What are the limitations on the charging speed of power CR2032 button cell batteries? Introduction to the basic working principle and structure of CR2032 button cell batteries

When discussing the charging speed of power lithium batteries, the battery's own tolerance is definitely the most unavoidable factor. No matter how powerful the peripheral charging equipment is, how powerful it is, and how strong the charging capacity is, if the battery itself has shortcomings in the acceptable charging capacity, then the charging speed will definitely not be fast. In addition, if the battery capacity is relatively large, the charging time will naturally be long.

If you have learned electrochemistry in high school, you will understand the charging and discharging process of power lithium batteries. The essence is that a series of redox reactions are carried out inside the battery to achieve the directional transfer of electrons between the positive and negative electrodes. Taking the current mainstream CR2032 button cell batteries as an example, although there are many types, the general structure is nothing more than positive electrode materials, negative electrode materials, diaphragms, electrolytes, etc. The charging process is basically the process of lithium ions escaping from the negative electrode, passing through the diaphragm and electrolyte, and diffusing to the positive electrode. The diffusion rate naturally becomes the key to the charging speed.

In theory, the charging speed can indeed be increased by increasing the current. However, if the current is too large, the diffusion speed of lithium ions inside the battery cannot keep up with the diffusion speed of electrons, which will cause the electron-ion transport to be disconnected, affect the battery performance, and reduce the charging capacity that can be achieved accordingly. The battery life is even more terrible, and there may even be a risk of fire and explosion.

So generally speaking, if you are not in a hurry, we recommend using slow charging as much as possible, which is conducive to extending the life of the battery.

The diffusion speed of lithium ions is closely related to temperature, positive electrode materials and structure.

The first is temperature. Generally speaking, the higher the temperature, the faster the diffusion speed. However, if the temperature is too high, it will also lead to problems such as reduced battery life and reduced charging safety. If the temperature is too low, it will not work either. When the temperature is too low, the metal lithium in the battery will be deposited, causing a short circuit inside the battery, especially for lithium iron phosphate batteries. Generally, the capacity of lithium iron phosphate batteries is only about 60-70% at 0℃, and only a pitiful 20-40% at -20℃. Therefore, in the cold winter in the north, electric vehicles must have the function of heating the battery module, which will naturally consume more power faster.

Secondly, the materials. The diffusion capacity of different materials varies greatly. Lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, NCM, NCA, etc. are all positive electrode materials with very good performance, and the latter two are also the two materials with the best performance and the highest application popularity. This is also an important reason why CR2032 button cell batteries are named after positive electrode materials today.

In the field of battery industry, the charge and discharge rate is usually used to describe the relationship between charging speed and current size. For example, the rate when the battery is fully charged in 1 hour is called 1C, and the rate that only takes 30 minutes is called 2C. By analogy, more than 1C can be called fast charging. Nowadays, the charging rate of CR2032 button cell batteries can generally reach 1C-3C, and the highest can reach 5C, but it is naturally far behind the discharge rate of 10C.

In addition to the bottleneck of the maximum charging rate, the charging rate that the battery can withstand under different SOC (State of Charge, that is, the remaining power) is also different. Generally speaking, the characteristics of the battery during the charging process are roughly similar to the above picture, and the charging rate will follow a rhythm of slow, fast and slow. Generally, when the SOC reaches more than 90%, the internal resistance of the battery will increase significantly, slowing down the charging rate. If you pay attention to most of the electric vehicles currently on sale, you will find that they will advertise that they can charge a large proportion of the power in a relatively short time, such as 1 hour or even 30 minutes, under a specific fast charging state, generally around 80%-90%. That's what it means.

So if you are an electric car user and want to save charging time as much as possible, try not to use the power below 10%, and you don't have to charge it fully when charging. It is enough to reach more than 90%, or to meet the mileage you need for your next trip.

What are the limitations on the charging speed of charging equipment?

In addition to the bottleneck of the battery itself, the peripheral charging equipment also has its own limitations. Simply put, the greater the output power of the charging pile, the shorter the charging time. But the charging pile cannot increase the charging power infinitely. Let's first talk about what the charging process of electric vehicles is.

When it comes to car charging, the first thing that comes to mind is naturally the charging pile. Simply put, the greater the output power of the charging pile and the smaller the battery capacity, the shorter the charging time will be. This is the same as filling a pool with water. The larger the drain pipe and the smaller the pool, the shorter the time will be. However, as an electric car user, of course, I hope that my battery capacity is large enough, so increasing the power of the charging pile is more important. Charging piles for cars are generally divided into two types: AC charging piles and DC charging piles. Let's talk about the two situations separately.

Let's talk about the AC charging pile with strong universality first. It mostly uses 220V AC charging with the same voltage as the household voltage. The general current is only 16A or 32A, and the charging speed is relatively slow. When the battery capacity is about 20kwh, it takes about 6-8 hours to fully charge.

Basic working principle and structure of lithium-ion battery

The basic principle of the battery: the positive electrode undergoes a reduction reaction to gain electrons; the negative electrode undergoes an oxidation reaction to lose electrons. Electrons pass through the load and flow from the negative electrode to the positive electrode, forming a current from the positive electrode to the negative electrode.

When introducing the working principle of CR2032 button cell batteries, taking the widely used 18650 lithium-ion battery as an example, the following is a schematic diagram and formula of the chemical reaction that occurs:

First look at the reaction during the discharge process (the cobalt oxide is removed first).

1 (+1) valence lithium ion <------(1-x) (+1/(1-x)) valence lithium ions + x (+1) valence lithium ions + x electrons

Let x=0.5, and we get:

1 (+1) valence lithium ion <------0.5 (+2) valence lithium ions + 0.5 (+1) valence lithium ions + 0.5 electrons

Multiply both sides by 2, and we get:

2 (+1) valence lithium ions <------1 (+2) valence lithium ion + 1 (+1) valence lithium ion + 1 electron

Simplify it further:

1 (+1) valence lithium ion <------1 (+2) valence lithium ion + 1 electron

This formula actually describes the overall reaction, not the reaction of a single individual. In simple terms:

The positive electrode has a (+1/(1-x)) valence (where 0

The negative electrode lithium atoms lose electrons and are oxidized to (+1) valence lithium ions. Electrons flow from the negative electrode into the load circuit, and lithium ions flow to the positive electrode through the electrolyte;

We are back to the basic principle of the battery. The core of the positive electrode is the (+1/(1-x)) valence lithium ions, and the core of the negative electrode is the lithium atoms. The two react to form (+1) valence lithium atoms, and the electron flow in the redox reaction forms an electric current.

In reality, when making batteries, materials are always needed to carry the lithium ions of the positive electrode and the lithium atoms of the negative electrode, just like goods always need shelves. Then the shelf of lithium ions is cobalt ions, which together with lithium ions form the positive electrode; the lithium atoms of the negative electrode are composed of materials such as porous graphite, so that the negative electrode will not be destroyed after the reaction. Between the positive and negative electrodes are electrolytes and separators , which is used for the flow of lithium ions and for isolating the positive and negative electrodes to prevent internal short circuits.

Why do we need to talk about the basic working principle and structure of CR2032 button cell batteries? This will be used later when we talk about the charging and discharging cut-off voltages of CR2032 button cell batteries and the hazards of overcharging and over-discharging.

Lithium-ion battery characteristics

The characteristic of CR2032 button cell batteries that users are most concerned about is the capacity. For example, the commonly mentioned 2000mAh refers to the number of charges that can be discharged by CR2032 button cell batteries under normal working conditions. Let's look at a specification sheet for a lithium-ion battery:

Several important parameters of this battery:

Capacity: 2500mAh

Charging cut-off voltage: 4.2V

Discharging cut-off voltage: 2.5V

Maximum charging current: 4000mA

Maximum discharge current: 20000mA

In short, they are all considered around battery capacity and charging and discharging. The battery capacity depends on how many electrons the negative electrode can release and how many electrons the positive electrode can absorb.

Why is there a charge cut-off voltage? In other words, what problems will occur after over-voltage charging? When describing the structure of CR2032 button cell batteries earlier, it was mentioned that the negative electrode is composed of graphite and lithium atoms. In fact, lithium does not exist in atomic form, but coexists with graphite in the form of lithium ions. After over-voltage charging, lithium ions will precipitate into crystalline lithium and cannot participate in charging and discharging, resulting in a decrease in battery capacity.

Why is there a discharge cut-off voltage? In other words, what problems will occur after excessive discharge? After excessive discharge, a large amount of lithium ions in the negative electrode flow to the positive electrode, causing the graphite to become empty and some areas to collapse, making it impossible to store lithium ions, which will also lead to a decrease in battery capacity.

Specifically for a lithium-ion battery, its capacity is different at different discharge currents and temperatures, and it changes with charging and discharging. The number of charging cycles increases and decreases. The following is the relationship between the temperature and battery capacity of a certain type of lithium-ion battery:

The following is the relationship between the discharge current and battery capacity of a certain type of lithium-ion battery:

Lithium-ion battery charging

The charging management of CR2032 button cell batteries is important to ensure that the charging current is not too large, not overcharged, the temperature is appropriate, and the charging speed is increased as much as possible. The following is a graph of the change in voltage, current and capacity during the charging process of CR2032 button cell batteries:

Charge with a constant current of 0.7C until the voltage rises to the charging cut-off voltage of 4.2V

Charge with a constant voltage of 4.2V until the current drops to 55mA

There are several important parameters here:

Constant current charging current

Constant voltage charging voltage

Charging cut-off current (a sign of charging completion)

The constant current charging voltage is fixed and cannot be modified at will. The constant current charging current can be adjusted as long as it does not exceed the maximum charging current, and its size will affect the charging speed. The charging cut-off current can be adjusted freely, and its size will affect the amount of electricity charged into the battery and the charging time.

Lithium-ion battery discharge

When CR2032 button cell batteries are discharged, it is important to pay attention to the discharge current not being too large and not over-discharging.

Lithium-ion battery power detection

The core issue of lithium-ion battery power detection is to obtain the remaining power and total capacity to prompt users of the remaining charging time and the remaining discharge time, and to provide a basis for users to arrange time reasonably.

In order to simplify the design, most devices now use battery voltage to judge the remaining power, which is acceptable in occasions where the requirements are not strict, but it is an imprecise behavior. When the battery is at the same remaining power state, the voltage is different when it is at different temperatures and different discharge currents. A more rigorous approach is to count the power.

After a new battery is installed on the device, it must undergo a complete discharge or complete charge. This is done with two points in mind: obtaining the total capacity of the battery and obtaining the current remaining power.

From no power to full charge, detect the number of charges charged to obtain the total capacity

After discharging for a period of time, the current power = previous power - discharge amount

After charging for a period of time, the current power = previous power + charge amount

With the current power, plus the current charging or discharging current, the remaining charging time and discharge time can be estimated; it can also be combined with the total capacity to provide power percentage information.

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