Lithium–sulfur battery

The lithium-sulfur battery is a accumulator in which the time is intensively researched and developed, because it promises a very high energy density. Prototypes exist, but there is no such batteries on the market. The theoretical energy density is among the highest of all batteries with 3350 Wh / kg. Has been realized in practice an energy density up to 350 Wh / kg.

While some researchers believe that the development of lithium - sulfur cells is so advanced that you 'm getting close to the industrial production, others expect that lithium-sulfur systems will be available until the end of the decade in the commercial, first for applications where it is not so much arriving on multiple recharging capability. The period of development from concept to production in electric cars has been estimated at 15 to 20 years beginning 2013.

Electrochemistry

During discharge, lithium is released at the anode. At the cathode, it combines with sulfur, there arise lithium sulfides, when fully discharged lithium sulfide Li2S:

During the charging process, the resulting compound is dissolved and re-formed sulfur. At the negative electrode side while lithium metal is again deposited or formed a lithium alloy:

Formed as intermediates during unloading and loading mixtures of different lithium sulfides. When unloading it takes the sulfur content in the mixture from getting further because the lithium content increases further. This can be schematically with the series

Are shown, but the sulfides Li2S8, Li2S6, Li2S5, Li2S4 and Li2S2 may be present in very different concentrations in the mixture together.

The reaction corresponds to the sodium -sulfur batteries, in which lithium has the function of sodium.

Since sulfur is an insulator, i.e., only has a very poor electrical conductivity, it must be available in a conductive mixture that the discharge can ever get off the ground. In general, the sulfur is added to carbon. Is the amount of carbon is too low, the sulfur is used incompletely lack electrical contact, and the specific capacity is too small. If the amount of conductive agent is too large, the additional mass associated also leads to electrochemically inactive material at low specific capacities. A significant proportion of current research activities therefore attempted by the use of specific types of carbon to optimize the battery: It will be tested not only graphite and different carbon blacks, but also graphs, carbon nanotubes, porous carbons and many other special forms and mixtures. Therefore, many variations are investigated, which are different on the sulfur side. But also by different electrolytes and different mixtures at the anode side, there are many variants: In addition to the use of pure lithium metal in particular silicon and tin ( in tin -sulfur rechargeable lithium battery ) has been proposed as anode materials to improve the cyclability.

Historical

The first patent for a battery, for in addition to other material combinations and the pair lithium and sulfur was proposed was 1957/1958 filed and granted in 1962.

Pros and Cons

Unlike many lithium -ion accumulators containing scarce, expensive and toxic heavy metals such as cobalt or nickel, are the most important addition to lithium components of the lithium-sulfur cell, namely sulfur and carbon, inexpensive, widely available and easily available - sulfur is also produced in huge heaps as a waste product in the desulfurization of fuels. Sulfur and carbon are non-toxic, however, incurred in the discharge lithium sulfides are toxic, they react with acids to form toxic hydrogen sulphide gas. Even so, the cells must be tightly closed. But that is state of the art, because all lithium batteries and lithium -ion batteries already need to be protected against the ingress of air or moisture due to the air-and water-sensitive lithium-containing anode.

The high theoretical energy and charge densities would - if they can be because in practical cells also realize - lead to very powerful batteries. Until around 2009 but the practically achievable recharging capability of such cells were too small. Only in recent years have been over a hundred, or since about 2013, hundreds - or even in some cases - to the thousand cycles, and more.

Classification

The lithium-sulfur battery of the charge transport takes place in the electrolyte by lithium ions, such as in the current lithium ion batteries. However, the lithium-sulfur battery, a chemical reaction takes place, to be completely converted in the substances, may also crystals of sulfur or lithium sulfide are newly formed or dissolved, while in today's lithium -ion batteries takes place intercalation. Such as lithium batteries, lithium -sulfur batteries containing lithium metal, or an alloy.

Current state of research

In April 2013, scientists of the Fraunhofer IWS Dresden before a new battery design with a silicon -carbon anode, the seven-fold the number of charge cycles and button cells from 200 to 1400.

In November 2013, researchers at the Lawrence Berkeley National Laboratory reported their optimized sulfur electrode was after 1500 charge-discharge cycles still had a higher capacity than the cathode in advanced lithium - ion cells. They used a special electrolyte, which is based on an ionic liquid. The number of cycles is the highest, was reported previously.

524936
de