10초만에 휴대폰 충전 가능한 배터리 소재 기술 개발

차세대 리튬이온 배터리 나온다…MIT 유학생 강병우씨 초고속 충전 신기술 개발 휴대전화 충전 10초…3년내 상용화 기대

MIT 한인 유학생이 차세대 리튬이온 배터리 기술을 개발해 주목을 받고 있다.

MIT 재료공학부 박사과정에 있는 강병우(34·사진)씨는 지난 12월 과학전문지 ‘네이처’에 지도교수 게브란드 시더와 공저자로 논문을 발표했다. 이 논문은 리튬이온 배터리의 충전시간을 종전보다 최대 1000분의 1까지 획기적으로 줄였고 충전된 전력을 순식간에 강하게 출력할 수 있는 신기술을 담고 있다. 그동안 전기자동차업계의 고민을 해결할 수 있다는 점에서 강씨의 논문은 주목을 끌기 충분했다. 강병우씨를 만나 신기술 개발 동기 등을 들었다.

-연구의 실용적 측면에 대해서 설명해 달라.

“ 과거 전기자동차의 약점은 급가속이 필요한 순간에 충분히 강한 전력을 배터리가 신속하게 내보내지 못한다는 데에 있었다. 신기술은 그 점을 개선할 수 있다. 또한 리튬이온 배터리의 고속충전 기술이 상용화되면 휴대전화는 10초, 랩탑은 1분, 자동차는 30분 이내에 충전이 가능할 것이다. 연구팀은 이미 두개의 전기자동차 배터리업체와 사용 계약도 맺었고 향후 2~3년이면 상용화될 것으로 보고 있다.”

-충전 및 출력 속도를 획기적으로 향상시켰는데 핵심은 무엇인가.

“리튬이온 자체는 전달 속도가 빠른데도 불구하고 전극에 빠르게 흡수가 되지 않아 충전 속도가 더뎠다. 진입로가 하나인 고속도로를 상상하면 이해하기 쉽다. 리튬이온이 전극을 통과할 때 일종의 병목 현상이 발생해 충전 속도가 느려지는 것이다. 우회로가 있으면 교통 흐름이 빨라지는 것에 착안해 리튬이온이 빠르게 전극에 흡수될 수 있도록 컨덕팅하는 특수 물질(LiFePO4)를 전극 표면에 코팅시켰다.”

-기존 배터리 기술은 왜 LiFePO4를 이용할 생각을 못했는가.

“LiFePO4 는 배터리에 사용하기에는 느리다고 인식된 물질이다. 그 견해가 뒤집힌 것도 비교적 최근의 일이다. 그런데 속도 말고도 LiFePO4에는 또다른 잇점이 있다. 상당히 안정적이어서 폭발 위험이 낮다. 그래서 랩탑이나 자동차용 배터리에 사용하기에 대단히 이상적인 물질이다.”

-다음 연구 단계는.

“원래 연구는 파워에 중심을 두고 있었다. 많은 전기를 저장하는 에너지 밀도에 방점이 찍힌 것이 아니다. 초고속으로 충전이 되면서도 오랜 시간 지속하는 배터리다. 랩탑으로 치면 뉴욕에서 비행기 타고 서울까지 충전 필요없이 사용할 수 있는 기술이 진정한 꿈의 배터리일 것이다.”

전자신문 | 입력 2009.03.12 13:24 |

 보통 2∼3시간 걸리는 휴대폰 배터리 충전시간을 10초 정도로 크게 단축할 수 있는 기술이 개발됐다.
11일 포브스 등 주요 외신은 미국 MIT의 게브란드 세데르 교수와 한국인 연구원 김병우씨가 기존 리튬이온 배터리의 충전 속도를 100배 가량 높일 수 있는 배터리 소재 기술을 개발했다고 일제히 보도했다.

연구진은 배터리 속의 에너지 저장 물질인 리튬이온 인산에 수 나노미터 두께의 유리 필름을 코팅, 충전 입자의 운동성을 크게 높임으로써 배터리 충·방전 속도를 획기적으로 향상시켰다고 설명했다. 이 기술을 이용하면 휴대폰은 10초 만에 충전할 수 있고 전기 자동차의 출력은 10배 가량 높아질 것으로 기대했다.

이번 연구성과는 12일자 과학저널 네이처에 게재됐으며, 이미 벨기에 배터리 소재 업체와 라이선스 계약이 이뤄져 이르면 2011년 초에 상용 제품을 만나 볼 수 있을 것으로 예상된다.

세데르 교수는 "이 방식을 활용하면, 자동차에 주유하듯이 전자기기를 빠르게 충전할 수 있을 것"이라며 "시간 단위에서 초 단위로 배터리가 충전된다는 것은 새로운 응용기술을 불러와 라이프스타일의 변화로 이어질 것"이라고 말했다.

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몇 초 만에 충전되는 작고 가볍고 오래 가는 리튬 배터리가 개발돼 휴대전화와 전기자동차에 일대 혁명을 예고하고 있다. 매사추세츠공대(MIT) 연구진은 기존 물질을 새로운 방식으로 이용한 이 배터리가 2~3년 안에 시판될 수 있을 것이라고 네이처지 최신호에 발표했다.

현재 사용되고 있는 재충전식 리튬(LiFePO4) 배터리는 많은 양의 에너지를 축적해 장시간 사용이 가능하지만 에너지 방출 속도가 느려 가속보다는 일정한 속도의 주행에 적합하며 재충전에도 많은 시간이 소요된다는 단점을 갖고 있다.

이는 전하를 띤 리튬 원자, 즉 이온들이 전자와 함께 배터리 물질 안에서 움직이는 속도가 너무 느리기 때문인 것으로 생각돼 왔다.

그러나 연구진은 이런 속도의 문제가 이온이 아니라 이온이 물질에 분포돼 있는 나노 수준의 터널들을 통과해 전자를 목표지점까지 운반하는 방식에 있다는 사실을 발견했다.

이들은 마치 하나로 합쳐지는 지선도로망처럼 이온들을 터널 속으로 밀어넣는 인산리튬 코팅으로 문제 해결을 시도했고 이온들은 순식간에 터널을 통과했다.

이런 기술을 적용하자 작은 휴대전화 배터리는 10초 만에 충전이 끝났다.

연구진은 현재 6~8시간이 걸리는 하이브리드 전기차량용 배터리 재충전이 이론적으로 5분이면 끝날 것으로 예상하지만 이를 위해서는 전압이 지금보다 훨씬 강화돼야 할 것으로 보고 있다.

또 이처럼 새롭게 코팅된 LiFePO4 배터리는 여러번 재충전을 거듭해도 약해지지 않는 것으로 밝혀져 더 작고 더 가벼운 배터리 개발의 길을 트게 됐다고 연구진은 밝혔다.

이들은 미국 정부의 지원으로 개발된 이 배터리에 대해 이미 두 회사와 라이선스 계약을 체결했다고 밝혔다.

youngnim@yna.co.kr
(시카고.파리 로이터.AFP=연합뉴스)
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MIT researchers announce lithium ion battery breakthrough; Industry experts respond

Today’s lithium ion battery technology as it exists today is scarcely an ideal energy storage device. It’s relatively expensive. The chemical formulation that optimizes for energy storage has safety issues and is limited in how fast it can charge and discharge as well as in the number of charge/discharge cycles. The formation that’s optimized for charge/discharge time (some usually some form of LiFePO4 and referred to as “lithium iron phosphate”), has a higher power capacity and is much safer, but is quite poor at energy storage.

Imperfect though they are, as things stand now lithium ion batteries are also a necessary link in the attempt to build a new energy industry that includes alternate forms of renewable but intermittent energy sources, like solar and wind, that require some form of energy storage. Batteries play an even more important role in the quest for a practical plug-in electric hybrid vehicle (PHEV) (aka extended-range vehicle or ERV) that requires a battery that can enable at least 40 miles of driving before the car’s small internal combustion engine kicks in for longer distances. Improvements in battery technology are necessary before renewable energy and petroleum-free transportation can be a reality.

This week MIT researchers Gerbrand Ceder and Byoungwoo Kang published an article in Nature magazine that reports on their research at MIT into a new lithium ion-based battery technology that can perform a complete discharge in under 10 seconds. You can read a summary of the paper here on ArsTechnica; The Nature article itself is behind a paid reg wall. Here’s an even terser summary: The new battery technology, which is based on the power-centric LiFePO4 chemistry, makes for rapid charge and discharge times, but does not improve energy storage density. The research is being greeted with descriptions such as “revolutionary” and “game changing”

The charge and discharge figures are impressive:  "... the authors tweaked the cathode to allow higher currents to be run into the cell. Increasing the rate by a factor of 100 dropped the total capacity down to about 110mAh/g, but increased the power rate by two orders of magnitude ... compared to traditional lithium batteries. Amazingly, under these conditions, the charge capacity of the battery actually increased as it underwent more charge/discharge cycles. Doubling the charge transport from there cut the capacity in half, but again doubled the power rate. At this top rate, the entire battery would discharge in as little as nine seconds. That sort of performance had previously only been achieved using supercapacitors. "

Some examples of what this performance might mean for common battery applications: “A 1Wh cell phone battery could charge in 10 seconds, but would pull a hefty 360W in the process. A battery that's sufficient to run an electric vehicle could be fully charged in five minutes—which would make electric vehicles incredibly practical—but doing so would pull 180kW, which is most certainly not practical.”

Leaving aside the problems of whether such rapid charging is practical (a concern that’s independent of battery technology), what conclusions can we draw from what’s known so far about this research? After all, not all university research results in a viable product. What questions should we be asking about this new formulation?

I went to three notables in the battery industry: Dr. Yevgen Barsukov, senior applications developer at Texas Instruments and TI’s go-to guy for batteries, Dr Robin Tichy, Technical Marketing Manager, Micro Power Electronics, a battery pack d esign and manufacturing house, and Dr. Christina Lampe-Onnerud, founder and CEO of Boston-Power, a manufacturer of the Sonata line of rapid-charge batteries currently being sold for laptops.

Dr. Barsukov of TI agrees that the discovery is important, but perhaps not as earth-shaking as it might initially appear. I’ll give his full, detailed response here (and you should read the article linked to above to understand all of his references): “This appears to be an important discovery that will help reduce diffusion limitations in LiFePO4 and possibly other materials.

“However, it is important to understand that that diffusion is not the only limiting factor in battery kinetics. Other important factors are ohmic conductivity of bulk active material and ionic conductivity of the electrolyte in the pores and separator, as well as electron transfer resistance on the surface. In fact these factors contribute 30-60% of total cell resistance depending on the design and will limit charging rate regardless of diffusion.

 “The relative contribution of these factors vs diffusion depends on the thickness of active material. Typical cells have layer of material which is 20-50um thick. So even if you drastically improve diffusion inside particles it will change only the small portion of overall impedance.

“ It appears that the cell they tested in the lab and reported charge rates with has extremely thin active layer, which hides this effect of bulk material resistance. Any modern LiFePO4 is already prepared in form of nano-particles which makes diffusion contribution quite low already because of short diffusion path in nano-particles. So if say A123 sys would make a cell with similar thickness of active material it could also be charged extremely quickly.

“But (!) it can’t be done for real batteries because it will mean a lot of current collectors that only contribute weight but no capacity and tiny active material, resulting in very bad energy density not acceptable to most applications.

“To summarize: This is some useful discovery to improve diffusion behavior and might find widespread use. 

“However the claims on magnitude of improvement are exaggerated. Even if diffusion impedance would be reduced to zero, it would only reduce overall cell impedance by 40% for a typical cell. That is the actual improvement to charge rate that can be expected in normal commercial cells.”

Next, here are the just-as-blunt comments of Dr. Tichy of MicroPower, the battery pack manufacturer: “I am struggling to see how the technology could change the market landscape.  

“Historically, Li-ion batteries were designed to maximize capacity and traditional materials served this purpose very well. More recently, materials like iron phosphate and manganese spinel have been designed for high c-rate applications (power tools, for example). In the case of the high rate cells, the capacity of the material is lower, but the cell capacity is limited by the size requirements of the current collectors and battery pack components. The charge time is limited by the design constraints on the power supply. The article makes reference to these limitations.

“So, this material change doesn't seem to compete with traditional high capacity cells, and it would have the same limitations as the high rate cells.”

And finally, Dr Lampe-Onnerud of Boston Power. I have interviewed Dr Lampe-Onnerud several times over the years as she has worked to bring a new battery formulation to market, including raising capital, perfecting the technology, developing manufacturing facilities, and establishing a reliable, repeatable process for an affordable pbattery product line. Her comments are both measured and tactful:

“Lithium-ion has earned its place as the battery technology of choice for rechargeable, efficient energy storage. Materials science research such as what is being done by Gerbrand Ceder and Byoungwoo Kang promises to be another strong step along the way to adding even more value. 

“Many in the industry have believed for some time now that lithium-ion batteries could be made to charge much more quickly, and this research appears to reinforce that belief. We’ll all watch closely as the process enters the stage of moving beyond a laboratory environment and into something that can be mass manufactured and delivered to the market. Batteries are pretty complicated devices, so that’s not a simple task. It will require a great deal of effort and we support their hard work….” (She also put in a strong plug for Boston-Power’s battery technology, but I cut that.)

Revolutionary? Game-changing? Maybe not. But important? Yes – as is every step forward we take  in improving our understanding of energy storage.

Reader Comments
at 3/13/2009 9:03:25 AM, Meredith Poor said:
High charge rate batteries might, in many cases, make it possible to recharge during operation, such as having rechargers built into traffic intersections for recharging electric cars as they wait for lights. Many hand held tools are shifted from stations that could host a recharger to stations that can't in a matter of seconds, such as on an automobile production line. This may end up creating a new class of tools (some of which might presently run on compressed air) that are pulled off the recharger for a minute or two out of tasks that might run for, say, fifteen minutes. Example: replacing or rotating tires.

at 3/13/2009 2:50:18 PM, VaD said:
But not so good, if we have to pay for a speed with a lot of extra power consumption.

at 3/13/2009 2:52:08 PM, Mark said:
Too often both the popular press as well as industry publications (including EDN) blindly parrot outrageous claims from both universities and industrial labs, leaving the trusting reader to expect fabulous new technology in their local store within 3 months. Examples include small things (such as nanoparticles replacing lightbulbs) to big things (like Segway). THANK YOU FOR TAKING THE TIME TO PRESENT an intelligent and balanced report.

at 3/13/2009 2:56:53 PM, Steve said:
I couldn't help but wonder if an extremely fast charge-cycle device wasn't exactly what the EV folks need to improve the efficiency of dynamic braking. I am guessing that current technologies do not gain much of an advantage in this braking/recharge cycle in that the total braking time is so short. . . . . but, perhaps a combination of current technology batteries for extended run-time, combined with this newer technology for the "short burst" braking/accelleration mode might yield something ?? Just a guess. . ..

at 3/13/2009 2:59:50 PM, Eric said:
Concise, honest, technical, contrary to popular excitement... I like this article.

at 3/13/2009 3:00:19 PM, TomW said:
Most people don't realize that the energy transfer rate at the gas pump can be 10MegaWatts! Even if an electric car is 10X the efficiency of a combustion engine, most peole do not want to very close to wire carrying 1MW. Charging the main battery in an electric car in such a short time is not practical. Of course short term storage for acceleration and regenerative braking would use a much smaller battery.

at 3/13/2009 3:14:03 PM, D. Marcroft said:
I find the increased discharge rate to be very interesting for certain applications. But what are the heat implications, meaning how much heat is generated and is the battery able to sustain such rise without destroying itself. Has any research been done to insure the battery will survive multiple discharges....???? The battery car manufacturers go to great length to remove the heat while charging and discharging batteries. Controlling the heat rise is big problem.

at 3/13/2009 3:39:01 PM, Meredith Poor said:
The skepticism is certainly justified. Clearly the charge rates represent huge current draws over a short period of time, but this is not necessarily any different from battery charging effiencies now, which may be no better than 50%. It would seem kind of obvious that recharging a car with 40 miles worth of electricity in five minutes is going to be a huge energy transfer. Current gasoline engine efficienies, however, are pretty miserable as well (less than one quarter of the energy of the gasoline ends up moving the car). The more the basket of alternatives is examined, the less material the efficiency issues appear to be.

at 3/13/2009 5:23:39 PM, GKRON said:
I WOULD LIKE TO SEE THE RESPONSE OF cEDER AND kANG TO THESE VARIOUS [ SOME RATHER SPURIUS ] COMMENTS

at 3/13/2009 6:14:38 PM, Mad Inventor said:
This is a case of My theoretical system costing a million dollars, with a cherry picked one in a thousand actually worked, microscopic test sample that''s been tested for an hour, can beat your mass produced $5 piece of junk that has a 2 percent reject rate and only lasts 18 months. More informative when I can buy them at the local electronics store. You can already get batteries with double the lifetime and performance and people won''t buy them because they cost two times as much because they have better packaging and electrodes. We want it all.

at 3/13/2009 10:24:08 PM, GlennW said:
The cost to run a prius, per mile, is very much influenced by the cost of the battery and the # of charge cycles. So, if we increase the # of charge cycles, we can reduce the cost per mile. The artical is not clear if that is what happens w/ these new batteries, when charging/discharging at the traditional rates.

at 3/14/2009 12:17:45 AM, StevenCYWang said:
This is a breakthrough in the battery energy storage industry. However, urgently needs compatibility, reliability, MTBF to define the application-specific solutions for all industries. As a new energy technology platform, the best solution of energy roadmap should be created after integrating green technologies, battery technologies, electric power technologies and solar PV technologies with high vision.

at 3/14/2009 1:36:25 AM, RR said:
Could be another cold fusion episode.