Patent Application
20230307614
The present disclosure relates to the technical field of lithium-ion batteries, and in particular, to a lithium-ion battery and an electric vehicle.
Lithium-ion batteries are widely used in portable electronic devices (such as mobile phones, tablet computers, etc.), unmanned aerial vehicles, electric vehicles and other fields because of the high energy density, small size, and no memory effect. However, lithium-ion batteries also have their own disadvantages, such as capacity fading. The loss of active lithium is one of the main reasons for the capacity fading of lithium-ion batteries during the cycle. Therefore, measures taken in the industry are generally to add a lithium replenishing agent capable of providing active lithium to the lithium-ion battery system in advance to make up for the irreversible loss of active lithium.
At present, mature lithium replenishing technologies for batteries include negative electrode lithium replenishing, mainly including wet lithium powder replenishing, dry lithium strip, lithium foil replenishing, etc. However, the lithium replenishing effect of such lithium replenishing methods is not easy to control. For example, the lithium replenishing amount of metal lithium should not be too high, otherwise it is necessary to increase the N/P ratio of the positive and negative electrodes of the battery to reduce the risk of lithium plating in the battery. However, a high N/P ratio may waste a lot of negative electrode materials and reduce the energy density of the battery, which is contrary to the original intention of lithium replenishing, and is not conducive to improve the battery capacity. Therefore, how to precisely control the lithium replenishing amount and the N/P ratio of the battery to realize a controllable design of a battery with a long cycle life has become an urgent problem to be overcome at present.
In view of this, the present disclosure provides a lithium-ion battery and an electric vehicle. The lithium-ion battery has a controllable long cycle life and is not prone to lithium plating.
A first aspect of the present disclosure provides a lithium-ion battery, which includes a cell including N battery units, where N is an integer greater than 0, each of the N battery units includes a positive electrode plate, a negative electrode plate, and a separator sandwiched between the positive electrode plate and the negative electrode plate; the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode material layer includes a positive electrode active material, a first conductive agent, and a first binder; the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material, a second conductive agent, and a second binder; the lithium-ion battery further includes at least one negative electrode lithium replenishing agent film, where the at least one negative electrode lithium replenishing agent film includes an independent lithium replenishing electrode that includes a current collector and a first metal lithium layer disposed on at least one surface of the current collector, or the at least one negative electrode lithium replenishing agent film includes a second metal lithium layer laminated on a surface of the negative electrode material layer;
an areal density σ of the first metal lithium layer or the second metal lithium layer satisfies the formula I as follows:
and a parameter θ satisfies a formula II as follows:
where α represents a ratio of an amount of pre-stored lithium at the lithium-ion battery with different numbers of cycles to a reversible capacity of the N negative electrode plates; e represents a tolerance of the areal density of the first metal lithium layer or the second metal lithium layer; σ1 and ε1 respectively represent an areal density of the positive electrode material layer and a tolerance thereof; σ2 and ε2 respectively represent an areal density of the negative electrode material layer and a tolerance thereof; c1 and ξ respectively represent a gram capacity of the positive electrode material layer and a tolerance thereof; c2 and ξ1 respectively represent a gram capacity of the negative electrode material layer and a tolerance thereof; η represents a first coulombic efficiency of the negative electrode active material; n represents a number of first metal lithium layers or second metal lithium layers in the lithium-ion battery; c3 represents a theoretical gram capacity of a material of the first metal lithium layer or the second metal lithium layer; k represents a correction factor, and k is a constant ranging from 0.5 to 0.95; and θ ranges from 1.0 to 1.3.
In the present disclosure, the lithium replenishing amount of the battery may be controlled by precisely controlling the areal density σ of the first metal lithium layer or the second metal lithium layer, so that a lithium-ion battery with a long cycle life can be controllably designed, and controlling the parameter θ to be in an appropriate range can avoid the risk of lithium plating in the battery, and enables the battery to have a high capacity and cycle performance.
A second aspect of the present disclosure provides an electric vehicle. The electric vehicle includes the lithium-ion battery according to the first aspect of the present disclosure. Therefore, the mile range of the electric vehicle can be improved, and a high safety performance is achieved.
A part of the advantages of the embodiments of the present disclosure will be set forth in the description which follows, and will be obvious from the description, or may be learned by the practice of the embodiments of the present disclosure.
The follows are some embodiments of the present invention, and it should be noted that for a person of ordinary skill in the art, a number of improvements and refinements can be made without departing from the principles of the present invention, and these improvements and refinements are also considered to be within the scope of protection of the present invention.
A first aspect of the present disclosure provides a lithium-ion battery 1000. Referring to
The lithium-ion battery 1000 further includes at least one negative electrode lithium replenishing agent film 4. The negative electrode lithium replenishing agent film 4 includes a metal lithium layer (e.g., the second metal lithium layer) laminated on a surface of the negative electrode material layer 201, or an independent lithium replenishing electrode including a metal lithium layer (e.g., the first metal lithium layer).
In some implementations of the present disclosure, the negative electrode lithium replenishing agent film 4 may be an independent lithium replenishing electrode. Referring to
In some embodiments, further referring to
In some implementations of the present disclosure, the negative electrode lithium replenishing agent film 4 may be in direct contact with the negative electrode material layer 201 (see
In the present disclosure, an areal density σ of the metal lithium layer in the negative electrode lithium replenishing agent film 4 satisfies the following formula (I), and a parameter θ satisfying the following formula (II) is defined:
where α represents a ratio of an amount of pre-stored lithium required by the lithium-ion battery with different numbers of cycles to a reversible capacity of N negative electrode plates 20, and the reversible capacity is measured in mAh; σ1 and ε1 respectively represent an areal density of the positive electrode material layer 101 and a tolerance thereof, σ2 and ε2 respectively represent an areal density of the negative electrode material layer 201 and a tolerance thereof, c1 and ξ1 respectively represent a gram capacity of the positive electrode material layer 101 and a tolerance thereof, c2 and ξ2 respectively represent a gram capacity of the negative electrode material layer 201 and a tolerance thereof, f represents a first coulombic efficiency of the negative electrode active material, η represents a number of metal lithium layers in the lithium-ion battery, c3 represents a theoretical gram capacity of the material of the metal lithium layer, k represents a correction factor, and k is a constant ranging from 0.5 to 0.95; and θ ranges from 1.0 to 1.3.
In the present disclosure, the lithium replenishing amount of the battery may be controlled by precisely configuring the areal density σ of the metal lithium layer, so that a long cycle life of the lithium-ion battery 1000 can be controllably designed, and configuring the parameter θ to be in an appropriate range can avoid the risk of lithium plating in the battery, and enables the battery to have a high capacity and energy density. The parameter θ can reflect a ratio of remaining vacancies capable of accommodating lithium ions in the negative electrode to vacancies capable of accommodating lithium ions in the positive electrode in the pre-lithiated battery. If the value of 0 is too low, there is a risk of lithium plating on the negative electrode plate 20 during charging. If the value of 0 is too high, the amount of material coated on the negative electrode plate 20 is too large, reducing the energy density of the battery. Through comprehensive consideration in the present disclosure, θ configured in the range of 1.0 to 1.3 can achieve a low risk of lithium plating and a high capacity. For example, 0 may be 1.05, 1.1, 1.12, 1.2, 1.3, etc. In some embodiments, the θ may range from 1.07 to 1.15.
The areal density σ1 of the positive electrode material layer and the areal density σ2 of the negative electrode material layer are parameters of the lithium-ion battery, and can be determined in combination with θ. The tolerances Fi, Ea, and F are empirical values, generally measured in %, and may be determined according to the preparation processes of the positive electrode material layer 101, the negative electrode material layer 201, and the metal lithium layer. The above parameters c1, ξ1, c2, ξ2, and η are measured values, and are obtained by electrochemical testing of coin cells prepared by assembling the positive electrode plate 10 or the negative electrode plate 20 with a lithium metal plate respectively. The tolerances ξ1 and ξ2 are also generally measured in %. The areal density σ1, σ2, and σ may be measured in g/m2, c1, c2, and c3 may be measured in mAh/g, and the parameter c3 of metal lithium elemental is 3860 mAh/g. In some implementations of the present disclosure, the tolerances ε1, ε2, ε, ξ1 and ξ2 generally do not exceed 5%, and for example, range from 1% to 3%.
The correction factor k is an empirical value and may be determined according to the form of the metal lithium layer in the negative electrode lithium replenishing agent film 4. For example, when the metal lithium layer is a lithium powder layer obtained by wet coating a metal lithium powder, the value of k generally ranges from 0.5 to 0.85; when the metal lithium layer is a dry-pressed lithium foil or lithium strip, the value of k generally ranges from 0.8 to 0.95; when the metal lithium layer is a lithium alloy, the value of k generally ranges from 0.6 to 0.9.
The parameter α reflects the pre-stored lithium level of the battery. The term “amount of pre-stored lithium” represents a difference between a lithium replenishing capacity of the negative electrode lithium replenishing agent film 4 and an irreversible capacity of the negative electrode plate 20 of the battery. The lithium replenishing capacity of the negative electrode lithium replenishing agent film 4 refers to an amount of lithium that can be deintercalated for the first time. Generally, when the number of cycles required by the battery increases, the value of a also increases. When α is equal to 0, it indicates that the lithium replenishing capacity of the negative electrode lithium replenishing agent film 4 is exactly equal to the irreversible capacity of a plurality of negative electrode plates 20 in the battery. A correspondence between the number of cycles c of the lithium-ion battery and the parameter a will be described in detail in Example 1 below. In some implementations of the present disclosure, a ranges from 0 to 18%. For example, a may be 0, 2%, 4%, 6%, 8%, 10%, 12%, 15%, or 18%. In some implementations of the present disclosure, a ranges from 4% to 15%.
In some implementations of the present disclosure, the metal lithium layer may have a patterned structure. For example, the lithium foil or lithium strip may have a porous structure. The patterned structure is beneficial to the wetting of the metal lithium layer in an electrolyte solution and the release of gas during the formation of an Solid Electrolyte Interphase (SEI) film on the negative electrode in the pre-lithiation process, so as to prevent the detachment of the metal lithium layer from the surface of the negative electrode.
In an implementation of the present disclosure, a plurality of through holes may be provided on the separator 3. The through holes can ensure that lithium ions can successfully intercalate or deintercalate through the separator during rapid charge and discharge of the battery. The through holes may have a porosity of 40% to 50%. The material of the separator may be Polypropylene (PP) or Polyethylene (PE).
In an implementation of the present disclosure, the positive electrode current collector 100, the negative electrode current collector 200, and the current collector 400 of the negative electrode lithium replenishing agent film 4 may include, but are not limited to, a metallic elemental foil or an alloy foil. The metallic elemental foil includes a copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, or silver foil. The alloy foil includes stainless steel, or an alloy containing at least one of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, or silver. In some implementations of the present disclosure, these elements are the main composition of the alloy foil. The positive electrode current collector 100 and/or the negative electrode current collector 200 may be etched or coarsened to form a secondary structure to facilitate effective contact with the corresponding electrode material layer. Generally, the positive electrode current collector 100 is an aluminum foil, and the negative electrode current collector 200 is a copper foil. The current collector 400 of the negative electrode lithium replenishing agent film 4 may be a copper foil.
For the lithium-ion battery, the positive electrode active material may be at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese nickelate, lithium nickel manganese oxide, nickel cobalt manganese (NCM), nickel cobalt aluminum (NCA), etc. The negative electrode active material may include at least one of graphite, hard carbon, a silicon-based material (including elemental silicon, silicon alloy, silicon oxide, and silicon-carbon composite material), a tin-based material (including elemental tin, tin oxide, and tin-based alloy), Li4Ti5O2, TiO2, etc.
In the present disclosure, the conductive agent and the binder are conventional choices in the battery field. For example, the conductive agent may include at least one of carbon nanotubes, carbon black, and graphene. The binder may be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), and sodium alginate.
In an implementation of the present disclosure, the lithium-ion battery 1000 may further include a battery case and an electrolyte solution. The electrolyte solution and the cell including the battery units 1 and the negative electrode lithium replenishing agent film 4 are packaged in the battery case. The cell is soaked in the electrolyte solution. The battery case may be made of an aluminum-plastic composite film.
The lithium-ion battery provided in the embodiments of the present disclosure has a high capacity, a long cycle life, and a low risk of lithium plating at the same time.
A second aspect of the present disclosure provides an electric vehicle. The electric vehicle includes the lithium-ion battery according to the first aspect of the present disclosure. Therefore, the mile range of the electric vehicle can be improved, and the high safety performance is achieved.
The embodiments of the present disclosure are further described below with reference to a plurality of examples.
A lithium-ion battery had a structure shown in
(1) Fabrication of a laminated cell of the battery:
a. A positive electrode plate using lithium iron phosphate as a positive electrode active material and including a positive electrode material layer with an areal density σ1 of 350 g/m2 and a compaction density of 2.4 g/m3 was prepared, and a preparation process was as follows: lithium iron phosphate, carbon nanotubes, and a binder PVDF were weighted according to a mass ratio of 96:2:2, dissolved in a solvent N-methylpyrrolidone (NMP), and fully dispersed to obtain a positive electrode slurry. The positive electrode slurry was coated on a surface of an aluminum foil, dried, rolled, and cut to obtain a positive electrode plate with a positive electrode material layer. A deviation ε1 (%) of σ1 was 1%.
b. A negative electrode plate using natural graphite as a negative electrode active material and having a negative electrode material layer with an areal density σ2 of 206 g/m2, a deviation ε2 of σ2 being 1%, and a compaction density of 1.5 g/m3 was prepared. A preparation process was as follows: graphite, a conductive agent super P, and a binder SBR were mixed in water according to a weight ratio of 96:2:2 to obtain a negative electrode slurry. The negative electrode slurry was coated on two sides of a copper foil, dried, rolled, and cut to obtain a negative electrode plate with a negative electrode material layer.
c. The positive electrode plate, a separator, and the negative electrode plate were stacked in sequence to obtain a battery unit, where the separator included a PE base film and ceramic layers formed on upper and lower surfaces of the PE base film, the PE base film had a thickness of 40 microns, and a total thickness of the ceramic layers on the two sides was 5 microns; N (N=3) battery units were obtained in a similar manner and stacked together to obtain a laminated cell, and two adjacent battery units are separated by a separator.
(2) Fabrication of an independent lithium replenishing electrode:
Two side surfaces of the current collector 400 (e.g., a copper foil) was coated with a dense semiconductor material having a composition of ZnO:NiO:Al2O3:Fe2O3=0.3:0.3:0.3:0.1 (by mass), and sintered at a high temperature of 800° C. for 24 h to obtain a heat-sensitive semiconductor layer 401 with a thickness of 80-120 nm. Then, a metal lithium layer 402 with an areal density of 1.98 g/m2 was arranged/disposed on the heat-sensitive semiconductor layer 401 for lithium replenishing, to obtain an independent lithium replenishing electrode. The metal lithium layer 402 with an areal density of 1.98 g/m2 (e.g., a lithium foil) may be calculated according to the aforementioned formula, which will be described in detail below.
(3) One independent lithium replenishing electrode was arranged/disposed on an outermost side of the laminated cell in step (1), then a tab of the lithium replenishing electrode and a negative electrode tab were welded together, followed by packaging with an aluminum-plastic film to form a pouch battery. Solution of 1.0 mol/L of LiPF6 in vinyl carbonate (EC):dimethyl carbonate (DMC)=1:1 to 1:5 (volume ratio) was used as an electrolyte solution. Then the electrolyte solution was injected into the battery, and the battery was sealed to obtain a full cell.
After the formation and capacity checking of the assembled full cell of Example 1 were completed at the room temperature, the state of charge (SOC) state of the battery was adjusted to 10%. Then the battery was heated to 60° C., and allowed to stand for 12 h. In this case, the heat-sensitive semiconductor layer conducted electricity, a path was formed between metal lithium and the current collector, and active lithium was released from the independent lithium replenishing electrode and intercalated into the graphite negative electrode. The voltage of the battery was monitored to control and adjust the lithium replenishing amount. When the open-circuit voltage of the battery rose by 0.2 V, the heating was stopped. Then the battery was cooled to 25° C. As such, the pre-lithiation of the full cell was completed. Afterward, the full cell was tested for the battery capacity, cycle performance, etc.
It should be noted that, in Example 1 of the present disclosure, the areal density σ=1.98 g/m2 of the metal lithium layer 402 of the independent lithium replenishing electrode is calculated based on the above formulas I and II. The parameter θ was controlled at 1.12, N=3, n=2, the correction factor k was 0.8, c3 of the lithium metal element was 3860 mAh/g, the gram capacity c1 of the positive electrode material layer was 148 mAh/g, the tolerance ξ1 of the gram capacity c1 was 2%, the gram capacity c2 of the negative electrode material layer was 330 mAh/g, the tolerance ξ2 of the gram capacity c2 was 2%, the first efficiency f was 94%, the pre-stored lithium level a required by the lithium-ion battery when the number of cycles was 3000 was 0%, and ε1, ε2, ε were 1%. The parameters c1, τ1, c2, ξ2, and η were obtained by electrochemical testing of coin cells prepared by assembling the positive electrode plate 10 or the negative electrode plate 20 with a lithium metal plate respectively. Test conditions were as follows: charging and discharging at a constant current of 0.1 C, a voltage window of a coin cell prepared from the positive electrode plate being 2.5 to 3.8 V, and a voltage window of a coin cell prepared from the negative electrode plate being 0.005 to 1.5 V.
In embodiments of the present disclosure, a was obtained by the applicant of the present disclosure according to a mapping relationship between batteries with different pre-stored lithium levels a and the number of cycles c when the capacity retention rates of the batteries drop to 80%, as shown in Table 1 below.
Table 1 above is a cycle fading curve (see
The lithium-ion battery of Example 2 differs from Example 1 in that: The areal density of the metal lithium layer in the independent lithium replenishing electrode was 4.42 g/m2, the areal density of the negative electrode material layer was 230 g/m2, and σ=6%.
The lithium-ion battery of Example 3 differs from Example 1 in that: The areal density of the metal lithium layer in the independent lithium replenishing electrode was 6.38 g/m2, the areal density of the negative electrode material layer was 249 g/m2, and σ=10%.
The lithium-ion battery of Example 4 differs from Example 1 in that: The areal density of the metal lithium layer in the independent lithium replenishing electrode was 11.48 g/m2, the areal density of the negative electrode material layer was 299 g/m2, and α=18%.
The lithium-ion battery of Example 5 differs from Example 2 in that: two independent lithium replenishing electrodes (n=4) were provided, the areal density of the metal lithium layer was 1.98 g/m2, the two independent lithium replenishing electrodes were respectively located on the two outermost side of the entire cell, and the areal density of the negative electrode material layer was 206 g/m2.
The lithium-ion battery of Example 6 differs from Example 1 in that: the independent lithium replenishing electrode included a current collector and a metal lithium layer arranged/disposed on each of two side surfaces of the current collector, and did not include a heat-sensitive semiconductor layer.
The lithium-ion battery of Example 7 differs from Example 6 in that: two independent lithium replenishing electrodes (n=4) were provided, the areal density of the metal lithium layer was 0.94 g/m2, the two independent lithium replenishing electrodes were respectively located on the two outermost sides of the entire cell, and the areal density of the negative electrode material layer was 196 g/m2.
The lithium-ion battery of Example 8 differs from Example 1 in that: the negative electrode lithium replenishing agent film was a lithium foil layer, directly attached to surfaces of two negative electrode material layers of the negative electrode plate on an outermost side of the cell (n=2).
The lithium-ion battery of Example 9 (the structure diagram is shown in
The lithium-ion battery of Example 10 differs from Example 2 in that: the areal density of the metal lithium layer in the independent lithium replenishing electrode was 4.14 g/m2, the areal density of the negative electrode material layer was 215 g/m2, and the value of the parameter θ was 1.05.
The lithium-ion battery of Example 11 differs from Example 2 in that: the areal density of the metal lithium layer in the independent lithium replenishing electrode was 4.92 g/m2, the areal density of the negative electrode material layer was 256 g/m2, and the value of the parameter θ was 1.25.
Table 2 summarizes the electrochemical testing results of the batteries of the above examples. A method for testing discharge capacities of the batteries was as follows: at the room temperature, each battery was charged at a constant current of 0.2 C and a constant voltage to 3.8 V, to a cutoff current of 0.05 C, allowed to stand for 10 min, then discharged to 2.0 V at a constant current of 0.2 C, and allowed to stand for 10 min; and the charge-discharge process was repeated three times, to obtain a stable discharge capacity. A method for testing cycle performance of the batteries was as follows: at the room temperature, each battery was charged to 3.8 V at a constant current of 0.5 C, allowed to stand for 10 min, then discharged to 2.0 V at a constant current of 0.5 C, and allowed to stand for 10 min; and the above charge-discharge process was cyclically carried out, and the testing was stopped when the capacity retention rate dropped to 80%. The energy density of the battery was calculated based on the weight of the cell.
As can be seen from Table 2, different cycle life of batteries can be achieved using different amount of pre-stored lithium. A higher pre-stored lithium level a indicates a longer cycle life of the battery. In addition, as can be seen from the comparison between Example 1 and Examples 6 to 9, when the lithium replenishing agent film of the battery was an independent lithium replenishing electrode with a heat-sensitive semiconductor layer, both the capacity and cycle life of the battery reached optimum at the same pre-stored lithium level, and were substantially close to an expected cycle life corresponding to a, while the actual cycle life in Examples 6 to 9 was slightly shorter than the expected cycle life corresponding to a. Moreover, as can be seen from Examples 2, 10 and 11, when the value of the parameter θ was too large, the cycle life and capacity of the battery were not greatly changed, but the energy density of the battery was reduced due to the increase of the weight of the negative electrode material. In the present disclosure, controlling the value of 0 to be within the range of 1.0 to 1.2 can enable the battery to reach a high energy density as much as possible while having a long cycle life.
The above-described embodiments are merely illustrative of several implementations of the present disclosure, and the description does not limit the scope of the present disclosure. It should be pointed out that for those of ordinary skill in the art, variations and improvements can be made without departing from the concept of the present disclosure, which all fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure is defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011401161.3 | Dec 2020 | CN | national |
This application is a Continuation application of International Patent Application No. PCT/CN2021/135420, filed on Dec. 3, 2021, which is based on and claims priority to and benefits of Chinese Patent Application No. 202011401161.3, filed on Dec. 4, 2020. The entire content of all of the above-referenced applications is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2021/135420 | Dec 2021 | US |
| Child | 18205175 | US |
