Disclosure of Invention
The invention aims to provide a charging method of a lithium ion battery, which combines the charging speed and the capacity maintenance through the cooperation of intermittent pulse charging with constant-current charging and constant-voltage charging in the charging process.
In order to solve the technical problem, the technical scheme of the invention is as follows: a charging method of a lithium ion battery is provided, the environment temperature of the lithium ion battery is-10 ℃ to-40 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging is carried out until the capacity of the battery is 20-30 percent of that of the battery;
step two, a constant current stage;
the charging multiplying power is 0.5C-1C, and the cut-off condition is the upper limit voltage of the battery;
step three, a constant pressure stage;
the charge cut-off condition was 0.05C.
Preferably, the intermittent pulse charging in the first step is performed according to a sequential cycle of forward pulse-stop charging for a period of time-reverse pulse to the pulse depth. The intermittent pulse charging function of the invention is depolarization and temperature rise, and reduces the internal resistance increase phenomenon of the battery caused by low-temperature environment, and the specific action mechanism is as follows: under continuous charging, lithium ions are accumulated on the surface of the negative electrode due to insufficient lithium embedding capacity of the negative electrode, intermittent pulse charging is that the sequence of positive pulse-charging stop for a period of time-reverse pulse is circulated to the pulse depth, the lithium ions migrate to the negative electrode during the positive pulse, and the lithium ions are embedded into the negative electrode; stopping charging for a period of time to allow the negative electrode to be embedded into the lithium ions remained in the positive pulse period, and relieving the phenomenon that the lithium ions which are not embedded into the negative electrode are accumulated on the surface of the negative electrode caused by the positive pulse, namely depolarization; the reverse pulse is a one-step rapid discharge process, and on one hand, the reverse pulse plays a role in guiding lithium ions still retained on the surface of the negative electrode back to the positive electrode and further depolarizing; on the other hand, the temperature rise of the system is large in the discharging process, the reverse pulse can improve the internal temperature of the battery, and the influence of low temperature on the internal resistance of the battery is reduced.
The preferred conditions for the forward pulse are: the forward constant-current charging multiplying power is 0.05C to 0.2C, and the single forward constant-current charging time is 1min to 10 min. The charging current of the forward pulse is too large, and lithium is easy to separate out; the single charge time of the positive pulse is too short, the charge capacity is less, the charge time is prolonged, and the single charge time of the positive pulse is too long, so that lithium ions are accumulated on the surface of the negative electrode to cause lithium precipitation.
Preferred conditions for the reverse pulse are: the reverse constant current discharge rate is 0.01C to 0.1C; the single reverse pulse time is 1s to 10 s. The single reverse pulse multiplying power is too large or the time is too long, so that the discharged electricity is large, and the charging time is prolonged.
The single stop charging time is 0.5s to 10 s. The single stop charging time is too short to buffer the lithium accumulation phenomenon caused by the C1 stage, and the single stop charging time is too long to prolong the charging time.
Preferably, the temperature of the battery is raised to-10 ℃ to 0 ℃ by intermittent pulse charging, the internal resistance of the battery is obviously reduced, the depolarization effect is obvious, and the lithium precipitation is effectively inhibited.
Preferably, the lithium ion battery is one of a lithium manganate battery, a lithium iron phosphate battery, a ternary battery, a cobalt acid lithium battery and a lithium ion secondary battery prepared from a composite material. The charging method provided by the invention is suitable for various battery systems and has remarkable universality.
The cutoff voltage in the constant current phase is preferably 3.65V. The constant current stage is used for increasing the overall charging speed, the internal resistance of a battery system is reduced and the temperature of the battery is increased after the gap pulse stage, at the moment, the battery can be charged by using a higher multiplying power relative to a low-temperature environment, the overall charging speed is increased, the charging and discharging multiplying power is 0.5C-1C in the constant current stage, and the cut-off condition is the upper limit voltage of the battery; the cut-off voltage does not influence the effect of the step, the multiplying power is set too small, the required time is too long, the multiplying power is set too large and exceeds the lithium intercalation capacity of the negative electrode under the environment, the lithium precipitation phenomenon occurs, and the battery is damaged. The constant voltage stage is used for eliminating polarization generated in the constant current stage, and the charge cut-off condition is 0.05C specified in GB/T31485.
By adopting the technical scheme, the invention has the beneficial effects that:
under the low-temperature environment, the ion conductivity of the internal electrolyte of the battery is poor, the steric hindrance for releasing and embedding lithium between the positive electrode and the negative electrode is large, the internal resistance of the battery is obviously larger than that of the battery at normal temperature, and if the battery is charged by continuously using the same charging rate as the normal temperature, the lithium ions cannot be embedded into the negative electrode, polarization is caused, and the phenomenon of lithium precipitation is generated. According to the design of a battery system, the invention provides a charge-discharge mode in a low-temperature environment, a pulse stage is added in the early stage of charging, at low temperature, pulse charging is utilized to reduce polarization, the multiplying power of each charging is reduced, the lithium ion is prevented from being deposited on the surface of a negative electrode to cause lithium precipitation, the front stage of the pulse is charged by using a low-current short-time wave band, the polarization phenomenon can be effectively reduced by the pulse, the temperature environment of the battery is improved, the internal resistance generated at low temperature is reduced, after the lithium ion is embedded into a certain amount, the internal environment of the battery is improved, and the current multiplying power and the charging time are subsequently improved, so that the integral charging speed is improved;
the pulse charging depth is 20-30%, the temperature rise of the battery is effectively guaranteed, the internal polarization of the battery is relieved, and the lithium separation phenomenon in the constant current charging stage is prevented; meanwhile, the charging time is considered, the charging efficiency is effectively improved, and the capacity retention rate is improved.
Thereby achieving the above object of the present invention.
Detailed Description
In order to further explain the technical solution of the present invention, the present invention is explained in detail by the following specific examples.
Example 1
In this example, a 2000mAh lithium iron phosphate battery was selected and charged at-20 ℃ according to the following steps and conditions:
the environment temperature of the lithium ion battery is-20 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging;
positive pulse is 0.05C for 1 min; stopping charging for 0.5 s; reverse pulse 0.01C, 1 s;
recycling to 20% of the capacity;
step two, a constant current stage;
charging to 3.65V at a multiplying power of 0.5C;
step three, a constant pressure stage;
the voltage is 3.65V to 0.05C.
Example 2
In this example, a 2000mAh lithium iron phosphate battery was selected and charged at-20 ℃ according to the following steps and conditions:
the environment temperature of the lithium ion battery is-20 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging;
positive pulse is carried out for 0.1C and 3 min; stopping charging for 3 s; reverse pulse 0.03C, 3 s;
recycling to 23% of the capacity;
step two, a constant current stage;
charging to 3.65V at a multiplying power of 0.6C;
step three, a constant pressure stage;
the voltage is 3.65V to 0.05C.
Example 3
In this example, a 2000mAh lithium iron phosphate battery was selected and charged at-20 ℃ according to the following steps and conditions:
the environment temperature of the lithium ion battery is-20 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging;
positive pulse is carried out for 0.15C and 5 min; stopping charging for 5 s; reverse pulse 0.05C, 5 s;
c1 to C3 cycle to 25% of capacity;
step two, a constant current stage;
charging to 3.65V at the multiplying power of 0.7C;
step three, a constant pressure stage;
the voltage is 3.65V to 0.05C.
Example 4
In this example, a 2000mAh lithium iron phosphate battery was selected and charged at-20 ℃ according to the following steps and conditions:
the environment temperature of the lithium ion battery is-20 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging;
positive pulse is 0.2C for 7 min; stopping charging for 7 s; reverse pulse 0.07C, 7 s;
recycling to 27% of the capacity;
step two, a constant current stage;
charging to 3.65V at a multiplying power of 0.8C;
step three, a constant pressure stage;
the voltage is 3.65V to 0.05C.
Example 5
In this example, a 2000mAh lithium iron phosphate battery was selected and charged at-20 ℃ according to the following steps and conditions:
the environment temperature of the lithium ion battery is-20 ℃, and the method sequentially comprises the following steps:
step one, intermittent pulse charging;
positive pulse is 0.2C for 10 min; stopping charging for 10 s; reverse pulse 0.1C, 10 s;
c1 to C3 cycle to 30% of capacity;
step two, a constant current stage;
charging to 3.65V at the multiplying power of 1C;
step three, a constant pressure stage;
the voltage is 3.65V to 0.05C.
Comparative example 1
In the embodiment, a 2000mAh lithium iron phosphate battery is selected and charged at-20 ℃ according to the following conditions: the charge was charged to 3.65V at a rate of 0.2C and was constant voltage to 0.05C.
Comparative example 2
In the embodiment, a 2000mAh lithium iron phosphate battery is selected and charged at-20 ℃ according to the following conditions: the charge was charged to 3.65V at a rate of 0.5C and was constant voltage to 0.05C.
The specific performance index data after the batteries of examples 1 to 5 and comparative examples 1 and 2 were completely charged are shown in table 1.
Table 1 list of charging performance indexes of examples 1 to 5 and comparative examples 1 and 3 at-20 deg.c
| Group of | temperature/deg.C of battery | charge/mAh | Time/h for charging | Internal resistance/m omega |
| Comparative example 1 | -16 | 1680 | 5.3 | 12 |
| Comparative example 2 | -15 | 1359 | 2.5 | 27 |
| Example 1 | -8 | 1959 | 3.4 | 7 |
| Example 2 | -6 | 1946 | 3.2 | 9 |
| Example 3 | -5 | 1940 | 3.1 | 10 |
| Example 4 | -2 | 1934 | 2.9 | 10 |
| Example 5 | 0 | 1930 | 2.8 | 11 |
As can be seen from table 1, in the comparative example 1, the charging was performed in the low-rate mode at-20 ℃, the time spent for 5.3 hours was too long, and the charged amount of electricity was only 1680 mAh; comparative example 2 at a rate of 0.5C, although the time of use was short, the charge amount was only 1359mAh due to the increase of internal polarization; in both modes, the effect is not ideal; by adopting the charging method of the present invention, the battery capacity in examples 1 to 5 is more than 20% more than the battery capacity charged in the comparative mode, and it can be seen that the charging mode is helpful for increasing the charging capacity of the battery in the low temperature environment; compared with the temperature of the battery after the battery is charged, the scheme provided by the invention effectively improves the overall temperature of the battery, the battery is beneficial to charging more electric quantity after being heated, and the higher the charging multiplying power is, the higher the temperature rise of the battery is, so that a small part of capacity is correspondingly damaged; compared with the internal resistance of the battery after charging, the proposal provided by the invention effectively slows down the accumulation of lithium ions on the negative electrode caused by high-rate charging and reduces the internal resistance of the battery; the lower the charging multiplying power is, the lower the internal resistance is, the larger the charged electric quantity is, the larger the charging multiplying power is, the shorter the charging time is, the whole charging time is less than 3.5h, the charged electric quantity is greater than 1930mAh and is 96.5% of the original capacity 2000mAh, the whole data accords with the market demand, and the low-temperature charging mode provided by the invention is proved to be practical and effective.
The battery pack of example 5 was tested for charge performance at-30 ℃ and-40 ℃ as detailed in table 2.
TABLE 2 Charge Properties at-30 ℃ and-40 ℃ of the battery obtained in example 5
| Temperature of | temperature/deg.C of battery | charge/mAh | Time/h for charging | Internal resistance/m omega |
| -30℃ | -5℃ | 1837 | 2.6 | 11 |
| -40℃ | -17℃ | 1548 | 2.4 | 16 |
As can be seen from Table 2, as the ambient temperature decreases, the surface temperature of the battery decreases, the charging amount decreases, the charging time is shortened, the internal resistance increases, but the charging amount is still 92% at-30 ℃, and 77% at-40 ℃ is far higher than the same level.