Patent Application
20250070121
This application relates to the field of battery technology, and in particular, to a positive electrode plate, a secondary battery, and an electrical device.
In recent years, secondary batteries have been applied wider in many fields, including energy storage power systems such as hydro, thermal, wind, and solar power stations, and other fields such as electric tools, electric bicycles, electric motorcycles, and electric vehicles, military equipment, and aerospace. The significant development of the secondary batteries gives rise to higher requirements on the energy density, cycle performance, and the like of the batteries.
In the related art, lithium/sodium supplementation is performed to compensate for irreversible loss of sodium occurring during a first charge-and-discharge cycle in a lithium/sodium-ion battery.
The applicant hereof finds that, for a jelly-roll cell, the temperature at the waist of the cell is higher than that at the end of the cell during operation. For a stacked type cell, the temperature at a center region of the cell is higher than that at an edge region of the cell during operation. A high-temperature region exhibits higher electrochemical activity than a low-temperature region. In the region with a higher electrochemical activity, lithium ions are consumed at a higher rate, and a positive electrode material is damaged irreversibly to a higher degree.
In view of the above problems, this application provides a novel positive electrode plate, a secondary battery, and an electrical device, which are described below.
A first aspect of this application provides a positive electrode plate applicable to a jelly-roll cell. The positive electrode plate includes a waist region close to a waist and an end region far away from the waist.
The waist region includes a first positive electrode film, and the end region includes a second positive electrode film.
A porosity of the first positive electrode film is greater than a porosity of the second positive electrode film.
When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
A second aspect of this application provides a positive electrode plate applicable to a stacked type cell. The positive electrode plate includes a center region close to a center and an edge region far away from the center.
The center region includes a first positive electrode film, and the edge region includes a second positive electrode film.
A porosity of the first positive electrode film is greater than a porosity of the second positive electrode film.
When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
In some embodiments, a ratio of the porosity of the first positive electrode film to the porosity of the second positive electrode film is (1.003 to 3): 1.
In some embodiments, a first alkali metal ion donating material and/or a second alkali metal ion donating material is distributed in the first positive electrode film. The first alkali metal ion donating material possesses an irreversible capacity, and the second alkali metal ion donating material possesses a reversible capacity. In the first positive electrode film, the first alkali metal ion donating material donates P1 ppm alkali metal ions, and the second alkali metal ion donating material donates Q1 ppm alkali metal ions.
A first alkali metal ion donating material and/or a second alkali metal ion donating material is distributed in the second positive electrode film, the first alkali metal ion donating material possesses an irreversible capacity, the second alkali metal ion donating material possesses a reversible capacity, and, in the second positive electrode film, the first alkali metal ion donating material provides P2 ppm alkali metal ions, and the second alkali metal ion donating material provides Q2 ppm alkali metal ions; and
The first positive electrode film and the second positive electrode film satisfy the following relationship:
In some embodiments, the first positive electrode film and the second positive electrode film satisfy the following relationship: (P1/Q1)>(P2/Q2).
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the first alkali metal ion donating material includes one or more of: an alkali metal nitride, an alkali metal oxide, a composite of an alkali metal oxide and a transition metal, an alkali metal peroxide, an excessively alkali-metalized alkali metal oxide, or an alkali metal oxycarbide.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the second alkali metal ion donating material includes one or more of:
In some embodiments, the alkali metal is selected from lithium, sodium, or a combination thereof.
In some embodiments, the positive electrode plate includes a waist region and two end regions. The waist region is located between the two end regions. The waist region includes a first positive electrode film. Each of the two end regions includes a second positive electrode film.
According to a second aspect, this application provides a secondary battery, including the positive electrode plate according to any one of the embodiments described above.
According to a third aspect, this application provides an electrical device, including the secondary battery.
This application brings at least the following beneficial effects.
One or more embodiments of this application achieve one or more of the following benefits:
The following describes and discloses in detail a negative active material and a preparation method thereof, a positive electrode plate, a negative electrode plate, a secondary battery, a battery module, a battery pack, and an electrical device according to this application with due reference to drawings. However, unnecessary details may be omitted in some cases. For example, a detailed description of a well-known matter or repeated description of an essentially identical structure may be omitted. That is intended to prevent the following descriptions from becoming unnecessarily lengthy, and to facilitate understanding by a person skilled in the art. In addition, the drawings and the following descriptions are intended for a person skilled in the art to thoroughly understand this application, but not intended to limit the subject-matter set forth in the claims.
A “range” disclosed herein is defined in the form of a lower limit and an upper limit. A given range is defined by a lower limit and an upper limit selected. The selected lower and upper limits define the boundaries of a particular range. A range so defined may be inclusive or exclusive of the end values, and a lower limit of one range may be arbitrarily combined with an upper limit of another range to form a range. For example, if a given parameter falls within a range of 60 to 120 and a range of 80 to 110, it is expectable that the parameter may fall within a range of 60 to 110 and a range of 80 to 120 as well. In addition, if lower-limit values 1 and 2 are listed, and if upper-limit values 3, 4, and 5 are listed, the following ranges are all expectable: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. Unless otherwise specified herein, a numerical range “a to b” is a brief representation of a combination of any real numbers between a and b inclusive, where both a and b are real numbers. For example, a numerical range “0 to 5” herein means all real numbers recited between 0 and 5 inclusive, and the expression “0 to 5” is just a brief representation of a combination of such numbers. In addition, a statement that a parameter is an integer greater than or equal to 2 is equivalent to a disclosure that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on.
Unless otherwise expressly specified herein, any embodiments and optional embodiments hereof may be combined with each other to form a new technical solution.
Unless otherwise expressly specified herein, any technical features and optional technical features hereof may be combined with each other to form a new technical solution.
Unless otherwise expressly specified herein, all steps described herein may be performed in sequence or at random, and preferably in sequence. For example, that the method includes steps (a) and (b) indicates that the method may include steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, that the method may further include step (c) indicates that step (c) may be added into the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), and so on.
Unless otherwise expressly specified herein, “include” and “comprise” mentioned herein mean open-ended inclusion, or closed-ended inclusion. For example, the terms “include” and “comprise” may mean inclusion of other items that are not recited, or inclusion of only the items recited.
Unless otherwise expressly specified herein, the term “or” is inclusive. For example, the expression “A or B” means “A alone, B alone, or both A and B”. More specifically, all and any of the following conditions satisfy the condition “A or B”: A is true (or existent) and B is false (or absent); A is false (or absent) and B is true (or existent); and, both A and B are true (or existent).
A secondary battery, also known as a rechargeable battery or storage battery, is a battery that is reusable after an active material in the battery is activated by charging the battery that has been discharged.
Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolytic solution. During charge and discharge of the battery, active ions (such as lithium ions) are shuttled between the positive electrode plate and the negative electrode plate by intercalation and deintercalation. Disposed between the positive electrode plate and the negative electrode plate, the separator primarily serves to prevent a short circuit between the positive electrode plate and the negative electrode plate while allowing passage of active ions. The electrolytic solution is located between the positive electrode plate and the negative electrode plate, and primarily serves to conduct the active ions.
The negative electrode plate includes a negative current collector and a negative electrode film disposed on at least one surface of the negative current collector. The negative electrode film includes a negative active material. The negative active material is the negative active material according to any one of the embodiments of this application.
As an example, the negative current collector includes two surfaces opposite to each other in a thickness direction of the negative current collector. The negative electrode film is disposed on either or both of the two opposite surfaces of the negative current collector.
In some embodiments, the negative current collector may be a metal foil or a composite current collector. For example, the metal foil may be a copper foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by overlaying the polymer material substrate with a metal material (for example, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy). The polymer material substrate may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).
In some embodiments, the negative electrode film further optionally includes a binder. As an example, the binder may be at least one selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylic acid sodium (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl acrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
In some embodiments, the negative electrode film further optionally includes a conductive agent. As an example, the conductive agent may be at least one selected from superconductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.
In some embodiments, the negative electrode film further optionally includes other agents, such as a thickener (for example, sodium carboxymethyl cellulose (CMC-Na)).
In some embodiments, the negative electrode plate may be prepared according to the following method: dispersing the ingredients of the negative electrode plate such as the negative active material, the conductive agent, and the binder and any other ingredients in a solvent (such as deionized water) to form a negative slurry, coating a negative current collector with the negative slurry, and performing steps such as drying and cold calendering to obtain the negative electrode plate.
A first aspect of this application provides a positive electrode plate applicable to a jelly-roll cell. The positive electrode plate includes a waist region close to a waist and an end region far away from the waist.
The waist region includes a first positive electrode film, and the end region includes a second positive electrode film.
A porosity of the first positive electrode film is greater than a porosity of the second positive electrode film.
When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
Without being limited by any theory, the theoretical basis for the positive electrode plate to improve the cycle life of a battery are as follows:
When the cell is working, the expansion degree at the waist region of the cell is greater than the expansion degree at the end region. Consequently, the waist region is squeezed to a higher degree by the battery shell than the end region, and therefore, the return flowability of the electrolyte solution at the waist region is weaker. In addition, the long-term squeezed state deteriorates the porosity of the negative electrode. After the porosity of the negative electrode plate compacted in a long term is reduced, the negative electrode plate is insufficiently infiltrated by the electrolyte solution, and the lithium intercalation kinetics of the negative electrode are worsened. Lithium plating is prone to occur at the center region in the middle and late stages of cycling and lead to failure. Therefore, by adjusting the porosity at the waist region of the positive electrode plate to make the porosity of the waist be greater than the porosity of the end region, this application can reserve a space for withstanding compression, and in turn, alleviate a series of adverse effects mentioned above caused by compression of the waist region.
In some embodiments, the term “waist” is a midpoint of the positive electrode plate applicable to a jelly-roll cell in a winding axis direction. Along the winding axis direction, the waist position is equidistant from the two end positions of the winding axis. The waist region may be symmetrical about the waist.
In some embodiments, closeness to the waist means that the waist region is closer to the waist than the end regions. The waist region may abut or encompass the waist.
In some embodiments, farness from the waist means that the end region is farther away from the waist than the waist region.
In some embodiments, the area of the waist region may be 10% to 90%, for example, 20% to 80%, 30% to 70%, 40% to 60%, or 50%, of the area of the positive electrode plate. In some embodiments, the area of the end region may be 10% to 90%, for example, 20% to 80%, 30% to 70%, 40% to 60%, or 50%, of the area of the positive electrode plate.
In some embodiments, the end region includes a first end region and a second end region. The area of the first end region may be 5% to 45%, for example, 10% to 40%, 20% to 30%, or 25%, of the area of the positive electrode plate. The area of the second end region may be 5% to 45%, for example, 10% to 40%, 20% to 30%, or 25%, of the area of the positive electrode plate.
A second aspect of this application provides a positive electrode plate applicable to a stacked type cell. The positive electrode plate includes a center region close to a center and an edge region far away from the center.
The center region includes a first positive electrode film, and the edge region includes a second positive electrode film.
A porosity of the first positive electrode film is greater than a porosity of the second positive electrode film.
When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
Without being limited by any theory, the theoretical basis for the positive electrode plate to improve the cycle life of a battery are as follows:
When the cell is working, the expansion degree at the center region of the cell is greater than the expansion degree at the edge region. Consequently, the center region is squeezed to a higher degree by the battery shell than the edge region, and therefore, the return flowability of the electrolyte solution at the center region is weaker. In addition, the long-term squeezed state deteriorates the porosity of the negative electrode. After the porosity of the negative electrode plate compacted in a long term is reduced, the negative electrode plate is insufficiently infiltrated by the electrolyte solution, and the lithium intercalation kinetics of the negative electrode are worsened. Lithium plating is prone to occur at the center region in the middle and late stages of cycling and lead to failure. Therefore, by adjusting the porosity at the center region of the positive electrode plate to make the porosity of the waist be greater than the porosities of the first end region and the second edge region, this application can reserve a space for withstanding compression, and in turn, alleviate a series of adverse effects mentioned above caused by compression of the center region.
In some embodiments, the positive electrode film with pores is obtained in the following way: adding a decomposable material (such as an alkali metal oxycarbide) to a positive electrode film, and then decomposing (such as liquefying or gasifying) the decomposable material under specified conditions, so that pores are generated in-situ on the positive electrode film after the decomposable material is decomposed, where “in-situ” means an original position at which the decomposable material is disposed. Optionally, the decomposable material releases a gas (for example, CO2) during the decomposition. The released gas increases the size and number of pores. By disposing decomposable materials with different contents/constituents in the first positive electrode film and the second positive electrode film separately, different voids can be formed in the first positive electrode film and the second positive electrode film, so that the porosity of the first positive electrode film is greater than the porosity of the second positive electrode film.
In some embodiments, the alkali metal oxycarbide is selected from A2C2O4, A2C4O4, A2C3O5, or A2C4O6. The element A is selected from Li, Na, K, or any combination thereof.
In some embodiments, the term “center” is a geometric center of the positive electrode plate applicable to the stacked type cell. The center region may have the same shape and geometric center as the positive electrode plate. The area of the center region may be 10% to 90%, for example, 20% to 80%, 30% to 70%, 40% to 60%, or 50%, of the area of the positive electrode plate. The area of the edge region may be 10% to 90%, for example, 20% to 80%, 30% to 70%, 40% to 60%, or 50%, of the area of the positive electrode plate.
In some embodiments, closeness to the center means that the center region is closer to the center than the edge region. The center region may abut or encompass the center.
In some embodiments, farness from the center means that the edge region is farther away from the center than the center region.
In some embodiments, the “first alkali metal ion donating material” exhibits a first-cycle Coulombic efficiency of 20% or less (for example, 15% or less, 10% or less, 5% or less, 1% or less), and possesses an irreversible capacity.
In some embodiments, the “second alkali metal ion donating material” exhibits a first-cycle Coulombic efficiency of 80% or more (for example, 85% or more, 90% or more, 95% or more, 99% or more), and possesses a reversible capacity.
In some embodiments, the first alkali metal ion donating material and/or the second alkali metal ion donating material is distributed in the first positive electrode film and the second positive electrode film separately. The first alkali metal ion donating material in the first positive electrode film may be identical to or different from the first alkali metal ion donating material in the second positive electrode film. The second alkali metal ion donating material in the first positive electrode film may be identical to or different from the second alkali metal ion donating material in the second positive electrode film.
In some embodiments, the term “first-cycle Coulombic efficiency” means initial Coulombic efficiency (ICE). The first-cycle Coulombic efficiency of the first alkali metal ion donating material and the second alkali metal ion donating material may be tested with reference to a conventional method or standard in the art. For example, a battery (such as a half battery) is assembled by using the sample material as a positive active material. A first-cycle delithiation capacity C1 and a first-cycle lithium lithiation capacity C2 of the sample material are measured, and then the first-cycle Coulombic efficiency is calculated as: first-cycle Coulombic efficiency=C2/C1×100%.
In some embodiments, a porosity of the first positive electrode film is greater than a porosity of the second positive electrode film. When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
In some embodiments, a ratio of the porosity of the first positive electrode film to the porosity of the second positive electrode film is (1.003 to 3): 1. When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits one or more improved performance indicators such as cycle life.
In some embodiments, a ratio of the porosity of the first positive electrode film to the porosity of the second positive electrode film is (1.003 to 1.01): 1, (1.01 to 1.1): 1, (1.1 to 1.2): 1, (1.2 to 1.3): 1, (1.3 to 1.4): 1, (1.4 to 1.5): 1, (1.5 to 1.6): 1, (1.6 to 1.7): 1, (1.7 to 1.8): 1, (1.8 to 1.9): 1, (1.9 to 2): 1, (2 to 2.1): 1, (2.1 to 2.2): 1, (2.2 to 2.3): 1, (2.3 to 2.4): 1, (2.4 to 2.5): 1, (2.5 to 2.6): 1, (2.6 to 2.7): 1, (2.7 to 2.8): 1, (2.8 to 2.9): 1, or (2.9 to 3): 1.
In some embodiments, a first alkali metal ion donating material and/or a second alkali metal ion donating material is distributed in the first positive electrode film. The first alkali metal ion donating material possesses an irreversible capacity, and the second alkali metal ion donating material possesses a reversible capacity. In the first positive electrode film, the first alkali metal ion donating material donates P1 ppm alkali metal ions, and the second alkali metal ion donating material donates Q1 ppm alkali metal ions.
A first alkali metal ion donating material and/or a second alkali metal ion donating material is distributed in the second positive electrode film, the first alkali metal ion donating material possesses an irreversible capacity, the second alkali metal ion donating material possesses a reversible capacity, and, in the second positive electrode film, the first alkali metal ion donating material provides P2 ppm alkali metal ions, and the second alkali metal ion donating material provides Q2 ppm alkali metal ions.
The first positive electrode film and the second positive electrode film satisfy the following relationship:
Without being limited by any theory, the reasons for the improved cycle life of the battery are analyzed as follows:
When the positive electrode plate based on the above technical solution is used in a secondary battery, the secondary battery exhibits an improved cycle life. Without being limited by any theory, the reasons for the improved cycle life of the battery are analyzed as follows:
The value of (P1+Q1) in the first positive electrode film is relatively large. Because the first positive electrode film is located in the waist region (or center region) with a relatively high temperature and a relatively high electrochemical activity, the relatively large (P1+Q1) value can make up for the capacity loss caused by insufficiency of reversible alkali metal ions arising from a too fast consumption rate of the alkali metal ions in the waist region (or center region), and increase the overall cycle life of the cell.
The value of (P2+Q2) in the second positive electrode film is relatively small. Because the second positive electrode film is located in the end region (or edge region) with a relatively low temperature and a relatively low electrochemical activity, the relatively small (P2+Q2) value reduces the overall cost and avoids the risk of a short circuit caused by metal dendrites on the negative electrode arising from excessive alkali metal ions.
In some embodiments, the first positive electrode film and the second positive electrode film satisfy the following relationship: (P1/Q1)>(P2/Q2).
The first alkali metal ion donating material and/or the second alkali metal ion donating material play different roles during operation of the battery. The alkali metal ions donated by the first alkali metal ion donating material are used for compensating for the consumption of the alkali metal ions during the lifespan of the battery, for example, the consumption in an initial film-forming reaction, and the consumption in a reparative film-forming reaction during cycling/storage. The alkali metal ions donated by the second alkali metal ion donating material is used for reversible deintercalation/electrochemical reaction in the positive and negative electrode materials. Because the inherent film-forming consumption is compensated for by the first alkali metal ions, more reversible alkali metal ions are available for providing electrochemical energy.
The value of (P1/Q1) in the first positive electrode film is relatively large. Because the first positive electrode film is located in the waist region with a relatively high temperature and a relatively high electrochemical activity, the relatively large (P1/Q1) value can make up for the capacity loss caused by insufficiency of reversible alkali metal ions arising from a too fast consumption rate of the alkali metal ions in the waist region, and increase the overall cycle life of the cell.
The value of (P2/Q2) in the second positive electrode film is relatively small. Because the second positive electrode film is located in the end region with a relatively low temperature and a relatively low electrochemical activity, the relatively small (P2/Q2) value reduces the overall cost and avoids the risk of a short circuit caused by metal dendrites on the negative electrode arising from excessive alkali metal ions.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the value of (P1/Q1) is 0.1% to 1%, 1% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, 45% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, or 65% to 70%.
In some embodiments, the value of (P2/Q2) is 0% to 0.1%, 0.1% to 1%, 1% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, 45% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, or 65% to 70%.
In some embodiments, the value of (P1/Q1)−(P2/Q2) is 0.1% to 1%, 1% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, 45% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, or 65% to 70%.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the value of P1+Q1 is 40000 to 41000 ppm, 41000 to 45000 ppm, 40000 to 50000 ppm, 50000 to 60000 ppm, 60000 to 70000 ppm, 70000 to 80000 ppm, 80000 to 90000 ppm, 90000 to 100000 ppm, 100000 to 110000 ppm, 110000 to 120000 ppm, 120000 to 130000 ppm, 130000 to 140000 ppm, 140000 to 150000 ppm, 150000 to 160000 ppm, 160000 to 170000 ppm, 170000 to 180000 ppm, 175000 to 180000 ppm, or 179000 to 180000 ppm.
In some embodiments, the value of P2+Q2 is 40000 to 41000 ppm, 41000 to 45000 ppm, 40000 to 50000 ppm, 50000 to 60000 ppm, 60000 to 70000 ppm, 70000 to 80000 ppm, 80000 to 90000 ppm, 90000 to 100000 ppm, 100000 to 110000 ppm, 110000 to 120000 ppm, 120000 to 130000 ppm, 130000 to 140000 ppm, 140000 to 150000 ppm, 150000 to 160000 ppm, 160000 to 170000 ppm, 170000 to 180000 ppm, 175000 to 180000 ppm, or 179000 to 180000 ppm.
In some embodiments, the value of (P1+Q1): (P2+Q2) is (1.001 to 1.01): 1, (1.01 to 1.02): 1, (1.02 to 1.03): 1, (1.03 to 1.04): 1, (1.04 to 1.05): 1, (1.01 to 1.1): 1, (1.1 to 1.2): 1, (1.2 to 1.3): 1, (1.3 to 1.4): 1, (1.4 to 1.5): 1, (1.5 to 1.6): 1, (1.6 to 1.7): 1, (1.7 to 1.8): 1, (1.8 to 1.9): 1, or (1.9 to 2): 1.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the term “active material region” means a region provided (for example, coated) with an active material on the positive electrode plate. The positive electrode plate may further include a tab region. The tab region is a region not provided with an active material.
In some embodiments, the width of the waist region is 0.05 D to 0.15 D, 0.15 D to 0.25 D, 0.25 D to 0.35 D, 0.35 D to 0.45 D, 0.45 D to 0.55 D, 0.55 D to 0.65 D, 0.65 D to 0.75 D, 0.75 D to 0.85 D, or 0.85 D to 0.95 D.
In some embodiments, the width of the end region is 0.05 D to 0.15 D, 0.15 D to 0.25 D, 0.25 D to 0.35 D, 0.35 D to 0.45 D, 0.45 D to 0.55 D, 0.55 D to 0.65 D, 0.65 D to 0.75 D, 0.75 D to 0.85 D, or 0.85 D to 0.95 D.
In some embodiments, the total area of the waist region accounts for 5% to 15%, 15% to 25%, 25% to 35%, 35% to 45%, 45% to 55%, 55% to 65%, 65% to 75%, 75% to 85%, or 85% to 95% of the total area of the active material region on the positive electrode plate.
In some embodiments, the total area of the end region accounts for 5% to 15%, 15% to 25%, 25% to 35%, 35% to 45%, 45% to 55%, 55% to 65%, 65% to 75%, 75% to 85%, or 85% to 95% of the total area of the active material region on the positive electrode plate.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the total area of the center region accounts for 5% to 15%, 15% to 25%, 25% to 35%, 35% to 45%, 45% to 55%, 55% to 65%, 65% to 75%, 75% to 85%, or 85% to 95% of the total area of the active material region on the positive electrode plate.
In some embodiments, the total area of the edge region accounts for 5% to 15%, 15% to 25%, 25% to 35%, 35% to 45%, 45% to 55%, 55% to 65%, 65% to 75%, 75% to 85%, or 85% to 95% of the total area of the active material region on the positive electrode plate.
In some embodiments, a part or all (for example, 50% to 100% by area, 70% to 100% by area, or 90% to 100% by area) of the waist region is covered by the first positive electrode film.
In some embodiments, a part or all (for example, 50% to 100% by area, 70% to 100% by area, or 90% to 100% by area) of the end region is covered by the second positive electrode film.
In some embodiments, a part or all (for example, 50% to 100% by area, 70% to 100% by area, or 90% to 100% by area) of the center region is covered by the first positive electrode film.
In some embodiments, a part or all (for example, 50% to 100% by area, 70% to 100% by area, or 90% to 100% by area) of the edge region is covered by the second positive electrode film.
In some embodiments, the first positive electrode film and the second positive electrode film possess substantially the same areal density, and an areal density ratio between the first positive electrode film and the second positive electrode film is, for example, (0.8 to 1.2): 1, (0.9 to 1.1): 1, or 1:1.
In some embodiments, the first alkali metal ion donating material includes one or more of: an alkali metal nitride, an alkali metal oxide, a composite of an alkali metal oxide and a transition metal, an alkali metal peroxide, an excessively alkali-metalized alkali metal oxide, or an alkali metal oxycarbide.
In some embodiments, the positive electrode plate is characterized by one or more of the following features:
In some embodiments, the alkali metal is selected from lithium, sodium, or a combination thereof.
In some embodiments, the positive electrode plate includes a waist region and two end regions. The waist region is located between the two end regions. The waist region includes a first positive electrode film. Each of the two end regions includes a second positive electrode film.
In some embodiments, the positive electrode plate of this application is obtained by disposing a positive electrode film with different constituents in each different region of the positive electrode plate.
In some embodiments, the positive electrode plate includes a first positive electrode film and a second positive electrode film. The first positive electrode film and the second positive electrode film are located in different regions of the positive electrode plate without overlapping each other. The first positive electrode film and the second positive electrode film each independently contain a first alkali metal ion donating material and/or a second alkali metal ion donating material. The constituents of the first positive electrode film are different from the constituents of the second positive electrode film.
In some embodiments, the positive electrode plate generally includes a positive current collector and a positive electrode film disposed on at least one surface of the positive current collector. The positive electrode film includes a positive active material (also referred to as “alkali metal ion donating material”).
As an example, the positive current collector includes two surfaces opposite to each other in a thickness direction of the positive current collector. The positive electrode film is disposed on either or both of the two opposite surfaces of the positive current collector.
In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, the metal foil may be an aluminum foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by overlaying the polymer material substrate with a metal material (for example, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy). The polymer material substrate may be, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).
In some embodiments, the positive active material may be a positive active material that is well known for use in a battery in the art. As an example, the positive active material may include at least one of the following materials: olivine-structured lithium-containing phosphate, lithium transition metal oxide, and a modified compound thereof. However, this application is not limited to such materials, and other conventional materials usable as a positive active material of a battery may be used instead. Of such positive active materials, one may be used alone, or at least two may be used in combination. Examples of the lithium transition metal oxide may include, but without being limited to, at least one of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2 and LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1/3Co1/3Mn1/3O2 (briefly referred to as NCM333), LiNi0.5Co0.2Mn0.3O2 (briefly referred to as NCM523), LiNi0.5Co0.25Mn0.25O2 (briefly referred to as NCM211), LiNi0.6Co0.2Mn0.2O2 (briefly referred to as NCM622), LiNi0.8Co0.1Mn0.1O2 (briefly referred to as NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi0.85Co0.15Al0.05O2), or a modified compound thereof. Examples of the olivine-structured lithium-containing phosphate may include, but without being limited to, at least one of lithium iron phosphate (such as LiFePO4 (briefly referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, or a composite of lithium manganese iron phosphate and carbon.
In some embodiments, the positive electrode film further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-tetrafluoroethylene-co-propylene), poly (vinylidene fluoride-co-hexafluoropropylene-co-tetrafluoroethylene), poly(tetrafluoroethylene-co-hexafluoropropylene), or fluorinated acrylate resin.
In some embodiments, the positive electrode film further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.
In some embodiments, the positive electrode plate may be prepared according to the following method: dispersing the ingredients of the positive electrode plate such as the positive active material, the conductive agent, the binder, and any other ingredients into a solvent (such as N-methyl-pyrrolidone) to form a positive slurry, coating a positive current collector with the positive slurry, and performing steps such as drying and cold calendering to obtain the positive electrode plate.
The electrolyte serves to conduct ions between the positive electrode plate and the negative electrode plate. The type of the electrolyte is not particularly limited in this application, and may be selected as required. For example, the electrolyte may be in a liquid state or gel state, or all solid state.
In some embodiments, the electrolyte is in a liquid state and includes an electrolyte salt and a solvent.
In some embodiments, the electrolyte salt may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro(bisoxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.
In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, methyl sulfonyl methane, ethyl methyl sulfone, and (ethylsulfonyl)ethane.
In some embodiments, the electrolytic solution further optionally includes an additive. As an example, the additive may include a negative film-forming additive or a positive film-forming additive. The additive may further include an additive capable of improving some performance of the battery, for example, an additive for improving overcharge performance of the battery, or an additive for improving high-or low-temperature performance of the battery.
In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in this application, and may be any well-known porous separator that is highly stable both chemically and mechanically.
In some embodiments, the separator may be made of a material that is at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene difluoride. The separator may be a single-layer film or a multilayer composite film, without being particularly limited. When the separator is a multilayer composite film, materials in different layers may be identical or different, without being particularly limited.
In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be made into an electrode assembly by winding or stacking.
In some embodiments, the secondary battery may include an outer package. The outer package may be configured to package the electrode assembly and the electrolyte. In some embodiments, the outer package of the secondary battery may be a hard shell such as a hard plastic shell, an aluminum shell, a steel shell, or the like. Alternatively, the outer package of the secondary battery may be a soft package such as a pouch-type soft package. The soft package may be made of plastic such as polypropylene, polybutylene terephthalate, or polybutylene succinate.
The shape of the secondary battery is not particularly limited in this application, and may be cylindrical, prismatic or any other shape.
In some embodiments, referring to
In some embodiments, the secondary battery may be assembled into a battery module. The battery module may include one or more secondary batteries, and the specific number of secondary batteries in a battery module may be selected by a person skilled in the art depending on practical applications and capacity of the battery module.
Optionally, the battery module 4 may further include a shell that provides an accommodation space. The plurality of secondary batteries 5 are accommodated in the accommodation space.
In some embodiments, the battery module may be assembled to form a battery pack. The battery pack may include one or more battery modules, and the specific number of battery modules in a battery pack may be selected by a person skilled in the art depending on practical applications and capacity of the battery pack.
Further, this application provides an electrical device. The electrical device includes at least one of the secondary battery, the battery module, or the battery pack according to this application. The secondary battery, the battery module, or the battery pack may be used as a power supply of the electrical device, or used as an energy storage unit of the electrical device. The electrical device may include, but without being limited to, a mobile device (such as a mobile phone or a laptop computer), an electric vehicle (such as a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, or an electric truck), an electric train, a ship, a satellite system, or an energy storage system.
The secondary battery, the battery module, or the battery pack may be selected for use in the electrical device according to practical requirements of the electrical device.
The following describes some embodiments of this application. The embodiments described below are illustrative, and are merely intended to construe this application but not to limit this application. Unless techniques or conditions are expressly specified in an embodiment hereof, the techniques or conditions described in the literature in this field or in an instruction manual of the product are applicable in the embodiment. A reagent or instrument used herein without specifying a manufacturer is a conventional product that is commercially available in the market.
The first alkali metal ion donating materials in all the embodiments and comparative embodiments described above exhibit a first-cycle Coulombic efficiency of 20% or less, and possess an irreversible capacity.
The second alkali metal ion donating materials in all the embodiments and comparative embodiments described above exhibit a first-cycle Coulombic efficiency of 80% or more, and possess a reversible capacity.
First positive active slurry: Mixing well a first alkali metal ion donating material (in this embodiment, Li2C4O4), a second alkali metal ion donating material (in this embodiment, NCM523), a conductive agent acetylene black, and a binder polyvinylidene difluoride (PVDF) at a mass ratio of 0.1%: 95.9%: 2%: 2%, and adding the mixture to an NMP solvent to form a first positive active slurry.
Second positive active slurry: Mixing well a first alkali metal ion donating material (in this embodiment, Li2C4O4), a second alkali metal ion donating material (in this embodiment, NCM523), a conductive agent acetylene black (SP), and a binder polyvinylidene difluoride (PVDF) at a mass ratio of 0%: 96%: 2%: 2%, and adding the mixture to an NMP solvent to form a second positive active slurry.
Providing a positive current collector (aluminum foil) applicable to a jelly-roll cell, where the positive current collector is strip-shaped and has dimensions of a width direction and a length direction. In a subsequent process of preparing a cell, the width direction of the positive current collector is used as a winding axis, and the length of the positive current collector is wound around the winding axis to form a jelly-roll cell. Along the machine direction of the positive current collector, the positive current collector includes a first end region, a waist region, and a second end region that extend along the length direction of the positive electrode plate. The waist region is located between the first end region and the second end region. The widths of the first end region, the waist region, and the second end region are 0.25 D, 0.5 D, and 0.25 D respectively, where D is the total width of the active material region (a region coated with an active slurry) on the positive current collector, and D=80 mm.
On one side of the positive current collector, the waist region is coated with a first positive active slurry, and the first end region and the second end region are coated with a second positive active slurry. Subsequently, the current collector is dried at 85° C. and then cold-pressed. The above operations are repeated on the other side of the positive current collector.
Finally, the current collector is die-cut and slit to obtain a positive electrode plate applicable to a jelly-roll cell in a lithium-ion battery.
The widths of the first end region 201, the waist region 101, and the second end region 202 are 0.25 D, 0.5 D, and 0.25 D respectively, where D is the total width of the active material region on the positive electrode plate 11.
The first positive electrode film is disposed in the waist region 101 of the positive electrode plate. A first alkali metal ion donating material and a second alkali metal ion donating material are distributed in the first positive electrode film (this region is of a first activity, and is also referred to as the first positive electrode film hereinafter). The first alkali metal ion donating material possesses an irreversible capacity. The second alkali metal ion donating material possesses a reversible capacity. In the first positive electrode film, the first alkali metal ion donating material donates P1 ppm alkali metal ions, and the second alkali metal ion donating material donates Q1 ppm alkali metal ions;
The first end region 201 and the second end region 202 of the positive electrode plate each include the second positive electrode film. A second alkali metal ion donating material is distributed in the second positive electrode film (this region is of a second activity, and is also referred to as the second positive electrode film hereinafter). The first alkali metal ion donating material possesses an irreversible capacity. The second alkali metal ion donating material possesses a reversible capacity. In the second positive electrode film, the first alkali metal ion donating material donates P2 ppm alkali metal ions, and the second alkali metal ion donating material donates Q2 ppm alkali metal ions.
The constituents of the first positive electrode film and the second positive electrode film are shown in Table 1. A sum (P1+Q1) and a ratio (P1/Q1) of P1 and Q1, a sum (P2+Q2) and a ratio (P2/Q2) of P2 and Q2, and the value of (P1+Q1)/(P2+Q2) are shown in Table 1.
Adding graphite as a negative active material, acetylene black as a conductive agent, sodium carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder into a water solvent at a mass ratio of 96:2:1:1, and mixing evenly to make a negative slurry. Coating a copper foil as a negative current collector with the negative slurry evenly, drying the copper foil at 85° C., and cold-calendering it to make a negative electrode plate of the lithium-ion battery.
Using a polyethylene microporous film as a porous separator substrate, mixing inorganic alumina powder, polyvinylpyrrolidone, and an acetone solvent evenly at a mass ratio of 3:1.5:5.5 to form a slurry, coating one side of the substrate with the slurry, and drying the substrate to obtain a separator. The coated side of the separator is oriented toward the positive electrode plate subsequently.
Dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (the dosage of the lithium hexafluorophosphate is 1 mol/L, and a volume ratio between the ethylene carbonate, the dimethyl carbonate, and the ethyl methyl carbonate is 1:2:1) to obtain an electrolyte solution of the lithium-ion battery.
Winding the positive electrode plate, the negative electrode plate, and the separator to obtain a jelly-roll cell.
As shown in
Packaging the jelly-roll cell in a battery housing, and performing steps such as electrolyte injection, chemical formation, and degassing to obtain the battery for use in the embodiment. The rated capacity of the battery is 200 Ah, and dimensions of the battery housing are 60 mm×200 mm×100 mm.
Embodiments 2 to 10 differ from Embodiment 1 in that the mass percent of the first alkali metal ion donating material (Li2C4O4) and the mass percent of the second alkali metal ion donating material (NCM523) in the first positive electrode film are different from those in Embodiment 1, as detailed in Table 1.
Comparative Embodiment 1 differs from Embodiment 1 in the constituents of the first positive electrode film. Specifically, the mass percent of the first alkali metal ion donating material (Li2C4O4) in the first positive electrode film in Comparative Embodiment 1 is 0.0 wt %, as detailed in Table 1.
Embodiments 11A to 11B and Comparative Embodiments 2A to 2B differ from Embodiment 6 in the constituents of the first positive electrode film and the second positive electrode film. Specifically, the type of the second alkali metal ion donating material is different from that in Embodiment 6, as detailed in Table 2.
Embodiments 12 to 19 differ from Embodiment 6 in the constituents of the first positive electrode film and the second positive electrode film. Specifically, the type of the first alkali metal ion donating material is different from that in Embodiment 6, as detailed in Table 3.
Embodiments 20 to 21 differ from Embodiment 6 in the constituents of the second positive electrode film. Specifically, the mass percent of the first alkali metal ion donating material (Li2C4O4) and the mass percent of the second alkali metal ion donating material (NCM523) in the first positive electrode film are different from those in Embodiment 6, as detailed in Table 4.
Comparative Embodiment 3 A differs from Embodiment 2 in the constituents of the first positive electrode film. Specifically, the lithium-rich material Li2MnO3·0.15(LiNi0.33Co0.33Mn0.33O2) is used to replace the first alkali metal ion donating material (Li2C4O4), as detailed in Table 5.
Comparative Embodiment 3B differs from Embodiment 5 in the constituents of the first positive electrode film. Specifically, the lithium-rich material Li2MnO3·0.15(LiNi0.33Co0.33Mn0.33O2) is used to replace the first alkali metal ion donating material (Li2C4O4), as detailed in Table 5.
Comparative Embodiment 3C differs from Embodiment 6 in the constituents of the first positive electrode film. Specifically, the lithium-rich material Li2MnO3·0.15(LiNi0.33Co0.33Mn0.33O2) is used to replace the first alkali metal ion donating material (Li2C4O4), as detailed in Table 5.
The first-cycle Coulombic efficiency of the lithium-rich material is 90% or more. The lithium-rich material in the first positive electrode film donates P*1 ppm alkali metal ions, and the lithium-rich material in the second positive electrode film donates P*2 ppm alkali metal ions.
The positive electrode plates in each embodiment and each comparative embodiment were tested with a true density meter (model: AccuPyc II 1340) with reference to GB/T 24586-2009.
(1) Test principle: The true volume of the sample material was measured precisely by using a displacement method of an inert gas (helium) with a small molecular diameter in conjunction with the Archimedes' principle and the Bohr's law (PV=nRT), so as to obtain the porosity of the sample.
In the formula: S—area of the sample, in cm2; H—thickness of the sample, in cm; A—number of samples, EA; V1—true volume of the sample, in cm3; V2—apparent volume of the sample, in cm3; α—porosity of the sample, %.
Table 1 to Table 5 show the porosities of the waist region and the end region of the positive electrode plate in each embodiment and each comparative embodiment.
Charge and discharge process (the rated capacity is 200 Ah; the potential range used in the cycle life test in a test case of this application is adjustable depending on the system characteristics, such as a V0 to V1 voltage range of 2.8 V to 4.3 V in a LiNi0.5Co0.2Mn0.3 system, a voltage range of 2.5 V to 3.65 V in a LiFePO4 system, or a voltage range of 2.5 V to 4.3 V in a LiFe0.4Mn0.6PO4 system):
The test temperature is 25° C., and the cycle process is as follows:
The cycle life of the battery in each embodiment and each comparative embodiment is shown in Table 1 to Table 5.
The following provides an exemplary detection method to detect the distribution of the first alkali metal ion donating material and the second alkali metal ion donating material on the positive electrode plate:
The physicochemical parameters include, but are not limited to:
The constituent elements may be detected with reference to a general method in the art. An exemplary detection method is to test the element content by using an iCAP 7400 inductively coupled plasma emission spectrometer with reference to the standard EPA 6010D-2014, in which the solvent is aqua regia.
The element content is calculated as: element content (mass fraction w/w %)=element mass/(mass of weighed sample−mass of current collector)×100%.
Based on the concentration of the alkali metal element of each sample cell, a sum of P1 and Q1 (ppm) can be determined, where P1 is the content of the alkali metal ions donated by the first alkali metal ion donating material and Q1 is the content of the alkali metal ions donated by the second alkali metal ion donating material in the first positive electrode film in the waist region and the end region; and a sum of P2 and Q2 (ppm) can be determined, where P2 is the content of the alkali metal ions donated by the first alkali metal ion donating material and Q2 is the content of the alkali metal ions donated by the second alkali metal ion donating material in the second positive electrode film in the waist region and the end region.
In the above embodiments, the positive electrode plate includes a first positive electrode film at the waist and a second positive electrode film at the end. The porosity of the waist is greater than the porosity of the first end region and the porosity of the second end region. Experimental results show that the batteries in the embodiments exhibit an improved cycle life.
In Comparative Embodiment 1, the waist region, the first end region, and the second end region possess an equal porosity. Experimental results show that the battery in the comparative embodiment fails to exhibit an improved cycle life.
Without being limited by any theory, the theoretical basis for the positive electrode plate to improve the cycle life of a battery are as follows:
When the cell is working, the expansion degree at the waist region of the cell is greater than the expansion degree at the end region. Consequently, the waist region is squeezed to a higher degree by the battery shell than the end region, and therefore, the return flowability of the electrolyte solution at the waist region is weaker. In addition, the long-term squeezed state deteriorates the porosity of the negative electrode. After the porosity of the negative electrode plate compacted in a long term is reduced, the negative electrode plate is insufficiently infiltrated by the electrolyte solution, and the lithium intercalation kinetics of the negative electrode are worsened. Lithium plating is prone to occur at the center region in the middle and late stages of cycling and lead to failure. Therefore, by adjusting the porosity at the waist region of the positive electrode plate to make the porosity of the waist be greater than the porosity of the first end region and the porosity of the second end region, this application can reserve a space for withstanding compression, and in turn, alleviate a series of adverse effects mentioned above caused by compression of the waist region.
In the above embodiments, the positive electrode plate includes a first positive electrode film at the waist and a second positive electrode film at the end. The first positive electrode film and the second positive electrode film satisfy the following relationship:
Experimental results show that the batteries in the embodiments exhibit an improved cycle life.
Embodiments 1 to 10 show that, when (P1+Q1) is greater than (P2+Q2), the value of (P1+Q1): (P2+Q2) is 1.001 to 1.998, and all the batteries exhibit an improved cycle life. In Comparative Embodiment 1, the battery satisfies (P1+Q1)=(P2+Q2), and the battery exhibits no improved cycle life.
Embodiments 11A to 11B show that, the batteries employ various positive active materials, and, when (P1+Q1) is greater than (P2+Q2), all the batteries exhibit an improved cycle life. In Comparative Embodiments 2A to 2B, the batteries satisfy (P1+Q1)=(P2+Q2), and the batteries exhibit no improved cycle life.
Embodiments 12 to 19 show that, the batteries employ various first alkali metal ion donating materials, and, when (P1+Q1) is greater than (P2+Q2), all the batteries exhibit an improved cycle life.
Embodiments 20 to 21 show that, the batteries satisfy (P1+Q1)>(P2+Q2), P1/Q1=20%, and P2/Q2=2% to 6%, and all the batteries exhibit an improved cycle life.
In Comparative Embodiments 3A to 3C, the first alkali metal ion donating material is replaced by a lithium-rich material. Different from the first alkali metal ion donating material, the lithium-rich material exhibits a first-cycle Coulombic efficiency of 90% or more, and possesses a reversible capacity. In Comparative Embodiments 5 to 7, the batteries fail to exhibit a significantly improved cycle life.
When the positive electrode plate based on the above embodiments is used in a secondary battery, the secondary battery exhibits an improved cycle life. Without being limited by any theory, the reasons for the improved cycle life of the battery are analyzed as follows:
The value of (P1+Q1) in the first positive electrode film is relatively large. Because the first positive electrode film is located in the waist region with a relatively high temperature and a relatively high electrochemical activity, the relatively large (P1+Q1) value can make up for the capacity loss caused by insufficiency of reversible alkali metal ions arising from a too fast consumption rate of the alkali metal ions in the waist region, and increase the overall cycle life of the cell.
The value of (P2+Q2) in the second positive electrode film is relatively small. Because the second positive electrode film is located in the end region with a relatively low temperature and a relatively low electrochemical activity, the relatively small (P2+Q2) value reduces the overall cost and avoids the risk of a short circuit caused by metal dendrites on the negative electrode arising from excessive alkali metal ions.
In the above embodiments, the first positive electrode film and the second positive electrode film satisfy the following relationship: (P1/Q1)>(P2/Q2), and the batteries exhibit an improved cycle life.
Without being limited by any theory, the reasons for the improved cycle life of the battery are analyzed as follows:
The first alkali metal ion donating material and/or the second alkali metal ion donating material play different roles during operation of the battery. The alkali metal ions donated by the first alkali metal ion donating material are used for compensating for the consumption of the alkali metal ions during the lifespan of the battery, for example, the consumption in an initial film-forming reaction, and the consumption in a reparative film-forming reaction during cycling/storage. The alkali metal ions donated by the second alkali metal ion donating material is used for reversible deintercalation/electrochemical reaction in the positive and negative electrode materials. Because the inherent film-forming consumption is compensated for by the first alkali metal ions, more reversible alkali metal ions are available for providing electrochemical energy. The value of (P1/Q1) in the first positive electrode film is relatively large. Because the first positive electrode film is located in the waist region with a relatively high temperature and a relatively high electrochemical activity, the relatively large (P1/Q1) value can make up for the capacity loss caused by insufficiency of reversible alkali metal ions arising from a too fast consumption rate of the alkali metal ions in the waist region, and increase the overall cycle life of the cell.
The value of (P2/Q2) in the second positive electrode film is relatively small. Because the second positive electrode film is located in the end region with a relatively low temperature and a relatively low electrochemical activity, the relatively small (P2/Q2) value reduces the overall cost and avoids the risk of a short circuit caused by metal dendrites on the negative electrode arising from excessive alkali metal ions.
It is hereby noted that this application is not limited to the foregoing embodiments. The foregoing embodiments are merely examples. Any and all embodiments with substantively the same constituents or exerting the same effects as the technical ideas hereof without departing from the scope of the technical solutions of this application still fall within the technical scope of this application. In addition, all kinds of variations of the embodiments conceivable by a person skilled in the art and any other embodiments derived by combining some constituents of the embodiments hereof without departing from the subject-matter of this application still fall within the scope of this application.
The application is a continuation of international patent application No. PCT/CN2022/104156, filed on Jul. 6, 2022. The disclosure of the aforementioned application is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2022/104156 | Jul 2022 | WO |
| Child | 18946569 | US |
