看起來，電力推進(jìn)系統(tǒng)似乎注定將在未來取代內(nèi)燃機(jī)，但現(xiàn)階段而言，電動(dòng)車電池仍然很貴，電池組還是很重，而且充電時(shí)間也仍然也比汽車加油慢的多。盡管存在眾多優(yōu)勢，但電動(dòng)車的這些弱點(diǎn)也同樣不容忽視。因此，從經(jīng)濟(jì)和市場規(guī)律來看，內(nèi)燃機(jī)很可能并不會在未來幾十年內(nèi)“謝幕”。
不過，現(xiàn)在來了解一下Tanktwo公司及一種真正創(chuàng)新的電動(dòng)車電池吧。
現(xiàn)階段電動(dòng)車電池架構(gòu)的基礎(chǔ)是一種名為“電芯”的組件。這些電芯通常采用圓柱 或矩形設(shè)計(jì)，已經(jīng)在消費(fèi)電子領(lǐng)域有大量應(yīng)用，因此對電動(dòng)車電池廠商很有吸引力。這些電芯可以首先組成電池模塊，而電池模塊經(jīng)過設(shè)計(jì)組合后又可以組成固態(tài)電池組。
Tanktwo計(jì)劃打造一種由“蛋型”電芯組成的電池組。這家芬蘭公司的創(chuàng)始人利用自身在遠(yuǎn)程通信領(lǐng)域的背景，打造了一款內(nèi)置小型編程計(jì)算機(jī)的“智能”電芯。他們可以直接將這些電芯“倒入”一個(gè)內(nèi)部具有觸點(diǎn)的平價(jià)容器內(nèi)，形成公司所稱的“串電池（String Battery）”。
常規(guī)電池尺寸太大
目前，Tanktwo已經(jīng)在美國紐約開設(shè)了辦公室，公司CEO Bert Holtappels表示，“串電池”最大的優(yōu)勢也正是傳統(tǒng)電池概念的劣勢所在：電池容量從設(shè)計(jì)之初就已經(jīng)嚴(yán)格確定，不能更改了。
“這樣的電池系統(tǒng)效率很低，為了將故障率控制在可以接受的范圍內(nèi)，傳統(tǒng)電池的尺寸通常都有較大富余。”Holtappels解釋說，現(xiàn)在很多廠商的電動(dòng)車電池組容量高達(dá)100 kW·h，而車主通常每年也只開20,000公里，這意味著“這些電池的折舊很大程度上來源于自然老化，而不是真正使用。”這是一種很大的資產(chǎn)損失。
對比來看，在使用Tanktwo的串電池時(shí)，用戶只需向電池容器中“倒入”所需數(shù)量的電芯，外加少量額外的備用電芯即可。而后電池組的外容器可以通過SAE J1772標(biāo)準(zhǔn)插頭為電芯充電。“這可以保證電池得到充分利用，”Holtappels解釋道，“這樣一來，在購買電動(dòng)車后，車主就可以隨時(shí)到經(jīng)銷商處輕松升級自己的電池組。”
商店里的吸塵器算的上是形式最簡單的換電設(shè)備。Holtappels承認(rèn)，我們必須改變電池結(jié)構(gòu)，才能實(shí)現(xiàn)便捷快速的電池更換，氫燃料電池就是一個(gè)例子。他推測說，“未來，這可能會自然而然地成為現(xiàn)實(shí)。”
新設(shè)計(jì)，高效率
“串電池”還有從其他方面提高電池效率的潛力。當(dāng)下的電池組設(shè)計(jì)需要平衡同個(gè)模塊內(nèi)所有電芯的電量水平。因此，我們假設(shè)有一個(gè)電芯有20%的損壞，那這個(gè)模塊中的剩余電芯也必須放掉20%的電量，從而保證整體的平衡。這樣一來，只要一個(gè)電芯出了問題，整個(gè)電池模塊的功能都會受到影響。
也正是這個(gè)原因，傳統(tǒng)電池通常需要設(shè)計(jì)更大的富余。這意味著如果一款電池希望在整個(gè)生命周期內(nèi)均保持8 kW·h以上的容量，那該電池一開始最少需要設(shè)計(jì)14或16 kW·h的容量。
對比來看，由于“串電池”很智能，因此電池組的能效并不會受到“狀況最差”的那個(gè)電芯的限制。根據(jù)Holtappels的描述，如果單個(gè)電芯壞了20%，那電池組供電時(shí)僅會繞過這20%的損壞電芯，并不會產(chǎn)生其他影響。每個(gè)電芯均盡最大能力為電池組供電，即使有所損壞也不會“拖累”其他電芯放電以保持平衡。
Holtappels估算，與額定功率相同的傳統(tǒng)電池組設(shè)計(jì)相比，Tanktwo串電池的效率高10%。
“從實(shí)用角度看，我們電池的使用壽命要長的多。”Holtappels表示，“大多數(shù)公司的共識是，當(dāng)電池組的可用部分還剩70%時(shí)，就該更換電池了，但只要剩余容量仍在10%以上，我們的串電池就完全可以繼續(xù)工作”
Tanktwo公司表示，完全或部分損壞的電芯對傳統(tǒng)電池有致命打擊，但串電池則可以繞過這部分故障電芯繼續(xù)工作，而且用戶還可以在服務(wù)站內(nèi)輕松換掉這部分電芯。因此，串電池的電池組尺寸是按正常使用情景，而非最壞情況設(shè)計(jì)的。此外，串電池組用來裝電芯的容器相當(dāng)簡單，類似總線等重要組成部分也采用了商品化的設(shè)計(jì)。由于自身特點(diǎn)，串電池對電池容器的形狀并沒有要求。
Holtappels表示，“這項(xiàng)技術(shù)不受電池化學(xué)種類的限制，電池化學(xué)領(lǐng)域的進(jìn)步也會同時(shí)提升串電池的性能。”
Holtappels表示，目前，Tanktwo已經(jīng)找到了多個(gè)行業(yè)伙伴，共同進(jìn)行串電池的初步研發(fā)，其中包括提供電動(dòng)服務(wù)汽車的Firefly公司。對于這部分用戶而言，能否進(jìn)行快速電池替換（Tanktwo稱“3分鐘”）至關(guān)重要。
Total Battery Consulting公司的Menahem Anderman博士認(rèn)為，“這絕對算的上一個(gè)開創(chuàng)性思路，但似乎相當(dāng)具有挑戰(zhàn)性。”在接受本文作者的采訪時(shí)，Anderman博士表示，希望未來這種“動(dòng)態(tài)”電池結(jié)構(gòu)能夠經(jīng)受考驗(yàn)，真正在系統(tǒng)復(fù)雜度、成本和可靠性等方面達(dá)到平衡。
Anderman博士表示，“我相信，這種電池概念轉(zhuǎn)為真正電池系統(tǒng)還需要相當(dāng)長的時(shí)間。”毫無疑問，Tanktwo公司也意識到自己面臨的挑戰(zhàn)。未來有關(guān)串電池的更多信息，敬請關(guān)注。
While electric propulsion appears destined to supplant the internal combustion engine at some point in the future, the laws of economics and market forces will likely keep ICEs around for decades. Batteries for EVs remain expensive. Packs are heavy, and recharging takes longer than pumping liquid fuel into a tank. Despite their many advantages, EV disadvantages are hard to ignore.
Enter Tanktwo and a truly novel approach to the basics of EV batteries.
The basis of EV batteries today starts with a small component collectively known as a cell. Typical cells are shaped as cylinders or rectangular slabs. What makes them attractive to electrified vehicle battery makers is they are widely used in consumer electronics. Cells are combined into modules, modules into a highly engineered, static battery pack.
Tanktwo’s vision is a battery pack composed of egg-shaped String Cells. The Finland-based company’s founders exploited their background in telecommunications to create 'smart' cells that contain small, programmed computers. Poured (literally) into an inexpensive passive container with contacts on the inside, they create a String Battery.
Conventional batteries too big
One of the biggest benefits of the String Battery lies in a problem with current battery concepts—capacity rigidly designed from the outset, according to Bert Holtappels CEO of Tanktwo which has an office in New York.
“These systems are inefficient because they need to be over dimensioned with significant margin, so that the likelihood of field failure is within an acceptable margin,” he said. Some EV makers are delivering cars with 100 kW·h battery packs when their owners might drive only 12,000 mi (19,311 km) per year, meaning that "most of the depreciation of the battery is coming from aging, not wear”—a costly loss of an asset, Holtappels explained.
Sizing the Tanktwo String Battery container for the maximum scenario requires filling only as many cells as needed for a typical usage, plus a healthy margin. The container would recharge the cells through the normal SAE J1772 plug as today. “This prevents underutilization of the pack,” he explained. “During the period he owns the vehicle, the same customer could visit the dealer and get an upgrade to the battery pack quite easily.”
The simplest version of the swapping device resembles a glorified Shop Vac. Holtappels recognizes that the more ambitious goal of convenient and fast battery swapping requires an infrastructure change that could inhibit adoption—think hydrogen fuel cell vehicles. “That might come naturally over time,” he speculated.
Efficient by design
There are some other potential efficiencies of the String Cell approach. Current battery packs need to level the charge between cells in each module. So, if one cell has deteriorated by, say 20%, the rest of the cells in the module must bleed off energy to balance the cells within the module. So, each module is limited by the deterioration of any individual cell.
This also causes traditional packs to need large safety margins. Often, this means a battery designed to maintain an 8 kW·h capacity over the life of the car might start out with 14 or 16 kW·h.
Because String Cells are ‘smart’, the pack is not limited by the least-charged cell. As Holtappels describes it, if an individual cell deteriorates by 20%, the cell is simply bypassed for 20% of the time when the pack is contributing power. Each cell contributes to the pack to the best of its ability without any need to bleed off charge.
He estimates this as providing 10% more energy efficiency when compared to traditional pack designs with the same rated energy.
“Our packs can last much longer on a practical level as well," Holtappels claimed. "Most companies [think they should retire their] pack from the vehicle even when it is still 70% usable. For String Cells, anything over 10% of initial capacity is OK for each cell.”
Dead or semi-dead cells that would be ruinous in a traditional pack can be bypassed in a String Battery, and easily replaced at a service or swap event, the company claims. So the packs are sized for the mean, not the worst case. The containers they go into are also fairly simple. Important components, such as bus communications and wire harnesses are already commoditized. Because of the unique character of the String Cells, there is flexibility in the shape of the container.
“This technique is agnostic about the battery cell chemistry: any improvement in the chemistry of cells would also improve the String Battery,” he said.
According to Holtappels, a couple of industry partners are already working with Tanktwo on initial deployments, including Firefly with an electric service vehicle. In these cases, the rapid battery replacement—3 minutes according to the company—was an important factor.
"This is definitely an out of the box idea, but it seems quite challenging," observed Dr. Menahem Anderman of Total Battery Consulting‘. Interviewed by the author for this article, Dr. Anderman would like to see future trials prove out the quality of the 'dynamic' electrical contacts between the cells, and examine complexity, cost and reliability in real life.
"I believe it will be quite a stretch to make a real viable system out of the concept," he said. There is no doubt the Tanktwo principals are just as aware of the challenges. Stay tuned.
Author: Bruce Morey
Source: SAE Automotive Engineering Magazine
Tanktwo串電池使用帶有多壓力觸點(diǎn)的“智能”電芯替代“普通”電芯。上圖所示的電芯具有6個(gè)外部觸點(diǎn)。
串電池可以在沒有人工干預(yù)的情況下，自動(dòng)“串聯(lián)”形成串電池。電池中的串聯(lián)算法可以持續(xù)監(jiān)測網(wǎng)絡(luò)情況，并在有必要時(shí)創(chuàng)造新的連接。
圖為串電池的仿真圖。由硅樹脂材料制成的充氣氣囊可以在車輛移動(dòng)時(shí)保證電芯不會隨意移動(dòng)。Tanktwo公司聲稱，對于擁有6個(gè)觸點(diǎn)的電芯而言，電池組完全可以取得98%以上的利用率，接觸點(diǎn)退化及可能的腐蝕問題也可以通過很多方法解決。