The Impact Of Lithium Batteries On Winter

- Jul 24, 2018-

Recently, friends of electric car owners all over the country have found that your car's cruising range has suddenly been greatly shortened. How far can it run? Isn't the "throttle" stepping down? Have they all started to feel worried about the cold winter, especially in the north, so the weather not only affects travel plans, but many people are not willing to drive warm air in order to save electricity, and there is almost a temperature outside the car. This kind of experience makes people doubt the value of the decision to buy an electric car.

The small partners in the northeast seem to be a commonplace in the winter. This allows them to have electric cars?

Why the electric car's battery life will be reduced in the cold winter, and it is related to low temperature without thinking about the brain. Xiaobian is thinking, this may be the same as the smart phone in the low temperature state clearly shows that the power is sufficient but the instantaneous shutdown. But why the low temperature will have such a big impact on their battery life, Xiaobian does not know the technology, find the information, by the way, give everyone the science.

Why is the life of a winter electric car not working?

Generally speaking, most of the electric vehicles and even electronic digital products on the market currently use lithium batteries, so let's take a look at what happened in the winter.

Start with the principle. The main types of lithium batteries used in electric vehicles, lithium iron phosphate, ternary lithium and lithium manganate are the three mainstream lithium batteries, and the negative graphite materials are the main ones. Their basic reflection principle is similar, and they are all "rocking chair" electrochemical energy storage processes.


  Lithium battery discharge process


As shown in FIG. During the charging process, due to the external voltage of the battery, the electrons in the vicinity of the positive current collector move to the negative electrode under the electric field. After reaching the negative electrode, they combine with the lithium ions in the negative electrode material to form a local electrical neutral storage in the graphite gap. The surface of the negative electrode that consumes a part of lithium ions has a low lithium ion concentration, and a difference in ion concentration is formed between the positive electrode and the negative electrode. Under the concentration drive, the lithium ions in the positive electrode material move from the inside of the material to the surface of the positive electrode, and along the electrolyte, pass through the separator to the surface of the negative electrode; further, under the action of potential, pass through the SEI film and deep into the negative electrode material. The diffusion occurs, and the electrons coming from the external circuit meet, and the local display is electrically neutral and stays inside the negative electrode material. The discharge process is just the opposite. After the circuit containing the load is closed, the discharge process begins with electrons flowing out of the negative current collector and through the external circuit to the positive electrode; finally, lithium ions are embedded in the positive electrode material and combined with the electrons coming from the external circuit.

The negative graphite is a layered structure, and the manner in which lithium ions are intercalated and extracted is not much different in different types of lithium ions. Different cathode materials have different lattice structures, and lithium ions diffuse in and out during charge and discharge, and the process is slightly different.

During the discharge process, lithium ions want to come from the negative electrode to the positive electrode, and it is necessary to overcome some resistance under the drive of some power. These resistances include: diffusion from the negative electrode structure to overcome the negative SEI film impedance; diffusion along the electrolyte needs to overcome the electrolyte conduction impedance; across the diaphragm between the positive and negative electrodes, it is necessary to overcome the impedance of the diaphragm; from the electrolyte into the positive electrode, the need Overcome the positive SEI film (the structure of this film is not particularly noticeable) and the internal diffusion resistance of the material.

So where does the power of lithium ions overcome these resistances come from? On the one hand, the potential difference between the positive and negative materials, the greater the potential difference between the positive electrode material and the negative electrode material, the higher the open circuit voltage exhibited by the battery, the more energy the battery stores, and this property is also the basic power that the battery can discharge; On the one hand, the difference in ion concentration at different positions in the electrolyte drives the ions to move from the high concentration position to the low concentration position, so-called concentration drive.

In this way, as long as we know how low temperature affects these resistances and dynamics, we can understand how the effect of low temperature on the performance of lithium batteries works.

The active material of the positive electrode material, the lower the temperature, the worse the activity, the lower the potential is exhibited; the more difficult the diffusion of the positive electrode lithium ion in the internal channel of the material is, the more the impedance is increased; the SEI film on the surface of the negative electrode is the electrolyte and the negative electrode material. A passivation film formed during the initial contact, its presence protects the negative electrode material from further corrosion by the electrolyte while allowing lithium ions to enter and exit. When the temperature is lowered, lithium ions also become difficult to pass through the SEI film, which is manifested by an increase in impedance; the activity of the electrolyte is also deteriorated at a low temperature, and the diffusion ability of ions in the electrolyte is lowered. The moving rate of charged ions, the macroscopic performance is the magnitude of the current value. Recall the definition of current: the amount of electricity flowing through any section of the conductor per unit time. In connection with the relationship between charge transfer rate and current, the low temperature reduces the ability of the electrolyte to pass current. The obstacle to the movement of charge is represented by the loop impedance. As the temperature drops, the electrolyte impedance rises.

On the whole, in the lithium battery system, the charge movement is not smooth, which is manifested by a decrease in potential and an increase in impedance. The potential or the open circuit voltage of the battery has a clear correspondence with the energy contained in the battery at a certain temperature, and the potential drop indicates a decrease in the electric energy in the battery.

The above explanation seems to be too complicated, so simply summarize why the electric car has less cruising range at low temperatures? Macroscopically, the available capacity of the lithium battery is reduced because of the low temperature, and the internal resistance becomes large. On the microscopic level, the low temperature reduces the potential energy of the discharge of the active material of the lithium battery, and on the other hand, increases the discharge resistance of the system. The available power is reduced, the mileage is inevitably reduced, and the increase in internal resistance of the battery, which directly converts some of the available electrical energy into ohmic heat, is wasted. When the two factors are combined, the driving range will be significantly reduced.

Hydrogen and hydrogen vehicles lead the new energy life revolution

With the advancement of technology, consumers' acceptance of new energy vehicles is constantly increasing. Guangdong Heide Energy Technology Co., Ltd. has made breakthroughs in terms of mileage and charging anxiety of consumers. The water and hydrogen vehicles developed by the team are among them. one.

The fuel of water-hydrogen automobile is 1:1 methanol and water. The freezing point of methanol before mixing: -97.8 °C, the freezing point of water-hydrogen fuel after mixing: -90 °C, no problem of fuel freezing even in severe cold regions. . Hydrogen-hydrogen vehicles do not have to worry about charging in the winter, and electric vehicles are “powered down” in cold weather. In addition, the water-hydrogen vehicle is equipped with a water-hydrogen temperature control management system, which can realize intelligent adjustment of the battery temperature, thereby improving the efficiency and service life of the battery pack, and ensuring high-efficiency power generation and cruising range of the vehicle under any climatic conditions.

Hydrogen-hydrogen vehicles do not need to store electricity, and hydroelectric power modules replace traditional electric vehicle batteries. The power generation principle is a combination of methanol steam catalytic reforming hydrogen production technology and hydrogen fuel cell technology. The vehicle owner only needs to add methanol water raw material to have the same endurance capacity as the traditional internal combustion engine. The methanol refueling station can be put into use with a little modification at the original gas station, and the reconstruction cost is much lower than that of a new charging station; the water-hydrogen car is filled with 45L of methanol raw material within 3 minutes, and can last for 450 kilometers. The electric car fast charge also takes at least half an hour and the cruising range is shorter. The raw material of the water-hydrogen automobile is methanol water, and the power generation of methanol is about 1/2-1/3 of that of gasoline, and the cost is also reduced.

Hydrogen-hydrogen vehicles emit no pollutants [sulfur oxides (SOX), nitrogen oxides (NOX), particulate matter (PM2.5)], and the emission products are only pure water and nearly zero CO2. Compared with lithium batteries, water-hydrogen vehicles driven by water-hydrogen and electric power truly achieve zero emissions and high efficiency, and become a dark horse of new energy vehicles with excellent characteristics.