Fast charging method for battery

This application claims the priority to Chinese Patent Application No. 201410553510.1, filed on Oct. 17, 2014 in the Chinese Intellectual Property Office, the disclosure of which is incorporated in its entirety herein by reference.

The present invention relates to the field of battery, and particularly relates to a fast charging method for battery.

After 20 years of development, the energy density of the lithium-ion battery has been promoted greatly, but now the promotion of energy density runs into the bottleneck. The acceleration of the battery charging speed in limited energy density can effectively improve user experience. Hence, the fast charge lithium-ion battery with high energy density will stand out from the future competition.

On the premise of holding high energy density, to improve the charging speed of lithium-ion battery, lithium-battery researchers have done a lot work by changing electrode active material and current collector, and optimizing electrolyte component. These works have improved the battery fast charge performance greatly. But along with the improvement, the cost of battery raises and the related technology becomes more complex. On the basis of unchanging the ingredients and the structure, the performance of lithium battery can be optimized by adjusting the charged conditions.

The present charging method is that the battery is charged continuously with a constant current to a certain potential, and then the battery is charged with constant voltage at the certain potential. This method will make the cathode potential constantly increasing and the anode potential constantly decreasing. When the anode potential is lower than 0V, lithium ion will be reduced to lithium metal, liberated at the anode surface. Especially at low temperature, due to the decrease of the ion conductivity and the electron conductivity of lithium battery, the polarization degree will increase in charging process. The sustained charging method will make the polarization phenomenon more obvious, increasing the probability of the liberation of lithium. And the accumulation of lithium dendritic crystal on the electrode surface will pose a big threat to the safety performance of battery.

In view of the problems mentioned in background, the present invention aims to provide a fast charging method for battery, which can improve the charging safety performance of batteries.

Another object of the present invention is to provide a fast charging method for battery, which can improve the charging speed of batteries.

In order to achieve above objects, the present invention provides a fast charging method for battery, including the steps as follows: (1) the battery is charged with a constant current I 1 and the charging time is t 1 ; (2) the battery is charged with a constant current I 2 and the charging time is t 2 ; (3) the battery is discharged with the constant current I 2 and the discharging time is t 3 , recycling until the voltage reaches a pre-charging voltage of battery; (4) the battery is standed after the voltage reaching the pre-charging voltage, and the rest time is t 4 , and then the battery is charged with a constant current I 3 until the voltage reaching a cut-off voltage of battery, and then the battery is charged with a constant voltage until the current reaching a cut-off current I 4 ; wherein, I 2 <I 1 , t 2 <t 1 , t 3 <t 1 , I 2 <I 3 ≦I 1 , I 4 ≦I 2 .

The benefits of the present invention include:

The charging method provided in the present invention employs a heavy-current pulse with a wide range and a trickle current pulse with a narrow range, which can decrease the polarization brought by large pulse current charging. Then a trickle current pulse with a narrow range is employed in discharging process to further eliminate the polarization. Thus it greatly eliminates the problems of battery polarization, decreases the concentration of lithium ion on the anode surface, avoids the liberation of lithium at the anode, and then avoids the safety problems caused by the liberation of lithium, resulting in the improvement of the safety battery performance. Meanwhile, the fast charging method provided in the present invention can decrease the polarization in pulse charging phase, increase the time of whole pulse charging phase, shorten the full-charging time, and thus improve the charging speed in pulse charging phase greatly (early period of charging process).

FIG. 1 is the process illustration of the fast charging method for battery provided in the present invention.

FIG. 2 is the process illustration of the fast charging method for battery provided in Example 1 of the present invention.

FIG. 3 is the process illustration of the fast charging method for battery provided in Comparative Example of the present invention.

FIG. 4 is the graph of the charging voltage and the charging SOC changing with the time, in Example 1 and Comparative Example.

The charging method provided in the present invention is illustrated in details, referring to the Figures.

Referring to FIG. 1 , the fast charging method for battery according to the present invention includes the steps as follows: (1) the battery is charged with a constant current I 1 and the charging time is t 1 ; (2) the battery is charged with a constant current I 2 and the charging time is t 2 ; (3) the battery is discharged with the constant current I 2 and the discharging time is t 3 , recycling until the voltage reaches a pre-charging voltage of battery; (4) the battery is standed after the voltage reaching the pre-charging voltage of battery, and the rest time is t 4 , and then the battery is charged with a constant current I 3 until the voltage reaching a cut-off voltage of battery, and then the battery is charged with a constant voltage until the current reaching a cut-off current I 4 ; wherein, I 2 <I 1 , t 2 <t 1 , t 3 <t 1 , I 2 <I 3 ≦I 1 , I 4 ≦I 2 .

In the fast charging method for battery provided in the present invention, pulse charge with heavy-current (I 1 ) (in step (1)) is benefit for shortening the charging time, and pulse charge with trickle current (I 2 ) (in step (2)) reduces the speed of lithium ion to the anode surface, which can decrease the generation of polarization, and provides a certain buffer time for lithium ion diffusing from the anode surface to the anode inside. The charging method provided in the present invention employs a heavy-current (I 1 ) pulse with a wide range (t 1 ) (in step (1)) and a trickle current (I 2 ) pulse with a narrow range (t 2 ) (in step (2)), which can decrease the polarization brought by large pulse current charging. Then a trickle current (I 2 ) pulse with a narrow range (t 3 ) (in step (3)) is employed in discharging process to further eliminate the polarization. Thus it greatly eliminates the problems of battery polarization, decreases the concentration of lithium ion on the anode surface, avoids the liberation of lithium at the anode, and then avoids the safety problems caused by the liberation of lithium, resulting in the improvement of the safety battery performance. Meanwhile, the fast charging method provided in the present invention can decrease the polarization in pulse charging phase, increase the time of whole pulse charging phase, improve the charging speed in pulse charging phase greatly (early period of charging process), and thus shorten the full-charging time.

In the fast charging method for battery provided in the present invention, said fast charging method for battery is performed at room temperature.

In the fast charging method for battery provided in the present invention, the current value of I 1 is at a range from 2.5 C to 3 C, and the charging time t 1 is at a range from 10 s to 30 s; the current value of 12 is at a range from 0.02 C to 0.2 C, and the charging time t 2 is at a range from 1 s to 10 s; the current value ratio of I 1 /I 2 is at a range from 12.5 to 125, and the ratio of t 1 /t 2 is at a range from 2 to 10. The current value of 12 is less than the current value of I 1 , retarding the polarization generated by charging with the current I 1 , and the charging time t 2 is less than the charging time t 1 , avoiding the negative influence on the charging speed induced by charging too long with the trickle current.

In the fast charging method for battery provided in the present invention, in the step (3), the discharging time t 3 is at a range from 1 s to 10 s, and the ratio of t 1 /t 3 is at a range from 3 to 10. The discharging time t 3 is at a range from 1 s to 10 s, which can further decrease the concentration of lithium ion on the anode surface. The long discharge time will influence the whole charging speed, while the short discharge time cannot eliminate the polarization.

In the fast charging method for battery provided in the present invention, in the step (4), the rest time t 4 is at a range from 10 s to 60 s, and the current value of I 3 is at a range from 1 C to 3 C, and the current value of 14 is at a range from 0.01 C to 0.1 C. The rest time t 4 is at a range from 10 s to 60 s, which can reduce the polarization brought by pulse charge, benefit for the follow-up charging step with constant current. The current value of 13 is at a range from 1.C to 3.C, which meets the needs of various batteries and is adaptable to different range of values.

In the fast charging method for battery provided in the present invention, in the step (3), the pre-charging voltage is at a range from V 0 to V k ; wherein, V 0 is the critical voltage value of battery, and V k is the voltage setting value lower than the critical voltage value to avoid the liberation of lithium at the anode. V k is set based on avoiding the liberation of lithium at the anode induced by too low potential, due to the great polarization brought by pulse charging phase.

In the fast charging method for battery provided in the present invention, 4.2≦V 0 <4.5V; 0<V k ≦0.05V. It should be pointed out that V k cannot be set too high, and if V k is set too high, pre-charging voltage in pulse charging phase will be decreased, thus reducing the technical effects of the present invention.

In the fast charging method for battery provided in the present invention, in the step (4), the cut-off voltage may be V 0 .

In the fast charging method for battery provided in the present invention, in one embodiment, the pre-charging voltage is 4.34V, and the cut-off voltage is 4.35V.

In the fast charging method for battery provided in the present invention, said battery is lithium-ion battery, lead-acid battery, nickel-hydrogen battery or nickel-cadmium battery.

The Examples using the fast charging method for battery provided in the present invention, Comparative Example, testing method and testing results are shown below.