Achieves the world's highest power output for passive-type bio batteries

Sony Develops “Bio Battery” thatGenerates Electricity from Sugar

When a glucose solution is poured into the white cubes, the Walkman begins to play.When an isotonic drink is poured in, a propeller starts to spin.In the summer of 2007, the Sony-developed bio battery was announced in newspapers, magazines,and TV reports, and evoked a strong response. Carbohydrates (glucose) are broken down to releaseenergy and generate electricity.This bio battery, which is based on mechanisms used in living organism, is not only friendly to theenvironment but also has great potential for use as an energy source.

This prototype bio battery has achievedthe world’s highest power output of 50mW*2 when employed for a passivetype*1 system.These research results were publishedat the 234th American Chemical SocietyNational Meeting & Exposition in August2007 and earned respect from an aca-demic point of view.

■ Bio battery specifications (1 unit)Dimensions: 39 × 39× 39 mmBattery compartment fluid capacity: Approx. 40 cc(effective volume excluding the case)

Maximum power output: Approx. 50 mW

Sony successfully demonstrated bio bat-tery powered music playback with a mem-ory type Walkman and passive speakers(which operate on power supplied by theWalkman) by connecting four bio batteryunits in series. The case of this bio battery,which is made from an organic plastic(polylactate), is designed to be reminiscentof a living cell.

*1 Passive typeA system in which the reactive substances, such asglucose and oxygen, are supplied to the electrodesby a process of natural diffusion. In contrast, systemsin which the reactive substances are supplied by force(for example, using a pump) are referred to as"active type" systems. In general, passive type sys-tems have a simpler structure and are more suitablefor miniaturization. While active type systems are larg-er and more complex, they are more suitable for high-er power applications.

*2 50 mW: According to Sony's research, this is the world'shighest power output as of August 23, 2007.

* Walkman is a registered trademark of Sony Corporation.

Driving a propeller with an isotonic drink

(3)The propeller starts to spin.

Walkman playback using electrical energy extracted from glucose.

(2)Pour the isotonic drink into the biobattery.

(1)Prepare the bio battery, a propeller,and a commercially available iso-tonic drink that includes glucose.

Since 2001, the Kano Laboratory (previously: Ikeda Laboratory) Graduate School ofAgriculture, Kyoto University, Biofunction Science Course has collaborated with Sony inthis area. The results presented here were achieved with technologies developed independentlyby Sony based on this leading-edge knowledge.

The mechanism of living organisms Applied to bio batteries

Electrode

Electrode

From plants

Electrons (e-)

Electrons (e-)

Energy to liveEnergy to live

Enzyme

Enzymes

Electron transport mediator

C6H12O6Carbohydrates

Electrons (e-) Proton (H+) Electrical energy

O2Oxygen

H2OWater

CO2Carbon dioxide

Electron transport mediator

If these electrons could beused outside the system,we'd have a bio battery!

CellsRespiration

Carbon cycling

Carbon is recycled and the amount of CO2 in the atmosphere does not increase.

Glucose has a high energy density

One bowl of rice is about 160 kcal The electrical energy provided by 64 AA alkaline dry cells.

Sun

Plants Animals

What a waste if these had to be eaten for the energy!

Fossil fuel

Photosynthesis

O2Oxygen

H2OWater

C6H12O6Carbohydrates

(glucose)

Fossil fuel power generators, cars, and other systems

Energy to liveLight energy

CO2Carbon dioxide

These increase the amount of CO2 in the atmosphere

Energy Conversion System by Living Organisms on Earth

The Energy Conversion Principles in Living Organisms and the Concept of Generating Electricity with a Bio Battery

Plants create both carbohydrates and oxygenby photosynthesis from carbon dioxide andwater. Animals take up those carbohydrates andoxygen and utilize them as an energy sourceand release carbon dioxide and water. Then thiscycle starts again.Since the carbon dioxide is recycled in this sys-tem, the amount of carbon dioxide in the atmos-phere does not increase. If electrical energy couldbe directly acquired from this cycle, we couldobtain more environmentally friendly energythan that from fossil fuels.Furthermore, renewable energy sources suchas glucose (which is present in plants andtherefore abundantly available) have an extreme-ly high energy density. One bowl of rice (about100 grams) is equivalent to 160 kilocalories,which corresponds to the energy about 64 AAalkaline dry cells.Therefore, this bio battery, which is based on

Energy for activity, that is the ATP and ther-mal energy commonly used in the living organ-ism, can be obtained from the exchange of theelectrons and protons through these two enzy-matic reactions.To take advantage of this living organismmechanism, the energy for activity from insidethe organism must be removed outside theorganism as electrical energy. That is, when theelectrons and protons move from enzyme toenzyme, it is necessary to extract just the elec-trons and divert them through a separate path.Thus Sony used an electron transport media-tor so that electrons could be exchanged smooth-ly between the enzymes and the electrodesthat are the entrance and exit to that detour.The principles of the bio battery are based onthe energy conversion mechanism in livingorganisms. However, in order to create thebio battery, several technologies needed to bedeveloped. These include immobilization ofenzymes that are normally incompatible withcarbon and metal electrodes, electrode struc-tures, and electrolytes.

mechanisms used in living organisms, is notonly friendly to the environment but is also like-ly to be of practical use as an energy source.Sony has focused on these advantages since 2001and has developed an electrical power gener-ation device that uses mechanisms similar tothose in living organisms.

When looking closely at energy conversion sys-tem in living organisms, there are two enzy-matic reactions coupled together: the glucoseoxidation reaction and the oxygen reduction reac-tion. The glucose taken by living organisms isbroken down into carbon dioxide. At the sametime, electrons and proton are extracted throughenzymatic oxidation reactions. On the other hand, oxygen acquired from out-side the organism reacts with both the electronsand protons through the action of other enzymesto generate water through the reduction reaction.

We can create environmentally friendlyenergy by imitating the energy conver-sion system in living organisms

Converting energy from “energy forlife” to “electrical energy”

creating an immobilizing film on electrodes,we have achieved high efficiency in breakingdown glucose and extracting electrons.

(2) Electrical performance improved byelectrolytes optimized for Sony'sunique bio battery structure

Under normal physiological condition, theconcentration of sodium phosphate buffer is typ-ically around 0.1 M. In contrast, however, theconcentration Sony uses for this newly-devel-oped bio battery electrolyte is the unusually highconcentration of around 1 M. This is based onthe discovery that such high buffer concentrationlevels are effective for maintaining the activ-ity of the enzymes when immobilized on theelectrodes through electrostatic interactions. ThusSony has succeeded in significantly improv-ing the electrical generation characteristics.

(3) Electrical performance improved bySony-developed cathode structurethat efficiently acquires oxygen

To make the enzymes which reduce oxygen workefficiently while taking up oxygen efficientlyat the cathode, it is necessary to maintain themoisture content on the cathode electrode at anappropriate level. In this work, we employedporous carbon and cellophane as the separator.By optimizing the structures and fabricationprocesses for these materials, Sony was able

to maintain optimal humidity at the cathode withhigh reaction efficiency.

(4) Prototype of a bio battery thatachieves both high power outputand compactness

Sony has made a prototype bio battery with highpower output and a compact size using thetechnologies described above. This bio batteryis a passive type battery that operates simplyby pouring a glucose solution into a reservoirthat contacts the anode with no stirring required.Furthermore, oxygen is supplied at the cath-ode by natural diffusion. A single unit of thisbio battery, a cube 39 mm on a side, achievesthe world's highest power output, 50 mW.(See the photograph on the first page of this arti-cle.)

●

Sony plans to continue working for improve-ments in electric performance and durabilitywith further development of enzyme immobi-lization methods and electrode materials.Through research and development on a widerange of elemental technologies, Sony plans tomake this bio battery into a commercial prod-uct in the future.

Current(e-) Proton (H+)

Enzyme

Enzyme

Gluconolactone

Separator

Electron transport mediator

Electron transport mediator

This battery has a structure in which a separator is sandwiched between an anode (the electrode that immobilizes an electron transport mediator and the en-zymes that break down the glucose) and a cathode (the electrode that immobilizes the electron transport mediator and the en-zymes that reduce the oxygen).

Electrons and protons are acquired when a solution that contains glucose is sup-plied externally at the anode and is oxida-tively decomposed by the enzymes.

The protons move from the anode to the cathode through the separator. At the cath-ode, oxygen is acquired from the air and water is generated by a reduction reaction between electrons and proton.

As a consequence of above two electro-chemical reactions, electrical energy can be obtained when electrons move through an external circuit.

Unique Technologies for Achieving High Power Output

(glucose -> gluconolactone + 2H+ + 2e-)

((1/2)O2 + 2H+ + 2e- -> H2O)

High-density immobilization of enzymes and the electron transport mediator (1)Sony developed procedures and conditions for main-taining enzyme activity despite high-density immobili-zation.

Buffer concentration higher than what was previously thought possible (2)The buffer material adjusts the pH at the electrodes so that the enzymes can react easily. The buffer con-centration was increased significantly as compared to physiological conditions.

Electrode structure that takes up oxygen efficiently (3)We were able to make the oxygen react efficiently by making it possible for the oxygen in the atmosphere to move through an air layer to the surface of the im-mobilized enzyme film at the inside of the electrode.

The world's highest power output for a passive-type test cell (4)By adopting a balanced design with these technologies, we were able to create a bio battery that achieves a high power output level despite being a passive type in which fuel and oxygen are not forced into the cell.

* Gluconolactone: This is a product of this reaction

and is often used as a food addi-tive.

O2Oxygen

H2OWater

Fuel: glucose

C6H12O6

Cathode

Electrolyte

Anode

Structure of the Newly Developed Bio Battery

The critical issues for achieving the world's high-est power output were how efficiently glu-cose and oxygen could be broken down byenzymes at the electrodes and how much elec-trical energy could be extracted. Here we pre-sent the main points of this research and devel-opment effort.

■ Main Research and DevelopmentPoints (See the figure above)

(1) Electric generation performanceimproved by high-density immobi-lization technologies for enzymesand electron transport mediators

At the anode, the enzymes and electron trans-port mediator must be immobilized at highdensity on the electrode in a state where theiractivities are maintained. In this work, weused two polymers as the material that playsthe role of a glue that holds these materials inplace. This immobilization method holds theenzymes and electron transport mediator fixedin place at high density by using the electro-static interactions of two polymers that haveopposite ionic polarities. By optimizing theionic balance and by developing a process for

Assuring that biomaterials exhibittheir functionality and significantlyincreasing the power generationcapacity

In moving towards practical implementation, we must extractthe potential of the sophisticated systems in living organisms.

Hideki SakaiAssistant ManagerGroup No.1Bio Electronics LaboratoryMaterials LaboratoriesSony Corporation

A New Technology that is alsoFunAlthough we had the basic ideas at the start,the power output levels were essentially zeroat first, and increased only gradually. Theprocess of improving performance took along time. For that reason alone, we wereoverjoyed when the propeller first turned.The members of the group all went out tocelebrate that night.The people who came to gather informa-tion for articles were fascinated, and broughtwith them a wide range of isotonic drinks,asking "will it work with this?" for each ofthem. Of course, if this technology everbecomes practical, we won't be using com-mercial soft drinks. That would only hap-pen in an emergency, although in an emer-gency you would be better off drinking thedrinks yourself.

We Are Also Considering theComplete Carbon CycleAt this time we are only presenting theresults of basic research; this is not the finalform of this device. Since this device canonly use part of the electrical energy storedin glucose, we must increase its genera-tion efficiency. We are moving forwardwith research in the direction of breakingdown gluconolactone to carbon dioxide byusing additional enzymes.We have built a team consisting of specialistsin both electrical engineering and life sci-ences. In addition to fusing the technolo-gies we are also "fusing the people" into acohesive group that is working togetherintently so that we may again create a pre-sentation with similar impact. Keep your eyeon Sony for the future of bio batteries.

Presentation at a Conferencein the United States and thePress ReleaseWe had two purposes in making thisannouncement. First, we wanted to earnsupport from the academic community bypublishing in an academic setting. This isbecause we still need many new ideas, tech-nologies, and materials to move towardspractical implementation.The other purpose was that in publiclyannouncing Sony's results to date in bio bat-tery development, we wanted not only toenergize this field but also to create strongpublic support by having large numbers ofordinary citizens become aware of thiswork.Although prior to publication, we were wor-ried about what sort of reception this workwould receive, by demonstrating high poweroutput even under passive conditions, andfurthermore, by demonstrating somethingactually being operated (we operated aradio controlled car at the conference in theUnited States), our presentation succeededin having a large impact. After this publi-cation, our web site was accessed fre-quently, not only by respected professors,but also by persons in related industries andthe media as well.

The Attraction of this Work asScienceBio batteries involve many aspects thatare of academic interest. The results weachieved were new knowledge and gen-erated either academic papers or patents.As such, it is not unreasonable to call thiswork "leading-edge science."For example, when immobilizing enzymeson electrodes, it was thought that the activ-ity changed with the molecule orientation

and structure. Although we did not go sofar as to control those aspects in the biobattery developed in this work, it is an areain which much research is being carried out,and if biotechnology and electronics are fur-ther fused and advanced, in the future, itwill be possible to freely control the func-tions that biomaterials and systems have.I hope to rapidly increase the performance(including the power output level) of thesedevices by incorporating the latest researchresults such as these in our bio batterydevelopment.Since we are now in an age where prod-ucts are created by combining a variety oftechnologies, it is important, not just for biobatteries, to move forward with research whilecarefully observing other technology devel-opments that are occurring.

My Difficulties in the Pastwere the CatalystI chose physics and chemistry in highschool and didn't study biology. In college,however, life sciences were a requiredcourse, and I suddenly found myself study-ing leading edge topics such as the natureof DNA. Since all I had was a junior highschool level of knowledge, it was difficult.However, at that time I did feel that the ener-gy conversion systems in living organismswere fascinating.In college, I studied catalytic chemistryand then worked on lithium ion batterycathode materials at Sony. Then, in my thirdyear at Sony, when we were consideringwhat new themes to work on at the researchlabs, I recalled the life sciences that hadbeen so difficult in college. This might leadto resolving the issues of high power capac-ities and environmental concern, I thought.One never knows what will prove useful.