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{{Original research|date=January 2025|reason=}}{{Cleanup|reason=Undue weight lent to the promising aspects|date=October 2023}}
A '''sugar battery''' is an emerging type of [[biobattery]] that is fueled by [[maltodextrin]] and facilitated by the [[Catalysis|enzymatic catalysts]].

The sugar battery generates [[electric current]] by the [[Redox|oxidation]] of the [[Glucose|glucose unit]] of [[maltodextrin]]. The oxidation of the [[organic compound]] produces [[carbon dioxide]] and electrical current. 13 types of [[enzyme]]s are planted in the battery so that the reaction goes to completion and converts most [[chemical energy]] into [[electrical energy]]. The experimental results have shown that the sugar battery of the same mass can store at least two times, up to ten times [[electrical energy]] than the traditional [[lithium-ion battery]] can. The sugar battery is expected to be the next general type of mobile electric power source and the possible power source for [[electric car]]s. But the sugar battery's [[Voltage|output voltage]](0.5V) is lower than that of the lithium-ion battery (3.6&nbsp;V), which causes its [[electric power]] (the rate of electrical energy transfer) to be low.

[[Sony]], a Japanese corporation, first published the theory of sugar battery in 2007. A research team led by Dr. Y.H. Percival Zhang at [[Virginia Tech]] provided the latest version of it in 2014.

== History ==
[[Sony]], a Japanese corporation, first published the theory of sugar battery in 2007. This type of sugar battery is air-breathing and utilizes the oxygen as the [[oxidizing agent]]. The battery achieved expected high [[energy density]] and reasonable output voltage. Then the company shifted its researching direction in 2012 to the [[paper battery]], which uses paper as fuel. After 2013, Sony didn't release more information about their research project on the [[biobattery]].<ref name=":3">{{Cite web|url=http://www.sony.net/SonyInfo/News/Press/200708/07-074E/index.html|title=Sony Develops|website=Sony Global - Sony Global Headquarters|access-date=2019-11-05}}</ref><ref>{{Cite news|url=https://www.bbc.com/news/technology-16288107|title=Bio battery turns paper to power|date=2012-03-08|access-date=2019-11-09}}</ref>

A research team led by Dr. Y.H. Percival Zhang at [[Virginia Tech]] started the project of the sugar battery in 2009. The team first focused on the connection with the [[hydrogen economy]]. In 2014, they published their research on the sugar battery that utilizes enzymes in oxidization. This type of sugar battery reached a high [[energy density]]. The sugar battery was expected to be realized in an application in 3 years.<ref name=Zhang2009>{{cite journal |last1=Zhang |first1=Y.-H. Percival |title=A sweet out-of-the-box solution to the hydrogen economy: is the sugar-powered car science fiction? |journal=Energy & Environmental Science |date=2009 |volume=2 |issue=3 |pages=272 |doi=10.1039/B818694D }}</ref><ref name=pmid24445859>{{cite journal |last1=Zhu |first1=Zhiguang |last2=Kin Tam |first2=Tsz |last3=Sun |first3=Fangfang |last4=You |first4=Chun |last5=Percival Zhang |first5=Y. -H. |title=A high-energy-density sugar biobattery based on a synthetic enzymatic pathway |journal=Nature Communications |date=May 2014 |volume=5 |issue=1 |pages=3026 |doi=10.1038/ncomms4026 |pmid=24445859 |bibcode=2014NatCo...5.3026Z |doi-access=free |hdl=10919/87717 |hdl-access=free }}</ref>

In 2017, Dr. Y.H. Percival Zhang was arrested by the [[Federal Bureau of Investigation|FBI]] (has been released in 2019). The federal government accused Dr. Zhang of over twenty counts {{example needed|date=September 2021}}. Dr. Zhang then resigned from his position at Virginia Tech. Since then, Virginia Tech stopped publishing the result of the sugar battery study.

In 2019, Dr. Zhang was acquitted of 19 counts but found guilty of conspiring to commit federal grant fraud.<ref>{{Cite web|url=https://www.justice.gov/usao-wdva/pr/former-virginia-tech-professor-found-guilty-grant-fraud-false-statements-obstruction|title=Former Virginia Tech Professor Found Guilty of Grant Fraud, False Statements, Obstruction|date=2019-02-25|website=www.justice.gov|access-date=2019-11-09}}</ref>

Since 2014, Several Chinese universities, including [[Zhejiang University]] and [[Tianjin University]], started working on researches on the sugar battery.

== Potential benefits ==
Compared to the currently widely used [[lithium-ion battery]], the sugar battery has potential benefits in many aspects.

=== Safety ===
Compared to the traditional lithium-ion battery, sugar battery does not require toxic metals in manufacturing and releases only carbon dioxide gases. The production of the standard lithium-ion battery would require several metals, including but not limited to [[lead]] (Pb), [[Cadmium]] (Cd), and [[Chromium]] (Cr). The leakage of these metals accumulates inside the vegetables and animals that humans depend on and finally reach humans.<ref>{{Cite web|url=https://eandt.theiet.org/content/articles/2016/10/lithium-ion-batteries-found-to-produce-toxic-gases/|title=Lithium-ion batteries found to produce toxic gases|last=Loughran|first=Jack|date=2016-10-24|website=eandt.theiet.org|access-date=2019-10-29}}</ref> Besides, overheating may cause the lithium-ion battery to release up to 100 types of harmful gases to the human body. In some instances, the rechargeable lithium-ion battery explodes to cause a physical casualty.

=== Availability of fuel ===
The primary fuel of the sugar battery, [[maltodextrin]], can be enzymatically derived from any starch, such as corn and wheat.<ref>{{Cite web |last=PubChem |title=Maltodextrin |url=https://pubchem.ncbi.nlm.nih.gov/compound/Maltodextrin |access-date=2024-04-04 |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref> Therefore, maltodextrin is renewable. In contrast, the primary constructing block of the lithium battery, [[lithium carbide]], is an unrenewable compound that occurs naturally in the earth. To obtain it, manufacturers need to mine, extract, and purify.<ref>{{Cite web|url=http://cleanenergytrust.org/enough-lithium-feed-current-battery-market-demand/|title=Is there enough lithium to feed the current battery market demand?|date=2018-02-13|website=Clean Energy Trust|access-date=2019-11-05}}</ref>

=== Environmental friendliness ===
The products of oxidation reaction inside the sugar battery are mainly water, carbon dioxide, and recyclable [[adenosine triphosphate]] (ATP). Whereas the disposal of lithium batteries produces heavy metals that contaminate the soil. According to the field experiments, several vegetable species extract the heavy metals from soil and store concentrated metals inside. The carbon dioxide produced by the sugar battery does not contribute to the crisis of [[greenhouse gas]], because the sugar battery uses bio-fuel that is [[Carbon neutrality|carbon-neutral]]. Since the production of the fuels involves the [[photosynthesis]] of plants, which removes carbon dioxide from the atmosphere, the new greenhouse gas released is counted as a net-zero [[carbon footprint]].<ref name="Chen et al 2014">{{cite journal |last1=Chen |first1=Ying |last2=Wu |first2=Pingping |last3=Shao |first3=Yufang |last4=Ying |first4=Yibin |title=Health risk assessment of heavy metals in vegetables grown around battery production area |journal=Scientia Agricola |date=April 2014 |volume=71 |issue=2 |pages=126–132 |doi=10.1590/S0103-90162014000200006 |doi-access=free }}</ref><ref>{{Cite book |last1=Lodish |first1=Harvey |last2=Berk |first2=Arnold |last3=Zipursky |first3=S. Lawrence |last4=Matsudaira |first4=Paul |last5=Baltimore |first5=David|last6=Darnell |first6=James |date=2000 |chapter=Oxidation of Glucose and Fatty Acids to CO2 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK21624/ |title=Molecular Cell Biology |edition=4th |isbn=0-7167-3136-3 }}</ref>

=== High energy density ===
The complete [[Redox|oxidation reaction]] of unit glucose in 15% [[maltodextrin]] solution enables the sugar battery to have an [[energy density]] of  596 Ah kg<sup>−1</sup>, which is over twice as high as that of the widely used lithium-ion battery(~270 Ah  kg<sup>−1</sup>).  In application, this means that the lifetime of the battery increases. Alternatively, the mass and volume of the battery reduce.<ref name=pmid24445859/>

== Drawbacks ==
As a newly invented idea, the sugar battery is not well developed yet. It has several drawbacks in the current state.

=== Relatively low voltage ===
Though the output voltage of sugar battery (0.5&nbsp;V) exceeds that of former enzymatic fuel batteries by the use of various enzymatic catalysts, it is still much lower than that of the commonly used lithium-ion battery (3.6&nbsp;V).<ref name=Zhang2009/> That results in low [[electric power]]. In application, it means that the sugar battery takes more time to charge the appliance than the lithium-ion battery does.

=== Water requirement ===
The production of the fuel of the sugar battery and the reaction inside the sugar battery require water to complete. If the battery is going to be used widely around the world, it will undoubtedly lead to a requirement for a considerable amount of water. Under current conditions, the consequence will be further intensifying the [[water scarcity]].<ref>{{Cite web|url=https://www.renewableresourcescoalition.org/biomass-energy-advantages-disadvantages/|title=Biomass Energy Advantages & Disadvantages {{!}} Renewable Resources Co|date=2016-12-09|website=Renewable Resources Coalition|access-date=2019-11-05}}</ref> Which is a weak argument against, because any type of farming or many other industrial process consume water in larger amounts.

== Design ==
The design of the sugar battery is based on the theory of the [[primary cell]]. The main components of a sugar battery are an [[anode]], a [[cathode]], a [[membrane]], and a synthetic pathway. The [[Redox|oxidation reaction]] happens in the anode side where the fuel, [[maltodextrin]], is oxidized. Electrons are released from the fuel and go through the wire connected to the cathode, forming a [[Direct current|direct electrical current]]. Electrical appliances are installed between anode and cathode so that the electrical current powers the appliance.<ref name=pmid24445859/>

=== [[Anode]] ===
The [[Redox|redox reaction]] that produces the electrical current happens in the synthetic pathway, where 13 [[enzyme]]s, such as [[glucose 6-phosphate]] and [[phosphoglucomutase]], act as [[Catalysis|catalysts]] (the substance that is both [[Reagent|reactant]] and [[Product (chemistry)|product]]). The fuel, [[maltodextrin]], is divided from [[polymer]] to [[monomer]] and then oxidized into carbon dioxide and [[hydrogen ion]]s during four reactions. The reactions involve the enzymatic catalysts, but since they act both as reactant and product, the amount of the enzymes does not decrease in the end so that they can keep facilitating the reaction. At the end of the reaction, One [[Glucose|glucose unit]] and a certain amount of water can produce 24 electrons. The electrons then flow to the [[cathode]] through the wire, causing an [[Electric current|electrical current]] flowing from cathode to anode.<ref name=pmid24445859/><ref name="Chen et al 2014"/>

=== Synthetic pathway ===
The synthetic pathway is composed of 13 [[enzyme]]s to ensure the [[Redox|redox reaction]] goes into completion (that is, 24 electrons produced per glucose unit). By adding all these [[Catalysis|catalytic]] enzymes into the pathway, the overall chemical equation goes as:

:<chem>C6H10O5 + 7H2O ->24e- + 6CO2 + 24H+</chem><ref name=pmid24445859/>

Theoretically, one [[maltodextrin]]'s glucose unit (C<sub><sub>6</sub></sub>H<sub><sub>10</sub></sub>O<sub><sub>5</sub></sub>) generates 24 electrons, which makes the sugar battery's maximum [[current density]] 35% higher than the maximum current density of a similar system based on 2 [[dehydrogenase]]s.<ref name=pmid24445859/> Practically, the researchers at Virginia Tech measures the [[faraday efficiency]] (the percent of measured output against theoretical output) of the sugar battery's redox reaction. The outcome was 97.6±3.0% under oxygen-free conditions for the anode compartment, suggesting high efficiency in the electron transmission.<ref name=pmid24445859/>

Different from the natural pathway, which utilizes NADP ([[nicotinamide adenine dinucleotide phosphate]])-dependent enzyme, the synthetic pathway makes use of the other cytosolic enzymes to mediate the reaction. As a result, the sugar battery does not depend on the use of complex organic chemicals (for example, [[adenosine triphosphate]]), which are expensive and unstable.<ref name=pmid24445859/><ref name=Zhang2009/>

== Improvements ==
The researchers developed the design of the sugar battery from the prototyped [[Enzymatic biofuel cell|enzymatic fuel cells]], which use enzymes as [[Catalysis|catalysts]] in the [[Redox|redox reaction]]. Based on the design of regular enzymatic fuel cells, the sugar battery employs several methods to enlarge the effect produced by the [[enzyme]]s so that the overall efficiency of the battery is improved.

=== Non-immobilized enzymes ===
The enzymes in sugar battery are no more fixed to the [[electrode]], nor entrapped in a limited space near the electrode. The enzymes in the sugar battery can move freely in a larger space and retain the enzymatic activity. To sustain high-speed [[mass transfer]], the researchers immobilized [[Vitamin K|vitamin K3]] to the electrode. The corresponding experiments suggest that the non-immobilization method helps the sugar battery to reach a higher and more stable [[energy density]] level than the regular enzyme fuel cells with [[immobilized enzyme]]s. Hence, the energy density of the sugar battery increased so that the battery life extended.<ref name=pmid24445859/>

=== Thermo Enzymes ===
Thermoenzymes, enzymes with high [[thermostability]], are used as the non-immobilized enzymes to ensure stability. In the sugar battery, the thermo enzymes are produced by [[Escherichia coli]]. Then the enzymes are purified through heat precipitation method and put into use.<ref name="Chen et al 2014"/>

=== Synthetic catabolic pathway ===
The [[Redox|oxidation reaction]] inside the sugar battery happens in a synthetic catabolic pathway, which contains 13 [[enzyme]]s.<ref name=pmid24445859/> This pathway is constructed as air-breathing rather than closed so that the researchers ensure the air pressure inside the battery stable and the oxidation reaction goes into completion. The enzymes act as [[Catalysis|catalysts]] so that the total amount of them remains the same. Therefore, the overall reaction consumes only the fuel and water while the enzymes recycle in the system. According to the lab experiments, the sugar battery reaches an electron-transmission efficiency of almost 24 electrons per [[monomer]] [[glucose]], which is the basic unit of organic fuels. In comparison, the oxidation reaction in the prototyped [[Enzymatic biofuel cell|enzymatic fuel cells]] could only generate 2 electrons per glucose unit, resulting in low [[energy density]].<ref name=pmid24445859/>

== See also ==
* [[Lithium-ion battery]]
* [[Biobattery]]
* [[List of battery types]]
* [[Paper battery]]
* [[Enzymatic biofuel cell]]

== References ==
{{Reflist}}

== External links ==
* https://vtnews.vt.edu/articles/2014/01/012213-cals-battery.html
* https://www.youtube.com/watch?v=yYaj2mrsWlc
{{Virginia Tech|state=collapsed}}

[[Category:Virginia Tech]]
[[Category:Battery types]]
[[Category:Rechargeable batteries]]