Tuesday, April 10, 2018

Silicon anodes will soon improve lithium-ion battery capacity

The main obstacle to producing mass electric cars (EVs) is the price and that is mainly caused by the cost of lithium-ion battery cells.
Some relief has come from the fact that performance of the cells has been improving at the rate of about 7 percent per year either through cost declines or more energy capacity for the same cost. The improvements come from a variety of sources including economies of scale, changes to the battery chemistry, fabrication improvement and higher energy yields.
Silicon Anodes
Battery engineers suggest that double-digit growth in lithium-ion battery capacity through the replacement of the present carbon anodes by silicon anodes could happen by 2020 to 2022. Five years ago the anodes were just being researched in the laboratory but are now much closer to production.
There are two electrodes in every battery the anode being the one that discharges lithium ions which travel through the electrolyte and are absorbed into the other electrolyte, the cathode. In charging the cell, the travel is reversed.
In theory, the silicon anode could absorb and hold many more times the number of atoms as the carbon anode can. However, the process needs to be limited to avoid destroying the anode.
At present, carbon anodes also have small amounts of silicon blended in with the graphite in order to boost range but at most by ten percent and likely less.
Several companies claim to be close to silicon anode production
Angstron Materials, Enovix, Enevate, and Sita Nanotechnologies all claim they are close to production of the silicon anodes.
The trick is to ensure that the lithium ions can be absorbed by the anode without swelling or shattering it. Nanoparticles are used do do this.
A nanoparticle is a very small particle between 1 and 100 nanometers in size. A nanometer is one billionth of a meter.
The companies claim that the new silicone anode batteries will increase the capacity of lithium-ion batteries by 20 to 40 percent over even the best graphite-anode batteries.
The new batteries will appear first in high-end electronic devices
The batteries are already being tested by potential customers but will first appear in smaller devices such as mobile phones. They should appear commercially within a couple of years.
However, before the batteries can be used in electric cars they will need far greater durability and be stress tested. In a mobile phone they need last only a few years but in an EV they should be able to last 10 or 15 years.
BMW hopes to use the batteries in an EV by 2023
BMW says it will use batteries from Sita Nanotechnologies in a plug in electric vehicles by 2023.
The German luxury car makesr intends to invest 200 million euros ($246 million) to staff and an establish its own battery research division for future EVs planned through the 2020s.
Need for safety and reliability may cut down capacity
Producers of the batteries may be too optimistic about the extent of the advantage of silicon-anode batteries over the present graphite ones. It may be necessary to cut down on capacity to ensure safety and durability.
BMW expects that the new batteries will have a 10 to 15 percent increase in capacity over the present graphite anode.
Range of EVs will increase with silicon anode batteries
The silicon-cathode batteries will not only reduce costs of batteries, an EV could have smaller batteries that would have the same range as present ones or alternatively there could a longer range with the same size as now. This gives designers of EVs more flexibility.

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