The Sugar Battery

Sugar is a natural, very concentrated source of energy; so it may make sense to generate electricity using it.
A research team at Virginia Tech has developed a sugar battery (or more accurately, fuel cell) they claim is not only cheaper, refillable and biodegradable, but also has “unmatched energy density”.
While not a new development, other sugar batteries in the past have had issues with energy density; frequently needing refilling.
Initially the team is looking to power small gadgets with their development that they believe could be on the market within 3 years.
The battery combines maltodextrin, which is derived from starch, with air to generate electricity and water as the main by-products. 
“We are releasing all electron charges stored in the sugar solution slowly step-by-step by using an enzyme cascade,” says lead researcher, Y.H. Percival Zhang, an associate professor of biological systems engineering in the College of Agriculture and Life Sciences and the College of Engineering..
A paper on the battery by Professor Zhang has been published in the journal Nature Communications; which states: “Enzymatic fuel cells containing a 15% (wt/v) maltodextrin solution have an energy-storage density of 596 Ah kg−1, which is one order of magnitude higher than that of lithium-ion batteries.”
The battery’s fuel raises the controversial issue regarding using food crops as a source. Professor Zhang has this covered too – he has previously published on the topic of extracting starch from non-food crop sources. 
The apparently very green Professor Zhang has also previously published an article on a new process to economically extract hydrogen in an environmentally friendly way to power vehicles.
Other novel battery, supercapacitor and energy storage concepts we’ve covered in the past (some of which are now used commercially) include.
Porous silicon
Wood battery
Greener lithium-ion batteries using plants
Lithium polysulfide
“Rust” battery
Zinc air
Iron phosphate
Molten salt 
Iron based flow
Vanadium based flow
Liquid metal
Silicon air