What are the performance evaluation indicators of cr2032 3v lithium battery?

In power lithium battery systems, various parameters can characterize different performances of the system. This article lists various parameters of lithium batteries.

Lithium battery monomer

Lithium-ion battery monomers are composed of positive and negative electrodes, electrolytes and diaphragms, and are the basic structural units of battery modules and battery packs. As an electrochemical power source, batteries naturally have characteristic parameters such as voltage, internal resistance, capacity, energy, and power.

People mainly want to measure and evaluate battery parameters for two purposes. One is to achieve the purpose of active control. For example, if the battery monomer voltage is inconsistent, the energy storage capacity of the system is reduced. If the monomer voltage of the two poles can be actively adjusted, the system capacity can be amplified. The other is for safety considerations. The battery parameters have a fixed range. Detecting battery parameters and monitoring their boundaries can play a role in characterizing the safety status of the battery.

Voltage

The monomer voltage mainly depends on the type of monomer positive and negative electrode materials. Generally, lithium cobalt oxide and ternary positive electrodes with graphite negative electrodes can obtain a full charge voltage of about 4.2V, while lithium iron phosphate can only reach a maximum of 3.6V. The voltage here, to be more precise, should be the potential, which depends on the material properties. The potential value is equal to the open circuit voltage of the battery after being left still for a long enough time. The single terminal voltage in the closed loop is the voltage value detected by us using an external instrument, and its value is equal to the battery potential minus the voltage occupied by the battery internal resistance. The internal resistance of the battery is not constant, and it will change due to many factors, which will be discussed in the following section.

Continuing with the voltage, in addition to being determined by the material, the single voltage will change with the change of the charge, and it is a one-to-one correspondence. Therefore, in many cases, the battery charge (SOC) that cannot be directly and simply measured is often inferred by the battery open circuit voltage.

The single voltage is related to the activity of the active material inside the battery, so the temperature that affects the activity can also affect the level of the single voltage in a small range.

The higher the single voltage, the more energy a battery of the same capacity contains. Therefore, under the premise of ensuring safety, increasing the upper limit of the single voltage is a technical route to increase the energy density of the system.

Internal resistance

Inside the lithium battery, lithium ions move from one pole to the other. The factors that hinder the movement of ions in the process together constitute the internal resistance of the lithium battery. Its main parts include the physical internal resistance of the conductive parts; the inherent impedance of electrochemical substances such as motor materials, diaphragms and electrolytes; the temporary increase in the resistance to the movement of lithium ions when there is current inside the battery; these three parts together constitute the main body of the internal resistance.

Internal resistance is most sensitive to temperature, and the internal resistance value can change greatly at different temperatures. One of the important reasons for the decline in battery performance at low temperatures is that the internal resistance of the battery is too large at low temperatures.

As a power source, from the outside, the internal resistance of lithium batteries must be as small as possible. Especially in power applications, small internal resistance is a necessary condition.

Capacity

Lithium battery capacity, measurable capacity, is the maximum amount of electricity that can be charged and discharged within the reasonable maximum and minimum voltage range of the battery. Before being installed on the vehicle, the capacity of the single cell can be measured by charging and discharging. Once on the vehicle, the battery capacity can only be estimated by algorithms. In the battery management system BMS, accurate estimation of the battery state of charge (SOC) is an important indicator of its design level. The current well-known practice is to integrate the loop current ampere-hour under dynamic working conditions, and use the battery open circuit voltage to verify the battery power in the non-working state. Although there are many other methods, they are either unstable or too computationally intensive, and are rarely used in batches.

The capacity of a single cell is obviously affected by the degree of aging. As we all know, when the capacity decays to a limit value, the battery is eliminated. It can be seen that the two are absolutely correlated. Secondly, the capacity is also affected by temperature. At low temperatures, the activity of active substances decreases, the ions that can be provided become fewer, and the capacity will inevitably decrease.

Power

The power here should be more accurately called specific power, which is the charge and discharge power capacity of a single cell or the charge and discharge power capacity of a cell per unit mass or per unit volume. Whether a lithium battery can be charged and discharged at high power is determined when it is designed. The same lithium iron phosphate material or ternary material can be used to adjust the power performance of the battery by adopting process means, changing the electrode thickness or adding additives, adjusting the structure of active materials, the properties of electrolytes, and the properties of electrode SEI membranes. In general, power performance and energy density often cannot coexist. For the same material, the pursuit of high power will partially sacrifice energy density.

Once the battery cell is produced, its reasonable maximum charge and discharge current has been determined. In addition to adjusting the battery heat dissipation conditions and being able to change its maximum charge and discharge power in a small range, there is almost no room for further adjustment.

In addition to specific power, there are several parameters that can be converted to unit mass or volume to better show the battery level.

Specific capacity, specific energy

Volume specific capacity is the capacity divided by the battery volume, and mass specific capacity is the capacity divided by the mass. Extending from here, converting the battery cost to unit capacity, that is, talking about the price from the perspective of battery charging and discharging capacity: the cost-effectiveness calculation method of battery cell capacity is price-to-capacity, that is, the amount of electricity that can be discharged by the battery at a unit price. However, this method is generally less used.

Similarly, the mass specific energy of a battery cell is energy divided by mass, that is, the energy that a battery per unit mass can release; the volume specific energy is the energy that a battery or active material per unit volume can release; defining the battery price from the unit energy price is a common way in the industry. When talking about the battery price, it is how much 1kWh is.

Lithium-ion battery module

The battery module is formed by a series-parallel combination of several battery cells and is an element that makes up the battery pack. In actual operation, the battery module is rarely evaluated as a single subject. Occasionally, its voltage value is detected in some systems.

In fact, people often regard the module as a large battery. The difference is that the module has a single cell consistency problem, and the internal cell voltage difference is the focus of the equalization function inspection. The performance of the battery module is often subject to the lowest performance battery cell in the battery module, and is mainly reflected in the capacity indicator. When charging, the single cell with high voltage is fully charged first; when discharging, the cell with low voltage is discharged first. And it is very likely that these two cells are not the same. Therefore, the consistency of the cell parameters inside the module has a decisive impact on the performance of the module. Consistency is a parameter that needs to be considered at the module level more than at the single cell level.

This parameter will be ensured by screening the cells through various means at the beginning of the module grouping; after the module is produced, consistency is an important indicator for its acceptance; during operation, it can only be guaranteed by the balancing function of the BMS.

Lithium-ion battery system

The battery pack is generally composed of modules in series. In addition to inheriting all the parameters of the module, the total voltage of the battery pack determines the voltage platform of the electric vehicle power system, which is a very important parameter.

There are several indicators related to safety that will be continuously monitored for the battery pack as a whole. The positive and negative poles of the battery pack output to ground resistance, system leakage current, high-voltage interlock signal, system maximum and minimum temperature, system maximum temperature difference, system maximum temperature rise rate, system maximum and minimum single cell voltage, etc.

The above are all from the perspective of electrical performance. As a structural whole, the battery pack has many parameters that need to be continuously paid attention to, as well as environmental tolerance performance and abuse tolerance performance, which are not listed here one by one.

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