lithium battery electrolyte additive, which is characterized in that it comprises the following steps: adding a new lithium salt, a carbonate solvent and a composite additive into a reaction kettle in a certain proportion, mixing and dissolving them at an appropriate temperature and stirring speed under nitrogen protection to fully and evenly mix the components to form a stable mixed electrolyte additive solution, filtering the mixed electrolyte additive solution through a filtering device to obtain the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive.

[0021] Furthermore, the mixed dissolution temperature is 35-50° C., and the stirring speed is 300-800 rpm.

[0022] The present invention also provides a low temperature and cycle resistant lithium battery electrolyte additive fertilizer synergist. The carbonate solvent quasi-linear carbonate has a low melting point and viscosity. Under low temperature conditions, they can maintain good fluidity of the electrolyte and provide channels for the migration of lithium ions. The cyclic carbonate has a high dielectric constant and is conducive to the dissolution and ionization of lithium salts. Under low temperature conditions, a relatively stable solvation structure is formed between the carbonate solvent molecules and the lithium ions. This solvation structure can reduce the desolvation energy barrier of lithium ions during the migration process, so that lithium ions can smoothly shuttle between the positive and negative electrodes at a lower temperature, thereby improving the charge and discharge performance of the battery at low temperatures. Chlorine trifluoride-hectorite can adsorb impurities and trace moisture in the electrolyte, preventing these impurities from crystallizing and precipitating due to factors such as solubility changes at low temperatures, thereby blocking ion transmission channels. At the same time, it can form a protective film on the surface of the electrode, and this film can also maintain a certain flexibility and ion conductivity at low temperatures, which is conducive to the embedding and extraction of lithium ions. The SEI film formed by 1,3-propane sultone can effectively prevent the corrosion of the electrode by the electrolyte, while the film formed by chlorine trifluoride-hectorite can further enhance this protective effect, allowing the electrode to maintain good performance after multiple cycles.

[0023] Beneficial effects:

[0024] The low-temperature-resistant and cycle-resistant lithium battery electrolyte additive of the present invention can improve the charge and discharge performance of the lithium battery at low temperatures, and the battery can still maintain good performance after multiple cycles, and also has good chemical stability in a high-temperature environment. DETAILED DESCRIPTION

[0025] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0026] Unless otherwise specified, the chemical reagents used in the present invention are all commercially available analytically pure.

[0027] Preparation of chlorine trifluoride-hectorite A:

[0028] S1: drying the hectorite at 120° C. for 4 hours to remove moisture, and setting aside;

[0029] S2: Put 2g of the dried hectorite in step S1 into a reaction container, then slowly introduce 1g of chlorine trifluoride into the reaction container, control the reaction temperature to 120°C, the reaction pressure to 3atm, and react for 24 hours;

[0030] S3: After the reaction in step S2 is completed, chlorine trifluoride-hectorite A is obtained by filtering, centrifuging, washing and drying.

[0031] Preparation of chlorine trifluoride-hectorite B:

[0032] The difference between this preparation and the preparation of chlorine trifluoride-hectorite A is that 1 g of chlorine trifluoride in step S2 is replaced by 2 g of chlorine trifluoride.

[0033] Preparation of Chlorine Trifluoride-Hectorite C:

[0034] The difference between this preparation and the preparation of chlorine trifluoride-hectorite A is that 1 g of chlorine trifluoride in step S2 is replaced by 0.2 g of chlorine trifluoride.

[0035] Preparation of composite additive A: 2 g of 1,3-propane sultone and 1 g of chlorine trifluoride-hectorite A were mixed.

[0036] Preparation of composite additive B: 4 g of 1,3-propane sultone and 1 g of chlorine trifluoride-hectorite B were mixed.

[0037] Preparation of composite additive C: 2 g of 1,3-propane sultone and 1 g of chlorine trifluoride-hectorite C were mixed.

[0038] Preparation of composite additive D: 6 g of 1,3-propane sultone and 1 g of chlorine trifluoride-hectorite A were mixed.

[0039] Embodiment 1:

[0040] The preparation of low temperature resistant and cycle resistant lithium battery electrolyte additive A comprises the following steps:

[0041] 5 g of lithium difluorophosphate, 5 g of lithium bis(fluorosulfonyl)imide, 24 g of fluoroethylene carbonate, 36 g of dimethyl carbonate, 25 g of ethyl methyl carbonate and 5 g of composite additive A were added into a reaction kettle, and stirred, mixed and dissolved at a speed of 500 rpm at 35° C. under nitrogen protection to form a stable mixed electrolyte additive solution, and the mixed electrolyte additive solution was filtered through a filtering device to obtain the low-temperature and cycle-resistant lithium battery electrolyte additive A.

[0042] Embodiment 2:

[0043] The preparation was carried out according to the preparation method of Example 1. The difference between this Preparation Example and Example 1 is that 5g of lithium difluorophosphate, 5g of lithium bisfluorosulfonyl imide, 24g of fluoroethylene carbonate, 36g of dimethyl carbonate, and 25g of ethyl methyl carbonate were replaced by 10g of lithium difluorophosphate, 2g of lithium bisfluorosulfonyl imide, 3g of lithium fluorosulfonate, 6g of vinylene carbonate, 6g of fluoroethylene carbonate, 4g of propylene carbonate, 20g of dimethyl carbonate, 20g of ethyl methyl carbonate, and 24g of diethyl carbonate.

[0044] Embodiment 3:

[0045] The composite additive A was replaced by the composite additive B in accordance with the preparation method of Example 1.

[0046] Embodiment 4:

[0047] The preparation was carried out according to the preparation method of Example 1. The difference between this preparation example and Example 1 is that 24 g of fluoroethylene carbonate, 36 g of dimethyl carbonate, and 25 g of ethyl methyl carbonate were replaced by 30 g of fluoroethylene carbonate, 30 g of dimethyl carbonate, and 25 g of ethyl methyl carbonate.

[0048] Embodiment 5:

[0049] Preparation of compound low temperature resistant and cycle resistant lithium battery electrolyte additives:

[0050] The preparation was carried out according to the preparation method of Example 1. The difference between this preparation example and Example 1 is that the composite additive A is replaced by the composite additive C.

[0051] Embodiment 6:

[0052] The preparation was carried out according to the preparation method of Example 1. The difference between this preparation example and Example 1 is that the composite additive A is replaced by the composite additive D.

[0053] Comparative Example 1:

[0054] The preparation was carried out according to the preparation method of Example 1. The difference between this preparation example and Example 1 is that the composite additive A is replaced by 1,3-propane sultone.

[0055] Comparative Example 2:

[0056] The preparation was carried out according to the preparation method of Example 1. The difference between this preparation example and Example 1 is that 24 g of fluoroethylene carbonate, 36 g of dimethyl carbonate and 25 g of ethyl methyl carbonate were replaced by 85 g of trimethylsilyl acetate.

[0057] Performance test experiment:

[0058] According to the "Lithium Ion Battery Industry Standard Conditions", lithium batteries were prepared, including lithium nickel cobalt manganese oxide material as the positive electrode, graphite material as the negative electrode, lithium battery separator and electrolyte containing lithium salt of low temperature and cycle resistant lithium battery electrolyte additives prepared in Examples 1-6 and Comparative Examples 1-2 respectively; the positive electrode, separator and negative electrode were stacked into a battery cell in sequence and loaded into a battery shell; finally, the electrolyte containing lithium salt of low temperature and cycle resistant lithium battery electrolyte additives prepared in Examples 1-6 and Comparative Examples 1-2 was injected into the battery cell and packaged to prepare a lithium battery. The prepared lithium batteries were subjected to the following tests respectively.

[0059] 1. Low temperature discharge performance test:

[0060] Place the fully charged lithium battery in a low temperature environment box at -30℃ for 12 hours to allow the battery temperature to reach equilibrium with the ambient temperature, then discharge it at a 0.2C rate until it reaches a termination voltage of 2.5V. Record the total amount of discharge when the voltage reaches 2.5V and the total discharge time when the voltage reaches 2.5V, which are the discharge capacity and discharge time.

[0061] 2. Low temperature cycle life test:

[0062] In a low temperature environment of -30℃, the lithium battery was subjected to multiple charge and discharge cycles. Each cycle included -30℃ low temperature charging and -30℃ low temperature discharging processes, 0.5C charging and 0.5C discharging. The number of cycles was recorded until the battery capacity decayed to 80% of the initial capacity.

[0063] 3. High temperature stability test:

[0064] Place the lithium battery in a high temperature environment box, set the temperature to 60℃, and let it stand for 24 hours. Test the battery's charge and discharge performance, observe whether the battery has abnormal phenomena such as bulging, leakage, etc., and check for corrosion and peeling of the battery electrode material and damage to the diaphragm.

[0065] Performance test results Table 1:

[0066]

[0067] As can be seen from Table 1, the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive of the present invention can improve the charge and discharge performance of the lithium battery at low temperature, the battery can be cycled many times, and still maintain good performance, and the appearance remains intact under high temperature environment, indicating that the additive can enhance the compatibility of the electrolyte with electrode materials, battery casings and other components at high temperature, prevent the violent chemical reaction caused by high temperature from producing gas, resulting in an increase in the internal pressure of the battery, thereby improving the safety and reliability of the battery, and avoiding a sharp decline in battery performance or even failure due to safety problems; specifically, from the comparison of Example 4 with Example 1, it can be seen that when the mass ratio of cyclic carbonate to linear carbonate in the carbonate solvent is unreasonable, the prepared low-temperature-resistant and cycle-resistant lithium battery electrolyte additive will lead to a weakened charge and discharge performance of the lithium battery at low temperature, and the number of battery cycles will be reduced, and the expected effect will not be achieved; from the comparison of Example 5 with Example 1, it can be seen that when preparing the composite additive, the mass ratio of chlorine trifluoride to hectorite is unreasonable, which will lead to the prepared low-temperature-resistant and cycle-resistant lithium battery electrolyte additive improving the charge and discharge performance of the lithium battery at low temperature. The performance of the battery is weakened, the number of battery cycles is reduced, and the expected effect cannot be achieved; from the comparison between Example 6 and Example 1, it can be seen that when the composite additive is prepared, the mass ratio of 1,3-propane sultone to chlorine trifluoride-hectorite is unreasonable, which will cause the prepared low-temperature resistant and cycle-resistant lithium battery electrolyte additive to improve the charge and discharge performance of the lithium battery at low temperature to be weakened, the number of battery cycles is reduced, and the expected effect cannot be achieved; Comparative Example 1 is compared with Example 1, and it can be seen that when the composite additive is replaced with 1,3-propane sultone, the prepared low-temperature resistant and cycle-resistant lithium battery electrolyte additive will cause the charge and discharge performance of the lithium battery to be weakened at low temperatures, the number of battery cycles is reduced, the battery bulges at high temperatures, and the stability deteriorates at high temperatures, and the expected effect cannot be achieved; Comparative Example 2 is compared with Example 1, and it can be seen that when the carbonate solvent is replaced with trimethylsilyl acetate on the market, the charge and discharge performance of the lithium battery at low temperatures prepared by the low-temperature resistant and cycle-resistant lithium battery electrolyte additive will be weakened, the number of battery cycles is reduced, the battery leaks at high temperatures, the electrode corrodes and peels off, and the stability deteriorates at high temperatures, and the expected effect cannot be achieved.

[0068] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A low temperature and cycle resistant lithium battery electrolyte additive, characterized in that: The low-temperature-resistant and cycle-resistant lithium battery electrolyte additive comprises the following raw materials: a new type of lithium salt, a carbonate solvent, and a composite additive.

2. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 1, characterized in that: The raw materials for preparing the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive include, by percentage, 100%, 10-15% of a new lithium salt, 80-85% of a carbonate solvent, and 5-10% of a composite additive.

3. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 1, characterized in that: The novel lithium salt is a mixture of one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide and lithium fluorosulfonate.

4. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 3, characterized in that: The carbonate solvent is a mixture of cyclic carbonate and linear carbonate; the mass ratio of the cyclic carbonate to the linear carbonate is 1:2.5-4.

5. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 3, characterized in that: The cyclic carbonate is a mixture of one or more of vinylene carbonate, fluoroethylene carbonate, and propylene carbonate; the linear carbonate is a mixture of one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

6. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 1, characterized in that: The composite additive is a mixture of 1,3-propane sultone and chlorine trifluoride-hectorite; the mass ratio of the 1,3-propane sultone to chlorine trifluoride-hectorite is 2-4:

1.

7. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 1, characterized in that: The preparation of the chlorine trifluoride-hectorite comprises the following steps: S1: drying the hectorite at 100-200°C for 2-4 hours to remove moisture and setting aside; S2: putting the hectorite dried in step S1 into a reaction container, and then slowly introducing chlorine trifluoride into the reaction container, controlling the reaction temperature to 80-120° C., the reaction pressure to 1-5 atm, and reacting for 12-24 hours; S3: After the reaction in step S2 is completed, chlorine trifluoride-hectorite is obtained by filtering, centrifuging, washing and drying.

8. The low temperature and cycle resistant lithium battery electrolyte additive according to claim 5, characterized in that: The mass ratio of hectorite to chlorine trifluoride in step S2 is 1:0.5-2.

9. The method for preparing a low-temperature-resistant and cycle-resistant lithium battery electrolyte additive according to any one of claims 1 to 8, characterized in that: The following steps are involved: The novel lithium salt, carbonate solvent and composite additive are added into a reaction kettle in a certain proportion, mixed and dissolved at an appropriate temperature and stirring speed under nitrogen protection, so that the components are fully and evenly mixed to form a stable mixed electrolyte additive solution, and the mixed electrolyte additive solution is filtered through a filtering device to obtain the low-temperature and cycle-resistant lithium battery electrolyte additive.

10. The method for preparing the low-temperature-resistant and cycle-resistant lithium battery electrolyte additive according to any one of claim 9, characterized in that: The mixed dissolution temperature is 35-50° C., and the stirring speed is 300-800 rpm.

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