Charging lithium battery fast charging method

　　Author ：Iflowpower – Portable Power Station Supplier

1 How can I call "fast charge" when charging? We charge the basic appeal: 1) Charge is fast; '2) Do not affect my battery life; 3) Try to save money, how much electric charge is released, try to charge it into my battery. So how quickly can you call fast? There is no standard literature to give specific values, we are temporarily referred to the number of thresholds mentioned in the most popular subsidy policy. The following table is the new energy passenger car 2017 subsidy standard.

It can be seen that the fast charge entry level is 3C. In fact, in the subsidy standard for passenger cars, there is no reflection requirements. From the propaganda materials of the general passenger car, you can see that everyone can generally be filled with 80% can be used as a fast charge, and they will be promoted.

So, then, the passenger car 1.6c can be entry level Charge reference value. According to this idea, the promotion is 15 minutes full of 80%, which is equivalent to 3.

2C. 2 fast charge bottleneck? In this context, the relevant parties follow physical subjects, including batteries, chargers, and power distribution facilities. We discuss fast charge, directly thinking that the battery will have problems.

In fact, before the battery has problems, the first is the problem of charging machine and distribution lines. We mentioned the charging pile of TSLA, its name is super charging pile, its power is 120KW. According to the parameters of Tslamodels85D, 96S75P, 232.

5ah, the highest 403V, ​​1.6C corresponds to the maximum demand power is 149.9kW.

It can be seen from here that there is a test of the charging pile of electric motor, 1.6C or 30 minutes. In national standards, it is not allowed to directly set the charging station directly in the original residential power network.

1 fast-filled pile used electric power has exceeded the electricity of dozen households. Therefore, both the charging station must set up a 10kV transformer separately, and a region's distribution network is not a new amount of 10kV substation. Then said the battery.

Can the battery carry 1.6C or 3.2C charging requirements, can be viewed from two perspectives of macro and micro.

3 The topic of the rapid charging theory of rapid charging theory is called "Macroable fast charging theory" because directly determined battery fast charging capacity is the nature, microstructure, electrolyte ingredients of the internal positive and negative electrode material of lithium ion batteries. Additives, diaphragm properties, etc., the content of these micro levels, we are temporarily placed on the outside of the battery, seeing the rapid charging of lithium-ion batteries.

Lithium-ion battery presence, the best charging current in 1972 US scientist Jamas proposes that the battery has the best charging curve during charging, and his Mas San Law, it is to be noted that this theory is proposed for lead-acid batteries, it defines The boundary condition of the maximum acceptable charging current is the emergence of a small amount of side, obviously this condition and the specific reaction type. But the system has the best solution, but it is quiz that it is. Specifically to the lithium ion battery, defining the boundary conditions of its maximum acceptable current can be re-meaningful.

Based on some research literature conclusions, its optimal value is still a curve trend similar to the law. It is worth noting that the maximum boundary condition of the lithium-ion battery, in addition to the factors of the lithium ion battery monomer, in addition to the factors of the system level, such as the heat dissipation ability, the maximum acceptable charging current of the system is different. Then we will continue to discuss down with this basis.

Maszer's formula description: i = i0 * e ^ αt; I0 ​​is the initial charging current of the battery; α is a charging acceptance rate; T is charging time. The value of I0 and α and the type of battery, structure and new and old. At this stage, research on battery charging methods is important based on optimal charging curve.

As shown in the figure below, if the charging current exceeds this optimal charging curve, not only the charge rate cannot be increased, but will add the quantity of the battery; if it is less than this best charge curve, although it will not harm the battery, it will extend Charging time, reduce charging efficiency. The elaboration of this theory includes three levels, which is for Masz trip: 1 for any given discharge current, the current of the battery charges in the battery is inversely proportional to the capacity of the capacity of α and battery; 2 About any given discharge The amount of the amount, α and discharge current ID is proportional; 3 The battery is discharged at different discharge rates, and its ultimate allowable charging current IT (acceptable capability) is the sum of the allowed charging current at each discharge rate. The above theorem is also the source of the concept of charging acceptance ability.

First understand what is charging acceptance. I found a circle and didn't see the unified official meaning. According to your own understanding, the charging acceptance ability is the maximum current of rechargeable battery charging at a certain amount of charge under certain environmental conditions.

The impact of acceptable means that there is no side effect that should not have, there is no adverse effect on the life and performance of the battery. Further, understand the three laws. The first law, after the battery is discharged, the charging acceptance ability and the current amount of power, the lower the charge, the higher the charging acceptance ability.

The second law, during charging, pulse discharge can help help the battery improve the real-time acceptance current value; the third law, charging acceptance ability will be superimposed by the pre-charge and discharge situation before charging. If the Mas is also suitable for lithium-ion batteries, the reverse pulse charging (the specific name is reflex fast charging method in the following] In addition to the view of the polarization, it is helpful to the temperature rise suppression, Massea is also active. Support for pulse methods.

Further, truly, it is a smart charging method, that is, the smart charging method, that is, the charging current value has always changed due to the Mascus curve of lithium-ion battery, so that the charging efficiency is maximized in the safety boundary. 4 Common Fast Charging Methods The charging method of lithium-ion batteries has a lot of species, for fast charging requirements, its important methods include pulse charging, Reflex charging, and intelligent charging. Different battery types, their applicable charging methods are not exactly the same, and this section does not make specific distinctions in this section.

Pulse charging This is a pulse charging mode from the literature, and the pulse phase is provided after the charging touch and the upper limit voltage is 4.2V, and continuously over 4.2V.

Do not mention the rationality of its specific parameter settings, different types of batches have differences. We pay attention to the pulse implementation process. Below is a pulse charging curve, and it is important to include three stages: precharge, constant current charging and pulse charging.

Charging the battery at a constant current during constant current charging, partial energy is transferred to the inside of the battery. When the battery voltage rises to the upper limit voltage (4.2V), enter the pulse charging mode: charging the battery with a pulse current of 1C.

The battery voltage is continuously increased in a constant charging time Tc, and the voltage will slowly fall when charging is stopped. When the battery voltage drops to the upper limit voltage (4.2V), charging the battery with the same current value, starting the next charging cycle, so recycled until the battery is full.

During the pulse charging process, the speed of the battery voltage will gradually slow, and the stop time T0 will become long. When the constant current charge duty cycle is as low as 5% ~ 10%, it is considered that the battery is full and end charging. Compared with conventional charging methods, the pulse charge can charge with a large current, and the concentration of the battery in the stopper battery and the ohmic polarization will be eliminated, so that the next round of charging is more smoothly, the charging speed is fast, The temperature is small, affecting battery life, and is currently widely used.

However, its disadvantages are obvious: a power supply to a limited stream function, which added the cost of the pulse charging method. Intermittent charging method, lithium-ion battery, intermittent charge, intermittent, intermittent electricity method, and variable voltage intermittent charge. 1) The change of the transistream intermittent transmission method is proposed by the professor of Chen Gongjia, Xiamen University.

It is characterized by changing constant current charging to a restricted current. As shown in the figure below, the first stage of the change of the change in the change is first, and the battery is charged with a large current value. When the battery voltage reaches the cutoff voltage V0, the charging is stopped.

At this time, the battery voltage has dropped sharply. After retaining a stop time, reduce charging current continues charging. When the battery voltage is raised to the cutoff voltage V0, the charging is stopped, so that the recovery time (generally approximately 3 to 4 times) charging current will reduce the set cutoff current value.

Then enter the constant voltage charging stage, charge the battery to the battery until the charging current is reduced to the lower limit, the charging ends. The main conference of the change in electricity-changing charge is increased by the intermittent manner that has gradually decreasing the current, that is, the charging process is accelerated, and the charging time is shortened. However, this charging mode circuit is more complicated, high cost, usually only considering when high-power fast charge.

2) Based on the change of the change in electricity, there is a change in electricity-resistant intermittent charge. The difference between the two is the first stage charging process, and the intermittent flow is changed to intermittently. Compare the above views (a) and Figure (b), visible constant pressure intermittent charge more conforming to the best charging charging curve.

In each constant voltage charging phase, due to the constant voltage, the charging current is naturally decreased according to the index law, and the battery current acceptance rate is gradually declined with charging. REFLEX fast charging method Reflex fast charging method, also known as reflection charging method or "snoring" charging method. Each of the work cycles of this method includes forward charging, reverse instant discharge and three stages.

It solves the battery polarization in a large extent and speeds up the charging speed. But reverse discharge will shorten lithium ion battery life. As shown in the figure above, in each of the charging cycles, the current charging time of 2C is 10s of TC, and then the TR1 of 0.

5 s, the reverse discharge time is 1 s TD, the stop time is 0.5 s TR2, each charging cycle time is 12s. As charging, charging current will gradually become small.

Intelligent charging method is currently a more advanced charging method. As shown in the figure below, its important principle is to apply DU / DT and DI / DT control technology. By checking battery voltage and current increments, the battery is charged, dynamic tracking The battery acceptable charging current makes the charging current from the beginning of the battery acceptable.

Such intelligent methods, generally combined with advanced algorithm technology such as neural network and fuzzy control, realizing automatic optimization of the system. 5 Charge mode The experimental data affecting the charging rate is compared with the constant current charging method and a reverse pulse charging. Constant current charging is charged the battery in a constant constant current throughout the charging process.

The constant current charging can have a large current charging, but over time, the polarization resistance gradually appears and adds more energy, causing more energy to heat, consumes and makes the battery temperature gradually increases. Comparison pulse charge method for constant current charging and pulse charging is a short reverse charging current after a period of charging. The basic form is as shown below.

In the charging process, increasing transient discharge pulses, the use of depolarization, reducing the effects of polarization resistance during charging process. Studies have specifically compared the effect of pulse charging and constant current charging. Take the average current of 1c, 2c, 3c, and 4c (c for the battery rated capacity value), which have been used in 4 sets of comparative experiments.

The amount of power released after the battery is filled with the battery. The figure shows the current and battery-side voltage waveform of the pulsed current when the charging current is 2C. Table 1 is a constant flow pulse charging experiment data.

The pulse period is 1s, the positive pulse time is 0.9 s, the negative pulse time is 0.1s.

ICHAV is a charging average current, QIN is charged; qo is the discharge power, η is the efficiency from the experimental results in the above table, the constant current charging and pulse charging efficiency are approximate, the pulse is slightly lower than constant current, but inward The total power supply of the battery is significantly more than constant current mode. 6 Different pulse duty cycle affect pulse charging The negative current discharge time is slow, there is a certain effect, and the longer the discharge time is, the slower charging; when the same flat, the unit is charged, the longer the discharge time. As can be seen from the table below, different duty cycle is efficient and admitted to electricity has a clear impact, but the numerical difference is not very large.

And this related, there are two important parameters, charging time and temperature are not displayed. Therefore, the selection of pulse charge is superior to the continuous constant current charging, and the specific choice of duty cycle, you must focus on the temperature rise and charging time demand. Reference 1 Wang Fei, Lithium Lithium Iron and Ternary Materials and Capacitance Charge Composite Electrode Due to Radio - charged Characteristics of Lithium Ion Battery in Electric Vehicles; 3 He Qiusheng, Lithium Ion Battery Charging Technology Summary.