Patent Description:
Chinese Patent <CIT> discloses a rapid charging method which increases the limited charge voltage to compensate the internal voltage drop of the battery. During the charging of lithium-ion battery and polymer lithium-ion battery, stop charging the battery when it is charged to the limited charge voltage; the limited charge voltage between the two poles of the battery is set as U=2U<NUM>-US, wherein US is the stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current charging; wherein U<NUM> is charge cut-off voltage and commonly recognized by the industry as the charge cut-off voltage used by the low power constant-current and constant-voltage charging method; The stabilized voltage US is selected by conducting timing when stopping constant-current charging the battery and starting to lay up the battery; from some time interval, when the open-circuit voltage drop of the battery over a certain time interval is smaller than a certain value, the battery voltage would reach a steady state; the voltage at the first time point is selected as the stabilized voltage US of the battery.

When the method is applied in lithium iron phosphate battery, U<NUM> is charge cut-off voltage of <NUM>. 6V which is commonly recognized by the industry as the charge cut-off voltage used in the low power constant-current and constant-voltage charging method; the battery is charged to U=2U<NUM>-US, which is not charged to saturation, but only reaches <NUM>% of the saturation point, thus failing to make the most of the battery. Also <NUM>. 65V and <NUM>. 7V are commonly recognized by the industry as the charge cut-off voltage used by the low power constant-current and constant-voltage charging method, however the battery is charged to U=2U<NUM>-USwhich is not charged to saturation, therefore, they all may not make the most of the battery efficiency.

When the method is applied in Lithium cobalt battery, U<NUM> is charge cut-off voltage of <NUM>. 2V which is commonly recognized by the industry as the charge cut-off voltage used by the low power constant-current and constant-voltage charging method; the battery is charged to U=2U<NUM>-US and is not charged to saturation, but only reaches <NUM>% of the saturation point, which may not make the most of the battery.

In order to make the most of the battery efficiency, it is necessary to make appropriate corrections to the limited charge voltage. Prior art in this technical field is disclosed in documents <CIT> and <CIT>.

The present invention provides a lithium-ion battery charging method for correcting and compensating voltage so as to make the most of the battery efficiency.

Ideal Battery Charging: Charge the lithium-ion battery by constant-current & constant-voltage charging method, break the open-circuit, then stabilized voltage reaches constant-voltage charging voltage. Theoretically charging the lithium-ion battery by constant- current and constant-voltage charging method, when the lithium-ion battery is charged to infinitesimal current, its open-circuit stabilized voltage may reach constant-voltage charging voltage after the charging circuit is broken. While practically charging the lithium-ion battery by constant- current and constant-voltage charging method, when the lithium-ion battery is charged to self-discharge current, the charging current and self-discharge current of the lithium-ion battery would be in a dynamic equilibrium state; when the charging circuit is broken, the open-circuit stabilized voltage of the lithium-ion battery may be approximate to the value of constant-voltage charging voltage. Standard stabilized voltage: constant-current charge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to U<NUM> and then constant-voltage charge the lithium-ion battery to the cut-off current regulated by the Industry Standard or stipulated by the suppliers, then stop charging the lithium-ion battery. Start timing when stopping constant-current and constant-voltage charging the lithium-ion battery and starting to lay up the battery, from some time interval, the open-circuit voltage-drop of the lithium-ion battery would be smaller than some certain value during some certain time interval, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of the time interval as stabilized voltage USO of the battery.

Freedom degree of lithium-ion means the degree of lithium-ion's free activities among the positive electrode. During the charging process of the lithium-ion battery, the lithium-ion would de-intercalate from the cathode and intercalate into the anode through electrolyte. The lithium-ion is freely distributed in the lattice of the positive electrode and would find the niche place that most fits for itself. During the de-intercalation process, the lithium-ion with closer-range and of larger freedom degree would be more easily to de-intercalate from the cathode, and the lithium-ion with longer-range and of smaller freedom degree would be less easily to de-intercalate from the cathode. The lithium-ion strictly bond to the cathode has smaller freedom degree and more difficult to de-intercalate from the cathode, or only de-intercalate from the cathode with more charge energy.

The charging method disclosed by <CIT> would stop charging when the lithium-ion battery is charged to U=2U<NUM>-US=U<NUM>+(U<NUM>-US), which compensates the internal voltage drop (U<NUM>-US) of the battery, said voltage drop (U<NUM>-US) is caused by constant-current I charging to U<NUM> and being laid up; However, it only compensates the ohmic voltage drop, the concentration polarization voltage drop, electrochemical polarization voltage drop and other impedance voltage drop, without considering that the lithium-ion battery doesn't reach saturation when it is charged to U<NUM> with constant-current I and the de-intercalation of some lithium-ion of smaller freedom degree, thus the voltage drop compensated fails to charge the battery to <NUM>% saturation, which is not an ideal charging state. Also the charging method disclosed by <CIT> fails to address the effects of equipment error and measuring error. The <NUM>% saturation means that constant-current charge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to U<NUM> and then constant-voltage charging the lithium-ion battery to the cut-off current regulated by the Industry Standard or stipulated by the suppliers, then stop charging the lithium-ion battery; constant -current discharge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to discharge cut-off voltage regulated by the Industry Standard or stipulated by the suppliers, the discharge capacity would be <NUM>%, thus the charging state of the battery before discharging would be <NUM>% saturation. The present invention adds (U<NUM>-USO) to U=2U<NUM>-US=U<NUM>+(U<NUM>-US), charging the battery to U=U<NUM>+(U<NUM>-US)+(U<NUM>-USO) =3U<NUM>-US-USO, and takes the de-intercalation of some lithium-ion of smaller freedom degree into consideration, thus making charging the battery approximate to <NUM>% saturation, reducing the effects of equipment errors and measuring errors, which is much more close to ideal charging state.

The technical solution disclosed by the present invention eliminates the above-mentioned defects as follows:
Charge the battery to saturation by standard constant-current and constant-voltage charging method and then lie up the battery in an open-circuit, it is found that the standard stabilized voltage of the lithium iron phosphate battery is greatly different from its standard charge cut-off voltage, while the standard stabilized voltage of the lithium cobalt battery is little different from its standard charge cut-off voltage, which directly correlates to the low charging saturation of lithium iron phosphate battery and high charging saturation of lithium cobalt battery.

To make the most of the battery efficiency and charge the battery to saturation, it is necessary to add modified value (U<NUM>-USO) to the original value U =U<NUM>+(U<NUM>-US), the voltage value for correcting and compensating is as follows:
<MAT>.

Charge the lithium iron phosphate battery and lithium cobalt battery based on the voltage value, the battery may be charged more close to <NUM>% saturation by correcting and compensating voltage.

It is tested and verified on ternary(LiNixMnyCozO<NUM>) lithium-ion battery, lithium manganate (LiMn<NUM>O<NUM>) battery and lithium titanate (Li<NUM>Ti<NUM>O<NUM>) battery in the same way and achieves the same effect.

Lithium-ion battery charging method for correcting and compensating voltage, during the charging process, start to constant-voltage charge the battery when it is charged to the voltage limited charge voltage U, keep on constant-voltage charging until the charging current decreases to <NUM>%~<NUM>% of the charging current before constant-voltage charging, and then stop charging the battery, wherein the limited charge voltage between the battery positive and negative electrodes is set as 3U<NUM>-US-USO.

USO is the standard stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current and constant-voltage charging, whose value is selected by the following steps: when stopping constant-current and constant-voltage charging the lithium-ion battery and starting to lay up the lithium-ion battery, start timing; from some time interval TUso, the open-circuit voltage-drop of the lithium-ion battery would be smaller than some certain value during some certain time interval TUso, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of the time interval TUso as stabilized voltage USO of the battery.

US is the stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current charging.

U<NUM> is stabilized charge cut-off voltage.

Specifically, constant-current charge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to U<NUM> and then constant-voltage charge the lithium-ion battery to the cut-off current regulated by the Industry Standard or stipulated by the suppliers, then stop charging the lithium-ion battery; when stopping constant-current and constant-voltage charging the lithium-ion battery and starting to lay up the lithium-ion battery, start timing , from some time interval TUso, the open-circuit voltage-drop of the lithium-ion battery would be smaller than some certain value during some certain time interval TUso, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of the time interval TUso as standard stabilized voltage USO of the battery.

US is the stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current charging, whose value is selected by the following steps: start timing when stopping constant-current and constant-voltage charging and starting to lay up the lithium-ion battery, from some time interval TUs, the open-circuit voltage-drop of the lithium-ion battery would be smaller than some certain value during some certain time interval TUs, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of the time interval TUs as stabilized voltage US of the battery. wherein U<NUM> is standard charge cut-off voltage which is commonly recognized by the industry as the charge cut-off voltage used by the low power constant-current and constant-voltage charging method.

As an improved technical solution, the present invention provides a lithium-ion battery charging method for correcting and compensating voltage, wherein the battery may be charged to U=3U<NUM>-US-USO by constant-current charging method, and then stop charging.

As an improved technical solution, the present invention provides a lithium-ion battery charging method for correcting and compensating voltage, wherein the battery may be charged to U=3U<NUM>-US-USO by multi-section constant-current charging method and then stops charging, US is determined by measuring the current of the end-section before stopping charging.

As an improved technical solution, the present invention provides a lithium-ion battery charging method for correcting and compensating voltage, start to constant-voltage charge the battery when it is charged to U=3U<NUM>-US-USO by multi-section constant-current charging method, keep on constant-voltage charging until the charging current decreases to <NUM>%~<NUM>% of the charging current before constant-voltage charging, and then stop charging the battery; US is determined by measuring the current of the end-section before stopping charging.

As a measurement method for USO, the present invention provides a lithium-ion battery charging method for correcting and compensating voltage, when stopping constant-current and constant-voltage charging the lithium-ion battery and starting to lay up the lithium-ion battery, start timing ; select every <NUM> minutes as a time interval; from some time interval T<NUM>, the open-circuit voltage-drop of the lithium-ion battery would be smaller than <NUM> mV during <NUM> minutes time interval T<NUM>, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of said <NUM> minutes time interval T<NUM> as standard stabilized voltage USO of the battery.

As a measurement method for USO, the present invention provides a lithium-ion battery charging method for correcting and compensating voltage, when stopping constant-current and constant-voltage charging the lithium-ion battery and starting to lay up the lithium-ion battery, start timing; select every <NUM> minutes as a time interval; from some time interval T<NUM>, the open-circuit voltage-drop of the lithium-ion battery would be smaller than <NUM> mV during <NUM> minutes time interval T<NUM>, which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of said <NUM> minutes time interval T<NUM> as standard stabilized voltage USO of the battery.

As a measurement method for US, the value of US is selected by the following steps: start timing when stopping constant-current and constant-voltage charging and starting to lay up the lithium-ion battery, from some time interval TUs', the open-circuit voltage-drop of the lithium-ion battery would be smaller than some certain value during some certain time interval TUs', which means the battery voltage has already been in a stable state, then select the voltage corresponding to the first time point of the time interval TUs, as stabilized voltage US of the battery.

Wherein U<NUM> is standard charge cut-off voltage which is commonly recognized by the industry as the charge cut-off voltage used by the low power constant-current and constant-voltage charging method.

When the battery is lithium cobalt battery and U<NUM> is selected as <NUM>. 2V, U<NUM>≈USO, stop charging when it is charged to U≈U<NUM>+( U<NUM>- US).

It should be clarified that the standard stabilized voltage USO correlates to standard charge cut-off voltage U<NUM> and standard charge cut-off current, and is not that relevant to the charging rate, or even has nothing to do with the charging rate.

It is well-known that for lithium iron phosphate battery, the standard charge cut-off voltage U<NUM> may be <NUM>. 65V or <NUM>. Different value of U<NUM> would attain different value of standard capacity C<NUM>. The definition of C<NUM>: constant-current charge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to U<NUM> and then constant-voltage charge the lithium-ion battery to the cut-off current regulated by the Industry Standard or stipulated by the suppliers; and then discharge the lithium-ion battery with the current regulated by the Industry Standard or stipulated by the suppliers to discharge cut-off voltage regulated by the Industry Standard or stipulated by the suppliers, the discharge capacity would be standard capacity C<NUM>. The standard charge cut-off voltage U<NUM> for lithium iron phosphate battery may selected from any the known voltage values (<NUM>. 65V or <NUM>. 7V), the charging method for correcting and compensating voltage of the present invention U=U<NUM>+(U<NUM>-US)+(U<NUM>-USO)=3U<NUM>-US-USO can be applied to all when charging the battery with capacity close to the value of standard capacity C<NUM> during rapid charging.

It is well-known that for lithium cobalt battery, the standard charge cut-off voltage that most commonly and regularly used would be <NUM>. Now it has been developed lithium cobalt battery with high voltage of <NUM>. 3V and <NUM>. 35V, and now it is developing lithium cobalt battery with high voltage of <NUM>. 4V and <NUM>. 5V, which means the standard charge cut-off voltage U<NUM> is <NUM>. 35V, <NUM>. 4V and <NUM>. Different value of U<NUM> would attain different value of standard capacity C<NUM>. The standard charge cut-off voltage U<NUM> for lithium cobalt battery of different voltage may be selected from any the known voltage values (<NUM>. 35V, <NUM>. 4V or <NUM>. 5V), the charging method for correcting and compensating voltage of the present invention U=U<NUM>+(U<NUM>-US)+(U<NUM>-USO) =3U<NUM>-US-USO can be applied to all when charging the battery with capacity close to the value of standard capacity C<NUM> during rapid charging.

It is well-known that for ternary lithium battery, the standard charge cut-off voltage that most commonly and regularly used would be <NUM>. Now it has been developed ternary lithium battery of high voltage <NUM>. 3V and <NUM>. 35V, which means the standard charge cut-off voltage U<NUM> is <NUM>. 3V and <NUM>. Different value of U<NUM> would attain different value of standard capacity C<NUM>. The standard charge cut-off voltage U<NUM> for ternary lithium battery of different voltage may selected from any the known voltage values (<NUM>. 3V or <NUM>. 35V), the charging method for correcting and compensating voltage of the present invention U=U<NUM>+(U<NUM>-US)+(U<NUM>-USO)=3U<NUM>-US-USO can be applied to all when charging the battery with capacity close to the value of standard capacity C<NUM> during rapid charging.

Special cases: when standard charge cut-off voltage U<NUM> for lithium cobalt battery is selected as <NUM>. 2V (as shown in <FIG>), U<NUM>≈USO, stop charging the battery when it is charged to U≈U<NUM>+(U<NUM>-US), and attain almost the same effects as the battery charged to <NUM>. 2V by constant-current and constant-voltage charging method, that is to say, as to when standard charge cut-off voltage U<NUM> for lithium cobalt battery is selected as <NUM>. 2V, the corrected value (U<NUM>-US) may be negligible. However, when standard charge cut-off voltage U<NUM> for lithium cobalt battery is selected as other values, such as U<NUM>=<NUM>. 35V shown in <FIG>, the value of U<NUM> is greatly different from that of USO, it should take the corrected value (U<NUM>-USO) into account so as to make the battery charged to <NUM>% saturation.

Compared to the existing charging method, the present invention has the following beneficial effects:.

The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:.

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

402045Fe15C is lithium iron phosphate battery of high charging rate and with power parameters of <NUM>. 2V190mAh, which belongs to the LiFePO4/C battery system single cell (U<NUM>=<NUM>. 6V), with nominal capacity Cr=190mAh. According to GBT18287-<NUM> standard charging method:.

The same lithium iron phosphate battery as comparing example <NUM>-<NUM> (402045Fe15C), it is expected to charge the battery to saturation within <NUM> minutes. According to the rapid charging method disclosed by <CIT>, the current used for constant-current and constant-voltage charging I=Cr/t*<NUM>=<NUM>/<NUM>*<NUM>=1140mA (6C charging rate).

The same lithium-iron phosphate battery as the comparing example <NUM>-<NUM> (402045Fe15C), and the same stabilized voltage US measured in the comparing example <NUM>-<NUM>;.

The experimental results of comparing example <NUM>-<NUM>, comparing example <NUM>-<NUM> and embodiment <NUM> are listed in table <NUM>:.

The saturation level of charging: charge the battery by standard charging method and discharge the battery by standard discharge method, the discharge capacity is <NUM>%; charge the battery by non-standard charging method and discharge the battery by standard discharge method, the percentage of discharge capacity of non-standard charging method to that of standard charging method is the saturation level of charging.

703048H10C is polymer lithium-ion battery of high charging rate and with power parameters of <NUM>. 7V800mAh, which belongs to the LiCoO<NUM>/C battery system single cell (U<NUM>=<NUM>. 2V), with nominal capacity Cr=800mAh. According to GBT18287-<NUM> standard charging method:.

The same polymer lithium-ion battery as comparing example <NUM>-<NUM> (703048H10C), it is expected to charge the battery to saturation within <NUM> minutes. According to the rapid charging method disclosed by <CIT>, the current used for constant-current and constant-voltage charging I=Cr/t*<NUM>=<NUM>/<NUM>*<NUM>=4800mA (6C charging rate).

Embodiment <NUM>: lithium cobalt battery charging method disclosed by the present invention.

The same polymer lithium-ion battery as comparing example <NUM>-<NUM> (703048H10C), and the same stabilized voltage US measured in comparing example2-<NUM>.

60120HV10C is polymer lithium-ion battery of high voltage <NUM>. 35V and with power parameters of 235mAh, which belongs to the LiCoO<NUM>/C battery system single cell (U<NUM>=<NUM>. 35V), with nominal capacity Cr=235mAh. According to GBT18287-<NUM> standard charging method:.

The same polymer lithium-ion battery as comparing example <NUM>-<NUM> (60120HV10C), it is expected to charge the battery to saturation within <NUM> minutes. According to the rapid charging method disclosed by <CIT>, the current used for constant-current and constant-voltage charging I=Cr/t*<NUM>=<NUM>/<NUM>*<NUM>=470mA (2C charging rate).

The same polymer lithium-ion battery as comparing example <NUM>-<NUM> (60120HV10C), and the same stabilized voltage US measured in comparing example <NUM>-<NUM>.

In the practical implementation, alternatively, (<NUM>). measure US and USO of every battery before every charging, and then charge the battery by the charging method of the present invention (or the charging method disclosed by <CIT>), obviously it is cumbersome charging the battery in this way; (<NUM>). measure US and USO of every battery before charging, and each time charge the battery by the charging method of the present invention (or the charging method disclosed by <CIT>), obviously it is cumbersome likewise; (<NUM>). measure US and USO of battery of every model before charging, and each time charge every battery of said battery model by the charging method of the present invention (or the charging method disclosed by <CIT>), which is much more convenient. Although there may be slight difference between different battery of the same battery model, or between every charging of the same battery, which doesn't affect the implementation of the patent. The present invention may charge the battery close to saturation by charging method, while it may not guarantee charging the battery to <NUM>% saturation.

Claim 1:
A lithium-ion battery charging method for correcting and compensating voltage, characterized in comprising: during the charging process, starting to constant-voltage charge the battery when it is charged to the voltage limited charge voltage U; keeping on constant-voltage charging until the charging current decreases to <NUM>%-<NUM>% of the charging current before constant-voltage charging; and then stopping charging the battery, the limited charge voltage between the battery positive and negative electrodes is set as 3U<NUM>-US-USO;
USO is the standard stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current and constant-voltage charging;
US is the stabilized voltage dropped from U<NUM> which the battery is charged to by constant-current charging;
U<NUM> is stabilized charge cut-off voltage.