## New aqueous rechargeable lithium battery shows good safety, high reliability, high energy density and low cost; another post Li-ion alternative

##### 08 March 2013
 Schematic illustration of the aqueous rechargeable lithium battery (ARLB) using the coated lithium metal as anode, LiMn2O4 as cathode and 0.5 mol l-1 Li2SO4 aqueous solution as electrolyte. Wang et al. Click to enlarge.

Researchers from Fudan University in China and Technische Universität Chemnitz in Germany have developed an aqueous rechargeable lithium battery (ARLB) using coated Li metal as the anode. In a paper published in Scientific Reports, the open access journal from the Nature Publishing Group, the team reports that the ARLB delivers an output voltage of about 4V.

The battery shows an energy density of up to 446 Wh kg-1—about 80% higher than conventional Li-ion batteries, and much higher than energy densities reported for earlier ARLBs (30–45 Wh kg-1). The battery, which can be low cost and reliable in terms of safety, provides another chemistry for post Li-ion batteries, they suggest, and with higher practical energy densities than Li-air systems for supporting applications including electric vehicles and large-scale grid energy storage.

Aqueous rechargeable lithium batteries (ARLBs), which use aqueous electrolytes and lithium intercalation compounds as electrode(s) based on redox reactions, were invented in 1994 and have attracted wide attentions since 2007 as a promising system because of their low capital investment, high reliability and good safety. Recent breakthroughs show clearly that they can present very good cycling performance and super-fast charge performance, which can be comparable with filling gasoline for engine cars.

Although several attempts have been made on the anode materials, the main disadvantages is that their energy density is still much lower than that of conventional lithium ion batteries due to the narrow electrochemical window of water. If anode materials of lower redox potentials can be stable in aqueous electrolytes, high energy density systems will be feasible.

Here we introduce a coating layer on lithium metal. The coated lithium metal is stable in aqueous electrolytes. Combining with the coated lithium metal as anode, LiMn2O4 as cathode and 0.5 mol l-1 Li2SO4 aqueous solution as electrolyte, an ARLB is built up. Its average discharge voltage is about 4.0 V, much higher than the theoretic stable window of water, 1.229 V. It presents an energy density of 446 Wh kg-1 together with excellent cycling performance.

—Wang et al.

In conventional lithium metal rechargeable batteries, the use of Li metal as anode material is restricted due to the safety issues caused by the formation of lithium dendrites during repeated charge-discharge cycles, leading to short circuiting. In the new ARLB, the coating prevents dendrite formation.

The coating of the Li metal consists of a home-made gel polymer electrolyte (GPE) and a LISICON film. LISICON film is a solid electrolyte which can also act as a separator; due to its solid structure, protons, water, hydrated and solvated ions cannot pass through. The GPE ensures the good electrochemical stability of the LISICON film, and only Li+ ions can transfer between Li metal and the outside.

The coated lithium metal is also very stable in the aqueous solution, with no hydrogen evolution observed. (Lithium metal reacts rapidly with water to produce hydrogen and lithium hydroxide, LiOH.)

Due to the “cross-over” effect, lithium ions at the higher potential side in the aqueous electrolyte can pass through the coating and arrive at the lower potential side of lithium metal. As a result, the coated lithium metal is very stable in the aqueous electrolyte and the average output voltage of this ARLB is 4.0 V.

—Wang et al.

In addition to its capacity and cycling performance, the ARLB offers another benefit, the researchers note: thermal management.

In this ARLB system, the aqueous electrolyte has high thermal capacitance and can absorb large amounts of heat. During the same charge and discharge process, the temperature of this system will be much lower than that for conventional lithium ion batteries. In addition, water or aqueous electrolyte is in direct contact with both of the Li metal anode and the LiMn2O4 cathode, and the cooling effects will be very efficient. The cooling system, which is usually needed for large capacity battery modules, is not needed for the application in electric vehicles. The safety and reliability is greatly improved when compared with conventional lithium ion batteries.

—Wang et al.

Compared with Lithium/air batteries, the ARLB offers the following advantages, the researchers said:

• Much better cycling performance.
• Higher practical energy density.
• Higher energy efficiency.
• Lower cost of production, using well-known materials.

Furthermore, they noted, the cycling performance of the ARLB is much better than that of lithium-ion batteries.

Replacing LiMn2O4 with LiCoO2 or Li[NixCoyMn1-x-y]O2 can deliver higher energy density in the ARLB, they suggested. Using LiCoO2 in the ARLB design could result in an energy density—on the basis of the electrode materials—above 570 Wh kg-1, with an estimated practical energy density above 285 Wh kg-1.

With Li[NixCoyMn1-x-y]O2, the estimated practical energy density would be above 300 Wh kg-1.

Based on these data, it means that this new ARLB chemistry can ensure electric vehicles to run above 300 km [186 miles] for one charge, which presents great promise.

—Wang et al.

Resources

• Xujiong Wang, Yuyang Hou, Yusong Zhu, Yuping Wu & Rudolf Holze (2013) An Aqueous Rechargeable Lithium Battery Using Coated Li Metal as Anode. Scientific Reports 3, Article number: 1401 doi: 10.1038/srep01401

"—on the basis of the electrode materials—above 570 Wh kg-1, with an estimated practical energy density above 285 Wh kg-1."

Now that's an interesting, and I believe, honest blurb to put in an announcement like this. Most of the time, they just give us the really high number of the anode material, but in this case they gave us the real world number including electrolyte, packaging, useful energy (considering state of charge limitations I assume), etc.

A real world energy density of ~300Wh/kg would be a good step forward, especially if the price is "low cost" as they say. :-)

If true, this could be another major step towards improved affordable EV batteries. Who is going to kill it this time?

In 2022 i will change my current dodge neon 2005. Im following the market closely each days for evolution in technologies. If this battery is good then i might like it in a hybrid instead of a pure bev. An electric like the volt with a small gasoline range extender is the best as i often do long trips of 1500 miles 2 time a year. I don't like to recharge on the road. A small 2 cylinder gasoline recharger is sufficient. The volt have a costly weighthy overbuilt gasoline recharger instead of a small efficient recharger. With a small battery like this that is efficient and light, then a pure electric range of 100 miles associated with a small gasoline recharger is the best combinaison for long or short trips without hassles.

@AD - have you considered renting a car for those 2 long trips a year?

I wonder what its low temperature performance is like?
An aqueous electrolyte could make it vulnerable to freezing.
That is why there is interest in solid state.

A good, well insulated BMS would take care of any concerns... There has been talk of metal salt batteries in cars so I don't think it would be that hard to imagine an aqueous solution in cars, all you have to do is open up your hood to see one....

Having said that, you can brick Pb-acid by fully discharging them in freezing weather, fully charged(or close to it) its safe in almost all circumstances we would find (consumer)cars in.

This should prove interesting, I am still waiting for retail of advanced Pb-acid batteries... If they can do what they say they can do, batteries might go for the life of the vehicle if cared for (I've seen 6-9 years, and yes of course I have seen far less) not to mention downsizing/weight reductions..

To me this seems suited for large-scale grid storage - high cycle life (2-3 cycles a day to level out peaks in the grid) and low cost production. Which is good, we need cheap grid storage.

If we can hit certain targets for grid storage, the incremental cost per kWh would be so low that the cost wont be that much when compared to expensive peaking power. For example, if you had a battery that cost $100/kWh, got 5,000 cycles, and was 80% round-trip efficient, then you'd end up with a effective cost for storage of 2.5c/kWh. Battery price is crucial. Anyway pure BEV would be not practical with such battery. Small range extender would be needed. @Darius: I don't follow you. How are you working out the figures to give you that result? Thank you for your attention. Having pure BEV with max. 300 km range anyway you should use predifind route and therefore it will be daily comute city car. I do not believe that fast charging network would be so dense as petrol stations becouse it woul cost realy a lot. Why to invest into fast charging in case small range extender will cost just peanuts and will guaranty you ultimate freedom. One fast multi-charger station may cost less than 10,000+ over equipped EVs for the occasional long distance drive? Why drive around with 200+ kWh of batteries when 60 to 75 kWh or so would do the job, except for the 3 or 4 long drives/year, if major highways were equipped with ultra quick chargers (less than 15 minutes) . Seems dangerous to have a pure lithium cathode in an aqueous solution. If the coating was to crack in an accident, you would have a major fire on your hands. It is becoming less and less certain that the Boeing 787 batteries are at fault. That aircraft has had many short circuits in related power distribution panels. The on-going investigation may very well discover that shorts in power distribution panels and inadequate battery load/short circuit and high temps protection caused the batteries to over heat etc. Boeing may have to go back to the design table. @ Darius. I agree. A small range extender in any bev is the way to go. It keep the battery in his natural operating range. Complete depletion is not good, overheating is bad, cold is bad also. So a small range extender increase the range and keep the battery in good shape and no need to find a fast charger when you need it. It's impossible to find fast chargers when you need it, except if you are very lucky. It would take 2 millions fast chargers to cover u.s.a roads and it will cost way more then these small range extenders and it's more practical to recharge when you drive. Installing an ultra fast charging station, at every major cross road (highways) in USA, would require only about (25 x 25 = 625) stations. BEV users would never be more than 60 miles from an ultra quick charge station while driving on highways. Each station could cost$4,000,000 to $5,000,000. The total worst case cost would be$3.1B. That's is equivalent to the cost of the last Oil war for a single day or the cost of imported crude oil for a single day.

Progressively multiply the initial installations 10X over the next 10 years or so with one day a year without an Oil war.

By 2023 or so, USA would have enjoyed a total of 10 days without an Oil war and would have an ultra quick charge station every 25 miles on all major highways.

Not to mention that 99% of all charging will be done at home. How often would you stop at a gas station if you left your home with a full tank every morning?

Very, very good news...now we just need to see them do the easy part (haha) and take it from research to production...but man this would be a step up (especially the cycle capacity issue) take me here ASAP.

A near future fuel to use which can be made at home is liquid chlorine and liquid sodium. They are compact and have a high energy density. Liquid sodium can also be used in combination with oxygen from the air. ..HG..

DD, yep those are cell energy densities, and pretty good too. Add the aqueous electrolyte (non flamable) and you may have a fairly safe cell as well, even with a little lithium foil in there (lithium burns in water). However, it's likely a less violent reaction (given the small mass) than having flamable organics like the standard carbonate electrolyte solvents or gasoline exploding. Yes, that's correct, the most dangerous thing about a lithium ion battery is the organic solvent (the gasoline like thing) volitilizing and exploding, just like your gasoline car. Although to be fair, there is more explosive liquid in your gas tank by far than in a typical li ion battery pack. So, your gas tank is way more dangerous than any li ion pack. But hey let's all fear the unfamiliar, it certainly works for the people who own the markets.

I'd be concerned with the rate capability however (the current density)on these cells. Cars need power and energy, but perhaps combined with ultracaps, or a smaller power battery. The lisicon layer is a lower ionic conductivity, and although thin, it will slow down conductivity. It's purpose is two fold, first to control chemical potential on the foil side so that lower driving force is applied to return the li ion to the metal foil, and the second is to prevent the aqueous electrolyte from contacting the metal foil. So, by design, current density has to be lowered somewhat.

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