WO2023184338A1

WO2023184338A1 - Electrochemical apparatus, charging method, and electronic device

Info

Publication number: WO2023184338A1
Application number: PCT/CN2022/084411
Authority: WO
Inventors: 刘伟; 赵士猛
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-31
Filing date: 2022-03-31
Publication date: 2023-10-05
Also published as: CN115668579A

Abstract

The present application provides an electrochemical apparatus, a charging method, and an electronic device. A charging process of the electrochemical apparatus comprises a plurality of constant-current charging stages and a plurality of constant-voltage charging stages, and when the electrochemical apparatus is charged to a first state of charge, the electrochemical apparatus undergoes at least one constant-voltage charging stage, wherein the first state of charge is less than or equal to 80%. On the basis of the solution of the present application, the charging capacity of the electrochemical apparatus may be increased when the internal resistance is relatively low, and the charging time in a high state of charge and high internal resistance is shortened, thereby shortening the total charging time of the electrochemical apparatus; in addition, long-time constant-voltage charging under a high voltage is avoided, such that a side reaction of a positive electrode and an electrolyte under the high voltage is reduced, thereby improving the high-temperature cycle performance of the electrochemical apparatus.

Description

Electrochemical devices, charging methods and electronic equipment

Technical field

The present application relates to the field of electrochemical technology, and in particular, to an electrochemical device, a charging method of the electrochemical device, and electronic equipment.

Background technique

As the market demand for energy density of lithium-ion batteries increases, materials with higher gram capacity (e.g., silicon and silicon-based materials) are considered to be promising anode materials. In recent years, silicon-based batteries using silicon-based negative electrodes have been widely studied.

For silicon system batteries, the currently commonly used battery charging method is constant current charging plus constant voltage charging, that is, constant current charging to the charging upper limit voltage (hereinafter also referred to as the specified voltage) or close to the specified voltage, and then switching to constant voltage charging. The main reason for using this charging method is that the battery has polarization during the charging process, and the greater the charging current, the more obvious the polarization of the battery. When the battery is charged to the specified voltage through constant current charging, the battery cells are not fully charged due to polarization, so constant voltage charging needs to be continued to eliminate polarization.

Due to the poor conductivity of silicon and silicon-based materials, the slow lithium insertion reaction speed, and the large polarization of silicon system batteries, when silicon system batteries are charged using the above charging method, constant voltage charging takes a long time, which results in silicon system The entire charging of the battery takes a long time. In addition, for high-voltage (for example, ≥4.5V) systems, long-term constant voltage charging at high voltages will deteriorate the high-temperature cycle performance of silicon-based batteries.

Contents of the invention

In view of this, embodiments of the present application provide an electrochemical device, a charging method for the electrochemical device, and electronic equipment to at least partially or fully solve the above technical problems.

According to a first aspect of an embodiment of the present application, an electrochemical device is provided. The charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages. When the electrochemical device is charged to the first The electrochemical device undergoes at least one constant voltage charging stage at a state of charge (SOC), wherein the first SOC is less than or equal to 80%. Through this design, the charging capacity of the electrochemical device can be increased when the internal resistance is low, and the charging time can be reduced under high SOC and high internal resistance, thereby shortening the total charging time of the electrochemical device.

In another possible implementation, combined with the above first aspect, the plurality of constant current charging stages include a first constant current charging stage in which constant current charging is performed with a first charging current, and the first charging current is 1.2 to 1.5 times the charging capacity of the electrochemical device; when the electrochemical device is charged to the second SOC, the electrochemical device undergoes at least one of the first constant current charging stages, wherein the second SOC Less than or equal to the first SOC. Through the design of segmented charging, the charging capacity of the electrochemical device is increased when the internal resistance is low while ensuring the safety of the battery.

In yet another possible implementation manner, combined with the above first aspect, the second SOC is less than or equal to 35%.

In yet another possible implementation manner, combined with the above first aspect, the constant current charging stage includes a second constant current charging stage of constant current charging with a second charging current, and the second charging current is the voltage of the battery. 1.0 to 1.3 times the charging capacity of the chemical device; when the electrochemical device is charged to a third SOC, the electrochemical device undergoes at least one of the second constant current charging stages, wherein the third SOC is greater than or Equal to the first SOC.

In yet another possible implementation manner, combined with the above first aspect, the third SOC is greater than or equal to 87%±3%.

In yet another possible implementation manner, combined with the above first aspect, the constant current charging stage includes a second constant current charging stage of constant current charging with a second charging current, and the second charging current is the voltage of the battery. 1.0 to 1.3 times the charging capacity of the chemical device, and the second charging current is smaller than the first charging current;

The electrochemical device undergoes at least one of the second constant current charging phases when the electrochemical device is charged to a third SOC, wherein the third SOC is greater than or equal to the first SOC.

In yet another possible implementation, combined with the above first aspect, the constant current charging stage includes a third constant current charging stage of performing constant current charging with a third charging current, where the third charging current is the voltage of the battery. 0.5 to 0.8 times the charging capacity of the chemical device; when the state of charge of the electrochemical device is greater than the third SOC, the electrochemical device performs the third constant current charging stage at least once, wherein the third SOC is greater than or equal to the first SOC. By designing like this,

In yet another possible implementation, combined with the above first aspect, the multiple constant current charging stages include N constant current charging stages, the multiple constant voltage charging stages include N constant voltage charging stages, and N is Integer and N≥2. The N constant current charging stages and the N constant voltage charging stages are executed alternately.

In yet another possible implementation, combined with the above first aspect, in the first constant current charging stage, the electrochemical device performs constant current charging with a first charging current and a first charging time, and in the first constant voltage charging stage stage, the electrochemical device performs constant voltage charging with a first cut-off voltage reached at the end of the first charging time and a second charging time, and the first charging current is 1.2 of the charging capacity of the electrochemical device. to 1.5 times.

In yet another possible implementation, combined with the above first aspect, in the rth constant current charging stage, the electrochemical device performs constant current charging with the second charging current and the kth charging time, and r and k are both integers. , and 2≤r≤N, k=2r-1; in the r-th constant voltage charging stage, the electrochemical device uses the r-th cut-off voltage reached at the end of the k-th charging time and the k+1-th charging time. Constant voltage charging is performed, and the second charging current is smaller than the first charging current.

In yet another possible implementation, combined with the above first aspect, when N>2, in the Nth constant current charging stage, the electrochemical device is charged with a third constant current charging current to the charging upper limit voltage; in the Nth constant current charging stage; In the N constant voltage charging stage, the electrochemical device performs constant voltage charging at the charging upper limit voltage to a charging cut-off current, and the third charging current is smaller than the second charging current.

In yet another possible implementation manner, combined with the above first aspect, the negative electrode material of the electrochemical device at least includes silicon-based material and graphite.

According to a second aspect of the embodiment of the present application, a charging method of an electrochemical device is provided. The charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages; in the charging process, When the electrochemical device is charged to a first SOC, the electrochemical device undergoes at least one constant voltage charging stage, wherein the first SOC is less than or equal to 80%.

According to a third aspect of the embodiments of the present application, an electronic device is provided, including the electrochemical device according to any one of the first aspects.

Based on the above technical solution, the charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages. When the electrochemical device is charged to the first SOC, the electrochemical device undergoes at least one constant voltage charging stage. Since the first SOC is less than or equal to 80%, the internal resistance of the electrochemical device is low when the SOC is low. Therefore, in this solution, the electrochemical device performs at least one constant voltage charge when the internal resistance is low. Since constant voltage charging is performed when the internal resistance of the electrochemical device is low, the current of the electrochemical device decreases rapidly and the capacity increases rapidly. Therefore, this solution increases the charging capacity of the electrochemical device when the internal resistance is low and reduces the charge at high temperatures. The charging time under the high internal resistance of SOC shortens the total charging time of the electrochemical device; in addition, by avoiding long-term constant voltage charging at high voltage, the side reaction between the positive electrode and the electrolyte under high voltage is reduced, thereby improving the electrochemistry. High temperature cycling performance of the device.

Description of drawings

In order to more clearly explain the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are: For some embodiments of the present application, those of ordinary skill in the art can also obtain other drawings based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram illustrating the relationship between constant voltage charging time, current and capacity of an electrochemical device provided by an exemplary embodiment of the present application;

Figure 2 is a schematic diagram of the lithium insertion degree of silicon and graphite under different SOCs of the electrochemical device provided by an exemplary embodiment of the present application;

Figure 3 is a schematic diagram of the charging process of an electrochemical device provided by an exemplary embodiment of the present application;

Figure 4 is a schematic flow chart of a charging method of an electrochemical device provided by an exemplary embodiment of the present application;

Figure 5 is a schematic structural diagram of an electronic device provided by an exemplary embodiment of the present application.

Detailed ways

In order to enable those in the art to better understand the technical solutions in the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and in detail below in conjunction with the drawings in the embodiments of the present application. Obviously, the description The embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the examples in the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art should fall within the scope of protection of the embodiments of this application.

One of the key technologies for electrochemical devices such as lithium-ion batteries lies in the development of negative electrode materials. At present, graphite materials are close to the theoretical gram capacity of 372mAh/g, reaching a capacity bottleneck and no longer able to meet the needs of electrochemical device applications. Silicon and silicon-based materials are considered to be promising anode materials due to their high gram capacity of 4200mAh/g.

Compared with graphite materials, silicon and silicon-based materials have poor electrical conductivity, slow lithium insertion reaction speed, and large polarization of silicon system batteries. Constant voltage charging takes too long when using the current constant current charging plus constant voltage charging method. , and long-term constant voltage charging (CV) at high temperatures will deteriorate the cycle performance of the cells of the electrochemical device.

To this end, embodiments of the present application provide an electrochemical device, a charging method for the electrochemical device, and electronic equipment to at least partially solve the above technical problems.

The specific implementation of the embodiments of the present application will be further described below with reference to the accompanying drawings.

Referring to Figures 1 to 3, embodiments of the present application provide an electrochemical device. The charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages. When the electrochemical device is charged to the first At one SOC, the electrochemical device undergoes at least one constant voltage charging phase, wherein the first SOC is less than or equal to 80%.

Among them, the electrochemical device is a rechargeable battery, which is used to provide electrical energy to electronic equipment. The electrochemical device includes a plurality of cells, and the electrochemical device can be repeatedly charged in a cyclic and rechargeable manner. In an implementation manner of the present application, the negative electrode active material of the electrochemical device at least includes silicon-based material and graphite.

In a charge-discharge cycle of an electrochemical device, the charging process includes multiple constant-current charging stages and multiple constant-voltage charging stages. For example, the electrochemical device uses a constant charging current for charging at the beginning of charging (i.e., constant current charging) in order to increase the efficiency of charging with a larger charging current, while avoiding the use of constant voltage charging at the beginning of charging (i.e., constant voltage charging). Charging) may cause problems with excessive charging current. When the electrochemical device is charged in a constant current charging mode for a predetermined time, or when the electrochemical device is charged to a predetermined voltage, the electrochemical device is charged in a constant voltage charging mode to reduce polarization. Constant current charging and constant voltage charging are repeated multiple times in a similar manner as above until the electrochemical device is charged to a fully charged state.

As the electrochemical device is charged, the state of charge (SOC) of the electrochemical device increases, and the internal resistance of the electrochemical device increases. Among them, SOC refers to the ratio of the remaining capacity of the electrochemical device to the full charge capacity of the electrochemical device. When the SOC of the electrochemical device is less than or equal to 80%, the internal resistance of the electrochemical device is relatively low. However, when the SOC of the electrochemical device is greater than 80%, the internal resistance of the electrochemical device increases significantly.

From the perspective of internal resistance, the electrochemical device undergoes at least one constant voltage charging stage when the electrochemical device is charged to a first SOC of less than or equal to 80%, which can also be understood as: the electrochemical device has a low internal resistance when its internal resistance is low. At least one constant voltage charge is performed, which includes one constant voltage charge and multiple constant voltage charges.

As shown in Figure 1, when the electrochemical device performs constant voltage charging, the current of the electrochemical device shows an exponential decreasing trend with time, and the capacity shows a negative exponential increasing trend with time. Specifically, as shown in Figure 1, at stage 1, as shown in the area to the left of the first dotted line 110, the current of the electrochemical device decreases fastest and the capacity increases the fastest. At stage 2, as shown in the area between the first dotted line 110 and the second dotted line 112, the current of the electrochemical device decreases faster than the current decreases at stage 1, and the capacity increases faster than the capacity increase at stage 1 speed. At stage 3, as shown in the area to the right of the second dotted line 112, the current of the electrochemical device slowly decreases and the capacity slowly increases. That is, compared to stage 3, at stage 1 and stage 2, the current decreases rapidly and the capacity increases rapidly. At stage 3, charging takes the longest time and charging capacity increases the least.

Based on the above characteristics, in the embodiments of the present application, when constant voltage charging is used to reduce polarization, stages 1 and 2 of rapid current reduction and rapid increase in capacity are utilized, that is, by making the electrochemical device operate at a lower SOC (i.e., Perform at least one constant voltage charge when the internal resistance is small), increase the charging capacity of the electrochemical device when the internal resistance is low, reduce the charging time under high SOC and high internal resistance, thereby shortening the total charging of the electrochemical device time. In addition, since long-term constant voltage charging at high voltage is avoided, side reactions between the positive electrode and the electrolyte under high voltage are reduced, thereby improving the high-temperature cycle performance of the electrochemical device.

It should be understood that in the embodiment of the present application, the charging currents in each current charging stage may be the same or different, which is not limited in this embodiment.

It should be understood that in the embodiments of the present application, preferably, the electrochemical device undergoes multiple constant voltage charging stages when the electrochemical device is charged to a first SOC less than or equal to 80%, that is, when the electrochemical device is at a low SOC (that is, when the internal resistance of the cell of the electrochemical device is small), perform multiple constant voltage charges to reduce polarization, and make full use of stages 1 and 2 where the current is rapidly reduced and the capacity is rapidly increased, so as to increase the battery life to a greater extent. The charging capacity of the electrochemical device when the internal resistance is low reduces the charging time at high SOC and high internal resistance, thereby shortening the total charging time to a greater extent.

Based on the foregoing embodiments, in one embodiment of the present application, the plurality of constant current charging stages include a first constant current charging stage in which constant current charging is performed with a first charging current, and the first charging current is the charging capacity of the electrochemical device. 1.2 to 1.5 times; when the electrochemical device is charged to the second SOC, the electrochemical device undergoes at least a first constant current charging stage, wherein the second SOC is less than or equal to the first SOC.

In an implementation manner of the present application, the charging capability of the electrochemical device can be determined based on the charger power corresponding to the electronic device powered by the electrochemical device and the rated voltage and rated capacity of the electrochemical device. For example, the charging current can be determined by dividing the charger power by the rated voltage of the electrochemical device, and dividing the charging current by the rated capacity of the electrochemical device to obtain a value to determine the charging capacity of the electrochemical device.

The second SOC may be determined based on the lithium insertion characteristics of the negative active material of the electrochemical device. For example, for an electrochemical device with a mixed system of silicon and graphite, the lithium insertion degree of silicon and graphite is different under different SOC of the electrochemical device.

As shown in Figure 2, in an electrochemical device with silicon content, in 0% to 72% SOC, silicon material dominates lithium insertion; in 72% to 100% SOC, graphite dominates lithium insertion. At this time, the second SOC can be set according to the dividing line between silicon material and graphite dominating lithium insertion, for example, 72% SOC.

For another example, in another electrochemical device with silicon content, in 0% to 35% SOC, silicon material dominates the lithium insertion; in 35% to 87% SOC, graphite dominates the lithium insertion, while silicon slowly inserts lithium. In 87% to 100% SOC, graphite dominates lithium insertion, and the silicon particle volume change rate is large. At this time, the second SOC can be set based on 35% SOC.

In the embodiment of the present application, before the electrochemical device is charged to the second SOC, silicon dominates the lithium insertion, and the lithium insertion potential of silicon is higher than that of graphite. Therefore, a large rate (specifically, a large rate) greater than the charging capacity of the electrochemical device is used. Ground, 1.2 times to 1.5 times the charging capacity of the electrochemical device (large rate) charging, the electrochemical device is not prone to lithium precipitation. In addition, due to the use of high-rate charging at this stage, the charging capacity at the stage of small internal resistance can be further increased, the charging time under high SOC and high internal resistance can be reduced, and the total charging time can be further shortened.

It should be understood that in the embodiment of the present application, before the electrochemical device is charged to the second SOC, the constant current charging stage of the electrochemical device may include only a first constant current charging stage as shown in FIG. 3 . Currently, this stage may also include multiple first constant current charging stages, which is not limited in the embodiments of the present application.

In order to reduce the possibility of lithium deposition in the electrochemical device, in one implementation of the present application, the second SOC is less than or equal to 35%, ensuring that when the SOC of the electrochemical device is less than the second SOC, the charging of the electrochemical device Charging at a high rate of 1.2 to 1.5 times the capacity, the electrochemical device will not produce lithium.

Based on the foregoing embodiments, in one embodiment of the present application, the constant current charging stage includes a second constant current charging stage of constant current charging with a second charging current, and the second charging current is 1.0 of the charging capacity of the electrochemical device. to 1.3 times; when the electrochemical device is charged to a third SOC, the electrochemical device undergoes at least a second constant current charging stage, wherein the third SOC is greater than or equal to the first SOC.

The third SOC may be determined based on the lithium insertion characteristics of the negative active material of the electrochemical device and/or the consideration of avoiding lithium deposition in the electrochemical device. As mentioned above, for the electrochemical device of the silicon and graphite mixed system, the order of lithium insertion is silicon-graphite-silicon. Specifically, when the SOC of the electrochemical device is low (for example, in the range below 35%), silicon dominates lithium insertion. As the SOC gradually increases (for example, in the range of 35% to 87%), graphite dominates the lithium insertion, while silicon slowly inserts lithium. When the SOC of the electrochemical device is high (for example, in the range above 87%), silicon dominates the lithium insertion, and the volume change rate of the silicon particles is large. Charging the electrochemical device at a large rate may cause excessive expansion of the silicon particles, affecting the battery life. Cycle life of chemical plants. At this time, the third SOC can be set according to the dividing line between silicon material and graphite dominating lithium insertion (for example, 87%). In addition, under high SOC and high internal resistance, charging the electrochemical device at a large rate may cause lithium deposition in the electrochemical device. Therefore, when setting the third SOC, it is also necessary to ensure that when the SOC is smaller than the third SOC of the electrochemical device, lithium precipitation will not occur in the electrochemical device when charging at a high rate of 1.0 to 1.3 times the charging capacity of the electrochemical device. .

In the embodiment of the present application, when the SOC of the electrochemical device is greater than the second SOC and less than the third SOC, graphite dominates the lithium insertion, and silicon slowly absorbs lithium. Therefore, at this stage, the charging capacity is equal to or slightly greater than the electrochemical device. Charging at a high rate (i.e., a high rate of 1.0 to 1.3 times the charging capacity of the electrochemical device) can ensure that the electrochemical device does not undergo lithium precipitation and at the same time increase the charging capacity at the stage where the internal resistance is small as much as possible, thereby maximizing the It greatly reduces the charging time under high SOC and high internal resistance, thereby further shortening the total charging time.

It should be understood that in the embodiment of the present application, before the electrochemical device is charged to the third SOC, the constant current charging stage of the electrochemical device may include a plurality of second constant current charging stages as shown in FIG. 3 . Currently, this stage may also include only one second constant current charging stage, which is not limited in the embodiments of the present application.

In order to avoid affecting the cycle life of the electrochemical device and avoiding the possibility of lithium precipitation in the electrochemical device, in an implementation manner of the present application, the third SOC is greater than or equal to 87%.

Based on the above embodiment, in another embodiment of the present application, the constant current charging stage includes a third constant current charging stage of performing constant current charging with a third charging current, and the third charging current is a proportion of the charging capacity of the electrochemical device. 0.5 to 0.8 times; when the state of charge of the electrochemical device is greater than the third SOC, the electrochemical device performs at least one third constant current charging stage, wherein the third SOC is greater than or equal to the first SOC.

As mentioned above, the third SOC may be determined based on the lithium insertion characteristics of the negative active material of the electrochemical device and/or the consideration of avoiding lithium evolution in the electrochemical device. When the electrochemical device is greater than the third SOC, silicon dominates the lithium insertion, and the silicon particle volume change rate is large. Moreover, the electrochemical device is under high SOC and high internal resistance at this time. In order to avoid lithium precipitation in the electrochemical device and excessive expansion of the silicon particles of the electrochemical device, which will affect the cycle life of the electrochemical device, charging is performed at a small rate that is smaller than the charging capacity of the electrochemical device at this stage.

Based on the foregoing embodiments, embodiments of the present application provide an electrochemical device. The charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages. The multiple constant current charging stages include N constant current charging stages, and the multiple constant voltage charging stages include N constant voltage charging stages, where N is an integer and N≥2. And the N constant current charging stages and the N constant voltage charging stages are executed alternately. As an example, the entire charging process includes the first constant current charging stage, the first constant voltage charging stage, ... the rth constant voltage charging stage, the rth constant current charging stage, ... the Nth constant voltage charging stage, ... N constant current charging stage. r is an integer, and N≥r.

Among them, N can be determined experimentally to ensure that the total charging time of the electrochemical device is minimized. In addition, in the embodiment of the present application, the charging currents in each constant current charging stage may be the same or different. For example, when the SOC of the electrochemical device is low, the charging current is large, and when the SOC of the electrochemical device is high, the charging current is relatively small.

The electrochemical device undergoes at least one constant voltage charging phase when the electrochemical device is charged to a first SOC, wherein the first SOC is less than or equal to 80%.

The meaning and principle of the first SOC are similar to the first SOC in the previous embodiment, and will not be described again here. In addition, as mentioned above, when the electrochemical device is charged to a first SOC of less than or equal to 80%, the electrochemical device undergoes at least one constant voltage charging stage, which can also be understood as: the electrochemical device has a low internal resistance when its internal resistance is low. Constant voltage charging was performed at least once.

In the embodiment of the present application, since at least one constant voltage charging is performed when the SOC is low (that is, the internal resistance is small), that is, the alternating constant current charging and constant voltage charging start at the lower SOC stage. The lower SOC stage eliminates polarization while charging, thus reducing the charging time at high voltage. Since the charging time at high voltage is reduced at high temperature, side reactions between the positive electrode and the electrolyte at high voltage can be reduced and the high-temperature cycle performance of the electrochemical device can be improved.

In an embodiment of the present application, in the first constant current charging stage, the electrochemical device performs constant current charging with a first charging current and a first charging time. In the first constant voltage charging stage, the electrochemical device performs constant current charging with a first charging current and a first charging time. The first cut-off voltage reached at the end of the first charging time and the second charging time are used for constant voltage charging, and the first charging current is 1.2 to 1.5 times the charging capacity of the electrochemical device.

The first charging time can be set according to the time required for the electrochemical device to charge to the second SOC with the first charging current. The meaning and principle of the second SOC are similar to those of the second SOC in the previous embodiment, and will not be described again here.

The second charging time can be determined based on experiments to ensure that the phase of rapid current decline and rapid capacity growth can be fully utilized in the first constant voltage phase to reduce the polarization caused by the first constant current phase.

The charging capability of the electrochemical device has a similar meaning and principle to the charging capability of the electrochemical device in the previous embodiments, and will not be described again here.

In the embodiment of the present application, since the internal resistance is small during the start of charging of the electrochemical device, and silicon dominates the lithium insertion, and the lithium insertion potential of silicon is high, a large rate of 1.2 to 1.5 times the charging capacity of the electrochemical device is used. Charging, electrochemical devices are not prone to lithium precipitation. At the same time, the use of high-rate charging at this stage can further increase the charging capacity at the stage of smaller internal resistance, reduce the charging time under high SOC and high internal resistance, and further shorten the total charging time.

Based on the foregoing embodiments, in one embodiment of the present application, in the rth constant current charging stage, the electrochemical device performs constant current charging with the second charging current and the kth charging time, r and k are both integers, and 2 ≤r≤N, k=2r-1; In the rth constant voltage charging stage, the electrochemical device performs constant voltage charging with the rth cut-off voltage reached at the end of the kth charging time and the k+1th charging time, and the second The charging current is smaller than the first charging current. In some embodiments, the difference between the k+1th charging time and the kth charging time is not greater than 20%. In some embodiments, the k+1th charging time is equal to the kth charging time. The degree of difference between two objects refers to the ratio obtained by subtracting the difference between the larger object and the smaller object, divided by the smaller object, and then multiplied by 100%.

The kth charging time (eg, the third charging time) and the k+1th charging time (eg, the fourth charging time) can be set according to specific application scenarios to minimize the total charging time of the electrochemical device.

In the embodiment of the present application, the rth constant current charging stage and the rth constant voltage charging stage may be executed alternately between the second SOC and the third SOC, where the second SOC and the third SOC are the same as in the previous embodiment. The meanings and principles of the second SOC and the third SOC are similar and will not be described again here.

In the embodiment of the present application, the second charging current is used in the second constant current charging stage to the Nth constant current charging stage. However, it should be understood that in other embodiments, different charging currents may be used in the second constant current charging stage to the Nth constant current charging stage, as long as the charging current is ensured to be smaller than the first charging current.

In an implementation manner of the present application, the second charging current may be 1.0 to 1.3 times the charging capacity of the electrochemical device.

Since for the mixed system of silicon and graphite, graphite dominates the lithium insertion during the intermediate stage of charging of the electrochemical device, by charging the electrochemical device with a constant current with a second charging current smaller than the first charging current, it can be ensured that the electrochemical device does not undergo decomposition. Lithium; at the same time, because constant current charging and constant voltage charging are performed alternately, polarization can be eliminated while charging, reducing charging time under high voltage. Since the charging time at high voltage is reduced at high temperature, side reactions between the positive electrode and the electrolyte at high voltage can be reduced and the high-temperature cycle performance of the electrochemical device can be improved.

Based on the foregoing embodiments, in one embodiment of the present application, in the Nth constant current charging stage, the electrochemical device is charged with a third constant current charging current to the charging upper limit voltage; in the Nth constant voltage charging stage, the electrochemical device Constant voltage charging is performed at the charging upper limit voltage to the charging cut-off current, and the third charging current is smaller than the second charging current.

The Nth constant current charging stage and the Nth constant voltage charging stage are the last two charging stages of the electrochemical device. As the SOC of an electrochemical device approaches 100%, the internal resistance of the electrochemical device increases significantly. In the Nth constant current charging stage, charging with a third charging current smaller than the second charging current can avoid lithium deposition in the electrochemical device and excessive expansion of silicon particles in the electrochemical device.

In an implementation manner of the present application, the second charging current may be 0.5 to 0.8 times the charging capacity of the electrochemical device.

In addition, through the Nth constant voltage charging stage, the electrochemical device is charged with a constant voltage at the charging upper limit voltage to the charging cutoff current to eliminate polarization. Since the polarization is eliminated while charging in the previous lower SOC stage, the charging capacity in the smaller internal resistance stage is increased, which shortens the charging time under high SOC and high internal resistance. For example, the Nth constant voltage charging stage takes significantly longer. shorten, thereby shortening the total charging time of the electrochemical device. In addition, by avoiding long-term constant voltage charging at high voltage, side reactions between the positive electrode and the electrolyte under high voltage can be reduced and the high-temperature cycle performance of the electrochemical device can be improved.

Embodiments of the present application also provide a charging method for an electrochemical device, which charging method is suitable for the electrochemical device provided in the foregoing device embodiments. As shown in Figure 3, the charging process of the electrochemical device includes multiple constant current charging stages and multiple constant voltage charging stages; when charging the electrochemical device to the first SOC in the charging process, the electrochemical device experiences at least one constant voltage Charging phase in which the first SOC is less than or equal to 80%.

In an embodiment of the present application, the multiple constant current charging stages include N constant current charging stages, the multiple constant voltage charging stages include N constant voltage charging stages, N is an integer and N≥2 . And the N constant current charging stages and the N constant voltage charging stages are executed alternately. As an example, the entire charging process includes the first constant current charging stage, the first constant voltage charging stage, ... the rth constant voltage charging stage, the rth constant current charging stage, ... the Nth constant voltage charging stage, ... N constant current charging stage. r is an integer. And N≥r. Correspondingly, as shown in Figure 4, the charging method includes steps S401 to S403.

In step S401, for the first constant current charging stage and the first constant voltage charging stage, the electrochemical device is charged with a first charging current and a first charging time. The first charging current is the charging capacity of the electrochemical device. 1.2 to 1.5 times; obtain the first cut-off voltage of the electrochemical device at the end of the first charging time; perform constant voltage charging of the electrochemical device with the first cut-off voltage and the second charging time. The meaning and setting method of the first charging time and the second charging time may refer to the aforementioned device embodiment.

In step S402, for the rth constant current charging stage and the rth constant voltage charging stage, perform constant current charging on the electrochemical device with the second charging current and the kth charging time, and the second charging current is smaller than the first charging current; obtain The r-th cut-off voltage of the electrochemical device at the end of the k-th charging time; perform constant voltage charging of the electrochemical device with the r-th cut-off voltage and the k+1-th charging time, r and k are both integers, and 2≤r≤N ,k=2r-1. The meaning and setting method of the k-th charging time and the k+1-th charging time may refer to the aforementioned device embodiment. In a specific implementation, the second charging current is 1.1 to 1.3 times the charging capacity of the electrochemical device.

In step S402, for the Nth constant current charging stage and the Nth constant voltage charging stage, the electrochemical device is constantly charged with a third charging current to the charging upper limit voltage, and the third charging current is smaller than the second charging current; to charge The upper limit voltage performs constant voltage charging of the electrochemical device to the target charging cut-off current. The target charge cut-off current can be determined experimentally. In one implementation, the third charging current is 0.5 to 0.8 times the charging capability of the electrochemical device.

It should be understood that the charging method shown in FIG. 4 is only an example. In other embodiments, the first charging current in the first constant current charging stage may be different from the second constant current charging stage to the Nth constant current charging stage. The second charging current is the same. In addition, in other embodiments, different charging currents are used in the second constant current charging stage to the Nth constant current charging stage, which is not limited in this application.

In another embodiment of the present application, the charging method further includes: for each constant current charging stage from the first constant current charging stage to the N-1th constant current charging stage, charging in the constant current charging stage The corresponding cut-off voltage obtained at the end of the stage is compared with the charging upper limit voltage; if the corresponding cut-off voltage obtained is the charging upper limit voltage, the electrochemical device is charged at a constant voltage to the target cut-off current with the charging upper limit voltage and then stops charging, thus increasing the Charging safety of electrochemical devices.

The charging method provided in this embodiment is applicable to the corresponding electrochemical device in the previous embodiment, and has beneficial effects corresponding to the corresponding electrochemical device, which will not be described again here. In addition, the meaning and setting method of each parameter in this embodiment can be referred to the description of the corresponding part in the foregoing device embodiment, and will not be described again here.

In order to make the invention purpose, technical solutions and technical effects of this application clearer, this application will be further described in detail below with reference to specific examples. The electrochemical device used in each comparative example and the example of the present application has a Si content of 10%. It should be noted that each comparative example and the examples of the present application can also use electrochemical devices of other chemical systems, that is, the negative active material can include other contents of Si or transition metal oxides, and the present application is not limited thereto.

Each comparative example and the embodiments of the present application are explained by taking the charging upper limit voltage of the electrochemical device as 4.5V and the system charging capacity of the electrochemical device as 0.7C. However, it should be understood that the embodiments of the present application can be applied to various applications. Voltage system, electrochemical device with various system charging capabilities.

The following is a cycle test of the electrochemical device using the charging method of Comparative Examples 1 and 2 and the electrochemical device using the charging method provided in the embodiment of the present application, and comparing the respective test cycle time and cycle performance. Among them, each comparative example and the embodiment of the present application use a constant current of 0.7C to discharge the electrochemical device to 3V during the discharge process.

Comparative example 1

Test temperature: 45℃

Step 1. Let the electrochemical device stand for 30 minutes.

Step 2: Use a constant current of 0.7C to charge the electrochemical device until the voltage of the electrochemical device reaches the charging upper limit voltage of 4.5V.

Step 3: Continue to charge the electrochemical device using a constant voltage of 4.5V until the current of the electrochemical device reaches the charging cut-off current of 0.2C.

Step 4: Let the electrochemical device stand for 5 minutes.

Step 5: Use a constant current of 0.5C to discharge the electrochemical device to 3V.

Step 6: Let the electrochemical device stand for 5 minutes.

Repeat steps two to six above until 300 cycles are performed.

Comparative example 2

Test temperature: 45℃

Step 1. Let the electrochemical device stand for 30 minutes.

Step 2: Use a constant current of 0.7C to charge the electrochemical device until the voltage of the electrochemical device reaches a predetermined voltage of 4.45V.

Step 3: Continue to charge the electrochemical device using a constant voltage of 4.45V until the current of the electrochemical device reaches the charging cut-off current of 0.2C.

Step 4: Let the electrochemical device stand for 5 minutes;

Step 6: Let the electrochemical device stand for 5 minutes.

Repeat steps two to six above until 300 cycles are performed.

This embodiment

Test temperature: 45℃

Step 1. Let the electrochemical device stand for 30 minutes

Step 2: Use a constant current of 1C to charge the electrochemical device for 17.5 minutes, and detect the first cut-off voltage V1 at the end of the 17.5 minutes.

Step 3: Continue to charge the electrochemical device using constant voltage V1 until the charging time reaches 15 minutes and the charging current of the electrochemical device is less than or equal to 0.7C.

Step 4: Use a constant current of 0.7C to charge the electrochemical device for 10 minutes, and detect the second cut-off voltage V2 at the end of the 10 minutes.

Step 5: Continue to use constant voltage V2 to charge the electrochemical device for 10 minutes.

Step 6: Use a constant current of 0.7C to charge the electrochemical device for 10 minutes, and detect the third cut-off voltage V3 at the end of the 10 minutes.

Step 7: Continue to use constant voltage V3 to charge the electrochemical device for 10 minutes.

Step 8: Use a constant current of 0.7C to charge the electrochemical device for 10 minutes, and detect the fourth cut-off voltage V4 at the end of the 10 minutes.

Step 9: Continue to use constant voltage V4 to charge the electrochemical device for 10 minutes.

Step 10: Use a constant current of 0.7C to charge the electrochemical device for 10 minutes, and detect the fifth cut-off voltage V5 at the end of the 10 minutes.

Step 11: Continue to charge the electrochemical device using constant voltage V5 for 10 minutes.

Step 12: Use a constant current of 0.7C to charge the electrochemical device for 10 minutes, and detect the sixth cut-off voltage V6 at the end of the 10 minutes.

Step 13: Continue to charge the electrochemical device using constant voltage V6 for 5 minutes.

Step 14: Use a constant current of 0.4C to charge the electrochemical device to the charging upper limit voltage of 4.5V;

Step 15. Use a constant voltage of 4.5V to charge the electrochemical device to 0.02C

Step 16: Let the electrochemical device stand for 5 minutes;

Step 17: Use a constant current of 0.5C to discharge the electrochemical device to 3V.

Step 18: Let the electrochemical device stand for 5 minutes.

Repeat steps 2 to 18 above until 300 cycles are executed.

Table 1 records the test cycle time and cycle performance of the electrochemical devices of each comparative example and the embodiment of the present application, including the total charging time of each cycle, CV time at high voltage (also called high voltage CV time), initial Capacity, capacity retention rate after 300 cycles at 45°C (expressed in the form of cycle number@45°C) and expansion rate after 300 cycles at 45°C (expressed in the form of expansion coefficient@45°C).

Table 1

As can be seen from Table 1, compared with Comparative Example 1, when the initial capacity reached 880mAh, the total charging time of the embodiment of the present application was reduced by 39 minutes, and the high voltage CV time was reduced by 45 minutes. The 45°C cycle performance There are a lot of enhancements. In addition, the embodiment of the present application has a retention rate of 87% and a collision rate of 9.2% when experiencing 300cls. Compared with the direct charging method of Comparative Example 1, the retention rate is increased by 9% and the expansion rate is reduced by 1.8%. In addition, compared with Comparative Example 2 with an initial capacity of 858mAh, the total charging time and high voltage CV time of the embodiment of the present application were also reduced by 17 minutes and 20 minutes respectively.

In summary, the embodiments of the present application can reduce the charging time under high voltage and shorten the total charging time of the electrochemical device; in addition, by avoiding long-term constant voltage charging under high voltage, the time between the positive electrode and the electrolyte under high voltage can be reduced. Side reactions improve the high-temperature cycle performance of electrochemical devices.

FIG. 5 is a schematic structural diagram of an electronic device provided by an embodiment of the present application. As shown in FIG. 5 , the electronic device 50 includes, but is not limited to, at least one processor 510 and an electrochemical device 520 . The above components can be connected through a bus or directly.

The electrochemical device 520 is the electrochemical device in the above device embodiment. The processor 510 may charge the electrochemical device 520 according to the charging method of the electrochemical device in the above method embodiment. The technical principles and technical effects can be referred to the foregoing embodiments and will not be described again here.

It should be noted that FIG. 5 is only an example of an electronic device. In other embodiments, the electronic device may also include more or less components, or may have different component configurations. The electronic device can be any suitable rechargeable device or component such as a watch, a mobile phone, a tablet, a personal digital assistant, a Wireless Fidelity (WiFi) unit, a Bluetooth unit, a speaker, etc.

Other embodiments of the present application will be readily apparent to those skilled in the art from consideration of the specification and practice of the invention claimed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary technical means in the technical field that are not applied in this application. . It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It is to be understood that the present application is not limited to the precise structures described above and illustrated in the accompanying drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the present application. within the scope of protection.

Claims

An electrochemical device, characterized in that the charging process of the electrochemical device includes a plurality of constant current charging stages and a plurality of constant voltage charging stages. When the electrochemical device is charged to a first state of charge, the The electrochemical device undergoes at least one constant voltage charging phase in which the first state of charge is less than or equal to 80%.
The electrochemical device according to claim 1, wherein the plurality of constant current charging stages include a first constant current charging stage in which constant current charging is performed with a first charging current, and the first charging current is the 1.2 to 1.5 times the charging capacity of the electrochemical device; and

The electrochemical device undergoes at least one of the first constant current charging phases when the electrochemical device is charged to a second state of charge, wherein the second state of charge is less than or equal to the first state of charge.
The electrochemical device of claim 2, wherein the second state of charge is less than or equal to 35%.
The electrochemical device according to claim 1, characterized in that the constant current charging stage includes a second constant current charging stage of constant current charging with a second charging current, the second charging current is the electrochemical 1.0 to 1.3 times the charging capacity of the device;

The electrochemical device undergoes at least one of the second constant current charging stages when the electrochemical device is charged to a third state of charge, wherein the third state of charge is greater than or equal to the first state of charge.
The electrochemical device according to claim 4, wherein the third state of charge is greater than or equal to 87%.
The electrochemical device according to claim 2, wherein the constant current charging stage includes a second constant current charging stage of constant current charging with a second charging current, the second charging current being the electrochemical 1.0 to 1.3 times the charging capacity of the device, and the second charging current is smaller than the first charging current;

The electrochemical device undergoes at least one of the second constant current charging stages when the electrochemical device is charged to a third state of charge, wherein the third state of charge is greater than or equal to the first state of charge.
The electrochemical device according to claim 1, characterized in that the constant current charging stage includes a third constant current charging stage of constant current charging with a third charging current, the third charging current is the electrochemical 0.5 to 0.8 times the charging capacity of the device;

When the state of charge of the electrochemical device is greater than a third state of charge, the electrochemical device performs at least one third constant current charging stage, wherein the third state of charge is greater than or equal to the first state of charge. power status.
The electrochemical device according to claim 1, characterized in that

The multiple constant current charging stages include N constant current charging stages, the multiple constant voltage charging stages include N constant voltage charging stages, N is an integer and N≥2; and

The N constant current charging stages and the N constant voltage charging stages are executed alternately.
The electrochemical device according to claim 8, characterized in that

In the first constant current charging stage, the electrochemical device performs constant current charging with a first charging current and a first charging time;

In the first constant voltage charging stage, the electrochemical device performs constant voltage charging with a first cut-off voltage reached at the end of the first charging time and a second charging time, and the first charging current is the electrochemical 1.2 to 1.5 times the charging capacity of the device.
The electrochemical device according to claim 9, characterized in that

In the rth constant current charging stage, the electrochemical device performs constant current charging with the second charging current and the kth charging time, r and k are both integers, and 2≤r≤N, k=2r-1;

In the rth constant voltage charging stage, the electrochemical device performs constant voltage charging with the rth cut-off voltage reached at the end of the kth charging time and the k+1th charging time, and the second charging current is less than the The first charging current.
The electrochemical device according to claim 10, wherein the difference between the k+1th charging time and the kth charging time is not greater than 20%.
The electrochemical device according to claim 10, characterized in that when N>2,

In the Nth constant current charging stage, the electrochemical device is charged with a third constant current charging current to the charging upper limit voltage;

In the Nth constant voltage charging stage, the electrochemical device performs constant voltage charging at the charging upper limit voltage to a charging cut-off current, and the third charging current is smaller than the second charging current.
The electrochemical device according to claim 1, wherein the negative electrode material of the electrochemical device at least includes silicon-based material and graphite.
A charging method for an electrochemical device, characterized in that the charging process of the electrochemical device includes a plurality of constant current charging stages and a plurality of constant voltage charging stages; in the charging process, the electrochemical device is charged to In a first state of charge, the electrochemical device undergoes at least one constant voltage charging stage, wherein the first state of charge is less than or equal to 80%.
An electronic device, characterized by comprising the electrochemical device according to any one of claims 1-13.