in almost every portable electronic device.

スマートフォンやノートパソコン

They're in smartphones, laptops, and even in our cars.

自動車にも

In fact, batteries are one of the keys to realizing

電池は再生可能エネルギー100％の 未来を実現する鍵なの

a 100% renewable energy future.

2018年時点で 500万台以上の電気自動車が

In 2018, there were over five million electric cars on the road,

ハイブリッド車を含めて 普及しており

which includes both hybrid vehicles

その人気は高まり続けている

and fully battery powered electric cars.

私たちの生活に欠かせない 電池の仕組みと―

And their popularity only continues to grow.

リチウムイオン電池の特長に迫る

Since batteries are powering more and more of our lives,

電池の種類はさまざまで―

why don't we explore how exactly batteries work,

それぞれ素材も形状も充電能力も異なるが

and what makes lithium-ion batteries so special?

基本的に 電池は電気化学セルでできている

Now, there are a bunch of batteries out there,

そして電気化学セルの素材が―

made of different materials, in different shapes,

電池の両端にあるプラスとマイナスを作り出す

and with different charge capabilities.

電気化学セル内には 電気を作るための主要部分がある

But on the most basic level,

電池の両端を正と負に分ける２つの電極よ

batteries are composed of electrochemical cells.

負極はアノードで

And the materials that make up an electrochemical cell

正極はカソードと呼ばれる

can create the positive and negative sides

アノードとカソードの間には電解質があり―

you see on the either end of that battery.

荷電イオンを２つの電極へ運ぶ 大事な役割を担っている

Inside a single electrochemical cell,

電解質は液体か個体

there are a few main parts

[番組ホスト　マレン･ハンスバーガー]

that help the cell create electricity.

化学反応を妨げない素材ね

Two electrodes, which are the materials

中央には―

that make the battery ends positive or negative.

セパレーターがあり 正極と負極を切り離している

The negative side is called the anode,

懐中電灯をつけるとしよう

and the positive side is called the cathode.

外部回路でアノードと電球 懐中電灯とカソードをつなぐ

The next part is called the electrolyte,

回路に電荷を加えると―

which sits between the anode and the cathode.

アノードと電解質の間に化学反応が起きる

And this is important, because it's what enables

すると電子が放出され アノードにイオンが残る

charged ions to flow between the two electrodes.

放出された電子は電気として回路を通り カソードへ移動する

The electrolyte can be liquid or solid,

同時に電解質は アノードに残されたイオンを―

or any material that helps the chemical reaction flow smoothly.

セパレーターを通して カソードの電子の元へ運ぶ

And finally, there's a semipermeable layer

この一連の過程を―

that keeps everything separate

酸化還元反応と呼ぶ

so that we can control the reaction.

レドックス反応とも言われるわ

Now, if we wanted to power, say, a flashlight,

酸化とは物質が電子を失うこと

you would add an external circuit

還元は電子を受け取ることよ

that connects the anode to the light bulb

電池性能は―

and the flashlight to the cathode.

エネルギー密度と出力密度で決まる

When we add a charge to this circuit,

２つの違いを明らかにする いい例えがある

we initiate a chemical reaction

マグカップと口の狭い大きな水差しを想像して

between the anode and the electrolyte.

水がエネルギーだとして両方を水で満たす

This releases electrons

水差しは容量が大きく―

and leaves leftover ions at the anode.

より多くの水を蓄えられる

These released electrons

でも水を注いでみると―

will travel through our circuit as electricity,

マグカップのほうが ずっと速く水を排出する

ending up in the cathode.

マグカップが高出力ということね

At the same time, the electrolyte

エネルギー密度は 単位質量あたりのエネルギーの量よ

will help the ions they left behind at the anode

エネルギー密度が高ければ―

flow through the semipermeable barrier

小さな質量に 大きなエネルギーを蓄えられる

and meet the electrons at the cathode.

一方の出力密度は―

This whole process is called

単位質量あたりの出力のこと

a reduction-oxidation reaction,

出力密度が高ければ―

also commonly referred to as a redox reaction.

短時間で多くのエネルギーを放出できる

Oxidation is where a material loses electrons,

高エネルギー密度で 低出力密度のデバイスは―

and reduction is when it accept electrons.

大量のエネルギーを蓄えられ 減りが遅いということ

Now, when we talk about battery performance,

例えば あなたのスマートフォン

we have to consider both energy and power density.

バッテリーは小さいけど持ちがいい

And a good example to highlight the difference

あまり電池を消費しないわ

between energy and power density,

すべてのアプリを開いて―

is comparing a mug to a large jug

動画を再生したって平気

with one of those narrow bottlenecks.

後で充電は必要だけどね

If your water represents energy,

スマートフォンの多くは リチウムイオン電池を使う

and you fill both vessels with water,

電池セルでの化学反応には 素材が重要よ

you see that the jug has a greater overall energy storage.

リチウムイオンセルの場合 アノードもカソードも―

It can simply hold more water or energy.

リチウムイオンを吸収する素材でできてる

But if we were to pour that water out,

イオンをしっかり閉じ込めて逃がさない

well, then it's clear that the water or that stored energy

一般的にアノードの素材は黒鉛

comes out of the mug at a much faster rate,

その炭素原子の構造により―

demonstrating that the mug has a higher power output.

アノードに正リチウムイオンが蓄えられる

Energy density is defined

カソードの素材はコバルト酸リチウムで

as how much energy is within a given mass.

やはりリチウムイオンを蓄えやすい

So if something has a high energy density,

これらの素材こそが鍵となる

it means it can store a lot of energy

同じ大きさでも セルに多くのエネルギーを蓄えられる

in a small amount of mass.

リチウムイオン電池は充電も可能よ

Power density, on the other hand, is defined as,

仕組みは普通の電池とほとんど変わらない

you guessed it, how much power is within a given mass.

セルが使われると アノードから電子が放出される

So when something has a high power density,

電子は外部回路を通ってカソードへ

it can output large amounts of energy

電子が電気として回路を動く間―

in a short amount of time.

残されたリチウムイオンは 電解質を通りカソードへ移動

So if you have a device with high energy density

デバイスの充電が開始されるまで―

and low power density,

その場に とどまり続ける

it means that the device can store a lot of energy

次は逆方向へ同じことを繰り返す

and doesn't use it up quickly.

カソードに使う金属酸化物は―

A good example of this is your very own phone.

必要なエネルギー密度によって異なるわ

It actually has a small battery,

スマートフォンにはコバルト酸リチウム

but can run for a long time.

テスラの車などにはリチウムニッケル コバルトアルミニウム酸化物

Now, you may notice your phone doesn't really generate that much power.

テスラの車がこんなに特殊な―

I mean, it probably has enough power

リチウムイオン電池を使ってるとは 知らなかったかもね

to have all of your apps open while streaming

電気自動車は ずっと進化し続けてきた

cool science videos like this one,

でも転換点を迎えたのは最近だ

but then you'd probably have to recharge it pretty soon afterwards.

ガソリン自動車に戻れない

You'll find that most phones today

[デレク･ミューラー]

use lithium-ion batteries,

その理由の１つは革新的なバッテリー技術

and materials are important

電気自動車の内部は 内燃機関の車と全く異なる

for chemical reactions in battery cells.

ここには何もないよね 物を入れるスペースだ

So, in the case of lithium-ion cells,

この車の電池は個別セル

both the anode and the cathode are made of materials

セルはモジュールに同梱され 電池パックを形成し―

that can enhance their ability to absorb lithium ions.

車の下部に搭載されている

This means the ions are held

とても重いから車は低重心だ

inside the structure of the material,

これらは見事なリチウムイオン電池だ

and they can't get loose.

テスラのモデルSは

In most cases, the anode is made of graphite,

7,000個の電池セルを搭載していて

which has this structure of carbon atoms.

１度の充電で―

This structure allows the graphite anode

595キロメートル以上を走行できる

to store positive lithium ions,

次に航続距離が長いのは ヒュンダイの車で415キロメートルよ

while the cathode, typically made of lithium cobalt oxide,

現時点ではテスラが群を抜いている

has a structure that also is conducive

エネルギー密度と出力密度の面でもね

to storing lithium ions.

比較的 手頃な価格になってきたけど

These enhanced materials are key

リチウムイオン電池には欠点もある

for a couple of different reasons.

パワーが弱くコストが高いし―

It means that the cell can store more energy

劣化する素材でできている

while remaining small, and that's energy density.

またリチウムイオン電池には 発火の危険性がある

And this also means the battery is rechargeable.

さらなる改善が必要ね

When we want to use a lithium-ion battery,

そのためには どうすればいい？

it works similarly to our other batteries.

次の動画で最新の取り組みを紹介する

As the cell gets used,

those electrons are freed from the anode,

and they shuffle through an external circuit to the cathode.

While the electrons move through the circuit as electricity,

the lithium ions left behind

travel through the electrolyte to the cathode.

And there, they get absorbed and stay put

until the device that uses the battery

is plugged in and begins the charging cycle.

Then they all do the whole process again, but backward.

Also, depending on how much energy density you need,

the cathode can be created with different metal oxides

for different applications.

For example, lithium cobalt oxide is what's used in our phones,

while something like a Tesla vehicle

uses lithium nickel cobalt aluminum oxide.

So you were probably aware

that electric cars use lithium-ion batteries,

but maybe you didn't know that Tesla cars used

such a different kind of lithium-ion battery.

DEREK: Electric vehicles have been developing for decades now,

but they only sort of hit a tipping point recently.

I've been driving one for a couple of years,

and I just wouldn't go back.

And part of that is due to their

very innovative battery technology.

Electric vehicles look pretty different under the hood

from internal combustion engine cars.

I mean, there's not much to see here,

it's just a storage space.

The batteries that this car uses are individual cells,

which are packaged together into modules,

and modules joined together to form the battery pack,

which actually sits down here

along the bottom of the vehicle.

And it's really heavy, so it gives the car

a low center of gravity.

Now, those batteries are pretty impressive.

Lithium-ion.

In the Model S version of this car,

there are 7,000 of them stuck together,

and that can give these cars a range

over 595 kilometers.

The next most efficient electric cars on the market

only have a range of about 415 kilometers.

And this huge gap demonstrates that Tesla

is leading the charge, at least for now,

in terms of energy density and even power density,

in a way that makes those electric cars

relatively affordable for a mass market.

But lithium-ion batteries do have their downsides.

They're not super powerful, they're expensive,

the materials they're made from are unsustainable,

and their electrolyte can be flammable,

making the product potentially hazardous.

So clearly there are improvements to be made.

But what's it gonna take to make an even better battery?

Check out our next episode

to learn what scientists are working on today.