Is there further improvement for the energy density of lithium batteries?

At present, the pure electric vehicles first obstacle facing large-scale industrialization, is the problem of "range anxiety".For pure electric vehicles, its range is made power battery system can store electrical energy, so the energy density of power system has become the decisive factor restricting electric vehicle range.

Whether the energy density of lithium-ion batteries and improve space?

BMW's calculations suggest that consumers of pure electric vehicles can accept the lowest actual mileage is 300 km (about the ordinary cars a third of the oil tank full range), if in keeping the power battery system and the weight of the existing ordinary family car power train (mAhle power train) were similar, the energy density of power battery system to achieve the level of 250 wh/Kg, that is to say, monomer energy density of batteries to reach 300 wh/Kg.

So the current lithium electricity system, to meet safety, under the premise of circularity and other technical indicators, its energy density can reach 300 wh/Kg?

Lithium ion batteries in terms of its theoretical energy density by anode materials are given and the estimation of working voltage.Here, the author put aside the concept of complex electrochemical and structural chemistry, do some plain analysis.

Existing system of lithium electricity, can only be "half" high energy battery, because of its high specific energy is mainly based on the cathode low electrode potential, and the commercialization of several transition metal oxide anode materials (LCO, LMO, LFP and NMC) working voltage and specific capacity were not significantly better than that of the water system of secondary battery cathode material.

Therefore, if you want to make lithium electricity "real" high-energy battery only two roads: increase the battery voltage or anode materials are given.Because the cathode has not reduce the possibility of working voltage, high pressure must focus on the anode material.Nickel manganese spinel and rich lithium manganese based solid solution cathode material (OLO) charging voltage of 5 V and 4.8 V respectively, must adopt new high-voltage electrolytic fluid system.

5 v nickel galaxite due to the low capacity, and actually cannot effectively improve the energy density of the battery.Currently OLO actual capacity can reach more than 250 mah/g, already very close to the layered theory of transition metal oxide anode capacity.

Si/C composite cathode materials and silicon alloy anode materials of specific capacity has reached 600-800 mAh/g, the capacity range is almost its practical (ensure proper circulation and suppress volume change) limit.If OLO and silicon-based high capacity anode collocation, the energy density of about 350 wh/Kg.

I want to emphasize here is for 3 c small cell volume energy density is more important than the quality of energy density.That is to say, the layered cathode material (LCO and NMC) to a higher voltage and higher Ni content development, hype than it is now very popular rich lithium manganese base solid solution the anode more practical application value.

LCO technology with higher voltage and higher nickel content NMC ternary material increasingly mature, the future a more high pressure or higher nickel content of layered cathode material with high Si/C composite cathode capacity or alloy anode materials, small 3 C lithium electricity energy density is likely to further enhance to the level of 300 wh/Kg.

To further improve the lithium electricity than energy, then it must break the bondage of reaction mechanism of embedded now, like other regular chemical power source adopts the phase-out REDOX mechanism, namely using lithium metal anode.But lithium dendrite is easy to cause short circuit and highly active dendrite and the strong reaction of organic electrolyte liquid, making the problem went back to the starting point for the lithium ion battery.

In fact, the root cause of the lithium ion battery using graphite cathode, it is because the graphite embedded lithium compounds (GIC) to avoid the formation of metallic lithium dendrite, GIC and reduces the metal lithium highly active make it possible to have a stable SEI interface.So, based on the embedded reaction of lithium ion battery is actually had to compromise!

In the past two years, the international research on lithium metal anode presented a burst of small, such as American Solid Energy hype is very popular recently.Actually from the Angle of basic research is well understood, and as I mentioned earlier, the capacity of the anode materials don't have much room to improve, the electrolyte will do little to improve the energy density has increased, so the rest can only start from the cathode the, use metal anode of lithium battery is naturally "ultimate lithium battery".

In theory, USES the inorganic solid electrolyte, polymer electrolyte or liquid electrolyte adding special additives are likely to ease the lithium dendrite formation, but in the actual production of the batteries will face many technical difficulties.As discussed in the security section, the writer with metallic lithium as negative "ultimate lithium battery", but security issues will be the first decisive factor.

I personally believe that All solid state lithium ion battery based on inorganic solid electrolyte (All - solid - state Li - ion battery) is likely to make it possible for the practical application of lithium metal anode.Japan's Toyota (Toyota) is the international on solid-state batteries, at present the developed prototype battery at the technical level is ahead of other companies and research institutions, and Toyota have nearly 20 years of research and development in this field.

But large power battery for a number of technical indicators of strictly limited, on the choice of electrode material, system collocation, pole piece process and design of cell structure is different with the 3 c small batteries.These factors make even if is the same across the system collocation, large power battery energy density than small capacity battery is low.

For example, based on safety considerations and cyclical factors, power battery needs to try to maintain in low voltage (V) 4.2/4.3 level, that is, the high voltage 3 c small battery strategy on power battery may not be suitable.

Currently LG large ternary material motivation monomer battery energy density is more than the level of 220 wh/Kg.I personally believe there is still a further promotion in the technology space, the monomer in the future ternary power battery should be able to reach the level of 250 wh/Kg.

But in meet safety and cyclical temperature performance and cost aspects of requirements under the premise of further improve general monomer liquid lithium ion battery energy density, it would be very difficult in technology.Energy density batteries after group generally lose about 20% (Tesla ModelS losses as high as 45%), that is to say 200 wh/Kg could be normalLithium ion power battery energy density of a bottleneck of the system.

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