CN113782811B - Electric equipment and method for heating electrochemical device - Google Patents

Abstract

The application relates to a heating method for electrical equipment and an electrochemical device. The electrical equipment includes an electrochemical device, an energy storage unit and a control unit, wherein the electrochemical device includes a first pole piece and a second pole piece with opposite polarities, and also includes a first tab, a second tab and a third pole Ear. Wherein the first tab and the second tab are respectively electrically connected to the first pole piece, and the third pole tab is electrically connected to the second pole piece. The energy storage unit includes a first conductive terminal and a second conductive terminal. When the temperature of the electrochemical device is lower than the first temperature threshold, the control unit controls the first conductive terminal to be electrically connected to the first tab and the second conductive terminal to be electrically connected to the The second tab is used to form a heating circuit to heat the first pole piece when the electrochemical device is at a low temperature, so as to improve the charging and discharging speed and capacity of the electrochemical device.

Description

Heating method for electrical equipment and electrochemical device

technical field

The present application relates to the technical field of energy storage devices, in particular to a heating method for electrical equipment and electrochemical devices.

Background technique

With the in-depth application of batteries in electronic products, electric vehicles and drones, consumers have higher and higher requirements for fast charging and discharging capacity of batteries. However, due to safety considerations, currently there are relatively strict restrictions on the charging current of the battery, so it is difficult to effectively increase the charging speed. Especially in a low temperature environment, the kinetics of the battery will become worse, the charging speed will be slower, or even unable to charge, and the discharge capacity will also decrease.

Contents of the invention

The application provides an electrical device and an electrochemical device, which can improve the charging and discharging speed and capacity of the electrochemical device in a low-temperature environment.

The first aspect of the present application provides an electrical device, including an electrochemical device, an energy storage unit, and a control unit. Wherein, the electrochemical device includes: a first pole piece, a second pole piece, a first tab, a second tab and a third tab. The polarity of the first pole piece is opposite to that of the second pole piece. The first tab and the second tab are respectively electrically connected to the first pole piece, and the third pole tab is electrically connected to the second pole piece. The energy storage unit includes a first conductive terminal and a second conductive terminal. When the temperature of the electrochemical device is lower than the first temperature threshold, the electrical device performs step S1: the control unit controls the first conductive terminal to be electrically connected to the first tab and the second conductive terminal to be electrically connected to the second tab to form Heating electric circuit.

In the above design, the first tab and the second tab are connected to the first pole piece, and the first tab and the second tab are electrically connected to the first conductive terminal and the second conductive terminal of the energy storage unit to form Heating electric circuit. In this way, the energy storage unit can be used to generate Joule heat on the first pole piece, thereby heating the electrochemical device, improving the kinetic performance of the active material in the electrochemical device, and further improving the charging and discharging speed and capacity of the electrochemical device as a whole.

In a possible design, before the electric device executes step S1, the electric device also detects whether the voltage of the energy storage unit is lower than the first voltage threshold. If the voltage is less than the first voltage threshold, the electric device first executes step S0: the control unit controls the first conductive terminal to be electrically connected to the first tab and the second conductive terminal to be electrically connected to the third tab to form a charging and discharging circuit ; Disconnect the electrical connection between the second conductive terminal and the third tab when the voltage of the energy storage unit is greater than or equal to the second voltage threshold.

In the above design, the electrochemical device is used to charge the energy storage unit lower than the first voltage threshold. On the one hand, the energy storage unit can have enough energy to heat the electrochemical device; Charging, improving the convenience of users.

In a possible design, the electric device also performs step S2: when the voltage of the energy storage unit is lower than the first voltage threshold, disconnect the electrical connection between the second conductive terminal and the second tab; the control unit controls the first The two conductive terminals are electrically connected to the third tab to form a charging and discharging circuit; when the voltage of the energy storage unit is greater than or equal to the second voltage threshold, the electrical connection between the second conductive terminal and the third tab is disconnected, and the control The unit controls the second conductive terminal to be electrically connected to the second tab to form a heating circuit; repeat the above step S2 until the temperature of the electrochemical device is greater than or equal to the second temperature threshold, and disconnect the second conductive terminal from the second tab. electrical connection between.

In the above design, by controlling the voltage of the energy storage unit and controlling the connection relationship between the tabs and the conductive terminals according to the corresponding relationship, the cycle between the heating and energy supply of the electrochemical device to the energy storage unit is realized, ensuring that the electrochemical The device completes heating at a faster rate.

In a possible design, the second temperature threshold is higher than the first temperature threshold.

In a possible design, the energy storage unit includes at least one of a capacitor or a battery.

In a possible design, the current flowing through the electric heating circuit includes at least one of direct current, alternating positive and negative direct current or alternating current.

In the above design, various types of current can be applied in the electric heating circuit to increase the application scenarios of the electrochemical device.

In a possible design, the current flowing through the heating electric circuit includes at least one of positive and negative alternating direct current or alternating current, and in one cycle, the electric quantity flowing through the heating electric circuit includes positive electric quantity _Qpositive and negative electric quantity _Qnegative . , and _{0.5≤Qpositive} / _{Qnegative≤2} .

In a possible design, in one cycle, the current flowing through the heating circuit includes forward current _Iforward and reverse current _Ireverse , and _{0.1≤Iforward} / _{Ireverse≤10} .

In a possible design, in one cycle, the forward current I _positive lasts for t _positive , and the reverse current I _negative lasts for t _negative , and 10≤t _positive /t _{negative≤50} .

In the above design, by applying positive and negative alternating direct current or alternating current to the heating circuit, while increasing the charging and discharging speed of the electrochemical device, it also improves the uniformity of lithium content distribution in the electrochemical device and reduces the safety risk of the electrochemical device .

In a possible design, the first pole piece includes a current collector, and through holes are opened on the current collector.

In the above design, by opening a through hole on the surface of the current collector, the cross-sectional area of the current collector is reduced, thereby increasing the resistance of the current collector and effectively increasing the temperature rise rate of the current collector; at the same time, more active materials can be accommodated in the through hole. material, thereby further increasing the capacity of the electrochemical device.

In a possible design, the electric device further includes a measuring unit. The measuring unit can measure and calculate the resistance R1 between the first lug and the second lug by measuring the voltage between the first lug and the second lug and the current flowing through the first lug and the second lug. Wherein, when (R1-R2)/R2>5%, it can be judged that there is a crack in the first pole piece. It can be understood that R2 is a reference resistance value between the first tab and the second tab.

In the above design, by measuring the resistance R1 between the first lug and the second lug, and comparing the actual resistance R1 with the reference resistance R2 between the first lug and the second lug, to judge the resistance of the first lug Check whether there is any crack in the first pole piece connected with the second pole lug. It can be understood that when a crack appears in the first pole piece, the cross-sectional area of the first pole piece decreases. According to the calculation formula of resistance, the resistance value of the first pole piece will also increase. When (R1-R2)/R2>5%, it can be judged that the first pole piece has cracks. In this way, the risk of using the electrochemical device due to cracks in the first pole piece can be warned in advance.

Another aspect of the present application also provides a heating method for an electrochemical device, wherein the electrochemical device includes: a first pole piece, a second pole piece, a first tab, a second tab and a third tab. Wherein, the polarity of the first pole piece is opposite to that of the second pole piece. The first tab and the second tab are electrically connected to the first pole piece, and the third tab is electrically connected to the second pole piece. The first pole lug and the second pole lug are connected with an external power source to form a heating electric circuit, and the current flowing through the heating electric circuit includes at least one of positive and negative alternating direct current or alternating current. In one cycle, the electricity flowing through the heating electric circuit includes positive electricity _Qpositive and negative electricity _Qnegative , and _{0.5≤Qpositive} / _{Qnegative≤2} .

In the heating method for electrical equipment and electrochemical devices provided in the present application, a heating electric circuit is formed by connecting the first tab and the second tab on the first pole piece. By heating the connection between the electric circuit and the energy storage unit/or external power supply, the electrochemical device is heated, thereby improving the charging and discharging speed and capacity of the electrochemical device. Further, the heating method of the electrical equipment and the electrochemical device provided by the present application also improves the uniformity of the lithium content distribution in the electrochemical device by applying positive and negative alternating direct current or alternating current to the heating electric circuit, thereby reducing the electrochemical device safety risks and delay the performance degradation of electrochemical devices.

It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are not restrictive of the application.

Description of drawings

FIG. 1 is a structural block diagram of an electrical device provided by an embodiment of the present application;

Fig. 2 is the structural representation of the electrochemical device shown in Fig. 1;

3 is a schematic diagram of the connection between the current collector and the tab in the electrochemical device shown in FIG. 2;

4 is a schematic circuit diagram of the electrochemical device and the energy storage unit shown in FIG. 1;

Fig. 5 is a working flow diagram of the electrochemical device and the energy storage unit in the electrochemical device shown in Fig. 1;

Fig. 6 is the change of lithium content in the cathode active material at the head and tail of the pole piece when the pole piece and the tab in the electrochemical device shown in Fig. 2 are applied with currents in different directions;

Fig. 7 is when applying same electric current, the curve that the temperature of the central point of the surface of two electrochemical devices changes with time;

Fig. 8 is the temperature curve of different positions on the same surface as a function of time when the same chemical device applies an electric current;

Fig. 9 is a schematic diagram of the positional relationship when the first tab and the second tab are connected to the current collector in one embodiment of the present application;

Fig. 10 is a schematic diagram of the positional relationship between the first tab and the second tab connected to the current collector in another embodiment of the present application;

Fig. 11 is a schematic diagram of the connection between the current collector and the tab provided by an embodiment of the present application;

Fig. 12 is a schematic diagram of connection between a current collector and tabs provided by another embodiment of the present application.

Description of main component symbols

Electrical equipment 300

Electrochemical devices 100

Shell 10

Electrode assembly 20

First pole piece 21

Second pole piece 22

Current collector 23

Active substances 24

Guide 30

First tab 31

Second tab 32

Third tab 33

Fourth tab 34

control unit 40

Temperature detection module 50

Energy storage unit 200

First conductive terminal 210

Second conductive terminal 220

Heating circuit P1

The first charging and discharging circuit P2

The second charging and discharging circuit P3

The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings.

Detailed ways

In order to better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below in conjunction with the accompanying drawings.

It should be clear that the described embodiments are only some of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in this application belong to the protection scope of this application.

Terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

It should be understood that the term "and/or" used herein is only an association relationship describing associated objects, which means that there may be three relationships, for example, A and/or B, which may mean that A exists alone, and A and B exist simultaneously. B, there are three situations of B alone. In addition, the character "/" in this article generally indicates that the contextual objects are an "or" relationship.

It should be noted that the orientation words such as "up", "down", "left", and "right" described in the embodiments of the present application are described from the angles shown in the drawings, and should not be interpreted as limiting the implementation of the present application. Example limitations. Furthermore, in this context, it also needs to be understood that when it is mentioned that an element is connected "on" or "under" another element, it can not only be directly connected "on" or "under" another element, but can also To be indirectly connected "on" or "under" another element through an intervening element.

Please refer to FIGS. 1 to 3 together. An embodiment of the present application provides an electrical device 300 , including an electrochemical device 100 , an energy storage unit 200 and a control unit 40 .

Please refer to FIG. 2 , where the electrochemical device 100 includes a casing 10 and an electrode assembly 20 inside the casing 10 . The electrode assembly 20 includes a first pole piece 21 and a second pole piece 22 . The polarity of the first pole piece 21 is opposite to that of the second pole piece 22 . It can be understood that an isolation film is also provided between the first pole piece 21 and the second pole piece 22 . In some embodiments, the first pole piece 21 , the second pole piece 22 and the separator form the electrode assembly 20 in a wound or laminated manner. It can be understood that the first pole piece 21 may be one of the cathode pole piece or the anode pole piece, and the second pole piece 22 may be the other one of the cathode pole piece or the anode pole piece.

Referring to FIG. 3 , in some embodiments, both the first pole piece 21 and the second pole piece 22 include a current collector 23 and an active material 24 covering the surface of the current collector 23 .

It can be understood that the current collectors 23 in the first pole piece 21 and the second pole piece 22 may be made of the same or different materials, and the active materials 24 in the first pole piece 21 and the second pole piece 22 are made of different materials. For example, when the first pole piece 21 is a cathode pole piece, the current collector 23 on the first pole piece 21 is a cathode current collector, and the active material 24 on the first pole piece 21 is a cathode active material. When the first pole piece 21 is an anode pole piece, the current collector 23 on the first pole piece 21 is an anode current collector, and the active material 24 on the first pole piece 21 is an anode active material. The same is true for the second pole piece 22 , which will not be repeated here.

It can be understood that in some embodiments, the cathode current collector may include Al foil, and similarly, other cathode current collectors commonly used in the art may also be used. Correspondingly, the cathode active material may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganate, lithium nickel oxide, lithium iron phosphate or lithium iron manganese phosphate.

In some embodiments, the anode current collector may include at least one of copper foil, aluminum foil, nickel foil, or carbon-based current collector. Similarly, other anode current collectors commonly used in the art may also be used. The anode active material may include at least one of carbon-based materials, silicon-based materials, or lithium metal and alloys thereof.

It can be understood that the casing 10 is used to protect the electrode assembly. For different electrochemical devices 100, the housing 10 may be a packaging bag sealed with a packaging film (such as aluminum-plastic film), or a container formed by injection molding of plastic or composite materials.

Please refer to FIG. 2 and FIG. 3 together, the electrochemical device 100 further includes a plurality of guides 30 . Each lead 30 is electrically connected to the corresponding electrode assembly 20 for leading out the electric energy generated by the electrode assembly 20 . In some embodiments, the guide member 30 at least includes a first tab 31 , a second tab 32 and a third tab 33 . Wherein, the first tab 31 and the third tab 33 are electrically connected to the first pole piece 21 and the second pole piece 22 in the electrode assembly 20 respectively. The second tab 32 is electrically connected to any one of the first pole piece 21 and the second pole piece 22 .

In some embodiments, the second tab 32 is electrically connected to the first pole piece 21 . In this way, the first tab 31 and the third tab 33 can jointly lead out the electric energy generated by the electrode assembly 20 , and the second tab 32 and the third tab 33 can jointly export the electric energy generated by the electrode assembly 20 .

It can be understood that the first tab 31 and the second tab 32 can be electrically connected to the empty current collector 23 on the first pole piece 21 . The third tab 33 can be electrically connected to the empty current collector 23 on the second pole piece 22 . It can be understood that the empty current collector 23 refers to the area on the current collector 23 that is not covered by the active material.

It can be understood that the control unit 40 is used for intelligent management and maintenance of the electrochemical device 100 . For example, in some embodiments, the control unit 40 can be used to monitor the voltage and current of the electrochemical device 100 and the energy storage unit 200 . In some embodiments, the control unit 40 may be a battery management system (Battery Management System, BMS). In this way, the control unit 40 and the electrochemical device 100 can be integrated to form an independent electronic device.

It can be understood that the energy storage unit 200 is used to store energy. Please also refer to FIG. 4 , the energy storage unit 200 further includes a first conductive terminal 210 and a second conductive terminal 220 . The first conductive terminal 210 and the second conductive terminal 220 are used to realize the electrical connection between the energy storage unit 200 and other electronic components.

It can be understood that in the electrical equipment 300 provided in the present application, the control unit 40 is electrically connected to each guide 30 and the energy storage unit 200 for controlling the conduction and disconnection of the guide 30 and the energy storage unit 200 .

That is, the control unit 40 is electrically connected to each of the first tab 31, the second tab 32, the third tab 33, the first conductive terminal 210, and the second conductive terminal 220, thereby controlling the first tab 31, the second tab The conduction or connection between the ear 32 and the third pole ear 33 and the first conductive terminal 210 and the second conductive terminal 220 .

It can be understood that when the first tab 31 and the third tab 33 are electrically connected to the first conductive terminal 210 and the second conductive terminal 220 of the energy storage unit 200 respectively, and/or the second tab 32 and the third tab When 33 is respectively electrically connected to the first conductive terminal 210 and the second conductive terminal 220 of the energy storage unit 200 , the energy conversion between the electrochemical device 100 and the energy storage unit 200 can be realized. For example, the energy storage unit 200 can charge the electrochemical device 100 , or the electrochemical device 100 can charge the energy storage unit 200 .

When the first tab 31 and the second tab 32 are electrically connected to the first conductive terminal 210 and the second conductive terminal 220 of the energy storage unit 200 respectively, the energy storage unit 200 can transmit electric energy through the first tab 31 and the second terminal 220. The pole lug 32 is transferred to the current collector 23 of the first pole piece 21 .

Please refer to FIG. 4 and FIG. 5 together. In some embodiments, when the temperature of the electrochemical device 100 is lower than the first temperature threshold, the electrical device 300 executes step S1 through the control unit 40: controlling the first conductive terminal 210 to It is connected to the first tab 31 , and the second control terminal 220 is electrically connected to the second tab 32 to form a heating circuit P1 .

In this way, the first conductive terminal 210 , the first tab 31 , the current collector 23 , the second tab 32 and the second conductive terminal 220 form a conductive loop.

Due to the Joule heating effect of the current collector 23 , the electrical energy of the energy storage unit 200 will be converted into thermal energy on the current collector 23 . Furthermore, the current collector 23 can also quickly conduct heat energy to the entire electrochemical device 100 , that is, the effect of rapidly and uniformly heating the entire electrochemical device 100 through the energy storage unit 200 is achieved.

It can be understood that the charging and discharging speed of the electrochemical device 100 is closely related to the temperature of its environment. For example, taking the electrochemical device 100 as a lithium-ion battery as an example, when the electrochemical device 100 is at a low temperature (for example, 0 degrees Celsius), the charging capacity of the electrochemical device 100 will deteriorate, and it will take at least 5 hours to fully charge; When the electrochemical device 100 is at a lower temperature (for example, minus 20 degrees Celsius), the electrochemical device 100 cannot even be charged. At the same time, the discharge capability of the electrochemical device 100 at low temperature will also be greatly affected. When the temperature of the electrochemical device 100 itself increases, its internal resistance decreases, the kinetic performance of the chemical reaction in the electrochemical device 100 is better, the charging and discharging speed is faster, the discharge capacity is larger, the temperature rise is smaller, and the energy utilization rate is improved. higher.

Please also refer to FIG. 1 , in some embodiments, the electrical device 300 further includes a temperature detection module 50 . When the temperature detection module 50 detects that the temperature of the electrochemical device 100 is lower than the first temperature threshold, the temperature detection module 50 sends a first control signal to the control unit 40 . After receiving the first control signal, the control unit 40 then controls the first conductive terminal 210 to be electrically connected to the first tab 31 , and the second conductive terminal 220 to be electrically connected to the second tab 32 to form a heating circuit P1 .

It can be understood that before the electric device 300 executes step S1, the control unit 40 also detects whether the voltage of the energy storage unit 200 is lower than the first voltage threshold. If it is less than the first voltage threshold, the electric device 300 first executes step S0 through the control unit 40: controlling the first conductive terminal 210 to be electrically connected to the first tab 31, and the second conductive terminal 220 to be electrically connected to the third tab 33 , to form the first charging and discharging circuit P2; when the voltage of the energy storage unit 200 is greater than or equal to the second voltage threshold, disconnect the electrical connection between the second conductive terminal 220 and the third tab 33 .

It can be understood that, in other embodiments, if the control unit 40 detects that the voltage of the energy storage unit 200 is lower than the first voltage threshold, before performing step S1, step S0 may also be: control the first conductive terminal 210 to be electrically connected to the first The tab 31 and the second tab 32, the second conductive terminal 220 is electrically connected to the third tab 33 to form two charging and discharging circuits (i.e. the first charging and discharging circuit P2 and the second charging and discharging circuit P3); to be stored When the voltage of the unit 200 is greater than or equal to the second voltage threshold, the electrical connection between the second conductive terminal 220 and the third tab 33 is disconnected. In this way, the energy storage unit 200 can be quickly charged by forming two charging and discharging circuits at the same time.

After step S1 is executed, the electric device 300 also executes step S2 through the control unit 40: when the voltage of the energy storage unit 200 is lower than the first voltage threshold, disconnect the electricity between the second conductive terminal 220 and the second tab 32. connection; control the second conductive terminal 220 to be electrically connected to the third tab 33 to form the first charging and discharging circuit P2; when the voltage of the energy storage unit 200 is greater than or equal to the second voltage threshold, disconnect the second conductive terminal 220 and The electrical connection between the third tabs 33 controls the electrical connection of the second conductive terminal 220 to the second tabs 32 to form a heating circuit P1; repeat the above step S2 until the temperature of the electrochemical device 100 is greater than or equal to the second The temperature threshold is to disconnect the electrical connection between the second conductive terminal 220 and the second tab 32 . In this way, the heating process of the electrochemical device 100 is alternately performed with the charging process of the energy storage unit 200 , which greatly increases the heating rate of the electrochemical device 100 .

It can be understood that in some embodiments, the second temperature threshold is higher than the first temperature threshold. The second voltage threshold is greater than the first voltage threshold.

It can be understood that, in some embodiments, the energy storage unit 200 includes at least one of a capacitor or a battery. Wherein, when the energy storage unit 200 is a battery, the polarity of the first pole piece 21 is the same as that of the first conductive terminal 210 , and the polarity of the second pole piece 22 is the same as that of the second conductive terminal 220 .

It can be understood that, in some embodiments, the current flowing through the electric heating circuit P1 includes but not limited to at least one of direct current, alternating positive and negative direct current, or alternating current. That is, the energy storage unit 200 can be a direct current power supply for outputting direct current or alternating positive and negative direct current; or the energy storage unit 200 can be an alternating current power supply for outputting alternating current.

It can be understood that applying direct current between the first tab 31 and the second tab 32 of the electrochemical device 100 is easier to control than alternating positive and negative direct current and alternating current. However, applying a direct current between the first tab 31 and the second tab 32 of the electrochemical device 100 will easily form a potential difference between the first tab 31 and the second tab 32, thereby making the current collector 23 active. The substance deviates from the equilibrium voltage, so that one of lithium intercalation reaction or delithiation reaction occurs on the first tab 31, and the other one of lithium intercalation reaction or delithiation reaction occurs on the second tab 32 . After a long period of accumulation, the lithium-enriched side is likely to precipitate lithium dendrites on the anode during the charging process of the electrochemical device 100 , thereby posing safety hazards.

It can be understood that when a periodic positive and negative alternating direct current or sine/cosine alternating current is applied between the first tab 31 and the second tab 32 of the electrochemical device 100, according to Joule's law P=I ² R, the current collector The heat production efficiency of 23 is related to the magnitude of the current and the resistance of the current collector 23, and has nothing to do with the direction of the current. Therefore, replacing the direct current with alternating positive and negative direct current or alternating current will not affect the heat generation efficiency of the current collector 23 . Further, since the current direction of positive and negative alternating direct current and alternating current changes regularly within a cycle, when the current direction is positive, the active material at the ear where the lithium intercalation reaction occurs will turn negative when the current direction is negative. A delithiation reaction occurs and vice versa. In this way, two opposite reaction processes occur alternately, which greatly reduces the influence of the potential difference on the generation of active materials at the tabs, and is conducive to maintaining stable performance of the electrochemical device 100 .

For example, referring to FIG. 6, FIG. 6 shows that two tabs (such as the first tab 31 and the second tab 32) are applied in different directions to the head and tail of the cathode pole piece (such as the cathode pole piece shown in FIG. 10 ). The change of lithium content in the active material at the head and tail of the current. It can be seen from the figure that the positive current is applied for 60 seconds first, and it can be seen that the cathode head is delithiated, so its lithium content decreases. On the contrary, the tail of the cathode is intercalating lithium, so its lithium content is increasing. At 60s, the lithium content difference between the cathode head and the tail is the largest, reaching 5%. Then apply a current with the same magnitude and opposite direction. It can be seen that the lithium content at the head and tail will return to the initial value after applying the reverse current for about 2s. In this way, when the current flowing through the heating circuit P1 is periodic positive and negative alternating direct current or sine/cosine alternating current, the uniformity of lithium ion distribution on the first pole piece 21 and the improvement of the material properties of the electrochemical device 100 can be effectively improved. stability.

It can be understood that, in some embodiments, when the current flowing through the heating electric circuit P1 includes at least one of positive and negative alternating direct current or alternating current, within one cycle, the electric quantity flowing through the heating electric circuit P1 includes positive electric quantity _Qpositive And negative electric quantity Q _negative , and 0.5≤Q _positive /Q _negative≤2 . That is, within one cycle, the current flowing through the heating circuit P1 includes forward current _Iforward and reverse current _Ireverse , and _{0.1≤Iforward} / _{Ireverse≤10} . Wherein, the duration of forward current I _is tpositive _{, and} the duration of _reverse current I is _tnegative , and _{10≤tpositive} / _{tnegative≤50} . In this way, the influence of the potential difference between the first tab 31 and the second tab 32 on the electrochemical device 100 can be further reduced, thereby improving the uniformity of lithium content distribution in the electrochemical device 100, thereby reducing the electrochemical device 100. Safety risks and delaying performance degradation of electrochemical devices.

In order to verify the effect of 0.5≤Q _positive /Q _negative ≤2, a current comparison test is carried out. During the experiment, the electrochemical device 100 and the ambient temperature of each experiment were the same, and the only difference was the current flowing through the heating circuit P1. The experimental results are as follows:

Table 1 Influencing factors of internal resistance and cycle life of electrochemical devices

Among them, it can be seen from the table that compared with direct current, positive and negative alternating direct current is used, and controlled within one cycle, the ratio between the positive power Q _positive and the negative power Q _negative flowing through the heating circuit P1 satisfies: 0.5 The embodiment of ≤ Q _positive /Q _negative ≤ 2 can significantly reduce the impact on the internal resistance and cycle life of the battery.

It can be understood that in this application, forward current and reverse current do not refer to specific current directions. The forward current and the reverse current are only used to refer to two opposite currents flowing through the heating circuit P1.

It can be understood that when heating the current collector 23 of the electrochemical device 100 , the temperature rise rate of the current collector 23 also needs to be considered. In this application, the rate of temperature rise is measured by calculating the temperature rise of the current collector 23 when heated for 1 minute. It can be understood that the higher the temperature rise of the current collector 23 after being heated for 1 minute, the higher the temperature rise rate, and vice versa. Wherein, when the temperature rise rate of the current collector 23 is low, it means that the electrochemical device 100 needs a long warm-up time, which will undoubtedly reduce the convenience of using the electrochemical device 100 .

Generally, the temperature rise rate of the current collector 23 of the electrochemical device 100 must be at least greater than or equal to 3° C./min to have a significant advantage. Since the temperature rise rate of the current collector 23 is directly proportional to the heating power P, and according to Joule's law P=I ² R, the temperature rise of the current collector 23 can be increased by increasing the current flowing through the current collector 23 rate.

In order to verify the temperature rise rate of the scheme of the present application, a current comparison experiment was carried out. During the experiment, the electrochemical device 100 and the ambient temperature of each group of experiments were the same, and the only difference was the magnitude of the current flowing through the first tab 31 and the second tab 32 . And in each group of experiments in the table below, the temperature at the center point of a surface perpendicular to the thickness direction of the electrochemical device 100 is measured. The experimental results are as follows:

Table 2 Influencing factors of the temperature rise rate at the center point of the surface of the electrochemical device

Current (A) Starting temperature (°C) End temperature (℃) Heating time (min) Temperature rise rate (℃/min) 10 26.46 36.62 5 2.03 15 25.71 40.76 3 5.02 20 26.4 44.65 2 9.13

It can be seen from the table that when a current of 10A is applied to the collector 23, the temperature rise rate can reach 2.03°C/min; when a current of 15A is applied to the collector 23, the temperature rise rate can reach 5.02°C/min; With a current of 20A, the temperature rise rate can reach 9.13°C/min. In this way, it can be predicted that the temperature rise rate of the current collector 23 will increase with the increase of the current.

Further, please refer to FIG. 7 and FIG. 8 together. 7 shows the temperature curves of the center points of the surfaces of the two electrochemical devices 100 perpendicular to the thickness direction as a function of time when the same current (for example, 20A) is applied to the two electrochemical devices 100 . Wherein, the curve Q1 represents the temperature curve of the central point of the surface perpendicular to the thickness direction of the electrochemical device 100 over time when a 20A electric current is applied to the heating circuit of an electrochemical device 100; The temperature curve of the center point of the surface perpendicular to the thickness direction of another electrochemical device 100 as a function of time when the heating circuit of the device 100 applies a current of 20A. It can be seen from FIG. 7 that when the heating method provided in the present application is applied and the same current is applied, the temperature difference at the center point of the surface perpendicular to the thickness direction of different electrochemical devices 100 is within 1°C. Thus, it shows that the heating method provided by the present application has good consistency for different electrochemical devices 100 , and the above heating method can be applied to multiple electrochemical devices 100 in the battery pack at the same time and in large quantities.

FIG. 8 shows the temperature curves of different locations on the same surface of the electrochemical device 100 as a function of time when a current is applied to the same electrochemical device 100 . Wherein, the curve Q3 represents the temperature curve of the left side on the surface of the electrochemical device 100 changing with time when the current is applied to the electrochemical device 100; the curve Q4 represents the right side of the electrochemical device 100 when the current is applied to the electrochemical device 100 The temperature curve of side changing with time; Curve Q5 represents when applying electric current to electrochemical device 100, the temperature curve of the central point of electrochemical device 100 changing with time; As can be seen from Fig. 8, the heating method provided by the application , on the same surface of the same electrochemical device 100, the temperature difference between the left side, the right side and the center point is within 2°C. In this way, it shows that the temperature distribution of the same electrochemical device 100 is relatively uniform by using the heating method provided in the present application, so that the safety risk caused by the uneven temperature during the charging and discharging process of the electrochemical device 100 can be reduced.

其中，ρ值表示电阻率，由集流体23本身性质决定；L表示集流体23的长度；S表示集流体23的横截面积。It can be understood that since the temperature rise rate of the current collector 23 is directly proportional to the heating power P, and according to Joule's law P=I ² R, the resistance of the current collector 23 can also be increased by increasing the resistance of the current collector 23 temperature rise rate. According to the calculation formula of resistance

Wherein, the ρ value represents the resistivity, which is determined by the nature of the current collector 23 itself; L represents the length of the current collector 23; S represents the cross-sectional area of the current collector 23.

In this way, on the one hand, the distance between the first tab 31 and the second tab 32 on the current collector 23 can be increased, thereby increasing the effective length of the current collector 23 , and further increasing the equivalent resistance of the current collector 23 . For example, referring to FIG. 9 , in one embodiment, the current collector 23 is connected with a first tab 31 and a second tab 32 . And when the width W1 of the current collector 23 is 69.4 mm, and the distance L1 between the first tab 31 and the second tab 32 on the current collector 23 is 415 mm, the distance between the first tab 31 and the second tab 32 is measured The resistance between them is 23.8 milliohms. Please refer to FIG. 10. In another embodiment, the width W1 of the current collector 23 is constant, and when the distance L2 between the first tab 31 and the second tab 32 is 1555 mm, it is measured that the first tab 31 and the second tab 32 are The resistance between the second tabs 32 is 86 milliohms.

On the other hand, the cross-sectional area of the current collector 23 can be reduced by opening a through hole 231 (refer to FIG. 11 ) on the current collector 23 . It can be understood that the through hole 231 is opened in the area between the first tab 31 and the second tab 32 on the current collector 23 . The present application does not limit the number and shape of the through holes 231 .

It can be understood that when the ambient temperature remains constant, the resistance of the current collector 23 also remains constant. And when the current collector 23 has cracks, the resistance of the current collector 23 will change. Therefore, the first tab 31 and the second tab 32 can be used to predict whether there is a crack in the current collector 23 connected thereto, thereby reducing the safety risk of the electrochemical device 100 .

In some embodiments, the electrical device 300 further includes a measuring unit (not shown). The measuring unit measures the voltage between the first tab 31 and the second tab 32 and the current flowing through the first tab 31 and the second tab 32 to obtain the voltage between the first tab 31 and the second tab 32. When (R1-R2)/R2>5%, it is judged that there is a crack in the first pole piece 21. Wherein, R2 is a reference resistance value between the first tab 31 and the second tab 32 . That is, R2 is the measured difference between the first pole piece 31 and the second pole piece 32 when there is no crack on the first pole piece 21 and the first pole piece 31 and the second pole piece 32 are connected to the first pole piece 21. resistance value between.

It can be understood that, in some embodiments, the measurement unit is electrically connected to the control unit 40 for sending measurement data to the control unit 40 . The reference resistance value R2 between the first tab 31 and the second tab 32 is stored in the control unit 40 . In this way, the control unit 40 can calculate the resistance R1 between the first tab 31 and the second tab 32 according to the voltage data and current data measured by the measurement unit. It can be understood that the measurement unit obtains the voltage and current data of the current collector 23 to be measured by applying a small current to the first tab 31 and the second tab 32 . For example, the small current can be 1mA to 500mA. In this way, the small current can reduce the Joule heat generated by the current collector 23 to be measured, thereby reducing the influence of measuring the resistance of the current collector 23 .

It can be understood that, in some embodiments, when the control unit 40 determines that (R1−R2)/R2>5% of the current collector 23, it may further prompt a corresponding risk.

Please refer to FIG. 12 , in some embodiments, the current collector 23 is not limited to setting two tabs, and in other embodiments, three or more tabs (such as the first pole) can also be set on the same current collector 23 ears 31, second tabs 32, and fourth tabs 34), and the application does not limit the position of the tabs on the current collector 23. In this way, it can be formed between the electrochemical device 100 and the energy storage unit 200. A number of heating circuits and a number of charging and discharging circuits.

Some embodiments of the present application also provide a heating method for an electrochemical device. Wherein, the electrochemical device includes: a first pole piece and a second pole piece, and the polarity of the first pole piece and the second pole piece are opposite; the first pole piece, the second pole piece and the third pole piece, the first pole piece The ear and the second lug are electrically connected to the first pole piece, and the third pole lug is electrically connected to the second pole piece; the first pole lug and the second pole lug are connected to an external power supply to form a heating circuit, and the electricity flowing through the heating circuit The current includes at least one of positive and negative alternating direct current or alternating current. In one cycle, the electricity flowing through the heating circuit includes positive electricity Qpositive and negative electricity Qnegative, and 0.5≤Qpositive/Qnegative≤2.

It can be understood that the positive and negative alternating direct current or alternating current both include forward current _Iforward and reverse current _Ireverse . Wherein, within one cycle, _{0.1≤Iforward} / _{Ireverse≤10} . That is to say, the duration of the positive current I _is tpositive _{, and} the duration of the reverse current I _{is tnegative} , then _{10≤tpositive} / _{tnegative≤50} .

It can be understood that the electrochemical device in the present application includes any device that undergoes an electrochemical reaction, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

It can be understood that the electrochemical device in the embodiment of the present application can be used in various fields, as long as the device can be powered by the electrochemical device, the electrochemical device in the embodiment of the present application can be used. For example, the electrochemical device can be used in components such as electrochemical device packages and electronic equipment of electric vehicles, and the electronic equipment can be mobile phones, tablet computers, desktop computers, laptop computers, handheld computers, notebook computers, super mobile personal computers (ultra-mobile personal computer, UMPC), netbook, and cell phone, personal digital assistant (personal digital assistant, PDA), augmented reality (augmented reality, AR) device, virtual reality (virtual reality, VR) device, artificial intelligence (artificial intelligence) , AI device, wearable device, vehicle-mounted device, smart home device and/or smart city device, the embodiment of the present application does not specifically limit the specific type of the electronic device.

Specifically, the electronic device may include components such as a casing, a screen, a circuit board, and an electrochemical device, wherein the screen, the circuit board, and the electrochemical device are all mounted on the casing, and the electrochemical device is the one described in any of the above embodiments. electrochemical device.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, there may be various modifications and changes in the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Claims (13)

1. An electric device comprising an electrochemical device, an energy storage unit and a control unit, wherein the electrochemical device comprises:

the polarity of the first pole piece is opposite to that of the second pole piece;

the first pole lug is electrically connected to the first pole piece, the second pole lug is electrically connected to the first pole piece, and the third pole lug is electrically connected to the second pole piece;

the energy storage unit comprises a first conductive terminal and a second conductive terminal;

when the temperature of the electrochemical device is lower than a first temperature threshold, the electric equipment executes step S1: the control unit controls the first conductive terminal to be electrically connected to the first lug and the second conductive terminal to be electrically connected to the second lug to form a heating electric loop;

before the electric equipment executes the step S1, detecting whether the voltage of the energy storage unit is smaller than a first voltage threshold, and if the voltage is smaller than the first voltage threshold, the electric equipment first executes the step S0: the control unit controls the first conductive terminal to be electrically connected to the first lug, the second conductive terminal to be electrically connected to the third lug to form a charge-discharge loop, and when the voltage of the energy storage unit is larger than or equal to a second voltage threshold value, the second conductive terminal and the third lug are disconnected.

2. The electric equipment according to claim 1, wherein after step S1, the electric equipment further performs step S2: when the voltage of the energy storage unit is smaller than a first voltage threshold value, the second conductive terminal is disconnected from the second pole ear; the control unit controls the second conductive terminal to be electrically connected to the third lug so as to form a charge-discharge loop; when the voltage of the energy storage unit is greater than or equal to a second voltage threshold value, the second conductive terminal is disconnected from the third lug, and the control unit controls the second conductive terminal to be electrically connected to the second lug so as to form the heating circuit loop;

and repeating the step S2 until the temperature of the electrochemical device is greater than or equal to a second temperature threshold value, and disconnecting the second conductive terminal from the second pole lug.

3. The powered device of claim 2, wherein the second temperature threshold is higher than the first temperature threshold.

4. The powered device of claim 1, wherein the energy storage unit comprises at least one of a capacitor or a battery.

5. The powered device of claim 1, wherein the current flowing through the heating electrical loop comprises at least one of direct current or alternating current.

6. The electrical apparatus of claim 5, wherein the current flowing through the heating electrical circuit comprises at least one of positive and negative alternating direct current or alternating current, and wherein the amount of power flowing through the heating electrical circuit during a cycle comprises a positive amount of power Q _{Is just for} And a negative electric quantity Q _{Negative pole} And 0.5 or less Q _{Is just} /Q _{Negative pole} ≤2。

7. The powered device of claim 6, wherein the current flowing through the heating electrical loop during a cycle comprises a forward current I _{Is just for} And reverse current I _{Inverse direction} And 0.1 is not more than I _{Is just} /I _{Inverse direction} ≤10。

8. The consumer of claim 7 wherein the forward current I is measured during a cycle _{Is just} For a duration of t _{Is just for} The reverse current I _{Inverse direction} For a duration of t _{Inverse direction} And t is not less than 10 _{Is just for} /t _{Trans form} ≤50。

9. The electric equipment as claimed in claim 1, wherein the first pole piece comprises a current collector, and the current collector is provided with a through hole.

10. The electric equipment according to claim 1, further comprising a measuring unit, wherein the measuring unit obtains a resistance R1 between the first tab and the second tab by measuring a voltage between the first tab and the second tab and a current flowing through the first tab and the second tab, and judges that the first pole piece has a crack when (R1-R2)/R2 >5%, wherein R2 is a reference resistance value between the first tab and the second tab.

11. A method of heating an electrochemical device, the electrochemical device comprising:

the polarity of the first pole piece is opposite to that of the second pole piece;

the first pole lug is electrically connected to the first pole piece, the second pole lug is electrically connected to the first pole piece, and the third pole lug is electrically connected to the second pole piece;

the method of heating the electrochemical device includes:

connecting the first lug and the second lug with an external power supply to form a heating circuit, wherein the current flowing through the heating circuit comprises at least one of positive and negative alternating direct current or alternating current, and the electric quantity flowing through the heating circuit in one period comprises positive electric quantity Q _{Is just} And a negative electric quantity Q _{Negative pole} And 0.5 or less Q _{Is just} /Q _{Negative pole} ≤2；

Before the first lug and the second lug are connected with an external power supply to form a heating electric loop, detecting whether the voltage of an energy storage unit is smaller than a first voltage threshold value, if so, electrically connecting a first conductive terminal of the energy storage unit to the first lug and electrically connecting a second conductive terminal of the energy storage unit to a third lug to form a charging and discharging loop, and when the voltage of the energy storage unit is larger than or equal to a second voltage threshold value, disconnecting the electrical connection between the second conductive terminal and the third lug.

12. The heating method of claim 11, wherein the current flowing through the heating electrical circuit during a cycle comprises a forward current I _{Is just} And reverse current I _{Inverse direction} And 0.1 is not more than I _{Is just} /I _{Inverse direction} ≤10。

13. The heating method of claim 12, wherein the forward current I is applied during a cycle _{Is just} Duration of time t _{Is just} The reverse current I _{Trans form} Duration of time t _{Inverse direction} And t is not less than 10 _{Is just} /t _{Trans form} ≤50。

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