How to solve the problem of low efficiency of lithium battery for the first time

Lithium ion batteries A few big upset: a pest The battery The first effect is low, filling the 10 9 Ann was laid; Two of cycle life is poor, less than 500 fall; Three vexed low battery voltage, 4.2 V concludes.

For lithium ion battery cycle life is poor, have done a lot of research work, in view of the electrode material measures, in view of the electrolyte measures, in view of the electrode structure measures, has been relatively mature, the service life of lithium ion battery has got great improvement.

And in view of the low battery voltage developed by high voltage electrode materials, as well as the supporting electrolyte has gradually mature, are gradually develop applications.

Only for the first time, the problem of low efficiency, has not been a good solution, there is no mature solution, there are 3 m company development of inert lithium powder, although can be used as a supplementary cathode source of lithium, but due to poor safety (dust explosion hazard), the high cost (material cost is high, the high cost of equipment modification) in the short term is difficult to obtain a wide range of applications, and the anode for lithium seems to be a possible option, the anode for lithium only need to join the lithium oxide in the anode, the cost is low, do not change the original process, does not involve the use of metallic lithium, so security is greatly increased.

In a typical LiCoO2 / C all batteries, for example, in the process of charging for the first time, with the embedding of Li +, graphite potential gradually reduce, when below the electrolyte stability potential, electrolyte will be on the surface of graphite anode reduction decomposition, consumption part of lithium, leading to the irreversible capacity of around 10%.When the cathode in the irreversible capacity higher hard materials such as carbon, silicon, the capacity loss will be more obvious.

Li5FeO4 is an ideal source of lithium anode, its specific capacity of 867 MAH/g, theory per mole Li5FeO4 may provide five Li +, through in the traditional anode material mixed with a certain amount of Li5FeO4, can significantly improve the efficiency of lithium ion battery for the first time and the energy density.

XinSu, etc for Li5FeO4 as related researches on the positive source of lithium, they took LiCoO2 cathode (coulomb efficiency was 98%), the cathode adopted hard carbon (coulomb efficiency only around 80%) for the first time, Li5FeO4 using solid phase synthesis. In the process of charging for the first time, the LFO material can release at least 4 Li +, equivalent to more than the specific capacity of 700 MAH/g, as shown in the following reaction equation:

In the process, most of the lithium ions are not reversible embedded in LiFeO2 again, but these lithium ion can be used to offset the negative with the irreversible capacity loss. So in use in the anode material we only need to join a small amount of Li5FeO4 can.

Experiment study found that by adding only 7% of LFO in the anode material, the positive charge capacity is 233 MAH/g, for the first time and first discharge capacity is 160 MAH/g, only 7% of the content of LFO provides an additional 31% of Li +, these lithium ion can eventually into the anode materials, so as to make up for the problem of low efficiency of the cathode for the first time.

So when the anode materials used graphite materials (irreversible capacity of around 10%), can be appropriate to reduce the content of the LFO in the anode.

Calculation can know when is the cathode capacity ratio of 1:1, due to the irreversible capacity of hard carbon is bigger, lead to, in fact, the positive residual capacity of only 129 MAH/g (charging voltage of 2.7-4.3 V), and after joining LFO in the anode, due to the lithium added LFO in the process of charging for the first time the loss of lithium, making the positive for the rest of the reversible capacity of 159 MAH/g, which means that the battery has about 10% of the energy density of ascension.

With 7% of LFO provides extra 31% of lithium ions, thus can reduce the amount of added LFO, appropriately to just meet the cathode of the irreversible capacity (such as graphite by about 10%, Si materials around 25%), so the energy density of the battery can also be improved further.

At the same time, the study also found that LFO add not only improve the efficiency of the battery for the first time, also because the LFO provides additional Li, significantly improve the performance of the cycle of the battery, 50 times circulation capacity retention increased from 90% to 95% (LCO/hard carbon).Cycle for a long time after the battery negative energy spectrum analysis and X-ray diffraction showed that LFO material after the release of the lithium ion generated LiFeO2 will remain in the positive, there is no element of Fe dissolves, again in the cathode precipitation Fe element of risk.

Li5FeO4 material is a safe, reliable and efficient anode added source of lithium, its cost is relatively low, can release a large number of lithium ion, when charging for the first time and release a product of lithium ion activity is extremely low, will not happen again or embedded lithium dissolved, therefore is a kind of extremely has the potential to the positive source of lithium, with silicon anode high capacity, the application of the high irreversible capacity of anode materials, market demand for lithium anode fill material will be further expanded.

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