Patent Publication Number: US-2019198864-A1

Title: Cathode of lithium ion battery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is based on, and claims priority from, Taiwan Application Number 106145979, filed on Dec. 27, 2017, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The disclosure relates to a cathode of a lithium ion battery. 
     BACKGROUND 
     Ternary material (NMC) has the advantages of low cost, high capacity, and good cycling performance, and has been widely used in many fields. However, batteries made from ternary material (NMC) have poor rate charge-discharge performance and poor safety. 
     Currently, a mixture of lithium iron manganese phosphate (LMFP) material and ternary material has been used to manufacture electrodes to improve the rate charge-discharge performance and safety of batteries. However, because lithium iron manganese phosphate (LMFP) material and ternary material are evenly distributed in an electrode made from a mixture of lithium iron manganese phosphate (LMFP) material and ternary material, different materials have different lengths of conductive paths, resulting in uneven electric currents during charging and discharging. In addition, a lot of contact interfaces may be formed between the two materials, increasing the impedance of batteries. 
     Therefore, a novel electrode capable of overcoming the above problems is needed to improve the performance of batteries. 
     SUMMARY 
     An embodiment of the disclosure provides a cathode of a lithium ion battery, including: a collector material; a first electrode layer, including a lithium manganese iron phosphate (LMFP) material, disposed on a surface of the collector material; and a second electrode layer, including an active material, disposed on the first electrode layer, wherein the active material includes lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), Li-rich cathode material, or a combination thereof. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of a cathode of a lithium ion battery according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional view of a cathode of a lithium ion battery according to another exemplary embodiment of the present disclosure; 
         FIG. 3A  illustrates the rate charge-discharge performance of the lithium ion battery according to an exemplary embodiment of the present disclosure; 
         FIG. 3B  illustrates the rate charge-discharge performance of the lithium ion battery according to a comparative example of the present disclosure; 
         FIG. 3C  illustrates the rate charge-discharge performance of the lithium ion battery according to another comparative example of the present disclosure; 
         FIG. 4A  illustrates the rate charge-discharge performance of the lithium ion battery according to another exemplary embodiment of the present disclosure; and 
         FIG. 4B  illustrates the rate charge-discharge performance of the lithium ion battery according to another comparative example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     In addition, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly 
     The cathode of a lithium ion battery provided by the embodiments of the present disclosure has a multi-layer structure, rendering uniform conductive paths and reducing the contact interfaces between different materials. Also, batteries made from the cathode of a lithium ion battery provided by the present disclosure have improved rate charge-discharge performance. 
     Referring to  FIG. 1 , in some embodiments of the present disclosure, a cathode  100  of a lithium ion battery is provided. The cathode  100  of a lithium ion battery include a collector material  102 , a first electrode layer  104  disposed on a surface of the collector material  102 , and a second electrode layer  106  disposed on the first electrode layer  104 . 
     In one embodiment, the collector material  102  may be an aluminum foil. 
     In one embodiment, the first electrode layer  104  may include a lithium manganese iron phosphate (LMFP) material. The lithium manganese iron phosphate (LMFP) material may have a chemical formula of LiMn x Fe 1-x PO 4 , wherein 0.5≤x&lt;1. 
     In some embodiments, the first electrode layer  104  may further include a binder and a conductive material. The first electrode layer  104  is a mixture made of a lithium manganese iron phosphate (LMFP) material, a binder, and a conductive material. The binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The conductive material may include conductive graphite, carbon black, carbon nanotubes, graphene, or a combination thereof. 
     In the first electrode layer  104 , the weight percentage of the lithium manganese iron phosphate (LMFP) material may be, for example, 80-99 wt %, the weight percentage of the binder may be, for example, 0.5-20 wt %, and the weight percentage of the conductive material may be, for example, 0.5-20 wt %, based on the total weight of the first electrode layer  104 . Because the lithium iron manganese phosphate (LMFP) material is the main source of electric capacity of the first electrode layer  104 , when the weight percentage of the lithium manganese iron phosphate (LMFP) material is too low, the electric capacity of electrode and the energy density decrease. The higher the weight of the conductive material, the better the electrical properties of the resulting batteries. However, since the conductive material does not provide electric capacity, when the weight of the conductive material is greater than, for example, 20 wt %, the electric capacity of the electrode and the energy density decrease. Moreover, since the conductive material has a lower density and a larger surface area, when the weight of the conductive material is too high, it will have a great influence on the density and the processability of the electrode. 
     For example, in some embodiments, the weight percentage of the lithium manganese iron phosphate (LMFP) material may be, for example, 90-95 wt %, based on the total weight of the first electrode layer  104 . In some embodiments, the weight percentage of the binder may be, for example, 2-10 wt %, based on the total weight of the first electrode layer  104 . In some embodiments, the weight percentage of the conductive material may be, for example, 2-10 wt %, based on the total weight of the first electrode layer  104 . 
     In one embodiment, the second electrode layer  106  may include an active material. In some embodiments, the active material may include, for example, lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), Li-rich cathode material, or a combination thereof. In one embodiment, the lithium nickel manganese cobalt oxide (NMC) may have a chemical formula of LiNi x Co y Mn z O 4 , wherein 0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;z&lt;1. In one embodiment, the lithium nickel cobalt aluminum oxide (NCA) may have a chemical formula of LiNi 0.80 Co 0.15 Al 0.05 O 2 . In one embodiment, the lithium cobalt oxide (LCO) may have a chemical formula of LiCoO 2 . In one embodiment, the Li-rich cathode material may have a chemical formula of xLi 2 MnO 3 .(1−x)LiMO 2 , wherein M is 3d transition metal and/or 4d transition metal, and 0&lt;x&lt;1. In some embodiments, the 3d transition metal may be, for example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn, and the 4d transition metal may be, for example, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, or Cd. 
     In some embodiments, the second electrode layer  106  may further include a binder and a conductive material. The second electrode layer  106  is a mixture made of the above active material, a binder, and a conductive material. The binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (P IFE), or a combination thereof. The conductive material may include conductive graphite, carbon black, carbon nanotubes, graphene, or a combination thereof. 
     In the second electrode layer  106 , the weight percentage of the active material may be, for example, 80-99 wt %, the weight percentage of the binder may be, for example, 0.5-20 wt %, and the weight percentage of the conductive material may be, for example, 0.5-20 wt %, based on the total weight of the second electrode layer  106 . Because the active material is the main source of electric capacity of the second electrode layer  106 , when the weight percentage of the active material is too low, the electric capacity of electrode and the energy density decrease. The higher the weight of the conductive material, the better the electrical properties of the resulting batteries. However, since the conductive material does not provide electric capacity, when the weight of the conductive material is greater than, for example, 20 wt %, the electric capacity of the electrode and the energy density decrease. Moreover, since the conductive material has a lower density and a larger surface area, when the weight of the conductive material is too high, it will have a great influence on the density and the processability of the electrode. 
     For example, in some embodiments, the weight percentage of the active material may be, for example, 90-95 wt %, based on the total weight of the second electrode layer  106 . In some embodiments, the weight percentage of the binder may be, for example, 2-10 wt %, based on the total weight of the second electrode layer  106 . In some embodiments, the weight percentage of the conductive material may be, for example, 2-10 wt %, based on the total weight of the second electrode layer  106 . 
     In some embodiments, the weight percentage of the second electrode layer  106  may be greater than 30 wt %, based on the total weight of the first electrode layer  104  and the second electrode layer  106 . For example, in some embodiment, the weight percentage of the second electrode layer  106  may be greater than or equal to 50 wt %, 70 wt %, 80 wt %, based on the total weight of the first electrode layer  104  and the second electrode layer  106 . Because the capacity of the active material of the second electrode layer  106  is higher than the capacity of the lithium manganese iron phosphate (LMFP) of the first electrode layer  104 , when the weight percentage of the second electrode layer  106  is too low, for example, less than 30 wt %, the capacity of the resulting battery and energy density decrease. 
     In some embodiments, the slurry for forming the first electrode layer  104  and the second electrode layer  106  may be simultaneously coated on a surface of the collector material  102  in a layered manner by using, for example, a roll-to-roll slot-die coating method. After drying, it is pressed by a roll press machine to obtain a cathode  100  of a lithium ion battery as shown in  FIG. 1 . 
     In some embodiments, the compaction density of the first electrode layer  104  may be, for example, 1.5-3 g/cm 3 , and the density of the second electrode layer  106  may be, for example, 2.5-4.2 g/cm 3 . 
     Referring to  FIG. 2 , other embodiments of the present disclosure provides a cathode  200  of a lithium ion battery. The cathode  200  of a lithium ion battery include a collector material  202 , a first electrode layer  204  disposed on one surface of the collector material  202 , and a second electrode layer  206  disposed on the first electrode layer  204 . The difference between the cathode  200  of a lithium ion battery and the cathode  100  of a lithium ion battery is that the other surface of the collector material  202 , with respect to the first electrode layer  204 , of the cathode  200  of a lithium ion battery further includes a third electrode layer  204 ′ and a fourth electrode layer  206 ′ disposed on the third electrode layer  204 ′. 
     The first electrode layer  204  and the second electrode layer  206  are similar to the first electrode layer  104  and the second electrode layer  106 , reference may be made to the foregoing description of the present specification, and are not described herein again. 
     In one embodiment, the third electrode layer  204 ′ may include a lithium manganese iron phosphate (LMFP) material. The lithium manganese iron phosphate (LMFP) material may have a chemical formula of LiMn x Fe 1-x PO 4 , wherein 0.5≤x&lt;1. 
     In some embodiments, the third electrode layer  204 ′ further includes a binder and a conductive material. The third electrode layer  204 ′ is a mixture made of a lithium manganese iron phosphate (LMFP) material, a binder, and a conductive material. The binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The conductive material may include conductive graphite, carbon black, carbon nanotubes, graphene, or a combination thereof. 
     In the third electrode layer  204 ′, the weight percentage of the lithium manganese iron phosphate (LMFP) material may be, for example, 80-99 wt %, the weight percentage of the binder may be, for example, 0.5-20 wt %, and the weight percentage of the conductive material may be, for example, 0.5-20 wt %, based on the total weight of the third electrode layer  204 ′. Because the lithium iron manganese phosphate (LMFP) material is the main source of electric capacity of the third electrode layer  204 ′, when the weight percentage of the lithium manganese iron phosphate (LMFP) material is too low, the electric capacity of electrode and the energy density decrease. The higher the weight of the conductive material, the better the electrical properties of the resulting batteries. However, since the conductive material does not provide electric capacity, when the weight of the conductive material is greater than, for example, 20 wt %, the electric capacity of the electrode and the energy density decrease. Moreover, since the conductive material has a lower density and a larger surface area, when the weight of the conductive material is too high, it will have a great influence on the density and the processability of the electrode. 
     For example, in some embodiments, the weight percentage of the lithium manganese iron phosphate (LMFP) material may be, for example, 90-95 wt %, based on the total weight of the third electrode layer  204 ′. In some embodiments, the weight percentage of the binder may be, for example, 2-10 wt %, based on the total weight of the third electrode layer  204 ′. In some embodiments, the weight percentage of the conductive material may be, for example, 2-10 wt %, based on the total weight of the third electrode layer  204 ′. 
     In one embodiment, the fourth electrode layer  206 ′ may include an active material. In some embodiments, the active material may include, for example, lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), Li-rich cathode material, or a combination thereof. In one embodiment, the lithium nickel manganese cobalt oxide (NMC) may have a chemical formula of LiNi x Co y Mn z O 4 , wherein 0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;z&lt;1. In one embodiment, the lithium nickel cobalt aluminum oxide (NCA) may have a chemical formula of LiNi 0.80 Co 0.15 Al 0.05 O 2 . In one embodiment, the lithium cobalt oxide (LCO) may have a chemical formula of LiCoO 2 . In one embodiment, the Li-rich cathode material may have a chemical formula of xLi 2 MnO 3 .(1-x)LiMO 2 , wherein M is 3d transition metal and/or 4d transition metal, and 0&lt;x&lt;1. In some embodiments, the 3d transition metal may be, for example, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn, and the  4 d transition metal may be, for example, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, or Cd. 
     In some embodiments, the fourth electrode layer  206 ′ may further include a binder and a conductive material. The fourth electrode layer  206 ′ is a mixture made of the above active material, a binder, and a conductive material. The binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The conductive material may include conductive graphite, carbon black, carbon nanotubes, graphene, or a combination thereof. 
     In the fourth electrode layer  206 ′, the weight percentage of the active material may be, for example, 80-99 wt %, the weight percentage of the binder may be, for example, 0.5-20 wt %, and the weight percentage of the conductive material may be, for example, 0.5-20 wt %, based on the total weight of the fourth electrode layer  206 ′. Because the active material is the main source of electric capacity of the fourth electrode layer  206 ′, when the weight percentage of the active material is too low, the electric capacity of electrode and the energy density decrease. The higher the weight of the conductive material, the better the electrical properties of the resulting batteries. However, since the conductive material does not provide electric capacity, when the weight of the conductive material is greater than, for example, 20 wt %, the electric capacity of the electrode and the energy density decrease. Moreover, since the conductive material has a lower density and a larger surface area, when the weight of the conductive material is too high, it will have a great influence on the density and the processability of the electrode. 
     For example, in some embodiments, the weight percentage of the active material may be, for example, 90-95 wt %, based on the total weight of the fourth electrode layer  206 ′. In some embodiments, the weight percentage of the binder may be, for example, 2-10 wt %, based on the total weight of the fourth electrode layer  206 ′. In some embodiments, the weight percentage of the conductive material may be, for example, 2-10 wt %, based on the total weight of the fourth electrode layer  206 ′. 
     In some embodiments, the weight percentage of the fourth electrode layer  206 ′ may be greater than 30 wt %, based on the total weight of the third electrode layer  204 ′ and the fourth electrode layer  206 ′. For example, in some embodiment, the weight percentage of the fourth electrode layer  206 ′ may be greater than or equal to 50 wt %, 70 wt %, 80 wt %, based on the total weight of the third electrode layer  204 ′ and the fourth electrode layer  206 ′. Because the capacity of the active material of the fourth electrode layer  206 ′ is higher than the capacity of the lithium manganese iron phosphate (LMFP) of the third electrode layer  204 ′, when the weight percentage of the fourth electrode layer  206 ′ is too low, for example, less than 30 wt %, the capacity of the resulting battery and energy density decrease. 
     In some embodiments, the slurry for forming the first electrode layer  204  and the second electrode layer  206  may be simultaneously coated on one surface of the collector material  202  in a layered manner by using, for example, a roll-to-roll slot-die coating method. Then, the slurry for forming the third electrode layer  204 ′ and the fourth electrode layer  206 ′ may be simultaneously coated on another surface of the collector material  202  in a layered manner by using, for example, a roll-to-roll slot-die coating method. After drying, it is pressed by a roll press machine to obtain a cathode  200  of a lithium ion battery as shown in  FIG. 2 . 
     In some embodiments, the compaction density of the first electrode layer  204  may be, for example, 1.5-3 g/cm 3 , the density of the second electrode layer  206  may be, for example, 2.5-4.2 g/cm 3 , the compaction density of the third electrode layer  204 ′ may be, for example, 1.5-3 g/cm 3 , and the density of the fourth electrode layer  206 ′ may be, for example, 2.5-4.2 g/cm 3 . 
     The Examples and Comparative Examples are described below to illustrate the cathode of a lithium ion battery provided by the present disclosure, batteries formed therefrom, and the properties thereof. 
     EXAMPLE 1 
     NMC/LMFP Bilayer Cathode 
     Firstly, the lithium nickel manganese cobalt oxide (NMC) slurry and the lithium manganese iron phosphate (LMFP) slurry were prepared respectively. 
     Lithium nickel manganese cobalt oxide (NMC) slurry was prepared by first adding polyvinylidene fluoride (PVDF) used as a binder to N-methylpyrrolidone (NMP) used as a solvent. The mixture was stirred at high speed and uniformly dispersed. Then, carbon black used as a conductive material was added and dispersed by stirring. Finally, lithium nickel manganese cobalt oxide (NMC) was added and stirred at high speed and uniformly dispersed to obtain the lithium nickel manganese cobalt oxide (NMC) slurry. The weight ratio of lithium nickel manganese cobalt oxide (NMC): conductive material: binder was 92:5:3. 
     Lithium manganese iron phosphate (LMFP) slurry was prepared by first adding polyvinylidene fluoride (PVDF) used as a binder to N-methylpyrrolidone (NMP) used as a solvent. The mixture was stirred at high speed and uniformly dispersed. Then, carbon black used as a conductive material was added and dispersed by stirring. Finally, lithium manganese iron phosphate (LMFP) was added and stirred at high speed and uniformly dispersed to obtain the lithium manganese iron phosphate (LMFP) slurry. The weight ratio of lithium manganese iron phosphate (LMFP): conductive material: binder was 90:4:6. 
     Next, the prepared NMC slurry and the prepared LMFP slurry were simultaneously coated on one surface of the aluminum foil in a layered manner by using a slot die, wherein the weight ratio of the active material lithium nickel manganese cobalt oxide (NMC) in the NMC slurry and the active material lithium manganese iron phosphate (LMFP) in the LMFP slurry was 8:2. The NMC slurry was coated on the upper layer, and the LMFP slurry was coated on the lower layer. In other words, the LMFP slurry was coated on one surface of the aluminum foil, and the NMC slurry was coated on the LMFP slurry. The aforementioned steps were repeated on the other surface of the aluminum foil with respect to the formed NMC/LMFP layers to form the same NMC/LMFP electrode. After drying, a cathode of a lithium ion battery as shown in  FIG. 2  was obtained. Finally, the electrode was pressed by a roll press machine to increase the density of the electrode and the preparation of the NMC/LMFP bilayer cathode was completed. 
     COMPARATIVE EXAMPLE 1 
     LMFP/NMC Bilayer Cathode 
     The same process as described in Example 1 was repeated to prepare the LMFP/NMC bilayer cathode, except that the NMC slurry was coated on the lower layer and the LMFP slurry was coated on the upper layer. 
     COMPARATIVE EXAMPLE 2 
     LMFP+NMC Mixed Cathode 
     The same process as described in Example 1 was repeated to prepare the LMFP+NMC mixed cathode, except that the NMC slurry and the LMFP slurry were mixed and coated on the aluminum foil. 
     Rate Charge-Discharge Performance of Batteries I: Graphite Anode 
     The resulting cathodes prepared in Example 1 and Comparative Examples 1 and 2 were cut into a size of 5.7 cm in length and 3.2 cm in width. A graphite of 5.9 cm in length and 3.4 cm in width was used as the anode. The cathode and anode were stacked to form cells. After adding an adequate amount of electrolyte, a soft pack battery was formed in a size of 3.5×6.0 cm by using vacuum packaging. Charging and discharging tests were conducted with different rates, and the rate charge-discharge performance of batteries formed from the NMC/LMFP bilayer cathode prepared in Example 1, the LMFP/NMC bilayer cathode prepared in Comparative Example 1, and the LMFP+NMC mixed cathode prepared in Comparative Example  2  were compared.  FIGS. 3A-3C  sequentially reveals the rate charge-discharge performance of batteries formed from the cathode prepared in Example 1, the cathode prepared in Comparative Example 1, and the cathode prepared in Comparative Example 2. The results of  FIGS. 3A-3C  are also shown in Table 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Cathode 
               
            
           
           
               
               
               
            
               
                   
                 Comparative 
                 Comparative 
               
            
           
           
               
               
               
               
            
               
                   
                 Example 1 
                 Example 1 
                 Example 2 
               
               
                   
                 NMC/LMFP 
                 LMFP/NMC 
                 LMFP + 
               
               
                   
                 bilayer 
                 bilayer 
                 NMC mixed 
               
            
           
           
               
               
            
               
                   
                 Anode 
               
            
           
           
               
               
               
               
            
               
                   
                 graphite 
                 graphite 
                 graphite 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 capacity 
                 working 
                 capacity 
                 working 
                 capacity 
                 working 
               
               
                   
                 retention 
                 voltage 
                 retention 
                 voltage 
                 retention 
                 voltage 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 C-rate 
                 (%) 
                 (v) 
                 (%) 
                 (v) 
                 (%) 
                 (v) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 0.1 
                 C 
                 100.0 
                 — 
                 100.0 
                 — 
                 100.0 
                 — 
               
               
                 0.2 
                 C 
                 98.2 
                 3.70 
                 99.4 
                 3.71 
                 88.2 
                 3.66 
               
               
                 0.5 
                 C 
                 98.4 
                 3.69 
                 98.8 
                 3.69 
                 93.1 
                 3.67 
               
               
                 1 
                 C 
                 96.5 
                 3.66 
                 97.4 
                 3.65 
                 93.4 
                 3.64 
               
               
                 3 
                 C 
                 91.9 
                 3.54 
                 91.3 
                 3.53 
                 84.7 
                 3.51 
               
               
                 5 
                 C 
                 85.5 
                 3.46 
                 73.6 
                 3.46 
                 73.4 
                 3.44 
               
               
                 10 
                 C 
                 37.8 
                 3.34 
                 20.5 
                 3.28 
                 29.6 
                 3.31 
               
               
                 12 
                 C 
                 21.4 
                 3.28 
                 10.0 
                 3.27 
                 18.9 
                 3.26 
               
               
                   
               
            
           
         
       
     
     Higher capacity retention and higher working voltage are preferable. It can be seen from  FIGS. 3A-3C  and Table 1 that, when C-rate was  3 C,  5 C,  10 C, or  12 C, the capacity retention and working voltage of the battery using NMC/LMFP bilayer cathode were significantly better than the capacity retention and working voltage of the batteries using LMFP/NMC bilayer cathode and LMFP+NMC mixed cathode. 
     Rate Charge-Discharge Performance of Batteries II: Lithium Titanate (LTO) Anode 
     The resulting cathodes prepared in Example 1 and Comparative Example 2 were both cut into a size of 5.7 cm in length and 3.2 cm in width. A lithium titanate (LTO) of 5.9 cm in length and 3.4 cm in width was used as the anode. The cathode and anode were stacked to form cells. After adding an appropriate amount of electrolyte, a soft pack battery was formed in a size of 3.5×6.0 cm by using vacuum packaging. Charging and discharging tests were conducted with different rates, and the rate charge-discharge performance of batteries formed from the NMC/LMFP bilayer cathode prepared in Example 1 and the LMFP+NMC mixed cathode prepared in Comparative Example 2 were compared.  FIG. 4A  and  FIG. 4B  respectively reveals the rate charge-discharge performance of batteries formed from the cathode prepared in Example 1 and the cathode prepared in Comparative Example 2. The results of  FIG. 4A  and  FIG. 4B  are shown in Table 2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Cathode 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Example 1 
                   
                 Comparative Example 2 
                   
               
               
                   
                 NMC/LMFP bilayer 
                   
                 LMFP + NMC mixed 
               
            
           
           
               
               
               
            
               
                   
                 Anode 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 lithium titanate (LTO) 
                   
                 lithium titanate (LTO) 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 capacity 
                 working 
                 capacity 
                 working 
               
               
                   
                 retention 
                 voltage 
                 retention 
                 voltage 
               
               
                 C-rate 
                 (%) 
                 (v) 
                 (%) 
                 (v) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 0.2 C   
                 100 
                 2.22 
                 100 
                 2.23 
               
               
                 1 C 
                 93.8 
                 2.18 
                 93.3 
                 2.18 
               
               
                 6 C 
                 84.5 
                 1.99 
                 75.3 
                 1.99 
               
               
                   
               
            
           
         
       
     
     Similarly, higher capacity retention and higher working voltage are preferable. It can be seen from  FIG. 4A ,  FIG. 4B , and Table 2 that, at  6 C, the capacity retention of the battery using NMC/LMFP bilayer cathode was 84.5%, which was better than the capacity retention 75.3% of the battery using LMFP+NMC mixed cathode. 
     It can be realized from the results shown in Table 1 and Table 2 that compared to the batteries formed from the cathode of the Comparative Examples, by using the cathode of a lithium ion battery provided by the present disclosure and different anode materials, the resulting batteries have improved rate charge-discharge performance. 
     The cathode of a lithium ion battery provided by the present disclosure has a multi-layered structure. By sequentially disposing a lithium manganese iron phosphate (LMFP) material and an active material such as ternary material like lithium nickel manganese cobalt oxide (NMC) on the collector material, the resulting lithium ion battery has improved rate charge-discharge performance. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims and their equivalents.