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    News

    One of the core hardware of electric vehicle: Battery

    2019-11-26 18:13:31 0

    At present, there are two kinds of known electric vehicle batteries, which can be divided into ternary lithium battery and iron phosphate lithium battery according to different anode materials. The former is the most popular type of battery at present. The poor activity of lithium iron phosphate battery results in its low energy density and unable to provide longer endurance.

    At present, the mainstream lithium-ion batteries have the advantages of high battery activity and higher energy density, so the new energy vehicles basically use lithium-ion batteries as energy storage mechanism. There are also two kinds of ternary lithium batteries, one is MCM (nickel cobalt manganese) ternary lithium battery used by most car enterprises, the other is NCA (nickel cobalt aluminum) ternary lithium battery used by Tesla.

    Why does the endurance of electric vehicles shrink dramatically in winter when it is cold? As mentioned before, the discharge process of the battery is that the lithium ion is removed from the negative electrode and "returned" to the positive electrode through electrolysis. At low temperature, the electrolyte will become "sticky" or even "frozen". This means that the process of lithium ion "swimming back" from the negative electrode to the positive electrode becomes more difficult. A higher power propeller is needed to push lithium ion, which means that the internal resistance of the battery increases.

    Therefore, the battery itself needs to consume more electric energy at low temperature, which leads to the reduction of the electric energy driving the vehicle. This is the reason why the endurance of electric vehicles is greatly reduced in winter.

    No matter what kind of lithium battery, its structure is basically the same. They are composed of positive electrode, negative electrode, diaphragm and electrolyte. Lithium battery charging is to generate charged lithium ions (equal amount) from the positive electrode, and separate from the positive electrode, "swim" through the electrolyte and diaphragm to the negative electrode, and embed them in the negative electrode material. However, the discharge process is just the opposite, and lithium ions are separated from the negative electrode and "swim" to the positive electrode. In short, the charging and discharging process of lithium battery is realized by lithium ion moving back and forth between the positive and negative poles.

    li-ion battery|geb|lithium polymer battery

    (schematic diagram of battery charging state)

    It's the current that propels the lithium ions back and forth. So we can simply understand the fast charging as a high-power propeller behind the lithium ion, which can push the lithium ion to "swim" from the positive pole to the negative pole quickly and forcibly, while the slow charging is a small power propeller, which takes the lithium ion to "swim" from the positive pole to the negative pole slowly.

    li-ion battery|geb|lithium polymer battery

    (schematic diagram of battery charging and discharging)

    It's the current that propels the lithium ions back and forth. So we can simply understand the fast charging as a high-power propeller behind the lithium ion, which can push the lithium ion to "swim" from the positive pole to the negative pole quickly and forcibly, while the slow charging is a small power propeller, which takes the lithium ion to "swim" from the positive pole to the negative pole slowly.

    li-ion battery|geb|lithium polymer battery

    (lithium crystal growth process)

    So why does fast charging have a certain impact on the battery? It's very simple. Many lithium ions with high-power thrusters "swim wildly" from the positive pole to the negative pole. Before the negative pole is on the bank (embedded in the negative pole), another lithium ion rushes over, and the two lithium ions collide and "die" together, losing their activity. In this way, the battery loses one lithium ion. Long down, the "dead" lithium ions will pile up together to form lithium dendrites. Most of the deflagration of batteries is caused by the short circuit inside the battery caused by the too long lithium dendrite penetrating the diaphragm.li-ion battery|geb|lithium polymer battery 

    (increased internal resistance of battery)

    In addition, let's extend it a little bit. Why does the endurance of electric vehicles shrink dramatically in the cold winter? As mentioned before, the discharge process of the battery is that the lithium ion is removed from the negative electrode and "returned" to the positive electrode through electrolysis. At low temperature, the electrolyte will become "sticky" or even "frozen". This means that the process of lithium ion "swimming back" from the negative electrode to the positive electrode becomes more difficult. A higher power propeller is needed to push lithium ion, which means that the internal resistance of the battery increases.

    Therefore, the battery itself needs to consume more electric energy at low temperature, which leads to the reduction of the electric energy driving the vehicle. This is the reason why the endurance of electric vehicles is greatly reduced in winter.



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