About the disparity between lithium ion batteries

For example, the stage Tiger lion performance must be directed by a trainer. At present, the "animality" of lithium batteries has not yet been clarified and mastered. It must be handled carefully under the conditions applicable to the operation of large-capacity storage and vehicles.

Sha Yongkang

The wave of Chinese enthusiasm for new-energy vehicles is making lithium-ion batteries, once a great convenience for mobile communications and audio and video mobility, one of the hottest areas of competition and concern.

But as more people struggle with mileage, battery life and even how to deal with used batteries, one of the fundamental questions that seems to be overlooked is -- is it safe enough?

In March 1978, when Sitanli·weitinghanmu, a chemist(engineer) at the Exxon Oil Company in the United States, invented lithium batteries, it may not have occurred to him that in the next 30 years or so, this invention brought great changes to human scientific and technological life. Lithium, The lightest metal known in nature has since become more intimate with humans.

At that time, Weitinghanmu made titanium sulfur compounds as negative poles and lithium metals as positive poles, making the world's first lithium battery prototype.

The working principle is to realize the process of charge and discharge by forming a current circulation between the positive and negative poles of the battery. Therefore, lithium batteries are also called lithium ion batteries.

Over the decades, with the continuous improvement of positive and negative materials, the manufacture of smaller lithium batteries with greater energy density and lower prices, the advent of mobile phones has further promoted their miniaturization and lightness, and has since become popular in Microelectronics. Music players, for example, are seen today as the inevitable choice for electric cars that are in vogue.

But the frequent explosions of cell phones and music players 'batteries in recent years seem to be sounding alarm bells -- something that makes life easier than it seems. Is the manufacturer loosening the quality management? Did the developer change some element of the battery? Or do people value power storage over safety?

A mobile phone lithium cell contains less than 5G of lithium metal, an initial electric micro-sedan, if the storage power is more than 30kWh, the battery pack contains about 50kg of lithium metal, and the explosion of the mobile phone cell will still be talked about. Change, if a group of micro-sedan batteries occur, The consequences are unimaginable.

There have been cases in China where lithium batteries were installed on electric vehicles and parked in garages. In the evening, they suddenly caught fire. Together with the entire vehicle, they were reduced to ashes. A few months ago, there was also a spontaneous combustion of hybrid buses, but it was discovered and disposed of. Early, It's not bad. Obviously, it is the responsibility of the battery and electric car industry to stay calm and plan for the future.

In fact, lithium-ion batteries have explosive safety hazards for many reasons that have yet to be solved, but they are obviously related to their own constituent elements.

Usually a lithium battery consists of five major elements: positive electrode, negative electrode, diaphragm, electrolyte, and monomer packaging. In that year, Sony successfully developed the first batch of commercial lithium batteries whose positive poles were made of lithium compounds, lithium cobalt, but because cobalt was a rare metal, manganese, iron, vanadium, nickel, etc. were later used, as well as polymers. Synthetic materials, even using air as an electrode medium, Different positive materials have different energy, safety, and working voltage.

The negative electrode is played by graphite and various mixing, synthesis, and composite materials. The graphite molecule space is a space lattice for lithium ion storage.

When charging, most of the positive lithium ions are transferred to the negative pole space. When the lithium ions on the negative pole accumulate excessively to a certain limit, the lithium ions will overflow and form dendritic crystals. These crystals grow and spread, piercing the diaphragm, and make the positive and negative poles. Contact, A short circuit then occurs. At this time, the short circuit will instantly release a large amount of heat, boiling hot and burning electrolytes, and eventually exploding, called "thermal failure." In addition, high temperature, puncture, breakdown, metal chip connection, and extrusion of the battery caused by vehicle collisions have all become the cause of thermal failure in the short-circuit of the positive and negative poles.

Therefore, although some lithium batteries that use solid polymers as electrolytes now reduce the possibility of explosion because they do not leak fluid, because lithium batteries convert external charged electricity into chemical energy and store it in the battery through internal chemical reactions, Chemical energy is also converted into the output of electrical energy through chemical reactions. This process produces temperature, and if the temperature is too high, the danger will follow.

What's more, the lithium battery itself has the characteristics of self-discharge, that is, under the condition that the battery is not charged or kept, it is undergoing chemical reactions of varying degrees of speed and speed. The battery has a low self-discharge rate with excellent performance, and vice versa. "Self-discharge rate" is very high. This internal chemical reaction will cause a music player placed on the table to explode itself when it is turned off.

Charging exothermic and discharge endothermic is a feature of lithium batteries, but sometimes charging too fast can also cause heat phenomenon. This is because the chemical reaction is too late to convert electrical energy into chemical energy. When discharging, the battery warming is chemical energy. Too late to convert into electrical energy. Therefore, when charging, it is generally managed by the management system, but there will be problems when discharging.

Based on this principle, the current discharged by a lithium battery should not be too large. If the current is too large and the duration is too long, it may cause the chemical reaction to heat up and heat up, and even explode.

In fact, the concept of lithium batteries that can be charged quickly and discharged quickly is relatively fast compared to lead-acid batteries. However, if the limit of lithium batteries is exceeded, the danger may be lurking not far away.

As for how much current discharge is suitable for lithium batteries, it should be determined by the actual situation. However, for the driving conditions of automobiles, instantaneous large current discharge is a common occurrence. This is a test for lithium batteries.

Now, the process of charging and discharging is controllable and can be reduced by manufacturing processes, metal powders, dust, artificial, etc., but the chemical reaction in the battery is currently difficult to control.

From this point of view, during the use of lithium batteries, it is a miniature "active volcano", and the end-of-life lithium battery seems to be an "extinct volcano." After scrapping, as long as the dismantling body is not understood, the "five major elements" are complete, and the chemical reaction will not be interrupted, but the degree will be reduced. Therefore, the battery recycling station will seal the lithium battery separately and regard it as a dangerous substance.

After analyzing the principle of lithium batteries and the factors that cause failure, developers and manufacturers need to recognize the dual faces of lithium batteries, angels and demons, and need to find a way to minimize safety hazards.

For example, the stage Tiger lion performance must be directed by a trainer. At present, the "animality" of lithium batteries has not yet been clarified and mastered. It must be handled carefully under the conditions applicable to the operation of large-capacity storage and vehicles.

The page contains the contents of the machine translation.