What makes a good lithium-ion battery?
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2020/12/19 10:22:40
Buying a good lithium-ion battery is very important.But what makes a good battery?Therefore, the characteristics of these good batteries are the important basis for our selection.
1. Life is long
Secondary battery life, including cycle life and calendar life two indicators.Cycle life is defined as a battery that has experienced the promised number of cycles but still has a residual capacity of 80% or more.Calendar life means that no matter whether it is used or not, the remaining capacity shall not be less than 80% within the period promised by the manufacturer.
2. The cost is low
The battery itself has a low price per unit of electricity, which is the most intuitive cost.In addition, as mentioned above, whether the cost is really low for users depends on the "full life cycle cost per kilowatt hour".The cost per kilowatt-hour (KWH) of the whole life cycle is obtained by multiplying the total power of the power battery by the number of cycles. The total price of the battery pack is divided by this sum to obtain the price per KWH of the whole life cycle.
3. High energy density/power density
Energy density refers to the energy contained in a unit weight or a unit volume;The average amount of electrical energy released per unit volume or mass of a battery.Generally, under the same volume, the energy density of lithium ion battery is 2.5 times that of nickel-cadmium battery and 1.8 times that of ni-MH battery. Therefore, under the condition of the same battery capacity, lithium ion battery will be smaller and lighter than nickel-cadmium and ni-MH battery.Battery energy density = battery capacity × discharge platform/battery thickness/battery width/battery length.
Power density refers to the value of the maximum discharge power per unit weight or volume.In the limited space of road vehicles, the overall energy and power can be effectively improved only by increasing the density.In addition, the current state subsidies take energy density and power density as the threshold to measure the level of subsidies, which further strengthens the importance of density.However, there is a certain contradictory relationship between energy density and security. With the improvement of energy density, security will always face newer and more difficult challenges.
4. High voltage
Since the cathode material is basically graphite electrode, the voltage of lithium battery is mainly determined by the material characteristics of the anode material. The upper limit of lithium iron phosphate voltage is 3.6V, and the highest voltage of ternary lithium and lithium manganese acid batteries is about 4.2V (the next part explains why the highest voltage of lithium battery cannot break through 4.2V).Research and development of high voltage cell is a technical route to improve the energy density of lithium batteries.To increase the output voltage of the cell, a positive electrode material with high potential, a negative electrode material with low potential and an electrolyte with high stable voltage are required.
5. High energy efficiency
Coulomb efficiency, also known as charging efficiency, refers to the ratio of the discharging capacity of the battery to the charging capacity during the same cycle.The percentage of specific discharge capacity and specific charge capacity.
For positive electrode materials, it is lithium embedded capacity/lithium deactivated capacity, that is, discharge capacity/charging capacity.For negative electrode materials, it is lithium removal capacity/lithium insertion capacity, that is, discharge capacity/charging capacity.
6. Good high temperature performance
Lithium battery has good high temperature performance, which means that the battery core is in a high temperature environment, the anode and cathode materials, the diaphragm and electrolyte of the battery can maintain good stability, can work normally at high temperature, the life will not accelerate the decay, high temperature is not likely to cause thermal accident out of control.
7. Good low temperature performance
Lithium battery has good performance at low temperature, which means that at low temperature, the lithium ions and electrode materials inside the battery maintain relatively high activity, high residual capacity, reduced discharge capacity and high charging rate.
8. It's safe
The safety of lithium batteries includes both the stability of the internal materials and the effectiveness of the safety auxiliary measures of the cell.Internal material safety cathode and anode materials, diaphragm and electrolyte, good thermal stability, good compatibility of electrolyte and electrode materials, good flame retardant of electrolyte itself.Safety auxiliary measures refer to the safety valve design, fuse design and temperature sensitive resistance design of the cell with appropriate sensitivity. After the failure of a single cell, it can prevent the fault from spreading and play an isolating role.
9. Be consistent
We learned about the importance of battery consistency through the barrel effect.Consistency refers to the small range of parameters such as capacity, open circuit voltage, internal resistance and self-discharge and similar performance of the cell applied to the same battery pack.If the cell monomer with excellent performance is not consistent, its excellence is often wiped out after it is grouped.Studies have shown that the capacity of battery pack is determined by the minimum capacity cell, and the life of battery pack is less than the life of the shortest cell.
10. Easy assembly
Lithium batteries have high energy density. In order to prevent single point energy from being too high, the energy of single battery is generally low.Batteries used in electric vehicles require a large number of cells to be organized and connected as a whole.The single cell is welded, pressed and other means to form a module, which is then connected by a high-voltage conductor to form a battery pack.In this process, whether the single cell is easy to be welded, whether the connection interface is designed for crimping, and whether the thermal management system is convenient for each cell to play a role, will affect the simplicity of the group design and the efficiency of the group.Some cell monomer density is high, but the shape is not friendly, after processing into the battery pack, the energy density is only half of the monomer.The cell's energy density will be wasted if the cell's connection characteristics are not good.
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