磷酸鐵鋰電池使用密度更低的新材料打造殼體
來源：寶鄂實業(yè)
2019-06-24 10:59
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1. Structural Design Requirements
Reliable structure: anti-vibration and anti-fatigue;
Controllable process: no over-welding, virtual welding, to ensure that 100% of the core is not damaged;
Low cost: PACK production line automation cost is low, including production equipment, production losses;
Easy to separate: Battery pack is easy to maintain and repair, low cost, and good use of the battery.
The necessary heat transfer isolation is achieved to avoid the rapid spread of thermal runaway. This step can also be considered in pack design.
Problem: The single energy density of the soft-clad core has a higher lifting space than that of the cylinder and the square, but it has a higher requirement for the module design and is difficult to control the safety. These are all problems that need to be solved by the structural design.
2. Thermal Design Requirements
The physical structure of the soft-wrapped core determines that it is not easy to explode. Generally, only the shell can withstand enough high pressure, it is possible to explode. When the inner pressure of the soft-wrapped core is large, it will start to relieve pressure and leak liquid from the edge of the aluminium-plastic film. At the same time, soft-wrapped cores are also several kinds of cores, with the best heat dissipation.
At present, the mainstream cooling mode has changed to liquid cooling and phase change material cooling. Phase change material cooling can be used in conjunction with liquid cooling, or alone in less harsh conditions. In addition, there is a process that is still widely used in China, glue filling. The heat conductivity is much greater than that of air. The heat emitted from telecommunications is transferred to the module housing by thermal conductive glue, and then further emitted to the environment. In this way, it is unlikely that the core will be replaced separately again, but to some extent, it also prevents the spread of thermal runaway.
Of course, it is not easy for lithium battery packed soft-packed cores to mature the liquid cooling technology. The fixing, sealing and insulation of the liquid cooling plate must be considered.
3. Electrical design requirements
Electrical design, including low-voltage and high-voltage two parts.
Low-voltage design, generally need to consider several aspects of the function. Through signal acquisition wiring harness, the battery voltage and temperature information is collected to the module slave control board or the so-called module controller installed on the module; the module controller generally designs the equalization function (active equalization or passive equalization or both); a small number of relay on-off control functions can be designed on the slave control board, or can be connected to the module controller through CAN communication; Group controller and main control board transmit module information.
High voltage design, mainly between the core and the core in series and parallel, as well as outside the module, designs the mode of conduction between the module and the module. Generally, only considering the mode of series connection between the modules. These high-voltage connections need to meet two requirements: first, the distribution of conductive components and contact resistance between the cores should be uniform, otherwise the single voltage detection will be disturbed; second, the resistance should be small enough to avoid the waste of electric energy in the transmission path.
4. Safety Design Requirements
Safety design can be divided into three retrogressive requirements: good design to ensure that no accident occurs; if not, accident occurs, it is best to give early warning, reflecting time; failure has occurred, then the design goal becomes to prevent the accident from spreading too quickly.
The first goal is to achieve a reasonable layout, a good cooling system and reliable structural design.
Secondary targets require sensors to be more widely distributed to every possible fault point, to detect voltage and temperature in an all-round way, and it is better to monitor the internal resistance of each core.
The lowest goal is to set fuses through cores and modules, and firewalls between modules and modules to design strength redundancy to cope with possible structural collapse after disasters. This is the direction of high performance soft package module.
5. Lightweight Design Requirements
Lightweight design, the most important purpose is to pursue the mileage, eliminate all redundant burdens, light loading into battle. And if lightweight can be combined with cost reduction, it will be a great joy.
There are many ways of lightweight, such as improving the energy density of the core.
In detail design, to ensure the strength of the pursuit of structural lightness (for example, choose thinner materials, dig larger holes in the plate);
Replace sheet metal with aluminium.
Use new materials with lower density to build shells, etc.
結構可靠：抗震動抗疲勞;
工藝可控：無過焊、虛焊，確保電芯100%無損傷;
成本低廉：PACK產線自動化成本低，包括生產設備、生產損耗;
易分拆：電池組易于維護、維修，低成本，電芯可梯次利用性好;
做到必要的熱傳遞隔離，避免熱失控過快蔓延，也可以把這一步放到pack設計再考慮。
問題：軟包電芯的單體能量密度比圓柱和方形有更高的提升空間，但對模組設計要求較高，安全性不易把控，這都是需要結構設計解決的問題。
2、熱設計要求
軟包電芯的物理結構決定了其不易爆炸，一般只有外殼能承受的壓力足夠高，才有可能炸，而軟包電芯內部壓力一大，便會從鋁塑膜邊緣開始泄壓、漏液。同時軟包電芯也是幾種電芯結構中，散熱最好的。
當前主流的冷卻方式，已經轉變?yōu)橐豪湟约跋嘧儾牧侠鋮s。相變材料冷卻可以配合液冷一起使用，或者單獨在環(huán)境不太惡劣的條件下使用。另外還有一種當前國內仍然較多應用的工藝，灌膠。這里灌得是導熱系數(shù)遠大于空氣的導熱膠。由導熱膠將電信散發(fā)的熱量傳遞到模組殼體上，再進一步散發(fā)到環(huán)境中。這種方式，電芯再次單獨替換不太可能但也在一定程度上阻止了熱失控的傳播。
當然鋰電池包軟包電芯要將液冷技術做成熟也并非易事，其必須考慮液冷板的固定，密封性，絕緣性等等。
3、電氣設計要求
電氣設計，包含低壓和高壓兩個部分。
低壓設計，一般需要考慮幾個方面的功能。通過信號采集線束，將電池電壓、溫度信息采集到模組從控板或者安裝在模組上的所謂模組控制器上;模組控制器上一般設計均衡功能(主動均衡或者被動均衡或者二者并存);少量的繼電器通斷控制功能可以設計在從控板上，也可以在模組控制器上;通過CAN通訊連接模組控制器和主控板，將模組信息傳遞出去。
高壓設計，主要是電芯與電芯之間的串并聯(lián)，以及模組外部，設計模組與模組之間的連接導電方式，一般模組之間只是考慮串聯(lián)方式。這些高壓連接需要達到兩個方面的要求：一是電芯之間的導電件和接觸電阻分布要均勻，否則單體電壓檢測將受到干擾;其次，電阻要足夠小，避免電能在傳遞路徑上的浪費。
4、安全設計要求
安全設計，可以分為3個倒退的要求：良好的設計，確保不要發(fā)生事故;如果不行，發(fā)生事故了，最好能提前預警，給人以反映時間;故障已經發(fā)生，則設計的目標就變成阻止事故過快蔓延。
實現(xiàn)第一個目的的，是合理布局，良好的冷卻系統(tǒng)，可靠的結構設計;
次級目標，則需要傳感器更加廣泛的分布到每一個可能的故障點，全面檢測電壓和溫度，最好監(jiān)測每一顆電芯的內阻;
最低目標，則可以通過電芯和模組設置保險絲，模組和模組之間設置防火墻，設計強度冗余應對災害發(fā)生后可能的結構坍塌。這都是高性能軟包模組的方向。
5、輕量化設計要求
輕量化設計，最主要目的是追求續(xù)航里程，消滅所有多余負擔，輕裝上陣。而如果輕量化再能跟降成本結合，則更是皆大歡喜。
輕量化的道路很多，比如提高電芯能量密度;
在細節(jié)設計中，確保強度的情況下追求結構件的輕薄(比如選更薄的材質，在板材上挖更大的孔);
用鋁材替換鈑金件;
使用密度更低的新材料打造殼體等。
鋰電池包行業(yè)市場前景廣闊，未來競爭激烈。存能電氣磷酸鐵鋰電池包具有體積小、重量輕、能量密度高、長壽命、綠色環(huán)保、無記憶效應等優(yōu)勢。相對于國內廠商而言在電池的一致性、穩(wěn)定性、安全性、環(huán)保性、循環(huán)壽命等方面都有比較大的優(yōu)勢，對下游廠家的吸引力也很大。未來我國鋰電池包地位將不斷提升，遲早會成為一匹行業(yè)的黑馬。
