TWI581480B - Inherently safe thermo-responsive gel electrolytes for electrochemical devices - Google Patents

Description

Phase change electrolyte for electrochemical device and preparation method thereof

The present invention relates to an electrolyte for an electrochemical device, and more particularly to a phase change electrolyte which can be used to improve the safety of an electrochemical device such as a lithium battery, and a method for preparing the same.

Since 1980, a large number of studies have been conducted on colloidal electrolytes for lithium batteries. Generally, the colloidal electrolyte contains a polymer main material, an organic solvent and an organic lithium salt. Due to the special requirements of the electrochemical material of the lithium battery, the organic solvent used in the colloidal electrolyte is an organic carbonate solvent having extremely high flammability, such as ethylene carbonate. (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC). In order to ensure that the lithium battery has a sufficiently high charging and discharging speed, the content of the organic carbonate lithium salt solution in the colloidal electrolyte is usually more than 80%.

In order to reduce the safety hazard of lithium batteries in order to reduce a large amount of flammable organic solvents, polymer colloidal electrolytes have emerged. This is mainly because the polymer colloidal electrolyte formed by adding the polymer host material to the organic lithium salt solution can fix the flammable electrolyte body and prevent leakage, thereby reducing the vapor pressure of the combustible gas, thereby improving the safety of the lithium battery. At present, the following four types of polymer materials are studied as the base materials for colloidal electrolytes of lithium batteries, which are polyvinyl ether (PEO), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF). . In addition, it has also been reported to use copolymers derived from the above polymers for polymer electrolytes of different formulations, for example PEO-co-polydimethyloxane (PDMS), PMMA-co-PDMS, PVDF-co-hexafluoropropylene (HFP) copolymer.

However, the use of the above polymer materials as a base material for a lithium battery colloidal electrolyte has a temperature limitation. Above the colloidal transition temperature, usually around 80 ° C, the colloid will melt into a liquid, so that above the colloidal transition temperature, the above-mentioned existing polymer colloidal electrolyte base material formulation can not achieve the purpose of improving battery safety. In addition, the electrolyte ionic conductivity is increased at high temperatures. However, above a certain set temperature, the high conductivity of the electrolyte may be very dangerous. For example, in the battery safety test, such as during the nailing test, the battery temperature will rise rapidly during the overcharge and overdischarge, causing the combustible gas to burn and explode. .

From the perspective of battery safety, when the battery is in an extreme condition such as overcharging or overdischarging, the battery will reach an abnormally high temperature within a few seconds due to the corresponding electrode reaction. At this time, if the conductivity of the electrolyte can be lowered, the electrochemical reaction can be slowed down or even interrupted, the battery can be turned off in time to avoid battery explosion. When the battery temperature returns to the normal operating temperature range, the colloidal electrolyte returns to a conductive electrolyte and the battery can continue to operate.

The invention is a novel reverse thermal reaction phase change electrolyte which can be used for electrochemical energy storage equipment, especially lithium batteries. The reason why the phase change material of the present invention is formed is the "inter-droplet bridging" theory developed according to the nano-emulsion type organic hydrosol research technology in recent years. The so-called "drip bridge" theory refers to a physical cross-linking caused by the "drip bridge" effect of a polymer nano-liquid. When a gel-forming agent with a bipolar functional group exists between the polymer nano-droplets, There will be a "drip bridge" effect. To achieve the "drip bridge" effect of organic solvent systems, two conditions are required: 1) special effect gelling agent--organic functional polymer compatibilizer to control organic dissolution Nano-phase reverse phase separation of the agent system; 2) High-efficiency high-pressure mixer can be used to prepare a polymer emulsion with a droplet size of less than 100 nm and has the following unique properties: at a temperature below the colloidal temperature, the nano-sized polymer The emulsion remains in a liquid state and has a high ionic conductivity, and in the liquid state, the conductive ions have a freely conductive polar solution channel. When the nano-type polymer emulsion is heated and exceeds the gelation temperature, the "drip bridge" effect occurs and the electrolyte changes from a liquid state to a colloidal state. At this time, the ion conductive channel composed of the polar solution is frozen. The ion conductive current is rapidly decreased, and the ion conductivity change is reversible between the colloid and the liquid. The reversible nature of the ion conduction can be used as a safety control switch in different electrochemical energy storage device systems.

The phase change electrolyte of the present invention can overcome the shortcomings of the existing colloidal electrolyte. Contrary to the general colloid, the present invention solidifies from a conductive liquid to a non-conductive colloid when the battery reaches a colloidal temperature or higher, and the battery is in a "closed" state at a high temperature; the battery temperature After the reduction, the phase change electrolyte of the present invention returns to a conductive liquid state, and the battery is returned to the "on" state to keep the battery in normal operation. In practical applications, when the lithium battery is rapidly increased to a certain set value due to overcharging or other different reasons, the present invention will promptly solidify from the conductive electrolyte to a non-conductive colloid, thereby cutting off the ion conductive channel, as in the case of Stopping the charging flow at the bottom of the bottom of the tank to prevent high temperature explosion and leakage of the electrolyte. It is worth mentioning that after the battery temperature is lowered, the present invention returns to a conductive liquid state and allows the battery to resume operation. The present invention can improve the inherent safety of electrochemical devices (e.g., lithium batteries) due to the thermal on/off characteristics.

100‧‧‧ phase change electrolyte

102‧‧‧Non-polar materials

104‧‧‧Bipolar gelling agent

106‧‧‧Ion Conductor

108‧‧‧Polar materials

200‧‧‧ Method for preparing water-based phase change electrolyte

Steps 202, 204, 206, 208, 210‧‧

300‧‧‧Method for preparing non-aqueous phase change electrolyte

302, 304, 306, 308, 310‧‧‧ steps

Figure 1A is a schematic view of the phase change electrolyte of the present invention below the colloidal temperature.

Figure 1B is a schematic view of the phase change electrolyte of the present invention above the colloidal temperature.

2 is a schematic flow chart of preparing a water-based phase change electrolyte according to the present invention.

3 is a schematic flow chart of preparing a non-aqueous phase change electrolyte according to the present invention.

The phase change electrolyte of the present invention can overcome the shortcomings of the existing colloidal electrolyte. Contrary to the usual colloid, the present invention solidifies from a conductive liquid to a non-conductive colloid when the battery reaches a colloidal temperature or higher, and the battery is in a "closed" state at a high temperature; the battery temperature After the reduction, the phase change electrolyte of the present invention returns to a conductive liquid state, at which time the battery is returned to the "on" state to keep the battery operating normally.

In practical applications, when the lithium battery is rapidly increased to a certain set value due to overcharging or other different reasons, the present invention will promptly solidify from the conductive electrolyte to a non-conductive colloid, thereby cutting off the ion conductive channel, as in the case of Stopping the charging flow at the bottom of the bottom of the tank to prevent high temperature explosion and leakage of the electrolyte. It is worth mentioning that after the battery temperature is lowered, the present invention returns to a conductive liquid state and allows the battery to resume operation. The present invention can improve the inherent safety of electrochemical devices (e.g., lithium batteries) due to the thermal on/off characteristics. It is expected that the present invention can further improve the safety of a lithium battery by cooperating with existing battery safety devices such as a temperature rise protection circuit (PTC) and a battery management system (BMS).

Figure 1A is a schematic illustration of the phase change electrolyte of the present invention below the colloidal temperature (T _gel ). The phase change electrolyte 100 can be comprised of a non-polar material 102 (non-polar nano-microdroplets), a bipolar gel-forming agent 104, an ion conductor 106, and a polar material 108 (or a polar continuous phase). When the phase change electrolyte 100 is lower than the colloidal temperature (T _gel ), the phase change electrolyte 100 maintains a liquid state of high conductivity. The ion conductor 106 has a free ion conduction path in the phase change electrolyte 100.

The polar material 108 (polar continuous phase) may be water, an alcohol compound, an ionic liquid compound, an acrylate compound, or an organic carbonate compound such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, A Base ethyl Carbonate. The non-polar material 102 (non-polar nano droplets) may be a compound containing a different functional group or molecular weight hydrocarbon-based oil or fat, or a compound having a different functional group or molecular weight decane, such as polydimethyl decane having a different functional group or molecular weight. (PDMS) compounds, and polyolefins containing compounds having different functional groups or molecular weights. The bipolar gel forming agent 104 may be a polymeric surfactant or a nonionic surfactant such as polyoxypropylene glyceride, polyoxyethylene glyceride, polydivinyl alcohol dimethyl ether or the like. The ionic conductor 106 may be a water-soluble inorganic salt or an organic salt such as sodium chloride (NACl), potassium chloride (KCl), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LIPF6), lithium sulfoxide (BETI). )Wait.

Figure 1B is a schematic view of the phase change electrolyte of the present invention above the colloidal temperature (T _gel ). At this time, the ion conductor 106 is confined in a three-dimensional physical crosslinked colloidal network structure formed of the bipolar gel-forming agent 104 having a functional group and the non-polar material 102. At this time, the electrolyte ionic conductivity is drastically lowered. The change in ionic conductivity between a low conductivity colloidal state and a high conductivity liquid state is reversible. This reversible change in ionic conductivity allows the phase change electrolyte material of the present invention to be used to improve the safety of electrochemical systems.

The phase change electrolyte 100 can be used as an oil-water system electrolyte for a water-based electrochemical device system or a non-aqueous system electrolyte for a non-aqueous electrochemical device system. To achieve the unique properties described above, this new retro-reactive colloidal electrolyte needs to be prepared by a high-efficiency high-pressure homomixer such that the resulting droplet size is between 10 and 100 nanometers (nm).

The phase change electrolyte 100 has an "on/off" function. By heating above the colloidal temperature (T _gel ), the phase change electrolyte 100 can be reversibly converted from a high ionic conductivity liquid "on" state to a low ionic conductivity colloid "off" state. Therefore, the phase change electrolyte 100 is different from the conventional physical crosslinked colloidal electrolyte. When the conventional physical crosslinked colloidal electrolyte is heated above the colloidal temperature (T _gel ), the colloidal electrolyte melts into a liquid state and increases the ionic conductivity. After the temperature is gone, the conventional physical crosslinked colloidal electrolyte solidifies into a colloid of low conductivity. The phase change electrolyte 100 has a reverse thermal reaction property as compared with a conventional physical crosslinked colloidal electrolyte.

2 is a schematic flow diagram of a process 200 for preparing a water-based phase change electrolyte. The preparation of the aqueous phase change electrolyte is prepared by the following steps:

Steps 202 to 204, water-based continuous phase preparation: water with a surfactant (such as sodium dodecyl sulfate), a polymer gelling agent (such as polyvinyl alcohol acrylate) and an inorganic salt (such as potassium nitrate) Conventional mixing is carried out at an appropriate ratio.

Step 206: Primary water-based emulsion preparation: a non-polar polymer material (such as polydimethyl decane) is conventionally mixed with the water-based material obtained in the first step.

Step 208, preparation of nano water-based emulsion phase change electrolyte: the primary water-based emulsion prepared in the second step is subjected to a nano phase by 15 to 20 high-efficiency homomixers (for example, Emulsiflex-C3 homomixer manufactured by Avestin). Variable electrolyte preparation. The pressure was set to 15 Kpsi, the temperature was 5 ° C, and the controlled emulsion size was between 10 and 100 nm, ending at step 210.

The representative formula of nano water-based phase change electrolyte is: 1M potassium nitrate aqueous solution, 200 mM sodium dodecyl sulfate (SDS), 30% polyvinyl alcohol acrylate (PEGDA) and 33% polydimethyl decane (PDMS). .

3 is a schematic flow diagram of a process 300 for preparing a non-aqueous phase change electrolyte. The preparation of the non-aqueous phase change electrolyte is prepared by the following steps:

Steps 302 to 304, organic phase carbonate continuous phase preparation: ethylene carbonate (EC) and diethyl carbonate (DEC) and organic gelling agent (such as polyvinyl alcohol dimethyl ether (PEGDME)) and organic salts (For example, lithium tetrafluoroborate (LiBF ₄ )) is conventionally mixed in an appropriate ratio.

Step 306, preparation of a primary non-aqueous emulsion: preparing a non-polar polymer material (for example, polydimethyl siloxane or polydimethyl decane-polyvinyl ether copolymer (PDMS-PEO)) and the first step The organic phase carbonate continuous phase is conventionally mixed in an appropriate ratio.

Step 308, preparation of a nano-aqueous non-aqueous emulsion phase change electrolyte: the non-aqueous primary emulsion prepared in the second step is passed through a 15-20 efficient homomixer (for example, an Emulsiflex-C3 homomixer manufactured by Avestin). Rice phase change electrolyte preparation. The pressure was set to 15 Kpsi, the temperature was 5 ° C, and the controlled emulsion size was between 10 and 100 nm, ending at step 310.

The representative formula of nano-water-based phase change electrolyte is: 1M lithium tetrafluoroborate, 30% polyvinyl alcohol dimethyl ether, and 33% polydimethyl siloxane-polyvinyl ether copolymer (PDMS-PEO) , 3:7 ratio premixed ethylene carbonate (EC) and diethyl carbonate (DEC).

Numerous modifications and other implementations will occur to those skilled in the art from the foregoing description of the method and the associated drawings. Therefore, the embodiments are not limited to the specific example embodiments disclosed, and other similar embodiments are included in the scope of the invention.

Claims (8)

A phase change electrolyte for an electrochemical device, wherein the phase change electrolyte is converted between a lower conductivity colloidal state and a higher conductivity liquid state, wherein the phase change electrolyte is composed of the following components: Up to 800 nanometers (nm) of non-polar material dispersed phase, bipolar gelling agent, ionic conductive material and polar material. When the temperature is higher than the colloidal temperature, the phase change electrolyte is a colloidal state of lower conductivity, the double The polar gelling agent forms a physical crosslink with the non-polar material and freezes the conductive path of the ion conductive material in the polar material. When the temperature is lower than the colloid temperature, the phase change electrolyte is in a liquid state of higher conductivity, and the polar material is An ion conductive channel is provided. The phase change electrolyte for an electrochemical device according to claim 1, wherein the polar material is water, an alcohol compound, an ionic liquid compound, an acrylate compound or an organic carbonate compound. The phase change electrolyte for an electrochemical device according to claim 1, wherein the non-polar material is a compound containing a different functional group or molecular weight hydrocarbon-based fat or oil, or a compound having a different functional group or molecular weight decane, for example. Polydimethyl methoxy siloxane compounds having different functional groups or molecular weights, and polyolefins containing compounds having different functional groups or molecular weights. The phase change electrolyte for an electrochemical device according to claim 1, wherein the bipolar gelling agent is a polymer surfactant or a nonionic surfactant, such as polyoxypropylene glyceride, polyoxygen. Ethylene glyceride, polydivinyl alcohol dimethyl ether, and the like. The phase change electrolyte for an electrochemical device according to claim 1, wherein the ion conductive material is a water-soluble inorganic salt or an organic salt, such as sodium chloride, potassium chloride, lithium tetrafluoroborate or lithium hexafluorophosphate. , lithium amide amine salts, and the like. A method for preparing a phase change electrolyte for an electrochemical device, comprising: preparing a polar substrate by mixing a bipolar gelling agent, an ion conductor, and a polar compound, and then preparing the polar substrate and the non-polar material by mixing the polar substrate The primary electrolyte emulsion is finally passed through a high efficiency homomixer to prepare a phase change electrolyte. A method of preparing a phase change electrolyte for an electrochemical device as described in claim 6, which comprises mixing a non-polar compound, a bipolar gelling agent, an ion conductor, and a polar compound. A method of preparing a phase change electrolyte for an electrochemical device according to claim 6, which comprises cooling a primary electrolyte emulsion treated by the high efficiency homomixer.