To do this, the thermal out of control will no longer be the immune disease of the safety of lithium battery!

To do this, the thermal out of control will no longer be the immune disease of the safety of lithium battery!

In today’s energy constraint, environmental pollution, etc., the state proposes to develop new energy as an important measure to improve the environment and save costs..

Among them, electric vehicles have recently become hot, more and more people choose electric vehicles, not only because of their low cost, and electric vehicles will not have exhaust gas during use, and there is no atmospheric pollution compared to traditional cars.. However, the electric car safety accident is frequent, and people have to re-examine the safety of electric vehicles.

. Battery thermal out of control is an important reason for fire explosion accidents. Like TSLA car, Samsung mobile phone and other fire events involve the thermal out of control of lithium-ion batteries.

The operating temperature range of the lithium ion battery is narrow, between 15 to 45 ° C, if the temperature exceeds the critical level, heat loss occurs. Once a lithium-ion battery occurs, it will cause a chain reaction that can’t be stopped. The temperature rises rapidly in a few milliseconds, and the internal heat is higher than the heat dissipation rate.

The internal heat saves a lot of heat, so that the battery becomes gas, causing the battery to fire and Exploding, and hardly threaten user security directly in conventional ways. The factors that currently cause the thermal out of control of lithium-ion batteries, summarizing the fever, overcharge, short circuit, collision, etc., etc.

. How to improve the safety of the battery, falling the risk of heat loss to the lowest in people’s research. Regarding the single battery, the safety is related to the correlation between the positive electrode material, and has a large relationship with other battery components such as negative electrode, diaphragm, electrolyte, and binder.

. The following shows how researchers reducing battery thermal out-of control risks on battery materials, and improve lithium-ion battery safety. First, the positive material material is good for safety, the polarity material and the compatibility and stability of the electrolyte.

Common positive electrode materials are relatively stable when the temperature is less than 650 ° C, and when charging is in a metastable state.. In the case of overcharge, the decomposition reaction of the positive electrode and its reaction of the electrolyte are released, resulting in explosion.

Lithium cobaltate, the thermostability of lithium nickel-nickel is relatively poor, and the lithium nickel-watery-containing three-membered material has a higher than energy density due to its higher than the energy density, and is an ideal choice for the current material material.. However, the content of nickel in the ternary material is high, and the circulatory performance of the material is difficult to ensure that the thermal stability is poor.

. The nickel positive material is structurally collapsed in a high voltage (4.3V) and high temperature (50 ° C).

. These microflakes disconnect the electrical passage between the particles, release oxygen during phase transition, resulting in deterioration of electrochemical properties. Jaephilcho Professor Tips Group [1] Based on the above problems of nano-surface modification of the nickel positive electrode material, the processed primary particle surface returned to cobalt, by inhibiting changes from the hierarchical structure to the rock salt structure.

Crack. Moreover, the surface high oxidation state can reduce the release of oxygen at high temperatures, improve structural stability and thermal stability..

Sangkyukwark et al. [2] proposed a method of increasing the positive stability of lithium ion battery. The NCA material was prepared by the classic calcination method, and then the NCA was immersed in a mixed solution of lithium acetate and cobalt acetate, further stirring, steam , Calcination to obtain improved positive material.

Interestingly, the NCA particles prepared by the method were filled with a spinel-like-containing cobalt-Lithium Cobi Crystal Glue-Layer (g-layer), which was able to connect NCA particles together, and the use of glue. It can improve the mechanical strength between the particles, protect the surface of the active particles, thereby enhancing the stability of the electrode..

Prof.yingjiezhu and Xianluohu cooperate [3], using hydroxyapatite super long nanowire, Cushen black nanoparticles, carbon fiber and lithium iron powder as raw materials, and successfully prepared by simple electrostatic assistance self-assembly. It can both high temperature resistance, and a high load of high loads (UCFR-LFP), which can be used as a lithium ion battery (Figure 1).

During self-assembly and filtration, lithium iron phosphate nanoparticles are uniformly dispersed in high-conductive and porous hydroxyapatite ultra-long nanoclands / Coripen nanoparticles / carbon fiber substrates, thereby forming self-supporting The unique composite porous structure of lithium resistant high-temperature positive electrode material has excellent thermal stability and fire resistance, even in high temperatures at 1000 ° C, it can also maintain its electrochemical activity and structural integrity.. Figure 1.

Application of jmfr-LFP composite electrode is schematically showing the thermal stability of the negative electrode material and the type of the negative electrode material, the size of the material particles, and the stability of the SEI film formed by the negative electrode.. If the size particles are made into a negative pole to achieve the expansion of the contact area between the particles, reduce the electrode impedance, new increasing electrode capacity, reduce the possibility of active metal lithium precipitation.

The quality of the SEI film forms directly affects the charge and discharge properties and safety of the lithium ion battery, weak oxidation of the surface of the carbon material, or it is conducive to the reduction, doping, surface-modified carbon material and the use of spherical or fibrous carbon materials. SEI film quality. The method of solving the safety of carbon negative electrode material is important to reduce the specific surface area of ​​the negative electrode material, improve the thermal stability of the SEI film.

. Third, the diaphragm Prof.zhenanbao and Yicui strong combination [4] reported a new technique that effectively prevent lithium-ion batteries from overheating, and they want to close the battery before the situation is not cleaned, and adding one in a lithium-ion battery Thermal polymer polymer film “switch” material, when the battery temperature is too high, the battery internal circuit is quickly cut down; when the temperature drops normally, the polymer film can return to the normal state, so that the battery is re-works ( figure 2).

They embed the nickel sodium particles having a graphene coating, and prepared a thin and flexible conductive plastic thin, a lithium ion battery assembled in this polymer film, at normal operating temperature. The current is easy to pass through the film, the battery can be charged and discharged, but when the temperature of the battery is raised to 70 ° C, the polyethylene begins to expand, and the nickel nanoparticles are pushed away from each other, so that the electrical conductivity of the separator is within 1 s. It will decrease by 1 billion times, the charge movement in the battery stops, thereby causing the temperature of the battery to drop.

Moreover, when the temperature is lower than this polymer 70 ° C, the polymer can be easily restored to the original configuration, and the conductivity is also normal, and the battery function is restored.. Figure 2.

Working mechanism of polymer film at high temperatures PROF.XIANLUOHU and YINGJIEZHU et al. [5] successfully developed a new hydroxyapatite ultra-long nanowire-resistant high temperature lithium-ion battery diaphragm, the battery diaphragm It has the characteristics of high flexibility, good mechanical strength, high porosity, good electrolyte, and adsorption performance, more important is high thermostability, high temperature resistance, flame retardant, and remain in high temperature at 700 ° C.

Structure integrity. The battery with hydroxyapatite ultra-long nanowire-resistant high temperature battery diaphragm can maintain normal operation in a high temperature environment in a high temperature environment, and a small light bulb is lowered, and the battery filled with the PP diaphragm is very fast at 150 ° C. Short-circuiting occurs, effectively improve the working temperature and safety of lithium-ion batteries.

Fourth, the electrolyte lithium ion battery electrolyte is substantially organic carbonate substance, is a class of flammable materials.. Commonly used electrolyte salt hexafluorophosphate (LiPF6) presence heat division release heat reactions.

Therefore, improve the safety control of the electrolyte is essential for the safety control of the power lithium ion battery.. The thermal stability of LiPF6 is an important factor affecting the thermal stability of electrolyte.

Therefore, important improvement methods are lithium salts that are better in thermal stability.. However, since the reaction of the electrolyte this body is very small, the impact on battery safety performance is limited.

. The impact on battery safety is its flammability. The way to reduce the flammability of electrolyte is important is to use flame retardant additives, but these flame retardants tend to have a serious impact on electrochemical properties of lithium ion batteries, so it is difficult to apply in actual applications.

. HONGFAXIANG et al. [6] use phosphate trimethyl ester (TMP) as a solvent, diofluorosulfonimide lithium is a solute, and has developed a new high concentration non-combustion electrolyte.

. At high concentration (5 mol / L), most of the TMP solvent molecules and Li + coordination in the electrolyte, form a special solvation structure, which reduces the sub-reaction between the solvent molecule and the negative electrode, greatly improves the safety of the battery..

The YUQIAO team of San Diego, California, the YUQIAO team [7] stores the flame retardant dibenzylamine (DBA) in the micro-capsule in the case of the capsule package, dispersed in the electrolytic solution, and does not appear on the performance of the lithium ion battery in normal state. Impact, when the battery is destroyed by extrusion, the flame retardant in the capsule will be released, and the “toxic” battery will fail to prevent the occurrence of thermal out of control..

After that, their team also uses the same technique, using ethylene glycol and ethylenediamine as a flame retardant, and is packaged in a lithium-ion battery after packaging, which can significantly reduce the risk of thermal out of control of lithium ion batteries [8]. Prof.atsuoyamada et al.

[9] employs high concentration NaN (SO2F) 2 or LIN (SO2F) 2 as a lithium salt, adding a common flame retardant phosphate TMP, the prepared electrolyte can significantly increase the heat of the lithium ion battery. Stability, and the addition of flame retardants does not affect the cycle performance of lithium ion batteries..

For the case where the power lithium battery may face the impact, Gabrielm.Veith et al. [10] attempts to prevent the short circuit in the lithium ion battery caused by the root cause, and designed an electrolyte with shear thickening characteristics.

(Fig. 3), the electrolytic solution utilizes the characteristics of a non-Newtonian fluid, in normal state, the electrolyte exhibits a liquid state, and after the sudden impact, the solid state will be present, it becomes unusually sturdy, and can even achieve the effect of bulletproof. Thus, the risk of short-circuit caused by thermal out-of control in the battery when the power lithium battery is collided.

Figure 3. Cut thickening electrolyte schematic Figure 5, the type and number of conductive agents and adhesive conductors and binders also affect the thermal stability of the battery, the binder and lithium reacts a lot of heat at high temperatures Different from different adhesives, the heat generation of PVDF is almost twice the fluorine-free binder, with a fluorine-free binder instead of PVDF to improve the thermal stability of the battery..

Jigangzhou et al. [11] recently carried out the imaging of a single electrode particle level by dividing the phase distribution before and after the complex composite electrode thermal out of control, and various phase separation phenomena have the correlation of nanometer-level visualization before and after heat loss. Lost control may be closely related to the distribution of conductors and binders.

They innovatively will have an element and orbit sensitivity sensitive transmission X-ray scanning microotechnology (PEEM) for studying the thermal out-of control of sorbate layer-shaped electrode particles in the porous electrode. behavior. The heat loss before and after the phase separation in a single electrode particle level exhibits unpredictable unevenness.

This non-uniformization and particle size, crystal surface structure is not obvious, but the distribution of conductive agents and binders is closely correlated.. Lithium-ion battery thermal loss seriously threatens the safety of users, improves the safety of lithium-ion batteries, preventing the occurrence of thermal out of control not only to make changes from battery materials, but also combined with battery formula design, structural design and battery Under the heat management design of the group, the combination of thermostability of lithium-ion battery and reducing the possibility of heat loss occurrence.

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