1. Capacity : Ah

This is a parameter that everyone is more concerned about. Battery capacity is one of the important performance indicators to measure the performance of the battery, which indicates that under certain conditions (discharge rate, temperature, termination voltage, etc.) the battery discharges the amount of electricity (available JS-150D discharge test), that is, the capacity of the battery, usually in amperage – hours as a unit (abbreviation, expressed in A-H, 1A-h = 3600C). For example, if a battery is 48V 200ah, then it means that the battery can store 48V*200ah=9.6KWh, i.e. 9.6 degrees of electricity. Battery capacity is divided into actual capacity, theoretical capacity and rated capacity according to different conditions. Actual capacity refers to the amount of electricity a battery can give under a certain discharge regime (a certain sedimentation level, a certain current density and termination voltage). The actual capacity is generally not equal to the rated capacity, which is directly related to the temperature, humidity, charging and discharging multiplier. Generally, the actual capacity is smaller than the rated capacity, sometimes even much smaller than the rated capacity; The theoretical capacity refers to the amount of electricity given by all active substances participating in the battery reaction. That is, the capacity of the most ideal state; rated capacity refers to the nameplate indicated on the motor or electrical appliances in the rated operating conditions can continue to work for a long time capacity. It usually refers to apparent power for transformers, active power for motors, and apparent or reactive power for phase-regulating equipment, and is measured in VA, kVA, and MVA; In application, the geometry of the pole plate, termination voltage, temperature, and discharge rate all have an effect on the capacity of the battery, e.g., in the winter in the north, the capacity of the battery drops rapidly if the cell phone is used outdoors.

2. Energy Density : Wh/kg-Wh/L)

Energy density, battery energy density, for a given electrochemical energy storage device, the ratio of the energy that can be charged to the mass or volume of the storage medium. The former is called “mass energy density”, the latter is called “volumetric energy density”, the unit is respectively watt-hour/kg Wh/kg, watt-hour/liter Wh/L. The power here, is the above mentioned capacity (Ah) and the operating voltage (V) of the integral. At the time of application, the metric of energy density is more instructive than capacity.

Based on the current lithium-ion battery technology, the level of energy density that can be achieved is about 100~200Wh/kg, which is still relatively low, and has become a bottleneck for many applications. This value is still relatively low, and has become a bottleneck in many occasions for the application of lithium-ion batteries. This problem also occurs in the field of electric vehicles, in the volume and weight are subject to strict limitations, the energy density of the battery determines the maximum driving range of electric vehicles, so the “mileage anxiety” this unique term. If the single driving range of electric vehicles is to reach 500 kilometers (comparable to traditional fuel vehicles), the energy density of the battery monomer must reach more than 300Wh/kg. The improvement of lithium-ion battery energy density is a slow process, much lower than the integrated circuit industry’s Moore’s Law, which results in the performance of electronic products and battery energy density improvement between the existence of a scissor gap, and with the time continue to expand.Energy density, battery energy density, for a given electrochemical energy storage device, the ratio of the energy that can be charged to the mass or volume of the storage medium. The former is called “mass energy density”, the latter is called “volumetric energy density”, the unit is respectively watt-hour/kg Wh/kg, watt-hour/liter Wh/L. The power here, is the above mentioned capacity (Ah) and the operating voltage (V) of the integral. At the time of application, the metric of energy density is more instructive than capacity.

Based on the current lithium-ion battery technology, the level of energy density that can be achieved is about 100~200Wh/kg, which is still relatively low, and has become a bottleneck for many applications. This value is still relatively low, and has become a bottleneck in many occasions for the application of lithium-ion batteries. This problem also occurs in the field of electric vehicles, in the volume and weight are subject to strict limitations, the energy density of the battery determines the maximum driving range of electric vehicles, so the “mileage anxiety” this unique term. If the single driving range of electric vehicles is to reach 500 kilometers (comparable to traditional fuel vehicles), the energy density of the battery monomer must reach more than 300Wh/kg. The improvement of lithium-ion battery energy density is a slow process, much lower than the integrated circuit industry’s Moore’s Law, which results in the performance of electronic products and battery energy density improvement between the existence of a scissor gap, and with the time continue to expand.

3. Charge/Discharge rate : C)

Charge/discharge multiplier is a measure of how fast or slow a charge is. This indicator affects the continuous and peak current of a lithium-ion battery when it is operating, and its unit is usually C (short for C-rate), such as 1/10C, 1/5C, 1C, 5C, 10C, etc. For example, if the rated capacity of a battery is 20Ah, and if its rated charge/discharge multiplier is 0.5C, it means that this battery, can be charged and discharged repeatedly with a current of 20Ah*0.5C=10A, up to the cut-off voltage of charging or discharging. If its maximum discharge multiplier is 10C@10s and its maximum charge multiplier is 5C@10s, then this battery can be discharged with a current of 200A for a duration of 10 seconds and charged with a current of 100A for a duration of 10 seconds.

The more detailed the definition of the charging and discharging multiplication index, the greater the significance of guidance for the use. Especially as an electric transportation power source of lithium-ion batteries, need to specify the continuous and pulse multiplier indicators under different temperature conditions to ensure that lithium ion batteries are used within a reasonable range.

4. 电压(Voltage, 单位：V)

The voltage of lithium-ion battery has some parameters such as open circuit voltage, operating voltage, charging cut-off voltage, discharging cut-off voltage and so on. Open-circuit voltage is not connected to any load or power supply outside the battery, measuring the potential difference between the positive and negative poles of the battery, this is the open-circuit voltage of the battery. Working voltage is the battery external load or power supply, in the working state, there is a current flow, measured by the potential difference between the positive and negative electrodes. Working voltage is related to the composition of the circuit and the operating state of the equipment, is the value of change. Generally speaking, due to the existence of the internal resistance of the battery, the operating voltage is lower than the open-circuit voltage in the discharged state and higher than the open-circuit voltage in the charging state. The charge/discharge cut-off voltage is the maximum and minimum operating voltage that the battery is allowed to reach. Exceeding this limit value will cause some irreversible damage to the battery, leading to the degradation of battery performance, and in serious cases, even causing fire, explosion and other safety accidents.

5. Cycle Life : times/Depth of discharge : DoD）

Depth of discharge is an indication of the percentage of battery discharge to the rated capacity of the battery. Shallow cycle batteries should not discharge more than 25% of their capacity, while deep cycle batteries can discharge 80% of their capacity. The battery starts discharging at the upper limit voltage and terminates discharging at the lower limit voltage. Define all discharged charge as 100%. Battery standard 80% DOD means to discharge 80% of the charge. For example, the initial SOC is 100%, I put it to 20% and stop, this is 80% DOD. lithium-ion battery life will gradually decline with the use and storage, and there will be more obvious performance. Still take smart phones as an example, after using the phone for a period of time, you can obviously feel the phone battery “not durable”, the beginning may only charge once a day, and later may need to charge twice a day, which is the embodiment of the battery life continues to decline. Lithium-ion battery life is divided into two parameters: cycle life and calendar life. Cycle life is generally measured in cycles, which characterizes the number of times a battery can be charged and discharged. Of course, there are conditions here, generally in the ideal temperature and humidity, with the rated charge and discharge current for the depth of charge and discharge (80% DOD), calculate the number of cycles experienced when the battery capacity declines to 20% of the rated capacity.

The definition of calendar life is a bit more complicated, the battery can’t always be charging and discharging, there are storage and shelving, and can’t always be in the ideal environmental conditions, it will go through all kinds of temperature and humidity conditions, and the charging and discharging multiplier is also changing all the time, so the actual service life needs to be simulated and tested. Simply put, the calendar life is the time span for the battery to reach the end-of-life condition (e.g., the capacity decreases to 20%) after a specific use condition under the use environment. Calendar life is closely related to specific usage requirements, which usually require specific usage conditions, environmental conditions, storage intervals, and so on. Calendar life is more meaningful than cycle life, but because calendar life is so complex and time consuming to measure, battery manufacturers generally only provide cycle life data. If you need to get the calendar life data, you usually have to pay extra and wait for a long time.

6. internal resistance : Ω）

The internal resistance of lithium-ion battery refers to the resistance of the current flowing through the inside of the battery when the battery is working, which includes ohmic internal resistance and polarization internal resistance, and polarization internal resistance includes electrochemical polarization internal resistance and concentration polarization internal resistance.
Ohmic internal resistance is composed of electrode material, electrolyte, diaphragm resistance and contact resistance of each part. Polarization internal resistance refers to the resistance caused by polarization during electrochemical reaction, including the resistance caused by electrochemical polarization and concentration polarization. The unit of internal resistance is generally milliohm (mΩ). Batteries with large internal resistance have high internal power consumption and serious heat generation during charging and discharging, which will cause accelerated aging and life span degradation of lithium-ion batteries, and at the same time limit the application of charging and discharging with large multiplication rate. Therefore, the smaller the internal resistance is, the better the life and multiplication performance of the lithium-ion battery will be.The internal resistance of lithium-ion battery refers to the resistance of the current flowing through the inside of the battery when the battery is working, which includes ohmic internal resistance and polarization internal resistance, and polarization internal resistance includes electrochemical polarization internal resistance and concentration polarization internal resistance.
Ohmic internal resistance is composed of electrode material, electrolyte, diaphragm resistance and contact resistance of each part. Polarization internal resistance refers to the resistance caused by polarization during electrochemical reaction, including the resistance caused by electrochemical polarization and concentration polarization. The unit of internal resistance is generally milliohm (mΩ). Batteries with large internal resistance have high internal power consumption and serious heat generation during charging and discharging, which will cause accelerated aging and life span degradation of lithium-ion batteries, and at the same time limit the application of charging and discharging with large multiplication rate. Therefore, the smaller the internal resistance is, the better the life and multiplication performance of the lithium-ion battery will be.

7. self-discharge

The phenomenon of self-discharge is the phenomenon that a battery will lose power even if it remains idle and unused. When a battery is sitting, its capacity is decreasing, and the rate of capacity decrease is called the self-discharge rate, usually expressed as a percentage: %/month. Self-discharge is what we do not want to see, a fully charged battery, put a few months, the power will be much less, so we hope that the lithium-ion battery self-discharge rate the lower the better. Here we need to pay special attention to, once the self-discharge of lithium-ion batteries lead to battery over-discharge, the impact is usually irreversible, even if re-charging, the battery’s usable capacity will have a great loss, life will be a rapid decline. So long-term placement of unused lithium-ion batteries, the battery must remember to charge regularly to avoid over-discharge due to self-discharge, performance is greatly affected.

8. Operating Temperature Range

Due to the characteristics of the internal chemical materials of lithium-ion batteries, lithium-ion batteries have a reasonable operating temperature range (common data between -20 ° C ~ 60 ° C), if beyond the reasonable range of use, will have a greater impact on the performance of lithium-ion batteries.  Different materials of lithium-ion batteries, its operating temperature range is not the same, some have good high-temperature performance, some can adapt to low-temperature conditions. The working voltage, capacity, charge/discharge multiplier and other parameters of lithium-ion batteries will change very significantly with the change of temperature. Prolonged high or low temperature use will also make the life of lithium-ion batteries to accelerate the decline. Therefore, efforts to create a suitable operating temperature range, in order to be able to enhance the performance of lithium-ion batteries to the maximum extent. In addition to working temperature restrictions, lithium-ion battery storage temperature is also a strict constraint, long-term high temperature or low temperature storage, will cause irreversible effects on battery performance.