Patent Publication Number: US-2022238970-A1

Title: Battery pack

Description:
RELATED APPLICATION INFORMATION 
     This application claims the benefit under 35 U.S.C. § 119(a) of Chinese Patent Application No. CN 202110105015.4, filed on Jan. 26, 2021, which application is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Based on the use requirement for portability, more and more power tools currently use battery packs as power sources. 
     The existing battery packs for supplying power to power tools mostly use cylindrical lithium batteries. Multiple cylindrical lithium batteries connected in series and in parallel ensure sufficient electric energy output so that the endurance capacity and operating efficiency of the power tools are improved. 
     However, with the continuous development of battery pack technology, the discharge current and charge current of a battery pack increase gradually. During use, the heat generation of components of the battery pack through which the currents flow increases gradually. The components include positive and negative terminal poles, circuit boards, and lead-out pieces connecting cells. Especially when a power tool keeps working for a while with a high current, the temperature on the components rises sharply, causing a problem about the safety and reliability of the battery pack. Additionally, the heat generation of the battery pack may shorten the life of the battery pack, raising the frequency for a user changing the battery pack and thus increasing the cost of use. 
     SUMMARY 
     A battery pack is provided. The battery pack includes a housing, a battery pack interface enabling the battery pack to be detachably connected to a power tool, and a cell assembly located in the housing. The battery pack interface includes a battery pack positive terminal and a battery pack negative terminal. The cell assembly includes a plurality of non-cylindrical cells. A cell includes a cell positive electrode and a cell negative electrode. The cell assembly includes a positive lead-out piece, a negative lead-out piece, a discharge path, and a protective element. The positive lead-out piece is connected in series between at least one cell positive electrode and the battery pack positive terminal. The negative lead-out piece is connected in series between at least one cell negative electrode and the battery pack negative terminal. The discharge path is configured to supply power to the power tool and consists of a cell assembly positive terminal, the positive lead-out piece, the battery pack positive terminal, a cell assembly negative terminal, the negative lead-out piece, and the battery pack negative terminal. The protective element is disposed on the discharge path. In response to the discharge current of the discharge path being greater than or equal to a preset current, the protective element turns off to disconnect the discharge path. The length of one of the positive lead-out piece or the negative lead-out piece close to the protective element is greater than the length of the other of the positive lead-out piece or the negative lead-out piece away from the protective element. 
     In one example, the protective element is connected between the positive lead-out piece and the battery pack positive terminal. The length of the positive lead-out piece close to the protective element is greater than the length of the negative lead-out piece away from the protective element. 
     In one example, the protective element is connected between the negative lead-out piece and the battery pack negative terminal. The length of the negative lead-out piece close to the protective element is greater than the length of the positive lead-out piece away from the protective element. 
     In one example, the cells are connected in series. 
     In one example, the positive lead-out piece and the negative lead-out piece are made of metal. 
     In one example, the cell assembly includes a first cell and a second cell. A positive electrode of the first cell is connected to a negative electrode of the second cell in series. The positive lead-out piece is connected to a positive electrode of the second cell. The negative lead-out piece is connected to a negative electrode of the first cell. 
     In one example, the discharge current of the battery pack is greater than or equal to 80 A. 
     In one example, the capacity of the battery pack is greater than or equal to 5 Ah. 
     In one example, the battery pack further includes a cell elastic piece disposed around the cell assembly. 
     A battery pack is provided. The battery pack includes battery pack terminals, a plurality of non-cylindrical cells, two lead-out pieces, and a protective element. A cell includes a cell output pole piece for outputting the electric energy of the cell. The two lead-out pieces are connected between the battery pack terminals and the cell output pole piece. The protective element is disposed between the battery pack terminals and the cell output pole piece. In response to the discharge current of the battery pack being greater than or equal to a preset current, the protective element turns off. One of the two lead-out pieces close to the protective element is defined as a first lead-out piece. The other of the two lead-out pieces away from the protective element is defined as a second lead-out piece. The length of the first lead-out piece is greater than the length of the second lead-out piece. 
     In one example, the cells are stacked in the up-down direction to form a cell assembly. The cell assembly has a first thickness in the up-down direction. The length of the first lead-out piece is smaller than or equal to the first thickness. 
     In one example, each of the cell has a second thickness in the up-down direction. The length of the second lead-out piece is smaller than or equal to the second thickness. 
     A battery pack is provided. The battery pack includes battery pack terminals, a plurality of non-cylindrical cells, and two lead-out pieces. A cell includes a cell output pole piece for outputting the electric energy of the cell. The two lead-out pieces are connected between the battery pack terminals and the cell output pole piece. One of the two lead-out pieces that has a first temperature in response to the battery pack discharging is defined as a first lead-out piece. The other of the two lead-out pieces that has a second temperature in response to the battery pack discharging is defined as a second lead-out piece. In response to the first temperature being greater than the second temperature, the length of the first lead-out piece is greater than the length of the second lead-out piece. 
     The present disclosure has the beneficial effect that the preceding technical solutions can reduce the heat generation of the battery pack, thus improving the safety and reliability of the battery pack and extending the service life of the battery pack. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view of a power tool system according to example one. 
         FIG. 2  is a perspective view illustrating the structure of the power tool in  FIG. 1 . 
         FIG. 3  is a view illustrating the structure of a battery pack according to example one. 
         FIG. 4  is a view illustrating the structure of the battery pack shown in  FIG. 3  with the upper housing removed. 
         FIG. 5  is a view illustrating the internal structure of the battery pack shown in  FIG. 3  with a housing and a cell elastic piece excluded. 
         FIG. 6  is a view illustrating the structure of a cell assembly according to one example. 
         FIG. 7  is a view illustrating the internal structure of a cell assembly shown in  FIG. 3  with a part of a cell elastic piece included. 
         FIG. 8  is a view illustrating the internal structure between a lower housing and a first support plate according to example one. 
         FIG. 9  is a view illustrating the internal structure between a lower housing and a first support plate according to example two. 
         FIG. 10  is a block diagram of a protective circuit provided for the battery pack according to example one. 
         FIG. 11  is a block diagram of a protective circuit provided for a battery pack according to example two. 
         FIG. 12  is a block diagram of a protective circuit provided for the power tool system according to example one. 
         FIG. 13  is a block diagram of a protective circuit provided for a charging combination according to example one. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is described hereinafter in detail in conjunction with drawings and examples. 
       FIG. 1  illustrates a power tool system  100 . The power tool system  100  includes a power tool  10  and a battery pack  20  that is adapted to the power tool  10  and supplies power to the power tool  10 . In  FIG. 1 , the power tool  10  is an impact wrench. Although this example relates to an impact wrench, it is to be understood that the present application is not limited to the disclosed examples and is applicable to a power tool  10  of another type. The power tool  10  may be a gardening tool, for example, a string trimmer, a hedge trimmer, a blower, or a chainsaw. Alternatively, the power tool  10  may be a torque output tool, for example, an electric drill or an electric hammer. Alternatively, the power tool  10  may be a sawing tool, for example, an electric circular saw, a scroll saw, or a reciprocating saw. Alternatively, the power tool  10  may be a grinding tool, for example, an angle grinder or a sander. 
     Referring to  FIG. 2 , the power tool  10  includes a tool body  11 , a tool interface  12 , and a tool matching portion  13 . The tool interface  12  and the tool matching portion  13  are disposed on the tool body  11 . 
     The tool body  11  includes a motor  111 , an output shaft  112 , and an impact mechanism  113 . The output shaft  112  is driven by the motor  111 . The impact mechanism  113  connects the motor  111  to the output shaft  112 . The impact mechanism  113  is driven by the motor  111  and applies an impact to the output shaft  112 . The body of the power tool  10  further includes a handle  114  that can be held by a user to operate the power tool  10 . The handle is provided with a trigger switch  115 . The trigger switch is configured to be driven by the user of the power tool  10  to start or stop the operation of the motor  111 . Additionally, at the lower end of the handle  114 , the power tool  10  is further provided with the tool interface  12  and the tool matching portion  13  that are configured to be detachably connected to the battery pack  20 . In some examples, the tool matching portion  13  is configured to enable the battery pack  20  to be detached from the tool matching portion  13  when the user slides the battery pack  20  toward the front of the body of the power tool  10 . 
     In the preceding description, the up-down direction and the front-rear direction are illustrated as directions shown in  FIG. 3 . 
     Referring to  FIG. 3 , the battery pack  20  includes a housing  23 , a cell assembly  24 , a battery pack junction portion  22 , and a battery pack interface  21 . The voltage of the battery pack  20  is usually 10.8 V, 24 V, 36 V, 48 V, 56 V, or 80 V. The capacity of the battery pack  20  is greater than or equal to 5 Ah. Further, the capacity of the battery pack is greater than or equal to 9 Ah. The battery pack  20  is provided with the battery pack interface  21  and the battery pack junction portion  22 . The battery pack interface  21  is configured to match the tool interface  12  to supply power to the power tool  10 . The battery pack interface  21  can further match a charger  30  to enable the charger  30  to charge the battery pack  20 . The battery pack junction portion  22  can be detachably connected to the tool matching portion  13  or the charger  30  so as to enable the battery pack  20  to supply power to the power tool  10  or enable the charger  30  to charge the cell assembly  24 . 
     The housing  23  includes an upper housing  231  and a lower housing  232  that are assembled at the interfacial position to form an inner cavity. The inner cavity formed by the assembly of the upper housing  231  and the lower housing  232  is configured to secure and accommodate the cell assembly  24 . 
     The cell assembly  24  is disposed in the inner cavity formed by the housing  23 . The cell assembly  24  includes a plurality of cells  241 . A cell  241  includes a cell tab  242 . The cell tab  242  further includes a cell positive electrode and a cell negative electrode that are configured to output the electric energy of the cell  241  or input electric energy for charging the cell  241 . The cell assembly  24  further includes a cell assembly positive terminal and a cell assembly negative terminal that are configured to output the electric energy of the cell assembly  24  or input electric energy for charging the cell assembly  24 . The cell assembly positive terminal is connected in series between at least one cell positive electrode and a battery pack positive terminal. The cell assembly negative terminal is connected in series between at least one cell negative electrode and a battery pack negative terminal. In general, the cells  241  are in series connection, in parallel connection, or in a combination of series connection and parallel connection to form the cell assembly  24 . The voltage of a single cell  241  is 4.2 V. In some examples, the cell  241  is a cylindrical structure, for example, a  18650  battery. In some other examples, the cell  241  is a flat bag-like structure, and the cells  241  are stacked sequentially in the up-down direction. The cell  241  may also be bent into an arc-shaped structure, for example, a pouch-type battery pack. The cell  241  further includes a shell of the cell  241 . For a cylindrical cell, a steel shell is usually used as the shell of the cell  241 . For a pouch-type battery pack, an aluminum-plastic film is usually used as the shell of the cell  241 . It is to be understood that the present application is not limited to the disclosed examples, and the structure of the cell  241  is not limited here. 
     The battery pack interface  21  is formed on one upper surface of the housing  23  and is at least electrically connected to the cell assembly  11  to establish the physical and electrical connection to the power tool. Specifically, the battery pack interface  21  is formed on the upper surface of the upper housing  231 . In some examples, the battery pack interface  21  includes a power supply positive interface  211 , a power supply negative interface  212 , and a power supply communication interface  213 . The battery pack  20  outputs electric energy through the power supply positive interface  211  and the power supply negative interface  212 . The battery pack  20  communicates with the attached power tool or charger through the power supply communication interface  213 . In a specific example, the housing is provided with two power supply positive interfaces  211  and two power supply negative interfaces  212 . It is to be understood that the battery pack housing  23  may be provided with more or less power supply positive interfaces  211  and power supply negative interfaces  212  based on the electrical characteristics of the battery pack. 
     The battery further includes a first support plate  25 , a main circuit board  26 , and a terminal assembly  27 . 
     The first support plate  25  is disposed on the upper side of the lower housing  232 . The first support plate  25  and the lower housing  232  form an accommodation space to accommodate the cell assembly. Referring to  FIG. 4 , the first support plate  25  is detachably connected to the lower housing  232  to form the accommodation space to accommodate the cell assembly. Similarly, the first support plate  25  and the upper housing  231  form an accommodation space to accommodate components including the main circuit board  26  and the terminal assembly  27 . Specifically, the first support plate  25  is a slab structure and is detachably connected to the lower housing  232 . 
     The terminal assembly  27  includes battery pack terminals and a terminal support base  271 . The terminal support base  271  is configured to accommodate and secure the battery pack terminals onto the first support plate  25 . The battery pack terminals further include a battery pack positive terminal  272 , a battery pack negative terminal  273 , and a battery pack communication terminal  274 . The battery pack positive terminal  272  is electrically connected to the cell assembly positive terminal, that is, at least one cell positive electrode, and is located in the power supply positive interface  211 . The battery pack negative terminal  273  is electrically connected to the cell assembly negative terminal, that is, at least one cell negative electrode, and is located in the power supply negative interface  212 . The battery pack positive terminal  272  and the battery pack negative terminal  273  are configured to match a tool terminal of the power tool  10  to output the electric energy of the cell assembly  24  to the power tool  10 . Specifically, the electric energy of the cell assembly  24  passes through the cell assembly positive terminal and the battery pack positive terminal  272  to the tool interface of the power tool and the motor of the power tool and then passes through the battery pack negative terminal  273  and the cell assembly negative terminal to return to the cell assembly  24 . Accordingly, the cell assembly  24 , the battery pack terminals in the battery pack interface, and the motor  111  of the power tool form a discharge circuit. The motor  111  consumes the electric energy of the cell assembly  24  through the discharge circuit. Moreover, the battery pack communication terminal  274  is located in the power supply communication interface  213  and configured to communicate with the connected power tool  10  or the charger. As a specific example, the battery pack terminals clamp the tool terminal with elastic force from both sides in the left-right direction. Accordingly, in the process of installing the battery pack to the power tool, the tool terminal of the power tool is led by the battery pack interface and inserted into the battery pack terminals so that the tool terminal is clamped by the battery pack terminals, thus enabling the power tool  10  to be electrically connected to the battery pack  20 . 
     The main circuit board  26  is disposed on the upper side of the first support plate  25 , is connected in series between the cell assembly  24  and the battery pack interface  21 , and is configured to collect an electrical signal related to the battery pack  20 . In some examples, the main circuit board  26  is connected in series between the cell assembly  24  and the battery pack communication terminal  274  and is configured to transmit the information of the battery pack through the battery pack communication terminal  274  to the power tool  10  attached to the battery pack  20 . The information of the battery pack includes the discharge current of the battery pack, the temperature of the cell assembly  24  and/or the temperature of the cell  241 , the voltage of the cell  241 , and the internal resistance value of the cell  241 . Since the information of the battery pack is usually detected by a sensor, the battery pack  20  further includes one or more detection sensors. In some examples, a detection sensor may be a temperature sensor disposed on the surface of the cell assembly  24  or the surface of the cell  241 . The temperature sensor may be specifically a thermistor. The detection sensor may also be a voltage sensor for detecting the voltage of the cell  241 . 
     Referring to  FIG. 5 , the battery pack  20  further includes a detection circuit board  28 . The detection sensor is integrated on the detection circuit board  28 . For ease of detection, the detection circuit board  28  is disposed on one side of the cell assembly where the cell tab  242  is located, that is, on one side of the cell assembly  24  where the cell positive electrode  2421  and the cell negative electrode  2422  are located. It is to be understood that the battery pack  20  further includes a sensor of another type so that the detection circuit board  28  collects the information of the battery pack through various sensors and transmits the collected information of the battery pack to the main circuit board  26 , and through the battery pack communication terminal  274  to the attached power tool  10  or the charger. In some examples, the cell tabs  242 , that is, the cell positive electrode  2421  and the cell negative electrode  2422 , are disposed on the front end surface of the cell  241  or the rear end surface of the cell  241 . 
     Additionally, the battery pack  20  further includes a protective element  29  disposed between the battery pack terminals and the cell tab  242 . In response to the discharge current of the battery pack being greater than or equal to a preset current, the protective element  29  turns off. The cell assembly  24  further includes two lead-out pieces. The two lead-out pieces are made of metal and are connected between the battery pack terminals and the cell tab  242 . In some examples, one lead-out piece (for example, a positive lead-out piece  243  as shown in  FIG. 5 ) of the two lead-out pieces close to the protective element  29  is defined as a first lead-out piece, and the other lead-out piece (for example, a negative lead-out piece  244  as shown in  FIG. 5 ) of the two lead-out pieces away from the protective element  29  is defined as a second lead-out piece. Here the length of the first lead-out piece is greater than the length of the second lead-out piece. The length of the first lead-out piece is a path length of the first lead-out piece on its extension path. The length of the second lead-out piece is a path length of the second lead-out piece on its extension path. The length of the first lead-out piece is a path length of the first lead-out piece on a discharge path. The length of the second lead-out piece is a path length of the second lead-out piece on the discharge path. 
     In some examples, the size of the first lead-out piece along the up-down direction is greater than the size of the second lead-out piece along the up-down direction. 
     In some examples, each of the cells  241  has a second thickness H 2  in the up-down direction, and the plurality of cells  241  are stacked in the up-down direction to specifically form the cell assembly  24  so that the cell assembly  24  has a first thickness H 1  in the up-down direction. Here the first thickness H 1  is related to the number of the cells  241 . Additionally, the length of the first lead-out piece is smaller than or equal to the first thickness H 1 . The length of the second lead-out piece is smaller than or equal to the second thickness H 2 . 
     Specifically, the two lead-out pieces are the positive lead-out piece  243  and the negative lead-out piece  244  respectively. The positive lead-out piece  243  enables the cell assembly positive terminal to be connected to the battery pack positive terminal  272 . The negative lead-out piece  244  enables the cell assembly negative terminal to be connected to the battery pack negative terminal. In this example, the plurality of cells  241  are connected in series to form the cell assembly  24 .  FIG. 6  is a view illustrating the structure of a cell assembly according to one example. Referring to  FIG. 6 , the cell assembly  24 ′ includes at least a first cell  241   a  and a second cell  241   b . Accordingly, a first cell positive electrode  2421   a  of the first cell is electrically connected to a second cell negative electrode  2422   b  of the second cell to enable the first cell and the second cell to be connected in series. A first cell negative electrode  2422   a  of the first cell is the cell assembly negative terminal  245 ′ of the cell assembly  24 ′. A second cell positive electrode  2421   b  of the second cell is the cell assembly positive terminal  246 ′ of the cell assembly  24 ′. In this example, the cell assembly positive terminal  246 ′ is connected to the positive lead-out piece  243 . The cell assembly negative terminal  245 ′ is connected to the negative lead-out piece  244 . With this arrangement, the cell assembly positive terminal  246 ′, the positive lead-out piece  243 , the battery pack positive terminal  272 , the cell assembly negative terminal  245 ′, the negative lead-out piece  244 , and the battery pack negative terminal  273  form the discharge path that is in the battery pack  10  and is configured to supply power to the power tool  10 . The positive lead-out piece  243  and the negative lead-out piece  244  are each a metal piece with a certain width so that the temperature does not rise rapidly when the positive lead-out piece  243  and the negative lead-out piece  244  output a large discharge current. Specifically, the width of the positive lead-out piece  243  and the width of the negative lead-out piece  244  are in the range of 5 mm to 40 mm. This arrangement enhances the heat dissipation effect of the positive lead-out piece  243  and the heat dissipation effect of the negative lead-out piece  244 , thus reducing the heat generation of the battery pack in use, improving the safety and reliability of the battery pack, and extending the service life of the battery pack. 
     The protective element  29  is disposed on the preceding discharge path. The protective element  29  is configured to, in response to the discharge current of the discharge path being greater than or equal to the preset current, turn off to disconnect the discharge path so that the battery pack stops outputting electric energy to improve the safety of the battery pack. As a specific example, when the discharge current rises abnormally to the preset current, the protective element  29  gets fused to disconnect the discharge path. The protection element  29  may specifically be one of a plug fuse, a wrapped fuse, or a surface-mount fuse, which is not limited here. 
     Since the protective element  29  generates a great amount of heat in operation, the length of one of the positive lead-out piece  243  or the negative lead-out piece  244  close to the protective element  29  is arranged to be greater than the length of the other of the positive lead-out piece  243  or the negative lead-out piece  244  away from the protective element  29 , further enhancing the heat dissipation effect of the battery pack  10  and reducing the effect of the heat generation of the protective element  29  on the cell assembly  24 . In some examples, when the protective element  29  is connected between the positive lead-out piece  243  and the battery pack positive terminal  272 , the length of the positive lead-out piece  243  close to the protective element  29  is greater than the length of the negative lead-out piece  244  away from the protective element  29 . In some other examples, when the protective element  29  is connected between the negative lead-out piece  244  and the battery pack negative terminal  273 , the length of the negative lead-out piece  244  close to the protective element  29  is greater than the length of the positive lead-out piece  243  away from the protective element  29 . This arrangement helps with the heat dissipation of the battery pack, preventing the heat generated by the protective element  29  from being transmitted through the positive lead-out piece  243  or the negative lead-out piece  244  to the cells  241 . 
     In some other examples, one lead-out piece (for example, the positive lead-out piece  243  as shown in  FIG. 5 ) of the two lead-out pieces that has a first temperature in response to the battery pack  20  discharging is defined as a first lead-out piece, and the other lead-out piece (for example, the negative lead-out piece  244  as shown in  FIG. 5 ) of the two lead-out pieces that has a second temperature in response to the battery pack  20  discharging is defined as a second lead-out piece. Accordingly, due to the existence of the protective element  29 , in response to the first temperature being greater than the second temperature, the length of the first lead-out piece is greater than the length of the second lead-out piece. When the protective element  29  is disposed between the negative lead-out piece  244  and the battery pack negative terminal  273 , the second temperature is greater than the first temperature and thus the length of the second lead-out piece is greater than the length of the first lead-out piece. This arrangement helps with the heat dissipation of the battery pack, preventing the heat generated by the protective element  29  from being transmitted through the first lead-out piece or the second lead-out piece to the cells  241 . 
     Referring to  FIG. 7 , the battery pack  20  further includes a cell elastic piece  201 . The cell elastic piece  201  is disposed on at least one side of the cell assembly  24  to protect the cell assembly  24 . The cell assembly has an upper surface, a lower surface, a front end surface, and a rear end surface that are disposed between the upper surface and the lower surface, and a left side surface and a right side surface that are disposed on two sides of a first end surface. The front end surface and the back end surface are disposed opposite to each other. In some examples, the cell elastic piece  201  is disposed around the cell assembly  24 . That is, the cell elastic piece  201  is disposed around the upper surface of the cell assembly  24 , the lower surface of the cell assembly  24 , the front end surface of the cell assembly  24 , the rear end surface of the cell assembly  24 , the left side surface of the cell assembly  24 , and the right side surface of the cell assembly  24  to seal the cell assembly  24  and thus implement functions including water resistance and dust resistance. In some other examples, the cell elastic piece  201  is disposed on two ends of the cell assembly, and at least part of the cell elastic piece  201  seals the tab to cover and secure the tab. With this arrangement, the cell elastic piece  201  is configured to protect the cell assembly  24 , to avoid a possible relative displacement between the cells  241  due to a bump or a vibration, and thus to prevent the cells  241  or the tab from being squeezed or kinked. Accordingly, the cell elastic piece  201  can improve the shock-resistant and shock-absorbent performance of the battery pack  20  and thus improve the reliability of the battery pack  20 . Moreover, as an elastic piece, the cell elastic piece  201  can better adapt to the expansion property of the battery pack  20 . Further, the cell elastic piece  201  can also enhance the heat dissipation performance of the battery pack  20 . 
     In some examples, the cell elastic piece  201  covers and secures the cell assembly  24 , the detection circuit board  28 , and other connection lines. To enable the cell assembly  24  to output or input electric energy, the positive lead-out piece  243  of the cell assembly  24  and the negative lead-out piece  244  of the cell assembly  24  extend out of the cell elastic piece  201  and protrude from the cell elastic piece  201  to be electrically connected to the battery pack positive terminal  272  and the battery pack negative terminal  273  respectively. In some examples, the cell elastic piece  201  is formed around the cell assembly  24  in the manner of glue injection. Specifically, the cell assembly  24  is disposed in the lower housing  232 , and the cell elastic piece  201  is formed on the outer surface of the entire cell assembly  24  in the manner of glue injection to seal the cell assembly  24  and thus implement functions including water resistance and dust resistance. 
     The battery pack  20  further includes a deformation sensor  202 . The deformation sensor  202  is disposed on one side of the cell elastic piece  201  and is configured to detect a parameter related to the deformation amount of the cell assembly  24 . Specifically, the deformation sensor  202  is located on the upper side of the cell elastic piece  201  and is spaced apart from the upper surface of the cell elastic piece  201  by a preset distance. Referring to  FIG. 8 , the deformation sensor  202  is disposed between the cell elastic piece  201  and the first support plate  25 . In some examples, the deformation sensor  202  is specifically disposed on the lower surface of the first support plate  25  and is spaced apart from the upper surface of the cell elastic piece  201  by 1 mm to 6 mm. That is, the preset distance is greater than or equal to 1 mm and smaller than or equal to 6 mm. 
     In this example, the deformation sensor  202  is connected to the main circuit board  26  through a first connection line  203  to output a sensing signal of the deformation sensor  202  to the main circuit board  26 . In one example, the deformation sensor  202  serves as a pressure sensor that outputs the sensing signal under pressure. Specifically, when the cell assembly  24  is deformed, for example, when the expansion of the cell assembly  24  causes the first thickness H 1  to increase, the cell elastic piece  201  is deformed accordingly and protrudes upward to come into contact with the deformation sensor  202 . Sensing the pressure from the cell elastic piece  201 , the deformation sensor  202  outputs the sensing signal and transmits the sensing signal through the first connection line to the main circuit board  26 . In this case, the deformation sensor  202  and the first connection line are disposed outside the cell elastic piece  201 , facilitating maintenance and replacement when the deformation sensor  202  malfunctions. 
     In one aspect, since the cell assembly  24  may be deformed to a certain degree in normal operation, the preset distance reserved between the deformation sensor  202  and the cell elastic piece  201  guarantees the space for the deformation of the cell assembly  24  in normal operation, thus improving the reliability of the deformation sensor  202  and reducing the probability of false triggering. In another aspect, since the cell elastic piece  201  covers the cell assembly  24  to form an enclosed cavity, the temperature change of the battery pack in operation may cause the air in the enclosed cavity to expand and increase the air pressure in the enclosed cavity. Accordingly, the arrangements in which the deformation sensor  202  is disposed outside the cell elastic piece  201  also help prevent the enclosed cavity formed by the cell elastic piece  201  from affecting the deformation detection of the cell assembly  24 , improve the reliability of the deformation sensor  202 , and thus improve the safety and reliability of the battery pack. Additionally, the first support plate  25  is disposed between the cell assembly  24  and the main circuit board  26  so that the first support plate  25  can effectively hinder the deformation of the cell assembly  24  even if the cell assembly  24  is deformed, protecting the main circuit board  26  and preventing the deformation of the cell assembly  24  from damaging the main circuit board  26 . 
     In some other examples, the battery pack  20  further includes a second support plate  204 . The second support plate  204  includes an elastic plate with a certain elastic coefficient. Referring to  FIG. 9 , the second support plate  204  is disposed between the cell assembly  24  and the first support plate  25  and is configured to support the deformation sensor  202 . In this example, the second support plate  204  is securely connected to the lower housing  232  through an elastic arm with a certain elastic coefficient. The second support plate  204  further includes multiple elastic arms detachably connected to the lower housing through screws. It is to be understood that the second support plate  204  may be made of elastic material and is not limited here, as long as the second support plate  204  can be deformed along with the deformation of the cell assembly  24 . Specifically, the deformation sensor  202  is disposed on the upper surface of the second support plate  204  and is spaced apart by 1 mm to 6 mm from the upper surface of the cell elastic piece  201  covering the outer surface of the cell assembly  24 . 
     In this example, the deformation sensor  202  is connected to the detection circuit board  28  through a second connection line  205  to output the sensing signal of the deformation sensor  202  to the detection circuit board  28 . Specifically, when the cell assembly  24  is deformed, for example, when the expansion of the cell assembly  24  causes the first thickness H 1  to increase, the cell elastic piece  201  is deformed accordingly and protrudes upward to come into contact with the second support plate  204 . The deformation sensor  202  disposed on the second support plate  204  protrudes upward accordingly till comes into contact with the first support plate  25 . Therefore, sensing the pressure from the first support plate  25  and the pressure from the second support plate  204 , the deformation sensor  202  outputs the sensing signal and transmits the sensing signal through the second connection line  205  to the detection circuit board  28 . The detection circuit board  28  collects the sensing signal and transmits the sensing signal to the main circuit board  26 . The specific shape of the preceding first connection line  203  and the specific shape of the preceding second connection line  205  may be arranged based on the specific structure of the battery pack and are not limited here. 
       FIG. 10  is a block diagram of a protective circuit of the battery pack. As shown in  FIG. 10 , the battery pack protective circuit  30  includes a cell assembly  31 , a switch  32 , a controller  33 , a battery pack positive terminal  341 , a battery pack negative terminal  342 , and a deformation sensor  35 . The battery pack positive terminal  341  and the battery pack negative terminal  342  are disposed in a battery pack interface  34 . The cell assembly  31  further includes a cell assembly positive terminal  311  and a cell assembly negative terminal  312 . 
     The switch  32  is connected between the cell assembly  31  and the battery pack interface  34  and is configured to electrically connect the cell assembly  31  to the battery pack interface  34  or electrically disconnect the cell assembly  31  from the battery pack interface  34 . The on or off state of the switch  31  is controlled by the controller  33 . In some examples, the switch is disposed between the cell assembly positive terminal  311  and the battery pack positive terminal  341 . In some other examples, the switch is disposed between the cell assembly negative terminal  312  and the battery pack negative terminal  342 . Specifically, the switch  31  is disposed on a circuit board. The switch  31  may be an electronic switch, for example, a metal-oxide-semiconductor transistor (MOS transistor), an insulated-gate bipolar transistor (IGBT), or a relay. 
     The controller  33  is connected to the deformation sensor  35  and is configured to, when the deformation sensor  35  detects that a parameter related to the deformation amount of the cell assembly  31  satisfies a preset condition, output a control signal for turning off the switch  31  to electrically disconnect the cell assembly  31  from the battery pack interface  34 . The deformation sensor  35  includes at least a detection terminal  351 . The detection terminal  351  is connected to the controller  33 . In some examples, the parameter related to the deformation amount of the deformation sensor  35  and cell assembly  31  is a voltage parameter. Specifically, after the deformation sensor  35  powers on, the output voltage of the detection terminal  351  changes constantly along with the change of the pressure received by the deformation sensor  35 . Accordingly, the controller  33  is specifically configured to acquire the voltage of the detection terminal  351  and, when the voltage of the detection terminal  351  is smaller than or equal to a first preset voltage, output the control signal for turning off the switch  31  to electrically disconnect the cell assembly  31  from the battery pack interface  34 . In this example, since the resistance of the deformation sensor  35  reduces along with the gradual increase of the received pressure caused by the constant deformation of the cell assembly  31 , the voltage of the detection terminal  351  reduces constantly along with the increase of the pressure received by the deformation sensor  35 . When the voltage reduces to the first preset voltage, the controller  33  determines the deformation of the cell assembly  31 , turns off the switch  31 , thus electrically disconnects the cell assembly  31  from the battery pack interface  21 , and protects the safety of the battery pack. Specifically, the deformation sensor  35  may be one of a strain gauge pressure sensor, a piezoresistive pressure sensor, a capacitive pressure sensor, a piezoelectric pressure sensor, an inductive pressure sensor, or a Hall effect sensor. Accordingly, based on the selected deformation sensor  335 , the parameter that is related to the deformation amount of the cell assembly  31  and is acquired by the controller  33  may also be, for example, a resistance value, a current value, or an inductance value and is not limited here. It is to be understood that the present application includes but is not limited to the disclosed examples. Due to different specific circuits of the deformation sensor  35 , the preset condition for the controller  33  controlling the switch  31  to turn on or off may be different. For example, the controller  33  may further be configured to, when the voltage of the detection terminal  351  is greater than or equal to the first preset voltage, output the control signal for turning off the switch  31  to electrically disconnect the cell assembly  31  from the battery pack interface  21  and protect the safety of the battery pack. 
     In some other examples, a battery pack protective circuit  40  includes an alarm  46  that can be triggered to give an alarm. Referring to  FIG. 11 , a controller  43  is configured to, when a deformation sensor  45  detects that a parameter related to the deformation amount of a cell assembly  41  satisfies the preset condition, output an alarm signal to trigger the alarm  46  to give an alarm. The deformation sensor  45  includes at least a detection terminal  451  connected to a controller  43 . The controller  43  is specifically configured to acquire the voltage of the detection terminal  451  and, when the voltage is smaller than or equal to the first preset voltage, output the alarm signal to trigger the alarm  46  to give an alarm. In this example, since the resistance of the deformation sensor  45  reduces along with the gradual increase of the received pressure caused by the constant deformation of the cell assembly  41 , the voltage of the detection terminal  451  reduces constantly along with the increase of the pressure received by the deformation sensor  45 . When the voltage reduces to the first preset voltage, the controller  43  determines the deformation of the cell assembly  41  and transmits the alarm signal to trigger the alarm  46  to give an alarm. The alarm  46  may specifically be a buzzer. After being triggered to give an alarm, the buzzer buzzes to remind a user that the battery pack has a safety hazard. The alarm  46  may also be another electronic device, for example, an LED light, which can be triggered to flash to remind the user that the cell assembly  41  of the battery pack is deformed and has a safety hazard. 
     In order to further improve the reliability of the deformation sensor  45 , the controller  43  needs to determine whether the deformation sensor  45  is reliable before determining whether the cell assembly  41  is deformed. The controller  43  is configured to acquire the voltage of the detection terminal  451  and, when the voltage is greater than a second preset voltage, output the control signal for turning off a switch to electrically disconnect the cell assembly  41  from a battery pack interface  44 . In this example, if the deformation sensor  45  is reliable, the voltage needs to be smaller than or equal to the second preset voltage. If the voltage of the detection terminal  451  is greater than the second preset voltage, it indicates that the deformation sensor  45  is open-circuited. Accordingly, it is determined that the deformation sensor  45  is disabled. To guarantee the safety of the battery pack, the controller  43  turns off the switch and thus electrically disconnects the cell assembly  41  from the battery pack interface  44 . On the contrary, if the voltage of the detection terminal  451  is smaller than or equal to the second preset voltage, it indicates that the deformation sensor  45  is reliable. It needs to be further determined whether the voltage is smaller than or equal to the first preset voltage so as to determine whether the cell assembly  41  is deformed. The first preset voltage is smaller than the second preset voltage. 
     In some other examples, the switch of the battery pack protective circuit is disposed in a power tool system and is specifically disposed on a discharge circuit.  FIG. 12  is a block diagram of a protective circuit of a power tool system according to one example. Referring to  FIG. 12 , the power tool system includes a power tool  50  and a battery pack  60 . The battery pack  60  is attached to the power tool  50 . The battery pack positive terminal  272  and the battery pack negative terminal  273  match a tool positive terminal  531  of the power tool and a tool negative terminal  532  of the power tool to output the electric energy of the cell assembly  24  to the power tool. The battery pack communication terminal  274  is connected to a tool communication terminal to communicate with the power tool. In this example, a switch  51  is disposed on a discharge circuit formed by a cell assembly  61 , a battery pack interface  64 , and a motor  52  of the power tool and is configured at least to turn on or off the electrical connection between the battery pack and the motor  52  of the power tool. The on or off state of the switch  51  is also controlled by a controller  63 . Specifically, the controller  63  transmits the control signal for turning off the switch  51  through a battery pack communication terminal  643 . The controller  63  is configured to, when the deformation sensor  62  detects that a parameter related to the deformation amount of the cell assembly  61  satisfies the preset condition, output the control signal for turning off the switch  51  to disconnect the discharge circuit and protect the safety of the power tool system. The deformation sensor  62  includes at least a detection terminal  621  connected to the controller  63 . The controller  63  is specifically configured to acquire the voltage of the detection terminal  621 . When the voltage is smaller than or equal to the first preset voltage, the controller  43  outputs the control signal for turning off the switch  51  to disconnect the discharge circuit. Since the resistance of the deformation sensor  62  reduces along with the gradual increase of the received pressure caused by the constant deformation of the cell assembly  61 , the voltage of the detection terminal  621  reduces constantly along with the increase of the pressure received by the deformation sensor  62 . When the voltage reduces to the first preset voltage, the controller  63  determines the deformation of the cell assembly  61 , turns off the switch  51 , thus disconnects the discharge circuit, and protects the safety of the battery pack. It is to be noted that although this example discloses that the switch  51  is disposed in the power tool, the switch  51  may also be disposed in the battery pack and is not limited here. 
     In order to further improve the reliability of the deformation sensor  62 , the controller  63  first determines whether the deformation sensor  62  is reliable before determining whether the cell assembly  61  is deformed. The controller  63  is configured to acquire the voltage of the detection terminal  621  and, when the voltage is greater than the second preset voltage, output the control signal for turning off the switch  51  to disconnect the discharge circuit. In this example, if the deformation sensor  62  is reliable, the voltage needs to be smaller than or equal to the second preset voltage. If the voltage of the detection terminal  621  is greater than the second preset voltage, it indicates that the deformation sensor  62  is open-circuited. Accordingly, it is determined that the deformation sensor  62  is disabled. To guarantee the safety of the battery pack, the controller  43  turns off the switch  51  and thus disconnects the discharge circuit. On the contrary, if the voltage of the detection terminal  621  is smaller than or equal to the second preset voltage, it indicates that the deformation sensor  62  is reliable. It needs to be further determined whether the voltage is smaller than or equal to the first preset voltage so as to determine whether the cell assembly  61  is deformed. The first preset voltage is smaller than the second preset voltage. 
       FIG. 13  is a block diagram of a protective circuit used for a charging combination according to one example. Referring to  FIG. 13 , the charging combination includes the battery pack  60  and a charger  80 . 
     The charger  80  is configured to charge the battery pack. Exemplarily, the charger  80  includes a charge path  82  and a direct current (DC) output interface  83 . The charge path  82  includes an alternating current (AC) input interface and an AC-DC conversion circuit. Specifically, the AC input interface is configured to access AC. In some examples, the AC input interface is connected to a power plug. The power plug is inserted into an AC socket to access AC commercial power. The value range of the AC accessed in the AC input interface is 110 V to 130 V or 210 V to 230 V. The AC-DC conversion circuit is electrically connected to the AC input interface to convert AC to DC. The DC output interface  83  is electrically connected to the AC-DC conversion circuit to output DC. The DC output interface  83  includes a charger positive terminal  831  and a charger negative terminal  832 . The charger positive terminal  831  and the charger negative terminal  832  match a battery pack positive terminal  641  and a battery pack negative terminal  642  output electric energy to the cell assembly  61 . A charger communication terminal  833  is connected to the battery pack communication terminal  643  to communicate with the battery pack. In this example, a switch  81  is disposed on a charge circuit formed by the cell assembly  61 , the battery pack interface  64 , and the charge path  82  and is configured at least to electrically connect the battery pack to the charge path  82  or electrically disconnect the battery pack from the charge path  82 . The on or off state of the switch is also controlled by the controller  63 . Specifically, the controller  63  transmits the control signal for turning off the switch through the battery pack communication terminal  643 . The controller  63  is configured to, when the deformation sensor  62  detects that the parameter related to the deformation amount of the cell assembly  61  satisfies the preset condition, output the control signal for turning off the switch to disconnect the charge circuit and protect the safety of the charging combination. The deformation sensor  62  includes at least the detection terminal  621  connected to the controller  63 . The controller  63  is specifically configured to acquire the voltage of the detection terminal  621 . When the voltage is smaller than or equal to the first preset voltage, the controller  43  outputs the control signal for turning off the switch to disconnect the charge circuit. Since the resistance of the deformation sensor  62  reduces along with the gradual increase of the received pressure, the voltage of the detection terminal  621  reduces constantly along with the increase of the pressure received by the deformation sensor  62 . When the voltage reduces to the first preset voltage, it is determined that the cell assembly  61  is deformed. The controller  63  turns off the switch, thus disconnects the charge circuit, and protects the safety of the battery pack. It is to be noted that although this example discloses that the switch is disposed in the charger  80 , the switch may also be disposed in the battery pack and is not limited here. 
     In order to further improve the reliability of the deformation sensor  62 , the controller  63  first determines whether the deformation sensor  62  is reliable before determining whether the cell assembly  61  is deformed. The controller  63  is configured to acquire the voltage of the detection terminal  621  and, when the voltage is greater than the second preset voltage, output the control signal for turning off the switch to disconnect the charge circuit. In this example, if the deformation sensor  62  is reliable, the voltage needs to be smaller than or equal to the second preset voltage. If the voltage of the detection terminal  621  is greater than the second preset voltage, it indicates that the deformation sensor  62  is open-circuited. Accordingly, it is determined that the deformation sensor  62  is disabled. To guarantee the safety of the battery pack, the controller  43  turns off the switch and thus disconnects the charge circuit. On the contrary, if the voltage of the detection terminal  621  is smaller than or equal to the second preset voltage, it indicates that the deformation sensor  62  is reliable. It is to be further determined whether the voltage is smaller than or equal to the first preset voltage so as to determine whether the cell assembly  61  is deformed. The first preset voltage is smaller than the second preset voltage. 
     The above illustrates and describes basic principles, main features, and advantages of the present disclosure. It is to be understood by those skilled in the art that the preceding examples do not limit the present disclosure in any form, and technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the scope of the present disclosure.