Power battery is the “heart” of new energy vehicles

As a new energy vehicle owner

Do you know the “heart” of your car?

Now let’s take lithium iron phosphate battery as an example

Let’s take a look at the “electrocardiogram” of your car

As shown in the figure above, lithium iron phosphate battery is a kind of lithium-ion battery. On the left side of the battery is the positive electrode composed of lithium iron phosphate (LiFePO4) material, which is connected to the positive electrode of the battery by aluminum foil. On the right side is a negative electrode composed of graphite, which is connected to the negative electrode of the battery by copper foil. In the middle is a polymer separator, which separates the positive and negative electrodes, through which lithium ions can pass and electrons cannot pass through the separator. The inside of the battery is filled with electrolyte.

During charging, lithium ions are removed from the positive electrode LiFePO4, transported by electrolyte, passed through the diaphragm, embedded in the surface of the negative graphite crystal, and then embedded in the graphite lattice. Discharge is the opposite.

Lithium ions release electrons in the process of free extraction and intercalation between the positive and negative electrodes to provide energy to the outside world.

Assuming that only lithium ion deintercalation occurs inside the battery, and no other changes occur, the battery can be recycled indefinitely. However, in actual use, there are many side reactions and changes in the internal structure of the battery at the same time, resulting in changes in battery performance. Improper use or operation can also exacerbate these changes, resulting in less battery capacity and reduced battery life.

Now that you know these principles, let’s answer the following questions.

Why are lithium batteries afraid of cold?

In the low temperature environment, the activity of the positive and negative electrode materials decreases, the viscosity of the electrolyte increases, the migration of lithium ions in the electrolyte slows down, the charge migration impedance increases, and the conductivity deteriorates.

The low temperature reduces the lithium intercalation ability of the anode material, and the lithium ion has not even been embedded in the negative electrode and has been reduced to metal lithium first. This reaction consumes lithium ions, drastically reducing battery capacity.

If the lithium battery is in a low temperature environment for a short time, this damage is only temporary and will not cause damage to the battery capacity. When the temperature rises, the performance will recover.

If you work and charge and discharge in a low temperature environment for a long time, some metal lithium persists on the surface of the negative electrode and cannot be embedded again, it will precipitate and precipitate to form lithium dendrite, if the lithium dendrite pierces the separator and causes a short circuit in the battery, it will damage the battery and even bring potential safety hazards.

Tips:

1. When the temperature is low, the vehicle is charged in time after use, at this time the battery is in a relatively warm state, the battery activity is good, and the charging efficiency is also high.

2. Try to park your vehicle in a warm garage.

3. Avoid placing the vehicle outdoors in the cold for a long time.

Why do lithium batteries prefer slow charging?

The nature of the embedded reaction determines that lithium batteries are not suitable for high-rate charging. Under high-rate charging conditions, the current density is too large, the crystal lattice of the cathode material is easily damaged, the anode graphite sheet layer may also be damaged, and the deposition of lithium ions will be more obvious. There is an increased risk of lithium dendrite formation on the surface.

When the battery is first charged and discharged, an SEI film will form at the negative electrode. SEI membranes are deposits formed by the decomposition of electrolytes and lithium ions. The formation of SEI membranes consumes lithium ions. The rapid deintercalation of lithium ions during fast charging will cause changes in the spacing of graphite structural layers, resulting in stress deformation. When the SEI is unstable, it will rupture and form a new SEI film, resulting in a further reduction of recyclable lithium, while increasing the internal resistance, causing the attenuation of battery capacity.

1. Because of the protection of a powerful battery management system, the damage of occasional DC fast charging to the battery is negligible.

2. When conditions permit, it is recommended to choose AC slow charging as much as possible.

3. Avoid sharp pedaling acceleration when driving, avoid instantaneous high-current discharge, and also protect the battery.

Why are lithium batteries afraid of overcharge and overdischarge?

Within the appropriate range, when lithium ions are removed from the positive electrode and embedding, it will cause a phase change in the crystal structure of the cathode material, which is reversible. When overcharge occurs, excess lithium ions are removed from the positive electrode, which will cause an irreversible phase transition or even collapse of the positive electrode structure, and the battery capacity will decay. Excessive lithium ions embedded in the negative electrode will also cause the deposition of metallic lithium on the surface of the negative electrode and even generate lithium dendrides. When overcharged, the electrolyte will also oxidize to form insolubles and gases, which will block the micropores of the electrode and hinder the migration of lithium ions, resulting in volume loss.

Similarly, when the battery is overdischarged, the negative carbon sheet structure may collapse, limiting the free deintercalation of lithium ions. Further overdischarge will also lead to oxidation of the negative copper foil, increased internal resistance of the battery, reduced capacity, and irrecoverable attenuation of life.

1. Pay attention to the remaining power information and avoid recharging when the power is exhausted.

2. If stored for a long time, it is recommended to fully charge the battery every three months, and then discharge it to 40%-60% storage to avoid over-discharge of the vehicle battery.

Why does the vehicle lose power when it is not parked for a long time?

When the battery is not in use, the capacity will also be naturally lost. This phenomenon is called self-discharge.

There are two situations of capacity loss caused by lithium battery self-discharge: one is reversible capacity loss; The second is the loss of irreversible capacity. Reversible capacity loss recovers while charging.

The oxidation rate of the electrolyte solvent has a direct impact on the self-discharge rate, and the positive and negative active materials may react with the solute during the charging process, resulting in lithium ion migration, making the battery capacity unbalanced and producing irreversible attenuation.

When self-discharging for a long time or frequently, lithium ions will form a certain deposition, increasing the degree of capacity imbalance between the two poles, and further leading to the loss of battery capacity.

1. When the vehicle cannot be stopped for a long time, it can be started remotely regularly to keep the battery active.

2. The zuijia way is, do not store for a long time.

Why should the right amount of charge be kept in a lithium battery?

From the moment the electrolyte is injected, the chemical reaction inside the lithium battery begins. The higher the voltage, the more intense the chemical reaction, the more unstable the structure of the electrode material, so a long time of storage with full charge will accelerate the aging of lithium batteries. Continuous cell usage in a fully charged state can also affect battery life.

1. When the vehicle is parked for a long time, it is recommended to keep the battery power between 40%-60%, which can effectively protect the battery and extend the battery life.

2. In normal use, under the premise of meeting the battery life, the power use between 30%-80% will make the “heart” of the car surging.

At first glance, does a lithium battery look like a particularly difficult baby? Can’t be hot, can’t freeze, can’t eat too much, can’t eat too little, can’t eat too fast… One careless life is discounted.

In fact, there is no need to worry too much, the cathode material of lithium iron phosphate itself has a more stable crystal structure, which determines its “longevity” gene, coupled with excellent battery management algorithms and strict thermal management design, the “blade battery” installed on the Han model has been experimentally verified, and the equivalent mileage can exceed 1.5 million kilometers, far exceeding the design life of the vehicle. As long as you use the car correctly under the guidance of the vehicle user manual, I believe that your battery will be able to “prolong life”!

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