The energy density of a lithium-ion battery

The energy density is the biggest bottleneck of development to restrict the current lithium ion batteries. Whether mobile phones or electric cars, people are looking forward that the battery energy density can reach a new level, which makes the battery life of the product or product range will no longer be the main troubling factors.

From the lead-acid batteries, nickel cadmium battery, nickel metal hydride batteries, to the lithium ion battery, the energy density have been continuously improvement. But the ascending velocity relative to the speed of the development of industrial scale, relative to the level of human demand for energy, is too slow. Some joke that the progress of the men were stuck in the "battery" here., of course, if which day can realize global power wireless transmission, where can the "wireless" get electricity (like a mobile phone signal), then humans will no longer need to battery, social development also won't naturally card on the battery.

In view of the situation of energy density become bottlenecks, all countries in the world to formulate the relevant battery industry policy goals, expected to lead the significant breakthrough in battery industry in terms of energy density., us, Japan and other countries in the 2020 targets set by the government or industry group, basically point to 300 wh/kg that figure, is on the basis of the current ascension is close to 1 times. Long-term target for 2030, 500 wh/kg, or even 700 wh/kg, battery industry must have a major breakthrough in the chemical system, has it been possible to achieve this goal.

There are many factors that can influence of lithium ion battery energy density, lithium ion battery of the existing chemical system and structure, specific what are the obvious limits?

We analyzed above, and ACTS as an energy carrier, is actually the lithium battery, other substances are "waste", but to get stable, persistent, the safety of power carrier, the "waste" is indispensable. For example, a piece of lithium ion batteries, lithium than the average of the quality in a little more than 1%, the remaining 99% of the ingredients are not bear the energy storage function of other substances. Edison's famous words, success is 99% perspiration plus 1% inspiration, it seems that everywhere all ah, 1% are red, the remaining 99% is green leaves, which are not.

So to improve the energy density, the first thing we think of is to raise the proportion of lithium, at the same time to make as much as possible of the lithium ion ran out from the anode, moved to the cathode, and then have to count from the cathode the original return to the positive (no less), the cycle of transport energy.

1. Improve the positive active material proportion

To improve the positive active material proportion, mainly in order to improve the proportion of lithium, in the same chemical system, the content of lithium (other things being equal), energy density also can have the corresponding ascension. So under a certain size and weight limit, we hope that the positive active material, some more.

2. Improve the proportion of the cathode active material

This is in order to cooperate with the increase of the positive active material, need more negative active material to accommodate swam to lithium ion, stored energy. If the cathode active material is not enough, the extra lithium ion deposition in the cathode surface, rather than embedded inside, irreversible chemical reaction and battery capacity attenuation.

3. To improve the anode material of specific storage capacity (g)

There is a cap of the positive active material of accounted, not unlimited. Under the condition of the amount of the positive active material must, only as much as possible of the lithium ions from the positive to take off the embedded, participate in chemical reactions, to improve the energy density. So we hope that we can take off the embedded lithium ion relative to the positive active material proportion is higher, the quality of the higher specific capacity index.

This is the reason why we study and choose different anode material, from cobalt acid lithium to lithium iron phosphate, and then to three yuan material, are heading for the goal.

It has already been analyzed, cobalt acid lithium may reach 137 mAh/g, and manganese acid lithium iron phosphate lithium actual values are around 120 mAh/g, nickel cobalt manganese three yuan can reach 180 mah/g. If you want to upward again, you need to research new anode materials, and the industrialization progress.

4. Improve the specific capacity of anode materials

Relatively, the specific capacity of anode materials is not lithium ion battery energy density is the main bottleneck, but if further enhance the specific capacity, of the negative means less negative electrode materials by the quality, can accommodate more lithium ions, thus achieve the objectives of the ascending energy density.

With graphite cathode carbon materials do, theoretical specific capacity in 372 mAh/g, on the basis of the research of hard carbon materials and nano carbon materials, the specific capacity can be increased to more than 600 mah/g. Tin and silicon based anode materials, can also will increase the specific capacity of anode to a very high level, these are the direction of the current research hot spot.

5. Weight loss slimming

In addition to the positive of negative active material, electrolyte, isolation film, adhesive, conductive agent, collection of fluid, matrix, shell material, etc., are all lithium ion batteries "dead weight", accounted for around 40% of the whole battery weight. If you can reduce the weight of the material, does not affect the performance of the battery at the same time, it also can improve the energy density of lithium-ion batteries.

In this essay, you need to electrolyte, isolation film, adhesive, matrix and fluid collection, shell material and manufacturing process detailed research and analysis, so as to find out a reasonable solution. All aspects to improve some, it can be energy density ascension a whole range of the battery.

Can be seen from the above analysis, to improve the energy density of the lithium ion battery is a system engineering, to improve the manufacturing process, improve the existing material performance, as well as the development of new materials and new chemical system this a few aspects, looking for short-term, medium-term and long-term solution.

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