In 2012, the State Council issued the “Energy Conservation and New Energy Vehicle Industry Development Plan (2012-2020)â€, which clarified that the development of new energy vehicles in China will focus on lithium-ion battery pure electric vehicles (LIB-EV). In recent years, lithium-ion battery pure electric vehicles have become the absolute mainstream route of new energy vehicles in China. Lithium-ion batteries have unified China's electric vehicle power battery market.
In December 2014, Toyota, the world's largest auto company, officially launched Mirai (FC-EV), the world's first mass-produced fuel cell (PEMFC) electric vehicle. Following this, Honda also released its new generation fuel cell vehicle FCVClarity in the second half of 2015. After that, Nissan, Hyundai, General Motors (GM), BMW and Volkswagen (VW) also released their own fuel cell electric vehicle industrialization plans in the past two years. .
We can see that China and Japan (actually including Korean and European mainstream car companies) have chosen different technical routes in the development direction of pure electric vehicles. In the face of the reality of small-scale commercial production of Toyota, Honda and Hyundai fuel cell vehicles (FC-EV), the first thing we need to seriously consider now is why China and Japan have chosen different technical routes in developing pure electric vehicles. Or what kind of power system is more suitable for pure electric vehicles?
In essence, a secondary battery including a lithium ion battery is an energy storage device that realizes storage and release of electrical energy through a reversible electrochemical reaction. The fuel cell (PEMFC) is a power production device that converts chemical energy in the fuel into electrical energy by electrocatalytic reaction. Although the fuel cell is also called "battery" (the reason for Chinese translation), its basic working mode is somewhat similar to that of an internal combustion engine, which is essentially different from a conventional secondary battery. The nature of these two electrochemical power systems works differently and will directly determine their different positioning at the application level.
At present, China's choice of electric vehicle power source (power battery) is basically the lithium-ion battery as the only choice, and the domestic lithium battery industry has also been popular this "lithium-ion battery will replace other secondary batteries unified rivers and lakes" or "The lithium-ion battery application field is very widespread and it is a universal battery."
The author believes that it is necessary to clarify some basic understanding of lithium-ion batteries. In my opinion, lithium-ion batteries have two major challenges, making it difficult to become the main source of power for medium and large-sized vehicles: the predicament of safety and the bottleneck of energy density.
The dilemma of safety: First of all, the author here emphasizes that from the most basic thermodynamic point of view, the existing lithium-ion battery system is thermodynamically unstable, and it can work stably because of the surface of the positive and negative electrodes. The passivation film kinetically isolates the further reaction of the highly active positive and negative materials with the electrolyte, and the thermal runaway caused by various factors is the most direct cause of destroying the passivation film on the positive and negative electrodes. An objective understanding of the safety of lithium-ion batteries will be crucial.
Any commercial secondary battery requires effective overcharge prevention measures to ensure that the battery is fully charged and avoids the safety problems caused by improper overcharging. Whether it is a water-based or organic secondary battery, its charging safety is based on the basic principle of positive limit capacitance (negative negative electrode capacity). If this premise disappears, the consequence of overcharging is that the secondary battery of the water system produces hydrogen, and for the lithium ion battery, it is the lithium of the negative electrode.
However, various water-based secondary batteries can effectively utilize the decomposition reaction of water to achieve overcharge protection using the principle of "oxygen cycle". Although the water-based secondary battery limits the further increase in energy density due to the decomposition voltage of water, it is not forgotten that water also provides a near-perfect and irreplaceable anti-overcharge solution for water-based secondary batteries. In a lithium ion battery, once the high-active metal lithium is precipitated in the negative electrode, safety problems are bound to occur because metal lithium cannot be eliminated inside the battery.
Therefore, in a sense, lithium-ion batteries have no solution to the safety problem! Comprehensive application of some technical measures, such as thermal control technology (PTC electrode), positive and negative surface ceramic coating, overcharge protection additive, voltage sensitive diaphragm and flame retardant electrolyte can effectively improve the safety of lithium battery, but These measures are impossible to fundamentally solve the safety problem of lithium batteries, because lithium batteries are thermodynamically unstable systems.
On the other hand, these measures not only increase the cost, but also reduce the energy density of the battery. Limiting the capacity of the battery cells of the power battery is still a necessary measure to ease safety. What I want to emphasize here is that BMS does not solve the safety problem of lithium-ion battery, which is determined by the basic working principle of BMS.
If we consider the above factors comprehensively, we will understand that the "safety" of lithium batteries is only relative. In recent years, the domestic lithium battery industry has been filled with the argument that lithium-ion batteries will dominate the rivers and lakes and replace other secondary batteries. From the perspective of safety, this argument is undoubtedly ridiculous.
Shenzhen Hongyian Electronics Co., Ltd. , https://www.hongyiancon.com