RU2534029C1 - Charging method for lithium ion battery discharged below permitted level - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: battery is connected to a charger; the latter is switched on thus ensuring delivery of power supply to the battery from an external source. In cases of early spontaneous stoppage of charging process (in overcharged state or in connection with it) the charger is switched off and switched on again. These actions are performed each time when charging process is stopped spontaneously before charging process reaches normal mode. The latter is characterised by charging current till standard automatic shutoff of the external source or forced stoppage of charging process.

EFFECT: recovery of the overcharged battery.

3 dwg

Description

The invention relates to electrical engineering, specifically to methods and devices for charging lithium-ion (Li-Ion) electric batteries from AC or DC via converters.

Charging and discharging lithium-ion batteries are distinguished by many features and potential improvement opportunities.

Charging, today, is carried out, according to the generally accepted methodology, as a rule, in two continuous stages (two charging phases): first at constant current, and when the battery reaches its rated voltage, the charger automatically switches to battery power mode with constant voltage. For 1-1.5 hours, the serviceable battery is fully charged. The external power is disconnected in the charger / in the battery also automatically. The discharge is carried out, according to the instructions, not to a zero voltage value, but to a certain “critical” value, for example 2.2 V, below which subsequent charging becomes problematic. It is possible that such a “rechargeable” battery will fail.

In literature and patent sources, no information was found on the charging methods (it is now more correct to say recovery or figuratively “resuscitation”) of overcharged lithium-ion batteries.

There is, however, a known method for recovering and charging not lithium-ion, but acid and alkaline lead “automobile” batteries, as well as cadmium-nickel (with the corresponding charging devices), called “pulse charging” [Pulse charging system of batteries. //https://docs.google.com/document/pub?id=1kYF96xDpz7tMH17HA1w8zxZwh2_L5yAkMtkAlllzF4o; Charging a car battery (how to charge a car battery). // http://www.avto3.com/Battery/battery.html. Section 2.5 “Charging the battery with pulse current”, Fig. 1.1].

However, firstly, the effectiveness of this method has been identified and recommended for batteries of types that do not include lithium-ion, with other specific features. In other words, the applicability of the well-known pulsed method of restoring and charging batteries to Li-Ion batteries has not been established (the question remained open).

Secondly, in the known method of impulse charging, impulses are applied forcefully, with a constant duty cycle, regardless of the “behavior” (current state) of the battery itself. The meaning of the critical nature of the last remark will become clear from the subsequent presentation of the material of this application.

Thirdly, the duration of each pulse is only microseconds.

Further, for the constant maintenance of the electric energy stored in the battery and to prevent its deep discharge, it is known, for example, to use the method of operating a rechargeable battery of a hybrid car / electric car (“The method of charging a lithium-ion rechargeable cell ...”), which can also be called “pulse charging” [ RU 2471276, H02J 7/04, H01M 10/44, 12/27/2012].

The method consists in determining whether the degree of accumulation of the lithium-ion battery cell has decreased to the first predetermined value. Determine if the hybrid vehicle is in a stopped state. The lithium-ion battery cell is charged to a second predetermined value when the hybrid vehicle is stopped. At the charging stage, the period is divided into two or more separate charging periods and periods without charging. Charging is carried out in a separate charging period. Suspension of charging or discharging is carried out in the period without charging. The duration of each of the separate charging periods is at least 40 seconds. This time, the duty cycle is variable, but still not tied to any spontaneous failure of the battery to be charged, it is determined by the algorithm of the vehicle’s cycle of movement on the ground (the variable duty cycle “discharge-charge” of the battery corresponds to the variable duty cycle “car-parking”).

The described "pulse charging" is carried out by the charging control device, in the second phase - charging the battery at constant voltage, with repeated automatic forced interruption of the charging current to switch to working discharge mode and automatic forced renewal of charging at short-term parking of the car when the battery is in working discharge not necessary. The technical result is to prevent a decrease in battery capacity. That is why the charging duty cycle in the general operational period is determined by the “duty cycle of the car’s parking, for example at intersections and in traffic jams. This process does not affect the initial charging area of a fully discharged battery.

We are in this case interested in the behavior of the battery in the field of "critical" and "supercritical" discharge. And not just any type of battery, but lithium-ion batteries. For there are no universal “recipes” here and cannot be.

In numerous instructions and recommendations for the operation of lithium-ion batteries, users are warned:

“Deep discharge will become stressful for the battery and can only shorten its life. If a protective shutdown has occurred, in no case do not leave the battery discharged for a long time - it is worthwhile to quickly charge it to at least 30-40% of the capacity. Lithium-ion and lithium-polymer batteries come in various sizes and shapes, but the rules for good handling are the same for all varieties. Do not leave the battery dead for long. After a few weeks, due to self-discharge, the voltage of a dead battery will drop below a critical voltage, to 2.2-2.9V. In this case, the protection circuit will put the battery into "sleep" mode and turn off. After that, the standard charger, most likely, will not be able to get it out of this state ”[How to extend the life of lithium-ion batteries. // http://aver.ru/repair/kak-prodlit-zhizn-litiy-ionnyh-akkumulyatorov/].

Closest to the claimed invention according to the purpose and combination of design features (prototype) is a method of charging a fully discharged lithium-ion battery ("System and method of inductive charging of the battery"), in which the battery is connected to the charger and include the latter, thereby applying to the battery converted to direct current power from an external source of electricity [RU 2469452, H02J 7/02, 10.12.2012, para. 5, 6, FIG. 1, i.e. regarding the description of ordinary, non-inductive charging].

In it, more precisely, in its overview part, including the graph in Fig. 1, the discharged battery (up to the maximum permissible residual value of about 2.2 V) is first charged at a constant current level in the range from 0.1C to 1C A, where C is the battery capacity in ampere-hours, until the required voltage of approximately 4.2 V is established on the battery. At this point, the battery charger switches to constant voltage mode, providing sufficient power to maintain the battery at this final voltage and at the same time providing additional battery charging. The charging schedule in figure 1 in the prototype reflects the standard two-stage charging process.

However, in an emergency situation - with the initial over-discharged state of the battery, characterized by its residual voltage below the maximum permissible level (mentioned 2.2 V), and precisely for this reason, already in the first minute of charging (the green LED on the charger blinks), As a rule, a premature spontaneous termination of the charging process (the transition of the green indicator from the pulsed glow mode to the constant glow mode) while maintaining the supply voltage of the charger (after oyannoe glow of the red LED).

Expecting an equally spontaneous renewal of the charging current (renewal of the pulsed glow of the green indicator) is futile, naive and, in general, unsafe.

The more the battery was initially re-discharged, the lower the probability of “starting” the charging current in the normal mode of operation of the charger, which usually prompts users, especially at the “kitchen” level, to come to terms with another financial and financial loss and throw the battery in the trash as “shrunken” (possibly “overgrown” with lithium dendrites).

In this case, the technological potential that is still beyond the borders of human knowledge and / or information access is not used.

In particular, the author-applicant of this application was uncomfortable due to the “failure” of the charger to charge batteries of the type EEMB LIR123A (3.7 V, 700 mAh) after their hidden excessive discharge as part of the PB-4-1ML self-defense weapon due to spontaneous power-up of the laser pointer). After about 30 seconds flowing through the battery, the charging current spontaneously disappeared.

Thus, the known prototype method is still not perfect enough, which is expressed in its limited ability to charge lithium-ion batteries in a state of the transcendent value of the residual (a priori, initial when charging) voltage. This, in turn, determines the technical and economic imperfection of not only the charging technology (charging method and charger), but also the insufficiently high reliability of those devices and systems whose functioning depends on the battery as an autonomous source of their power.

The effectiveness of the application, as a “recovery procedure”, of a pulsed, and also high-frequency (microsecond) recovery and charging method with constant duty cycle (successfully used for other types of batteries), has not been established. Although this is also a pretty close analogue of the proposed method.

The task to which the invention is directed is to increase the technical and operational (technological) and economic characteristics of the method of charging lithium-ion (Li-Ion) batteries by providing the ability to restore over-discharged (discharged below an acceptable level) batteries to achieve their full charge when failure to charge in the normal mode of operation of known specialized chargers.

The technical result in accordance with the task is achieved due to the fact that in the method of charging a fully discharged lithium-ion battery, in which the battery is connected to the charger and include the latter, thereby supplying the battery converted to direct current from an external power source, at premature spontaneous termination of the charging process, according to the indication of the charging current indicator, in the case and due to the initial over-discharged state of the battery, generated by its residual voltage below the maximum permissible level, turn off and turn on its external power, repeating these steps until the charging process returns to normal mode, characterized by the absence of the indicated premature spontaneous interruption of the charging current until the regular automatic shutdown of the external power when charging to a predetermined value or forced end of charge.

Among the known charging methods, no such combination of essential features would coincide with the claimed combination of features. At the same time, it is due to the latter that a new technical result is achieved.

In more detail the essence of the invention is disclosed in the following two examples of implementation and is illustrated by drawings, which show:

figure 1 shows the simplest diagram of the implementation of the method;

figure 2 - combined charging graphs in normal mode (as in the prototype method) - A, and with the present method - B, where t - time; U - battery voltage; U_cr - “Critical” residual voltage during discharge; U₀- the actual residual voltage at the beginning of charging; U_max - maximum (rated) voltage; I is the charging current;

figure 3 is an example of a block diagram of an upgraded charger.

To implement the proposed method in the first, simplest embodiment, no new device is required at all, except for a standard (suitable for charging a battery in a known manner) charger.

The author-applicant in his empirical studies (in fact, in actual practical use as a user), which led to the claimed invention, used the aforementioned LIR123A mass series batteries with the power supply specialist ROBITON Art. Smart Charger Universa / (output voltage 7.4 V).

Battery 1 insert (see figure 1) in a specially provided for him bed (disputes between the spring electrical contacts "+" and "-") of the charger 2 and include the latter by inserting his plug 3 to a power outlet 4 (220-230 V, 50/60 Hz). Make sure that there is an external power supply when the red LED 5 lights up. They are also convinced of the appearance and flow of the charging current I in the battery (see Fig. 2) by the green LED 6 blinking and glowing in blinking mode (the battery 1 is supplied with the power converted from the device 2 into direct current I from an external network power source). Continue to constantly or periodically monitor the behavior of the LED 6 as an indicator of the charging current.

In case of premature (depending on the degree of overdischarge (how much the residual voltage of the battery is less than the passport “critical” value U_cr., usually within the first 0.5 min) spontaneous termination of the charging process, as evidenced by the clearly premature transition of LED 6 from flashing to solid, in the case and due to the initial over-discharged state of battery 1 (characterized by its residual voltage below the maximum permissible level: U₀<U_cr) remove the plug 3 from the outlet 4 (or disconnect the local connector on the mains cable of the charger 2) and immediately reconnect them. Thus, they turn off and immediately turn on the external power (temporarily interrupt it). In this case, of course, both LEDs 5 and 6 first go out and then light up again, and green 6 starts to work again in a blinking mode, which indicates the continuation of the spontaneous charging process, in fact the current failure in the charging process (abnormal mode).

After ascertaining the existence of such a “step” of restoring the battery’s charge properties (“the patient is more likely alive than dead”), they continue to monitor the behavior of LED 6.

In the second (from the author’s experimental studies, about another 1 minute of charging), the third and, possibly, subsequent (so far in an unpredictable amount), spontaneous shutdowns, they perform actions identical to those described before the charging process enters the “stationary” mode when the green LED will flash until the battery is fully charged (more precisely, to its specified value or until the charge is forcibly completed for any organizational reasons). Charging is completed automatically (automatic operation in charger 2 and / or battery 1 is triggered), which is manifested in the regular transition of the glow of LED 6 to non-blinking mode, now no longer simulating full charge initially, but testifying to it.

Thus, on the charging graph (see Fig. 2), an intermittent charging curve (function f) U = f (t) with a variable (unpredictably increasing up to unity) duty cycle is formed. The indicated duty cycle depends on the degree of overcharge of the battery U₀/ U_cr, moments of time of spontaneous zeroing of the charging current I, moments of detection of zeroing and production of switching off and on (manual switching). That is why it is called here “unpredictable, i.e. a priori unknown. As well as the unpredictability of the number of pulses before reaching the normal charging mode (and therefore - recovery).

In order to distinguish the indicated imitation of charging with a rechargeable battery from an attempt to charge a fully or almost fully charged battery in this way (by erroneous a priori estimation of it as a rechargeable battery), it is necessary, of course, to make a more correct assessment - either by measuring the electrical parameters with the device or by checking the operation devices from this battery (the author-applicant did this according to the brightness of the laser target designator, more precisely - the absence of the glow at all or its quick-fading to zero).

To charge the battery 1 of the inventive method in the second embodiment (with automation) requires a very simple refinement of the electrical circuit of the charger 2. An example of such an improvement (modernization) is shown in Fig.3.

The charger 2 further comprises an automatic switching device 7 (shown conventionally taken out of the initial volume of the base charger), for example, based on electrical relays or their electronic counterparts.

When the charging current I appears in the battery 1, the device 7 prepares a power-off / on (interrupt) circuit for the power supply of the battery 1, and when the charging current is spontaneously zeroed, it performs the indicated turn-off / on (“switching”, “unlock-lock”), while the device itself 7 returns to its initial state until the next likely cycle.

The specific implementation of such a device (at the level of the electric / electronic circuit) is available to any electrical engineer and is not given here, especially since the author-applicant does not claim patent protection of such a device in this application.

The described examples of the proposed method do not exclude other possible variants within the scope of the claimed combination of essential features (see the claims).

Using the invention allows you to restore re-discharged (discharged below an acceptable level) lithium-ion batteries (and thus extend their actual life), achieve their full charge, and immediately, during charging, directly in the charger. This has a pronounced economic efficiency and increased reliability of the entire complex, which includes this battery.

Claims (1)

A method of charging a fully discharged lithium-ion battery, in which the battery is connected to the charger and the latter is turned on, thereby supplying the battery with an external power source converted to direct current, characterized in that when the charging process is terminated spontaneously, according to the current indicator charging, in the case and due to the initial over-discharged state of the battery, characterized by its residual voltage below the maximum permissible level they turn off and turn on its external power again, repeating these steps until the charging process returns to its normal mode, characterized by the absence of the indicated premature spontaneous interruption of the charging current until the regular automatic shutdown of the external power when charging to a predetermined value or forcing charging to end.

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